Modifying Battery Chargers

Now I know what you’re thinking clicking on this thread title, and no, I’m not talking about doing anything to change the charge rate or do anything to affect the circuitry. I don’t like getting splashed with acid from exploding batteries. :wink:

My question is regarding the legality of charging a competition battery with a charger that has been modified.

Specifically I would like to take the internals of several Schumacher chargers (from Amazon) out of their cases and put it in a custom enclosure (integrated into a battery cart). The chargers are mostly empty space inside (probably for air flow) and I think we can do a better packaging and cooling job ourselves.

I would assume this is legal since these chargers are used by many teams and they all have to be “modified” in order to attach an SB50 connector. Anyone have an opinion on this? Or a rule I’m missing?

I don’t see any rules that would prohibit this. The only rules that mention battery chargers are R34 and R35, which do not require any particular packaging of the charger. It might make it harder to verify R35 (6 amp peak charging current) in case a question comes up.

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Legal per robot rules? I can’t see why not.

Likely to attract some attention from UL Safety Advisors and venue staff? More than in stock form.

(If relevant: We really like these ones, which are an @AllenGregoryIV find and about the size of two bigger USB power banks if that gives you a sense of scale.)


Is your custom enclosure going to have any metal parts? You will want to maintain sufficient clearance from those metal parts to ensure that the internals of the chargers don’t arc to those metal parts. Those metal parts will also have to be grounded properly. Lastly, those metal parts must be able to resist deformation so that the clearance from the charger internals is maintained.

There are likely to be parts of the charger circuitry that get hot. There needs to be sufficient clearance from the enclosure that you do not melt or burn any non-metal parts of the custom enclosure. The airflow through the custom enclosure must also be sufficient to not cause an unreasonable temperature rise in the charger circuitry.

That is the gist of the UL safety standards (and other international safety standards).

I have had several different Schumacher battery chargers for my own use. Every few years, one fails and I have to replace it. They are clearly built down to a price using very cheap parts. It is quite likely that in a few years you will be looking for new chargers. It may be difficult to find new ones that fit your custom enclosure at that time.

As you state, the rules in fact require you to use a battery charger that has been modified, see R34.


If we cared about improving this program for rookie teams, including one of these in the gray tote would be a nice ripe piece of low-hanging fruit.

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Oh we haven’t gotten that far into the design. Checking legality was the first step. We’ve been wanting to build a proper battery cart for a while, but the volume is pretty restrictive so I was thinking about doing what I asked about here.

Generally I was thinking polycarbonate or G10/FR4 for the enclosure.

I had 6 of the FC battery chargers in the priority list, before I chickened-out. They were 5a vs 5.5a, and I don’t know the build quality, but they were fairly compact. They were in the rookie kit this year.

I should have done it, we really need to get space to charge 6 batteries in the cart and it would have only been 120 FC points. There are 644 left, for those with remaining credits.

Compact, but I’m not 100% sure it’s more than a glorified power supply based on my basic internet searching for the part number. Add in the lack of a website on the FC and KoP checklist, and it just gives me the willies.

Judging by Alibaba prices (where everyone and their grandmother is selling a power supply under that same part number), it would only be a $10-per-unit bump to the pretty excellent PowerStream charger I linked to above, and that’s if FIRST couldn’t work a further price break (or live with a lower peak charge rate). If they really wanted to ball out, maybe $20 at worst to get an SB-50 put on it somewhere with the labor. It’s a massive opportunity for improvement.

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While it may be legal according to FRC rules, I would recommend that you don’t take the chargers out of the enclosure they were originally manufactured with. If there is ever a fire and the insurance company finds that you modified the charger in that way, it is likely they will use that as a reason to not pay out.

I would also recommend that you don’t make the space for the chargers too tight so that when you have to replace them, you can fit a different charger.

Be careful when working G10/FR4. The dust contains glass particles so you really don’t want to breath it in or have it on your clothing.

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