How To Add Batteries In Parallel

Since this commodity was published I take received a lot of questions most connecting batteries. How To:Connect ii batteries in parallel – Part ii answers the questions asked the about.

Similar most things in that location is a right style and a incorrect way of doing it and one that I receive emails about is how to connect ii batteries in parallel and get even more people finding the site by request the question on Google. So hither is a quick "How To" guide with some explanations on the right fashion and the wrong way.

Most people who want to connect two batteries together are trying to expand the battery chapters of their existing setup. 1 affair to recollect, if you lot are going to install a second bombardment, yous are going to have to start with two new, identical batteries. Aforementioned make, Amp hour (Ah) rating and if y'all can the same manufacture date. Connecting batteries with different Ah ratings or from dissimilar manufactures is not a practiced idea as it can/volition atomic number 82 to one bombardment trying to charge the other (due to the internal frontward and opposite resistance beingness different) and can atomic number 82 to all sorts of other problems.

So now we take two new identical batteries how do we go about connecting the ii batteries together? Well the most obvious is to simply connect a new bombardment to the original battery using some cable and new battery terminal clamps like this….

The WRONG way to connect two batteries in parallel

OK, that will work. Hang on though lets have a closer look.

Battery A is the primary battery and Battery B is our newly installed secondary battery. At present when we put the whole system on load… starting the engine for instance, there will be a slight voltage drop across the ii cables linking the two batteries together… lets say it'south 0.5 volts on each link or bridge cable, that's one volt in total. Then Battery A will always supply more power than Battery B as battery B's credible voltage is always less than Bombardment A because of the volt drop. Now over a period of time, Bombardment A will ever be 'used' slightly more than Battery B so at some bespeak Battery A will have cycled more and be 'aging' faster than Battery B and it will somewhen lead to problems and will need replacing. But remember what I said earlier, yous should always apply batteries from the same manufacturer with the same rating and manufacture appointment… well that still applies and at present yous will be replacing Battery B that is probably even so working OK.

The other side of this is charging. We will notwithstanding have the voltage drop – although it will be smaller as the charging electric current is a lot less than the cranking electric current for starting your engine, lets call it one/four volt (0.25 volts) on each cable, so now the engine is running and the batteries are charging .. but Battery A gets the full charging voltage – xiv.0 volts for example only Battery B only gets 13.0 volts, and so not really enough. So now we are in a situation where Bombardment A is doing more work and Battery B is not getting charged properly. And then what'due south the solution?

Well, this isn't going to cost y'all much….. simply connect them slightly differently!

The CORRECT way to connect two batteries in parallel

Past taking the electrical feed from the 2nd battery nosotros now fifty-fifty up 'the pack' electrically. When nosotros kickoff our engine at present, Battery A has no volt drop to world and 0.5 volts to the output…. and Battery B has 0.v volt drop to earth and no volt drop to the output. Then simply past moving one connection we have evened out the volt drop to both batteries. At present the same happens in reverse when charging. Battery A has a volt drop on the +Ve side and Battery B has a volt drop on the -Ve side. So we are now charging both batteries identically.

A few notes on installing a 2d battery

As I said earlier, ever utilise identical batteries – same make, aforementioned Ah rating and same manufacture date if possible.

Earlier installing the batteries, accept the time to charge them upwards individually using a smart charger so that when you link them together they will both have identical charges – you will ensure that y'all get most out of your batteries this way.

E'er try to use identical size cable or larger as the existing cables connecting your old battery.

Always endeavour to keep the link or bridge cables the same length and route them through the same hole in any metal bodywork. This volition stop the chance of any elevated/quasi DC fields and ramping DC fields, especially with cables conveying 100 Amps upwards (inverters etc.) In that location are also other considerations when switching on/off high DC loads too. It's how the professionals in the marine and aviation industry exercise it and so that'southward how I'd recommend y'all do it.

NEVER connect both batteries earth connections to the chassis of the vehicle and rely on the torso of the vehicle as the electrical path . But ever link them to each other and have ONE connection the chassis or bodywork.

All installations are different. It may be that instead of moving the positive lead to the new battery (B) is is meliorate to leave that where information technology is and motility the negative (world) to the new battery instead. But think one lead from 1 battery, the other lead from the other battery. Take time to plan before committing to anything.

NEVER cut a few of the strands off the cable to try to go 2 heavy-duty cables in a battery concluding designed for 1 cablevision. There are specialist battery terminals designed to take ii cables out at that place… check out the on-line specialist stores.

As yous are probably doing this because you lot demand more capacity, it is worth checking the existing heavy-duty cables… it would be a good time to think well-nigh if the existing stuff needs upgrading also.

If you want to install a 2d battery in your iv x four as you are installing a winch, this is not the fashion to do it. I'll comprehend that in a future "How To"

Exist Rubber…

At that place is a huge amount of energy stored in these batteries, if y'all brusque one out it will become Blindside… if yous connect two together the wrong way… it still goes BANG but a lot LOUDER! Seriously, if you lot have any doubts, get an Auto Electrician to do information technology. Getting information technology wrong volition seriously hurt you lot.

If you found this useful, I'd appreciate information technology if you would click on the rating star practise-hicky at the top of the page, thanks.

UPDATE: If you are thinking of installing a second bombardment in your vehicle, exercise y'all actually need to connect them direct parallel to make one big battery? If y'all don't need pure starting power (cranking amps) from your battery, in that location may exist other options available that would give you carve up charging and the power to combine them if required. Accept a read through "Relay, VSR, SCR… what'southward the divergence?" to come across if there is a amend option that would suit your needs.

I have fastened a PDF drawing (Below) of the above cartoon that yous can down load and print out with the wiring diagrams higher up.How to connect two batteries in parallel 01