Electronic – How much current can lead acid batteries safely supply

battery-operatedlead-acidover-discharge

I have a motor I wish to drive with an 18V lead acid battery. The motor can draw quite a lot of current when stalling and I am worried of overdischarging the lead acid battery. Unlike LiPo batteries with have a maximum current rating, the lead acid battery only stated the "initial current", which is used for charging. The label stated not to short the battery. Hence, may I know what/how to find out the safe current to draw? How will the battery fail if I draw too much current (explode/lifespan decreased/?)? Thanks

Best Answer

Lead acid batteries are fantastic at providing a lot of power for a short period of time. In the automotive world, this is referred to as Cold Cranking Amps. From GNB Systems FAQ page (found via a Google search):

Cranking amps are the numbers of amperes a lead-acid battery at 32 degrees F (0 degrees C) can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12 volt battery).

A car actually doesn't need 30 seconds, normally only a few seconds to start, except in very cold weather or other extreme situations. But 30 seconds means you could give it a few tries before the battery (if it started charged and in good shape) becomes a problem.

Picking one battery at random from Sears DieHard, I found 730 CCA. That's 730 Amps at 12 V. That is a LOT of power.

The end result is that you have to find the right battery combination of:

  • Max. surge current or CCA
  • Total capacity, typically in Amp-hours
  • Size & weight
  • Cost

An 18 V lead-acid battery could be a tiny little thing. Or it could be like a typical car battery, only 18 V instead of 12 V.

If you are looking at a one-off or small production run you may be better off leveraging car battery technology - mature, inexpensive, easy to replace - rather than 18 V or something else more unusual. But that only works if the size & weight parameters work for your particular project.

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