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DC current sources

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  DC current sources Clifford Heath <no.spam@please.net> - 2017-05-03 22:15 +1000
    Re: DC current sources George Herold <gherold@teachspin.com> - 2017-05-03 05:55 -0700
      Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-03 19:40 +0100
        Re: DC current sources tabbypurr@gmail.com - 2017-05-06 00:39 -0700
    Re: DC current sources Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2017-05-03 14:06 +0100
      Re: DC current sources Winfield Hill <hill@rowland.harvard.edu> - 2017-05-03 11:06 -0700
        Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-03 19:43 +0100
          Re: DC current sources Winfield Hill <hill@rowland.harvard.edu> - 2017-05-03 13:02 -0700
            Re: DC current sources Winfield Hill <hill@rowland.harvard.edu> - 2017-05-03 17:22 -0700
          Re: DC current sources tabbypurr@gmail.com - 2017-05-06 00:41 -0700
    Re: DC current sources "dcaster@krl.org" <dcaster@krl.org> - 2017-05-03 06:15 -0700
    Re: DC current sources Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> - 2017-05-03 11:10 -0400
    Re: DC current sources Tim Wescott <tim@seemywebsite.com> - 2017-05-03 11:27 -0500
      Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-03 19:47 +0100
        Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 12:41 +1000
          Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-04 20:55 +0100
            Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-05 08:39 +1000
    Re: DC current sources "dcaster@krl.org" <dcaster@krl.org> - 2017-05-03 09:37 -0700
    Re: DC current sources Tim Wescott <seemywebsite@myfooter.really> - 2017-05-03 13:53 -0500
      Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 12:24 +1000
        Re: DC current sources mike <ham789@netzero.net> - 2017-05-04 00:48 -0700
        Re: DC current sources whit3rd <whit3rd@gmail.com> - 2017-05-04 14:09 -0700
          Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-05 08:42 +1000
    Re: DC current sources mike <ham789@netzero.net> - 2017-05-03 13:22 -0700
    Re: DC current sources whit3rd <whit3rd@gmail.com> - 2017-05-03 13:25 -0700
      Re: DC current sources Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-05-03 13:45 -0700
        Re: DC current sources whit3rd <whit3rd@gmail.com> - 2017-05-03 15:40 -0700
          Re: DC current sources Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-05-03 16:04 -0700
        Re: DC current sources krw@notreal.com - 2017-05-03 21:26 -0400
      Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 12:27 +1000
    Re: DC current sources John Robertson <spam@flippers.com> - 2017-05-03 22:48 -0700
      Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 16:36 +1000
    Re: DC current sources Jasen Betts <jasen@xnet.co.nz> - 2017-05-04 04:59 +0000
      Re: DC current sources Chris Jones <lugnut808@spam.yahoo.com> - 2017-05-04 22:50 +1000
      Re: DC current sources tabbypurr@gmail.com - 2017-05-06 00:53 -0700
    Re: DC current sources John Robertson <spam@flippers.com> - 2017-05-03 23:38 -0700
      Re: DC current sources Clifford Heath <no.spam@please.net> - 2017-05-04 16:45 +1000
        Re: DC current sources John Robertson <spam@flippers.com> - 2017-05-04 11:16 -0700
      Re: DC current sources Winfield Hill <hill@rowland.harvard.edu> - 2017-05-04 14:32 -0700
        Re: DC current sources "Ian Field" <gangprobing.alien1@virginmedia.com> - 2017-05-05 20:21 +0100
        Re: DC current sources Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-05-06 05:59 -0700
          Re: DC current sources Steve Wilson <no@spam.com> - 2017-05-06 14:04 +0000
    Re: DC current sources Robert Baer <robertbaer@localnet.com> - 2017-05-04 19:32 -0800
      Re: DC current sources mike <ham789@netzero.net> - 2017-05-05 00:18 -0700
        Re: DC current sources Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-05 08:28 +0000
          Re: DC current sources Robert Baer <robertbaer@localnet.com> - 2017-05-05 22:09 -0800
            Re: DC current sources Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-06 06:17 +0000
              Re: DC current sources Robert Baer <robertbaer@localnet.com> - 2017-05-06 20:47 -0800
                Re: DC current sources Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2017-05-07 08:27 +0000
        Re: DC current sources Robert Baer <robertbaer@localnet.com> - 2017-05-05 22:07 -0800

