Reply
 
Thread Tools Display Modes
 
Old 07-15-2015, 07:57 AM   #1
Junior Member
 
Join Date: Aug 2014
Posts: 9
General questions

Hi all, my wife and I just did a shop visit in Huntington, In and after talking things over later in the day came up with a few questions I was hoping you might be able to help out with.

1. I love the 7 cubic foot fridge but am concerned the energy use might be too great, would we be better off with a smaller one?

2. How long will an electric heater run on battery power through the inverter?

3. Can a toaster or a crock pot be run via battery through the inverter?

4. If we were to go with diesel appliances (much more expensive I know) will there be a residual smell of diesel fuel that hits your nose every time you enter?

Thanks for your help!
__________________

TallGuy is offline   Reply With Quote
Old 07-15-2015, 08:32 AM   #2
Senior Member
 
yvrr's Avatar
 
Join Date: Oct 2007
Location: Newark, CA
Posts: 795
Re: General questions

Note that the 7 CF refrigerator can only be installed in Sprinters. According to the SMB website, the amperage draw is about the same as the smaller one which is a little surprising/suspicious. We have a 4.6 CF Isotherm in our van and it works out fine for us. If we are gone for a week, we might eat lunch along the way several days and go out to dinner once or twice. We will BBQ something for dinner about half the evenings. We have been out for as long as 3 weeks in Mexico and only purchasd a few items along the way.

We have a propane heater in our van which has a very low-draw fan. With the top up and sleeping in the penthouse, the heater doesn't come on at night even when snow camping. A standard electric heater can only be used with a generator or shore power...electric heat is not very efficient.

Likewise, a crock pot that is left on during the day will drag down the house battery. You are probably fine with a toaster but Iwould want to keep an eye on the house battery voltage.
__________________

__________________
Jack
'01 Ford EB50p Quigley 4WD
yvrr is offline   Reply With Quote
Old 07-15-2015, 08:42 AM   #3
Senior Member
 
boywonder's Avatar
 
Join Date: Jul 2013
Location: So Cal
Posts: 2,952
Re: General questions

Quote:
Originally Posted by TallGuy

1. I love the 7 cubic foot fridge but am concerned the energy use might be too great, would we be better off with a smaller one?
From an energy point of view, smaller is better, since heat loss "into" the fridge would be less with less surface area. From a convenience standpoint, that's a question only you can answer.

I'm not familiar with the fridges that SMB is spec'ing, but the 3 popular sizes of Truckfridges that folks here commonly install all have the same size compressors/evap/condensers. None of those are near 7 ft3. The larger units will just take more time to cool down and use a bit more power due to heat loss.


Quote:
Originally Posted by TallGuy
2. How long will an electric heater run on battery power through the inverter?
Not very long.......only really viable on shore power. Let's take a 1200W heater for easy math....that's less than a typical blow dryer. Ignoring the inefficiencies of an inverter, 1200W at 12V draws 100 amps. So if you have a 100ah battery you will be 50% discharged in 30 minutes. As a general rule-of thumb, you only want to discharge lead acid batteries to about 50% before recharging.

So, best case 30 minutes.......let's assume your heater is 1200W at 120V (using the inverter) and let's also assume that your inverter is 90% efficient, then 30 minutes x .9=27 minutes.


Quote:
Originally Posted by TallGuy


3. Can a toaster or a crock pot be run via battery through the inverter?
Sure, just not very long.....these both have very similar power requirements to the heater example above, so they are only really viable on shore power. Same with an electric coffee maker. Toaster maybe, since making one batch of toast is maybe 3-4 minutes.

If you can handle lots of battery capacity and solar, you could get more time, but it will never be enough to run a crock pot or an electric heater for too long.
__________________
2008 E350 RB passenger 4WD SMB penthouse
2013 KTM 350 EXC
2008 KTM 250 XCF-W
2000 KTM 200 EXC
2003 Honda Element
boywonder is offline   Reply With Quote
Old 07-15-2015, 10:29 AM   #4
Senior Member
 
Viva's Avatar
 
Join Date: Feb 2012
Posts: 874
Re: General questions

Presuming both of the refrigerators are 12 volt compressor type fridges (not propane powered) I agree that a 7 cu. ft. refrigerator speccing the same draw as a much smaller one seems suspicious. If it WERE true, (and presuming the 7 cu. fit one is not the size of a barn due to miles of insulation), then the 7 cu. ft. one would have to have a much higher percentage duty cycle, meaning it would use more energy in the end. Here are a couple of examples of what I mean:

Example 1, from my Vitrifrigo catalog:

Vitrifrigo, a common brand of good-quality 12 volt compressor refrigerators, does have much higher draw spec on the 8 cu. ft than the 4 cu. ft. (they don't have a 7). This tells me they are using an appropriately larger compressor (probably a Danfoss 50 as opposed to a Danfoss 35). I would expect these refrigerators to have similar duty cycles (maybe a bit more for the larger one). By duty cycle I mean what percentage of a 24-hour period it's actually running, vs. coasting.

