How many here have more than 200 aH for battery power?

Wrinkledpants · 06-10-2016, 10:53 AM

In the planning stages for a Sprinter 4x4 SMB, high roof, 144. It'll have 200w solar panels, so not too concerned with summer camping. But, this will also be our weekend ski-mobile, and will spend nearly every weekend parked at a resort or TH for backcountry skiing during the winter months.

Our SMB will have a shower, and as such, will need to be heated the entire time. With that in mind, would a single 200 Ah battery be sufficient? While it'll have solar, there will be weekends where it snows and covers the panels. Will have a fridge, and all the usual electrical accessories that an SMB comes with. We're also flirting with the idea of going electrical for the stove, and my guess is that will put us into the 400 Ah range.

Our SMB will come with a high idle, but have not decided on a 2nd alternator. Wold prefer to not have to idle the engine, so if 400 Ah will do the job, but 200 Ah will not, then that would be our preference.

**daveb** · 06-10-2016, 11:54 AM

The problem is that most AGM batteries are designed to be taken to 50% depth of discharge. That doesn't leave much room for items that pull high amps. When you figure a 1500 watt item like a hair drier or small heater pulls about 125 amps, something like that will suck down your reserves quickly. My microwave pulls over 60 amps on high and I'd never run it for any length of time w/o the engine running. I have two 210AH batteries.

Here is a pretty good web site that explains it:
RV Electrical Power for Dry Camping

Lithium batteries are a different story but are expensive.

1der · 06-10-2016, 03:13 PM

We did 5 weeks skiing out of our van earlier this year. Many times we had to stay in campgrounds because of parking restrictions. This provided hook ups.

We have 350 ah house plus 130 ah via engine Batteries, all AGM. 300 watts of Solar on the roof. I would not want any less. This worked great when we dispersed camped for days this past winter.

If panels are generating all is good. If panels are partial or none due to snow, etc., we have about three days if we are careful about conserving power before we have to start the engine to charge.

Your main issues will be keeping your lines and water tank from freezing. This is serious high risk if unattended for more than a day. Here is the way I look at it -
Cold weather and away at the at the TH or even all day skiing at zero degrees, means fridges are going to draw very little. You need a very reliable heating system which is thermostatically controlled and able to be set at about 40 deg. The heater fan will be the biggest draw. Hopefully all your fresh water plumbing is in the environmentally controllable space. Calc the fan draw plus the fridge x days away, add safety margin, then double that to get your battery bank size.

Gas or diesel, I would be looking at the Espar Airtronic Heaters. The hydronic a add pumps which increase the draw. If you are already doing propane, then you have other options.

Re: electric stove? - not for dry, disconnected multi day camping unless you want to run your engine or are bringing a generator. If you are not going propane, check out the smaller high quality butane units like the Iwatani.

Oh, and another big gotcha will be your battery bank at 10 deg F will have 37% less capacity than the 25 degree C rating, but your draws will still be the same. Eg a 300 ah (25 deg C)bank has a bit less than 200 amp capacity at 10 deg F. (Means 150 usable amp hours (50% of 300) becomes 100 amp hours just due to lower temps.

LenS · 06-10-2016, 05:53 PM

Do not know where you live but in winter the panels typically put out 20-30% of their summer value. Snow reduces it more of course.

LenS · 06-10-2016, 05:59 PM

Side note. Is there a rule of thumb for how large the alternator has to be for a 50% discharged house battery bank of X size? We have a 230 Ah house battery bank with a 100 amp alternator. Have not seen a problem but dream of going to 4 6v batteries that would have a total of 460Ah and IF we went to 50% discharge the alternator would have to provide 230Ah of juice to recharge those batteries while driving.

Abitibi · 06-11-2016, 09:19 AM

I noticed dhally's post in another unrelated thread and I think he mis-post it so I'm copying it here on his behalf...

Dhally
We have two group 27s, which is about 200 ahr. We can stay in a snow park two or three nights with our 8 gallon propane tank no problem. Or frig is propane too. The main load is the furnace, which we keep running all day.

Sent from my SGP511 using Tapatalk

arctictraveller · 06-11-2016, 01:46 PM

Quote:

Originally Posted by LenS

Side note. Is there a rule of thumb for how large the alternator has to be for a 50% discharged house battery bank of X size? We have a 230 Ah house battery bank with a 100 amp alternator. Have not seen a problem but dream of going to 4 6v batteries that would have a total of 460Ah and IF we went to 50% discharge the alternator would have to provide 230Ah of juice to recharge those batteries while driving.

Just to clarify, your alternator puts out amps, not amp hours. An amp hour is one amp for one hour, so you could replace 230Ah's with a 30 amp alternator by simply running it long enough. Bigger alternators put out more current (amps), so they can recharge the battery faster. Still, if you had a 230A alternator, you would not be able to put 230A's into your battery in a hour due to the acceptance rate of the battery. The acceptance rate dictates how much current the battery will accept, and that current decreases a lot as the battery gets closer to being fully recharged. The last 10 to 20% will take far longer than you think, but if you drive long enough you can do it.

As for having an electric stove, a generator will be manditory for more than a few minutes use a day, even with a large battery bank.

Wrinkledpants · 06-13-2016, 06:49 PM

Thanks guys. After reading through this and researching some more, we're still convinced electric will be the way to go, but now we're looking into wiring the SMB for lithium rather than your typical AGM. We've heard of a few people using diesel cooktops with mixed results, and we really really do not want propane for a variety of reasons.

I think as battery tech improves, AGM's will go the way of the dinosaur. Weight will be a concern for us as we would like a lot of water and a bigger fuel tank, so the lithium route seems the most appealing. A 300 Ah lithium costs around 3500, but weights 95 lbs. And, you can use the bulk of that 300 Ah without that life expectancy reduction for quick drawdowns. From a future-proofing standpoint, I don't see many people with a vehicle like this where weight is a concern still using AGM's in 10 years.

arctictraveller · 06-13-2016, 11:04 PM

Quote:

Originally Posted by Wrinkledpants

A 300 Ah lithium costs around 3500, but weights 95 lbs. And, you can use the bulk of that 300 Ah without that life expectancy reduction for quick drawdowns. .

There's no doubt lithium batteries are great, but be sure to look into how you intend to recharge them. They take a very well controlled charge routine that can cause big problems if things get out of whack. There have been many fires due to lithium batteries charging issues, starting with Boeing, Tesela, Hoverboards and lots more. Still, I see them getting used a lot more in the future.

Wrinkledpants · 06-14-2016, 08:47 AM

If we do lithium, it'll be with a proper lithium charge controller - the whole SMB will be built around the idea of using lithium. There are a few manufacturers of lithium batteries that offer a drop-in replacement to AGM's, and they have their own built in charge controllers.

I think the technology around lithium will only get better in the coming years, and hopefully that also means a lower cost.