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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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#458546 — DC current sources

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.

[toc] | [next] | [standalone]

#458549

On Wednesday, May 3, 2017 at 8:15:42 AM UTC-4, 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.

No idea what might work, but there are a lot of "PMIC LED drivers" listed 
on digikey.  (I assume switch mode, but don't know.)

George H. 

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#458603

"George Herold" <gherold@teachspin.com> wrote in message 
news:15893772-a2d3-4199-b7de-cfe487a7099d@googlegroups.com...
> On Wednesday, May 3, 2017 at 8:15:42 AM UTC-4, 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.
>
> No idea what might work, but there are a lot of "PMIC LED drivers" listed
> on digikey.  (I assume switch mode, but don't know.)

Current control as the primary regulation mode can be tricky with switchers.

There are off the shelf PWM front end chips for dimmable LED bulbs, but I've 
only seen mains type.

It demonstrates the possibility - so a bit of searching might do something. 

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#459060

On Wednesday, 3 May 2017 19:40:06 UTC+1, Ian Field  wrote:

> Current control as the primary regulation mode can be tricky with switchers.

ISTR making 2 transistor smpsus that just switched off when inductor current reached a set value, and on again when it dropped. And a screw for an inductor core.


NT

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#458550

On 03/05/2017 13:15, 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.

Why not use a high power switched mode DC to DC converter to supply 8.5v 
to the anodes through a crude rheostat and power resistor?

That way the titanium wires can never be damaged by over voltage no 
matter what the engineers do to the anode wiring.

> 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.

You would need to assume in addition that the current was fairly 
constant to work out how much charge had been delivered to each node. A 
quick and dirty LED jig to measure voltage across the load would be one 
way to speed up testing which loads are slow (ie high impedance).

I assume that fast, nominal and slow will be good enough here.

> 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.

LED driver modules but it seems like overkill and unlikely to survive on 
a building site! (also offers no over voltage protection)

-- 
Regards,
Martin Brown

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#458602

Martin Brown wrote...
>
>On 03/05/2017 13:15, 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.
>
> Why not use a high power switched mode DC to DC converter
> to supply 8.5v to the anodes through a crude rheostat and
> power resistor?

 Or buck smps down to 9.7 volts and an LM317 with resistor
 current limiting for each, w/o overheating issues.  LM317
 thermal limits, protecting itself in case of shorts, etc.


-- 
 Thanks,
    - Win

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#458604

"Winfield Hill" <hill@rowland.harvard.edu> wrote in message 
news:oed67g0240p@drn.newsguy.com...
> Martin Brown wrote...
>>
>>On 03/05/2017 13:15, 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.
>>
>> Why not use a high power switched mode DC to DC converter
>> to supply 8.5v to the anodes through a crude rheostat and
>> power resistor?
>
> Or buck smps down to 9.7 volts and an LM317 with resistor
> current limiting for each, w/o overheating issues.  LM317
> thermal limits, protecting itself in case of shorts, etc.

But it won't do the 3A top limit mentioned - the 78xx appnotes show how to 
increase current with an external bypass transistor, it should work with the 
317.

There used to be a higher current adjustable in TO3 - no idea whether there 
still is. 

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#458613

Ian Field wrote...
>
> Winfield Hill wrote...
>> Martin Brown wrote...
>>>
>>>On 03/05/2017 13:15, 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.
>>>
>>> Why not use a high power switched mode DC to DC converter
>>> to supply 8.5v to the anodes through a crude rheostat and
>>> power resistor?
>>
>> Or buck smps down to 9.7 volts and an LM317 with resistor
>> current limiting for each, w/o overheating issues.  LM317
>> thermal limits, protecting itself in case of shorts, etc.
>
> But it won't do the 3A top limit mentioned - 

 Oh, sorry (referring quickly to AoE Table 9.2), I meant
 the LM350T (3A) or the LM338T (5A), in TO-220 packages.
 Or if pressed, a few LM317 (1.5A) in parallel.  Examine
 the spec sheets to see if more than 9.7 volts is needed.


