diy solar

diy solar

Rick's "Charge from the TV" solution for owners of MPPT-charge Solar in the Trailer

You've made an interesting question. Here's my answer, involving some relevant details - but I agree with you, I would rather have used AWG-8 on the Tow Vehicle "12V" side leading into the Boost Converter. The input lead to that Converter Box may be even smaller than 10-AWG, so I cut it fairly short before plugging into my relay output lead. My "automotive Relay" socket base couldn't handle anything larger than 10-AWG (and even that was a bit of struggle, I ordered custom bases to make them take #10 AWG on the 3 "power legs" in question, and I blew up one of the two I bases which I ordered while trying to squeeze in the wire).

But you're assuming that I attempt to pull the full RATED watts of the Boost Converter. I'm only pulling about 480 watts maximum for wire losses to reach the MPPT, MMTP inefficiency, and the MMPT's rated maximum output power 28A at about 14.4 Volts. 480W /13.4V = 35.82 Amps. 35.82 Amps / 0.90 efficiency yields 39.8 Amps total draw at maximum output, a figure slightly lower than your 43 amp calculation.

These wire distances are also short (heat can dissipate at the copper ends, not just through the insulation) and most of what goes on in here can arguably be called "chassis wiring". This is also THWN-2, for which I typically see ampacity ratings of 40A @ 90 degrees C. That's with conduit allowed, while the hood underside at this location (with wires in free air) has substantial airflow when driving at speed. But temperature is already a bit high in that location, somewhat reducing ampacity back down a bit.

The bottom line for wiring size in my scheme is whether it has performed OK in the real world, leaving its insulation undamaged. And for that question, I'm happy to report that I have seen no heat-related issues on the connectors, exposed insulation, or even the electric tape, over multiple years. Neither have the friends who use the same scheme.
Well explained.
Thanks for reminding me about chassis wiring.
 
This is also THWN-2, for which I typically see ampacity ratings of 40A @ 90 degrees C.
I've never used THWN-2 if its actually thhn-2 with a different name, its usually rated for to 105C for MTW="machine tool wiring" which should be near equivalent to appliance wiring me thinks.
I did some research a couple of years back and found that as near as I can figure the same wire and insulation is marketed with multiple usage designations.
 
Exactly - you're usually looking at dual rated THHN-2 / THWN-2 when you go shopping for decent stranded wire. My connectors and tape would probably show "issues" before reaching 105C, but I'm not sure of my actual experience - I only use it while the SUV is in motion, and haven't invested in a recording thermometer which could later show the highest temps reached by the wires in question, while driving at highways speeds.
 
Back
Top