jameshowison
New Member
- Joined
- Jul 30, 2021
- Messages
- 184
I'm planning a 48v system for a travel trailer. I'm trying to figure out the arrangement so that I can purchase the MPPT solar charge controllers.
My understanding is that I need to design the voltage on the solar to two numbers. The minimum is sufficient to charge a 48v battery. The maximum is to stay under the VoC limit of the SCC, including headroom for over-production in cold temperatures. This seems pretty difficult to do with SCC with a max input of 100 VoC (e.g., Victron 100/20 as shown here: https://backwoodssolar.com/product/victron-energy-smartsolar-mppt-100-20-12-24-48vdc/
I'd like to use the smaller MPPT SCC for two reasons. The first is that I see us having three separate arrays, one on the travel trailer, one on the truck, and one portable one. I'm thinking separate given that these will probably see different conditions during the day, the truck might drive off for a bit during the day, and the portable ones might not be set out. The second is cost, the smaller SCC are half the price of the 150 VoC.
Some sources place the minimum for charging 48v batteries as high as 72v. Presumably that's the number under load, so the VoC would be even higher? With a multiplier of 1.25 to account for potential cold weather that seems to leave a very small window for charging 48v batteries from smaller MPPT SCC?
For example I'm looking at the Rich Solar 160W CIGS modules. https://richsolar.com/products/160-watt-cigs-flexible-solar-panel Those show a VoC of 23.3v and a Vmp of 18.9. To get sufficient Vmp to charge 48v I think I need four panels (4 x 18.9 = 75.6) but that puts me at unadjusted VoC of 93.2 or multiplying by 1.25 I get 116.5 VoC. So I can't do 3 panels because the Vmp would only be 56.7 but I can't do 4 panels because the VoC would be too high. So I have to bump up to the Victron 150/35 controller? That's almost double the price and for three small arrays it just seems a lot (like $500 extra).
Am I thinking about this right? I tried to use the more advanced calculators but I can't find the temperature coefficient of the panels.
Any experiences in designing to charge 48v systems from small solar arrays? (btw, I'm committed to 48v due to the 48v DC HVAC system from Hotspot, already bought along with 48v batteries.)
My understanding is that I need to design the voltage on the solar to two numbers. The minimum is sufficient to charge a 48v battery. The maximum is to stay under the VoC limit of the SCC, including headroom for over-production in cold temperatures. This seems pretty difficult to do with SCC with a max input of 100 VoC (e.g., Victron 100/20 as shown here: https://backwoodssolar.com/product/victron-energy-smartsolar-mppt-100-20-12-24-48vdc/
I'd like to use the smaller MPPT SCC for two reasons. The first is that I see us having three separate arrays, one on the travel trailer, one on the truck, and one portable one. I'm thinking separate given that these will probably see different conditions during the day, the truck might drive off for a bit during the day, and the portable ones might not be set out. The second is cost, the smaller SCC are half the price of the 150 VoC.
Some sources place the minimum for charging 48v batteries as high as 72v. Presumably that's the number under load, so the VoC would be even higher? With a multiplier of 1.25 to account for potential cold weather that seems to leave a very small window for charging 48v batteries from smaller MPPT SCC?
For example I'm looking at the Rich Solar 160W CIGS modules. https://richsolar.com/products/160-watt-cigs-flexible-solar-panel Those show a VoC of 23.3v and a Vmp of 18.9. To get sufficient Vmp to charge 48v I think I need four panels (4 x 18.9 = 75.6) but that puts me at unadjusted VoC of 93.2 or multiplying by 1.25 I get 116.5 VoC. So I can't do 3 panels because the Vmp would only be 56.7 but I can't do 4 panels because the VoC would be too high. So I have to bump up to the Victron 150/35 controller? That's almost double the price and for three small arrays it just seems a lot (like $500 extra).
Am I thinking about this right? I tried to use the more advanced calculators but I can't find the temperature coefficient of the panels.
Any experiences in designing to charge 48v systems from small solar arrays? (btw, I'm committed to 48v due to the 48v DC HVAC system from Hotspot, already bought along with 48v batteries.)