What happens if you charge an SLA battery backwards?

[vtpeaknik]

Don't laugh!  No, I didn't do that myself.  But I was stupid enough (?) to buy a motorized electric wheelbarrow thingy at a yard sale (cheap).  2 motorized main front wheels (with separate motors) and one swiveling rear wheel.  It seemed to only go in reverse, and strongly so - but that was in the fast-forward switch setting.  Also, the charger they said went with it was clearly not the original, as it says "Linksys" on it (tiny switching supply, 12V, 0.25A or so).

After taking it home, I found that it runs on a 12V SLA battery of about 20 AH size.  Checked the battery voltage.  About -12V.  That is, the polarity is reversed!  The positive side of the battery was connected to the red wire though.  Checked the polarity of the "charger" as is appears on the wires leading to the battery, and sure enough, it's reversed: negative to the red wire.

So, if the 12V SLA battery was charged in reverse, all the way to -12 volts, should I:
* keep using it that way, or
* discharge it to zero and then charge it the right way, or
* throw it away?

This wheelbarrow is an old model and the control circuit is all electromechanical relays, 6 of them.  So the good news is that probably nothing got fried from the reverse polarity battery.  The bad news is that something is not right with the relays, in particular, in the normal-forward switch setting I hear a click but the motors do not turn.  May have to replace a relay or two?

[Flux]

I have not heard of this before with a SLA. I suspect the technology doesn't respond at all well to being reversed. I am surprised they haven't vented and got all the water out.  As you have no idea how long it has been reversed it is difficult to suggest anything. To get it back the right way round you will need to discharge it to zero and recharge pretty quickly before it sulphates and it may not stand another reversal. If you leave it as it is it may work but I suspect the performance will be far from the original spec.  I think I may be tempted to try it reversed and swap the leads to get the barrow to run the right way and see how it performs. If the capacity is lousy you could try reversing it back.

I have seen car batteries reversed and they started a large diesel engine for several years in that state but they are a lot more robust than SLA.

Flux

[OperaHouse]

Keep using it that way.  Both plates are the same.  Discharging it again to zero will only do more damage.

[David HK]

Just an idle thought.

Would be possible for the control switch to have been wired in reverse. Select forwards and goes backwards. Select backwards and goes forwards.

The reason for this suspicion is "the positive side of the battery was connected to the red wire though"

Its worth a check.

David in HK.

[vtpeaknik]

Doesn't look like the switch wiring is reversible.  And the charger that was given to me with it charges the battery in reverse, regardless of the switches.

[David HK]

Something isn't right here.

Is there any possibility of a couple of photographs showing the charger, the relays and the switch.

I would be very wary of charging the SLA's directly from a charger in reverse polarity.

have you checked the battery polarity with no wires connected to the battery?

The charger unit seems hopelessly small for your requirements especially a 20Ah 12 volt battery.

Whats the make of the wheelbarrow?

An interesting enigma which probably has an easy soloution.

Regards,

David in HK

[vtpeaknik]

It's definitely the wrong charger.  And no I would not suggest charging a battery in reverse!  I'm only reporting the strange thing I've run into.  Right now I've got the battery out by itself, topping off the reverse charge (with a proper SLA charger, rated 1A i.e. C/17), later I'll measure how much charge it holds that way.  The battery is probably rather old so perhaps it wouldn't have held a lot of charge in either direction.

[joestue]

i have considered doing this as an experiment to see if the negative battery plates could be recovered and converted into a battery (since they always outlive the positive plates) but who really wants to do that with a forklift battery?

here's what i would do: discharge the battery to -10 volts (from -12v) and measure the amp hours.
you've probably only got a few amp hours of capacity. if so discharge through zero and change the polarity back.

[vtpeaknik]

I'm still undecided on whether to reverse it back to its original polarization.  But meanwhile I gave it an incomplete top-off charge in its current reversed state, then ran an LED lamp, about 120 mA, off of it for over 24 hours, i.e., about 3 AH.  During that time the voltage under load gradually declined from about 12.5 to 11.5.  This is more capacity than I expected, given the age and condition of this battery, which is nominally 17 AH.

I've also deciphered the control circuit (with 6 "S9U" type relays) and found out interesting and mysterious things there, but that's beyond the scope of this "storage" section.  I'll only say that the motorized two-wheeled module in its strong metal chassis is easily disconnected from the plastic wheelbarrow part and could some day be the basis for some other slow electric vehicle, whether a cargo-moving flat platform or cart, or a tricycle for a mobility-challenged person.  The original device was made by DR Power Tools, but I can't figure out the model number, it's too old to appear in their web site!

[vtpeaknik]

Hmmm, trying to recharge it after my discharge experiment, I can't seem to get it to settle on a rest voltage higher than about 12.1, while it was about 12.6 earlier.  Does that hint that it's tired of living in reverse?  Should I put it on a LONG float charge in reverse (which is what I think was done to it in the past), or should I discharge it fully and try charging it the other way?  Life's persistent questions...

[REdiculous]

I'd recycle/repurpose it.

At this point I bet you can replace it w/ one of these and see a gain in capacity.