diy solar

diy solar

Powering a Mint Split unit in an RV by solar and lithium batteries

Any reason not to do roof mounted units? They can be ducted.

I have some real world data that might help predict loads and system needs. I have a dometic duo therm roof AC and heat pump. likely 15k BTU, 90% certain. If not that, 12.5k.
900W (3) of 60 cell panels mounted flat. Magnum PT100 MPPT charge controller. Magnum 2800W pure sine inverter / charger.
280Ah x 13.2V home grown battery.
Bus is fairly well insulated for a mobile vehicle. Good 3" of spray foam from Bluebird Wanderlodge RV factory.
85F ambient. Thermostat set to 73F. AC unit would get get down to temp quickly and then cycle maybe every five or ten minutes for a few minutes. Duty cycle approximately 30% to 50% for AC unit.
I was drawing NET between -120 and -160 DC amps. So with duty cycle, -50Ah to 80Ah per hour of AC use for -13F vs. ambient.
Each 300W panel puts out about 20 amps @ 13.2V DC in full mid-day sun.
Total DC load would then be 180A to 220A from the AC unit.
My Magnum inverter had no issue with compressor startup. My AC unit is stock, but I have on hand a heavy duty startup capacity to install.

So with twice as many panels, you'd probably still draw -60 and -100 amps @ 12V, but only when the unit is cycling, assuming similar capacity unit in terms of BTUs. You could pro-rate against 15k BTUs to determine the approximate draw.
If you are in HIGH ambients, your duty cycle on the AC unit would likely approach 100%. I was in 100F with hookup and AC runs pretty much non stop.

Hope this helps. #s might get you in the ballpark.

Doug
the roof units are grossly inefficient. They are out in the sun, the air ducts are right underneath the plastic shroud with little insulation. I had 29ft Class A Winnebago - the 13K Roof unit barley kept it cold. A 10.000 BTU window unit had no issues with cooling the space to freezing. So speaking - how bad they Roof Units are.
 
the roof units are grossly inefficient. They are out in the sun, the air ducts are right underneath the plastic shroud with little insulation. I had 29ft Class A Winnebago - the 13K Roof unit barley kept it cold. A 10.000 BTU window unit had no issues with cooling the space to freezing. So speaking - how bad they Roof Units are.
There you go! Good info.
So another solution will be much more efficient than what I've experienced. Maybe I'll add some insulation if there is room to mine.
 
Any reason not to do roof mounted units? They can be ducted.

I have some real world data that might help predict loads and system needs. I have a dometic duo therm roof AC and heat pump. likely 15k BTU, 90% certain. If not that, 12.5k.
900W (3) of 60 cell panels mounted flat. Magnum PT100 MPPT charge controller. Magnum 2800W pure sine inverter / charger.
280Ah x 13.2V home grown battery.
Bus is fairly well insulated for a mobile vehicle. Good 3" of spray foam from Bluebird Wanderlodge RV factory.
85F ambient. Thermostat set to 73F. AC unit would get get down to temp quickly and then cycle maybe every five or ten minutes for a few minutes. Duty cycle approximately 30% to 50% for AC unit.
I was drawing NET between -120 and -160 DC amps. So with duty cycle, -50Ah to 80Ah per hour of AC use for -13F vs. ambient.
Each 300W panel puts out about 20 amps @ 13.2V DC in full mid-day sun.
Total DC load would then be 180A to 220A from the AC unit.
My Magnum inverter had no issue with compressor startup. My AC unit is stock, but I have on hand a heavy duty startup capacity to install.

So with twice as many panels, you'd probably still draw -60 and -100 amps @ 12V, but only when the unit is cycling, assuming similar capacity unit in terms of BTUs. You could pro-rate against 15k BTUs to determine the approximate draw.
If you are in HIGH ambients, your duty cycle on the AC unit would likely approach 100%. I was in 100F with hookup and AC runs pretty much non stop.

Hope this helps. #s might get you in the ballpark.

Doug

The 12K btu, 115v mini-splits I have draw between less than 600w and a high of about 800w most of the time they are operating and are FAR less noisy than any rooftop unit I have ever been around....both the inside and the outside units are so quiet it is almost unbelievable. I like to have a fan on low all night long and the mini-split in my bedroom is so quiet it doesn't make enough sound to satisfy me, so I have to have a small fan on low and with the noise that makes I have to look at the mini-split to see the numbers that light up in order to know it is even on. The one in my living room is even quieter than that one. My wife wanted a rooftop in the living room but now that the mini-split is installed she is very thankful I went that direction instead.
 
Ditching the roof unit provides much better efficiency and free's up a lot more space to put solar panels. Roof real estate on my truck camper is a premium.
 
The 12K btu, 115v mini-splits I have draw between less than 600w and a high of about 800w most of the time they are operating and are FAR less noisy than any rooftop unit I have ever been around....both the inside and the outside units are so quiet it is almost unbelievable.