4.2 cu. foot = 3.8 amps. At 50% duty cycle this would be 45.6 amps used in a 24-hour period.
8.0 cu. foot = 5.38 amps. At 60% duty cycle this would be 77.5 amps in a 24-hour period.
5.3 cu. foot = 5.38 amps. The 5.38 figure tells me it's the same compressor as the 8, and so it should have a smaller duty cycle, say 40%. That would be 54 amps per 24-hour period.

******
Example 2

A company that theoretically uses the same compressor for a 4 cu. ft. fridge and a 7 cu ft fridge (hence same amp draw listed for both).

Theoretical 4 uses 3.8 amps. At 50% duty cycle this is 45.6 amps per 24-hour period.

Theoretical 7 uses 3.8 amps. At 75% duty cycle this is 78 amp hours per day.

*******
So as you can see there sort of isn't a "free lunch" on refrigerator draw. If a larger refrigerator is specifying a lower draw, that likely just means that they are using a smaller compressor, BUT it will have to run more to remove heat from a larger "box." The only way around that would be to have it be disproportionately large on the outside (more insulation), but then it would likely not fit reasonably in a van. There is also the chance of more wear on the compressor if a smaller on is used in a larger box (they have figures for compressor/box sizing -- or at least Danfoss does -- so this can be determined).

I think most refrigerator makers do not specify duty cycle because who knows what your ambient temperature will be. However I WISH they would specify that for a set temp, say 77. Having that figure along with the hourly amp draw of the compressor would allow one to plan for a power system, plus compare insulation value of various refrigerators.

PS: In general, when planning for your power system, think about three things:

1) What sort of draw and for how long in a 24-hour period on each appliance.

2) How much power storage capability do you have (batteries) (don't plan to draw them down 100% or they will die very prematurely).

3) How are you planning to "put back" power you have used, and how often.

With these three pieces you can get a basic perspective on your use. Two opposite examples:

A) Parsimonious boondocker.

1) Uses 85 amp hours in a 24-hour period
(refrigerator = 50; computer, etc. = 15; lights and water pump = 10; misc. = 10)

2) Has a 300 amp hour battery bank, so the daily draw uses around 28% of that. Hence 2-3 days without charging (or with meager charging due to clouds etc.) are not an issue.

3) Has 200-300 watts of solar to "put back" the power used. Can be supplemented by occasional driving (alternator will reliably charge batteries back up to 85%).

B) Luxuriies of Home folks

1) Uses 300 amp hours in a 24-hour period (luxuries of home )

2) Has a 300 amp hour battery bank, so the daily draw would be 100% of that (not acceptable, but see #3)

3) But is plugged in every night (110 charger), and/or runs generator to charge (110 charger).

Both of the above scenarios "work," but the Parsimonious Camper has to watch usage carefully (or change system). The Luxuries of Home folks have to plug in every night and/or run generator. So the main thing is to match the system to the style (and of course there is middle ground).
Viva is offline   Reply With Quote
Old 07-15-2015, 09:18 PM   #5
Site Team
 
daveb's Avatar
 
Join Date: May 2007
Location: Turlock Ca
Posts: 9,806
Garage
Re: General questions

I'd ask them to do an amp check on the fridge. Norcold made some changes over the last year and I'm guessing that is what they're installing. Even Norcold's web site was incorrect back in November.

Yep an electric device like microwave, toaster, heater or crock pot will pull a lot as mentioned. That is why people with such items often need a generator or shore power. A large battery bank can run a microwave for a few minutes but it's usually best to run the engine while it's going.

They do make propane powered crock pots.
__________________
2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer

Sportsmobile 4X4 Adventures..........On and off road adventures
daveb is offline   Reply With Quote
Old 07-16-2015, 10:00 AM   #6
Senior Member
 
86Scotty's Avatar
 
Join Date: Jul 2011
Location: TN
Posts: 8,227
Re: General questions

Quote:
Originally Posted by TallGuy
Hi all, my wife and I just did a shop visit in Huntington, In and after talking things over later in the day came up with a few questions I was hoping you might be able to help out with.

