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Author Topic: all electric class B  (Read 728 times)

rothskeller

  • Posts: 4
all electric class B
« on: January 07, 2018, 06:16:37 PM »
I'm researching to buy my first RV, and there's something I don't understand.  Several of the manufacturers offer lithium battery systems that, as far as I can tell, have sufficient capacity and sufficiently fast recharge that they could reasonably power all of the RV systems heat, A/C, cooking, hot water, etc.  For example, the Roadtrek/Hymer models offer 400Ah Lithium batteries that recharge in under an hour.  So why, then, do virtually all of these RVs still have propane systems as well?  In my research which was limited to class Bs under 22' length, my purchase criteria I found only a single model that was all electric (the Winnebago Revel).  And it doesn't suit me for unrelated reasons.

Have I misunderstood something about the power needs?  Let's say a ceramic electric space heater runs about 1500W, and let's figure it runs 50% of the time for 6 hours a day.  (The rest of the time, I'd either be driving or out doing something, not in the RV.)  So, if I've got the math right, that's 375Ah for a day.  Add in the various other power consumers and let's figure I'd need to charge the batteries twice a day.  Roadtrek says that takes about half an hour (200A charge rate, parallel across four 100Ah batteries).  Running the engine for half an hour, twice a day doesn't seem too onerous?  (And maybe less than that, with solar?)

It's pretty obvious I'm missing something fundamental here; the entire class B market can't be completely wrong: there must be some reason why everyone still runs propane.  :-)  Can someone clue me in as to what I'm missing?

SeilerBird

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Re: all electric class B
« Reply #1 on: January 07, 2018, 06:21:28 PM »
Propane is a lot cheaper than electricity.
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TonyDtorch

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Re: all electric class B
« Reply #2 on: January 07, 2018, 06:35:36 PM »
electricity is almost free if the sun shines on you.

rothskeller

  • Posts: 4
Re: all electric class B
« Reply #3 on: January 07, 2018, 06:48:51 PM »
Propane is a lot cheaper than electricity.

In terms of running costs, I'm guessing you mean?  I'm surprised.  The energy content of gas is about 25% higher than propane, and burning gas to charge batteries loses maybe 20% of the energy, so I'd expect to use roughly the same amount of gas as propane for the same heating.  And the price per gallon for each is pretty similar as far as I can tell.  So why is propane a lot cheaper?  I'm sure you're right but I don't understand why.

rothskeller

  • Posts: 4
Re: all electric class B
« Reply #4 on: January 07, 2018, 06:53:30 PM »
electricity is almost free if the sun shines on you.

And the times when it doesn't are the times when you most need heating.  :-)

Isaac-1

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Re: all electric class B
« Reply #5 on: January 07, 2018, 07:00:57 PM »
Where do you get that 20% energy loss converting gasoline to electricity number? From a thermal efficiency standpoint a typical gasoline engine is about 20-30% efficient with some newer designs pushing 40%, take another hit converting to electricity and then battery charge losses.  So when it comes to cooking, heating water, or heating the cabin propane is a reasonable choice.
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SeilerBird

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Re: all electric class B
« Reply #6 on: January 07, 2018, 07:07:38 PM »
In terms of running costs, I'm guessing you mean?  I'm surprised.  The energy content of gas is about 25% higher than propane, and burning gas to charge batteries loses maybe 20% of the energy, so I'd expect to use roughly the same amount of gas as propane for the same heating.  And the price per gallon for each is pretty similar as far as I can tell.  So why is propane a lot cheaper?  I'm sure you're right but I don't understand why.
I don't know or care why propane is cheaper. I have been RVing all my life and comparing running a refer on propane to electricity is a no-brainer. An all electric refer running on battery power would last me about 6 hours. On propane a few weeks.
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TonyDtorch

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Re: all electric class B
« Reply #7 on: January 07, 2018, 07:22:46 PM »
And the times when it doesn't are the times when you most need heating.  :-)

it's an RV, ......Just hold down the Home button on your Iphone and ask Siri for   "Directions to Perfect Weather USA"  ... 8)   
« Last Edit: January 07, 2018, 07:36:08 PM by TonyDtorch »

rothskeller

  • Posts: 4
Re: all electric class B
« Reply #8 on: January 07, 2018, 07:42:09 PM »
Where do you get that 20% energy loss converting gasoline to electricity number? From a thermal efficiency standpoint a typical gasoline engine is about 20-30% efficient with some newer designs pushing 40%, take another hit converting to electricity and then battery charge losses.

