Newbie advice

[ewarnerusa]

Agreed Wrybread. My RV solar experience has only been for about 10 years, but we never owned a generator with the first camper at all. I bought one to go along with our current camper with the intent of using it to run the air conditioner. Turns out it was just barely marginal for that due to us living at relatively high elevation and only wanting to use it when it is super hot out. So I quit bringing it with for the past couple years. This summer I bought a soft start kit for the air con (Micro Air) and I'm looking forward to having the capability to run it when desired.

I'd say a full time RVer that actually relies on using its appliances on a day to day basis throughout a year should have more of a priority on a backup. But for campers like myself who typically do it as a long weekend type of thing, it is very easy to get by without a generator and the emergency backup is hooking the camper trailer connection up to the tow vehicle and running the engine. I've never had to do that thankfully. I'm certainly not saying that having a generator is a bad idea.

[Wrybread]

I wouldn't call that opinion on generators universal. I've been using solar in RVs for probably 20 years and have never used a generator. The first thing I do when I get a new camper is rip the gennie out. But I don't need air conditioning. For everything except AC I don't see any reason for a generator. Especially if you've got good panels (I'm a big fan of 600 watts of solar for an Rv). That way even when it's cloudy you get a bit of a charge.

[littleharbor]

Any quality charge controller, if not all, will, once the batteries are near full will allow available amperage over what the batteries are drawing to bypass to your load. You don't need any add ons or switching apparatus. That being said you need enough solar power to charge your batteries AND power your daytime load, otherwise your loads will not allow you to ever be able to top off your battery.

[SunEagle]

Ok I see. Your plan is coming together then and you'll have a generator to bail you out if the sun doesn't cooperate.

Anyone that depends on a solar / battery system for electricity will eventually end up with dead batteries due to the weather not always being cooperative to allow you to use the sun to recharge.

A generator is not only a smart addition to your system but is necessary if you want to keep your batteries charged and run electrical appliances every day of the year.

[ewarnerusa]

Ok I see. Your plan is coming together then and you'll have a generator to bail you out if the sun doesn't cooperate.

[Carv]

I need the Genny for microwave, 1600 watt electric water heater, air conditioner, lights.

The solar is just to run the fridge & 12v lights and occasionally a TV/dvd and radio.

[ewarnerusa]

Why use a generator at all if you're putting this system together?
I don't know much about various controller features, but the Morningstar TriStar models will do diversion load. That isn't quite what you're imagining I think; it transfers array input to another load when not needed for charging such as a water heater element.

[Carv]

Yes I'm looking at 300 to 400 Watts, I'm only running the fridge, I'm usually out 3 days, never more than 4-5, and I have a generator I use to run other on demand loads.

Is there a controller that fills the batteries then uses the excess to run any draw on the system?

Thanks

[Wrybread]

There's a chart here showing how charged your batteries are based on their voltage at rest:

http://www.trojanbattery.com/tech-su...y-maintenance/

According to to that your batteries were about 30% charged when they were 11.8 volts. Which isn't bad for the type of use you describe. Grab a couple of ~300 watt panels and a controller and you should be fine. And if you find that you're under powered, you can make adjustments.

[ewarnerusa]

Well I have converted a mini stand up freezer rated at 1.1A to a fridge with a digital temp controller.

I did a test run off my 2 -6Vs in series through my pure sine wave inverter (no charging source) and it ran for 72 hours and only dropped the batteries to 11.8V at rest and 11.6 under load.

Based on this I think the set up will work just fine for my needs especially when I start feeding the system with a panel or two.

and as I stated earlier for the price of a propane fridge I can set up the whole system.

I am interested in finding a charge controller that with act as a switch and once batteries are full, it'll run the fridge off the excess when it's availiable. Do you know of a 30 or 40 A mppt controller that'll do this, that's reasonablly priced?

Thanks

Seems like you've answered your own question as to why running a compressor fridge with AC electric only is not favorable for boondocking. Although 3 days is pretty dang good, you've discharged those batteries to like 25% SOC. While you have interpreted these results as favorable, I see it as the fridge alone used more battery capacity than is available for a long weekend without even considering any other power usage that will be required. You're right that the solar will offset this, though. One answer is more battery capacity and therefore more solar to go along with more batteries. If you've got the space for more panels, the cargo capacity and space for more batteries, and the comfort of being able to make it through any long spells of poor solar harvest, then it should work.

