Advice on RV Set up & Wiring?

[littleharbor]

I just pulled up a "typical" 310 watt 72 cell panel. Voc. 46.4 volts. That is pretty high at STC. 2 series wired 310 watt panels in a cold morning sunrise will exceed the 100 Voc. rating. There are 60 cell 300+ watt panels available now that would eliminate that problem if you want/need the extra wattage.

[sensij]

I just pulled up a "typical" 310 watt 72 cell panel. Voc. 46.4 volts. That is pretty high at STC. 2 series wired 310 watt panels in a cold morning sunrise will exceed the 100 Voc. rating. There are 60 cell 300+ watt panels available now that would eliminate that problem if you want/need the extra wattage.

It depends on where that are used. Along the coast, where Wrybread hangs out, it probably is ok. In the desert, where Carv likes to go, not so much.

[Wrybread]

I just pulled up a "typical" 310 watt 72 cell panel. Voc. 46.4 volts. That is pretty high at STC. 2 series wired 310 watt panels in a cold morning sunrise will exceed the 100 Voc. rating. There are 60 cell 300+ watt panels available now that would eliminate that problem if you want/need the extra wattage.

Have you confirmed that? I've never seen the voltage get anywhere near that on my two 310 watts/72 cell panels. I'll have a look at the highest voltage recorded when I'm there next, since the Tracer logs all that stuff. The temps where I am don't really get below 35 degree F though.

[sensij]

For those of you who can handle it, are there any issues with wiring the system this way?

A downside to running the controller through the distribution block, and not attached directly to the battery, is that there is some opportunity for the voltage feedback used by the controller to overestimate the battery voltage (depending on the specific feedback technique used by that controller), due to the resistance of additional terminations and wire. With 10 ft 1/0 conductors, even at 40 A charge current that influence should only be about 0.1 V, so it shouldn't be a deal breaker in this case.

[littleharbor]

That's for the open circuit voltage. Your controller will only see that for a fraction of a second when it first wakes up. If your controller does log that I would be curious what voltage it sees compared to the STC rating. It should be higher unless your early morning temps are quite warm.

[bcroe]

A downside to running the controller through the distribution block, and not attached directly to the battery, is that there is some opportunity for the voltage feedback used by the controller to overestimate the battery voltage (depending on the specific feedback technique used by that controller), due to the resistance of additional terminations and wire. With 10 ft 1/0 conductors, even at 40 A charge current that influence should only be about 0.1 V, so it shouldn't be a deal breaker in this case.

Quality battery chargers have solved this with remote sensing for eons. Has solar caught up? Bruce Roe

[Sunking]

You know Sk if I'm too dumb to help

Problem is I am not to dumb to help. The problem is you are to slow to learn. It had to be explained to 6 times by three people why you cannot use the frame as a Circuit Conductor, fine for a Ground Conductor

[Sunking]

For those of you who can handle it, are there any issues with wiring the system this way?

T

Try learning how to draw a circuit for which I did for you a long time ago. Where are your fuses and distribution. Again here are the two basic layouts. Ignore the battery isolator.

[Sunking]

I just pulled up a "typical" 310 watt 72 cell panel. Voc. 46.4 volts. That is pretty high at STC. 2 series wired 310 watt panels in a cold morning sunrise will exceed the 100 Voc. rating.

Yeah I pounded that into wyebreads head a few months ago and he still does not get it.

[Sunking]

That's for the open circuit voltage. Your controller will only see that for a fraction of a second when it first wakes up. If your controller does log that I would be curious what voltage it sees compared to the STC rating. It should be higher unless your early morning temps are quite warm.

Wyebread does not know the difference between Voc and Vmp. Yet another reason to use 60-cell 200 to 250 watt panel building blocks.

[Carv]

I'm sure it's just a typo, but of course you'll need the negative line from your panels to the charge controller. You can't use chassis ground for that, as I'm guessing you know.

And if you want to save a few hundred dollars you don't need so fancy a controller, this one will do fine with the added benefit of having an affordable remote monitoring box:

https://www.amazon.com/gp/product/B015ZBOHKC/

That said, the Morning Star is definitely better and if you don't mind the extra $$ for the project you won't regret it, especially a year from now when you have a different project in mind. The downside of the cheaper controller is that it's 100 volts instead of 150, so doing 3 panels in series is pushing it.

