How can I evaluate a charger before I buy it? I don't own any kind of amp meter or electrical test devices other than a 30 year old $15 multimeter. I'm looking to buy a used, high-amperage, manual battery charger to run an electrolysis tank for de-rusting iron parts a few times a year.

  • Was your test battery discharged? If it was fully charged already, a sensibly designed charger wouldn't shorten its life by banging 40A through it.
    – alephzero
    Jun 8 '19 at 15:56
  • How do I tell if it is charged or discharged?
    – Mic
    Jun 8 '19 at 18:10

You shouldn't be shopping for a battery charger but for a power supply.

A properly designed battery charger will have protection circuits that stop it frying batteries (and on a bad day, starting fires) just because the user set it to the highest charge rate. That will most likely make it useless for electrolysis.

On the other hand, if you tell an adjustable 40A power supply to output 40A, that is what it will do, at whatever voltage is necessary.

  • Yep, short of a large battery charger, have an old PC power supply I can use.
    – Mic
    Jun 8 '19 at 18:25

I use a wall-wart for electrolysis - 20V at 2Amps... works fine.

Testing that charger properly may take much more gear than you have, seeing it work on a battery probably meant it was fine.

But it may have control circuitry that will prevent it working to do your electrolysis...

  • I have large rusty items and want it done in a few hours.
    – Mic
    Jun 8 '19 at 15:14

It occurred to me that good test setups are close to operating conditions, so an evaluation better than battery trials would be electrolysis itself. Before that occurred to me, I drained my core-battery by hooking it up to a spare old fashion head light. When the light dimmed to almost nothing, I figured it was really low.

I scheduled a revisit, and brought the drained battery, some washing soda, a large rusty car part, an even larger rubbermaid tub, and a rebar electrode. Used their garden hose to make the solution. The charger generated heavy gassing, much heavier than my 2/6 amp charger. After, we just dumped the solution since there's nothing evil about it. I bought the charger.

  • Glad you found a solution! I edited you answer to make it a bit more concise, since the first paragraph wasn't really needed ;)
    – Cullub
    Jun 10 '19 at 3:36

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