Electrical system design questions

[Anhedonic]

Lead acid batteries are different from other chemistry batteries.  

Thank you most kindly. This was extremely informative. I knew some of what you said, though not all the detail you included. I was hoping to work around the limitations by ultimately spreading the whole thing out among a bunch of individual cells so that the large draw would be pulling from each only partially, but it sounds like that might have been a bit optimistic.

 

[Anhedonic]

one more time,  idling a gasoline vehicle engine overnight is going to seriously shorten your engine life.  gasoline vehicle engines are not designed to idle for long periods of time.  I hate to keep harping on this but relying on your vehicle engine to power an AC is a very bad option.

your alternator,  solar charge controller,  and better battery chargers all have built in regulators to regulate the charging current.

I appreciate the advice and don't mind the repetition on an important point. I'm not really a "car guy" but I was honestly hoping that, since I won't be full time, that a week or two here and there running like that wouldn't be so terrible. It sounds like my guesses might not have been correct. 

Thanks also for clarifying the regulator. I was concerned that I had somehow forgotten a vital component.

 

[John61CT]

Sorry, is this really just for occasional use, like vacation trips only?

I thought fulltiming. . .

 

[Anhedonic]

I'm really hoping to take some trips lasting as much as a month, but pretty much yeah, though this is also my daily use vehicle. I didn't think this would be a viable solution for full time.

 

[John61CT]

OK, well a month at a time off grid needs the same design as full time dwelling.

So what is your thinking now?

A. run a genset when aircon is on

B. stay at powered campsites when aircon is needed

C. spend thousands of dollars to enable running aircon off batteries

?

 

[Anhedonic]

I do wish it were that simple. I need the wheelchair and the AC because I have heart problems. If it were *just* the AC, I might choose option A, but I've got to come up with about 100ah @ 24v if not more every day for my wheelchair...

I suspect it will have to be mostly A. B isn't an option because most places I want to go will not be camp sites with hookups. C isn't an option for me because who can afford that?

The generator will get me going, but it will remain to see how flexible a solution it will be and that does grieve me. It is certainly a frustrating thing to have to work with so many limitations and requirements.

What I'm going to do now is work with the generator and try to think of ideas that will supplement it to make it more workable.

 

[John61CT]

Well super insulation will empower a very small aircon unit to be more effective.

Then surplus energy is available to charge a battery bank at the same time.

Ideally LFP so you don't need any solar. Or just replace a lead bank more frequently.

But to actually accomplish even the cheapest option will not be cheap, certainly several grand just for electrics, not counting labor costs if you can't DIY.

Make sure to also calculate the per-hour fuel costs.

As I said cheaper to stay in a low-rent S&B, grid power is a very tiny fraction of the cost of an off-grid setup for high-consumption needs like this.

Better to be frustrated and not waste your money than to be frustrated and have none left.

 

[Anhedonic]

A friend is coming over to help me insulate this afternoon.

Unfortunately, LFP is clearly far out of my price range. At this point, I'll probably have a 200ah AGM battery bank for running things like the vent fan, the CPAP, and eventually a refrigerator when I can afford one. When I have to charge the chair or run the AC, I'll just have to find a place I can either plug in or run my generator. It kills the option of going out to the middle on no place for longer periods, but it is what it is.

I will be adding solar at some point, when I can save up enough for it, though I have no idea when that might be.

 

[John61CT]

Good on ya for facing reality, especially since your budget is that limited.

Spend some time learning how to semi-DIY LFP while saving up for it.

Since you need to run the genny regularly anyway, that chemistry will let you capture the charging output so much faster, that as you build up your AH capacity you will directly reduce expensive runtime.

You may not ever get big enough to be able to run aircon off the bank for more than a few hours at a time, but for all your other needs, if following the 60°s, you may get by just running it an hour a day.

With big AH/day requirements, solar is pretty useless, other than helping a lead bank last longer, but since that will only cost a couple hundred bucks, and will likely last at least a year, probably better to keep your eyes on the LFP target.

Of course, getting access to shore power solves all electrickery problems, so also focus on getting creative to get that cheaply.

 

[Weight]

Unfortunate, what you want is going to be expensive. The least would be a portable generator. You could run a small air with a 2000w such as Honda. Then you have to deal with fuel for the generator. Gasoline cans or propane bottles. A more costly solution would be a built in generator such as found in RV Campers. That would use fuel from your vehicle fuel tank eliminating carting, storing, and pouring extra fuel. The push button start would be nice.

 

[John61CT]

Nice thing about the quiet little portables is the ability to put it off in the woods far from the van.

The Frigomar I mentioned will apparently run 16000 BTU off 2KVA, usually under 10A and no surge issues, and very quiet.

Around $3500 though.

 

[Anhedonic]

I think at this point, I'm going to go ahead with my old generator plan:
https://vanlivingforum.com/showthread.php?tid=32284

A number of you chimed in on that. Since then, I have done more research and found similar things being done in travel trailers as well as in other, non-mobile applications that indicate that it can be done both well and safely.

I really did just want a solution that didn't depend on toting around a ton of gasoline and installing another non-negotiable 8+ cubic feet in the van.