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#458672

On 5/3/2017 7:24 PM, Clifford Heath wrote:
> On 04/05/17 04:53, Tim Wescott wrote:
>> On Wed, 03 May 2017 22:15:36 +1000, Clifford Heath wrote:
>>
>>> A friend works in concrete reinforcing corrosion remediation,
>>> and has been asked to take over a project that's underway despite not
>>> having been properly designed or specified.
>>>
>>> The contractors are installing 400 anodes into the structure,
>>> and each one needs a specific amount of charge to be deposited into it,
>>> all over a week or two. The resistance is unknown and could change from
>>> day to day, but the voltage must not rise above +9V, or the titanium
>>> wires rapidly corrode. So they want to adjust the current for each
>>> anode, probably in the range of 100ma to 3000mA. They're intending to
>>> feed the whole protection thing from banks of 12V lead acid batteries, I
>>> guess because it's a remote site.
>>>
>>> The initial thought was to walk around and measure the current on each
>>> anode every day, and switch off any that have dumped the required
>>> charge... but that's quite labour-intensive.
>>>
>>> So I was thinking about current regulators. What's the easiest way of
>>> sourcing 400 adjustable DC current sources in a short time?
>>>
>>> I was thinking of LM350T regulators, programmed with a power resistor in
>>> the range 0.6-10 ohms... but the 2degC/W heat sink for each one could be
>>> an issue (thinking 2A, 14.7V, shorted to earth; 30W).
>>>
>>> Is there any other off-the-shelf quick solution that comes to mind?
>>>
>>> Clifford Heath.
>>
>> Go eBay shopping.  No guarantees, but this was the top result in my third
>> search:
>>
>> <http://www.ebay.com/itm/DC-DC-Buck-Converter-Constant-Current-Voltage-
>> Adjustable-Module-Regulator-0-1-3A-/371904719117?
>> hash=item56973fa90d:g:EQYAAOSwSlBY2cTv>
>
> This looks like a winner, 12 units delivered by DHL for under $AU100:
> <https://www.aliexpress.com/item/5A-Adjustable-CC-CV-Display-Step-Down-charge-Module-LED-Panel-Voltmeter-Ammeter/32670081212.html>.
>
> The electricians can be told to set the voltage limit to 9V (output
> open circuit), then connect the output and set the current to the
> specified level. The connectors are a bit flimsy, might be best to
> wire them to external connectors on the waterproof case, even though
> wires will enter through a gland.
>
> I got more detail on the problem. The 400 anodes are being installed
> in a sea wall during its construction, and each one needs a calculated
> charge (depending on its location) to be dumped into it, once only,
> over about a week's duration. Only about 10 will be active at a time,
> so the units and the batteries will be moved along as the wall is
> being built. They'll be moved each week or so, but the regulators
> mean they don't need to be visited every day and unhooked for
> monitoring. I don't know more about the chemistry (that's his domain)
> but the prevalence of chloride is the main factor. I suspect that the
> treatment passivates metal surfaces that were exposed during
> construction but are now encased in protective concrete (high pH).
>
> The time factor is because the job has commenced before the previous
> project manager (now departed, not sure if ignominiously) figured
> out how to run the passivation procedure. The treatments would
> ideally have started last week, so there's no time to design a new
> regulator. There's also no mains power available.
>
> Clifford Heath.
>
>
Problem gets a lot easier if you ignore the initial statement of
requirements and reduce the quantity by a factor of 40. ;-)

Current is a fine measure of delivered electrons as long as the
voltage at the desired current never wants to go over the max
voltage setpoint.  If that happens, your delivered electrons won't.

Stated another way, if you want 3 amps and 9V, you'd better not
have more than 3 ohms in the loop at any time in the process.

Good thing the vendor gave you a schematic so you'd understand
that the current limit sense resistor is between the battery negative
and the output (-).
Watch out for issues if somebody decides to put more than one on the
same battery...or if current from one can be induced into (-)
of another thru some rebar.

If my math is right .1A x .05 ohms is 5mV controlling the current.
Not much margin for noise.
Gets better at 3A.
A nearby lightning strike can make a mess of things.  I'd
put real fuses in series.

I'd do some serious QC on those Chinese clones of Chinese clones
that can be delivered to your door for under $5, at a profit.

My point is to pay close attention and don't assume you can
just have any technician set it all up in any situation.

I'd be interested to learn the range of series resistance
encountered in this "plating" process.

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#458787

On Wednesday, May 3, 2017 at 7:24:31 PM UTC-7, Clifford Heath wrote:
> On 04/05/17 04:53, Tim Wescott wrote:
> > On Wed, 03 May 2017 22:15:36 +1000, Clifford Heath wrote:
> >
> >> A friend works in concrete reinforcing corrosion remediation,
> >> ... want to adjust the current for each
> >> anode, probably in the range of 100ma to 3000mA. They're intending to
> >> feed the whole protection thing from banks of 12V lead acid batteries, I
> >> guess because it's a remote site.

> This looks like a winner, 12 units delivered by DHL for under $AU100:
> <https://www.aliexpress.com/item/5A-Adjustable-CC-CV-Display-Step-Down-charge-Module-LED-Panel-Voltmeter-Ammeter/32670081212.html>.

That depends on your polarity.  These units have the current sense resistor in the negative
return line,  so if you're running several off a battery, and the ground return goes to the negative
terminal, the battery negative terminal and the 'negative' output pole are interconnected.
If you use a battery for TWO units, the negative ground stake will ensure that neither
gets an accurate current reading.   So, to run your twelve units, will take
twelve batteries.

I think that if you have positive ground, the situation is worse; because all the positive outputs
connect together, and so do all the GND (to the battery); it still takes twelve batteries
to run (all the battery terminals have to float).

