Solar fuseing, confuseing
Were installing a Renogy 400 watt solar system on our fith wheel. We stay on our property about two months in the summer up near Canada in Washington.Anyway this is the kit I bought. Mind you I'm comp...
Forum Discussion
"By definition, Isc is short circuit current measured at the solar panel output. Zero resistance for a short circuit means you will see the maximum current the panel can provide. You will never see Isc with a battery hooked up in place of the short circuit because a battery has resistance which will limit the current provided by the panel."
Right, except in real life, the Isc you get on your ammeter depends on how much sun there is on the panel. If you are seeing "rated Isc" then IMO that means you are in STC or as good as.
On a 12v panel's IV curve, Isc is related to battery voltage, so with rising battery voltage Isc does come down a bit. Once you get over about 13.4v that starts to show.
With 12v PWM I have compared (many times!) the Isc at the disconnected panel with the amps I get showing on the Trimetric when I connect back up and they are the same (within meter accuracy), so it is "close enough for government work" for what I need to know.
(What drives me crazy is people saying you should get Imp doing that. They don't seem to know that Imp is strictly for MPPT work and has nothing to do with ordinary PWM solar, where the higher amp Isc is the "expected amps")
-----------
You can't trust panel specs very much either. I have a 100w panel, which I know from the "usual" ratings, should get about 6.2 amps Isc.
(it is all proportionate--a 130w will get 8.2, and a 120 will get 7.6)
On its label it says Voc 21.5, Vmp 17.1, Imp 5.8 (no Isc listed) and on its package it said output is 5.8a. In the sun it gets 6.2 amps like it is supposed to.
Then I got a pair of 100w panels made in India with these specs:
Voc 22.7, Isc 5.8, Vmp 18.8, Imp 5.3 So I wanted to put these three together but was worried about them not being close enough in voltage etc. Put the India ones in the sun and sure enough--6.2a Isc! Vocs were the same too, in the sun.
Putting all three in parallel aimed at sun, my PWM Solar30 controller said 18.3 amps to the battery (confirmed by Trimetric)
So I then ran all three together all last summer with my Tracer MPPT and was able to connect them in series or parallel no issues either way. The panels are your basic 100w panels that get 6.2 amps. Too easy! (I still only got 18ish amps using the MPPT though, due to panel heating loss with MPPT)
Right, except in real life, the Isc you get on your ammeter depends on how much sun there is on the panel. If you are seeing "rated Isc" then IMO that means you are in STC or as good as.
On a 12v panel's IV curve, Isc is related to battery voltage, so with rising battery voltage Isc does come down a bit. Once you get over about 13.4v that starts to show.
With 12v PWM I have compared (many times!) the Isc at the disconnected panel with the amps I get showing on the Trimetric when I connect back up and they are the same (within meter accuracy), so it is "close enough for government work" for what I need to know.
(What drives me crazy is people saying you should get Imp doing that. They don't seem to know that Imp is strictly for MPPT work and has nothing to do with ordinary PWM solar, where the higher amp Isc is the "expected amps")
-----------
You can't trust panel specs very much either. I have a 100w panel, which I know from the "usual" ratings, should get about 6.2 amps Isc.
(it is all proportionate--a 130w will get 8.2, and a 120 will get 7.6)
On its label it says Voc 21.5, Vmp 17.1, Imp 5.8 (no Isc listed) and on its package it said output is 5.8a. In the sun it gets 6.2 amps like it is supposed to.
Then I got a pair of 100w panels made in India with these specs:
Voc 22.7, Isc 5.8, Vmp 18.8, Imp 5.3 So I wanted to put these three together but was worried about them not being close enough in voltage etc. Put the India ones in the sun and sure enough--6.2a Isc! Vocs were the same too, in the sun.
Putting all three in parallel aimed at sun, my PWM Solar30 controller said 18.3 amps to the battery (confirmed by Trimetric)
So I then ran all three together all last summer with my Tracer MPPT and was able to connect them in series or parallel no issues either way. The panels are your basic 100w panels that get 6.2 amps. Too easy! (I still only got 18ish amps using the MPPT though, due to panel heating loss with MPPT)
