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An online resource for everything about overland expedition travel.
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Robin began expedition and overland travel over 15 years when he started building aluminum Land Cruisers for bush and travel purposes. His career as an aluminum boat fabricator led to the eventual design and construction of an all aluminum Land Cruiser completed in 2001, in which he and Raenelle have travelled extensively.
Currently Robin is a civil engineer in Victoria, British Columbia, Canada. His combined expertise as a designer, builder, problem solver, and ultimately traveller brings much of the value in his articles on this site.
Connecting Batteries in Series and Parallel at the Same Time
A few days ago Larry Amato from Amato Consulting replied to our previous article that describes how to create 24 volts from two 12 volt automotive batteries. He continued our thought process by showing that you could take four automotive batteries and connect them in both series and parallel at the same time to achieve a 24 volt battery bank with double the capacity of a single 12 volt battery.
His application was for a solar installations where capacity is usually important, along with a typical requirement for 24 volts which is a common voltage on solar panel systems.
He describes how to do it using a matrix – I had to take a pencil to write it down to follow what he was saying. Then I had to think about it for a bit, so I figured some you might have had to think about it for a bit too…hence this article. I’ll try to give some more detail to break it all down. Here is what he said:
My need was 24VDC power with 200 amp hours.
I purchased 4 each 12VDC AGM 110 amp hour batteries. Picture the 4 batteries in 2 rows (R) x 2 columns (C).
1) R1C1 positive is connected to R1C2 positive.
2) R2C1 negative is connected to R2C2 negative.
3) R1C1 negative is connected to R2C1 positive.
4) R1C2 negative is connected to R2C2 positive.
5) R1C1 positive and R2C1 negative provide 24VDC power with 220 amp hours.I take the R1C1 positive and R2C1 negative and run through a 24VDC Photovoltaic Charge/Controller which is connected Solar Panels with output to my various 24VDC devices including Programmable Controller, Instrumentation, and Spread Spectrum Radio.
Like I said, you need to draw it out. And for your benefit, I’ve done that (click to enlarge):
On the left is what Larry describes, and on the right is what I would have done. I’ve gotta say, Larry’s way is WAY better. Less wires, less complex. So let’s talk about it.
“My need was 24VDC power with 200 amp hours”
24 volts from 12 volt batteries: if you read our last article then you know that when you connect batteries in series, the voltages add together. So Larry took two of his batteries and connected the positive and the negatives together. Then he did it for the other pair. On the diagram, each pair is vertical – the negative of a top battery is connected to a positive of the battery directly below it. And so now there are two 24 volt battery banks, side by side.
On to the second criteria, 200 amp hours.
It’s pretty tough to find an automotive battery that stores much more than 100 amp hours. In this case Larry found some 110 amp hour AGM batteries. But how do you get 200 amp hours? I describe this in detail in the last article, and if you’ve read it you know that if you connect batteries in parallel the amperages add together.
And so he added the amperages of the two battery banks together by connecting the positives on each bank and connecting the negatives on each bank. Presto, 100 amps plus 100 amps is 200 amps.
Lastly by taking a lead from the positive and a lead from the negative, he’s got a 24 volt system, with the full capacity of 200 amp hours in reserve. On the image above you’ll see what I call “our method”. While it does the same thing, it’s more complex, and after seeing how Larry does it, I’m converted. See if you can follow the differences – but really, they each do the same thing.
A few paragraphs ago I mentioned the AGM batteries that Larry purchased for his application. AGM battery – what is that?
What are Advanced Glass Mat Batteries?
AGM stands for Advanced Glass Mat, and is a type of deep cycle battery. Battery types is a whole other article that we need to write, but if you are reading this and you care to contribute, go ahead and leave a comment below. Hey, if you want to write a full blown article and give some good detail on what an Advanced Glass Mat battery is, go to our article submission page and do so – we come with benefits!
On to the second criteria – 24 volts. You also know from the last article that when you connect batteries in series, the voltages add together. So Larry then took his two 12 volt battery banks, and connected them together in series – in other words the negative of one bank to the positive of the other.
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Hello,
My need is 12V DC power is to be converted into 220v AC.
i need to connect them to my wind tubine o/p 12v DC.
i have planned to purchase 4 batteries.
