Generator vs Car - Fiberglass RV


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Old 03-04-2009, 06:45 PM   #1
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This is probably a basic question, but here goes. Reading a few recent threads about portable generators, and not knowing much about the technical side of it all since I've never been close to one myself, I was wondering whether a car can be considered as a viable long-term alternative to a portable generator. The way I see it, a car is more quiet, has a much larger gas tank, and does not require any extra handling of equipment or fuel. Wouldn't a car run cleaner than a generator and provide more than enough power? I'm pretty sure I'm missing on something, but I'm not sure what yet. What if direct car battery hookup was used? If it is indeed a viable option I could see, for example, a remote car starter as an auto-starting cheap generator. So how many watts are we talking about? Could a car realistically replace, say, a 1000W portable generator?

(On edit): same question asked differently could be "what is the maximum size inverter you can put on a typical car, and would it be more or less efficient than a same capacity portable generator".
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Old 03-04-2009, 07:31 PM   #2
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I am no expert on auto electronics, so I will leave the "how much" answers to someone who is. Most folks use thier generators to provide AC, however, and your car will only supply dc.. so an inverter would indeed be required. How MUCH it can supply to what size of inverter.. I restate.. an expert, I ain't.

That said, I have used my car for emergency power more than once. I have had batteries fail, and less than desirable solar weather so my battery charging has been compromised.

I use the car when I take a shower under these conditions, to run the water pump. And sometimes, if a TV thing is needed (Most the time I live without) I will run the car long enough to do that.

But, Do you really want your engine idling for extended periods? It's gotta be hard on the rig. As mentioned, I use it in a pinch, but would not rely on it as a soul generation source.
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Old 03-04-2009, 07:42 PM   #3
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We have 2000 watt inverters on our work trucks, we power lots of equipment and charge batteries.
But they are on noisy diesels, which when idleing, uses very little fuel. Now gas on the other hand, uses more fuel and could have a 2000 watt inverter/generator hooked up. THe problem to me, of using your vehicle as a generator would be fuel consumption. My 2000 watt Honda will idle all night, 7 or 8 hours on less than a gallon of gas, your car would use gallons for the same time period..

Now just letting it run to charge a battery I am not sure, but it will use more than a generator.
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Old 03-04-2009, 07:45 PM   #4
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But, Do you really want your engine idling for extended periods? It's gotta be hard on the rig. As mentioned, I use it in a pinch, but would not rely on it as a soul generation source.
Thanks Gina, and I agree with you on the idling. But I'd imagine people don't typically leave their generator running for extended periods either. How long do you think you'd have to leave your vehicle running to replenish your trailer batteries if you weren't running anything else? Would it be much longer than a generator?

I guess what I'm trying to figure out is whether it makes more sense to use the car's alternator to recharge the trailer's battery(ies), or to get a generator to do the same thing. My biggest concern being noise levels vs duration, then fuel economy.
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Old 03-04-2009, 08:34 PM   #5
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You can likely get away with idling your TV in CG with NO Generator signs...
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Old 03-04-2009, 10:50 PM   #6
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You can likely get away with idling your TV in CG with NO Generator signs...
Not if "El Gringo" is camped next to you...
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Old 03-04-2009, 11:00 PM   #7
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using the car to actually get a reasonable charge on the battery is a losing proposition. It takes several hours of driving to bring a battery back up IF you aren't running the fridge on the road.

I had a bad solar couple of days in Quartzsite last month. I ran the car for 1/2 hour or so and it gave me maybe a couple hours of TV watching at nite and enough to run my LED fixtures only + an occasional turn on of the water to wash a dish.

during the day, I let the solar take over, but I didn't get a full charge and ended up huddled in the rig with a blanket, a puppy, and my black cat.. + a good book and internet. (Forced relaxation!)
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Old 03-04-2009, 11:47 PM   #8
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For what it is worth, I just dont immagine that the car is an efficient charger. The primary function of the car's engine is to move thousands of pounds. It has attached a generator/alternator (there is a difference, I think) that can charge a battery. However, as I said, it is an accessory, rather than the main purpose or function of the car's engine. It is an afterthought, not its reason for being.

