Help with my off grid RV setup

[Derek884]

Im living completely off grid in my 35ft keystone 5th wheel in Colorado. Its cold in the winter and hot in the summer.

i mounted 4 x100watt Renogy panels on my roof.

Renogy 100 Watt 12 Volt Polycrystalline Solar Panel	RNG-100P	4

I wired the 4 panels in parallel and fed the wires down the wall into my front compartment to a Renogy 12/24V 30amp PWM charge controller.

I bought 4 100ahr deka intimidator AGM batteries from a guy off Craigslist for $200 total that were 2 years old.i wired these in parallel.

That is pretty much to run my lights and keep the DC on my propane refrigerator on.

Then I bought a MicroSolar 1000watt pure sine wave inverter. And connected it to my batteries. I ran 14/2 romex from the inverter to a breaker I installed on my electrical panel. I just flip the breaker on if I want the inverter, and leave it off when I use the generator. The pain is it only powers half the panel because it is made for a 220v 50amp shire power so half of the panel is one phase and the other half is the other phase.

Over the winter I was somewhere I could plug in. I just went back off grid and my batteries got really low. I want even running the inverter. I feel like I have more power than I possibly need but the batteries drained.

so, I was thinking my batteries might be bad. I charged them up with my generator all day. I took them and got them load tested at batteries plus. They tested good by holding 900amps for 15 seconds. They said they couldn't test the capacity.

so, i hooked the batteries back up but didnt connect the solar to them and hooked up a bayite DC meter to measure how much energy i was using from them. After 24 hours I used 640 watts and the batteries were at 12.4v. So that should be 25% drained. The batteries are 12v x 100ahr x 4 = 4800 watt/hr capacity. So, 25% should be 1200 watts. So, i figure the batteries are at about 50% of their original capacity or 200ahr.

Even at 200ahr, that should be enough batteries for what i need. So, why are they not getting charged up with my system?

I parked under a couple of trees that dont have leaves. Its minimal shade on my solar but definitely shades my camper which really helps keep it from turning into a hot box on sunny days.

my charge controller only gives me Kw reading. When they were connected, it said it generated 1kw. Over one day. It could have been 1.1kw or 1.9kw. I don't which one it is, but I will test it over a couple of days.

But, if I used 650 watts in one day, my 1kw should have more than charged it.

[Mike90250]

That is pretty much to run my lights and keep the DC on my propane refrigerator on.

A propane fridge, often used 12V DC to run a electric heater to run the fridge, saving propane while you drive. It's a pretty big heater and will drain batteries quickly

[Sunking]

I parked under a couple of trees that dont have leaves. Its minimal shade on my solar but definitely shades my camper which really helps keep it from turning into a hot box on sunny days.

You cannot have any shade on your panels period. Just one cell with a leaf or branch shade essentially turns the whole panel off.

If you can charge your batteries on a generator but not on solar is screaming you do not have enough solar power. Additionally you configuration is very poor using a PWM controller, panels and batteries in parallel. Your PWM controller is turning your 400 watts panels into 250 watts that only provide you roughly with 20 amps of charge current at solar noon. 20 amps of charge current is just big enough to only support a 200 AH battery, not 400 AH. Compounding your problem is panels on a RV laying flat looking straight up really degrades the panels so I find it hard to believe they are generating anywhere near 1000 WATT HOURS in a day.

With a PWM controller OUTPUT CURRENT = INPUT CURRENT. Now take a look at your panel Imp spec. Says roughly 5.3 amps right? With 4 of them in parallel = 21.2 amps. Do some simple math Watts = Voltage x Current. 12 volts x 21.2 amps = 254 watts. However I guarantee you are not getting anywhere near 21 amps on an RV with panels facing straight up in the shade. Right now this time of year you are getting less than 4 Sun Hours with optimal panel tilt, orientation, with no shade issues. My educated guess is you are generating less than 500 watt hours and that estimate is very optimistic.

Basically it is time for an upgrade and new batteries. With a MPPT Controller Output Current = Panel Wattage / Battery Voltage. So 400 watts / 12 volts = 33 amps enough to support up to a 12 volt 350 AH battery. So what I would recommend is reconfigure your panels to either 4S or 2S2P depending on what 35 amp or larger MPPT Controller you buy, and replace your 4 dead batteries with a pair of 6-volt 300 to 350 AH batteries wired in series to make 12 volts. Lastly get the panels out in the sun where they have absolutely no shade from sun rise to sun set.

[Derek884]

Sunking, thanks for responding!

Batteries - so I do need to replace them? I ended up using 1500 watts and it drained it down to 12.07Volts. I'm guessing that is 70% capacity. So, that would be 178ahr capacity. Is that considered dead? Does that mean the efficiency of their charge decreases? Or, are they still equally efficient on charging, just not holding the charge? I ask because I can use them to just charge battery banks. (I could use them for lighting in my workshop and I use batteries around the property for infrequent use - dump truck, tractor, vehicles, water pumps, etc.) That brings me to another question - I have also used my battery bank to charge up these batteries I use around the property. I just put a jumper cable on my solar battery bank to the battery that needs to be charge (usually 20ahr battery) Is that bad? Should I run a separate system to do that?

MPPT controller - It looks like they run $300-500 for a good controller. From your math, I get about 63 watts per panel. That is a loss of 150watts. For $300, I could buy 3 more panels. That would get me an extra 300watts in panels or 210watts effective. That seems cheaper with the same result. What do you think?

Panels wiring - you suggest 4S or 2S2P. 4S would be a 48V system, 2S2P would be a 24V system. The way I understand it is, a PWM is just on/off. So the panels would have to match the voltage of the batteries. A MPPT controller will match the voltage. So, I could have a 48V panel system and 12v battery system. Is that correct?

