Puma Battery Queries

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Originally Posted by DazzaTD5

This thread reminded me of something...

I use small cheap solar panels connected to vehicles I am dismantling until I'm ready to move them into the workshop.
Some time ago I had one that I hadnt connected to a charger or the vehicle for a few months I guess, one day I connected the solar panel and didnt think any further.
Some months later, I went to move vehicle into workshop, connected battery to vehicle, cranked over but wouldnt start, then dreaded smoke started to come out of the harness somewhere.
Battery was hot considering I only cranked it for a small amount of time, disconnected it and walked away from the hot battery.

Later that arvo, when battery was cold and no fear of exploding in my face, I connected a multi meter and it read -12.45V ... it had reverse charged, see pic (The alligator clip is the NEG probe)

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Gee. This is a bit of a worry. The solar panel I picked up notes 'The built in blocking diode prevents any drain on your battery at night'. Did the solar panels you used contain any safety measures, or more to the point, can the 'built in blocking diode' be trusted not to discharge a battery.

Another quick question, how much can a voltmeter be trusted to accurately indicate a battery charge level?

Andrew

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Originally Posted by 4xsama

Gee. This is a bit of a worry. The solar panel I picked up notes 'The built in blocking diode prevents any drain on your battery at night'. Did the solar panels you used contain any safety measures, or more to the point, can the 'built in blocking diode' be trusted not to discharge a battery.

Another quick question, how much can a voltmeter be trusted to accurately indicate a battery charge level?

Andrew

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No no... to be clear, the battery was in the vehicle, both leads disconnected, the solar panel also was NOT connected. It was only after quite a few months that I connected the solar panel (the correct way) and then I guess it slowly charged up the battery the wrong way. A battery that is completely flat will take a charge either way.

Normally any vehicle I get in to dismantle, if its going to sit for a bit, I will put the solar panel straight onto a good battery, which keeps them topped up.

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Originally Posted by DazzaTD5

No no... to be clear, the battery was in the vehicle, both leads disconnected, the solar panel also was NOT connected. It was only after quite a few months that I connected the solar panel (the correct way) and then I guess it slowly charged up the battery the wrong way. A battery that is completely flat will take a charge either way.

Normally any vehicle I get in to dismantle, if its going to sit for a bit, I will put the solar panel straight onto a good battery, which keeps them topped up.

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Ok. Cheers Dazza. I was a bit worried there. I've disconnected the panel and will put a meter on the battery tomorrow. It should have a reasonable charge in it so shouldn't be flat to the point it will charge negatively (I didn't realise you could neg charge a battery so thanks for the info-good for future reference). I could turn over/start the car 90% of the time so out of interest is there a % full where a battery can still turn over the engine or is the measure (Amps I assume a totally different measure to volts?

Thanks again.

Andrew

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Originally Posted by 4xsama

I've disconnected the panel and will put a meter on the battery tomorrow. It should have a reasonable charge in it so shouldn't be flat to the point it will charge negatively (I didn't realise you could neg charge a battery so thanks for the info-good for future reference).

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I had a look at the battery this morning. Indicates 10.62V on the meter. Battery back on the solar panel so I'll check weekly to see how/if it charges.

Andrew

Hi Andrew, a battery polarity reversal is an EXTREMELY RARE event and you do not have to worry about it because your battery, at 10.62v, is just flat and your readings are showing it is fine, just low.

If the battery terminal voltage was below something like 5v then you could, in a very extreme case, end up with a battery polarity reversal event.

Just connect your solar panel and leave it.

It will take about two to three weeks to fully charge your battery from that low state, but you can see how it is progressing by measuring the voltage every morning.

You can measure in the evening but you will be seeing a slight surface charge voltage after a day’s charging. So morning readings are closer to the actual SoC of the battery.

Tim/ Dazza

1st year uni chemistry was a few years ago
And of course I could search an answer
But reversing polarity of a lead acid battery has me intrigued

Assuming the battery is made with and anode and a cathode
Cathode providing electrons and anode receiving them
How does reversal work?

Surely the chemical structure of the anode/ cathode doesn’t change
So is it simply a “reverse charge” within the electrolyte
Ie the battery would not be able to do much work in reverse?

S

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Originally Posted by drivesafe

Hi Andrew, a battery polarity reversal is an EXTREMELY RARE event and you do not have to worry about it because your battery, at 10.62v, is just flat and your readings are showing it is fine, just low.

If the battery terminal voltage was below something like 5v then you could, in a very extreme case, end up with a battery polarity reversal event.

Just connect your solar panel and leave it.

It will take about two to three weeks to fully charge your battery from that low state, but you can see how it is progressing by measuring the voltage every morning.

You can measure in the evening but you will be seeing a slight surface charge voltage after a day’s charging. So morning readings are closer to the actual SoC of the battery.

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Yes just to high light what has been said here. In any normal situation even with a flat battery (as in as far as it wont start your vehicle) you are not going to get it to reverse charge.
Its not something that anyone should be bothered about and in all my years its the first time I have seen it.

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Originally Posted by roverrescue

Tim/ Dazza

1st year uni chemistry was a few years ago
And of course I could search an answer
But reversing polarity of a lead acid battery has me intrigued

Assuming the battery is made with and anode and a cathode
Cathode providing electrons and anode receiving them
How does reversal work?

Surely the chemical structure of the anode/ cathode doesn’t change
So is it simply a “reverse charge” within the electrolyte
Ie the battery would not be able to do much work in reverse?

S

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I would suggest starting a new thread on this rather than putting the fear of death in some people with regards to charging their car battery.
(is a lead acid battery not constructed the same and its the amount of electrons on either side that determines pos or neg?)

Quote:

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Originally Posted by drivesafe

Hi Andrew, a battery polarity reversal is an EXTREMELY RARE event and you do not have to worry about it because your battery, at 10.62v, is just flat and your readings are showing it is fine, just low.

If the battery terminal voltage was below something like 5v then you could, in a very extreme case, end up with a battery polarity reversal event.

Just connect your solar panel and leave it.

It will take about two to three weeks to fully charge your battery from that low state, but you can see how it is progressing by measuring the voltage every morning.

You can measure in the evening but you will be seeing a slight surface charge voltage after a day’s charging. So morning readings are closer to the actual SoC of the battery.

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Battery is taking a charge which is nice.

At the risk of asking a stupid question, do I need to remove the caps on an AGM battery when charging or is that for a lead acid battery only?

If your battery is an AGM, then it should not have access caps.

So no, do not attempt to remove the “CAPS”

BTW, there is no such thing as a stupid question, but you may feel stupid if you don’t ask the question and then you stuff something up.