Parallel batteries

[MMACH 5]

I have a headlight that runs on 2x CR123 batteries. I'd like to increase the run time for my commute. My thinking is that I can use 4x CR123 batteries, but do it so that there are 2 pairs, (each pair set up as a series) running parallel.

The diagram shows my plan.
Did I think this through correctly or is this going to dump 12 volts into my bulb and fry it?
The black is the existing setup and the red is how I'm planning to wire into it.

Thanks.

 

[nleahcim]

I have a headlight that runs on 2x CR123 batteries. I'd like to increase the run time for my commute. My thinking is that I can use 4x CR123 batteries, but do it so that there are 2 pairs, (each pair set up as a series) running parallel.

The diagram shows my plan.
Did I think this through correctly or is this going to dump 12 volts into my bulb and fry it?
The black is the existing setup and the red is how I'm planning to wire into it.

Thanks.

The way you have it drawn you'll be paralleling two cells with one cell. I'm not sure if the series resistance of your cells is enough to cause them to catch fire, or just die. Either way, badness.

It'd be a lot better for you to have two sets of parallel cells.

 

[MMACH 5]

The way you have it drawn you'll be paralleling two cells with one cell. I'm not sure if the series resistance of your cells is enough to cause them to catch fire, or just die. Either way, badness.

It'd be a lot better for you to have two sets of parallel cells.

Yikes! What you described is actually what I was attempting. The switch's placement between the batteries is what threw me.

And Thank you! You saved me some heartache tonight.

Would this setup correct the problem?

 

[nleahcim]

Yikes! What you described is actually what I was attempting. The switch's placement between the batteries is what threw me.

And Thank you! You saved me some heartache tonight.

Would this setup correct the problem?

Well... yes and no. Yes - when the sets of cells are balanced with respect to each other - it will work fine. But having two switches makes me nervous - I'm worried that you'll use only one switch at a time or something... because that could then cause the sets of cells to become unbalanced with respect to each other - and then when you flipped both switches the more full ones would rapidly discharge into the other set.

What I'd rather see is just one switch to control the whole thing.

If you'll excuse the crude ASCII... this is what I'd prefer to see

 ______ 
 |    |
|-|  |-|
| |  | |
|+|  |+|
 |____|
    |
    \
    |
 ___|__ 
 |    |
|-|  |-|
| |  | |
|+|  |+|
 |____|

 

[MMACH 5]

Thanks. I'm starting to think I'll be stuck with carrying extra batteries to change out on my ride home.

The current light setup (in black) is actually factory made with the switch on the battery case, between the batteries. The DIY, external battery holder is an old flashlight that I re-purposed for this. It does still have the switch on it so I figured I'd need to use it to keep the LED from getting constant power. If I go with this setup, I'll be turning on the two switches at the same time, (or at least within a few seconds of each other).

It sounds like parallel wiring is a bit more precarious than series wiring.

 

[Lynx_Arc]

Thanks. I'm starting to think I'll be stuck with carrying extra batteries to change out on my ride home.

The current light setup (in black) is actually factory made with the switch on the battery case, between the batteries. The DIY, external battery holder is an old flashlight that I re-purposed for this. It does still have the switch on it so I figured I'd need to use it to keep the LED from getting constant power. If I go with this setup, I'll be turning on the two switches at the same time, (or at least within a few seconds of each other).

It sounds like parallel wiring is a bit more precarious than series wiring.

use a single pole double throw switch and connect both minus sides to the circuirt and both battery plus sides to opposite sides of the switch with the middle pole to the plus side of the circuit. that way you can switch from one set to the other at whim

 

[MMACH 5]

use a single pole double throw switch and connect both minus sides to the circuirt and both battery plus sides to opposite sides of the switch with the middle pole to the plus side of the circuit. that way you can switch from one set to the other at whim

Hmmmm. Thanks for the suggestion. I suppose there's no reason that I have to be drawing juice from all four batteries at the same time, is there?

I'll mull over my wiring options here...

Thanks again for everyone's help on this!

 

[jankj]

Hmmmm. Thanks for the suggestion. I suppose there's no reason that I have to be drawing juice from all four batteries at the same time, is there?

Nope. An added benefit is that you get much better control over which batteries that needs charging.

Personally, I would prefer this setup for this very reason :thumbsup: