Sealed Lead Acid Battery - Do I need to current limit for a low current application?

Hello there,

Somebody once said there are no dumb questions... so here's mine!

I have a device that I would like to run for an extended period of
time, say 2-4 days. The device requires 12V and 80mA and provides a
constant load i.e. there is no power surging.

I recently acquired a Power Patrol SLA1146 battery (12V, 26AH). Can I
contact this battery to the device without any power buffering
circuitry? I'm concerned about blowing the device. Will the device
only draw the 80mA is needs?

Yes, I missed that day in Physics class!

-bonzo3671

 

Subject: Sealed Lead Acid Battery - Do I need to current limit for a low

You'd have to describe your load circuit to get a better evaluation. If it
says 80 mA, there might be a capacitor input that requires a momentary surge in
current. Lead-acid batteries are OK with this -- it's the non-momentary short
that you have to worry about. That causes heating in the battery, with
potentially bad results.

When you're looking at protecting battery power supplies, you have to look at
what *could* go wrong. Worst case, if your load shorts out, you could have
some serious problems. If you feel it's worth it, a 1/4A 3AG fuse with in-line
fuseholder is cheap protection, and will add practically no voltage burden.
They're available at Radio Shack, hobbyist sources, hardware and auto parts
stores.

Good luck
Chris

 

Thanks Chris! Your comments make sense. You're right about the no load
situation, that's what I'm worried about - the last thing I want is a
fire in an enclosed space. The "device" is one of those cheapo cameras
and I'd like to use it to monitor my driveway and garage. Unless the
RF circuitry needs some kind of charge pump, I don't think there are
any caps(?). Is the fuse you suggested put on the "+"ve side of the
SLA battery?

-bonzo3671

 

Strictly speaking, as long as it's anywhere in the circuit, it will
interrupt the current. But in the positive lead is probably the most
common.

And, I dunno about that 80 mA load on a 26 AH battery ... lessee ...
26 / .08 equals, um - almost two weeks?

Cheers!
Rich