diy solar

diy solar

DIY portable power box upgrade, circuit protection design debate


New Member
Dec 1, 2022
Hey, DIYers. TLDR; With a 200A Eaton Bussmann 187-series circuit breaker/switch for primary portable DIY battery box protection, and using Anderson PowerPole 120 series connectors for an external panel mount inverter connection, would you add a separate 187-series breaker/switch on the inverter out circuit?

My initial plan was yes, but given that the Anderson PowerPole connectors are well protected, and given that my Samlex inverter is switched, I'm now thinking that another (also 200A) 187-series downstream breaker/switch dedicated to the inverter out might be unnecessary overkill. This box is entirely under my control, and I don't think I mind if I have a live PowerPole output switched only be the main breaker that switches everything else. Plus, battery box space is limited.

Since the 187-series has just a 5kAIC rating, along with the upgrade to a 230Ah 4s LiFePO4 battery I plan to add a Class-T (300A) before the main breaker. I also plan to have another unswitched (but fused) PP120 connector for external battery INPUT, since the current 100Ah battery, while degraded, still has approx. 70Ah available. That of course opens up a whole 'nother can of worms: it would originate at the BATT side of the main breaker so that box loads would never be powered by the external battery without circuit protection (plus I believe the 187-series MRCBs are one-way), but it /could/ be used as an output protected only by the Class T fuse. I'm planning to use a blue housing on the positive side for that, to make it obviously different.

I built v1 of this battery box in 2020 when I needed a COVID project, initially designed for emcomm (ham radio) and camping use but since batteries die prematurely when not used and because a lot of testing goes into emcomm gear as one works out usage guidelines and reliability, in practice we use it to charge our laptops and phones daily, and harvest solar about half the year when our apartment gets sun (or when camping). Pretty amazing that prismatic cells will more than double energy capacity in the same footprint. I might need to work out more if I want to be able to continue to lift it... or maybe a dolly is in my future.
I should add that I'm not sure this post belongs in the DIY Powerwall forum; if a more suitable forum seems appropriate, please feel free to recommend.