For comparason, a generator's engine is designed to only to generate electricity. I would think that if the goal is to generate electricity, a generator is your best bet.

The other question that comes to mind is "why". What is the goal? Do you want to power the camper/run things or recharge batteries. If I wanted to run the camper, then the Honda generator will run the AC and (well 'or') microwave a lot better than my car would. The generator/alternator (whichever it is) in the car is just not effective.

As a practicle example, I was in NM in November and it got to 9 degrees. I dont have the furnace option as I didnt think that I would ever be stupid enough to be camping in 9 degree weather! I ran the honda to keep the heat strip going. Had that failed, I guess that I would have slept in the TV with the engine and heater going. The car could not otherwise have powered the camper enough to warm it.

In rereading the original post, I dont think that you can compare even a tow package equipped car's alternator with a honda generator. The alternator in the car just isnt likely of comparable size of the honda. Of course, if you dont stay in one place too long, you can eventually recharge the battery if you travel far enough.
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Old 03-05-2009, 06:54 AM   #9
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This is an interesting question for sure and the tough thing about it is ones view of what "Efficient" means I think?

All we are really talking about is supplying a 12vdc charging voltage to a battery.
So the most direct method of doing this would seem to be the most efficient?
Or would it?
If it were just a simple matter of charging with the most current,the fastest then it may seem the Car method would be best. But this can oversimplify things to the point of the untimely destruction of your batteries......if you believe in properly charging and conditioning RV House Batteries.

Smart Charging and Conditioning relies on a series of different charging currents and durations often with the charger sampling the process and adjusting as required.
When using the car connected directly to the battery to charge there is a sufficient bulk charge rate supplied but it will remain constant and never taper or change to create a "Smart " charge. Connecting a generator directly to the battery has the same effect but the Honda for example will only deliver a 8amp DC unregulated charge current where most cars could deliver easily three time the current to bulk charge.

Now if instead of direct battery charging you wanted to use the Trailer to charge the battery just as if it were plugged into house power,the nature of your onboard charger will determine the rate and type of charge.
Whether connected to a genset or car for this,both would have to use an inverter of some type to connect from house power or 120vac.
Gensets have inverters built-in or generate the AC power as that is what they are about. Using an inverter on a car to supply AC power is literally making 12vdc to use an inverter to make 120vac to power the trailer which will then make it back into 12vdc to charge the battery. Does this sound efficient?

Does it sound like saving the $1000.00 over buying the Generator?

Kind of depends on what you really consider "Efficient" to mean doesn't it?

Considering that we all already have vehicles and likely an inverter this has to be a consideration.

I feel rather strongly about battery conditioning but only because I have 4 expensive batteries.
I will not install them or charge them in my Scamp until I can provide all of the required gear to charge and maintain them properly so until that time I see no compelling reason not to use the most convenient means available to get a quick bulk charge if needed and the direct car connection should certainly deliver that.

I do however own a Honda 2000 Genset and really like just running the trailer from it as needed and not giving any other thought to it than I would while plugged in anywhere other than keeping gas in it.

I guess what I am trying to say is that you really need to understand the process to ask yourself some basic questions before deciding which way to go here.

I love this stuff though.

Ed
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Old 03-05-2009, 08:02 AM   #10
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This is a frequently discussed topic for which even a casual search would turn up many opinions. But, like the old firehouse dog, when the bell rings I reflexively rise to the occasion.

Based on actual tests done with amphour meters and hours-long drives towing the trailer I've decided that for my trailer (Casita), my tow (F150 w/trailer tow package) and the physics in my universe, the tow vehicle makes a lousy trailer battery recharger. In oversimplified terms, it boils down to the tow's voltage regulator and what voltage it sees in a two battery system (tow vehicle battery and trailer battery). That combined voltage matters because it determines how many amps the alternator will put out and for how long.

Now, if you yanked the battery out of the tow, pulled the trailer battery and installed it in the tow and then run the tow you'd up the efficiency considerably but probably never approach that of even the least efficient converter/charger.

