Dustin Henderson
New Member
- Joined
- Nov 2, 2022
- Messages
- 17
I am a newb putting together a very modest and very simple travel trailer solar charge installation - and this is key- in a trailer that is “pre wired for solar”. Bear with me on the specifics of why I am asking.
I am just about ready to start gathering final materials and installing, and realized something I had not previously accounted for. As such, I need to understand more about how actual current output is calculated for an MPPT solar charge controller.
Let’s assume I have 2 100w panels wired in SERIES, each with the following specifications: (Vmp): 20.4V, (Voc): 24.3V (Imp): 4.91A (Isc): 5.21A
Let’s assume I have a 100/40 MPPT Solar charge controller.
Let’s assume a LiFePo “12v” battery.
What determines the actual max output amperage in the scenario above? Is it 16.7 Amps in my example? Can a SCC only output the current that it is receiving in watts and volts as limiting factor, and nothing greater? Ie, that’s not the job of an SCC.
The reason I need to know this is, while tracing the preinstalled wiring in my install I realized the pre wire from the “rooftop solar” runs through a bus bar with individual “fuses” (actually self resetting breakers?) that continue to the battery. According to the wiring diagram, the rooftop solar wire is attached to a fuse that is actually shared with the “tow vehicle charge line”. The breaker is 30 Amp. I was preparing to install 40 Amp fuses in my wiring when I realized I need to evaluate what is already there. in this case a 30 Amp fuse. I want to retain the original routing.
Clearly, at 200 watts this will not be an issue with tripping a 30 amp breaker, but what if I eventually expand to 2S2P and 400 watts total? Now I am at 33.3 Amps. In addition, what amperage draw is the meager “tow vehicle charge line” likely to be adding while towing?
Caveats:
The native bus bar is full so moving this to it’s own lug and adding a 40amp fuse is out. I am not going to replace this bus bar just for this.
These will be warm weather flat mounted panels unlikely to ever achieve optimal conditions.
Assume AWG and lengths are well within capacity to handle more than 50 Amps current, and other disconnects and fuses are in place. The limiting factor is the native 30 Amp breaker.
Thanks for your thoughts.
I am just about ready to start gathering final materials and installing, and realized something I had not previously accounted for. As such, I need to understand more about how actual current output is calculated for an MPPT solar charge controller.
Let’s assume I have 2 100w panels wired in SERIES, each with the following specifications: (Vmp): 20.4V, (Voc): 24.3V (Imp): 4.91A (Isc): 5.21A
Let’s assume I have a 100/40 MPPT Solar charge controller.
Let’s assume a LiFePo “12v” battery.
What determines the actual max output amperage in the scenario above? Is it 16.7 Amps in my example? Can a SCC only output the current that it is receiving in watts and volts as limiting factor, and nothing greater? Ie, that’s not the job of an SCC.
The reason I need to know this is, while tracing the preinstalled wiring in my install I realized the pre wire from the “rooftop solar” runs through a bus bar with individual “fuses” (actually self resetting breakers?) that continue to the battery. According to the wiring diagram, the rooftop solar wire is attached to a fuse that is actually shared with the “tow vehicle charge line”. The breaker is 30 Amp. I was preparing to install 40 Amp fuses in my wiring when I realized I need to evaluate what is already there. in this case a 30 Amp fuse. I want to retain the original routing.
Clearly, at 200 watts this will not be an issue with tripping a 30 amp breaker, but what if I eventually expand to 2S2P and 400 watts total? Now I am at 33.3 Amps. In addition, what amperage draw is the meager “tow vehicle charge line” likely to be adding while towing?
Caveats:
The native bus bar is full so moving this to it’s own lug and adding a 40amp fuse is out. I am not going to replace this bus bar just for this.
These will be warm weather flat mounted panels unlikely to ever achieve optimal conditions.
Assume AWG and lengths are well within capacity to handle more than 50 Amps current, and other disconnects and fuses are in place. The limiting factor is the native 30 Amp breaker.
Thanks for your thoughts.
