Voltage vs. PWM controller & wire size

[Calkidd]

Ok, there is a recent thread out there MPPT vs. PWM and some post were a little confusing to me. Instead of hijacking his thread I started a new one.

My set up is two 208 watt Sony panels with 28.71 volts (I.E. 24 volt panel) which is 14.5 amps. (V * A = Watts).

What I don't understand is the difference in amp production between the MPPT and PWM. In the other thread there was some math that did not add up or followed Ohm's law formula. Someone mentioned with the higher voltage it was better to go with a MPPT controller rather than a PWM. But why? I know some will say the MPPT handles the extra voltage and turns it to amperage. HUH?

Regardless of what voltage is going into the controller it will come out at 14.4 - 14.8 volts. Right? Thus ohm's law says my system amperage, on a perfect day, would produce 28 amps out from the controller, no?

I understand using such a higher voltage panel for 12 volt charging system is an overkill, but these panels are left over from a previous residential install I own. As long as the controller can handle the voltage a PWM should work fine. For example I am using the Bogart 2030 controller with the Trimetric monitor.

On a side note another rant.

I read Handy Bob's information and other research about wire size. Ok, I get that, but if 10 ga works why in the hell are people using 8 or even 6 ga to run their solar panels when the loss is 2-5% with 10 ga? After doing the voltage drop calculations with my system with a run of 30 feet (being very liberal here) I only have a 3% loss of voltage.

Also, why are some using 1/0 ga for inverter and battery wiring? HOLY ****! We are talking about a cable that can handle 150 amps. Tell me what 12 volt load could anyone be possibly using in an RV that produces that much amperage? Wouldn't 2 ga be just fine?

[-Oz-]

That looks awesome. Well done!

[westend]

Nice work. That combiner box is a beaut!

[Calkidd]

I did installed a 125 mega fuse for now because that is all I had. I'll replace it later with a higher amperage.





I just finished up the install today. I fired it up at about 1400 hrs today. I saw 28 amps on the Trimetric. Not bad.



Here is my wiring. I am not sure if I like the single post with that many positive terminals on it. I might look for a distribution block.




I ran the wiring down through the reefer vent, but I didn't like the wires rubbing on the metal meshing. I slit a hose and zipped tied it to protect it.





My custom combiner box.

[grizzzman]

Looking great. I would suggest a 200ish Amp catastrophic fuse at the battery.(more if you have an electric start generator).

Thanks for the update.

[Calkidd]

-Oz- wrote:

grizzzman wrote:

Calkidd wrote:
Thanks again for those who were informative and encouraging. I'll let this thread die. I'll update it later with my installed, inefficient, underrated system.

For what its worth, If in the same situation i would do the same.
Please keep us informed.

Me too. Go for it you have nothing to lose, some to gain, and the possibility to upgrade at a later date.

Its slowly but surely coming together. I mounted up the controller and the 50 amp breaker. I'll run the solar through the breaker. I am wondering if I need some type of breaker between controller and batteries, maybe fuse style?



I move the batteries from their tiny hole to the storage compartment. Eventually I'll tie in two more batteries. They're tied in with 2 gauge for now. I don't run heavy loads with the inverter.



The compartment above where the batteries use to be is where the house 12 volt, jacks and generator leads came in to. I installed two distribution posts to power these without running more cable.



I have almost 16 feet x 8 feet of empty space on the roof with no obstructions. Perfect for 4 panels.

[-Oz-]

grizzzman wrote:

Calkidd wrote:
Thanks again for those who were informative and encouraging. I'll let this thread die. I'll update it later with my installed, inefficient, underrated system.

For what its worth, If in the same situation i would do the same.
Please keep us informed.

Me too. Go for it you have nothing to lose, some to gain, and the possibility to upgrade at a later date.

[CA_Traveler]

OP, Free panels tip the scales of course. Your CC verification of your plan and driveway setup and test covered the bases, maybe test 2+ panels.

The other plus is that your Sharp panels are the standard size 24V panels which means that mechanically a possible future change to a higher wattage panel and/or a MPPT controller would be rather easy.

Keep us informed.

[grizzzman]

Calkidd wrote:
Thanks again for those who were informative and encouraging. I'll let this thread die. I'll update it later with my installed, inefficient, underrated system.

For what its worth, If in the same situation i would do the same.
Please keep us informed.

[red31]

Almot wrote:
Details are being slowly dragged out.

I thought the OP had some specific questions.

[Calkidd]

Thanks again for those who were informative and encouraging. I'll let this thread die. I'll update it later with my installed, inefficient, underrated system.

[Almot]

Details are being slowly dragged out. Just like Ca said, few pages ago 🙂

[Calkidd]

One thing needs to be understood this is not my home. This is a toyhauler / weekend camper that we spend at most 5-6 days straight in. I am glad you have a HUGE system that will run a small city.

What needs to be understood is I OWN these panels so why not use them and at least get some use out of them. Want to send me a MPPT so I can get the MOST benefit from it?

[Almot]

One thing I've learned from reality of using my system is that there is no such thing as too much solar.
15-20A is a fair weather system for minimal to moderate loads in summer.
Minus-side of energy balance sheet is normally done before the plus-side. Purchase of controller comes the last 🙂

[Calkidd]

Almot wrote:

Calkidd wrote:
I have nothing to loose using these panels. I think I will use 3 panels starting out.

Nothing to lose, except for size/current efficiency. Those 208W look same large as mine 245W, and PWM will process less than half of available wattage.

If Trimetric clips it off like - apparently - it says in the manual, why only 3 panels, what is the purpose? To see if solar will make any energy? 🙂 It will. 21A is a very modest system, even die-hard Handy Bob has 2 times bigger equivalent, considering tilt. Enough for a minimalist but not if you want to run your rig on solar the same way as on grid.

Thanks I keep that in mind.....I know you're trying hard to be realistic, but at the same time a Debby Downer.