2 or 4 AGM batteries with 300W solar array?

Sprintrek

New member
We have 2 - Kyocera KD135GX panels, Blue Sky and 2 batteries - 2 1/2 years good experience.

One thing we do is wait for the batteries to be charged up from overnight use and then do our electronic device charging - typically between 11AM and 3:00 PM on sunny days. Plenty of power for our needs - refrig, water pump, heater overnight when needed, low v. lighting and CPAP machine. And, we park in the sun! :thumbup:
Another encouraging comment to stick with a 2 battery set-up. Thanks. About device charging, do you use the inverter for plugging 110V adapters or simply go with 12DC? I wonder if RT installs 12V outlets, seems to be the solution for charging those low voltage devices, instead of firing up the inverter.
 

icarus

Well-known member
It is typically much morefficint to charge those evinces directly from 12 vdc. Adding 12 vdc outlets is as easy as anything, just ensure that they are people fused.

Most inverters are very inefficient with small loads. It is only when they arre loaded near capacity do they achieve thier advertised eff numbers. The exception (that I know of) is the Morninstar Suresine 300, a great little inverter, not often used in Rv applications...mores the pity! I run my entire off grid house on one.

As for the number of batteries, and the total Ah capacity. It is usually a trade off between total Ah delivered oer the life span at what cost of say a 200Ah bank, versus more (but less deep) cycles with a larger bank.

In RV applications, most batteries don't die from using up thier designed number of cycles, but rather they are "killed" from over drawing, under charging, heat and vibration. Is use the same calculus when I design off grid applications. If twice as much battery lasts less than twice as long, in total, and in total Ah delivered, then it is cheaper to go with the smaller set, draw them further each cycle, and place time sooner. As I said, in an Rv application they ease likely to be killed early from other causes, so going with the small bank, monitoring performance with something like a Tri-Metric, and then deciding what to do with the next set. That would be my suggestion.

Icarus
 

NBB

Well-known member
I will enquire about the brand and get back to you. My understanding is that they are outsourcing them, not buying them off the shelf. And they are very clearly stating in their specs that they are 100W panels.
Okay - after some searching around, it looks like those panels can be had for ~$150, free shipping on Ebay. Search "100 Watt Solar Panel"

There are a lot of ~47x21 panels out there, pretty sure that's exactly what Roadtrek is using. It appears 100W is the current max for this size, unless someone has a link...?

Looks like Roadtrek wants $2730 for 3 panels + charger...
 

d_bertko

Active member
I've got 4 agms (420ah) and no solar panels. We drycamp virtually all of the time.

Our compressor fridge uses about 2/3 of my daily draw. Total draw is about 1/2 a battery per day. (Translates as four days sitting still without any alternator input.)

We also do similar electronics charging and music et al. But we also use our microwave in limited daily use in camp. (Some mag induction burner use. Mostly propane campstove while boondocked)

If your camping style is as mobile as ours then the 4 agm solution will likely displace any need for a genset. A large bank powers short-use high-draw devices like a microwave as well as providing lots of low-draw fridge time.

Solar panels are incrementally improving and continuing to drop in price. If it were me I would order the large bank. Have an aftermarket supplier install a solar array once your camping experience shows how much, if any, solar wattage you need.

I bought a eu2000i genset when I built my DIY figuring it would be needed. Wrong about that and should have gotten some camping in first.

Dan
 

Graphite Dave

Dave Orton
It's good to get various opinions on these matters, because all of the specs are either BS or useless in calculating reality.

Others have noted the variation in solar power from ratings, but also consider the fridge. So, you have "amps" and there's some number there for when the motor is running. Now, consider your venting, insulation, ambient temps, yada yada and tell me how much that motor will be running? That's right, you have absolutely no idea.

The other thing is that I think people here tend to romanticize their installations and how well they really work.

All that said, I have a 185 watt panel, 440 ah of batteries, Dometic CR-1110 3.8 cf 12V fridge. In short, I would say my battery bank is par for this fridge, the solar inadequate for boon docking and barely adequate for driving every 3-4 days. I plan to add more solar capacity. I just returned from a 10 day trip. My batteries became more and more depleted as the trip went on, even with some driving. 70% was the lowest, so it worked but another week would have been an issue. The fridge is a pig in warmer temps. Mine is super well vented, too, as it sits where a propane fridge used to be.

