OK to install Fox EES 3.3kwH battery alongside existing 5.2kw battery?

[Krob25]

I recently had a Fox system installed to replace a defunct old inverter/battery system, but kept old solar panels (4kw peak).
Looking at system performance so far, it might merit adding a little more battery capacity and I am thinking about adding a 3.3KWh battery to the existing 5.2kwh. I guess the system should theoretically cater for different battery capacities, but does anyone have any practical experience on this?

[Dave Foster]

It's a fairly common experience for solar users, I always say add as much battery as you can when it's new but they are very simple to retrofit - it is better to add batteries when they are newer, if you delay too long you risk adding a new battery which won't be able to reach it's full potential as the oldest battery in the pack will set the state of health.

I can see you have an EP5 battery, you can't mix different EP models (they each have a different voltage) but you can add another EP5 battery.

When you fit more than one EP battery you have to install a junction box (basically a 4 into 1 connector box), it's possible your installer already fitted this if you said you might expand later but if not it will need to be added ( a few hundred £'s) and then you can connect the EP5's together and have a single connection from the junction box to the inverter.

[Krob25]

Hi Dave,
Thanks for the tips, much appreciated.I have checked out connector box and also looked at datasheet voltages etc, as you suggested.

It looks like the EP3 and EP5 have same voltage, output and current charging characterisics. EP3 is much cheaper and I am not sure I really need the larger EP5. However, wondering if the fact that the EP3 will discharge much quicker (capacity wise) than the EP5 rules the EP3 option out. Or is the FOX battery monitoring system clever enough to handle that do you think.
Keith

[Dave Foster]

Hi Dave,
Thanks for the tips, much appreciated.I have checked out connector box and also looked at datasheet voltages etc, as you suggested.

It looks like the EP3 and EP5 have same voltage, output and current charging characterisics. EP3 is much cheaper and I am not sure I really need the larger EP5. However, wondering if the fact that the EP3 will discharge much quicker (capacity wise) than the EP5 rules the EP3 option out. Or is the FOX battery monitoring system clever enough to handle that do you think.
Keith

The junction box effectively places the batteries in parallel and the EP's are not designed to have dis-similar sized batteries, unfortunately you'll have to go with the same model EP5.

[Krob25]

Thanks Dave, understood.

Looks like I will be raiding the piggy bank!

Appreciate the steer.