Momentum 21G electrical use estimates

[NickinCO]

I did some testing with a single SOK 206Ah battery and a Victron smart shunt. Below are the estimates I came up with.

Furnace 10a startup, 7.5a continuous.
Fridge 5a
TV 2a
Inverter 2a
Main lights 1.5a
Bedroom lights 0.5a
Bath lights 0.5a
Radio 0.5a

The generator replaces 30a when running.

300watts of solar should replace 100-125 amp hours per day.

The below assumptions are for spring and fall desert trips in Utah.

-The furnace will run approximately 13 hours a day= 97.5a
-The fridge will run half time- 12 hours= 60a
Misc accessories- lights, TV/Inverter, phone charging = 22 amp hours

Total = 180 amp hours per day used.


Does the furnace and fridge run time estimates seem on point for those that have had more time with their trailers? The furnace is set to 64F.


I'm wondering if I can get by with a single 206ah battery. Assuming the furnace draw is over night, and the fridge will run mostly in the day, the solar should negate the fridge draw and help replenish from the nights use of the furnace. Worst case I run the generator for an hour or two in the evening to give the battery enough of a bump to make it the night. Thoughts are welcome.

[howson]

NickinCO -- what kind of refrigerator? Residential (120vAC), absorption ("RV" refrigerator that can run on propane) or 12vDC compressor?

With that generator you almost can't go wrong with a single battery, but if the budget and space will allow go for two batteries. I have 400aH and find it is enough for normal needs plus there's always some reserve, but our habits and location may not be the best comparison to yours.

[NickinCO]

NickinCO -- what kind of refrigerator? Residential (120vAC), absorption ("RV" refrigerator that can run on propane) or 12vDC compressor?

With that generator you almost can't go wrong with a single battery, but if the budget and space will allow go for two batteries. I have 400aH and find it is enough for normal needs plus there's always some reserve, but our habits and location may not be the best comparison to yours.

The fridge is an 8cuft Furrion 12vDC compressor. If my assumptions are right that means I'd have to run the generator every day (in the evening) for 8 hours under poor weather, or every third day under ideal conditions. I think a second battery is in order to have a little buffer. Probably double the solar also.

I think ideally we would like to get to where we can go 4 days without the generator in perfect conditions or every other day in poor weather.

[74barrio]

NickinCO I was at Glamis over Presidents Day weekend with my new 23G and a very similar setup to your 21G, the only difference is I have two 100Ah Battleborn Batteries. All of your numbers roughly matched mine with the exception of furnace runtime (and solar production, see below). Since the weather was relatively mild, the furnace only ran at night that weekend and I would be surprised if total runtime was more that 3 hrs per day. To bring the batteries back up to full charge at least once every day I would have to run the generator 1.5-2 hours. I could reduce that time with a more powerful charger, but I'm using the stock WFCO panel with the lithium converter/charger installed that only puts out about 30amp max 12v DC (it pulls about 9 amps AC).

If the batteries were at 100% around 9pm after running the generator for a bit, when I wake up in the morning the batteries would be at about 80%. I guess if I was to only rely on solar for charging, the batteries would lose about 30% per day so I could have gone 3 days without running the generator with the batteries going down each day and being around 10% on the third morning (total guess here). Another variable is time of year, since the sun is pretty low in February I'm guessing the solar would put out more the closer to summer your trip will be which would reduce the daily loss and extend battery live another day or two.

[74barrio]

Also, FWIW I've had the fridge on since Presidents Day weekend with the inverter off and the trailer parked since I didn't want to empty the fridge in between trips. The 300W solar panel is topping the batteries off every day without additional shore power. The batteries start off at 85% each morning and the solar has them charged up by noonish. Solar production is going up as the sun gets higher in the sky.

[NickinCO]

Thanks Dan, that's really good to hear. I have a tendency to go overboard lol. Do you have a rough idea of what your day time/night time temps were? We're looking at average lows in the high 30's and highs in the mid 60's.

[74barrio]

NickinCO I think the temps were high 40s at night and mid 70s during the day. At night I would set the thermostat at 65 degrees, off during the day.

