Increasing current of a car battery charger.

[Acebars]

Hello everyone, my first post here although I have been reading here intently.

I'm zinc plating motorcycle parts at home via electrolysis and I'm currently using a 6V battery charger with I believe a 6A current. This is ok for small-medium sized parts however I'd like to go bigger and zinc plate a motorcycle tank.

Question is how do I increase the current (A), decreasing the voltage is not necessary but I am lead to understand in between 1V-3V is optimum.

I understand an inverter is required but I'm an electrical noob (GCSE was my last splash with electrics).

Appreciate any help!

 

[BradtheRad]

It would be great if you could take the 6 A at 6 V, and convert it to 12 A at 3 V.

Do you know what kind of waveform the charger is putting out? Pulsed DC? Smooth DC?

If smoothed DC, one efficient way would be to chop it through a full H-bridge, then through a step-down transformer, 2:1 or 3:1 ratio. At the same time it steps up the current. Such a transformer will need a primary to carry 6A, and to carry 10A or more in the secondary. It will get expensive.

If it is pulsed DC, you might run it directly through the transformer, but that transformer will be expensive too.

A stack of switched capacitors may work. Charge two in series. Discharge them in parallel.

You'll take an efficiency hit due to losses.

 

[Acebars]

Hi Brad,
Thanks for the reply,

Just had a look at the charger, it's quite old (a 70s Bradex 10 (coincidence! :lol in brown). I have no idea about it being pulsed or not? (First time I ever heard such a thing) but I suppose it is standard DC so not pulsed?

I actually had a look at the charger and it said max 10A, suprised such a small box can give out that much.

I must say a lot of what you've said is over my head :lol: but I don't want to be buying in any expensive kit as I'm trying to do a cheap homejob! You mentioned a step-down transformer for smoothed DC, I thought transformers were only for AC currents?

What about transistors are they no good? My other option is just to use a large 6V batter I'm sure the Amperage must be high, trouble is 6V is a little high for the plating application.

 

[chuckey]

The two moves you can try is to replace any selenium rectifiers with silicon ones. look inside and if there is a block made out of loads of thin square fins, then its a selenium rectifier, these have a high voltage drop across them, but do protect the transformer. So wire silicon diode across them... Come back for more advice if required. the other thing is to wire a large electrolytic capacitor across the output. This will charge up on the voltage pulses and maintain the current for longer. The current you read on the meter is the "average" current, its actually going from 0 to 1.6 X what the meter is reading. Beware you can be over loading the transformer, put a cooling fan on it. if its overheating, you could try re-wiring the mains lead, so as to put a resistor in series with lead. which can be a large light bulb or small fire - beware mains is LETHAL.
Frank

 

[BradtheRad]

A smoothing capacitor has little purpose in a battery charger because it will always rise to the same volt level as the battery being charged.

I think the DC resembles mountains peaks going as high as 11 or 12V. It needs to go that high in order to push 10 A into a 6 or 7 V battery.

Anyway if the recommendation is that the power source should be a few volts, then it could help to install a smoothing capacitor, since that will have the effect of leveling the peaks and raising the valleys. You might start with a Farad value of 3300 to 10,000 uF (microFarads). The volt rating must be higher than the peak of the waveform coming from your charger. 25 V is a reasonable, common rating for electrolytic capacitors.

I do not have experience with electroplating, but seems to me that the way to get more current is by (1) enlarging the electrodes, and (2) by cleaning them so as to make it as easy as possible for ions to come and go at the electrodes, and (3) by ensuring good connections capable of carrying several amperes, and (4) possibly by enlarging the cables to the electrodes.

I imagine the bath itself appears as a resistor to your power source (the charger). Does the charger have an ammeter? If not, then you can try measuring voltage on the electrodes while out of the bath, and then watch how much it drops as you put them in the bath to plate. That will give you an idea what is the load on the charger.

Whatever amount of current you desire, your power source will need to provide a high enough volt level, to push the current through the bath. It's possible that a smooth 3V waveform is better than a pulsed 10V waveform, I don't know.