DIY Electric Car Forums banner

1 - 4 of 4 Posts

·
Registered
Joined
·
70 Posts
Discussion Starter #1
A friend of mine built an EV a few years ago (maybe 3
or so). He put in 13 Group 31 Optimas. He drove it
probably < 200 miles. I know it was less than 30 days
due to registration issues he had. He couldn't
legally drive it. The car sat (with a very low
parasitic drain on the batteries) and was parted out a
few months ago. I took the batteries. As lead scrap,
they are worth about $20 total. I thought, well maybe
something can be done with these. Probably not, but
maybe. So, I asked around for some ideas.

Here is what I did:

1. I checked the voltages. They were all resting at
about 6 V. Bad ... very bad.

2. I tried to charge one with a regular battery
charger. No luck. It just gave an error and turned
off. Another one started charging but never
terminated the charge. After I took off the charger,
the voltage sagged from say 12.8 all the way to 12.4 -
12.5. I'd say it has very bad self discharge.

3. I tried the charger and desulfator and left it on
for about 2 weeks. No luck. Still can't hold 12.8 V.
Still has bad self discharge. So much for the black
magic solution.

4. I hooked the battery to another battery (in
parallel). That's basically constant voltage 13.0 V /
high current charging. That didn't work. It's
shocking the battery back to life - quite literally.

5. I hit the battery with high discharge rates in a
pulsed fashion. I literally shorted the terminals
instantaneously over and over again. I was trying to
burn off any microshorts between the plates. The
voltage would go from 10 or so almost to zero and
back. That is very dangerous. Don't try it. Then, I
got even more agressive and tried to push more current
by paralleling (momentarily very quickly off and on)
two batteries with reverse polarity - positive to
negative, negative to positive. I was again trying to
burn off the micro shorts. These batteries have
almost no CCA, so I didn't even get that much of a
current inrush. DON'T TRY THAT WITH FRESH BATTERIES
OR YOU'LL PROBABLY GET A SERIOUS EXPLOSION!!!

6. I hooked up the battery to my variac with full wave
bridge and set it for 15 A charge rate. I let it sit
about 2 hours. The voltage came up, but it got hot
and still self discharged.

7. Finally, I hooked a fresh battery from the pack
(sitting at 6 V) in series with a 120 V / 100 W light
bulb and put it on my Variac with full wave bridge. I
turned it all the way up to 163 V DC. The bulb lit
and I was pushing 1 A through the battery. I let it
sit like that for 12 hours or so. The voltage on the
battery came up from 6 V steadily up to about 11.5 V.
It's still going. I'm not sure when to cut it off,
12.0 V, 12.2 V, 12.4 V, 12.6 V, 12.8 V. Probably no
higher than that. Is there a better way to do this
without wasting > 90% of the energy used in waste
light and heat (the 100 Watt bulb)?

So, can someone explain chemically what happened to
these batteries and what I was technically doing in
each of these experiments - why the last one worked
best, but the constant voltage didn't ...

I still think they are scrap, but it was worth a try
to see if any capacity could be recovered from them.
Otherwise, they make a very nice set of large yellow
paperweights.


Thanks,

Steve

__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
 

·
Registered
Joined
·
70 Posts
Discussion Starter #2
Hello Steve,

The electrolyte of a lead acid battery is a mixture of water (H2O) at a
specific gravity of 1.0 SG and sulfuric acid (H2SO4 at a specific gravity of
1.8 SG.

We then mix 3 parts of H2SO4 and 5 parts of H2O which becomes:

1.8+1.8+1.8+1.0+1.0+1.0+1.0+1.0+1.0 = 10.4

The average specific gravity of these 8 parts are 10.4/8 = 1.30 SG

When these compounds are initially mix, there is a increase in heat, which
makes the specific gravity read about 1.30 SG. Let it cool and it may come
down to 1.275 SG at about 80 F.

The negative grids are pure lead with sponge lead (Pb) pasted into the grids
to form a plate. The positive grids are pure lead with lead oxide (PbO2)
that is pasted into the grids to form a plate.

These two plates are then inserted into the liquid medium call a electrolyte
which does a chemical exchange from the positive plate (PbO2) to the
electrolyte (H2O + H2SO4) to the negative plate (Pb).

The discharge of current is from the positive plate to the electrolyte and
to the negative. The charger current if from the negative to the
electrolyte and to the positive plate.