[SunEagle]

Well I have converted a mini stand up freezer rated at 1.1A to a fridge with a digital temp controller.

I did a test run off my 2 -6Vs in series through my pure sine wave inverter (no charging source) and it ran for 72 hours and only dropped the batteries to 11.8V at rest and 11.6 under load.

Based on this I think the set up will work just fine for my needs especially when I start feeding the system with a panel or two.

and as I stated earlier for the price of a propane fridge I can set up the whole system.

I am interested in finding a charge controller that with act as a switch and once batteries are full, it'll run the fridge off the excess when it's availiable. Do you know of a 30 or 40 A mppt controller that'll do this, that's reasonablly priced?

Thanks

Dropping the voltage of a 12volt battery to less than 12volt is a sure sign of giving it a very short life. You really should never go below 12.4volts and 11.6v is not good.

[Carv]

Well I have converted a mini stand up freezer rated at 1.1A to a fridge with a digital temp controller.

I did a test run off my 2 -6Vs in series through my pure sine wave inverter (no charging source) and it ran for 72 hours and only dropped the batteries to 11.8V at rest and 11.6 under load.

Based on this I think the set up will work just fine for my needs especially when I start feeding the system with a panel or two.

and as I stated earlier for the price of a propane fridge I can set up the whole system.

I am interested in finding a charge controller that with act as a switch and once batteries are full, it'll run the fridge off the excess when it's availiable. Do you know of a 30 or 40 A mppt controller that'll do this, that's reasonablly priced?

Thanks

[Wrybread]

As far as powering a 125 - 200 watt fridge off your batteries, you could certainly try. The worst that'll happen, assuming you use appropriate sized wiring and fuses (which you must do!), is that you'll find that your batteries can't keep up, and then you can make the appropriate upgrades and changes. A lot depends on how often the compressor in your fridge is kicking on of course.

I made a system that powers my propane/AC fridge off solar when my batteries are fully charged and the panels are putting out more than 200 watts, details here (fair warning, the thread gets pretty mindlessly hijacked):

https://www.solarpaneltalk.com/forum...my-setup/page9

It works well as a way to minimize the amount of propane use and maximize the use of the power from my panels, and for me the most important part is that if my propane runs out while I'm away my fridge stays cold and doesn't turn into a science experiment mess. I'll probably post the code to my Github page at some point, but since it runs on Linux it still takes a bit of programming skill to install.

Personally I'm surprised the ability to turn on an external load after the batteries are fully charged isn't a more common feature on charge controllers. It's so close on these Tracers (the controllers linked above), since it already has an output that you can configure to only turn on when the sun is out, or not out, etc, it would be nice if they released a firmware update that added an option to power it when the excess power is being generated.

No matter what, you might want to get a battery monitor so you can keep track of your batteries' charge and get a sense of the loads. These work well enough and are super cheap:

https://www.amazon.com/bayite-6-5-10.../dp/B013PKYILS

And personally I'd confirm what the actual power consumption of your fridge is with one of these.

[Wrybread]

If you want to avoid propane another option is these trucker style coolers. They've come a long way and now have dorm-fridge sized units:

https://www.amazon.com/dp/B0012EGZ9S

They're very low power (60 watts) and work well. I've never owned one but I know lots of people who swear by that particular model, mostly because of the Danfoss compressor. Further reading including some mods to improve them:

http://www.cheaprvliving.com/forums/...y-usage-please

http://forum.expeditionportal.com/th...light=edgestar

I don't know how well the other trucker style units compare, but I'm guessing favorably.

[Carv]

Thanks for the post wrybread.

I'm putting together a similar system and was wondering why you say no compressor fridge?


I've done the math and a used propane 2 way (propane/dc) is $500 or more plus it's 60" tall and you have to run propane if you don't already have it.

A small mini fridge is rated at 1.1 to 1.7 amps and at 115 volts it's only drawing 127 to 196 watts when running and I can buy one for $50 and take the other $450 and build my solar system to run it.