Can you fix a lead-acid battery that's charged backwards?

[mike]

I bought a pair of electric scooters. They'd "fixed" the charger
and managed to get the batteries charged backwards. Can I discharge
them and charge 'em up forwards? Any special techniques? Fast/slow/
charging?
May be a moot point as I expect the speed controller box is fried too.
mike

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[James Sweet]

I bought a pair of electric scooters. They'd "fixed" the charger
and managed to get the batteries charged backwards. Can I discharge
them and charge 'em up forwards? Any special techniques? Fast/slow/
charging?
May be a moot point as I expect the speed controller box is fried too.
mike

Generally no, since you can't access the individual cells inside the battery
separately you'll normally end up with some cells charging ok and others
reversed, it's easier to just buy new batteries.

The speed controller is probably pretty simple, crack it open and have a
look.

 

[Just Another Theremin Fan]

Can I discharge them and charge 'em up forwards?

ROTFPML!!!!! Is this post serious?

 

[satellite_jim]

I actually have some experience with backwards batteries. I grew up in my
fathers auto repair shop in the sixties. Back then if you hooked up the
jumper cables to a generator equipped car you could start the car and the
generator would reverse polarity and you could go on your merry way with a
positive ground American car. We would just leave the lights on over night
and then charge the battery the correct way and polarize the generator (jump
the positive to the generator output lead for a second) in the morning. If
the battery was good to start with it would recover fine.

Jim.........

 

[Dave Plowman (News)]

I actually have some experience with backwards batteries. I grew up in
my fathers auto repair shop in the sixties. Back then if you hooked up
the jumper cables to a generator equipped car you could start the car
and the generator would reverse polarity and you could go on your merry
way with a positive ground American car.

I don't see how, as the cutout wouldn't pull in. That only happened when
the generator started producing more than battery volts which it couldn't
when reverse connected.

One way to instantly polarize the dynamo was to flick the cutout in
manually.

 

[Jim Adney]

I bought a pair of electric scooters. They'd "fixed" the charger
and managed to get the batteries charged backwards. Can I discharge
them and charge 'em up forwards? Any special techniques? Fast/slow/
charging?

I think you should have a good shot at this. Try just discharging them
first, use a light bulb that lights normally across the battery to
discharge them, and let it go a couple days past the time when the
bulb is no longer glowing.

Then connect the charger properly and try to charge them, slowly. If
they take too much current, insert the light bulb again as a current
limiter, but you should be able to take the bulb out of the circuit
after a day or 2.

Let us know how this progresses.

-

 

[Jim Adney]

I don't see how, as the cutout wouldn't pull in. That only happened when
the generator started producing more than battery volts which it couldn't
when reverse connected.

I guess I'll have to think about the WHY of this, but I've seen it
happen. I agree that it's odd. The time I saw it, the owner had
installed the battery backwards, then realized his mistake and put it
in correctly. When I got to it the battery was correct, but I
eventually determined that the generator was polarized backwards.

Now I have to admit that it never occurred to me to wonder why putting
the battery in backwards would reverse polarize the generator while
putting the generator in forwards wouldn't correct it.

-

 

[Bill Janssen]

I guess I'll have to think about the WHY of this, but I've seen it
happen. I agree that it's odd. The time I saw it, the owner had
installed the battery backwards, then realized his mistake and put it
in correctly. When I got to it the battery was correct, but I
eventually determined that the generator was polarized backwards.

Now I have to admit that it never occurred to me to wonder why putting
the battery in backwards would reverse polarize the generator while
putting the generator in forwards wouldn't correct it.

I think the key to an explanation is that the cut out relay senses
current direction as determined
by referencing the magnetic field of the current to the magnetic field
of a voltage fed electromagnet.

Since both were reversed the cut out relay didn't have a clue as to the
polarity.

I hope I explained my thinking clear enough.

Bill K7NOM

 

[Dave Plowman (News)]

I think the key to an explanation is that the cut out relay senses
current direction as determined by referencing the magnetic field of
the current to the magnetic field of a voltage fed electromagnet.

Since both were reversed the cut out relay didn't have a clue as to the
polarity.

I hope I explained my thinking clear enough.

In the UK, when I were a lad, most cars were positive ground. This of
course made no sense to the average punter, and it was very common for the
clueless to fit a new battery the wrong way round. And the symptoms were
the battery didn't charge.
As electronics became more popular, the change was made back to negative
ground for new vehicles. And if the owner of an older vehicle wanted to
fit a modern stereo, the easy answer was to convert it to negative earth,
and I've done dozens. And always had to re-polarise the dynamo before it
would cut in and charge. If the cut in had operated with the battery the
'wrong' way round, that would have re-polarised the dynamo and made this
unnecessary.