I had a 200 ah battery bank with a propane fridge for ~3+ yrs. I thought the 200 ah was too small for anything. I was basically boon docking with furnace on in the evenings (not while sleeping). This cooked the battery every evening, forget an electric fridge. The solar would recharge it (sometimes) during the day. The batteries didn't last very long.
I am curious why your system does not seem to work as well as mine. You have a 185 watt solar panel with 440 ah of batteries and I have 205 watt panel and only 255 ah of battery capacity. Yours should be better. Mine has no trouble getting back to 100% SOC each day on sunny days. Something must be different. I have a Dometic 12v/120v refrigerator that draws 4 amps when running. The refrigerator has 1 1/2" of rigid insulation on 4 1/2 sides and is wrapped in Reflectix. I have a hole in the floor behind the refrigerator and leave the Maxxair vent open unpowered. I do not turn on the 1000 watt inverter unless I need 120 volt power and all lights are LED. Do occasionally use the 600 watt microwave and when I do it drops the SOC by 2% for each 2 1/2 minutes of use.
So what is different? If anything my battery size is larger than necessary for my use.
 

NBB

Well-known member
Our compressor fridge uses about 2/3 of my daily draw. Total draw is about 1/2 a battery per day.
That kind-of sort-of sounds like the reality of my fridge - ~36 ah / day - or ?

It sounds like you have some sort of measurement, but many of these posts don't sound that way.

I have an amp-h meter. The gage will say "empty" at 50% discharge, a good rule of thumb. 55 ah/day for 4 days = 50% of 440 ah sounds reasonable to me, for a rig with a larger electric fridge.

If you are just reading volts (or nothing at all) and then conclude your system works fine, I'd say you really have no idea...

I never use my microwave on battery. The load is just too much, the discharge too rapid - kind of waste. I have a high idle switch, so I just start the motor for a few minutes.
 

NBB

Well-known member
I am curious why your system does not seem to work as well as mine.
This past trip (my first with the new fridge) was to Yosemite Valley. You don't get sun all day because of the valley walls and trees, even though I would generally be parked in sunny places. Throughout my ownership, though, I've found pretty much the same thing - it's nicer to park in the shade, and most [nice] campsites are shaded. I'll leave it in the sun if I am away from the vehicle. I therefore recommend way more solar than you'd think.

I also often camp in colder temps, when daylight is short and sun angles are low. #2 consumer of power is the fan motor for my furnace - ~2.8 amps. Even with a propane fridge, hanging out in the evenings in winter, between an early sunset, for several hours, until I went to bed, that furnace, radio and LED lights would pretty much suck my [old] 200 ah bank dry in a few nights, even with the solar and clear skies during the day. Winter requires way more power than summer, and the solar is way weaker. I'm interested to see how the new fridge factors in during winter.
 
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d_bertko

Active member
That kind-of sort-of sounds like the reality of my fridge - ~36 ah / day - or ?

It sounds like you have some sort of measurement, but many of these posts don't sound that way.

...I never use my microwave on battery. The load is just too much, the discharge too rapid - kind of waste. I have a high idle switch, so I just start the motor for a few minutes.
In my research I came across an obscure Engel spec chart that showed my MT60 chest would average 18w over a 24 hr period at 75F. I was pleasantly surprised that my real-world measured consumption for similar conditions was very close to that test spec. A bigger or vertical door fridge or more time in southern summers might challenge my lack of solar panels.

But I'd add an insulating wrap around my fridge before adding solar. Efficiency trumps most things for low cost.

I've about 9 years use of the microwave on the original agm bank. The "dorm" micro draws about 1100w input and got rave reviews on Consumers Reports at the time. It was cheap and the small interior is very efficient. Never the slightest qualm about just running it off the bank.

A high-idle switch sounds like a useful option. My white water addiction often causes frequent interspersed alternator use.

Dan
 

Graphite Dave

Dave Orton
Not parking in the sun explains the difference.

Do you have a backup method of charging the house battery in addition to solar? I have a second inverter powered by the Sprinter electrical system that provides 120 volt power while driving. That can be used for house battery charging if I have multiple days without sun. Almost never use the backup.

I also use a different method of heating in winter. I have a diesel Espar water heater that was an option from Dodge. I turn it on at night before going to bed to raise van temperature and then turn it off. Use a 12 volt heating pad under the sleeping bag during the night to stay warm and let the van interior get cold. Refrigerator does not run much in a cold van (and is quiet) so that lower energy use offsets the heating pad power usage. In the morning I again turn on the Espar to warm the van. With the refrigerator running I will drop to around 92% SOC in the morning and normally will be back to 100% SOC by noon.

I have learned that my Magnum 1000 watt inverter/charger/transfer switch does consume a lot of power if it is on even without any 120 volt power use. The other day I forgot to turn it off after use and the next morning the battery was at 92% SOC. Normally I have a SOC reading of 99% in the morning. I do have some small loads that consume power: Magnum meter, Morningstar solar controller and a battery conditioner. They cause the 1% loss overnight.

I also do not have a TV and do not listen to a radio. I seldom (almost never) power the Maxxair fan. The hole in the floor with the vent open works very well in the winter to create a draft from the hole and then out the vent. Hole does not work near as well in the summer because the outside air is not cold.
 
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