# Can you connect batteries in series and parallel at the same time?



## SciTech02 (Jun 21, 2008)

I have been getting mixed information on this site, so this is why I am asking if you can have batteries in parallel and series in the same system. For example: if you had 10 batteries, each 6 volt and 10 amps, could you wire 5 of them in series and 5 of them in parallel so that the system would be 30 volts and 50 amps? Sorry if this is a stupid question.


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## ww321q (Mar 28, 2008)

check out this thread it has some good info 
http://www.diyelectriccar.com/forums/showthread.php?t=15483
J.W.


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## rctous (Jun 18, 2008)

SciTech02 said:


> I have been getting mixed information on this site, so this is why I am asking if you can have batteries in parallel and series in the same system. For example: if you had 10 batteries, each 6 volt and 10 amps, could you wire 5 of them in series and 5 of them in parallel so that the system would be 30 volts and 50 amps? Sorry if this is a stupid question.


There is no stupid questions better to ask than to blow yourself up. When you wire in series the voltage increases by the # of cells in series 2 - 6 v batteries is 12 volts 3 =18 volts etc.
when you parallel cells the voltage of the cell stays the same but the "AMPS" increase. so 2 - 10 amp 6 volt batteries in parallel will remain at 6 volts but now become 20 amps 3 in parallel will still be 6 volts but 30 amps etc. 

To answer your question with 10 -6 volt batteries 5 of them in series would equal 30 volts
if you did that again with the remaining 5 cells (put them in series) then you would have created another 30 volt battery at 10 amps. Now by connecting both packs together in parallel (positive to positive negative to negative) you now create a 30 volt pack rated at 20 amps, we commonly refer to this as a 5S 2P (multiply the cells in series by the cells in parallel and it = 10 cells total) for you to acheive 30 volts at 50 amps you need 5 batteries in series(30 volts) then 5 more in parallel to acheive 50 amps so this would be a 5S 5P battery or 25 cells needed. Did this make sence?

PS NO is the answer

B


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## SciTech02 (Jun 21, 2008)

I understand what you are saying, but I was thinking of a single row of 5 batteries connected + to + and - to -. For example (sorry for the crude model):

[+ -]
[+ -]
[+ -]
[+ -]
[+ -]

Would this create a 6 volt 50 amp system (if I used 6v 10amp batteries), or is my idea of a parallel circiut completly off?


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## enganear (Jun 16, 2008)

SciTech02 said:


> I understand what you are saying, but I was thinking of a single row of 5 batteries connected + to + and - to -. For example (sorry for the crude model):
> 
> [+ -]
> [+ -]
> ...


Your idea is completely off. Series connections add voltage, but because the same current must pass through each battery, the capacity stays the same.

Parallel connections add capacity, but voltage stays the same.

5 batteries in series would provide 60V @ 10 amps
5 batteries in parallel would provide 12V @ 50 amps

Hope this helps,
-enganear


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## Whitey_87 (May 30, 2008)

I am asking a similar question a couple threads up.

I don't see why that cannot be done, but the responses seem like whatever # of batteries you hook in series, you want the same # of batteries in the parallel string. Is it a battery principle or something?


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## enganear (Jun 16, 2008)

Whitey_87 said:


> I am asking a similar question a couple threads up.
> 
> I don't see why that cannot be done, but the responses seem like whatever # of batteries you hook in series, you want the same # of batteries in the parallel string. Is it a battery principle or something?


You cannot connect strings of different Voltage. You can connect a string of (5 series connected batteries) in parallel with another string of (5 series connected batteries). 5 parallel connected bateries would only be 12V using the batteries outlined in the 1st thread.


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## Whitey_87 (May 30, 2008)

enganear said:


> You cannot connect strings of different Voltage. You can connect a string of (5 series connected batteries) in parallel with another string of (5 series connected batteries). 5 parallel connected bateries would only be 12V using the batteries outlined in the 1st thread.


got it, major answered it it in my other thread too.


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## major (Apr 4, 2008)

Whitey_87 said:


> I am asking a similar question a couple threads up.
> 
> I don't see why that cannot be done, but the responses seem like whatever # of batteries you hook in series, you want the same # of batteries in the parallel string. Is it a battery principle or something?


 
Hey ******,

This works: 

[- +] [- +] [- +]
[- +] [- +] [- +]
[- +] [- +] [- +]
[- +] [- +] [- +]
[- +] [- +] [- +]


This sucks: 

[- +] [- +] [- +]
[- +]
[- +]
[- +]
[- +]

Hope that illustrates it for you. 

major


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## SciTech02 (Jun 21, 2008)

That makes sense, you would not want to connect a 6 volt battery in parallel with a 12 volt battery (that would mess them up, if I understood enganear's comment). Anyway, a few comments up, you (enganear) said you could connect 5 batteries in parallel to get 12 volts @ 50 amps. Is it possible you could show us how they would be wired, although it looks like major did that already (parallel circiuts are a newer concept to me and I just want to be careful and not shock myself).

