September 15, 20169 yr 19 minutes ago, HeinTheTerrible said: The prices are also ridiculous! Yup. They have a PWM charge controller there for about a grand. It has Ellies stamped on it but it's ye good olde China special You can buy that same thing from other local places for R450, and you can get it straight from ebay for even less. And yes, I bought one to serve stop-gap duty at one point and disassembled it afterwards to see what it's like, it's bog standard two-MOSFET PWM setup with another one for the load. Voltage measurement is horribly inaccurate too. It's not worth a grand...
September 22, 20169 yr Author Small update! Some goodies arrived in the mail! Got a couple of fuse holders from Rubicon and my order from thepowerstore arrived. On the tin it says Renesola Replus blah blah fishpaste but its just a rebranded MPP solar PCM60X. The same people who make the much loved Axpert inverters! Did a quick test with a small battery and 20w panel. Works like a charm! The software (MPPTracker) is a lot like the Watch Power. You can monitor, check for faults and change all the setting of the charge controller. Not too shabby! Now I have to find time to redo the wiring on the panels, install new fuse holders, redo wiring, install bigger db box, fit isolator switch and make it all look pretty so I can score more internet points
September 22, 20169 yr On 8/31/2016 at 3:35 PM, plonkster said: It has diodes already. Just put in the fuses (if you don't have them already) so that a reverse breakdown blows a fuse instead of a panel :-) Fuses or circuit breakers are nice to have and essential if they will blow/trip when they are supposed to do so. My concern is that ANY fuse rating/circuit breaker rating higher than the short circuit current of a string, will not blow (fuse)/trip, so what is the point having it? Or is this a dumb question?
September 22, 20169 yr 18 minutes ago, SOLARWIND said: Fuses or circuit breakers are nice to have and essential if they will blow/trip when they are supposed to do so. My concern is that ANY fuse rating/circuit breaker rating higher than the short circuit current of a string, will not blow (fuse)/trip, so what is the point having it? Or is this a dumb question? 3 strings burn out 1 string, reverse breakdown.
September 22, 20169 yr On 8/31/2016 at 3:35 PM, plonkster said: It has diodes already. Just put in the fuses (if you don't have them already) so that a reverse breakdown blows a fuse instead of a panel :-) Fuses or circuit breakers are nice to have and essential if they will blow/trip when they are supposed to do so. My concern is that ANY fuse rating/circuit breaker rating higher than the short circuit current of a string, will not blow (fuse)/trip, so what is the point having it? Or is this a dumb question? 6 minutes ago, Weasel said: 3 strings burn out 1 string, reverse breakdown. Thank you! This makes sense!
September 22, 20169 yr Yeah, normally fuses are to protect wires, but not here. The PV panel has a maximum current, and even at short circuit you won't get more than that. The cable will be rated higher than that, and so will the fuse, so on any single string a fuse won't blow and the fuse is essentially pointless. The reason you put it in, as Weasel said, is where you have strings in parallel. There the job of the fuse is to protect one string from being damaged by the other, because a fault between strings can and will push the current higher than your fuse rating.
September 23, 20169 yr 9 hours ago, plonkster said: Yeah, normally fuses are to protect wires, but not here. The PV panel has a maximum current, and even at short circuit you won't get more than that. The cable will be rated higher than that, and so will the fuse, so on any single string a fuse won't blow and the fuse is essentially pointless. The reason you put it in, as Weasel said, is where you have strings in parallel. There the job of the fuse is to protect one string from being damaged by the other, because a fault between strings can and will push the current higher than your fuse rating. As an interesting sidenote: Some time ago, one of my installers accidentally connected 2 250W solar panels directly together. Instead of putting the - (black) wire from the MPPT to the 2nd panel, he connected the 1st panel to the 2nd panel. No problem so far, the problem arose when there were two wires left, so the + (red) wire went into the remaining - wire from the MPPT, and the last wire into the other panel. Downstairs, I couldn't figure out which set of wires goes to which set of panels. Eventually I get up on the roof to see the mistake! It was like this for about 30 or 40 minutes, since I had to identify 3 pairs of panels. I flipped and thought we'd have to replace the client's new panels! Got on the roof, cut the wires (the original panel MC4's sometimes get stuck when using generic MC4's on the other end) and tested them - all was well. Phew! Fuses are there to protect the wires, but could also lend some protection to the panels. On a 8A string (1, 2 or 3 panels) I often see 10A fuses blow, probably due to solar cloud edge affect. On smaller panels / strings, it may possibly not be an issue, but on larger strings it would. I always use fuses, it cost about R70 per string!
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