[Country Campers]

NickinCO

Not sure if you read this yet but check out post # 9 in this thread Replacing Lead Acid Battery with Lithium - Grand Design Owners Forums (gdrvowners.com). It might help you with battery usage, note that I do not have an inverter.

Brian

[NickinCO]

NickinCO

Not sure if you read this yet but check out post # 9 in this thread Replacing Lead Acid Battery with Lithium - Grand Design Owners Forums (gdrvowners.com). It might help you with battery usage, note that I do not have an inverter.

Brian

Thanks Brian! I missed that one. I ended up ordering a second battery so I can hopefully "set it and forget it". We're going to the desert for 7 days/8 nights the end of this month and boondocking the entire time. I'm keeping the solar to the factory setup for now along with holding off on a DC-DC charger until after this trip.

[NickinCO]

Decent weather today. Got my "Battery box" all hooked up. I have a feeling 412ah will be WAY overkill for us but whatever. Now I don't have to worry about it. Also turned on the furnace and fridge to monitor power consumption with solar. It was cold enough still the fridge wasn't actually running though. With 9:15am sun in early March in Denver, CO i was making around 10 amps which put me right at 0 power draw. That's with the factory 300w panel mounted flat on the roof. It's only going to get better from there. The battery box is a Dewalt tough box 2.0 with the wheels taken off, the handle removed and a little work with a sawzall. It fits two SOK 206ah batteries perfectly with a little foam for cushioning and insulation. A piece of plywood in the bottom of the box that the batteries are strapped to is bolted to the tongue of the trailer. I used a 90* wire gland to run wires underneath the tongue where a couple distribution blocks are mounted. I also have a temp sensor mounted on my Victron smart shunt, the low last night was in the high 20's and the batteries stayed about 10 degrees warmer. I don't see a need for heat pads either.

[mtnwest]

I'm right behind you in this journey, thank you for posting your findings. Picked up my 21g in Jan and have been figuring things out with solar, lithium, etc. and my next step is where to put my 200ah battery. Had thought of a trailer tongue box from harbor freight. I'm also debating on installing heat pads and a controller. I'm in Boise, Idaho so freezing morning temps in the mountains are common.

How is the box mounted to the trailer? Wood in bottom of dewalt bolted through to plywood(?) mounted to trailer tongue?

[NickinCO]

I'm right behind you in this journey, thank you for posting your findings. Picked up my 21g in Jan and have been figuring things out with solar, lithium, etc. and my next step is where to put my 200ah battery. Had thought of a trailer tongue box from harbor freight. I'm also debating on installing heat pads and a controller. I'm in Boise, Idaho so freezing morning temps in the mountains are common.

How is the box mounted to the trailer? Wood in bottom of dewalt bolted through to plywood(?) mounted to trailer tongue?

Yep, exactly. Seems very secure.

[bbinge]

NickinCO I have a 21G that I just put a 200ah Li battery in (along with a few other things) but due to the similarities in our setups, I was excited to see this post and I didn't see an update on how your system worked. Was it overkill, or just right? Would you recommend getting another 200ah battery?

Thanks!

[acoleman43]

With our 21G energy audit I came up with about 3000W per day usage. This includes everything (microwave, charging phones/laptops, fans running, lights, fridge, furnace/stove, water pump,etc) EXCEPT air conditioning. I used this to size my battery bank.

I wanted 3 days energy from my battery bank, so 3000W X 3 is 9000W of battery bank. I ended up with about 10,000W. It has worked well with us. We even use the air conditioner occasionally (just a few hours a day).

IF we have good sun, we can, essentially, have enough power indefinitely. However, if we don't have enough sun, things get stressful. If you are in an area that does not allow generators, and there are no hookups, and you have trees overhead and/or overcast skies for days.....you start to find your limitations quickly.

In Utah, assuming your panel is not shadowed by trees, you should get good amounts of sunlight. I think your 2 batteries will do fine. However, you may find you want to add some solar panels in the future