-- 
 Thanks,
    - Win

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#458630

Winfield Hill wrote...
> Ian Field wrote...
>> Winfield Hill wrote...
>>> Martin Brown wrote...
>>>>
>>>> On 03/05/2017 13:15, 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.  ...
>>>>
>>>> Why not use a high power switched mode DC to DC converter
>>>> to supply 8.5v to the anodes through a crude rheostat and
>>>> power resistor?
>>>
>>> Or buck smps down to 9.7 volts and an LM317 with resistor
>>> current limiting for each, w/o overheating issues.  LM317
>>> thermal limits, protecting itself in case of shorts, etc.
>>
>> But it won't do the 3A top limit mentioned - 
>
> Oh, sorry (referring quickly to AoE Table 9.2), I meant
> the LM350T (3A) or the LM338T (5A), in TO-220 packages.
> Or if pressed, a few LM317 (1.5A) in parallel.  Examine
> the spec sheets to see if more than 9.7 volts is needed.

 That's one (or a few) buck converter we're suggesting,
 to be shared among CL circuits and stations.


-- 
 Thanks,
    - Win

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#459061

On Wednesday, 3 May 2017 19:43:42 UTC+1, Ian Field  wrote:
> "Winfield Hill" <hill@rowland.harvard.edu> wrote in message 
> news:oed67g0240p@drn.newsguy.com...

> >> Why not use a high power switched mode DC to DC converter
> >> to supply 8.5v to the anodes through a crude rheostat and
> >> power resistor?
> >
> > Or buck smps down to 9.7 volts and an LM317 with resistor
> > current limiting for each, w/o overheating issues.  LM317
> > thermal limits, protecting itself in case of shorts, etc.
> 
> But it won't do the 3A top limit mentioned - the 78xx appnotes show how to 
> increase current with an external bypass transistor, it should work with the 
> 317.
> 
> There used to be a higher current adjustable in TO3 - no idea whether there 
> still is.

Parallel 317s do the job with overheat protection - external pass lacks that unless you complicate things.


NT

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#458552

On Wednesday, May 3, 2017 at 8:15:42 AM UTC-4, Clifford Heath 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).
> 
> Is there any other off-the-shelf quick solution that comes to
> mind?
> 
> Clifford Heath.

Have you looked for a pulse width modulated current regulator?  That would be more efficient putting less heat into the regulator.  And would also use less power from the batteries.

Microcontrolers are very cheap now and might be a cheap and reliable 
way to adjust the current instead of having variable resistors.

                                    Dan

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#458561

On Wed, 3 May 2017 22:15:36 +1000, the renowned 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.
>
>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.

A voltage regulator with a crude adjustable current limit, plus a
ammeter + charge meter/setpoint per anode. Could be with a micro
easily, and relatively quickl depending on what 'quick' means. 

What's the idea if the total current is too large for the batteries?
Go around and turn a few hundred knobs? Seems like a hassle. 

--sp 


-- 
Best regards, 
Spehro Pefhany

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#458577

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.

You gonna make circuit boards, or just hand-wire, or what?

How about a good old LM723 with a honkin' big pass transistor?  You 
should be able to make a nice constant-current supply with voltage 
limiting.

You should be able to do the same thing with switchers, but the design 
time would be longer -- the all-linear way just means you need big heat 
sinks.

Surely if this is a known procedure then there must be products to do it.

-- 
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work!  See my website if you're interested
http://www.wescottdesign.com

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#458605

"Tim Wescott" <tim@seemywebsite.com> wrote in message 
news:5Mydnddrq4l6mZfEnZ2dnUU7-LmdnZ2d@giganews.com...
> 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.
>
> You gonna make circuit boards, or just hand-wire, or what?
>
> How about a good old LM723 with a honkin' big pass transistor?  You
> should be able to make a nice constant-current supply with voltage
> limiting.
>
> You should be able to do the same thing with switchers, but the design
> time would be longer -- the all-linear way just means you need big heat
> sinks.
>
> Surely if this is a known procedure then there must be products to do it.

Could be a bodge - they used to mix lime in the concrete to make it set 
faster, but it eats the steel reinforcements - there were some spectacular 
disasters hit the news. 

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#458644

On 04/05/17 04:47, Ian Field wrote:
> "Tim Wescott" <tim@seemywebsite.com> wrote in message
> news:5Mydnddrq4l6mZfEnZ2dnUU7-LmdnZ2d@giganews.com...
>> 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,

>> Surely if this is a known procedure then there must be products to do it.

There are, but usually in the context of also installing long-term
monitoring equipment (e.g. in an old skyscraper with concrete cancer).
This is new work that won't be monitored continuously.

> Could be a bodge - they used to mix lime in the concrete to make it set
> faster, but it eats the steel reinforcements - there were some
> spectacular disasters hit the news.

