Connecting 6 volt batteries in series/parallel

[RickB]

Hi all,

I have a 2000 watt xantrex inverter and I just bought 4  6 volt trojans. Is the optimum hookup to make the needed 12 volts series parallel?

Just to be clear series parallel with 4 batteries would be to connect two of the batteries + to - and then the remaining +'s and -'s would be connected together and ran to my inverter correct?

Which wires do I connect first and which ones are last or does it matter?

I don't know diddly about electrical stuff

Thanks for the help

Rick

[bevans6]

Yes.  Series parallel.  Connect  two of the batteries in series, positive to negative. Connect the other two batteries in series the same way.  They now form two 12v batteries each with a negative and a positive post with nothing connected.  Connect the two negative posts together and the two positive posts together, you have the two 12v batteries in parallel.  Now you have a compound series parallel battery.  after you have that all done, connect up the positive to the inverter and the negative to ground and you are done.

Brian

[bobofthenorth]

Someone else will chime in with a more technical explanation Rick but here's a way to visualize what you are going to do:

Take two of the 6 volt batteries and connect the + of 1 to the - of the other.  At that point you have a 12 volt battery between the remaining + & - posts.  Then you'll do the same with the other pair of 6 volt batteries.  At that point you have the equivalent of 2 twelve volt batteries which you will then connect in parallel before or as you connect them to your inverter.

There's a whole bunch of theoretical stuff that someone else will likely explain regarding cable lengths and routing of the cables but for my money the important thing is to keep the cables as short as you can and buy as big a diameter cable as you can afford.

[gumpy]

Try this...

[pvcces]

And it is unwise to connect some inverters to positive first and negative last.

There is a specific warning in the Link 2000 manual to never disconnect the inverter negative from the battery bank while it is running. We have lost an inverter by doing just that.

The problem comes from the fact that when you power up an inverter, some models turn on immediately. If you make a shaky connection, the inverter may turn on before you get it solidly connected. That could mean that the negative could be lost while the inverter is operating.

I figured out that when the negative is lost, the ground voltage will be whatever the inverter output does with it, such as reversing polarity and input going way over the rated voltage because the inverter negative is connected directly to the neutral of the output.

This is one application where connecting the negative after the positive can cost you.

For what it's worth.

Tom Caffrey

[Sean]

As far as connection sequence, follow the recommendations of your inverter manufacturer for connecting it to and disconnecting it from the batteries.

However, before you connect the inverter, the last connection you should make on the battery bank is the connection from the batteries to "ground" (vehicle chassis).  This is also the first connection you should break before any maintenance on the batteries, after first disconnecting the inverter per its manufacturer's instructions.

Also, since it has not been mentioned here yet, I will make explicit something that is shown in Craig's (Gumpy's) diagram: connect the load to the positive of one string, and connect the ground to the negative of the other string.  You can think of this as "connecting on the diagonal."  This will keep the load and charge profiles even across both strings.

-Sean
http://OurOdyssey.BlogSpot.com

[gumpy]

Hey, I just noticed something about my diagram. If you look at it in the small icon-like photo, it looks like a happy little diagram.   
That wasn't planned when I drew it.

I guess that must mean if you follow the recommendations here, you will be a happy little busnut. 

[RichardEntrekin]

Here is a technical paper on the point that Gumpy and Sean made.

http://www.smartgauge.co.uk/batt_con.html

[Sean]

Richard,

That's a very well-presented explanation, thanks for the link.  I will add that to my arsenal of explanatory resources for the future.

-Sean
http://OurOdyssey.BlogSpot.com