Please let me know
what kind of batteries i need to purchase?
how to connect them in series to get the 12v DC o/p ?
Regards
Raghu S P
Raghu,
You’ve asked a bunch of questions there – I’ll work up an article to try to answer them. But in short you’ll need:
1) An inverter to convert the 12V DC output of your turbine/battery system to 220V AC
2) Buy 12 Volt deep cycle batteries, try to find some with at least 100 Amp hour rating.
3) Connect the batteries in parallel, not series.
My questions for you are
1) Why 4 batteries?
2) What are you going to be powering? What is the load? For how long will you expect to run the devices without wind?
3) What are the specifications of your wind turbine? How many amps does it put out at a given wind speed?
4) Do you have the right electronics to charge your battery such as a blocking diode and charge controller?
Hope this helps,
Robin
i bought inverter that is 24vdc and i connected 2nos of 200ah batteries i connected the positive to negative and positive to negative to get 24vdc after that i connected the inverter positive cable to positive of battery A and the negative of the inverter negative cable to the negative of battery B hence it is still not working can you pls. help me thanks
pretendo ligar 3 baterias de 12v 17ha para scoter para motor 36vdc 19ha
I saw the article on connecting 4 12 110Ah batteries in series and parallel to achieve 24V at 200Ah. Will this work with 3 12V 75Ah SLA batteries to achieve 36V at 225Ah? If so what would the wiring look like?
Ed
No it won’t work. You would need 3 banks of 3 – 12 Volt batteries. Each bank of 3 batteries would be connected in parallel to make 36 volts. Each 36 volt bank would have 75 Ah capacity. You would then string the three banks together in series to make 225 Ah capacity.
In short you would need 9 batteries! But then 225 Ah @ 36 Volts is a bunch of power…
i was trying to find out how to charge 2 12 volt batteries in series with 1 12 volt battery charger
found your pages and this one helpfull
Many thanks for a clear, informative site suitable for novices like me!
I have an antique electric master/slave clock system that runs on a 24v battery happily for about 6 weeks, until the battery flattens, then it’s a recharge and half a day to reset them all!
If I wanted to add a trickle charger to Larry’s set-up, would I need a 12v or 24v one, and which terminals on which batteries should I connect to?
Many thanks in advance!
Ken, you would need a 24 volt charger for this, and the charger would be connected to the 24v positive and negative leads shown on the diagram (positive to positive, negative to negative).
But why add a trickle charger when you could add a transformer instead? Do you know how many amps the clock system draws? A small 120V AC to 24 V DC transformer available at an electronic supply store would do the trick. That way you get rid of the batteries altogether. You just need to make sure the output of the transformer meets the maximum number of amps drawn by the clock.
Check out this video on how to measure amperage from a small system.
I have three 12V12Ah batteries. I need 36V36Ah.Is the following thought correct ?
I connect all the plus together, then all the minus together. The result is: in parallel I would have 12V and 36Ah.
Then I connect from first battery plus to second battery minus and from the second plus to the third battery minus. This would be series and I achieve the 36V.
Thanks for your help Robin
George, it’s not going to work quite like that. I’ve written an article that hopefully explains the difference. Take a look at it here.
I want to run a low power 24volt lighting system and a low power 12 volt TV off two 12v 110a batteries.
Both batteries in series for the lights – fine.
But can I also put the batteries in parallel to run the tv? Parallelled so that they are used equally.
Trevor, you can’t put them in parallel as well. What you are trying to do is important though; load equalization when drawing 12 volts off the “low side” of a 24 volt cell. You either need to draw 24 volts and transform that down to 12 (your transformer needs to be rated for the current drawn by your TV), or else draw 12 volts from the low side and install a battery equalizer that shifts voltage between the two batteries to keep them on equal voltage.
Take a look at this article I’ve written on installing a battery equalizer.
Robin, I’m looking at a larger installation of battery back-up and considering using 40 x NiFe 1.2V battery array with each battery rated at 1220 Ah. This is for a large villa that is off the grid in Bali. We will have a 100Kva genset integrated in the system which should cover any power needs that arise, but I want to maximize on usage of the batteries to reduce gen-set time. How would you go about configuring the system for max amp hours? Would you series them up for 48volt system or do a series/parallel configuration and 24volt system? Any suggestions you have would be appreciated.