Of course, this was with the infamous Lucas electrics. Could be that other
makes work differently.

 

[jakdedert]

Of course, this was with the infamous Lucas electrics.

....the Prince of Darkness....

jak

 

[Jonathan]

I had this happen (by accident) with a NiCad pack. I just flattened it and
re-charged it the correct way no preoblems.

JD

 

[Jim DeClercq]

In technical terms, you probably have a "sulfated" battery.
In car sizes, 5 amps for 24 hours should get it charging in the
right direction. Smaller battery, less current. It will take a
while. You will be forming the battery, giving it its initial
charge.

Go for it.

Jim



: I bought a pair of electric scooters. They'd "fixed" the charger
: and managed to get the batteries charged backwards. Can I discharge
: them and charge 'em up forwards? Any special techniques? Fast/slow/
: charging?
: May be a moot point as I expect the speed controller box is fried too.
: mike

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: Return address is VALID but some sites block emails
: with links. Delete this sig when replying.
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[mike]

In technical terms, you probably have a "sulfated" battery.
In car sizes, 5 amps for 24 hours should get it charging in the
right direction. Smaller battery, less current. It will take a
while. You will be forming the battery, giving it its initial
charge.

Go for it.

Jim



: I bought a pair of electric scooters. They'd "fixed" the charger
: and managed to get the batteries charged backwards. Can I discharge
: them and charge 'em up forwards? Any special techniques? Fast/slow/
: charging?
: May be a moot point as I expect the speed controller box is fried too.
: mike

Thanks for the advice.
I fixed the charger and re-reversed the batteries. One scooter seems to
be working fine. The batteries seem to be ok on the other one, but
somebody ran it with insufficient air in the rear tire and hurt the
inner tube. Won't hold air long enough to give it a good test.
mike

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[Dave Plowman (News)]

In technical terms, you probably have a "sulfated" battery.
In car sizes, 5 amps for 24 hours should get it charging in the
right direction. Smaller battery, less current. It will take a
while. You will be forming the battery, giving it its initial
charge.

If the battery is sulphated, most modern chargers won't deliver enough
volts to get anywhere near 5 amps due to the high cell resistance. Many
are voltage limited to perhaps 14 volts or so, and might need several days
to get any result - if ever.

 

[Jim Adney]

If the battery is sulphated, most modern chargers won't deliver enough
volts to get anywhere near 5 amps due to the high cell resistance. Many
are voltage limited to perhaps 14 volts or so, and might need several days
to get any result - if ever.

That's probably for the best anyway. A sulfated battery should never
be charged at a high rate. That will just hydrolize water and can
damage the plates. IF recovery is possible, and it sometimes is, then
your best bet is with a very small charging current over a number of
days. I find that a week is typical for a car battery, but I had one
that took 2 weeks.

If you insist on instant gratification, you should just buy a new
battery.

-

 

[Dave Plowman (News)]

That's probably for the best anyway. A sulfated battery should never
be charged at a high rate. That will just hydrolize water and can
damage the plates. IF recovery is possible, and it sometimes is, then
your best bet is with a very small charging current over a number of
days. I find that a week is typical for a car battery, but I had one
that took 2 weeks.

Yup. I was just worried someone might try using a variable bench supply to
push through the 'required' 5 amps if their charger didn't do this.

If you insist on instant gratification, you should just buy a new
battery.

Think you'll end up doing this anyway. ;-)

 

[Jim Adney]

Yup. I was just worried someone might try using a variable bench supply to
push through the 'required' 5 amps if their charger didn't do this.


Think you'll end up doing this anyway. ;-)

It's generally pretty easy to tell whether you have a good chance or
not. If you just measure the voltage while trickle charging it, the
voltage should rather quickly come up to 2 V or more per cell. If your
battery seems to be low by some multiple of 2V, then you probably have
a shorted cell, which generally can't be fixed. If you can get to the
2V per cell threshold, on a trickle charge, then you have a pretty
good chance of recovery.

Make sure the water is covering the plates.

If there is a broken connection in the battery the charging voltage
will be high, but it will drop quickly as soon as you stop charging
and put a very small load on it. You won't be able to fix a broken
connection, either.

-