3
\$\begingroup\$

We all know the Michael Bay-esque excitement you get if you misuse lithium-based cells, but I've heard lead acid batteries are a lot more durable. The datasheet for my sealed lead acid battery says it can deliver 65 amps safely for 5 seconds. What if I draw more? What if I draw 65 amps continuously? Or what if I short out the terminals and draw the theoretical 300 amps it can deliver (40 mohm ESR)?

I haven't found much information on this. I've only seen the effects of deep discharging, over charging, and very briefly shorting lead acid batteries (rather than continously). None of which are what I'm talking about.

\$\endgroup\$
6
  • 1
    \$\begingroup\$ search on youtube for exploding lead battery... \$\endgroup\$
    – PlasmaHH
    Commented Jan 19, 2017 at 9:51
  • \$\begingroup\$ @PlasmaHH no luck, all the ones I found were about overcharging. I'm looking specifically for the effects of drawing too much current. \$\endgroup\$
    – Daffy
    Commented Jan 19, 2017 at 9:59
  • 2
    \$\begingroup\$ The voltage will drop, and when you reach the lower limit the battery will be damaged. It won't take a full charge. \$\endgroup\$
    – Leon Heller
    Commented Jan 19, 2017 at 11:18
  • 1
    \$\begingroup\$ Unless you over-discharge it, I am guessing nothing too terrible will happen to the battery. However, those are large currents (65A and above), and you could have wires or connection points get very hot. Just making and breaking a circuit with that much current will produce some sparks and can weld contacts. \$\endgroup\$
    – user57037
    Commented Jan 19, 2017 at 16:20
  • 1
    \$\begingroup\$ Drawing lots of current from a lead Acid battery will simply make it hot as mkeith mentioned, it may in some circumstances melt the terminals or part of the internal connections. The internal heat may also boil the acid electrolyte so you may have boiling acid spray, but given how much energy it takes to boil water (which most of the electrolyte is) you'd need to short it out for a while for that to be an issue. It's more of a problem with big lead acid batteries (some optima packs have SC currents of 4000A) as the currents are much higher, internal heat can build up much faster. \$\endgroup\$
    – Sam
    Commented Jan 20, 2017 at 0:26

1 Answer 1

Reset to default
3
\$\begingroup\$

Well...

If your battery says it can deliver 65 amps safely for 5 seconds, that likely means that exceeding this time limit (or even further increasing the amperage) will most certainly pose a moderate to severe fire risk. Trust me, boiling acid is not fun, not even for an AP chemistry student. Always remember to have a class D fire extinguisher on hand if you ever try to do these kinds of things.

If however you decide to pull this [really stupid] stunt and your luck prevails, get ready to take cover, because your battery might be internally shorted due to the bulging of the lead plates and beginning to enter thermal runaway: a positive feedback loop in batteries that is basically a unintentional self-destruct mechanism. However, this risk is most prevalent in flooded-type lead acid batteries. AGM and Gel batteries have different internal construction that prevent this from happening, but it still does happen on occasion due to manufacturing defects.

If you should have a flooded lead-acid battery, that has no PRV (Pressure release valve) installed, your results might lean more on the volatile side; spraying scalding acid everywhere as the gas pressure inside the case exceeds the case's structural integrity.

However, if you're luck prevails again, and the battery in question has a PRV, your results will most likely be milder, as the PRV does it's job and vents the excess gas, preventing a catastrophic explosion and saving your beautiful face.

However, after either of these events occur, it is strongly recommended that you dispose of the battery, as it is now a serious liability, and you'll be better off just buying a new one than trying to recharge or repair (how you repair a lead acid battery, I will never know) the battery.

Edit: Fixed typos and general stupidity.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.