Adding 200ah Lithium...Electrical Gurus Advice Needed

manyman297

I'm replacing the two 6v Harris batteries with two 12v LiTime Lithium batteries but I'm a little confused about a couple of things:

Bus Bars: Reputable places like Battle Born say you don't need to worry about adding bus bars for parallel installations until you put more than 4 batteries in a bank. LiTime installation shows the use of a bus bar for two batteries in parallel. I'm not sure if there's a reason other than to sell you the bus bars they provide? There's not much room to add bus bars so I'm hoping to skip this step if possible.

Fuses and Wire Gauge: I'm assuming I can still use the existing 4AWG wiring? And will the 40amp breaker still suffice?

Thanks for any insight. I'm versed at the mechanics of installing electrical components but when it comes to the math and calculations for breakers, wire, etc. I'm always second guessing. 

Grumpy_G

You don't need bus bars for two parallel batteries but they could make the wiring a little cleaner. 

The wiring and the breaker don't need to be changed unless something else is changed that increases the current demand significantly. The breaker protects the wiring, not the batteries.

manyman297

Thanks @Grumpy_G

So I assume since the inverter would probably be the biggest draw, if that is ever upgraded that would require upsizing the breaker? 

elbolillo

My suggestion would be to use 2/0 awg wire to connect the batteries together. If you ever decided to add more batteries and/or increase the inverter size, then you wouldn’t have to swap those cables out. Not absolutely necessary but I think to try and future proof things if at all possible. Shouldn’t be any need to change the 40 amp breaker.

Yoshi_TAB

Hi, 

To determine wire and fuse size for any circuit including inverter, you first determine the amps the circuit will/can carry, then you size the wire based on the potential  amps in that circuit.

Just need to do a bit of math :( to determine sizing:

Minimum Fuse Size = ((Inverter Wattage/Inverter Efficiency) / Lowest Voltage )) x 1.25

Where 90% is used for inverter efficiency and 1.25 is a safety factor of 25% on fuse sizing in most cases.

So if you have a 2000W inverter;

Fuse size= ((2000W/0.9)/12V ) x1.25= 231 amp fuse

Since they do not make a 231 amp fuse you could go 250 for a bit more safety factor or 225 for a bit less.

Then you go to the many wire tables out there and look for what minimum size wire can handle your potential fuse current.  In this case, 2/0 AWG wire would work.

Hope this helps.

manyman297

Thanks everybody!

kevmon

Bus bars make it much easier for connecting solar, future solar, 120 volt chargers, etc. will make future changes easier. I used the li time ones. Fairly cheap through Amazon. 

Grumpy_G

IIRC from working on a friend's 400 boondock a few weeks ago the inverter wiring is separate from the rest of the trailer. My statement above about the breaker and wiring is still correct unless I'm missing something.