And if you're just doing two panels and have room, personally I'd get the 300 - 310 watt panels.
.

Thanks for CC recomendation Whrybread. I've looked at that one but I'm not 100% sure what direction I'm going to head now.

I've done some testing with my Kill-A-Watt and after 96 hours (4 days) on the dot of running my converted freezer it took 1.3 KHW or about .33 KHW or 330 Watts per day to run it. The first 24 hours took 360Watts then gradually declined from there so I'd estimate an average 360 watts a day getting in out out of it a few times and being in a hotter enviroment.

So based on my earlier calculations from page 1 of this post:

1) .36KHw needed per day

2) Fudge factor for battery &amp of 5% Battery & line loss; So .36 X 1.05 = .38KHW OR 380 watts per day

3) Sun Hour day calculation: Per the solar map where I'll be using the panels in December my factor is 5.0 -5.5, (I'll go with 5)

4) determine the size of my array: 380/5 = 76W is the min panel needed for fridge only.

5) Determine Voltage used: "0 to 600 watts = 12 Volts or higher" -I'm using 12V

6) Determine Charge controller size 76W / 12V = 6.33A min


So based on the real wattage usage again those pesky assumptions are waaaay off from the actual, so instead of 1,400 watts guessed I need 380 watts to run the fridge ONLY on grid supplied AC.

Now I also checked and according to the manual my inverter is a 10% to 12% loss on conversion but the real kicker is according to the manual my inverter uses 1.45A or 174Watts when not in use and not in sleep mode. I can't use sleep mode as the fridge does not pull enough watts to wake up the inverter out of sleep mode when it wants to kick on so I can't use sleep mode and the inverter is probably using more electricity than the fridge.

I did run a test run with both the fridge running off the inverter over 72 hours and it ran the batteries down to 11.7V from 12.8V so about 70% capasity used, so RUFF estimation with both fridge & inverter running for 3 days they used 149 amp hours out of my 214 aviable. So using a trimetric battery monitor from bogart engineering ($125), I need to run another test of the whole system to confirm how much my whole system uses and see if I need to ditch the 1500W inverter for a smaller one that uses less when not under draw from A/C side as that might be sucking more than what I need for the fridge PLUS it's 10%-12% loss on conversion.

If you want to monitor your battery charge in comming and out going in amps & amp hours the trimetric by Bogart engineering seems to be a very good add on to your system so you know exactly what is really happening to your system in real time on the charge & discharge in amp hours, this way you're not guessing, you've got real world figures & facts. Check out the trimetric 2025 & 2030 and you can pick them up fairly cheap used. Unless there is a better product for monitoring your batteries I'm pretty sure I'm going to throw one of these on my system.

Also, for those of you RV guys who want real advice from a real RV guy who lived off grid/solar only in his RV full time check out this blog I found: (I learned a ton of stuff from this guy):

https://handybobsolar.wordpress.com/

It's a little old (2008-2014) so the guy uses PWM controllers with properly matched panels.

In fact I'm considering using 2 -150 watt 12-18V "RV panels with a Morning star TS 45 PWM controller as I can buy the whole set up for $450
VS.
2 -255 watt grid ties panels with a Morning star TS 45 MPPT controller as this set up will cost me $600

And seeing that I don't really need that much wattage to run my fridge only 380watts a day, RV panels with a PWM might be a better, smaller, chaper set up that will serve my needs just fine.

Also Bob talks about the need to "overwire" your system and reduce the distance from panels to the CC to batteries to help get maxium charge, seems like it makes a big difference.



Also here are some wiring pictures of actual RV solar systems that work properly similar to what I proposed above
Occasional Weekend use system: Copy of Handy Bob -Solar Wiring Set Up -Occasional Use Trailer.jpg





Full time daily use system: Handy Bob -Solar Wiring Set Up -Full Time Use Trailer.jpg

[Wrybread]

but the real kicker is according to the manual my inverter uses 1.45A or 174Watts when not in use and not in sleep mode.

Wow, you're sure? I'd confirm that, since that sounds pretty over the top. I've seen 20 watts from cheapie inverters idling, but not more than that.

If you need a new inverter, I have and love the Xantrex 600. Get the remote on/off switch too. I've got mine powering my fridge part time and it hasn't burped yet.

