I picked up a Schwinn electric scooter off of craigslist.
It had 2 batteries@12v, 10ah VRLA for 24v. Zhongshan Hengli Elec. Enduring Battery CB 10-12. Stamped into the case of both batteries is "OBMHT2" on one end and "0309 06" on top.
The batteries were toast.
The craigslist ad ended up being a pawn shop so the available history of the scooter was slight but if the code "0309 06" is a date code, 2006 would seem about right.
When they had taken the scooter in it ran. I haven't been able to find out when they received the scooter but they told me someone had come in to look at it and it's green light on the throttle came on but that's it. They put it on the charger overnight and when they tried it again the 12inch wheel did about an 1/8th of a turn and that was it.
We hooked the charger up to see if it ran at all, it did so I snagged it.
When I got it home I took the battery bag out of the scooter's deck and then removed the batteries from the bag and stuck a meter on them. Hooked in series for 24v, the batteries measured 320milivolt... not good.
I plugged the batteries into the supplied charger and left them overnight, about 20 hours of charge time, and measured them again. The meter read somewhere around 1.5 volts then immediately dropped back to 320milivolt.
I separated the batteries and tried hooking up a Black&Decker/Vector smart charger in the desulphate mode, the charger shut down immediately so I hooked up a good 12v 9ah SLA in parallel to keep the charger happy and running. 24 hours of that did nothing... the now familiar 320milivolt.
I tried zapping them a few times with a 50v 10000µF capacitor charged up by the pedal gen but that also did nothing, as did hooking the pedal gen straight to the battery.
The scooter needed some work. It looked to have had the front end built backwards, possibly from the factory, and a flat rear tire so I got busy working on the scooter, figuring the batteries were a loss.
As I was tinkering with the scooter my mind pondered battery sulphation. I started thinking about it in a more physical sense versus a chemical sense.
A thought popped into my head that the sulphation was a blockage that wasn't letting the battery do it's thing, kind of like a spit wad stuck in a straw, and I thought "Why not hook the battery up backwards and try pushing the blockage backwards, such as you might try to do with a spit wad if it had gotten stuck in a straw.
With the batteries behaving as they were, I figured I had nothing to lose and all I had to do was bypass the pedal gen's blocking diode and pedal backwards.
With the pedal gen it's easy to gauge how much power you're putting into something by how hard it is to pedal/turn the cranks.
I could tell the pedal gen was pushing current when I reversed the polarity to the batteries. I pedaled the voltage to about -12v with the batteries still in series then tried hooking them up and pedaling with the correct polarity and still nothing. The batteries just wouldn't take a charge.
Since they had seemed to be doing "something" with the reverse polarity, I pedaled them again but this time to about -18v but pedaling again with correct polarity still produced nothing.
I decided to hook them back up to their charger, leaving the meter hooked to them, and get back to work on the scooter.
As I worked something caught my eye... the meter, which had been frozen at 27.8v, float voltage of the charger, was starting to drop. It worked it's way down to around 26v then started heading back up.
I took them off charge and the pack showed 6v. I had a 12v automotive test light near and hooked it up and the bulb glowed for a bit then died out. Hmmmmmmm
After a few more tries back pedaling and seeing things getting a little better every time, I drained the batteries as near to 0v as I could then hooked them up to the scooter's charger with reverse polarity and took them all the way to the chargers float voltage of around (-)27.8v. I did this a few times, the longest time leaving them on the reversed polarity was about 5 minutes. Every time the batteries were hooked back up with the correct polarity they showed a better standing voltage and gave a longer run time on a 24v handicap scooter motor.
The batteries now get pretty warm during the charge routine and last night they never would get to the point where the scooter's charger would shut off. They kept pulling amps from the charger for over 4 hours and although not hot, they did get warm. I took them off charge and let them sit for about 8 hours and the pack measured 24.6v this morning.
The handicap scooter motor ran for about 15 minutes pulling around 2.5amp and brought the pack down to around 20v and once disconnected, the pack came back up to 23.6v.
I don't know if these batteries will ever be any good but coming from, more or less, zero voltage to a half way respectable voltage of 24.6 impressed me.
I'm also working on a tired and abused pair of 6v Powerwheel batteries that were left drained and uncharged in a garage for about 5 years and they are starting to show similar signs of coming back to life.
When I first started seeing results from reversing the polarity I was more than surprised. I've read quite a bit on desulphating over the years and not once... have I seen anything about reverse charging. I decided to see if I could find anything online and found 2 interesting sites.
http://www.candlepowerforums.com/vb/showthread.php?t=28498
and another post here
http://www.electro-tech-online.com/340094-post12.html
-- W A R N I N G --
Batteries are inherently dangerous and even more so when reversing the battery's polarity.
Do NOT attempt this if you are unfamiliar or uncomfortable with batteries and high current or voltage.
Don't experiment indoors or near the batteries and wear protective clothing.
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