In the discharge cycle the O2 from the positive plate combines with the
electrolyte which forms H2O + H2SO4 + O2. One part of the O2 or just O1
combines with the H2 of the H2S04 which makes the electrolyte solution more
water (H2O + H20 + SO4).

The SO4 (Sulfate) is now separated from the [email protected] (Hydrogen), is starts to
combine with the negative plate (PbS04) which coats this plate that looks
like a white compound that looks like plaster of paris.

The negative plate becomes more resistance to the current flow and the
electrolyte becomes more weaker (more water) which is now venting more
hydrogen.

If you leave this battery in this state for a long time, becomes less
conductive with more SO4 coating not only the surface of the battery plates,
but deep inside all the pores of this plate.

If the electrolyte level drops which is normal during the discharge cycle
and even drops below the plates, leaving the surface expose, the sulfate
(SO4) becomes very hard coating over these negative plates.

If the plates have a very hard coating and if a high ampere charge was done
on them, this will cause the SO4 to exploded off the negative plates, which
can even cause larger holes in the plates and even clean off the paste of
the grids.

I seen these test of a high ampere discharge and charge on a battery cell
that has a clear glass case or call JARS. The 1/3 top portion of the
battery plates had its paste blown clear off leaving the grids expose.

You may be able to bring these batteries back up to 70 to 80 percent by
charging them at a very low ampere, so as not to blow more SO4 off the
plates which will settle in the bottom well.

As they are charge at a very low ampere for a very long time, the S04 starts
to combine with the H2O to make more H2SO4. Lets say you have a 200 ah
battery and it was depleted at 100 percent, than a 1 amp charge may take 200
or more hours.

To hurry up this time, the ampere could be increase 1 amp per day aa more
negative plates become more conductive.

Too high of a charge will also expand these plates, which causes the
separators to spread a little. The pasted material in the grids are not
compress as much and the paste becomes very soft and looses it conduction to
the grids. I have remove plates from a single cell battery which is call a
JAR because it is not part of a battery of cells, and just holding it
horizontal to the force of gravity, the pasted material just fell out.

Roland




----- Original Message -----
From: "Steve Powers" <[email protected]>
To: <[email protected]>
Sent: Saturday, November 03, 2007 6:54 AM
Subject: [EVDL] Batteries sat too long (at very low drain rate)


> A friend of mine built an EV a few years ago (maybe 3
> or so). He put in 13 Group 31 Optimas. He drove it
> probably < 200 miles. I know it was less than 30 days
> due to registration issues he had. He couldn't
> legally drive it. The car sat (with a very low
> parasitic drain on the batteries) and was parted out a
> few months ago. I took the batteries. As lead scrap,
> they are worth about $20 total. I thought, well maybe
> something can be done with these. Probably not, but
> maybe. So, I asked around for some ideas.
>
> Here is what I did:
>
> 1. I checked the voltages. They were all resting at
> about 6 V. Bad ... very bad.
>
> 2. I tried to charge one with a regular battery
> charger. No luck. It just gave an error and turned
> off. Another one started charging but never
> terminated the charge. After I took off the charger,
> the voltage sagged from say 12.8 all the way to 12.4 -
> 12.5. I'd say it has very bad self discharge.
>
> 3. I tried the charger and desulfator and left it on
> for about 2 weeks. No luck. Still can't hold 12.8 V.
> Still has bad self discharge. So much for the black
> magic solution.
>
> 4. I hooked the battery to another battery (in
> parallel). That's basically constant voltage 13.0 V /
> high current charging. That didn't work. It's
> shocking the battery back to life - quite literally.
>
> 5. I hit the battery with high discharge rates in a
> pulsed fashion. I literally shorted the terminals
> instantaneously over and over again. I was trying to
> burn off any microshorts between the plates. The
> voltage would go from 10 or so almost to zero and
> back. That is very dangerous. Don't try it. Then, I
> got even more agressive and tried to push more current
> by paralleling (momentarily very quickly off and on)
> two batteries with reverse polarity - positive to
> negative, negative to positive. I was again trying to
> burn off the micro shorts. These batteries have
> almost no CCA, so I didn't even get that much of a
> current inrush. DON'T TRY THAT WITH FRESH BATTERIES
> OR YOU'LL PROBABLY GET A SERIOUS EXPLOSION!!!
>
> 6. I hooked up the battery to my variac with full wave
> bridge and set it for 15 A charge rate. I let it sit
> about 2 hours. The voltage came up, but it got hot
> and still self discharged.
>
> 7. Finally, I hooked a fresh battery from the pack
> (sitting at 6 V) in series with a 120 V / 100 W light
> bulb and put it on my Variac with full wave bridge. I
> turned it all the way up to 163 V DC. The bulb lit
> and I was pushing 1 A through the battery. I let it
> sit like that for 12 hours or so. The voltage on the
> battery came up from 6 V steadily up to about 11.5 V.
> It's still going. I'm not sure when to cut it off,
> 12.0 V, 12.2 V, 12.4 V, 12.6 V, 12.8 V. Probably no
> higher than that. Is there a better way to do this
> without wasting > 90% of the energy used in waste
> light and heat (the 100 Watt bulb)?
>
> So, can someone explain chemically what happened to
> these batteries and what I was technically doing in
> each of these experiments - why the last one worked
> best, but the constant voltage didn't ...
>
> I still think they are scrap, but it was worth a try
> to see if any capacity could be recovered from them.
> Otherwise, they make a very nice set of large yellow
> paperweights.
>
>
> Thanks,
>
> Steve
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam? Yahoo! Mail has the best spam protection around
> http://mail.yahoo.com
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
 

