3 AA in series vs 3 14500 in parallel

[Tsuki]

I've not much experience in modding my electronics, but I was thinking today about this.

Electronics powered by 3 AA batteries in series. How well would this function on 3 14500's in parallel instead?

Any major downside or benefit to this change? I was thinking they should function about the same...

 

[Lynx_Arc]

I've not much experience in modding my electronics, but I was thinking today about this.

Electronics powered by 3 AA batteries in series. How well would this function on 3 14500's in parallel instead?

Any major downside or benefit to this change? I was thinking they should function about the same...

They are close to the same voltage the only difference would be in charging and balancing the lithium ion batteries as if they were too far off in voltage before connected together the higher voltage ones could try and charge the lower voltage ones very fast. Instead of 3 14500s in parallel it would probably be a better idea to use one larger cell like an 18650.

 

[Tsuki]

That would make less batteries for me to carry around. I'll have to see if I can fit an 18650 in there. Hopefully it won't need much modding of the case.

I assume the "charging fast" would in the best case, reduce battery life.. worst case fire/explosions?

 

[moderator007]

As far as energy between a quality AA Nimh and a quality 14500 there are very close to the same. As far as working there should be no problem other what has been stated by Lynx Arc. For the price and reliabilty the Nimh is probably the better way to go if thats what works in the space you have.

 

[fivemega]

Electronics powered by 3 AA batteries in series. How well would this function on 3 14500's in parallel instead?

If there is room for single 18650, you will gain more stored energy.

 

[ncbill]

Series better than parallel.

 

[mvyrmnd]

Series better than parallel.

Not necessarily. 3 Li-ions in series run the risk of one cell discharging quicker then the others, resulting in reverse-charging and :poof:

If they're run in parallel, then the cell that discharges more quickly just drags the other two down , resulting in shorter runtimes, rather than exploding.

I'd take parallel any day.

 

[Lynx_Arc]

Not necessarily. 3 Li-ions in series run the risk of one cell discharging quicker then the others, resulting in reverse-charging and :poof:

If they're run in parallel, then the cell that discharges more quickly just drags the other two down , resulting in shorter runtimes, rather than exploding.

I'd take parallel any day.

I think he was equating nimh in series vs 14500 in parallel. Pesonally the nimh are safer to deal with and cheaper to replace. I think one lithium ion battery matching the 3 nimh would be better to avoid any cell balancing issues.

 

[mvyrmnd]

I think he was equating nimh in series vs 14500 in parallel. Pesonally the nimh are safer to deal with and cheaper to replace. I think one lithium ion battery matching the 3 nimh would be better to avoid any cell balancing issues.

He was a little non-specific ;)

But yes. One big Li-Ion would be better than a bunch of NiMH's...

 

[Wrend]

Not necessarily. 3 Li-ions in series run the risk of one cell discharging quicker then the others, resulting in reverse-charging and :poof:

If they're run in parallel, then the cell that discharges more quickly just drags the other two down , resulting in shorter runtimes, rather than exploding.

I'd take parallel any day.

Yes, parallel with Li-ion is the way to go. However, the cells don't "drag" each other down. They balance at the same voltage and stay at the same voltage while they are used and discharge evenly, even regardless of their capacity.

The exception to this would be if they're discharge very quickly. Then differences in balance could show up from the different relative internal resistances of the cells, though they would once again balance after the discharge rate was reduced. You should limit the discharge rate to the lowest of the "C" ratings of the cells in parallel, but applied to the full resulting capacity of the paralleled cells.

...

To answer the original question, I'd go with 3 AA Eneloops in series over 3 14500 Li-ion cells in parallel. Keep in mind Li-ion cells shouldn't be fully discharged if you want good cycle life from them. 80% depth of discharge from a full charge is the general recommendation. If the 3 AA NiMH cells are balanced at a full charge, are the same kind of cells, and have same usage history, then more deeply discharging them shouldn't be much of an issue. This puts AA NiMH and 14500 Li-ion at about equal with each other in terms of energy. (Though higher capacity NiMH AA cells such as the 2500mAh XX Eneloop cells would have the advantage, the standard "1500" cycle ones are more cost effective for general use in the long run.) With Eneloops in particular (not all NiMH cells are created equal), you're likely to get a much higher cycle life and cumulative lifetime energy.

In fact, I wish they made a cell phone that ran on 3 AAs so I could use Eneloops in it. I've been looking around, but can't seem to find one.

 

[yellow]

when connecting any cells together, the "equaling" is basically a SHORTING!
So the electronics of protected cells would immediately close this one cell - when connecting the next one this also - so in the end You only have just one cell to use
(when the difference in voltage and the current floating is big enough that the electronics start working)

no question at all
--> as both setups are CRAP & mean more "loose" cells & make for a larger setup than a single 18650 :rolleyes:
--> goto 18650

 

[Wrend]

I don't use protected loose Li-ion cells, so I don't have a working knowledge of how they perform in this regard. Connecting unprotected cells in parallel isn't an issue though, provided the cells are at or near the same voltage level before being connected. I imagine paralleling protected cells that are at the same voltage level should work though, since there won't be much balancing current between them.

I agree that an 18650 cell could provide more energy than 3 14500 cells or 3 AA NiMH cells, but if you're following the 80% depth of discharge guideline for Li-ions, 3 higher capacity NiMH AA cells still have an advantage compared to, for example, an AW 18650 cell. Personally, I'd rather take the longer useful cycle life of standard Eneloops though.