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#458804

On 05/05/17 07:09, whit3rd wrote:
> On Wednesday, May 3, 2017 at 7:24:31 PM UTC-7, Clifford Heath wrote:
>> On 04/05/17 04:53, Tim Wescott wrote:
>>> On Wed, 03 May 2017 22:15:36 +1000, Clifford Heath wrote:
>>>
>>>> A friend works in concrete reinforcing corrosion remediation,
>>>> ... want to adjust the current for each
>>>> anode, probably in the range of 100ma to 3000mA. They're intending to
>>>> feed the whole protection thing from banks of 12V lead acid batteries, I
>>>> guess because it's a remote site.
>
>> This looks like a winner, 12 units delivered by DHL for under $AU100:
>> <https://www.aliexpress.com/item/5A-Adjustable-CC-CV-Display-Step-Down-charge-Module-LED-Panel-Voltmeter-Ammeter/32670081212.html>.
>
> That depends on your polarity.  These units have the current sense resistor in the negative
> return line,  so if you're running several off a battery, and the ground return goes to the negative
> terminal, the battery negative terminal and the 'negative' output pole are interconnected.
> If you use a battery for TWO units, the negative ground stake will ensure that neither
> gets an accurate current reading.   So, to run your twelve units, will take
> twelve batteries.
>
> I think that if you have positive ground, the situation is worse; because all the positive outputs
> connect together, and so do all the GND (to the battery); it still takes twelve batteries
> to run (all the battery terminals have to float).

That's good information, thanks. The negative will be connected to the
reinforcing, the positive to the temporary anodes. If the anodes are
interconnected, it'll cause dramas, as you say.

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#458617

On 5/3/2017 5:15 AM, Clifford Heath wrote:
> A friend works in concrete reinforcing corrosion remediation,
> and has been asked to take over a project that's underway
> despite not having been properly designed or specified.

That's the key!  Not properly designed or specified.
Hard to design a solution when you don't understand the problem.
>
> The contractors are installing 400 anodes into the structure,
> and each one needs a specific amount of charge to be deposited
> into it, all over a week or two. The resistance is unknown and
> could change from day to day, but the voltage must not rise
> above +9V, or the titanium wires rapidly corrode. So they
> want to adjust the current for each anode, probably in the
> range of 100ma to 3000mA. They're intending to feed the whole
> protection thing from banks of 12V lead acid batteries, I
> guess because it's a remote site.

Am I the only one who thinks that 1200 amps for two weeks
is a lot to expect from batteries at a remote site?
>
> The initial thought was to walk around and measure the current
> on each anode every day, and switch off any that have dumped
> the required charge... but that's quite labour-intensive.

Since we have an unspecified problem, how about a random answer?
Consider a plating process with a limited amount of source
material.  It takes a specific number of electrons to use up
all the material.  Then the plating, and current, stops.
It's the same process used in the old-style mercury timers
for equipment usage...or a battery.
Use a 6V battery to limit the voltage.
If you think the current may exceed the 3A, use an incandescent
light bulb in series to limit the current.  Also gives you visual
fault location.
Or just size the plating electrodes to limit current.
The actual design of the plating cells is currently "unspecified".
How many sites need 400 of them?  Might be a market opportunity.

Or maybe build 400 Brown's gas generators.  Water level drops
as gas is generated.  Don't know the number of electrons so
may not be able to gauge the water level accurately.
Might have to use the gas to displace different water to gauge
the electrons delivered.  Something akin to a manometer.  It's all about 
the numbers.
But you can burn the Brown's gas to get back some of the power
wasted. ;-)

Or maybe one resistor (with a diode across it) feeding a 400-way
switch from an 8V battery.
Every hour, turn off current to all the anodes.  Cycle thru
all 400, logging individual currents and integrating.
Then turn the ones that have not reached terminal charge back on.
It's not like they'll be changing rapidly.
Bluetooth to a phone for readout.  If you have control
of the programmer/logger end, I'd use serial IR and something
like an old Palm Pilot.  Wouldn't expect current phones to
support that.
There may be better methods, but PICbasic could make all that
work in an hour.  400 transistors or relays and a 400-bit
shift register might take longer.  That system segments/scales well.

Or maybe something akin to 400 buck converters.
Charge a cap. Discharge it into the anode.
You know how many cycles required to deliver the required
charge. Count them.  Use a smoothing cap at the anode
and limit the cycle frequency to limit the average current.
8-pin microcontroller programmed by serial port to stop
after delivering required number of electrons.

I haven't seen any mention of fault tolerance.  How critical is
that total charge number?   What happens when someone trips
over the cable and interrupts power?  Microcontroller addresses that.

Bottom line...if you want to measure electrons delivered,
design a tool based on that process. The devil is in the details.


>
> So I was thinking about current regulators. What's the easiest
> way of sourcing 400 adjustable DC current sources in a short time?
>
> I was thinking of LM350T regulators, programmed with a power
> resistor in the range 0.6-10 ohms... but the 2degC/W heat sink
> for each one could be an issue (thinking 2A, 14.7V, shorted to
> earth; 30W).
>
> Is there any other off-the-shelf quick solution that comes to
> mind?
>
> Clifford Heath.

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#458618

On Wednesday, May 3, 2017 at 5:15:42 AM UTC-7, Clifford Heath wrote:

> The contractors are installing 400 anodes into the structure,
> and each one needs a specific amount of charge to be deposited
> into it, all over a week or two. The resistance is unknown and
> could change from day to day, but the voltage must not rise
> above +9V, or the titanium wires rapidly corrode. So they
> want to adjust the current for each anode, probably in the
> range of 100ma to 3000mA. They're intending to feed the whole
> protection thing from banks of 12V lead acid batteries

Rust never sleeps.

Interesting mix of problems.   To make sure nothing gets above 9V,
it might be useful to start with a DC/DC converter that efficiently
downconverts from "12V" to 9V (Vicor makes suitable modules)
and then attach each wire through a sense/current limit resistor.  At circa
1A, that means lots of power resistors in the 4 to 10 ohm range.

