Using existing Zamp "solar ready" wiring on travel trailer

[Splat32]

I have a 23 foot travel trailer with 2 Zamp solar ports on the roof and a port on the driver's side wall. The existing SCC is the 10A PWM made by Zamp. The wire from the roof to the SCC is 10AWG (15 feet max) and the wire from the SCC to the 2 220Ah 6V GC batteries is 8AWG (20 feet max). There is a 20w Zamp panel mounted on the A/C unit which serves as a trickle charger for the battery.

I would like to NOT have to pull new wire. We have modest power needs. We occasionally use a 500w PSW inverter, which plugs into a 12v socket in the camper, to recharge our GMRS radios, an 18v battery for a Bosch vacuum and drill, and of course the water pump, refrigerator, LED lights, and 2 Maxxair fans. If we are out camping, we are outside doing something except to sleep and occasionally eat. This past weekend, after 2 full days of boondocking, our battery monitor showed that we had used 36% of the battery capacity. This would be the norm.

I am looking at a 3 panel, 600w kit, which will just about max out the open space on the roof. The kit comes with a 40A MPPT controller. We live in New Mexico and typically shading isn't much of an issue. Will I be able to use the existing solar ports on the roof to safely and efficiently recharge my batteries? Thank you.

 

[snoobler]

Welcome to the forum.

Quality 10awg wire can handle 30A at 65°C. At 90°C, it's 40A.

8awg, 40A+. At 90°C, it's 55A.

You'll want to configure the array in a 2S3P or 3S2P config to keep the current below the 10awg wire rating.

The 8AWG should be good for the 600W you'll get from the panels, 600W/12V = 50A, provided it's 90°C wire; however, the length of wire is a concern. The drop will be substantial.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

1.26V/9.24% - this is pretty bad. Not only will you lose about 10% of your incoming power, but charging will be very slow as the 1.26V drop will cause the controller to start tapering its current much earlier than usual.

Is it possible to locate the new SCC closer to the batteries? You could simply remove the old SCC and tie the 10awg to the 8awg for the longer run to the new SCC location near the batteries. The higher PV voltage and lower current would have a much less significant drop.

A 3S2P array would run about 54V and 22A. This would only have a 2.2% drop assuming 10awg for 15' and 8awg for 20'.

 

[Whinny]

If the solar controller is going near the existing converter you could utilize what is probably the #6 battery feed from it....You could pick up a spare fuse slot and the negative bussbar that is probably behind it.

 

[fratermus]

Will the 40A controller tolerate the 3 panels in series? {Edit: I see snoobler posted a useful analysis}

Perhaps counterintuitively, 600w of panel on 220Ah of GC with light loads will be not generally be shoveling tons of power down the wires. Meaningful charging will start early enough in the day that the heavy lifting (Bulk charging) will typically be complete well before solar noon when the system might get near rated power. Without heavy loads to run the ample panel is more for "rainy day" support than "how much pOwah does yer solar make????" armchair competitions.

Example: My use case is similar to yours, although I use more power overnight and therefore discharge deeper. Camped today in Capitan, NM my 750w:220ah system maxxed just under 250w because my GC bank hit Vabs by before 10am, Cooking with a crockpot right now and still only making/using 231w.

It's supposed to rain Sunday and I'll be making just enough to get the batts fully charged. No crockpot action on Sunday.

 

[Supervstech]

His kit only has 3 panels... he needs to know if the controller can tolerate all in series, or if the wire can tolerate all in parallel.

 

[Supervstech]

Of course, we don’t know the panel voltages. So, it is a guessing game. 22vmp? 38? 72?

 

[snoobler]

I figured they were 200W, 12V panels. Most "kits" seem to stick with 12V panels, but yes, Voc/MPPT PV limit should be confirmed.

 

[Splat32]

Here are the panel specs.

 

[snoobler]

I was assuming Vmp of 18, so 20.31 isn't too far off. 3S2P would be best to minimize wiring losses.

 

[Splat32]

Here’s the SCC specs.

 

[Splat32]

Correct, only 3 200w panels.

 

[Supervstech]

All 3 in series, #10 will work fine, 75V open circuit well under the max voltage of the controller.

 

[snoobler]

Correct, only 3 200w panels.

LOL... yeah. Got confused with another thread....