Adding another lithium battery

[Jo662]

I have 2 x 100ah lithium battery’s , with a 60a B2B, Victron Multiplus inverter/charger and a Victron shunt.
Can I add a 200ah under seat lithium battery, and how would I link them with the other two so they charge and work together ?

 

[LostInSpace]

The simple answer is - Yes.

But the are serious pecautions to take - Searching here may well help.
It is not a simple, one paragraph answer.

 

[suavecarve]

I have 2 x 100ah lithium battery’s , with a 60a B2B, Victron Multiplus inverter/charger and a Victron shunt.
Can I add a 200ah under seat lithium battery, and how would I link them with the other two so they charge and work together ?

You may be able to get 280 ah under your seat.
We, and others, have got the 280 Fogstar on its side under a fiat ducato front seat. Same price (atm) for the 230 underseat as the 280 which fits under some seats

 

[mcfun]

You can add a 3rd battery, though you need to make sure that the cable resistance to the 3rd is the same as that to the 1st and 2nd, in order to ensure that the load current is equally balanced between them. You may need a larger cable to the 3rd and adjust its length to give the correct resistance. Each battery will require a fuse located adjacent to or on the battery. Victron's "The Wiring Book Unlimited", which can be downloaded from their website, may prove helpful. It is worth bearing in mind that adding a new 3rd battery to an existing pair means that they will be of a different age and this may or may not affect how they distribute the load current between them.

 

[Jo662]

You can add a 3rd battery, though you need to make sure that the cable resistance to the 3rd is the same as that to the 1st and 2nd, in order to ensure that the load current is equally balanced between them. You may need a larger cable to the 3rd and adjust its length to give the correct resistance. Each battery will require a fuse located adjacent to or on the battery. Victron's "The Wiring Book Unlimited", which can be downloaded from their website, may prove helpful. It is worth bearing in mind that adding a new 3rd battery to an existing pair means that they will be of a different age and this may or may not affect how they distribute the load current between them.

Thank you ,very good info

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[Googlebot]

I have one battery under the seat and another in the usual place. I connected them with 25mm cable to a common bus bar. One cable length is at least twice as long as the other.

I know this is bad practice and I know it isn’t quite correct, however it’s more than adequate size cable and other than loop lots of very thick cable in a tight space, I had no other option. I haven’t checked individual voltages, it’s all been working fine since I did it though.

 

[Jo662]

I have one battery under the seat and another in the usual place. I connected them with 25mm cable to a common bus bar. One cable length is at least twice as long as the other.

I know this is bad practice and I know it isn’t quite correct, however it’s more than adequate size cable and other than loop lots of very thick cable in a tight space, I had no other option. I haven’t checked individual voltages, it’s all been working fine since I did it though.

Thank you for your reply,sounds similar to what I’d like to do .

 

[Googlebot]

Thank you for your reply,sounds similar to what I’d like to do .

This thread details my install, a few years old now.

Making the change from lead acid to lithium - a thread with pictures

So, after being lucky enough to get a lithium battery for less than half price, (thanks Jim), this thread will be the process for how I have changed over. I may be talking to myself a lot but that’s okay, I always search for rubbish like this when I do anything so I am hoping it will help in...

www.motorhomefun.co.uk

A lot of people gave me a lot of help.

 

[Jo662]

This thread details my install, a few years old now.

Making the change from lead acid to lithium - a thread with pictures

So, after being lucky enough to get a lithium battery for less than half price, (thanks Jim), this thread will be the process for how I have changed over. I may be talking to myself a lot but that’s okay, I always search for rubbish like this when I do anything so I am hoping it will help in...

www.motorhomefun.co.uk

A lot of people gave me a lot of help.

Thanks John

 

[autorouter]

Yes, it's possible. But they are different Ah capacity and a different location. As mcfun and others have said, you'll have to do a bit of calculation to ensure that the voltage drops in the cables are correct, so that the charging currents are what you want.

Basically you need to ensure that the charging amps to the 200Ah battery is the same as the total going to the two 100Ah batteries. You need to work out the existing cable resistance, and get a cable with about the same resistance for the 200Ah battery.

The reason it needs the same resistance is that the new battery capacity, 200Ah, is the same as the existing total Ah capacity. If it was different the resistance calculation would be a bit more involved.

There are plenty of online calculators that will give you the resistance of a wire, and the voltage drop along it for particular amps value. For example this one.

Voltage Drop Calculator | 12 Volt Planet

Use our Voltage Drop Calculator to select the correct Cable for your campervan, motorhome or boat wiring application. Auto and Marine Electrical Components from 12 Volt Planet - Cable Size Calculator

www.12voltplanet.co.uk

It gives the total 'flow and return' voltage drop, so for the actual voltage drop of a length of wire, divide by 2. It also gives the resistance of the wire in ohms per metre, which is the figure you need

For example, the calculator gives the resistance of 16mm² wire as 0.00126 ohms per metre, ie 1.26mΩ per metre, so 2m is 2.52mΩ.

To find the cross-sectional area of the existing wire, it is often written on the cable. Sometimes it is stamped into the cable sheath. To show it up better, shine a flashlight at a very shallow angle to the cable.

Once you know the resistance of the existing wire, and the length of the new wire, you can work out the required resistance per metre of the new wire. Then use the voltage drop calculator to find the cable thickness required for that resistance per metre. It's not a precision calculation, you just want to know which of the various cable thicknesses to select for the job.

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[MichaelT]

I have installed a 200AH KS underseat battery (under floor rather than seat) and a Fogstar 280AH. They are connected using exactly the same length 50mm2 cable to bus bars. They charge and discharge fairly equally and work well together.

 

[dobbyt]

To emphasise further the importance of understanding your battery setup check out section:
3.3. Parallel battery bank wiring; (page 17), in the essential and recommended reading:

https://www.victronenergy.com/upload/documents/The_Wiring_Unlimited_book/43562-Wiring_Unlimited-pdf-en.pdf