The next problem, is monitoring daily.  For preference, you'd want
to scan a barcode next to each connection as the measurements
are made each day, and have an alert on any connection
that reaches its intended charge (so the wire can be detached).
Not sure how to instrument that, but with 400 wires, it's gotta
be organized, or your corrosion won't stop.   A detached wire
means at least one zero-current measurement to be logged against
that barcode.

The measurements kept in  a log (and maybe imported into a spreadsheet)
will be subject to inspection, of course.   

Then, there's the battery issue: you'll want to top up any weak battery
(maybe take a wheelbarrow of fresh batteries on the inspection tour and
do some swaps), so the DC/DC comverter will want a pilot light to show
'battery good'.   It might be useful to log the input and output voltages
at the convertar, separately.   Some kind of quick-connect (Anderson powerpole
connector?) for the batteries is recommended, because a polarity error
is a BAD thing.  So is a loose connection.   

I'm thinking a box around the DC converter, with an accessible terminal
strip, screw down on each wire (and probe point exposure).   If the DC 
converter handles 150A (Vicor BCM3814V60E10A5C02), and takes
four 12V batteries in series, you'd want to allow for 50 to 100W of heatsinking
as well as ventilation around the sense resistors.   And, you'll want 
several such boxes.   

If this was gonna be done often, the boxes ought to be elaborate enough
to do their own monitoring, and you'd just check the logs into
your laptop on each inspection...

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#458620

Den onsdag den 3. maj 2017 kl. 22.25.17 UTC+2 skrev whit3rd:
> On Wednesday, May 3, 2017 at 5:15:42 AM UTC-7, Clifford Heath wrote:
> 
> > The contractors are installing 400 anodes into the structure,
> > and each one needs a specific amount of charge to be deposited
> > into it, all over a week or two. The resistance is unknown and
> > could change from day to day, but the voltage must not rise
> > above +9V, or the titanium wires rapidly corrode. So they
> > want to adjust the current for each anode, probably in the
> > range of 100ma to 3000mA. They're intending to feed the whole
> > protection thing from banks of 12V lead acid batteries
> 
> Rust never sleeps.
> 
> Interesting mix of problems.   To make sure nothing gets above 9V,
> it might be useful to start with a DC/DC converter that efficiently
> downconverts from "12V" to 9V (Vicor makes suitable modules)
> and then attach each wire through a sense/current limit resistor.  At circa
> 1A, that means lots of power resistors in the 4 to 10 ohm range.
> 

cheap dc-dc set for 9V, add a resistor and pnp to limit current?

http://imgur.com/a/YKrRt

> The next problem, is monitoring daily.  For preference, you'd want
> to scan a barcode next to each connection as the measurements
> are made each day, and have an alert on any connection
> that reaches its intended charge (so the wire can be detached).
> Not sure how to instrument that, but with 400 wires, it's gotta
> be organized, or your corrosion won't stop.   A detached wire
> means at least one zero-current measurement to be logged against
> that barcode.
> 
> The measurements kept in  a log (and maybe imported into a spreadsheet)
> will be subject to inspection, of course.   
> 
> Then, there's the battery issue: you'll want to top up any weak battery
> (maybe take a wheelbarrow of fresh batteries on the inspection tour and
> do some swaps), so the DC/DC comverter will want a pilot light to show
> 'battery good'.   It might be useful to log the input and output voltages
> at the convertar, separately.   Some kind of quick-connect (Anderson powerpole
> connector?) for the batteries is recommended, because a polarity error
> is a BAD thing.  So is a loose connection.   
> 
> I'm thinking a box around the DC converter, with an accessible terminal
> strip, screw down on each wire (and probe point exposure).   If the DC 
> converter handles 150A (Vicor BCM3814V60E10A5C02), and takes
> four 12V batteries in series, you'd want to allow for 50 to 100W of heatsinking
> as well as ventilation around the sense resistors.   And, you'll want 
> several such boxes.   
> 
> If this was gonna be done often, the boxes ought to be elaborate enough
> to do their own monitoring, and you'd just check the logs into
> your laptop on each inspection...

ESP8266 wifi modules are a <$2 from China

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#458623

On Wednesday, May 3, 2017 at 1:45:10 PM UTC-7, Lasse Langwadt Christensen wrote:
> Den onsdag den 3. maj 2017 kl. 22.25.17 UTC+2 skrev whit3rd:
> > On Wednesday, May 3, 2017 at 5:15:42 AM UTC-7, Clifford Heath wrote:
> > 
> > > The contractors are installing 400 anodes into the structure,
> > > and each one needs... in the
> > > range of 100ma to 3000mA. 

> > Interesting mix of problems.   To make sure nothing gets above 9V,
> > it might be useful to start with a DC/DC converter that efficiently
> > downconverts from "12V" to 9V (Vicor makes suitable modules)
> > and then attach each wire through a sense/current limit resistor.  At circa
> > 1A, that means lots of power resistors in the 4 to 10 ohm range.
> > 
> 
> cheap dc-dc set for 9V, add a resistor and pnp to limit current?
> 
> http://imgur.com/a/YKrRt

Holding up construction might be expensive; it's easy to heatsink
a few two-horsepower 97% efficient converters, and power resistors
are cheap, self-heatsinking.   Four hundred heatsinked PNP limiters?   Not so 
quick an assembly project.


