Running an inverter on 6-8 volts?

[48Rob]

All the inverters available (that I've found) are designed to take 12 volts, and produce 120 volts.

Can these inverters be adapted to take 6-8 volts instead, and still produce 120 volts?

Rob

[Q]

No.

Q

[Trackstriper]

Rob,

What are you trying to do? Are you looking to have 120v AC in the Cabin Car, although it may be sometimes pulled by a tow vehicle with a 6v system?

If so, you might consider using two 6v golf cart batteries. With some creative switching you could have the batteries hooked up in parallel and charge them with a 6 volt system. While camping, the batteries could be switched to a series connection for 12v output and you could use a standard inverter. Also, you could also keep the batteries in series and charge with a 12v tow vehicle. I suspect that the Cabin Car is not light and would not be upset with the weight of two batteries. You might also find 6v deep-cycle batteries that are smaller than the 200-210 amp/hr golf cart units if weight is a concern.

You'd have to stay on top of the battery charging configuration so that it was correctly set for the correct tow vehicle voltage. It would not be idiot proof. Some of the electrical guys could advise on correct high load switches.

Hope this is where your question was leading.

J.B.

[48Rob]

Q and JB,

Thanks for the replies!

I have a 120 system in the Cabin car, as well as a 12 volt system run by two 6 volt golf cart batteries, and both work very well (but thanks for the tips!).


I pull the trailer about half the time with a 6 volt car, but that isn't an issue either.

What I'm trying to accomplish, or am thinking about... is using a 2000 watt inverter to run the a/c.

It works well of course when connected to shore power, but usually don't have any to connect to.
A generator would work, but they are expensive, and I have to store it.

An inverter sounded like a reasonable compromise.

Changing the car to 12 volts isn't something I'm interested in.

Of course I could run the inverter off my trailers battery system, but only for an hour or so before the system went dead.
I could charge the batteries with the 6 volt car, but it would never keep up, and begins to get complicated and labor intensive.
I just want to start the car, plug in the a/c, and relax.

It was just a wild thought...if 12 volts can be magically transformed into 120 volts inside a little box, why couldn't 6 volts...


Rob

[Trackstriper]

Rob,

I'll have to defer to real world input from the electrical guys ('cause I'm only dangerously knowledgeable) but this is what I think you're up against:

a) I have not searched the internet to see if a 6 volt inverter is available. A 6 volt inverter could be built, but I think the problem is that there is no/very little commercial need for it so it won't fly economically. Average man has 12v in his car or truck or boat. My impression is also that inverters, like automotive electrical systems, work more efficiently at higher voltages. Like a golf cart, 40-50 volts DC might be a sweet spot. It would not be reasonable to redesign a $200 inverter to work on 6v, thus Q's answer.

b) Let's assume that the AC unit that you have is 5000btu and draws 5 amps at 110 volts, yielding about 550 watts. If you need 550 watts at 12 volts it would require about 45 amps....factor in inverter efficiency of 85% and you'd need to feed the inverter about 55 amps when the window shaker is running. Can your car's generator/alternator provide that kind of amperage at idle? The alternator draw would be buffered somewhat by the batteries if the air conditioner cycles. That is, if the AC unit ran for only 50% of the time, the car would only need to resupply the batteries 27 amps on a continuous basis. That might be doable...but is the Cabin Car insulated? It looks like you have an uninsulated roof with exposed spars but that's only what I see in the photos.

c) Do you want to have your car engine idle for relatively long periods of time to run a small generator? This is generally tough on engines. You also might need to bump up the engine idle rpm to get sufficient alternator output. How much fuel will you burn idling the engine?

d) Carrying enough battery capacity to run more than a couple of hours is not reasonable due to the weight.

How about getting the generator. If you have a 5000btu AC, you could look at the small, quiet 1000 watt inverter generators...half the weight of a single golf cart battery. I know they're spendy because I haven't spent the money for one yet, but it's on my need to have list. I tried the Honda EU1000i at an RV show and it would run my small AC unit just fine. The Honda EU2000i has more grunt and will run more tools for just a little more money, but it is also bigger and heavier. When the time is right I will buy the EU1000i to do the dedicated job of running my AC. Lots of information on various generator discussion threads.

I know this is long and windy. I work as a contractor and have to be at job sites that typically don't have power where I am. I use a 750 watt inverter in my van for most of my 110v AC needs...no big tools to run. I also have a sleeping compartment in the van and have been struggling with this air conditioning issue. How to run an AC without the land line. Idling my van and running dash AC just wastes fuel and tends to tax the engine's cooling system. But it's simple and that's what I do to get a break from the heat for a half hour here or there. It's not a good solution though. I'll be reinstalling a window shaker in the mid-section bulkhead and get that generator one day. The $$$ are the impediment, I have a budget too.

I hope this will help you in some way. If I'm wrong somewhere, I'm sure someone will politely point it out. That's what is great about this forum. We can all learn a little more about our common issues. When I first saw your Cabin Car's photos a number of month's ago, I called my wife in from the other room and said "Wow, look at this trailer. Isn't that so cool and classy?" We lived in a small log home for two years and your trailer reminded us of that time.


J.B.

[Q]

The only way I can think of to do what you want would be to install a second alternator on the vehicle. A 100 amp or larger truck alternator with a couple welding cables to the cabin car battery. The alternator would just charge the cabin car battery and not be connected to the vehicle electrical system at all.

Or you could build an engine/alternator using a 5 hp engine driving a truck alternator that could be run to charge the cabin car battery, then use the inverter as desired to run the air conditioner.

Q

[48Rob]

JB and Q,

Thank you again for taking the time to think it over and reply!

JB, your reply is well thought out.

As you suspect, it is not insulated.
The 5000 btu a/c does a great job if the trailer is in a bit of shade, and will keep up if in the sun, but it doesn't cycle much...

The biggest problem with this whole situation is me...
I'm cheap.
I can't see spending over a thousand dollars for a generator to run the a/c for two-three nights a year.
I didn't have a problem spending more than 6 grand for parts to build the trailer, but it went for something that will last me 50+ years.

Guess on the next trailer I'll have to break down and build a generator in like the big boys do.

I've been reading with interest all the threads about running a 5000 on a 1000, and it seems right on the edge...
It works for some, but it sounds like a 1500-2000 would be a safer bet.

I run a 750 in my truck too, for remote power needs.
I could justify the larger inverter, and then use it in the old car as well.

I understand the economic reasons for 6 volt systems being left in the cold, was just hoping there might be some electronic doo-dad that would make it all work.

Q,

Your engine/alternator idea works, but by the time it was built, it would be as large or larger than a compact generator.
Part of the issue here is weight and space.
The roadster has a small trunk, so the power plant has to be small.
I have a 2500 and 6000 generator now, but they are way too big to put in the trunk...and noisy!

The second alternator idea is a good one, and holds promise.
Just have to decide if all that work is really warranted for a few nights a year.


Thank you for your replies!

Rob

[brian_bp]

I would vote for the separate generator, but if that's out the second generator on the car engine would be a workable second choice. My only suggestion for that would be to mount an inverter in the car, with very short cable to the add-on alternator, and send the 120V AC the longer distance. If the intention is to charge the trailer battery as well (running the air conditioner on the car-mounted inverter when it's running, and the trailer-mounted/battery-supplied one when the car is not running), then a "smart" charger running on the AC power will do a better job pf charging than directly connecting the extra alternator, especially through long cables.