Or you could go the two alternator route. Spend the money for the marine alternator and the marine multistage high efficiency voltage regulator (I'm thinking Balmar) and I think you could duplicate the charging efficiency of the better 120v powered chargers. But, more expensive than a Honda or Yamaha 1000 generator.

I was thinking that at 60 mph my truck gets about 15 mpg. That works out to be 4 gallons of gas per hour. Idling, I'm thinking about 0.5 gallons per hour. I remote start my truck in these single digit mornings and it runs for about 10 minutes before I go out the door. I really see the effect on the gas gauge. 0.5 gallons per hour at idle seems about right to me. My Honda 1000, running on the eco throttle setting will return about 25 amphours to my trailer battery through the Casita's converter/charger in about 3.5 hours and there will still be plenty of gas left in the 0.6 gallon tank.

I don't see the tow vehicle as more efficient from a charging scheme or from fuel usage. And inserting an inverter to convert 12vDC to 120vAC to power a charger running on 120vAC to generate 12vDC and all the inherent inefficiencies that suggests kinda makes my head hurt.

A word of caution, and again it really only applies to my universe, but I've seen claims about running the tow vehicle for a couple hours and reading high voltages at the trailer battery and feeling that based on that reading they've recharged their batteries. A battery has to rest for 30 minutes to an hour after charging or discharging before the voltage reading accurately reflects the state of charge. Besides, 25 amp hours out needs 25 amp hours back in (more than 25 to be accurate) to be recharged fully. As I mentioned earlier, it takes about 3.5 hours for my trailer's 45 amp converter/charger to recharge the only battery it sees and it was designed to recharge deep cycles.
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Old 03-05-2009, 09:49 AM   #11
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but would not rely on it as a soul generation source.
Isn't that why some people buy red sports cars? For their "soul" ?
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Old 03-05-2009, 10:03 AM   #12
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Seriously, though...keep in mind that there are huge losses while running your vehicle, as opposed to a generator whose sole purpose in life is to charge your batteries or run your television. The engine on your vehicle, while appropriately huge to move thousands of pounds of metal, also runs or is designed to run its transmission, a/c, heater, wheels, etc.
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Old 03-05-2009, 10:40 AM   #13
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This is probably a basic question, but here goes. Reading a few recent threads about portable generators, and not knowing much about the technical side of it all since I've never been close to one myself, I was wondering whether a car can be considered as a viable long-term alternative to a portable generator. The way I see it, a car is more quiet, has a much larger gas tank, and does not require any extra handling of equipment or fuel. Wouldn't a car run cleaner than a generator and provide more than enough power? I'm pretty sure I'm missing on something, but I'm not sure what yet. What if direct car battery hookup was used? If it is indeed a viable option I could see, for example, a remote car starter as an auto-starting cheap generator. So how many watts are we talking about? Could a car realistically replace, say, a 1000W portable generator?

(On edit): same question asked differently could be "what is the maximum size inverter you can put on a typical car, and would it be more or less efficient than a same capacity portable generator".
Sorry if someone answered this like I will because I didn't read *all* of the responses.
A 2000 watt Honda EU is extremely quiet when switched to eco mode. Eco mode is low rpm and low output and extremely low fuel consumption. When the demand for juice goes up then it jumps out of eco mode and runs full bore until the demand falls back and then it idles down into eco mode again.
I think the problem you "may" have in inverting your car's DC is wattage over time. Not sure your alternator is made to do that but I just don't know.

Wondering if your idling diesel fuel consumption is comparable to the honda... mine will run all night on one tank of gasoline as long as the demand is no too high.,

Ron
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Old 03-05-2009, 11:47 AM   #14
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I'm pretty sure I'm missing on something, but I'm not sure what yet. What if direct car battery hookup was used? If it is indeed a viable option I could see, for example, a remote car starter as an auto-starting [b]cheap generator.
I think I may be on to the crux of the discussion.

Define CHEAP.

The mistake that many people might make here, is that since they already own the car, and they would have to shell out extra money to acquire the generator, the car option would be cheaper. "Free" vs $850-$1000 wins, right?

Not if you take into consideration of the TOTAL COST of each option.
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