> ESP8266 wifi modules are a <$2 from China

Good idea; but, you also need ADC and mux, smarts,  and some way to wire to 
all the current limiters (circa 5W, not surface-mount parts).   

It won't save much trouble.   Battery-swap visits to the nodes
are probably required in any case.   When one of the anodes hits its target,
detaching it also requires a physical visit to the box; that'll happen 400 times.

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#458625

Den torsdag den 4. maj 2017 kl. 00.40.31 UTC+2 skrev whit3rd:
> On Wednesday, May 3, 2017 at 1:45:10 PM UTC-7, Lasse Langwadt Christensen wrote:
> > Den onsdag den 3. maj 2017 kl. 22.25.17 UTC+2 skrev whit3rd:
> > > On Wednesday, May 3, 2017 at 5:15:42 AM UTC-7, Clifford Heath wrote:
> > > 
> > > > The contractors are installing 400 anodes into the structure,
> > > > and each one needs... in the
> > > > range of 100ma to 3000mA. 
> 
> > > Interesting mix of problems.   To make sure nothing gets above 9V,
> > > it might be useful to start with a DC/DC converter that efficiently
> > > downconverts from "12V" to 9V (Vicor makes suitable modules)
> > > and then attach each wire through a sense/current limit resistor.  At circa
> > > 1A, that means lots of power resistors in the 4 to 10 ohm range.
> > > 
> > 
> > cheap dc-dc set for 9V, add a resistor and pnp to limit current?
> > 
> > http://imgur.com/a/YKrRt
> 
> Holding up construction might be expensive; it's easy to heatsink
> a few two-horsepower 97% efficient converters, and power resistors
> are cheap, self-heatsinking.   Four hundred heatsinked PNP limiters?   Not so 
> quick an assembly project.
> 

shouldn't need a heatsink, the PNP doesn't dissipate any significant power
it just pulls up the feedback pin so the DC-DC reduces the output voltage 

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#458637

On Wed, 3 May 2017 13:45:00 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>Den onsdag den 3. maj 2017 kl. 22.25.17 UTC+2 skrev whit3rd:
>> On Wednesday, May 3, 2017 at 5:15:42 AM UTC-7, Clifford Heath wrote:
>> 
>> > The contractors are installing 400 anodes into the structure,
>> > and each one needs a specific amount of charge to be deposited
>> > into it, all over a week or two. The resistance is unknown and
>> > could change from day to day, but the voltage must not rise
>> > above +9V, or the titanium wires rapidly corrode. So they
>> > want to adjust the current for each anode, probably in the
>> > range of 100ma to 3000mA. They're intending to feed the whole
>> > protection thing from banks of 12V lead acid batteries
>> 
>> Rust never sleeps.
>> 
>> Interesting mix of problems.   To make sure nothing gets above 9V,
>> it might be useful to start with a DC/DC converter that efficiently
>> downconverts from "12V" to 9V (Vicor makes suitable modules)
>> and then attach each wire through a sense/current limit resistor.  At circa
>> 1A, that means lots of power resistors in the 4 to 10 ohm range.
>> 
>
>cheap dc-dc set for 9V, add a resistor and pnp to limit current?
>
>http://imgur.com/a/YKrRt

How about a switching regulator set up as a current source with a
switch to yank the FB pin to the input (or some voltage above Vref) if
Vout>9V?

>
>> The next problem, is monitoring daily.  For preference, you'd want
>> to scan a barcode next to each connection as the measurements
>> are made each day, and have an alert on any connection
>> that reaches its intended charge (so the wire can be detached).
>> Not sure how to instrument that, but with 400 wires, it's gotta
>> be organized, or your corrosion won't stop.   A detached wire
>> means at least one zero-current measurement to be logged against
>> that barcode.
>> 
>> The measurements kept in  a log (and maybe imported into a spreadsheet)
>> will be subject to inspection, of course.   
>> 
>> Then, there's the battery issue: you'll want to top up any weak battery
>> (maybe take a wheelbarrow of fresh batteries on the inspection tour and
>> do some swaps), so the DC/DC comverter will want a pilot light to show
>> 'battery good'.   It might be useful to log the input and output voltages
>> at the convertar, separately.   Some kind of quick-connect (Anderson powerpole
>> connector?) for the batteries is recommended, because a polarity error
>> is a BAD thing.  So is a loose connection.   
>> 
>> I'm thinking a box around the DC converter, with an accessible terminal
>> strip, screw down on each wire (and probe point exposure).   If the DC 
>> converter handles 150A (Vicor BCM3814V60E10A5C02), and takes
>> four 12V batteries in series, you'd want to allow for 50 to 100W of heatsinking
>> as well as ventilation around the sense resistors.   And, you'll want 
>> several such boxes.   
>> 
>> If this was gonna be done often, the boxes ought to be elaborate enough
>> to do their own monitoring, and you'd just check the logs into
>> your laptop on each inspection...
>
>ESP8266 wifi modules are a <$2 from China
>

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#458642

On 04/05/17 06:25, whit3rd wrote:
> On Wednesday, May 3, 2017 at 5:15:42 AM UTC-7, Clifford Heath wrote:
>
>> The contractors are installing 400 anodes into the structure,
>> and each one needs a specific amount of charge to be deposited
>> into it, all over a week or two. The resistance is unknown and
>> could change from day to day, but the voltage must not rise
>> above +9V, or the titanium wires rapidly corrode. So they
>> want to adjust the current for each anode, probably in the
>> range of 100ma to 3000mA. They're intending to feed the whole
>> protection thing from banks of 12V lead acid batteries
>
> Rust never sleeps.

