Parallel Batteries

[ATannahill]

What we are planning to do for our t-shirt shooter is install a maxi block, like used back in 2008 and some years prior, backwards to connect the three batteries together. We will put fuses in to prevent any battery failure.

[Stephen Kowski]

Originally Posted by rtfgnow

What we are planning to do for our t-shirt shooter is install a maxi block, like used back in 2008 and some years prior, backwards to connect the three batteries together. We will put fuses in to prevent any battery failure.

If I understand you correctly there is nothing in between the individual batteries to prevent 'failure' (like the diode alan suggested). Do you me failure like thermal runaway? Failure like a dead battery (possible)? I'm not sure what you are preventing here, fuses are for overcurrent protection.

Generally though putting them in parallel is a relatively safe bet with sealed lead acid batteries so I doubt there would be any failure to begin (faster aging if anything). Don't combine a old battery with a newer battery in parallel. Make sure the batteries are from the same manufacturer (preferably new). Practice what Alan said about charge and discharge.

[sanddrag]

SLA batteries are commonly paralleled without any ill-effects in large industrial uninterruptable power supplies. Sometimes you'll see entire pallet-racks full of them. In these systems, I don't believe there are typically any diodes or switching. However, all the batteries start off new, and are all always charged and discharged together, for their entire lives, and aren't discharged often.

[Al Skierkiewicz]

Brett et al,
This question comes up every year. I have asked the manufacturer and the Battery Institute for their recommendation in the past. Neither recommends that robot batteries be wired in parallel. As pointed out, if the certain batteries are new and always used in parallel (both charge and discharge) they may be wired this way. Large UPS power supplies and large DC current loads (like WWII submarines) use batteries in this fashion but monitor the specific gravity of the electrolyte constantly to insure that one battery will not discharge the remaining batteries.

[MrForbes]

I think the large UPS systems have something that most don't....they're being charged all the time, except when they're under heavy load, so there is little opportunity for one battery to run down the others.

And I think the "real life" answer to the original question here is that it should be fine to parallel the batteries we use on a robot, if they are disconnected from each other when the robot is turned off. If you could figure out a reliable way to do this, I doubt you'd have any problems. But I still don't see the need for running them in parallel on a T shirt cannon