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Re: DC current sources

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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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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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