Indeed. That's partly why he chose this career :).
Normally there's mains power available, and they're installing
wired long-term monitoring. Not this time though.

> The next problem, is monitoring daily.

The reason for the adjustable constant current supply is to avoid
the need for daily monitoring.

Clifford Heath.

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#458657

On 2017/05/03 5:15 AM, Clifford Heath wrote:
> A friend works in concrete reinforcing corrosion remediation,
> and has been asked to take over a project that's underway
> despite not having been properly designed or specified.
>
> The contractors are installing 400 anodes into the structure,
> and each one needs a specific amount of charge to be deposited
> into it, all over a week or two. The resistance is unknown and
> could change from day to day, but the voltage must not rise
> above +9V, or the titanium wires rapidly corrode. So they
> want to adjust the current for each anode, probably in the
> range of 100ma to 3000mA. They're intending to feed the whole
> protection thing from banks of 12V lead acid batteries, I
> guess because it's a remote site.
>
> The initial thought was to walk around and measure the current
> on each anode every day, and switch off any that have dumped
> the required charge... but that's quite labour-intensive.
>
> So I was thinking about current regulators. What's the easiest
> way of sourcing 400 adjustable DC current sources in a short time?
>
> I was thinking of LM350T regulators, programmed with a power
> resistor in the range 0.6-10 ohms... but the 2degC/W heat sink
> for each one could be an issue (thinking 2A, 14.7V, shorted to
> earth; 30W).
>
> Is there any other off-the-shelf quick solution that comes to
> mind?
>
> Clifford Heath.

Not that I know much about concrete, but if you what are trying to 
measure is the concrete's drying time is it possible that ESR may have a 
role? My experience is one area shows that ESR can tell you how well a 
lead acid or ni-cad battery is behaving based on its past ESR when fully 
charged and that value changes as the battery ages. So I'm sitting here 
wondering exactly what your clients are trying to measure and if there 
is a way to do so. This might give you a variable that could control the 
battery voltage. Such as the resistance starts as X and thus the voltage 
should be Y, and as the resistance increases/decreases the voltage 
should change in a linear/exponential/inverse/? rate.

The fact that we sell the Bob Parker ESR kit has little to do with my 
suggestion, it is more that you need to be able to measure the 
properties if you want to automate the voltage setting. And ESR is as 
good a place to start as any...

John :-#)#

-- 
(Please post followups or tech inquiries to the USENET newsgroup)
John's  Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
                      www.flippers.com
        "Old pinballers never die, they just flip out."

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#458659

On 04/05/17 15:48, John Robertson wrote:
> On 2017/05/03 5:15 AM, Clifford Heath wrote:
>> A friend works in concrete reinforcing corrosion remediation,
>> and has been asked to take over a project that's underway
>> despite not having been properly designed or specified.
>>
>> The contractors are installing 400 anodes into the structure,
>> and each one needs a specific amount of charge to be deposited
>> into it, all over a week or two. The resistance is unknown and
>> could change from day to day, but the voltage must not rise
>> above +9V, or the titanium wires rapidly corrode. So they
>> want to adjust the current for each anode, probably in the
>> range of 100ma to 3000mA. They're intending to feed the whole
>> protection thing from banks of 12V lead acid batteries, I
>> guess because it's a remote site.
>>
>> The initial thought was to walk around and measure the current
>> on each anode every day, and switch off any that have dumped
>> the required charge... but that's quite labour-intensive.
>>
>> So I was thinking about current regulators. What's the easiest
>> way of sourcing 400 adjustable DC current sources in a short time?
>>
>> I was thinking of LM350T regulators, programmed with a power
>> resistor in the range 0.6-10 ohms... but the 2degC/W heat sink
>> for each one could be an issue (thinking 2A, 14.7V, shorted to
>> earth; 30W).
>>
>> Is there any other off-the-shelf quick solution that comes to
>> mind?
>>
>> Clifford Heath.
>
> Not that I know much about concrete, but if you what are trying to
> measure is the concrete's drying time

Not trying to measure anything. Trying to convert rust on newly-
installed reinforcing. The amount of rust per section has been
calculated (surface area, duration and type of exposure), so the
required charge can be approximately calculated. All that's now
required is a sane way to deliver that charge. There are various
series resistances, some with parallel capacitances, and most
of the parameters vary during treatment and with dampness, so
voltage-mode doesn't work to control total charge.

>  is it possible that ESR may have a role?

Perhaps, but it's not relevant here.

> The fact that we sell the Bob Parker ESR kit has little to do with my
> suggestion, it is more that you need to be able to measure the
> properties if you want to automate the voltage setting.

(a) they don't expect to automate it and (b) it's a current setting.

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#458658

On 2017-05-03, Clifford Heath <no.spam@please.net> wrote:
> A friend works in concrete reinforcing corrosion remediation,
> and has been asked to take over a project that's underway
> despite not having been properly designed or specified.
>
> The contractors are installing 400 anodes into the structure,
> and each one needs a specific amount of charge to be deposited
> into it, all over a week or two. The resistance is unknown and
> could change from day to day, but the voltage must not rise
> above +9V, or the titanium wires rapidly corrode. So they
> want to adjust the current for each anode, probably in the
> range of 100ma to 3000mA. They're intending to feed the whole
> protection thing from banks of 12V lead acid batteries, I
> guess because it's a remote site.
>
> The initial thought was to walk around and measure the current
> on each anode every day, and switch off any that have dumped
> the required charge... but that's quite labour-intensive.