If you want to monitor your battery charge in comming and out going in amps & amp hours the trimetric by Bogart engineering seems to be a very good add on to your system so you know exactly what is really happening to your system in real time on the charge & discharge in amp hours, this way you're not guessing, you've got real world figures & facts. Check out the trimetric 2025 & 2030 and you can pick them up fairly cheap used. Unless there is a better product for monitoring your batteries I'm pretty sure I'm going to throw one of these on my system.

I absolutely love the Trimetric from Bogart. And they get big props from me: I had an old one, probably 10 years old, and one of the digits on the display went out. I emailed them asking if they could repair it at my expense, and they did it for free, and with a smile.

In fact I'm considering using 2 -150 watt 12-18V "RV panels with a Morning star TS 45 PWM controller as I can buy the whole set up for $450
VS.
2 -255 watt grid ties panels with a Morning star TS 45 MPPT controller as this set up will cost me $600

I wouldn't go PWM, you lose so much power. If you want to cut corners, get a cheaper MPPT charge controller like the Epsolar Tracer 4210a. Or get the 30 amp version, but it's really nice to have those 40 amps so you can expand your system. And given what you want to power from your system, I have a feeling you'll want to expand it.

And if you're absolutely sure about the two 150 watt panels ok, but I'd go 250 watts each if you have the room. I haven't priced those, but I've got two 72-cell 310 watt panels that I got for $150 each. That means $450 for 600 watts of solar with the charge controller.

My two 72-cell panels have never gone above 90 volts, but that's pretty close to the 100 volt rating of the charge controller, and some folks say there's a chance that morning sun in the desert could break that. Personally I'm skeptical, but to be safe you might not want to wire two 72-cell panels in series with that 100 volt charge controller, get 60 cell panels instead.

[sensij]

1.45 A idle draw is on the battery side (12 V), not the AC side. That is less than 20 W, as Wrybread said.

With your updated usage numbers, the cheaper pwm system might be enough for your needs. However, you are getting *way* less for your money. If the absolute dollars spent is what matters to you, ok, but bang for your buck matters at all, what Wrybread suggested is hard to beat.

[Sunking]

So based on my earlier calculations from page 1 of this post:

1) .36KHw needed per day

2) Fudge factor for battery &amp of 5% Battery & line loss; So .36 X 1.05 = .38KHW OR 380 watts per day

3) Sun Hour day calculation: Per the solar map where I'll be using the panels in December my factor is 5.0 -5.5, (I'll go with 5)

4) determine the size of my array: 380/5 = 76W is the min panel needed for fridge only.

5) Determine Voltage used: "0 to 600 watts = 12 Volts or higher" -I'm using 12V

6) Determine Charge controller size 76W / 12V = 6.33A min

I am only going to deal with this part because it is way wrong.

If you need 360 wh per day the panels must generate 540 wh if you use MPPT or 720 Watt hours if you use PWM. I do not know where you got your formula from, but they are way off. How did you come up with 5 Sun Hours in winter? Very few places in the USA get that many sun hours in winter.. Secondly a panel on top of an RV pointing straight up in the air will get nowhere close, more like 75% turning 5 Sun Hours into 3.75. So with that and assuming you use MPPT Panel Wattage = 540 watt hours / 3.75 Hours = 144 watts, round up to 150 watts.

As for battery in an RV you want at least 3 days autonomy which gives you 2-days run time before you must shutdown and recharge, 5 days is ideal. At 3 days using 12 volts would require 3 x 360 wh / 12 volts = 90 AH, at 5 days is 5 x 360 / 12 = 150 AH.

That throws your Charge controller way off. 150 watts / 12 volts = 12.5 amps

[Carv]

1.45 A idle draw is on the battery side (12 V), not the AC side. That is less than 20 W, as Wrybread said.

With your updated usage numbers, the cheaper pwm system might be enough for your needs. However, you are getting *way* less for your money. If the absolute dollars spent is what matters to you, ok, but bang for your buck matters at all, what Wrybread suggested is hard to beat.

Sensi J,
So I did the math wrong on the inverter draw, it takes 1.45A x 12V = 17.4 Watts?

If so what is the total draw for 24 hours then; 17.4W x 24hrs = 417.6 KHw?


On the Epsolar Tracer mppt controller does anybody know if it has amp limiting, volt controls, and is a3 stage?