Also, I agree with you Whitey_87, there is a lot of talk about "buddy paring" batteries in parallel to reinforce each other (as a safety precaution). Funny we post similar threads at the same time. What are the odds? 

Edit: Two comments were made while I was typing this


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## frodus (Apr 12, 2008)

enganear said:


> You cannot connect strings of different Voltage. You can connect a string of (5 series connected batteries) in parallel with another string of (5 series connected batteries). 5 parallel connected bateries would only be 12V using the batteries outlined in the 1st thread.


 
except the original poster said they were 6V batteries....



> each 6 volt and 10 amps


so, the way he illustrated 



> _I understand what you are saying, but I was thinking of a single row of 5 batteries connected + to + and - to -. For example (sorry for the crude model):_
> 
> _[+ -]_
> _[+ -]_
> ...


is actually correct. 6V system because all are in parallel, current adds, voltage stays the same. Making that a 6V-50Ah system.


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## frodus (Apr 12, 2008)

you cannot simultaniously connect a battery in parallel and series. you can parallel batteries packs, and series batteries packs, but you can't have a mixed pack or you'll create shorts.


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## SciTech02 (Jun 21, 2008)

Thank you frodus. This answers my original question (I can't connect the 6 volt 50 Ah system to the 30 volt 10 Ah because it will cause shorts, right?).


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## enganear (Jun 16, 2008)

frodus said:


> except the original poster said they were 6V batteries....


DOH! Got my threads tangled. Thanks for the correction.
-enganear


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## frodus (Apr 12, 2008)

SciTech02 said:


> Thank you frodus. This answers my original question (I can't connect the 6 volt 50 Ah system to the 30 volt 10 Ah because it will cause shorts, right?).


well, you can't put the batteries in a grid and connect them all and try to get a higher Ah, higher voltage pack.

And why don't you just pack as high a voltage pack as you can. The current is lower, but the POWER stays the same. The controller has a Cap Bank in it and will discharge at the same time the battery does when the FET's turn on. 

My motorcycle pulls 80A from the batteries, and puts out 350+A at the motor. Of course this decreases with speed, the power input to the controller 80A at 72V, stays pretty much the same up to a certain speed.


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## Whitey_87 (May 30, 2008)

major said:


> Hey ******,
> 
> This works:
> 
> ...


It makes a little bit of sense how you described it in the other thread but I still do not understand why the controller will not see a combined voltage and a combined Ah (following the rules of parallel and series connections)...Why would the 12v high Ah set will drain first?


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## frodus (Apr 12, 2008)

you CAN parallel battery packs of equal voltage
you CAN series battery packs of equal Ah rating
You CAN series battery packs of different voltage

YOU CANNOT parallel battery packs of different voltage.

YOU SHOULD NOT series batteries of different AH ratings, because the batteries will become unbalanced.
YOU SHOULD NOT parallel batteries of different AH ratings, because when you charge, the lowest Ah battery may become unbalanced.

You should pick one standard size Ah rating and voltage and keep the pack all the same. You can series parallel them for higher current or higher voltage, or a combination of the two, as explained.

You could make 2 packs of 60V (5 batteries) using 12V 50Ah batteries. Then parallel those 2 individual packs for 60V 100Ah.

Its better to parallel individual batteries and THEN series, from what I've seen. basicall you make 5 individual parallel packs of 2 batteries, and then series those packs together.


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## ww321q (Mar 28, 2008)

I think you can put 6 volt and 12 volt batteries in a series string just not in parallel J.W.


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## frodus (Apr 12, 2008)

> You CAN series battery packs of different voltage


I said that 

I wouldn't do it because its going to be hard to match the impedance of a 6 and 12V so they balance equally. Best to stick to the same voltage and Ah cells.

A 72V pack is made up of a 36V, 24V and 12V pack  but the cells are matched.


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## ww321q (Mar 28, 2008)

See that's another thing I don't believe in is charging in series . Using a charger for each battery in a series pack is the best way to charge them . Charging in series at pack voltage is a compromise . J.W.


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## frodus (Apr 12, 2008)

ww321q said:


> See that's another thing I don't believe in is charging in series . Using a charger for each battery in a series pack is the best way to charge them . Charging in series at pack voltage is a compromise . J.W.


I couldn't agree more. I'm series charging right now, but I've got balancers. I'm working on my parallel charging system, should be ready by the end of next week.


