Discussion in 'General Electronics Chat' started by stube40, Mar 10, 2010.

1. ### stube40 Thread Starter Member

Feb 3, 2010
42
0
I've recently been doing some work with lead-acid batteries. As most of you know, these things are nuts in terms of the amount of power they can deliver - effectively they are a power supply that can deliver hundreds of amps in a small space of time. The upper limit is only defined by the limits of the chemical equation going on inside, coupled with the melting point of the matterials used to make the battery.

I'm wondering if there's any existing or new battery technologies that have an inherently more stable chemical equation that results in some sort of integral virtual current limiting or current control?

It's been a while since my high-school chemistry lessons, but maybe there are some chemical equations that cannot be speeded up? The assumption here is that the speed at which the chemical equation takes place is proportional to the power delivery.

Can anyone can shed any light on this?

2. ### retched AAC Fanatic!

Dec 5, 2009
5,201
316
This is true. Lead-acid batteries have a temperature offset- that rises with temperature.

So at 25deg C The a 6 cell battery (12v) is 2.2v per cell or 13.2v for the battery. For every degree over that, the voltage inside each cell increases. This also can result in a run-away train. If you decide to heat a 12v battery to the point that it is producing 18v, that production will create internal heating that can in turn destroy the battery. This can also be done by using a stronger electrolyte ratio. Trading power for battery life.

So with stability, I think lead-acid is pretty good... especially economically...Cycles and amperage per dollar.

Deep Cycle batteries use a solid lead plate to even out the speed of the chemical reaction to current process, giving a longer cell cycle life.

Starter batteries use a "sponge" like lead plate that will be converted to current much quicker, decreasing the life of the cells.

I have been looking into various existing chemical batteries and some experimental approaches, and lead-acid is the most stable...for the current/power levels.

I have only been researching as a hobbyist, so I'm hopeful there are things on the horizon.

stube40 likes this.
3. ### Yevgen Barsukov New Member

Mar 11, 2010
1
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Just like any other battery chemistry, Lead Acid battery discharge rate is limited by its internal resistance, which is in turn a result of many different limitations such as resistance of electrodes, electrolyte, energy loss of electron transfer, diffusion etc.
While depending on many factors, battery internal resistance is inversely proportional to their capacity. Lead Acid batteries are usually very large, and that is making their internal resistance tiny those allowing high discharge currents.
There are many other chemistry on the market, including Ni-Cd, Ni-MH,
Li-ion. All of them have actually even higher current capability (lower internal resistance) than Lead-Acid, if comparing the same capacity batteries.

Lead acid battery has some unique properties that make it suitable as cranking battery - it is most stable in fully charged state. Other chemistry are degrading faster when stored in fully charged state.
Of cause it is also the cheapest chemistry, which make it suitable for the "bulk" applications where you need a lot of energy, but don't care about
space or weight. But for weight or space limited applications Li-ion batteries are the king, because of its highest energy density.

For more details, you can see an overview of different battery chemistry types here: