Two Drivers in Parallel? Two batteries in Parallel?

[Hank]

If i connect two 18650 batteries in parallel, i should be able to draw 1.5Amp from each of the batteries safely to get a total draw of 3 Amps right?

What if say I connect two O-Like 1W 445nm laser drivers in parallel? I believe they are rated at 1.2 Amp, so i can safely draw 2.4A of current into a diode? Will something like that work? if not, why? Since the current going through each of the driver is still 1.2A.

 

[Bionic-Badger]

You can only do that if your batteries are properly matched, that is, they were made in the same batch of batteries and have the same discharge characteristics. Otherwise, one battery will inevitably discharge faster than the other, and the resulting voltage difference between the batteries will cause one to "charge" the other, which can also damage the battery. I would not try it.

A single 18650 battery ought to be able to source 3 Amps or so anyway, so you could get away with using just one. You could also look into some NiMH battery packs. They have very good current draw capabilities for motors and stuff.

Not sure how O-like's drivers work. They may be able to provide that much current, but they may also produce different voltages, which isn't good.

 

[Cyparagon]

^You're thinking series.

You could probably put a cr123a and an 18650 in parallel without problems.

 

[BShanahan14rulz]

I think this would be dangerous because there would then be a reverse voltage applied across the weaker cell. Keep them in series, keep them matched fairly well, or even safer, just use single cells or single protected cells.

 

[Cyparagon]

there would then be a reverse voltage applied across the weaker cell.

Best not to ever charge batteries then, since it applies an even greater reverse voltage

 

[Bionic-Badger]

^You're thinking series.

You could probably put a cr123a and an 18650 in parallel without problems.

No! That is not a good thing to do. The two batteries have completely different capacities which guarantees that they will change voltage at different rates.

I did mean parallel. If they're in parallel, and one has different discharge/voltage characteristics, the other cell has to compensate in order to maintain the same voltage at the terminals. This is why you need to have matched cells if you need them in parallel, or else the differences in the batteries will have a detrimental effect on the overall circuit. You might as well just stick with a single cell in that case.

Read up on these things before making erroneous and possibly dangerous statements.

 

[Cyparagon]

They will both discharge at appropriate rates. If one is slightly higher in voltage at a given time, it will provide more current (since the voltage is higher) and that will lower the voltage. It will also work to equalize the voltage of the lesser cell by charging it very slightly. I'll perform a test if you like. What would you like me to measure? Would current/voltage of each cell on a 2.7Ω load as well as temperature be enough to convince you?