On our post about installing a 24 volt battery equalizer, Parker Sharpe asked in the comments section how to wire two 12 volt batteries to make 24 volts.
The Short Answer
Connect the negative terminal of one battery to the positive terminal of the second battery. You will be left with two battery terminals free of the total four. One will be positive on one battery, and one will be negative on the other battery. Take the free positive terminal and connect it to the power lead on your 24 volt device. Connect the negative to the ground connection of your 24 volt device. That's it!
The Longer Answer
It is called wiring the batteries in series, as opposed to in parallel. Here is the difference:
To connect batteries in parallel, connect the negative of each battery to the negative of the next battery. The same goes for the positive terminals - connect the positive terminals together. Here's what you get: the combined voltage of the batteries averages out, but the combined available amperage is additive. For example, two 12 volt batteries connected in parallel gives a combined average voltage of 12 volts. And if one of the batteries is capable of delivering 400 amps and the other can deliver 600 amps, the combined amperage is 1000 amps.
What does the combined average voltage mean? Here is another example. Say you have one 12 volt battery and one 6 volt battery. If you combined them in parallel you would have a combined average voltage of 12+6 / 2 = 9 volts. And most people will be connecting 12 volt automotive batteries together. So the combined average voltage is 12+12 / 2 = 12 volts. Get it?
Why Connect Batteries in Parallel?
In the examples above you keep the voltage the same (you don't normally connect batteries that are not of the same voltage), but you get more available amperage. This translates into the ability to do any of the following:
- run your equipment longer (i.e. car stero)
- run a more powerful piece of equipment (i.e. a large starter)
- run equipment at colder temperatures (say starting your car in the middle of winter).
Why Connect Batteries in Series?
And this leads you to the next question, why connect batteries in series in the first place?
Since the voltage is additive when you connect batteries in series, you will be able to run equipment that is designed with a different voltage. The example that Parker asked about was for his 24 volt troller motor for his boat.
A lot of marine equipment is often 24 volts. And this presents a problem for boats that have a 12 volt starter on the main motor, and the owner has purchased a simple trolling motor that came off-the-shelf for 24 volts. Now you have two systems on your boat - a 12 volt main system for your main motor and boat accessories including the charging system, and a 24 volt system for running the trolling motor.
All of a sudden the whole problem gets a lot more complex. The question is how to connect batteries in series and parallel at the same time? The short answer, is no you can't. The soluton is another article.
But in the short term you can use the brute force method: buy two 12 volt batteries, connect them in series to make 24 volts, and run your troller directly from them. Eventually the troller will drain the batteries, and you'll have to quit, go to shore, hump the batteries back home, connect them to a charger to recharge them, and bring them back to the boat on your next fishing trip. What a hassle, but it would work (make sure you've still got your main motor to get home or else bring a paddle!).
Very well done but I have another question. Would it make any difference if you hooked in series two 12 volt batteries, pos to neg and neg to pos and then hooked the 24 volt troller to the pos on one battery and the neg to the other.
Parker, that is exactly what you’re supposed to do!
This was a good explanation of making 2 12VDC batteries either Series for 24 VDC or Parallel so as to increase the amperage.
You CAN connect 12VDC batteries both Series and Parallel if you double the battery count which I am doing for some Solar locations.
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.
Larry, I like the way you do this. Without the aid of images it’s pretty hard to follow so I’ve written another article detailing what you talk about. Thanks!
Would either way of wiring the batteries make any difference to the charging process with regard to balancing and would Larry’s way cause more problems if one of the batteries had deteriorated would this hinder the charge for the battery its connected in series with…. Due to it having a high resistance because electricity will always take the path of least resistance
so in the ” brute force method” you have 3, 12 volt batteries, one connected to your 12 volt system, and two not connected to that system for the 24v that you charge by hand? i there a way to pull 12v off a set of batteries connected in series (24v)?
Vlad
You can take a lead from the low side battery in a 24 V system. This would give you 12 volts.
But you need to be carefull because you run the risk of discharging the batteries unevenly. We’ve written about this in detail on our post 24 volt battery equalizer install
Hope this helps.
This the best and easiest info I found on the net. Thank you. Bob
One picture is worth a 1000 words!!!
I have a question along the same line, but slightly different. I need a battery box with only two out terminals; one +, and one -. I will have a switch (I assume it will be a dbl. pole, dbl. throw, ctr. off) inside the box. With the switch in one [on]position I need 12 v. out. With the switch in the other [on] position I need 24v. I have done this in the past, but cannot remember how. To charge all the batteries at once, the switch needs to be in the 12v. poaition. In my case, the batteries will be about 8 amps, so huge relays are not needed. How did I do it??
How do I connect eight 12 volt battery to give me 48volt?
how do I connect eight 12 volt battery to get 48volt at the terminal?
how to charge a 12 volt battery with two 12v chargers?
I have a question on 12vdc charging systems.
Can you take an 12vdc to 120vac inverter powered by a 12vdc 8oo amp car battery and charge the same battery with a 12vdc 6 amp 120vac Charger plugged in to the same inverter?
like a loop..?
So, for my motorhome, do I want the batteries in parallel or in series? The only large motor that runs off the battery is the slide.
Is it possible to hook 2 12 v batteries together and still get just 12v? I am just looking to make my trolling motor power last longer?
Andy.
+ to + and – to – two batteries of same capacity would double the life of single.
As a disabled person regarding the replacement of batteries for my power chair. There are not many battery retailors here in South Africa who are able to give me any reliable infomation and advice. I seem to be having trouble getting units that last longer than one year although I do have a second chair with a set of 12v gel batteries that have lasted me well over 4 years now. The drive motors are 24v each. Your article has deen a great help but it would be great to hear what batteries you would suggest I pruchase.
How do i hoock-up 4 6volt batterys to get 12 volts
I have two good 12 volt batteries that read 12.3 with meater. I connected the postive of one bettery to the negative of the other with a good #10 CABLE BUT NO RESULT S TO GET 24 VOLTS Any sugguetion.
Hi is it posible to conect 3 12 volt bateries together to produce 24 volts and how is it done many thanks
Hi is it posible to conect 3 12 volt bateries together thanks
Is this possible: 3 12v batteries, two (2) hooked up in parallel however all 3 batteries rigged as a 24v system? That way you get some additional amp hours and satisfy the 24v needs? Thx
Hi How do you connect 3NO 12 volt bateries together to get 24 volts thanks