Battery wiring - I've read that parallel batteries are less efficient that series. The reason I have a parallel system is because my RV has a AC converter that charges the batteries at 13.5V. And the camper is 12V. If I made my batteries 48V, I would need to buy a converter to change AC to 48V, and I would need to put a transformer before the DC panel to convert the 48V battery to 12V for the camper. Since 12V runs around the clock, it seems like the transformer converting the 48V to 12V would create any inefficency that the 48V system saves. Is that correct? My understanding is the main advantage is when you run a large inverter, it reduces the amp draw. So, its really a cable sizing issue. Thoughts?

Batteries - So, I need to get new batteries. You suggested 6Vx2. How about this: Lowes - $150 Item # 599952 Model # GC15 Deka 6-Volt 448-Amp Golf Cart Battery

That would get me 448Ahrat 12V for $300. Would that work?

Thanks for helping! Sorry for all my questions!

[Derek884]

Sorry for the title typo. I can't change it.

[littleharbor]

BIG typo on those batteries. They are actually 230 ah. You need to look at L-16 size batteries to get over 300 ah.
With an MPPT controller you want to wire your solar panels in series to bring up the voltage. The controller steps down the voltage to your battery voltage. Plus series wiring is simpler, uses less wires and in many cases eliminate the need for fusing the array.

[Sunking]

Sunking, thanks for responding!

You are welcome

Batteries - so I do need to replace them? I ended up using 1500 watts and it drained it down to 12.07Volts. I'm guessing that is 70% capacity. So, that would be 178ahr capacity. Is that considered dead? Does that mean the efficiency of their charge decreases? Or, are they still equally efficient on charging, just not holding the charge? I ask because I can use them to just charge battery banks. (I could use them for lighting in my workshop and I use batteries around the property for infrequent use - dump truck, tractor, vehicles, water pumps, etc.) That brings me to another question - I have also used my battery bank to charge up these batteries I use around the property. I just put a jumper cable on my solar battery bank to the battery that needs to be charge (usually 20ahr battery) Is that bad? Should I run a separate system to do that?

Slow down, one subject at a time. You said you bought 2 year old used batteries right? They were tired and needed replaced when you bought them. Deka'a are only good for about two years. Stop using batteries to charge batteries. You can use the solar panels and controller if you have that kind of time on your hands like days to wait. Swap around batteries.

MPPT controller - It looks like they run $300-500 for a good controller. From your math, I get about 63 watts per panel. That is a loss of 150watts. For $300, I could buy 3 more panels. That would get me an extra 300watts in panels or 210watts effective. That seems cheaper with the same result. What do you think?

I think you are missing a lot of points. With a PWM controller you are forced to wire you panels in parallel. With more than two panels in parallel requires combiners, fuses, and some very large wire to handle the current. It also forces you to use 36-cell 12 volt battery panels which cost 2 to 3 times per watt more than a higher voltage 60 or 72 cell Grid Tied Panel panel

Panels wiring - you suggest 4S or 2S2P. 4S would be a 48V system, 2S2P would be a 24V system. The way I understand it is, a PWM is just on/off. So the panels would have to match the voltage of the batteries. A MPPT controller will match the voltage. So, I could have a 48V panel system and 12v battery system. Is that correct?

Yeas and that is what you are missing. With PWM you must wire 12 volt panels in parallel. You have 4 panels and each is 5.3 amps and 4 in parallel is 20 amps. So you have 20 amps in, and 21 amps out into a 12 volt battery for a total of 20 amps x 12 volts = 240ish watts out of 400 watts

MPPT is a different animal and is a dc to dc Buck Power Converter much like an AC transformer. Very little loss involved. With A MPPT controller with a Voc rating of 150 Voc you can wire all 4 panels in series. using small 14 AWG wire, no combiner or fuses required. You panels Vmp voltage is 18.9 volts and Imp = 5.3 amps. So wired in series you have 75.6 volts @ 5.3 amps (400 watts) into a MPPT Controller, and on the output you have 12 volts @ 33 amps (400 watts).

In fact there are 600 Voc Input controllers and you can charge a 12 volt battery with them. Example go in with 500 volts at 2 amps (1000 watts) with very small wire from a single string of panels as an example, and on the output 12 volts at 80 amps.

They pay for themselves by using much less expensive panels and a lot less harware, plus much higher efficiency. Higher voltage is always more effficient and uses a lot smaller wires. That is why utilities run as high as 1 million volts.

Battery wiring - I've read that parallel batteries are less efficient that series. The reason I have a parallel system is because my RV has a AC converter that charges the batteries at 13.5V. And the camper is 12V. If I made my batteries 48V, I would need to buy a converter to change AC to 48V, and I would need to put a transformer before the DC panel to convert the 48V battery to 12V for the camper. Since 12V runs around the clock, it seems like the transformer converting the 48V to 12V would create any inefficency that the 48V system saves. Is that correct? My understanding is the main advantage is when you run a large inverter, it reduces the amp draw. So, its really a cable sizing issue. Thoughts?

Hopefully the light is starting to turn on and see you see the error in your thinking. Never ever parallel batteries. If you need 400 AH batterries, use 400 AH batteries. That would be 2 x 6-volt 400 AH batteries wired in series.

Batteries - So, I need to get new batteries. You suggested 6Vx2. How about this: Lowes - $150 Item # 599952 Model # GC15 Deka 6-Volt 448-Amp Golf Cart Battery

That would get me 448Ahrat 12V for $300. Would that work?

Not my first choice, but you need to work out the controller thing first. But yeah it works on a budget.