Is this a one off? stick a 7.5V battery of the desired charge
capacity on each electrode.  when the batterys go flat you're done.

-- 
This email has not been checked by half-arsed antivirus software 

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#458690

On 04/05/2017 14:59, Jasen Betts wrote:
> On 2017-05-03, Clifford Heath <no.spam@please.net> wrote:
>> A friend works in concrete reinforcing corrosion remediation,
>> and has been asked to take over a project that's underway
>> despite not having been properly designed or specified.
>>
>> The contractors are installing 400 anodes into the structure,
>> and each one needs a specific amount of charge to be deposited
>> into it, all over a week or two. The resistance is unknown and
>> could change from day to day, but the voltage must not rise
>> above +9V, or the titanium wires rapidly corrode. So they
>> want to adjust the current for each anode, probably in the
>> range of 100ma to 3000mA. They're intending to feed the whole
>> protection thing from banks of 12V lead acid batteries, I
>> guess because it's a remote site.
>>
>> The initial thought was to walk around and measure the current
>> on each anode every day, and switch off any that have dumped
>> the required charge... but that's quite labour-intensive.
>
> Is this a one off? stick a 7.5V battery of the desired charge
> capacity on each electrode.  when the batterys go flat you're done.
>

Provided the total charge required is within reason, this might be not a 
bad idea at all. 6V alkaline lantern batteries or similar, if the 
capacity is right.

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#459062

On Thursday, 4 May 2017 07:31:08 UTC+1, Jasen Betts  wrote:
> On 2017-05-03, Clifford Heath <no.spam@please.net> wrote:
> > A friend works in concrete reinforcing corrosion remediation,
> > and has been asked to take over a project that's underway
> > despite not having been properly designed or specified.
> >
> > The contractors are installing 400 anodes into the structure,
> > and each one needs a specific amount of charge to be deposited
> > into it, all over a week or two. The resistance is unknown and
> > could change from day to day, but the voltage must not rise
> > above +9V, or the titanium wires rapidly corrode. So they
> > want to adjust the current for each anode, probably in the
> > range of 100ma to 3000mA. They're intending to feed the whole
> > protection thing from banks of 12V lead acid batteries, I
> > guess because it's a remote site.
> >
> > The initial thought was to walk around and measure the current
> > on each anode every day, and switch off any that have dumped
> > the required charge... but that's quite labour-intensive.
> 
> Is this a one off? stick a 7.5V battery of the desired charge
> capacity on each electrode.  when the batterys go flat you're done.

That's close to what I was thinking. Select voltage tapping to keep current lowish. Mark the battery with the number of charges at each anode. NiMH would handle it better than lead acid. Very quick & dirty but it would do the job. And no mucking about building stuff time.


NT

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#458660

On 2017/05/03 5:15 AM, Clifford Heath wrote:
> A friend works in concrete reinforcing corrosion remediation,
> and has been asked to take over a project that's underway
> despite not having been properly designed or specified.
>
> The contractors are installing 400 anodes into the structure,
> and each one needs a specific amount of charge to be deposited
> into it, all over a week or two. The resistance is unknown and
> could change from day to day, but the voltage must not rise
> above +9V, or the titanium wires rapidly corrode. So they
> want to adjust the current for each anode, probably in the
> range of 100ma to 3000mA. They're intending to feed the whole
> protection thing from banks of 12V lead acid batteries, I
> guess because it's a remote site.
>
> The initial thought was to walk around and measure the current
> on each anode every day, and switch off any that have dumped
> the required charge... but that's quite labour-intensive.
>
> So I was thinking about current regulators. What's the easiest
> way of sourcing 400 adjustable DC current sources in a short time?
>
> I was thinking of LM350T regulators, programmed with a power
> resistor in the range 0.6-10 ohms... but the 2degC/W heat sink
> for each one could be an issue (thinking 2A, 14.7V, shorted to
> earth; 30W).
>
> Is there any other off-the-shelf quick solution that comes to
> mind?
>
> Clifford Heath.

There is a bit on line about the how and why of sacrificial anodes are 
used in contaminated concrete:

http://cp-tech.co.uk/duoguard-hybrid-anode

Some patents too...

Interesting.

John

-- 
(Please post followups or tech inquiries to the USENET newsgroup)
John's  Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
                      www.flippers.com
        "Old pinballers never die, they just flip out."