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## panther_dust (Apr 2, 2013)

sorry to bring up an old post but can i connect batteries this way...

they are all the same v and ah eg each batt is 3.7v 1800ah (bad example and forget the ...'s they are there to space out the image.. red is battery connections 2 parallel sets connected using series

\ ............. /
.\ ........... /
[+ -]---[+ -]
.{ } ..... { }
[+ -]....[+ -]

would that combo make it 7.4v and 7200ah? or would it have to be like this? 2 parallel into 2 series 

\ .............  /
.\ ........... /
[+ -]---[+ -]
.{ } ..... { }
[+ -]---[+ -]

if not what would ^^ that do?


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## Ziggythewiz (May 16, 2010)

Nothing can make it 7.4v and 7200ah. You have 1800AH @ 3.7V x 4

That's 26.6kWh no matter how you slice it. You can have 7200ah @ 3.7V or 3600AH @ 7.4V or 1800AH @ 14.8V


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## panther_dust (Apr 2, 2013)

Ziggythewiz said:


> Nothing can make it 7.4v and 7200ah. You have 1800AH @ 3.7V x 4
> 
> That's 26.6kWh no matter how you slice it. You can have 7200ah @ 3.7V or 3600AH @ 7.4V or 1800AH @ 14.8V



so if i set 2 batteries parallel and another two

both sets would be 3.7v at 3600ah

and then if i series them it would become 7.4v and 3600ah

would it be a simple wiring or not, another site i looked on really made it look complicated


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## njloof (Nov 21, 2011)

It does not have to be difficult, but sometimes the geometry of your battery box or the length of your copper bars may dictate that the batteries face a particular way.

I wired up a series set of Headway cells once; they're on a hex grid, and I had to arrange them 3x8, and the bars were on both sides, so the result was not regular in structure. I had to double check every bar before I screwed it in just to be sure I wasn't shorting something or skipping a battery.


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## panther_dust (Apr 2, 2013)

that seems fair enough, what if i was to tell you it wasn't for a car, its for an android tablet, the original battery is over 4 times the size of just one of mine so 4 will sit in there easily (they are ps3 controller batts), the original also had 2 cells all silver foiled up and taped etc, damn cheap Chinese sh&t in other words, but the principles should all be the same right?

i cant tell what the original ah was but the voltage is 7.5


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## Ziggythewiz (May 16, 2010)

panther_dust said:


> and then if i series them it would become 7.4v and 3600ah
> 
> would it be a simple wiring or not, another site i looked on really made it look complicated


That's correct. No, it's not complicated, either of your original diagrams would do it. Where you may have problems is in keeping the cells balanced. Laptops are usually 3S2P packs and have leads going to each one to control charging.

With an EV it's easy to use safer cells (LiFePO4), do an initial balance, and known charge/discharge routines to protect the cells.

In your case you probably don't know how far the tablet will charge or discharge the cells, so you can't know if it's safe or not without adding extra circuitry that probably won't fit.


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## panther_dust (Apr 2, 2013)

so take my chances and risk it blowing up then haha


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## njloof (Nov 21, 2011)

Or buy a multimeter and check the voltages every so often. If they get badly out of whack, you rewire them in parallel, let them sit for a while to balance (a day or so), then rewire back.

Probably overkill for 4 batteries though.

Personally I use one of these. Lets me keep a tablet and phone charged even when using them on a 12+ hour flight, so they're still charged when I land.

http://www.isound.net/shop-by-type/accessories/i-sound-portable-power-16000-mah.html


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## panther_dust (Apr 2, 2013)

i suppose, i was originally only going to wire 2 together as is there already, but its always with asking, thanks for your help anyway guys


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## Ziggythewiz (May 16, 2010)

Adding the cells in parallel doesn't increase the risk any. 

If they just had the two cells in series without a middle monitoring/charge wire their charge curve probably has good safety margins and your upgrade would be fine.


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## panther_dust (Apr 2, 2013)

i would show a picture nut i cba to upload it, the one it came with it is one silver foil wraped battery but you can see feel and manouver 2 so they have obv been bodged together and it has 1 wire coming off, no circuits, no extra boards just plain and simple battery's


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## kewlrane (Aug 23, 2013)

Yes you can. You can string into 2 series sets and then parallel the sets. http://www.batterystuff.com/kb/articles/battery-articles/battery-bank-tutorial.html


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## eze (Sep 22, 2021)

major said:


> Hey ****,
> 
> This works:
> 
> ...


Is this really possible??


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## galderdi (Nov 17, 2015)

eze said:


> Is this really possible??


Both those scenarios are possible. The first scenario will have an acceptable outcome. the second scenario will not have an acceptable outcome.


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