Help with PV wire size on rv! Maybe mistake ?
- Thread starter Benihanas
- Start date
yes mike you are right I realized that when I saw it hovering around 500. I had another brain fart. The constant switching around of plans and new learning the last 24 hours spun me out a little but I understand how to handle everything now. I believe the 60amp will be a better choice and perhaps keep my DCDC50s around for auxiliary charging like a foldable over the windshield or an outdoor ground array
Vigo
Solar Addict
If you have 2 pairs of 10ga the absolute minimum voltage drop would be to parallel both pairs together. Can always undo it later if you expand the system.
chrisski
Solar Boondocker
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- Aug 14, 2020
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IME with an RV build, It is very common to have voltage drop. I don’t see a problem with your voltages. I see things like you describe in my RV build.
When you measure this before, you get open circuit voltage VOC because it’s “fake” voltage with no power.
Once you hook it up and it’s working, the voltage will drop to max power voltage VMP. VMP is the voltage at max production. If panels are not working there hardest it will be slightly more. If there’s any shading or clouds it’ll be less.
When you measure this before, you get open circuit voltage VOC because it’s “fake” voltage with no power.
Once you hook it up and it’s working, the voltage will drop to max power voltage VMP. VMP is the voltage at max production. If panels are not working there hardest it will be slightly more. If there’s any shading or clouds it’ll be less.
Pappion
Retired Engineer Tech
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He said it was (18.1 optimal voltage) per panel. Which makes sense for 12v charging with 1 panel. Never said VOC. Never responded to my request for more specs. or Brand/Model info. So best to guess he made a mistake or has a shaded panel.
3S is a better fit for the 55V result.
18.1v * 4S = 72v
18.1v * 3S = 54.3
55v / 4S = 13.75
I go over what I’ve got in the post here but they’re 8 hqst 100watt panels the renogy /hqst brand that will recommends. 18 volts. None of the panels are shaded. Panels aren’t the issue anymore. Panels arrays read 72 volts then drop to 55 when I plug in the mppt
No shaded panel. No bad wiring. Voltage is 72 until the mppt kicks on and it drops it. Mppt max voltage is 100 so no clue really why this is happening
acdoctor
Solar Enthusiast
It is normal for panel voltage to drop when mppt kicks in.
Vmp Optimum Voltage operating. Loaded voltage.
Voc Open circuit voltage. Non loaded voltage.
These are on the panel label.
Vmp Optimum Voltage operating. Loaded voltage.
Voc Open circuit voltage. Non loaded voltage.
These are on the panel label.
Pappion
Retired Engineer Tech
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100w Hqst Mono Panels
- Open-Circuit Voltage ( Voc ): 24.3V
- Optimum Operating Voltage ( Vmp ): 20.3V
- Optimum Operating Current ( Imp ): 4.93A
- Optimum Operating Voltage (Vmp): 18.1 V
- Open-Circuit Voltage (Voc): 21.6V
- Optimum Operating Current (Imp): 5.53 A
Your VOC should be 20.3v * 4s = 81.2v
Vmp = 18.1 * 4S = 72v
It is not OK.
Last edited:
Pappion
Retired Engineer Tech
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Could be 1 panel has a shorted bypass diode or installed backwards. Maybe wired backwards.
Ampster
Renewable Energy Hobbyist
Why would that show up when the MPPT controller is hooked up?
I have tried to say this 5 times now…….. the panels are wired properly and the voltage is correct until the moment the mppt is connected to the PV. No panel backwards. No shade. No bad bypass diode.
Voltage is good …. Until MPPT I plugged in.
Pappion …
I repeat … voltage is good until mppt is plugged in.
If you just keep repeating the same thing and don’t read anything I respond with it’s not super helpful
He’s absolutely 10000% wrong. It wouldn’t. If the problem originated from the PV the voltage wouldn’t read strong until the mppt is plugged in….. I believe you and @acdoctor are on the right track. Thank you guys for actually reading and then responding to what I said. I will contact renogy when they’re open tomorrow and figure out exactly what it is. I’m also going to order the river 60amp so we’ll see if it happens to that one too
HighTechLab
AKA Dexter - CTO of Current Connected, LLC
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- 1,722
When this happens, how many amps is the solar controller outputting?
also, VOC goes down as panel temp goes up. Just as is the opposite (hyper VOC) when they are cold.
also, VOC goes down as panel temp goes up. Just as is the opposite (hyper VOC) when they are cold.
Still the 10-11 amps. (5 if I remove half the panels). I understand that the panel voltage will move around; But it drops literally as soon as PV is connected
Vigo
Solar Addict
I don't know if all solar controllers behave the same (doubtful), but if current flows as soon as you connect to the mppt, then it is expected that the voltage will drop.
If no current flows you should be at VOC minus 'local conditions' ie depending on time of day, angle of panels, 'sky conditions' like ppm particulates, humidity etc. So you're really never guaranteed to see the full VOC x number of panels voltage number, although you should get close in ideal conditions.
So determine if current is flowing the instant the panels connect to mppt. If it is flowing, then depending on how much is flowing (you say 10-11a?) and then how much of that ends up being battery charging current, it may or may not be ok. But i can tell you if you actually 'short' the array you won't drop from 72v to 55v, you'll drop from 72 to ~0-1v, so it is not dead shorting, and in the absence of a dead short it's quite likely that whatever it's doing, is ok.
At this point you would just need to measure battery circuit current under that same condition, and see if it lines up. ~55v X ~11a = 600w. If you are charging a 12v nominal battery that charges at ~14v, then 600w / 14v = ~42a. Minus some efficiency losses, you should have something close to 40a on the battery circuit when you have 11a on the pv circuit. If you don't, then your mppt is a 600w space heater locked up in a tiny box and the smoke is gonna come out real fast.
If no current flows you should be at VOC minus 'local conditions' ie depending on time of day, angle of panels, 'sky conditions' like ppm particulates, humidity etc. So you're really never guaranteed to see the full VOC x number of panels voltage number, although you should get close in ideal conditions.
So determine if current is flowing the instant the panels connect to mppt. If it is flowing, then depending on how much is flowing (you say 10-11a?) and then how much of that ends up being battery charging current, it may or may not be ok. But i can tell you if you actually 'short' the array you won't drop from 72v to 55v, you'll drop from 72 to ~0-1v, so it is not dead shorting, and in the absence of a dead short it's quite likely that whatever it's doing, is ok.
At this point you would just need to measure battery circuit current under that same condition, and see if it lines up. ~55v X ~11a = 600w. If you are charging a 12v nominal battery that charges at ~14v, then 600w / 14v = ~42a. Minus some efficiency losses, you should have something close to 40a on the battery circuit when you have 11a on the pv circuit. If you don't, then your mppt is a 600w space heater locked up in a tiny box and the smoke is gonna come out real fast.
