Wiring in Series 2x 100ah - Cable Sizing help + More questions!

[upwinger]

Hi everybody

So I am looking at building a 24v solar system. There will be about 1000w of power going into an mppt. Now my question is,

Ive got 2x 100ah lifepo4 batteries I want to connect together. They will be next to each other. I understand that to get 24v they'll need to be connected in series. Now my questions are:

1) What size does the cable need to be to connect the 2 batteries? (I have highlighted the cable in blue - forgive me for the horrendous drawing). I am thinking it is 6awg/16mm2 because max draw will be around 2500 (inverter of 2000w + 500w of load) divided by 24 which is 104 amps. I was going to buy this cable from ebay which the seller stated can handle 110amps: https://www.ebay.co.uk/itm/142796139227

2) Am I correct in thinking that with the series connection, I only need the one cable to connect the two batteries?

3) If I require a larger cable, then I have a problem because my MPPT has a max terminal size of 6awg/16mm2. How would I connect a thicker cable to the MPPT?

Thanks for all your help

 

[TacomaJoe]

The ebay seller doesn't note how long of a cable run that the wire can handle his listed current. Run some numbers through an online calculator. The blue jumper needs to handle the full load so it will be as large as the inverter wires. How close is the inverter to the batteries? I'm thinking 2AWG for the inverter and jumper, 8AWG for the MPPT.

 

[740GLE]

FYI

You can run 6awg to the MPPT and run larger to the inverter, say 4awg or 2awg.

It’s best to provide the largest conductor for the invert you can.

Also people feel it’s best to only have one connection to the battery terminals vs two that you show. Less chance of error in one connection that double stacking lugs.

 

[upwinger]

The ebay seller doesn't note how long of a cable run that the wire can handle his listed current. Run some numbers through an online calculator. The blue jumper needs to handle the full load so it will be as large as the inverter wires. How close is the inverter to the batteries? I'm thinking 2AWG for the inverter and jumper, 8AWG for the MPPT.

Inverter is about 1 metre from the batteries.

FYI

You can run 6awg to the MPPT and run larger to the inverter, say 4awg or 2awg.

It’s best to provide the largest conductor for the invert you can.

Also people feel it’s best to only have one connection to the battery terminals vs two that you show. Less chance of error in one connection that double stacking lugs.

When you say its best to have one connection to the battery terminals, I'm not sure I understand. Do you mean I should connect a bus bar or something to the terminal and attach the mppt wires and inverter wires to the bus bar?

Thanks for all your help.

 

[mikefitz]

You need fuses at the battery suitable for the expected current.
50 or 60 amps In the MPPT feed, 16 mm2 cable. The inverter needs a 100 amp fuse and 25 mm2 cable.
The 500 watt DC load needs a 30 amp fuse and its feed cable, 6mm2.
To make neat connections use a positive and negative buss bar. Battery cable to the buss bars and joining the batteries, 25mm2.

 

[740GLE]

Inverter is about 1 metre from the batteries.



When you say its best to have one connection to the battery terminals, I'm not sure I understand. Do you mean I should connect a bus bar or something to the terminal and attach the mppt wires and inverter wires to the bus bar?

Thanks for all your help.

Yeah bus bars are great ways to add more connections.

 

[upwinger]

Thanks everyone for your help. I've gone with 35mm2 in the end.

 

[littleharbor2]

This is one neat solution. You can safely fuse both the inverter and SCC

Dual MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

Easily and economically satisfies ABYC 7 circuit protection rule by mounting on a 3/8 battery post, battery switch or bus bar.

www.bluesea.com