Not sure about that Ian - it's the high pH of concrete that protects
the steel. Concrete cancer results when water leaches the pH down
from 13-ish to about 8.5, esp. when chloride is present (e.g. marine
air). More lime should help protect the steel, but the most important
things are to (a) stop the rusting process, (b) passivate existing
rust and (c) prevent water and chloride ingress with appropriate
coatings. If you haven't done that, that's when you need to call in
the experts to passivate, seal and monitor the rusted steel.

Clifford Heath.

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#458781

"Clifford Heath" <no.spam@please.net> wrote in message 
news:590a94db$0$53186$c3e8da3$fdf4f6af@news.astraweb.com...
> On 04/05/17 04:47, Ian Field wrote:
>> "Tim Wescott" <tim@seemywebsite.com> wrote in message
>> news:5Mydnddrq4l6mZfEnZ2dnUU7-LmdnZ2d@giganews.com...
>>> 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,
>
>>> Surely if this is a known procedure then there must be products to do 
>>> it.
>
> There are, but usually in the context of also installing long-term
> monitoring equipment (e.g. in an old skyscraper with concrete cancer).
> This is new work that won't be monitored continuously.
>
>> Could be a bodge - they used to mix lime in the concrete to make it set
>> faster, but it eats the steel reinforcements - there were some
>> spectacular disasters hit the news.
>
> Not sure about that Ian - it's the high pH of concrete that protects
> the steel. Concrete cancer results when water leaches the pH down
> from 13-ish to about 8.5, esp. when chloride is present (e.g. marine
> air). More lime should help protect the steel, but the most important
> things are to (a) stop the rusting process, (b) passivate existing
> rust and (c) prevent water and chloride ingress with appropriate
> coatings. If you haven't done that, that's when you need to call in
> the experts to passivate, seal and monitor the rusted steel.

The rust is pretty difficult to get at until it starts to expand to the 
point where chunks of concrete drop off. 

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#458802

On 05/05/17 05:55, Ian Field wrote:
>
>
> "Clifford Heath" <no.spam@please.net> wrote in message
> news:590a94db$0$53186$c3e8da3$fdf4f6af@news.astraweb.com...
>> On 04/05/17 04:47, Ian Field wrote:
>>> "Tim Wescott" <tim@seemywebsite.com> wrote in message
>>> news:5Mydnddrq4l6mZfEnZ2dnUU7-LmdnZ2d@giganews.com...
>>>> 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,
>>
>>>> Surely if this is a known procedure then there must be products to
>>>> do it.
>>
>> There are, but usually in the context of also installing long-term
>> monitoring equipment (e.g. in an old skyscraper with concrete cancer).
>> This is new work that won't be monitored continuously.
>>
>>> Could be a bodge - they used to mix lime in the concrete to make it set
>>> faster, but it eats the steel reinforcements - there were some
>>> spectacular disasters hit the news.
>>
>> Not sure about that Ian - it's the high pH of concrete that protects
>> the steel. Concrete cancer results when water leaches the pH down
>> from 13-ish to about 8.5, esp. when chloride is present (e.g. marine
>> air). More lime should help protect the steel, but the most important
>> things are to (a) stop the rusting process, (b) passivate existing
>> rust and (c) prevent water and chloride ingress with appropriate
>> coatings. If you haven't done that, that's when you need to call in
>> the experts to passivate, seal and monitor the rusted steel.
>
> The rust is pretty difficult to get at until it starts to expand to the
> point where chunks of concrete drop off.

I guess that's why these people have a business. They can passivate
that rust electrolytically. It does involve some fancy gear to find
the reinforcing and ensure it's all electrically connected, without
demolishing the entire structure. After treatment with the impressed
current, it still needs some cathodic protection, but that's as often
galvanic (zinc anodes, etc) than powered. If powered, it's monitored.

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#458582

On Wednesday, May 3, 2017 at 8:15:42 AM UTC-4, 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, I
> guess because it's a remote site.
> 


> Is there any other off-the-shelf quick solution that comes to
> mind?
> 
> Clifford Heath.

Not sure I really understand the problem. But would tend toward using a micro controler and have the mirco controler figure out what the current needs to be.

I would expect that any system for corrosion prevention is going to be used for a long time.  The first person  who sets the current will probably do a good job.  But after several changes in personel. you might run into someone that does not understand all the reasoning.

It also sounds as if using a solar panel to charge the batteries might also be the economic  thing to do.  Hauling batteries around to get charged takes labor.

                           Dan

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#458608

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>



-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

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#458640

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.

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