Extra Batteries

[Shawn Kane]

Just wondering if you can use a regular car battery as extra power rather than the deep cycle types?

[Jim Stoltz]

Yes - 2 "traditional" propane-fired furnaces, each with a blower fan. The one in the bedroom is smaller - it just does the rear bedroom. The front furnace is much bigger and does the rest of the rig. Like the dual a/c units, running just the front furnace keeps the rear bedroom sort of comfortable. But in order to get that back bedroom really cool or really warm I need to run the rear a/c or furnace. The good thing is that I can close off the back bedroom at night and just run the small furnace. I sometimes need to keep the front one on very low to keep the plumbing from freezing up there tho. The good thing - and I'm sure that this is by design - is that both furnaces or their ducts occupy space where there's plumbing. Simply running the furnaces for comfort keeps every inch of plumbing warm, too.

[John "T" Nordhoff]

 Wow, if you have 2 furnaces each with a blower fan, then for sure Id go with 200 watts as those typical forced air units (unlike a no fan catalytic) suck a lot of power. Still, the thing is you need enough stored battery amp hours of to get you through the night REGARDLESS how much solar you have to recover the next day. Many of those furnaces have a safety feature whereby if the voltage drops too low they will fail to ignite although the fan keeps running and you wake up cold plus a low battery grrrrrrrrrrrr. Its easy to compute the amp hours if you know the amperage of the furnaces then estimate how many hours they run at night then compare to how many total amp hours your batteries are HOWEVER at X volts they may no longer operate so the calculations get fairly critical.

 John T

[Jim Stoltz]

Thanks John. I think I'd go with the 200 watt kit. The incremental cost over the 100 isn't a lot. I have 2 furnaces that draw the batteries down quick. When trying to conserve power I can close off the bedroom to keep it warm and turn the heat way down up front. I like the idea of keeping the batteries charged without running one of the engines (genny or the truck engine).

[John "T" Nordhoff]

  Jim PS, my buddy has what you referred to, he has two 6 volt deep cycle batteries and a 100 amp (moveable and can angle towards sun) Solar Panel. Okay, he can pretty well keep up, he gets enough solar energy in the day to re charge what energy his furnace runs at night. HOWEVER in the AM his battery voltage may be down to say 12 to 12.2 while with my four batteries and 200 watts of solar mine may just get down to 12.2 to 12.4. Then in the daytime his solar eventually gets the battery voltage up to say 13.2 while my 200 watt solar gets up to then regulates at 13.8 volts max. In good overhead sun I can get near 14 amps of charge while he gets maybe 6+.  BOTTOM LINE 100 WATTS WOULD LIKELY GET YOU BY but not as good as 200 in event there wasn't much sun and furnace had to run a lot at night. I wouldn't mess with less then a 100 or 120 watt single panel.

 John T

[John "T" Nordhoff]

Jim, your question isnt a hi jack because its battery related. How many watts of solar are required?? Of course, that depends on the panels angle to the sun, how much and how intense and how many hours of sunlight, your load etc etc. THAT BEING SAID I can tell you this. Unless youre using a furncace often the only daylight requiremetns are occassional water pump and vent fan and minimal lighting so it doesnt draw your batteries down that much. However if its cold and the furnace runs a lot at night plus light use in the night (plus water pump and fans maybe inverter) thats where you use up energy. I researched and did some calculations and for two of us I chose 200 watts of roofop solar and even in cloudy days or rain with 200 watts (and thats laying flat NOT optimal) we recovered any electrical energy we used up at night even in cooler location where furnace ran often. The thing is if you look at sizes and prices you would want at least a 100 watt panel but if you need furnace to run a lot and it may be cloudy or rainy 200 watts will get you by just fine. We dry camp a lot in the mountains and use the furncae at night and even when its been cloudy or rainy with 200 watts of rooftop solar we have alwyas kept up and could camp indefinitely and never run out of energy. However, I have 4 golf cart batteries for a total of 460 amp hours but with only 2 and 200 watts on the roof you could pretty well keep up based on my experience.

AGAIN it depends on sun and angle and load and your use so this may not be correct but a 100 or 200 watt panels is my suggestion for 2 people. I also recommend an MPPT Charge Controller.

pS the calculations are easy, compute the amp hours you use in a typical day,,,,how may amp hours of battery storage you have,,,,how many amp hours a solar panel can supply given x hrs at x angle at x watts theres your answer.....

ID GET 200 WATTS or more but with 200 we have never ran low

John T Retired Electrical Engineer

[Jim Stoltz]

Not to thread jack, but I was looking at solar panel kits recently. How many watts are required to keep a pair of 12V deep cycle batteries charged? I don't have an inverter - would just be running lights (all LEDs), water pump and furnaces when it's cold. If memory serves, running both furnaces can kill those batteries overnight. I have a generator, and the alternator will charge the house batteries in a pinch, but it would be nice to have solar power maintaining the batteries.

[John "T" Nordhoff]

   NOPE, Jim is exactly right. While an automotive battery will "work" to some extent, for house 12 VDC power RV use and dry camping you really should use a true Deep Cycle Battery, NOT an auto starting battery, NOT a semi deep cycle RV/Marine Battery, i.e. Golf Cart Battery is preferred. Of course, most are 6 volt, so you need to series two for the 12 volts required.

 An auto starting battery is designed to deliver very high current for a short time to crank the engine over, while a true Deep Cycle Battery is designed more for a long, slow, typically less current draw but deeper discharge cycle. Its the ability to still deliver current while becoming much deeper discharged (yet not damaged) then an automotive starting battery that's more accurately its purpose. The Marine battery (semi deep cycle) is designed to BOTH deliver high current to start those big honkin engines then still run the trolling motor for long periods.

 I'm running four 6 volt true deep cycle batteries in series/parallel for 12 volts and 460 Amp Hours of energy storage plus have rooftop solar panels and an Onan backup genset as we do a lot of long term dry camping in Utah and Colorado on BLM and Natl Forest and Natl Park grounds and love every minute of it being able to stay 7/8+ days with no hook ups before we start to run out of water and need to dump, but we never run out of energy with the batteries and solar.

 Sure, 2 or 4 or more Golf Cart batteries will cost you more, but if you do much extended dry camping (especially if you don't have solar panels) they are almost a necessity in my view. Ever pull into a Wal Mart enroute to Florida when its 20 degrees and the furnace has to run a lot and the batteries run down and you wake up frozeeeeeeeeeee lol You will be battery shopping the next day.

 John T  Yes, still a retired electrical engineer and attorney despite some peoples dismay lol

[Jim Stoltz]

Nope. If you look at the link, the deep cycle batteries are designed to provide consistent power over a long period of time and to be drained over and over again. If you treat a car battery the same way, you'll kill it quickly. I have a regular car battery feeding the A/V system and lights in my limo. It lasted about 3 months before it stopped holding a charge. Trying to charge it again pretty much killed my alternator, too. I'm on my 3rd 250-amp alternator in that car. I need to invest in a deep cycle battery.

I bought 2 new deep cycle batteries for my Allegro. They work awesome. They very rarely drain below 50% (furnaces kill them quicker than anything else). I haven't gone the 6-volt golf cart battery route yet, but my understanding is that's the way to go.

[Russell E Johnson]

Here is a link to an article that should answer your question:

http://auto.howstuffworks.com/question219.htm