DC current sources

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.

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.

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.

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

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Regards, 
Martin Brown

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

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

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Best regards,  
Spehro Pefhany

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

Not sure I really understand the problem. But would tend toward using a mic ro 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 some one 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 tak es labor.

Dan

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

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.

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.

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.

Go eBay shopping. No guarantees, but this was the top result in my third search:

--

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

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

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

That's the key! Not properly designed or specified. Hard to design a solution when you don't understand the problem.

Am I the only one who thinks that 1200 amps for two weeks is a lot to expect from batteries at a remote site?

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.

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...

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

ESP8266 wifi modules are a

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

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

--
 Thanks, 
    - Win

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?