diy solar

diy solar

48v isolation switches stopping 58v pylontech batteries?

We've been running a 48v solar system for about 18 months. I used the cheap Harbor Freight battery disconnect switches on the solar input and the battery, and they work fine. Fusing the battery was not difficult as I used a giant ANL type 100A fuse. The odd problem was in fusing or protecting the panel input to the charge controller--it can be up to 100v unloaded and about 70-80v at 25-28 amps in full sunlight. I put in a commonplace AGU type 40 amp fuse in a cheap holder intended for automotive stereo applications--the fuse worked fine for more than a year, until it popped on a very hot sunny day. I never saw more than 30 amps in that circuit, but the fuse holder got very hot, melting some of the plastic. So the voltage and power going thru that circuit (it never saw more than 1900 watts max) is a little too much for some "automotive" type hardware. But the Harbor Freight disconnect switches have given no problems.
This advice/description is what is known as a fire waiting to happen and how NOT to do things safely.
Spec sheets from the manufacturer are very helpful.

Here is a breaker on Amazon that looks like a cheap AC breaker :

However, I did see that breaker used in a 48V nominal commercial server rack battery and thought that couldn’t be right.

So, the next step is to look for a spec sheet from the manufacturer which I found here :

You can see that it’s rated for up to 125V DC.

Looking further you will find :

Which shows an AIC of 10kA. As a bonus you can even see the tripping curve in that pdf.

So that’s the basic info and how I did the “research” which took less than 10 minutes 😎.

Hope that helps.

The devil is in the details with this. In that same series breaker some are rated AC and some are rated AC/DC .... if the breaker doesn't explicitly state DC on it then using it for DC is asking for a fire.

In the doc linked scroll down to the table listing usage for that specfic breaker -- number of digits in the breaker makes a difference and in the case of these the 4th space must contain a 'Z' to be rated for DC. The amazon link is not rated for DC and shouldn't be used for that.

See the two attached charts for the AC and DC rated breakers.

Another tipoff for DC rated breakers is most of the time they are polarized and have the polarity marked on the casing. Sometimes they do this just by marking 'line' or 'load' and detailing which pole is used for positive in the docs. Wiring a DC breaker backwards is another way to have a fire.

IMO it is worth buying either midnight solar or other well known breakers used for DC voltage.

what is known as a fire waiting to happen and how NOT to do things safely

Anyone looking to buy cheap breakers, fuses or switches should read this thread. 22 pages in 4 days.