1. I love the 7 cubic foot fridge but am concerned the energy use might be too great, would we be better off with a smaller one?

2. How long will an electric heater run on battery power through the inverter?

3. Can a toaster or a crock pot be run via battery through the inverter?

4. If we were to go with diesel appliances (much more expensive I know) will there be a residual smell of diesel fuel that hits your nose every time you enter?

Thanks for your help!
1. I have no idea of the power draw, but we can fit a LOT of food in our 4+/- cubic ft. Truckfridge. We take a small cooler for tall drink bottles, beer and soft drinks, and that's where we keep ice too. It works out great. Keep in mind that fridge will take up a lot of your space as well as possibly eating a lot of power.

2. I suspect a very short time. Home electrics (toasters, hair dryers, heaters, crock pots) use a whole lot more power than you think.

3. I think you could do this with the motor running. That's what we do with our microwave. We just crank up the van, and usually for the 5 minute cycle of using a coffee pot too, when we use it. It's not necessary with our two big AGM batteries but it keeps from zapping them so they can carry on supporting our lights and other small electronics. We have often thought of traveling with our Crock Pot and just letting it sit in the sink or somewhere and cook food while we drive all day, using the inverter supported by the running van. This isn't perfect, but crock pot food is perfect, so it might be a good trade off on a long driving day.

4. I don't think they put out any smell at all. I've been in a few vans with diesel appliances and never detected a smell. I would PM Pschitt. He has all diesel stuff I think.

It seems to me you are looking to avoid propane, but it is cheap after the original tank install, and worry free. Also, your biggest choice of appliances will be propane. The only thing propane I would avoid is a fridge due to the better and cheaper electric choices these days.

__________________
Currently vanless. Weird.
86Scotty is offline   Reply With Quote
Old 07-16-2015, 10:08 AM   #7
Senior Member
 
mikracer's Avatar
 
Join Date: Sep 2013
Location: San Luis Obispo, CA
Posts: 2,158
Re: General questions

Quote:
Originally Posted by 86Scotty
We have often thought of traveling with our Crock Pot and just letting it sit in the sink or somewhere and cook food while we drive all day, using the inverter supported by the running van. This isn't perfect, but crock pot food is perfect, so it might be a good trade off on a long driving day.
^^ That sounds like a pretty good idea to me! If you stopped along the way, you could just turn it off and let the residual heat continue to do its thing. Only downside would be storing the crockpot afterwards.
__________________
2005 E350 Chateau - V10 - Agile Offroad 4x4
2012 CTS-V Wagon - For the baby...
mikracer is offline   Reply With Quote
Old 07-16-2015, 11:19 AM   #8
Senior Member
 
Viva's Avatar
 
Join Date: Feb 2012
Posts: 874
Re: General questions

To pile onto a tangent, you might consider a thermal cooker to do the job of an electric crockpot, if you haven't already. It's basically like a non-electric crockpot, stainless/vacuum-insulated. You heat it up at first on any stove (with the stew or whatever inside it), then then set it aside (such as in the sink) and it does the crockpot thing on its own. Then holds things warm. Here is one example, the Thermos Shuttle Chef (not particularly endorsing this one, but just wanted to show a photo and grabbed it in a search).

Viva is offline   Reply With Quote
Old 07-16-2015, 09:29 PM   #9
Site Team
 
daveb's Avatar
 
Join Date: May 2007
Location: Turlock Ca
Posts: 9,806
Garage
Re: General questions

Have had one for years (still use it) and it fits some situations but not quite like a crock pot.
I can cook more things via a propane stove than that mind you there is fuel to consider.
It all depends how you need to cook.
__________________
2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer

Sportsmobile 4X4 Adventures..........On and off road adventures
daveb is offline   Reply With Quote
Old 07-17-2015, 02:30 AM   #10
Senior Member
 
Viva's Avatar
 
Join Date: Feb 2012
Posts: 874
Re: General questions

Fair enough, DaveB. And, I haven't even used a thermal cooker - just thought they looked interesting. I don't cook in a crockpot either though (lot of use I am!).

Glad you commented.
__________________

Viva is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

» Sportsmobile Registry

Turtle

rafeman

AWOL

Twoxentrix
Add your Sportsmobile
Powered by vBadvanced CMPS v3.2.3
Disclaimer:

This website is not affiliated with or endorsed by Sportsmobile SIP or any of its affiliates. This is an independent, unofficial site.


All times are GMT -6. The time now is 08:29 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.