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I'm trying to select an output breaker voltage for my 150/70-Tr MPPT. I know I should use a 150vdc breaker on the input (PV) side. However, I'm unclear about the voltage requirements on the output (battery) side. My battery is a 12V LifePO4. Does this mean a 0-48Vdc breaker will be sufficient, or should I use a breaker rated for 150vdc? I'm not clear if a failure could deliver PV voltage directly to the battery. That seems pretty unlikely to me, but I just wanted to confirm. Thanks.
Hi @Createthis
indeed, on the battery side your breaker (or fuse) should be rated for your (maximum) battery voltage, thus a 32VDC breaker or fuse is more than enough for a 12V system.
Hi Createthis ! Onthe PV side, I'll suggest you to use a 1000VDC / 16/32A breaker per input.
Regarding the breaker on the battery bank, usually if you load the batteries during extended periods, the breaker will heat and disconnect the load. My setup is running a 120VDC / 125A breaker. I'll suggest you using at least a 120VDC / 80A or 100A.
These breakers tend to heat with the power passing through them and disconnect in some occasions.
These pictures were taking during the modification / installation of the new breakers.
Michel
Why do you recommend a 1000vdc breaker when the max voltage for this charge controller is 150vdc?
Several reasons. I tried the breakers below and had several times issues, so I decided to install other kind of breakers, with different specs, and no more problems. This kind of breakers were unable to cope with the power. The new ones have no issues. Remember, Amps are what you are looking for, and it is recommended to use breakers with a margin of 25% more than maximum current.
I don't think the breaker you linked is a quality hydraulic-magnetic breaker. It looks like a no-name thermal breaker to me, likely with a 48vdc spec.
They do, however, make quality 150vdc hydraulic-magnetic breakers. The midnite solar dc breakers are pretty popular from what I can tell. For my 150/70-Tr, and because my application calls for panel mount, the mnedc50 is likely adequate. 
Also, why 120vdc on the battery side? Your charge controller accepts 150vdc on the PV side. Your charge controller only accepts up to a 48vdc battery. Why not use a 48vdc breaker on the battery side?
In my installation, I need to have trusted elements, I don't want to mess into it for any reason. It happened to have "burned" cables, because of the heat, wrong type of cables, wrong type of breakers.
Now, everything is fine and more issues. Breakers do arcs when disconnected (automatically or manually). The models I have installed have arc arrestors integrated in them. That's also a reason why you need DC breakers.
Model with arc suppressor / arrestor :
This way, the breaker itself is protected and will not melt.
Michel
I've personally used the blue sea systems 187 series of thermal breakers under fairly high amp loads at 12Vdc. I haven't seen one fail yet. I suspect what you are currently using is overkill. Just a heads up.
Can you tell me where you got (and maybe provide a link to) the breaker enclosure in your picture?
Hi TexasCharlie, it comes from Aliexpress. The reseller is very serious, in Europe it is almost impossible to find such kind of breakers at a "correct" price !
https://www.aliexpress.com/store/4046040?spm=a2g0o.store_home.1000001.12.31055375D0EzkQ
I hope it helps.
Michel