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#458661

On 04/05/17 16:38, John Robertson wrote:
> On 2017/05/03 5:15 AM, Clifford Heath wrote:
>> A friend works in concrete reinforcing corrosion remediation,
>> and has been asked to take over a project that's underway
>> despite not having been properly designed or specified.
>>
>> The contractors are installing 400 anodes into the structure,
>> and each one needs a specific amount of charge to be deposited
>> into it, all over a week or two. The resistance is unknown and
>> could change from day to day, but the voltage must not rise
>> above +9V, or the titanium wires rapidly corrode. So they
>> want to adjust the current for each anode, probably in the
>> range of 100ma to 3000mA. They're intending to feed the whole
>> protection thing from banks of 12V lead acid batteries, I
>> guess because it's a remote site.
>>
>> The initial thought was to walk around and measure the current
>> on each anode every day, and switch off any that have dumped
>> the required charge... but that's quite labour-intensive.
>>
>> So I was thinking about current regulators. What's the easiest
>> way of sourcing 400 adjustable DC current sources in a short time?
>>
>> I was thinking of LM350T regulators, programmed with a power
>> resistor in the range 0.6-10 ohms... but the 2degC/W heat sink
>> for each one could be an issue (thinking 2A, 14.7V, shorted to
>> earth; 30W).
>>
>> Is there any other off-the-shelf quick solution that comes to
>> mind?
>>
>> Clifford Heath.
>
> There is a bit on line about the how and why of sacrificial anodes are
> used in contaminated concrete:

Yes. There's a lot of experience too - which this company has already,
since it's been their primary business for decades. Galvanic protection,
impressed current protection, $30,000 penetrating radar equipment (to
find re-bar in old structures), post-hoc passivation, remediation and
monitoring, they do it all.

The specific problem I mooted is one they don't encounter often and
didn't have a standard solution for. Surprisingly.

Clifford Heath.

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#458761

On 2017/05/03 11:45 PM, Clifford Heath wrote:
> On 04/05/17 16:38, John Robertson wrote:
>> On 2017/05/03 5:15 AM, Clifford Heath wrote:
>>> A friend works in concrete reinforcing corrosion remediation,
>>> and has been asked to take over a project that's underway
>>> despite not having been properly designed or specified.
>>>
>>> The contractors are installing 400 anodes into the structure,
>>> and each one needs a specific amount of charge to be deposited
>>> into it, all over a week or two. The resistance is unknown and
>>> could change from day to day, but the voltage must not rise
>>> above +9V, or the titanium wires rapidly corrode. So they
>>> want to adjust the current for each anode, probably in the
>>> range of 100ma to 3000mA. They're intending to feed the whole
>>> protection thing from banks of 12V lead acid batteries, I
>>> guess because it's a remote site.
>>>
>>> The initial thought was to walk around and measure the current
>>> on each anode every day, and switch off any that have dumped
>>> the required charge... but that's quite labour-intensive.
>>>
>>> So I was thinking about current regulators. What's the easiest
>>> way of sourcing 400 adjustable DC current sources in a short time?
>>>
>>> I was thinking of LM350T regulators, programmed with a power
>>> resistor in the range 0.6-10 ohms... but the 2degC/W heat sink
>>> for each one could be an issue (thinking 2A, 14.7V, shorted to
>>> earth; 30W).
>>>
>>> Is there any other off-the-shelf quick solution that comes to
>>> mind?
>>>
>>> Clifford Heath.
>>
>> There is a bit on line about the how and why of sacrificial anodes are
>> used in contaminated concrete:
>
> Yes. There's a lot of experience too - which this company has already,
> since it's been their primary business for decades. Galvanic protection,
> impressed current protection, $30,000 penetrating radar equipment (to
> find re-bar in old structures), post-hoc passivation, remediation and
> monitoring, they do it all.
>
> The specific problem I mooted is one they don't encounter often and
> didn't have a standard solution for. Surprisingly.
>
> Clifford Heath.
>

Can I borrow their ground penetrating radar? I want to see the ICs used 
on some old potted chip modules to 'read' them out. (ducking).

John ;-#)#

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#458789

John Robertson wrote...
>
> I was thinking of LM350T regulators, programmed with a power
>> resistor in the range 0.6-10 ohms... but the 2degC/W heat sink
>> for each one could be an issue (thinking 2A, 14.7V, shorted to
>> earth; 30W).

 Yes.  I had suggested an efficient buck converter
 to about 9.5V to set the Vmax compliance range,
 then LM350T, etc., as individual current sources.
 If there's a short fault on a channel, the '350T
 will thermally limit, you probably want it to do
 that anyway, well below 2A to save power.  Just
 a simple clip-on heat 2W heat sink for each one.


-- 
 Thanks,
    - Win

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#458958

"Winfield Hill" <hill@rowland.harvard.edu> wrote in message 
news:oeg6mb08fu@drn.newsguy.com...
> John Robertson wrote...
>>
>> I was thinking of LM350T regulators, programmed with a power
>>> resistor in the range 0.6-10 ohms... but the 2degC/W heat sink
>>> for each one could be an issue (thinking 2A, 14.7V, shorted to
>>> earth; 30W).
>
> Yes.  I had suggested an efficient buck converter
> to about 9.5V to set the Vmax compliance range,
> then LM350T, etc., as individual current sources.

A lot of them delivering up to 3A is going to waste a hell of a lot of 
energy heating up linear regulators.

When I wanted to build a switch-mode Ni-Cd charger, I found current control 
was difficult to implement and had a tendency to go bang.

My solution was to use a diode-capacitor charge pump, which provides a 
half-decent approximation to constant current. Usually you have to draw some 
DC load current to keep the PWM doing something useful. That current will 
make up some proportion of the total current - you select the charge pump 
capacitor against the switcher frequency to make up the difference.

If you modify an off the shelf SMPSU - it will already have the voltage 
regulation circuitry that you can adjust for the maximum allowed voltage.

You leave that in anyway - it stops the SMPSU going bang when there's no 
load. 

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