Solar Power wiring. I've looked everywhere ! (1 Viewer)

[rubicondon53]

Any solar experts among us? Even basic 12 volt guys. (which I can be on occasion)
I hope I’m not asking a question with an obvious answer. I searched and could only find answers about everything else except this: I’m using a Renogy PWM 30 amp controller; two panels, one mounted on the racks and one portable totaling 220 watts. I have a #6 Hotwire from the house battery to a fuse box, where power is distributed to the small Engle freezer and an ARB 63 fridge. A small subwoofer and an 800 watt power inverter are also fed from this junction/fuse panel. My entire solar system is negative ground wired in parallel. I’ve already found out that with my vehicle it is quite acceptable to run negative to ground, for the controller everything else is wired that way. However, every PMW instruction book says "don’t tie in to the power inverter line". I’m no electrical engineer but if two hot wires are fastened to the same battery post is that not doing the same thing? Isn't it nothing more than a "Y" connection at the battery? Why can't that "Y" connection be anywhere along the line? It is a closed system, within the vehicle, unless there is a switch to isolate the power inverter it’s all one big common current on that # 6 line anyway. I just don’t see the sense in running another big line through the firewall and out to the battery again.. help me out here solar experts, and thanks..

 

[Stevesnj]

Here's a section on solar. Try here. Power Systems

 

[iptman]

Where is your ground wire going from your fuse panel? My house/solar setup on my 80 goes like this.

House battery <-> fuse panel under passenger seat <-> fuse panel in rear quarter panel.

I used 6AWG wire and terminated both the positive and negative at the house battery and essentially daisy chained both +/- from the front fusel panel to the rear. I have a 50 amp circuit breaker within a foot of the positive terminal on the house battery for both safety and ease of disconnecting the house loads. My Victron solar controller is mounted in the rear quarter panel and connects directly to the fuse panel in there. I have a "Load" output on the controller which is what I use for my 60qt Engel since the Engel doesn't have a low voltage cut off and the controller does. The controller also will track energy consumption through the Load terminals which is interesting to see. In testing I only had a drop of a couple hundredths of a volt from the battery to the +/- terminals on the rear fuse panel. Not electrically significant to matter.

I installed this setup with the blessing of our 12v guru @emorth. I think the idea of going back to the battery for both +/- is to keep the entire circuit short and within a known path you can control. If you just (what it sounds like you're saying) ground to whatever chassis or body ground is closest to your fuse panel or controller you don't really know what path current will travel. It probably will work but might not be advisable. @emorth has told countless stories about current going through paths not intended with varying degrees of bad consequences.

 

[Crusha]

Ahem...

@emorth

 

[emorth]

Sorry for the delayed response. Asleep at the switch (pun?)

Here is the concern...
- The PWM (pulse width modulation) output of the solar controller is looking at the voltage of the battery and determining how long to make the pulses (on time) to charge the battery. Low battery voltage long on pulses. High battery voltage short on pulses.
- The inverter is also switching on and off for different time periods bases on the AC output load. An 800W inverter is going to be switching on and off (to make AC) more than 70 Amps under full load (A x V = W). 66.6A x 12V = 800W (assuming 100% efficient, which it is not). 70+ Amps will cause a voltage drop unless the wire is adequately large.
- The battery acts as a "shock absorber". Ideally, the solar charger and the inverter should be connected directly to the battery so the battery can fill in the gaps between the on/off cycle of the PWM output and the on/off cycles of the inverter. If the PWM controller and the inverter are connected together at the end of a wire (especially if that wire is not sufficiently large enough to hand the full load of the inverter), there will be a voltage drop when the inverter cycles on. This on/off voltage drop while the inverter is cycling will confuse the PWM controller because it is expecting to see the battery voltage not the changing voltage at the end of a wire powering a switching load like an inverter.
- Suggestion: A 6 gauge wire may be large enough to minimize the voltage drop from the inverter. Try it and see what happens. If the solar controller goes bonkers when the inverter is running, you will probably have to wire it to the battery. Sorry.

One more note. A lot of solar chargers are advertized as PWM when they are just analog voltage regulators. Read the fine print. Ebay has lots of "PWM" solar chargers that are not PWM.

Hope this helps.

 

[rubicondon53]

Sorry for the delayed response. Asleep at the switch (pun?)

Here is the concern...
- The PWM (pulse width modulation) output of the solar controller is looking at the voltage of the battery and determining how long to make the pulses (on time) to charge the battery. Low battery voltage long on pulses. High battery voltage short on pulses.
- The inverter is also switching on and off for different time periods bases on the AC output load. An 800W inverter is going to be switching on and off (to make AC) more than 70 Amps under full load (A x V = W). 66.6A x 12V = 800W (assuming 100% efficient, which it is not). 70+ Amps will cause a voltage drop unless the wire is adequately large.
- The battery acts as a "shock absorber". Ideally, the solar charger and the inverter should be connected directly to the battery so the battery can fill in the gaps between the on/off cycle of the PWM output and the on/off cycles of the inverter. If the PWM controller and the inverter are connected together at the end of a wire (especially if that wire is not sufficiently large enough to hand the full load of the inverter), there will be a voltage drop when the inverter cycles on. This on/off voltage drop while the inverter is cycling will confuse the PWM controller because it is expecting to see the battery voltage not the changing voltage at the end of a wire powering a switching load like an inverter.
- Suggestion: A 6 gauge wire may be large enough to minimize the voltage drop from the inverter. Try it and see what happens. If the solar controller goes bonkers when the inverter is running, you will probably have to wire it to the battery. Sorry.

One more note. A lot of solar chargers are advertized as PWM when they are just analog voltage regulators. Read the fine print. Ebay has lots of "PWM" solar chargers that are not PWM.

Hope this helps.

Yes it does, a great deal. I had one of those cheap PMWs for a while included in the original kit. I’ll follow your suggestion and if it doesn’t work well no harm done and off to the hardware store for more #6. I’m not too concerned about the inverter draw, it’s only used to charge camera batteries and to operate an aquarium pump for 4 or 5 minutes a day.

 

[fireball]

Don - how expo of you, having an aquarium as part of your overlanding setup!!!

 

[emorth]

You won’t need 6 gauge wire for the solar panels. 220 W at a charge voltage of about 14 volts is less than 20 A. 12 or 14 gauge should be good depending on the length of the run.

 

[rubicondon53]

Don - how expo of you, having an aquarium as part of your overlanding setup!!!

You’d be amazed at how well a pair of oscars guard our camp while we are out and about.

 

[rubicondon53]

You won’t need 6 gauge wire for the solar panels. 220 W at a charge voltage of about 14 volts is less than 20 A. 12 or 14 gauge should be good depending on the length of the run.

View attachment 2361935

Ill end up pulling 10 just in case I ever add another panel..

 

[rubicondon53]

It’s all up and running, several tests with a mix of partly and all sunny will keep the freezer and the fridge running indefinitely, with plenty of power to spare for charging batteries. My next project on my learning curve is to clean up all the other wiring I’ve installed. It looks a bit like a spaghetti bowl.
Thanks for all your advice !