Charger polarity help

[yoyoman]

I bought a bike w/ a front hub motor, a controller, and 2 SLA 12V12Ah batteries. What's lacking now is the charger. From a scrapped scooter purchase, I have 3 12V batteries and a charger. I'd like to use the scooter charger to charge the bike batteries, or at least to see if they usable. Together, they're down to a mere 1.93V.

I've spliced a phono plug connector that I'm going to connect to the ends of the charger's 3 prong plug. To prevent any mishaps, I'd like to ask for input on my connections. See my photos:

The charger has a red and green wire. When plugged in and connected to the multimeter,you can see the +41.8V.
The battery wiring has an inner insulated wire surrounded by wire. With the insulated wire connected to Red and the outer wire connected to Black, I get +1.93V.

So, would I take the battery's inner insulated wire and connect it to the charger's red, and take the battery's outer wire and connect it to the charger's black? That seems somewhat logical, but something in the back of my mind, from my physics days, reminds me of connecting + to - .. sort of alternating that way, like how you'd connect two batteries together.

I don't want any mishaps, so you're assistance would be greatly appreciated!

 

[Link]

The charger + should go to the battery + and charger - to battery -.

I'll be surprised if you get those batteries revived. I doubt they'd be able to take 0.16V per cell and live. :?

 

[fechter]

So, would I take the battery's inner insulated wire and connect it to the charger's red, and take the battery's outer wire and connect it to the charger's black?
...
I don't want any mishaps, so you're assistance would be greatly appreciated!

Sounds right to me.

I agree with Link that your batteries are unlikely to recover. They have a tendency to short cells when they go that dead, so things could overheat when charging. Watch them carefully and make sure nothing gets hot.

 

[Rassy]

I may be missing something, but it sounds like you plan to charge two batteries (24V) with a 36V charger. Not a good plan. Also, with old batteries like you have, I would recommend you try to recover them individually with either an automotive charger, or even a small accessory charger.

Good luck.

 

[yoyoman]

I tried an car battery charger the other day, and the charger would always show "check". I attributed this to either the charger wasn't working properly or the batteries were not usable. I thought I'd try this battery charger from my scooter as a last resort.

Hmm, so if charging the two 12V batteries (24V) is not good with the 36V charger, I'll add another battery from the scooter. Heh, I probably would have saved time by just introducing these two batteries into the scooter charger system instead of going this route ...

 

[Rassy]

Hi again yoyoman. You are getting close to understanding the problem. If you put the two (bad) batteries in series with a good battery and then hook them to a 36V charger the good battery may get way overcharged and thus ruined. If you go ahead and try this, keep a watch and check the individual batteries with your voltmeter. You don't want a 12V battery to be charged much over 14V.

Good luck.

edit: It sounds like those 12V 12AH batteries are probable shot.

edit: Why not just use the "scooter" batteries on the bike?

 

[yoyoman]

The scooter batteries are wedged in tightly into a steel frame, and I haven't found a good way to get them out. Maybe if I turn the scooter upside down, the gravity will be enough to get them out. I don't see anything other than gravity and a tight fit holding them in place. I would have used these batteries earlier, but the battery wires are soldered directly to the battery, and for some reason my old 15W soldering iron wasn't able to melt the solder so that I could remove the connectors. So, all 3 batteries are wired together with some super solder!

I bought a butane soldering iron today that I assume should be sufficient for me to melt the solder to have access to the battery tabs, and thus I can connect these to the bike motor to see if it even works.

For $50, I got a 2000 Univega Rover 300 mtb that is a bit rusty and needed a new chain, a 24V front hub motor, two 12V batteries in a nice bag that sits on a rack, a controller, and a cateye bike "computer". So, hopefully at least the motor and controller still work. If not, after I add the new chain, hopefully I can sell the bike for close to the $50 I paid and call this a lesson learned.

 

[Rassy]

Sounds like a fun project. I like "deals" like that. Your hub motor would probably be ok at 36V if you were to try using all three batteries, and then you would have the proper charger. Don't know if the 24V controller on the bike can take 36V. Of course the batteries would not fit in the bag. If you end of running at 36V, PM me and I'll give you an original WE bag that velcros to the rack and holds three 12V 12AH batteries. If both motors are brushed motors, or both motors are brushless motors, then the controller from the scootor could be used on the bike.

Good luck.

edit: Be careful with the butane. Some here have reported damage to batteries with too much heat. Part of My thought with using all three batteries on the bike was that you would not have to disconnect them. Another way, just snip the wires between the batteries and splice or add new connectors to the wires.