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A series/parallel battery bank

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Terryhes

New Member
I'm just a beginner with a lot of questions,

Is there anyway to have a (3) 3.7 lithium ion batteries in parallel to get suffient battery power to run a given device @3.7 VDC and then run another device @7.4 VDC off the same 3.7VDC batteries but using (2) in series, the 7.4VDC circuit would need to have a 2.5 - 3 amp draw capacity, the draw would only be for short durations approx 5-15 sec

Any and all help is appreciated thanks
 

MikeMl

Well-Known Member
Most Helpful Member
No. If the bats are in series, then you cannot simultaneously have them in parallel, or vice versa. Now if you forget about simultaneously, a double-pole double-throw switch would work.

ps, where is Hinton? My wife is from Vulcan
 
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Willbe

New Member
With switching and large capacitors I think you could do it. How much voltage ripple can you stand?
 

Sceadwian

Banned
You wouldn't want to do the switch thing anyways, you'll unbalance the individual cells, you have to draw from all three at the same time or the pack will eventually fail because you're drawing more current from two of the cells than you are from all three. Although a switch mode like Willbe is suggesting is pretty simple, switched capacitor voltage doublers are pretty basic.
 
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audioguru

Well-Known Member
Most Helpful Member
I looked for Hinton, Alberta in Google Earth and saw that it is due West of Edmonton in the foothills of the Rocky Mountains. Ffffffreezing most of the time including today where they have SNOW!.
 

Terryhes

New Member
Yes snow we do have, But also nice summers for the most part by nice I mean 65 - 80 degree range, We also don't have heavy traffic, heavy pollution or a lot of crime, The standard of living is high but so is our income, I can look out my window and see the mountains, quad/snow mobile /ride my horses right from my back door into hundreds of square miles of crown land (federal land) I wouldn't trade it for the WORLD, Vulcun is towards farm land a flatter, less trees and a lot of private property, more heavily populated but still okay
 

Terryhes

New Member
I'm just a beginner with a lot of questions,

Is there anyway to have a (3) 3.7 lithium ion batteries in parallel to get suffient battery power to run a given device @3.7 VDC and then run another device @7.4 VDC off the same 3.7VDC batteries but using (2) in series, the 7.4VDC circuit would need to have a 2.5 - 3 amp draw capacity, the draw would only be for short durations approx 5-15 sec

Any and all help is appreciated thanks
The duration time is 5-15 secs but not on a regular basis,
 

Sceadwian

Banned
Terry use a switch mode power supply IC to boost the voltage from the parallel config, it's not practical or safe to draw unevenly from a multi cell lithium pack.
 

Terryhes

New Member
Thanks Sceadwian thats what I was already figuring, So I had also put in a post looking for some D.C. step up, D.C, doubler, But I am looking for a complete assembled unit, not just the chip, Or a very good diagram with well detailed descriptions and comments. Because if I was to build it myself sure a God made little green apples I'd mess it up

Thanks Terry
 

Sceadwian

Banned
Try Linear technologies website, they have simple setup examples in the PDF's for their controllers. They have a parametric search on their website as well, you tell them your voltage in your desired voltage out and the current you need and they tell you what IC's they sell that will work. Read the pdf for one and see if you could make it from the examples given.

This is the page is spat out when I put your values in.
Linear Technology - Product Category Parametric Table
 
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