Somewhat scary solar meltdown

[86Scotty]

Originally Posted by Flux

I honestly don't know the advantages of a breaker over a fuse other than you can reset a breaker

I think you nailed it. All homes used to have fuses but breakers are just a better idea and so they've become the norm. Also, they're cheaper in the long run because you only purchase them once (unless you have pretty unusual trouble).

[ShuttlePilot]

One advantage of breakers over fuses is to Midnight Solar. If you google the breakers in that diagram it shows the breakers are sold by Midnight Solar. Could they be re branded? Just to be forthcoming I have a well developed opinion about Midnight Solar. And I'm not an electrical engineer.

One thing that I believe is good practice (with low voltage DC) is to touch your stuff. With each piece of equipment running (inverter, solar, charger, hot water heater, ect) at it's full capacity follow the wire, connectors, fuses, with your hand and see what is getting warm. You might have to run it for half an hour or more. Every component that is warm is lost power. In the case of a solar system that's watts of precious expensive power not getting to your batteries. All that warm air blowing out of your inverter, that's the 10-15% of loss that's in the literature. It seems like old Dad advice but it's a cheap way to find where to improve the efficiency of your system.

Just a note, when I still had the original SMB fuse block (12volt) it had an automotive type breaker for the main incoming power. 50 amp I think. That thing was always hot with just a few amps running. I put a volt meter on it and I was losing something like .75 volt of loss across it which seemed unreasonable. I've since made drastic changes.

[edit] Flux- in case you were wondering, in an ideal most safe solar design you would want a fusable device everywhere there is a breaker in that schematic. It wouldn't nessacarily need to ba a circuit braker though and that layout is the norm for permanant/house type solar. I don't have quite that many fuses in my system. Like between the panels and the junction box or a GFI.
-Eric

[boywonder]

Originally Posted by Flux

I honestly don't know the advantages of a breaker over a fuse other than you can reset a breaker

well......you know what I know.......I have several 150A breakers on my 2AWG cables that connect the van battery to the house batteries.

I think it could be argued that fuses are more robust because they operate on first principles of physics......resistive heating melting the filament. Most circuit breakers are thermal devices but require a few more things to trip than a fuse.

[boywonder]

Originally Posted by MadScience

At some point there was a very large batch of bad automotive blade fuses that went into circulation; they would cook rather than blow. Might be worth testing one of the others and replacing them all if it behaves that way.

I bought a pack of 5 zillion fuses on ebay from China for 99 cents shipped....they are junk.......when you yank them out the blades either stay behind or get mangled....

The Fuses in the picture are Littlefuse brand fuses.......good quality.....unless I had a short (which doesn't seem to be the case) the fuse wasn't involved in this failure. Even on a cold sunny morning I don't think my panels can put out anything close to 25A...the fuse rating.

[arctictraveller]

Originally Posted by boywonder

I think it could be argued that fuses are more robust because they operate on first principles of physics......resistive heating melting the filament. Most circuit breakers are thermal devices but require a few more things to trip than a fuse.

As for resistance and voltage drop across fuses versus circuit breakers, as you said, it's the resistance that heats and melts the element, so it would seem fuses might have a higher resistance. Still, I wonder if you were to measure the voltage drop across a fuse near full capacity versus a circuit breaker, the results might be surprising. Someone should do this and let us know. I would, but really far away from any 12V equipment.

[Flux]

This thread is an eye opener for sure.

[Scalf77]

Originally Posted by ShuttlePilot

One advantage of breakers over fuses is to Midnight Solar. If you google the breakers in that diagram it shows the breakers are sold by Midnight Solar. Could they be re branded? Just to be forthcoming I have a well developed opinion about Midnight Solar. And I'm not an electrical engineer.
-Eric

Spoken like a true Morningstar user.

I Think that fuses are the better choice for most application in our vehicles. they are be less susceptible to problems caused by vibration, heat and other things we encounter, and should be cheaper. In applications where you expect a possibility of higher inrush currents and such, then a breaker may be a better choice, For the majority of our circuits, you should not be replacing fusses unless something has gone wrong.

The resistance of the fuse (or voltage drop caused by the fuse) should be minor in the overall circuits that we are using. It would be true that the resistance on a breaker would most likely be less, at least when new. Over the life time (especially if used like a switch) the contacts will become pitted and build up additional contact resistance.

It does not like it was a fusing problem with Boywonder's set up, but the issue was most likely arcing due to loose connections as he diagnosed. We have a variety of fuses that we can use, While ATO fuses I believe goes to 40 Amps, I think above 30 I start looking at the Maxi fuse that Eric used.

There are other fuse types that have higher AIC ratings that are better for main circuits such as Class-T, AMI, ANL.


-greg