mattheww50
Flashlight Enthusiast
I takes a lot of of overcharging to deplete the electrolyte. Getting rid of 18 grams of electrolyte in a cell will require about 60 amp hours.
Charging 12 volt gel cells
- Thread starter hotbike
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Your idea of a "smart" or two-stage charger is a good one. But check the prices on those. They are generally too expensive to include with the product - the manufacturer's use only the cheapest charger they can get away with.
Note that volts & "trickle charge" don't necessarily go together. For a trickle charge the important factor is amps (or ma), the voltage doesn't matter. Obviously, for any particular battery, you would expect a certain charge at a certain voltage. But I can show you identical gell cell batteries (from the same lot) where the current is a factor of 2 different with both batteries connected in parallel (which, obviously, means they are at the same voltage). And that's with new batteries that have not had a chance to be altered by use in different environments.
13.8v is regarded as the standard trickle charge voltage for a wet cell. Gell cells are usually specified for trickle charging at 13.6-13.9v, often with a current limit, too. Above that voltage, they normally specify a maximum allowable current. I sometimes use a charge rate up to 14.4v with a suitable current limit (often just a resistor) when necessary on gell cells. I have found that they last longer if you don't do that. Keeping them on float isn't ideal either, tho. An occasional use, running the battery down, seems to make them last longer. They don't last more than 8 years in any case - it appears that the plates dissolve if they don't sulfate or run out of electrolyte first. HTH,
Note that volts & "trickle charge" don't necessarily go together. For a trickle charge the important factor is amps (or ma), the voltage doesn't matter. Obviously, for any particular battery, you would expect a certain charge at a certain voltage. But I can show you identical gell cell batteries (from the same lot) where the current is a factor of 2 different with both batteries connected in parallel (which, obviously, means they are at the same voltage). And that's with new batteries that have not had a chance to be altered by use in different environments.
13.8v is regarded as the standard trickle charge voltage for a wet cell. Gell cells are usually specified for trickle charging at 13.6-13.9v, often with a current limit, too. Above that voltage, they normally specify a maximum allowable current. I sometimes use a charge rate up to 14.4v with a suitable current limit (often just a resistor) when necessary on gell cells. I have found that they last longer if you don't do that. Keeping them on float isn't ideal either, tho. An occasional use, running the battery down, seems to make them last longer. They don't last more than 8 years in any case - it appears that the plates dissolve if they don't sulfate or run out of electrolyte first. HTH,
That sounds about right. So it (the 17ah gell cell)might last 3 years (at constant 14.4v float) before you deplete the electrolite enough to seriously damage the capacity. That's consistant with my experience. It's very difficult to find a properly regulated small charger when Chinese wall warts are selling at $2-3 each. And it may not be worth it for every application, particularly flashlights. Even so, I've found it worthwhile to add $2.00 regulators to several of my chargers for gell cells.
Tomas
Banned
Just a quick comment that probably means nothing overall ...
In this apartment building the last time there was a major bulk changeout of the 6V gell cell batteries in the emergency lights scattered throughout the building was 1990. About 70 percent of those lights have had no battery service since then and appear to work fine ... the other 30 percent have had batteries replaced.
These lights keep a constant trickle (float) across the cells as long as commercial power is available, and only draw power during monthly tests (Does it light up? OK.) or when there is a power failure. Once a year there is a 90 minute run test required.
I have NO idea if this has any value to this thread, but it might ... /ubbthreads/images/graemlins/blush.gif
In this apartment building the last time there was a major bulk changeout of the 6V gell cell batteries in the emergency lights scattered throughout the building was 1990. About 70 percent of those lights have had no battery service since then and appear to work fine ... the other 30 percent have had batteries replaced.
These lights keep a constant trickle (float) across the cells as long as commercial power is available, and only draw power during monthly tests (Does it light up? OK.) or when there is a power failure. Once a year there is a 90 minute run test required.
I have NO idea if this has any value to this thread, but it might ... /ubbthreads/images/graemlins/blush.gif
I think it brings up a good point, applicable to most rechargeable (and primary) batteries not just gell cells. Usually, the battery life is taken to be the point at which a certain percentage (usually 50%) will no longer hold a particular charge (50% is normal for gell cells, NiCads, NiMH, IIRC). I'm surprised that 70% of your gell cells are still working after 13 yrs - maybe being out in the cold helps. But it is obvious that they aren't doing much of a test. Those emergency lights may not run very long if and when they are really needed. I had an 11 year old gell cell that still worked - for about 5 minutes, and then it would dim fast. It was a 4AH 12v feeding a less than 1 amp bulb, on float in an emergency light. When I cut it open there was no sign of lead plate - the entire inside was a mushy black damp powder. You couldn't tell the positive plates from the negative because there weren't any. IIRC, the positive side uses a spongy lead (doesn't look much like lead) and the negative side is lead. I replaced all of the 12v gell cells in that emergency light several months ago - 3, 4ah gell cells in parallel power it when my power goes out. I have lots of flashlights using 4ah gell cells, although most of them are 6v.