Would love to get a Mini Split, just don't have the space for a regular one. Would love to get one from https://www.forestair.ca/en/serie-mini-anglais

But they are expensive and I can not find them in the US.
 
I just got one from ebay and installed it. Just a little over $600.00 and that was not the cheapest 12K unit on there. I don't that $450-$600 is expensive at all really.
I got a 12K Inverter Unit from my Local Craigslist for $350, got it installed in my Garage, Love that thing. Getting Split units and installing are not my issues - its just simple size constrains on my Van.
 
I have been running a 12K mini split in a 40ft rv for almost 3 years... due to lack of wall space I put in a ceiling cassette unit (240V). I run 1800W Solar, and 200AH 48V Lithium battery. When I run ac you can see that the unit pulls 350 to 850Watts (AC) I do start my A\C before the heat load gets too large. I am also able to charge the batteries when running the A\C, solar sized for this, at about 6-8 amps. On days where the outside temp reaches 100 degrees the unit is able to keep the rig at about 78. By about 6ish in the evening I can see the system start pulling from the battery.
 
I will be installing another mini-split (12K 110V) on the new trailer we have purchased. removing the roof A\C will give me plenty of space for 1500W solar. I have seen people in vans put the outside unit on a reciever hitch platform with the gas genny right next to it and gave up the wall space for the indoor unit. They built a raised rail frame for the solar panels to cover the entire roof (4 300W panels). They built lithium banks from 3.2 cells and deploy them under the bed. They run all day in the sun no issues.... They have full size vans.. it can be done
 
I will be installing another mini-split (12K 110V) on the new trailer we have purchased. removing the roof A\C will give me plenty of space for 1500W solar. I have seen people in vans put the outside unit on a reciever hitch platform with the gas genny right next to it and gave up the wall space for the indoor unit. They built a raised rail frame for the solar panels to cover the entire roof (4 300W panels). They built lithium banks from 3.2 cells and deploy them under the bed. They run all day in the sun no issues.... They have full size vans.. it can be done

Saw that, too. Everything can be done. But I need the hitch for towing a heavy trailer.
I will go with the Inverter Window Unit, for my use-case the better option.

To cool a Van you don't need that much power.
 
Got the exact same unit in my Garage. 12000 BTU Daizuki. Works great.

Yeah, got it running on Sunday and did the last of the finish up work today. Really happy with it so far. Might even be quieter than the Air Con 12K I have in the bedroom.
 
Yeah, got it running on Sunday and did the last of the finish up work today. Really happy with it so far. Might even be quieter than the Air Con 12K I have in the bedroom.

I got mine running since March, works perfectly and cools like 600 sqft., Slowly the cheap small rubber mounts underneath the feet are getting hard. Need to get some bigger mounts - my wall starts resonating.

If I where you I would start looking for some better mounts, an inch thick or so.
 
I have vibration dampening material in between the3/4" plywood it is mounted on and a couple of pieces of 3/4" plywood on either side of a large hole in the floor. That gave me enough clearance to put a furnace filter over the whole in the floor so I have even more air flow than just the grated door. So even if those harden some I should have enough vibration dampening. I will keep an eye on it though.
 
Just wanted to throw this out. I think what I may do is to assemble my system one part at a time. I just bought a Honda 2200i generator use in good shape,(
I did a test with the Honda gen on a 8000 btu window unit and it only pulls 8 amps with no problems on compressor start up)
then I'm going to use a DC to DC alternator hook up and some Battle Bourne batteries, maybe four to assist in charging if needed and now I'm looking at the Battle Bourne flexible solar panels. Maybe with three different source of charging. I can run a 25 seer split unit all night, heat or cooling all night for the stealth I want..
 
I have been running a 12K mini split in a 40ft rv for almost 3 years... due to lack of wall space I put in a ceiling cassette unit (240V). I run 1800W Solar, and 200AH 48V Lithium battery. When I run ac you can see that the unit pulls 350 to 850Watts (AC) I do start my A\C before the heat load gets too large. I am also able to charge the batteries when running the A\C, solar sized for this, at about 6-8 amps. On days where the outside temp reaches 100 degrees the unit is able to keep the rig at about 78. By about 6ish in the evening I can see the system start pulling from the battery.
Great feedback... Question: Is the 200AH 48V Lithium battery bank for your whole rig, or is that a separate bank?
 
Great feedback... Question: Is the 200AH 48V Lithium battery bank for your whole rig, or is that a separate bank?
That was for the whole rig. Reused existing cabling saved time and money. Inserted (with breaker) 48V to 12V converter to handle 12V loads.
Just built out new rig with 24V system (544AH) with single 3k Multiplus and a wall mount mini split. kept propane for cooking and wave6 heater this time.. 1480W on the roof
 
Great feedback... Question: Is the 200AH 48V Lithium battery bank for your whole rig, or is that a separate bank?
forgot to mention that I also had a 21 cu ft residential fridge and cooking on induction cooktop on the old rig...if your setup is different you may not be as much of a power hog as we were. I did a quick laod worksheet to ballpark my needs on the new rig...still over built
 
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