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Old 29-12-2013, 07:35   #1
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Desulphate Discharged Batteries?

After desulphating my batteries, the specific gravity went down. Could this result from the batteries not being fully charged when they were desulphated?

They were fully charged a few weeks prior to desulphating but sat in the garage at about 0* C in the intervening time.

The two batteries went from 85% and 75% fully charged capacity a few weeks before desulphation, down to 80% and 70% after.

The desulphation was preformed at 0*C, however, the charger does compensates for temperature.
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Old 29-12-2013, 08:22   #2
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Re: Desulphate Discharged Batteries?

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Originally Posted by Neo View Post
After desulphating my batteries, the specific gravity went down. Could this result from the batteries not being fully charged when they were desulphated?

They were fully charged a few weeks prior to desulphating but sat in the garage at about 0* C in the intervening time.

The two batteries went from 85% and 75% fully charged capacity a few weeks before desulphation, down to 80% and 70% after.

The desulphation was preformed at 0*C, however, the charger does compensates for temperature.
Was this an equalization voltage or a "battery desulfator" device.....

In order to do a safe and effective equalization the batteries should ideally be at room temp and charged to full at normal absorption voltages. Once full then an equalization charge can be performed.

Checking SG also requires temp compensation.so the first and last SG can only be directly compared if the batt/electrolyte temps were identical.....

We really need a lot more info as to what was performed, what was measured, what was measured at what temp etc....

Keep in mind that at low temps it can take weeks not days for a surface charge to dissipate so open circuit voltage readings may also not be accurate. I have some batts in my shed that I measured last week at 12.87V and they have been off charge for approx three weeks. Normal full charge on these batts is 12.72V - 12.73V. They are still holding the surface charge due to the temps...

Best to charge batteries and condition them at room temps or close..
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Old 29-12-2013, 20:37   #3
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Re: Desulphate Discharged Batteries?

Below are my notes. I used the desulphation program on my pro ultra battery charger. It applies a temperature compensated voltage for about 4 hours. I used a table with temp adjusted values for specific gravity and open circuit voltage readings to estimate battery capacity. I didn't record the values after desulphation, but they were all lower.

Before Desulphation (Equalization)

West Marine Deep Cycle Battery , Fully Charged
Resting open circuit voltage @ 30F = 12.5V = 85% capacity

Specific Gravity @ 30F
(+) term 1.270 1.270 1.270 1.265 1.265 1.260 (-) term
Average specific gravity = 1.265 = 85% capacity

Starter Battery, Fully Charged
Resting open circuit voltage @ 30F = 12.5V = 85% capacity
Specific Gravity @ 30F
(+) term 1.245 1.243 1.246 1.245 1.246 1.242 (-) term
Average specific gravity = 1.243 = 75% capacity
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Old 29-12-2013, 20:45   #4
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Re: Desulphate Discharged Batteries?

I'll bring the batteries up to room temperature and try again.

The batteries have only been used for one season. I guess my 30W solar isn't enough to keep them topped off.
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Old 29-12-2013, 20:54   #5
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Re: Desulphate Discharged Batteries?

check out what Handy Bob has to say about lead acid batteries and desulphanization. Very long read but worth it.

HandyBob's Blog Making off grid RV electrical systems work
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Old 29-12-2013, 21:02   #6
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Re: Desulphate Discharged Batteries?

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I guess my 30W solar isn't enough to keep them topped off.
30W...so that is like 2-3A
Do you have loads on the boat that are outstripping your 30W solar panel?
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Old 30-12-2013, 05:34   #7
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Re: Desulphate Discharged Batteries?

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30W...so that is like 2-3A
Do you have loads on the boat that are outstripping your 30W solar panel?
The solar panel puts out 1.2 amps max. It's usually more like 0.7 amps. We are on a mooring.
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Old 30-12-2013, 08:50   #8
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Re: Desulphate Discharged Batteries?

I brought the batteries into the kitchen to warm up, charged them overnight, then desulphated again at 70F. I got a much better result. They are both close to 100% capacity.

Maine Sail says that the batteries probably did not lose charge for the few weeks they sat in the garage before they were desulphated, so there are two possible reasons that the first desulphation didn't work:

1. Batteries don't desulphate well below 0*C.

2. The 1/4 cup of distilled water that I added to each cell just prior to desulphating did not mix well during the desulphation and thus reduced the specific gravity readings I obtained after desulphation. I thought the desulphation would cause mixing, plus I rocked the batteries a bit to facilitate mixing.

What do you think???

Second desulphation data below.

West Marine Deep Cycle Battery , Fully Charged
Specific Gravity @ 70F
(+) term 1.272 1.278 1.275 1.272 1.281 1.272 (-) term
Average specific gravity = 1.275 = 105% capacity

Starter Battery, Fully Charged
Specific Gravity @ 70F
(+) term 1.253 1.255 1.258 1.258 1.256 1.256 (-) term
Average specific gravity = 1.256 = 91% capacity
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Old 31-12-2013, 08:16   #9
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Re: Desulphate Discharged Batteries?

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Originally Posted by Nicholson58 View Post
check out what Handy Bob has to say about lead acid batteries and desulphanization. Very long read but worth it.

HandyBob's Blog Making off grid RV electrical systems work
It is long, but I read a few pages and it looks to be just what we need to evaluate the solar on our boat.

Thanks
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