Horray for electric scooters!

May 22, 2008 5:07 PM

I want to charge this scooter w/o buying another bunch of crap. Can you help me?

Ok, so...I bought this scooter today reaaaalllly cheap off craigslist. It's been modified with a newer, bigger controller and newer, bigger batteries.

In its current configuration it's 36v, instead of the stock 20v. It's got an extra battery to be run at 48v, which is what I *want* to do, and yes the controller is rated for that kind of power.

This is the plug: here. I've got a 36v charger for it.

This is what the battery connections look like: here.

I'm assuming that if I install the 4th battery and charge w/ the 36v charger, it just won't charge the last battery?

What if I do two at a time, will that overpower the batteries?

I've also got a 12v "smart" car charger that can operate as low as 2A. Is there any way I can use it to charge the batteries? Should I use it just to charge the single battery and use the 36v to charge the 3? Will that even work?

Basically I don't want to spend another $40 on a cheap import charger if I've already got what I need.

Lend me your electrical knowledge!

posted by TomMelee to technology (6 comments total)

I'm guessing that if you charge the 48v string with a charger rated for 36v, it won't charge at all— the charger will say, "Hmmm, 44v. Fully charged!" and do nothing (if it's a smart charger), or try and fail to float charge (if it's a dumb charger with a diode or something).

I can't think of a reasonable way to charge that string without a 12v, or a 24v, or a 48v charger.

I'm assuming thos are lead-acid batteries, fwiw; if they aren't, then you really do want to get a charger designed for what you have.
posted by hattifattener at 6:48 PM on May 22

Oh, I missed your last question. Yes, you could charge three batteries with your existing charger and the fourth one with another charger. Try to keep them all at the same level of charge though: when you're actually using them, as the battery runs down, the weakest cell can get forcibly reverse-charged by the stronger ones, which bad for it. Invest in a $5 voltmeter. Measure each individual battery's voltage after they've been sitting for a while (not right after charging) and if one is lower than the rest put it on the 12v charger for a while to even them out.
posted by hattifattener at 6:53 PM on May 22

Thanks. I actually have a supermegabadass multimeter I got at an auction for $7, so I can test a lot more than just voltage. However---THANKS for the idea of swapping them around.

So, for clarification, you're saying that YES, I can use my 12v auto charger to do 1, and the 36v scooter charger for the other 3 at once, especially if I alternate which "1" gets charged now and then?

They are lead-acid batteries.
posted by TomMelee at 7:01 PM on May 22

Yes— connect the 36v charger across a string of three batteries, with the fourth one out of the loop (either before both charger connections or after both charger connections, so the charger current doesn't flow through it).
posted by hattifattener at 9:46 PM on May 22

Wikipedia talks about series and parellel circuits. Your batteries all connected in series externally would look like a single 48v battery, with the current of 1 battery. If you hooked them in parrellel, it would be a 12v hookup with the current of all 4 batteries. This link talks about series batteries and parrellel batteries. This link to a specific brand charger talks about how to hook up batteries in different configuration for different voltage rated chargers. This should apply to your charger as well.

From my understanding you have 2 good options -- Use the 36 volt to charge 3 batteries in series and charge the final battery with your 12 volt charger OR use the 12 volt charger connect to all the batteries in parrellel to charge them up.
posted by garlic at 12:41 PM on May 28

You know, I sort of thought about charging them in parallel but didn't get as far as making that leap in logic. Thanks for the heads up---I totally just bought a 48v charger though, it was only like $25, seemed like it was worth it for the hassle.
posted by TomMelee at 8:05 PM on May 28