12v questions for furnace in cold weather

[Rich W.]

Reminds me of myself about 14 years ago. I had one battery (can't remember the size) and an old 40-watt solar panel on the roof of my truck camper. I didn't know much about anything electrically-speaking, but knew I needed a solar charge controller between the panel and the battery. So I bought a cheap on/off controller (at the time all I knew was that it didn't cost much). After a few days out boondocking, my battery was nearly dead (well below 50%, I'm sure). I had some long jumper cables so I ran those from the truck's battery back to the battery compartment for the camper and left those connected for the 4-5 hour drive the next day. I was sure I'd be all charged up at my next stop. Lol. After running things for about 30 minutes it was down to where it had been the night before. That battery was soon worthless.

The following year I knew I didn't want to go through that ever again. I read up on solar, and put a system together while I was boondocking out in the desert. I bought two 109ah 6V golf cart batteries and wired them in series, put 190 watts of solar on the roof and bought a GOOD PWM charge controller along with a Trimetric meter to monitor the situation. Best thing I ever did. That system is still running today (almost 14 years later) and has never left me without power. Not even once. And the 2 six-volt batteries that are in it now have been there almost 8 years. They're getting weaker, but are still working.

You might want to look into something like this. It's such a relief not to have to worry about batteries going dead.

The link I posted above for battery monitors takes you to BestConverter - Converters, Inverters, Electrical Supplies, Electronics and they sell Trimetric monitors. They are somewhat primitive I guess by today’s standards but I had very good results with mine.

 

[gibsito]

The link I posted above for battery monitors takes you to BestConverter - Converters, Inverters, Electrical Supplies, Electronics and they sell Trimetric monitors. They are somewhat primitive I guess by today’s standards but I had very good results with mine.

I'm setting up another system now and have an MT-50 meter to go with the Epever charge controller. I am not sure how much it can do yet, but expect it doesn't have all the capabilities of the Trimetric 2025A in my other system, which is fine. But I'm curious, what features do these newer meters have as opposed to the Trimetric? I really don't know as I haven't kept up with the technology over the years. I've found the Trimetric to be an excellent way to monitor the system, with the exception of lacking short-circuit protection. I had to pull the original one off the wall while I was painting and somehow the wires shorted, which ruined it immediately. Expensive lesson.

 

[Redsand]

We're relatively new to modern day RV tech and opted to upgrade our '05 class c from a group 27 FLA to two AGM 100ah Renogy batteries with an Renogy shunt monitor. As I understand from numerous posts draining battery below 50% is very bad news for the long term life. We recently did some overnight camping with 12v propane furnace on overnight and a fair amount of evening TV with a 300w inverter and used around 30%. I know this is subjective and depends on so many variables it's impossible to say what is right for a given situation but I vote for at least two parallel 12v batteries for the average RV and solar if your budget allows. Lithium is by in large a better solution as they can be drained to almost zero without damage except to your wallet.

 

[gibsito]

We're relatively new to modern day RV tech and opted to upgrade our '05 class c from a group 27 FLA to two AGM 100ah Renogy batteries with an Renogy shunt monitor. As I understand from numerous posts draining battery below 50% is very bad news for the long term life. We recently did some overnight camping with 12v propane furnace on overnight and a fair amount of evening TV with a 300w inverter and used around 30%. I know this is subjective and depends on so many variables it's impossible to say what is right for a given situation but I vote for at least two parallel 12v batteries for the average RV and solar if your budget allows. Lithium is by in large a better solution as they can be drained to almost zero without damage except to your wallet.

Sounds like you've got a nice setup going. What do you use to recharge the batteries and do you have any problem recouping the 30% deficit the next day? Do you have LED lighting? I found that to be a big help in lowering my electricity usage. But yes, running the furnace overnight is going to use some power. The furnace in my truck camper pulls 2.5 Amps and sometimes I leave it on overnight too. I hate being cold. But my electrical usage is very low. The most I've ever drained my 200ah battery bank is 16%, which probably explains why the batteries are almost 8 years old and still going. I could have gotten by with one battery but wanted two in case I was ever in a situation where I wasn't getting any solar for days on end. I don't have a generator (and don't want one).

LiFeP04 batteries are much less expensive than they were just a couple of years ago, if you don't mind using inexpensive Chinese brands. I recently bought two Weiss 100ah LiFeP04 batteries with low temp cutoff for $299 each. It wasn't very long ago when you'd be hard pressed to find a similar one for less than $1000. I just installed them last week and so far they are working great. Of course time will tell how they hold up. They have a 10-year warranty, but if I have an issue with them I believe the shipping is on me, so not the best warranty but I decided to take a gamble on them.

Two years ago my sister bought a 100ah Interstate AGM battery for her Lance trailer. They were going for over $300 but she got it for around $250 when they were on sale. Of course Interstate is a well-known, reliable brand whereas Weiss is an inexpensive Chinese product, but it is interesting how the price gap is closing between the two types of batteries.

 

[TheLooks]

If I was going to go Lifepo4 I would opt for ones that allow me to "fix" them by replacing the cells inside. They are all the same inside, but most have cases that will not allow them to be opened.

 

[Redsand]

The first thing I did when we bought the rig last year was replace all the inside incandescents and running markers with leds. I didn't check how long to recharge from 30% loss but the next day after a four hour drive we were back at 100%. We have a 4k generator which recharges the house batteries in less than 30 minutes. I looked at lithium last year but appeared cost was way over benefit. In addition to batteries I would need a newer converter/charger system and chasis alternator. Granted one could just swap out batteries and hope for the best but seemed too many unknowns. I think I paid $200 ea on sale before the economy went wonky. My challenge was building another platform as it came designed for one battery. Tight fit but worked out well.

 

[TheLooks]

You may be right as you already had much of the system in place for LA or AGM. It cost $$$. But there is no comparison whatsoever with Lithium. People that like to live in a cave can make do and seem to enjoy the struggle with lack of power and the challenge of not using any power to live. Those that have been living in modern times and homes like the Lithium and large solar arrays along with a nice generator. Flip the switch and something comes on.....But it takes $$$ and maybe $$$$$.

 

[Redsand]

Amen

 

[gibsito]

Yep. It's nice that there are options for every kind of camper. I have a good friend who is comfortable in a mid-90s Ford van with a bed he made himself, an icebox, a camp stove and a modified insecticide sprayer for showers. Obviously, his power needs are about as minimal as you can get. I don't need much in my truck camper, but my wife and I are heading out in the 5th wheel next month for the first time, and I know we will use much more power than I'm used to. Time will tell how the system works.