·
Registered
Joined
·
70 Posts
Discussion Starter #3
Steve Powers wrote:
> 13 Group 31 Optimas...
>
> 1. I checked the voltages. They were all resting at
> about 6 V. Bad ... very bad.
>
> 2. I tried to charge one with a regular battery
> charger. No luck.
>
> 3. I tried the charger and desulfator and left it on
> for about 2 weeks. No luck.

It's always good to try normal solutions first.

> 4. I hooked the battery to another battery (in
> parallel). That's basically constant voltage 13.0 V /
> high current charging. That didn't work.

I suspect you didn't really get much charging current at all. These
batteries will have very high internal resistance.

> 5. I hit the battery with high discharge rates in a
> pulsed fashion. I literally shorted the terminals
> instantaneously over and over again. I was trying to
> burn off any microshorts between the plates.

You don't get shorts like this in lead-acid batteries. That's a trick
used for nicad batteries.

With lead-acids, if there's a short, it's caused by lead sulfate shed
from the plates that piles up as sediment at the bottom and shorts the
plates. You can't burn it out. The only way to remove it is to
physically disassemble the battery and wash it out (not practical with
these batteries).

> 6. I hooked up the battery to my variac with full wave
> bridge and set it for 15 A charge rate. I let it sit
> about 2 hours. The voltage came up, but it got hot
> and still self discharged.

Again, this is because the battery has very high internal resistance.
Almost all the charging current is just converted to heat.

The resistance is high because all the acid has been converted to lead
sulfate. The electrolyte is almost pure water, which has high electrical
resistance.

> 7. Finally, I hooked a fresh battery from the pack
> (sitting at 6 V) in series with a 120 V / 100 W light
> bulb and put it on my Variac with full wave bridge. I
> turned it all the way up to 163 V DC. The bulb lit
> and I was pushing 1 A through the battery. I let it
> sit like that for 12 hours or so.

I think this has the best chance of recovering at least some use from
these batteries. But, you have to leave that 1 amp charging current on
for *days*! Keep charging at 1 amp or less with no voltage limit until
the voltage stops rising. It could take 2-4 days. The peak voltage could
easily be 30 volts or more. (Floodeds won't normally exceed 20v; doing
this with gels will go even higher.)

If the battery isn't totally shot, the voltage will slowly rise as tiny
amounts of lead sulfate get converted back into sulfuric acid. This
lowers the resistance, which allows more charging, which converts more
lead sulfate, etc.

Eventually/hopefully, enough lead sulfate converts back so the battery
begins to behave again like a "normal" dead battery. Typically, after
some period of days, the voltage peaks, starts to fall slowly, and then
falls faster until it gets back down to 12.x volts. At this point,
remove the battery from the trickle charger, and it should charge
normally with a conventional 12v charger.

The battery will have lost considerable capacity, and will have much
higher internal resistance; but it may still be good enough to use for
non-demanding applications.

> Is there a better way to do this without wasting > 90% of the energy
> used in waste light and heat (the 100 Watt bulb)?

I use a 12 car tail light and a 20-30v power supply. Or, you can connect
several batteries in series so the total up most of the applied voltage.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
 

·
Registered
Joined
·
70 Posts
Discussion Starter #4
Lee Hart has talked about this. It seems a very high voltage with very low
amps is just what the battery needs to be cured. Look up in the archeives
or maybe Lee will chime in. Lawrence Rhodes......

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
 
1 - 4 of 4 Posts
Top