The 20% I quoted was for the last item you mentioned, the battery charge losses.  I'm afraid I neglected the other factors you mentioned.  I knew I was missing something!  :-)

Thanks, all, I can see now why one doesn't find all-electric.  On a related note, however, I have seen some manufacturers that use the chassis fuel (diesel or gas) for heating rather than propane (some called "Alde" or "Espar", if that helps).  Where does this fit in terms of running costs?

TonyDtorch

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Re: all electric class B
« Reply #9 on: January 07, 2018, 08:12:20 PM »
 Seilerbird (Tom) is actually right.

RVs makers perfected the propane heating, hot water, and refrigerator systems decades ago.

IMO..   the RV switch over to all electric is still kinda a work in progress.
« Last Edit: January 07, 2018, 08:21:04 PM by TonyDtorch »

Lou Schneider

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Re: all electric class B
« Reply #10 on: January 07, 2018, 08:44:31 PM »
It's a matter of energy density and convenience.

Propane stores an incredible amount of energy in a compact package, 91,000 BTU/hrs per gallon.

A 12 volt, 400 amp hour battery pack stores 4.8 KwH.  At 3412 BTU/hr per KwH, that's 16,300 BTU/hrs.  Or as much energy as about 3 cups of propane, less than one of those little disposable canisters.

I'd rather fill a 20 gallon propane tank once a month than have to run my engine for a couple of hours each and every day to produce the same amount of energy.

To replace 4.8 KwH in one hour requires 4800 watts.  That's 40 amps at 120 VAC, ignoring conversion losses.

I've yet to see a 12 volt alternator that will put out even a fraction of that amount of power at idle, so to you're talking about putting a Greyhound Bus size alternator in your Class B and running the engine at highway speeds for a couple of hours a day.  There's a big difference between an engine quietly idling in a campground and one that sounds like it should be out on the highway.

Then there's the costs of running a several hundred horsepower engine to get the 5.5 HP it takes to drive a 400 amp alternator.  Besides the wear and tear on the engine, you'll burn far more gasoline ($$) than you would to buy an equivalent amount of propane to use directly.

Use the most efficient fuel for the job at hand.  Propane burns cleanly and excels at producing heat, which is why it's so popular for heat producing appliances (stove, furnace, water heater, refrigerator).

Use electricity where it's the superior energy source.
« Last Edit: January 11, 2018, 08:21:19 PM by Lou Schneider »

newfurrows

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  • Dan Nelson
Re: all electric class B
« Reply #11 on: January 08, 2018, 03:37:42 PM »
One very serious consideration here is the low efficiency of the automotive alternator.  Makes running the engine to charge batteries an expensive business.  Better to run a small generator to power a good battery charger.
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JosephGrey

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    • Living On The Stealth
Re: all electric class B
« Reply #12 on: January 11, 2018, 05:36:40 PM »
In addition to these other comments, sure electricity is free when the sun shines.   I have a theoretical 540 watts of solar on the roof of my van.  In the wintertime the very, very best I have ever seen it put out is 160 watts for maybe an hour during the brightest part of a really clear, sunny, day.

To provide enough solar to run that 1500w electric heater you would need to be pulling a fairly long trailer of solar panels.

Oh, also, btw 400A/H of batteries only has 200A/H of usable electricity in them. 

--jg
Blogging my Stealth Camper build.  Check out the whole project at http://livingonthestealth.blogspot.com

gravesdiesel

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Re: all electric class B
« Reply #13 on: January 12, 2018, 08:46:28 AM »
Homeowners have also known for years the superior heating efficiency of propane (and natural gas).  I have a propane water heater, stove, clothes dryer and furnace in my house.  I love all the propane appliances I hook to the the TT also (Blackstone griddle, portable two eye burner, grill and old school Atlanta heater).  We are camping this weekend and the temperature will be below freezing most of the time.  These things sure come in handy!  With my new setup, I can hook two appliances up at the same time.  I know it is personal preference, but I would choose propane over electric any time.
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1996 Dodge 3500 extra cab flatbed 4x4 diesel 5 speed
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Many other diesels on the farm!

 

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