Any electronics experts out there??? (really geeky question)

I'd think a cap would do it.

 

Maybe just use a small lightbulb like for a flashlight?

 

What you're describing is a smart charger and it sounds like you need a dumb charger/power supply/battery.

Most smart chargers work by sensing an initial discharged cell voltage and monitoring that cell voltage to achieve a charging profile that is correct for the type of cell that it is charging. So let's say it is a NiCad, it thinks that it sees 1.1v and it then starts cranking the voltage up to 1.3-1.4 volts to achieve a desired charging current (determined by the charging voltage and the internal resistance of the cell). That initial cell voltage would not be present on a capacitor, so no that probably wouldn't work; also if it did work (some smart chargers put out a trial voltage to see if there's a really deep discharged cell on the load and whether that will hold some voltage and what that voltage is - that's how it decides how many cells are in the load) then it probably wouldn't work for long as the capacitor would charge immediately to whatever voltage the smart charger was trying to put out and the charger would say it was charged and stop.

Anyway, when you put another load on that in parallel or in series (the plating tank), then the plating tank has a completely different voltage differential but the power supply doesn't know that, it still thinks that it is a NiCad, but one that is behaving strangely. The results may differ, depending on the charger and whether it is in parallel or series load configuration, but overcharging the NiCad is certainly a possible outcome.

What is the voltage rating on the power supply (most battery chargers aren't actually 1.5 volts, but 4.8 to 12 volts) and what is the plating voltage you're trying to achieve? Also was the trial that you did with the Nicad in series or parallel?

 

What you need is just a beefy power supply that will put out 1.5 volts at 6 amps. No smart charger, no trickle charger, no charger or current limiting of any kind,....just a power supply. I've de-rusted metal with a beefy power supply before. You just need a beefy power supply without any fancy electronics. And use a REAL power supply,....NOT a switching power supply with all it's unnecessary circuitry.

By the way, if you want to de-rust some steel, suspend the pieces in water and add a little salt to the water in order to increase the conductivity. I've run 10 or 15 amps at 15 volts through some rusty metal before and it really takes the rust away.

 

Not completely true, which is why I asked. The current determines the amount of material deposited/removed, but there will be a certain voltage characteristic of that plating bath for a given desired current. That voltage is part of the circuit and the other stuff in the circuit cares about the value.

Let's say the voltage is 2 volts to get 6A of plating current. If the Nicad is in parallel, then you've got 2V applied across a 1.2V Nicad (that wants to see at most 1.6-1.7V for charging) and the plating tank, which will eventually overheat the cell. Note that it's not the 6A that causes the overheating, most of that current is flowing through the tank, not the cell; but a fraction is flowing through the internal resistance of the Nicad and causing that to heat up over time.

If the characteristic voltage of the plating tank is closer to 1.5-2V, then a nicad cell pack set up as you describe would only put out 1.3-1.35V when fully charged and probably wouldn't source 6A through the plating tank at that low a voltage.

If you're putting the Nicad in series with the charger and the plating tank, then you're flowing 6A through the internal resistance of the Nicad and it will get very hot. I think parallel is better.

6A through the resistor will get very hot and you'll need a 10-20 watt resistor for just 1-2V across the resistor. Also, I don't see how the resistor will solve your "how get the charger to see a cell and start charging" problem. As I mentioned first, a DUMB power system solves most of your headaches. Given the pieces you have, that might be done by using charged Nicad cells. The problem I mentioned above is that 1.2-1.3V might not be enough for your plating tank.

If you want to continue to try to outsmart your smart charger (not something I would necessarily endorse), then I might try a single Nicad with a series resistor in parallel with the plating tank. The Nicad with a series resistor presents a triggering voltage to the smart charger, but the resistor keeps the current in that branch of the circuit low; with most of the current going through the circuit branch of the plating tank. A 10-ohm 1/4 watt resistor is probably good for up to 0.5-0.7 volts of additional voltage drop in that branch without burning up (allowing the power supply to put out up to 2V), while having a low enough resistance that the smart charger might still think it was seeing a battery.

 

Problem is you are putting the battery in series, you should put it in parallel, that way the charger will still see the voltage but it won't have to pump 6A through it to get to the tank. Put a resistor in series with the battery (but NOT in series with the tank) - that will ensure a small current flows through the resistor/battery and keeps it from overheating but should still turn on the charger.

It sounds like the charger works by sensing the voltage on the line so the value of the resistor shouldn't have a major impact on whether it turns on because the voltage will still be there. Try a 100 Ohm resistor which could be just 1/4 watt and you should be OK. I'm assuming the voltage and current (same thing really) from the charger vary to a predetermined level so you may need to play with the resistor a bit. I dont know what the max charge rate of that battery is but they can usually take an amp easily. a 100-Ohm is only going to be 20mA (20 thousandths of an amp) so you will not overheat it. You could try dropping the resistor value down if you need to. Or, just add another resistor in parallel with the 1st and it will drop it to 50-Ohm, 4 of them would be 25-Ohm.

If your PS is a POS you could also use a PC power supply. The 12V rail would put out 20 amps on a 240-watt supply which should be way more you need. Just dont come back whining if it explodes on you (just kidding, but do be careful). The solution will have a decent amount of resistance which will control the amp output and I doubt you'll hit anything near 20A. I anodize and even with some big parts you're way below 20A.

Mind if I ask what you're doing? I have all the stuff at my shop to zinc plate. I do it before copper plating to help the copper have a nice base.

EDIT: LOL, yeah just read Yins post... coulda saved my typing

 

You live in WI / Chicago area and can not find a plater?