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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300047 is a reply to message #300045] |
Mon, 02 May 2016 15:35   |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Bob, the inverter would require more than 10 amps @ 12 vdc from the
batteries to supply 120 V. @ 5 amps to the fridge. Probably more, depending
upon the efficiency of the inverter. If the engine were running, probably
no problem. But when stopped, overnight, dry camp mode, propane is the best
choice.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On May 2, 2016 1:16 PM, "Bob Dunahugh" wrote:
> I'm putting in a new 110 volt plug in the refrigerator compartment. The
> frig requires 110 volt 5 amp to work. Why not have the other plug space in
> the duplex plug run the frig while on the roar. Powered by the
> invertor. Thus save the LP. Or if you're on the road. And run out of
> LP.Bob Dunahugh
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300054 is a reply to message #300047] |
Mon, 02 May 2016 18:00 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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James Hupy wrote on Mon, 02 May 2016 15:35Bob, the inverter would require more than 10 amps @ 12 vdc from the batteries to supply 120 V. @ 5 amps to the fridge. Probably more, depending upon the efficiency of the inverter. If the engine were running, probably no problem. But when stopped, overnight, dry camp mode, propane is the best choice.
Jim Hupy
Salem, Or
78 GMC ROYALE 403 If the fridge actually pulls 5A at 120VAC (600W), the inverter will have to suck more than 50A at 12VDC. I guess that might be right for an absorption type fridge(?). You will have to upgrade your alternator if planning to power that fridge off the inverter while under way.
[Updated on: Mon, 02 May 2016 20:46] Report message to a moderator |
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300055 is a reply to message #300054] |
Mon, 02 May 2016 18:27 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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The Vitrifrigo 7 cu. ft. fridge/freezer takes 4 or 5 Amps of 12V when compressor is running!
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ Since 30 November '53 ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ Member GMCMI and Classics ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~~ k2gkk + hotmail dot com ~~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
______________
|[ ]~~~[][ ][]\
"--OO--[]---O-"
> Date: Mon, 2 May 2016 17:00:26 -0600
> To: gmclist@list.gmcnet.org
> From: markbb1@netzero.com
> Subject: Re: [GMCnet] Restoration. Invertor to power the frig while on the road.
>
> James Hupy wrote on Mon, 02 May 2016 15:35
>> Bob, the inverter would require more than 10 amps @ 12 vdc from the batteries to supply 120 V. @ 5 amps to the fridge. Probably more, depending
>> upon the efficiency of the inverter. If the engine were running, probably no problem. But when stopped, overnight, dry camp mode, propane is the
>> best choice.
>> Jim Hupy
>> Salem, Or
>> 78 GMC ROYALE 403
> If the fridge actually pulls 5A at 120VAC (600W), the inverter will have to suck more than 50A at 12VDC. I guess that might be right for an absorption
> type fridge(?). You will have to upgrade your alternator if running that inverter while under way.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands Parts Unit For Sale
> Upper Alabama
> Why don't they sell spray paint that washes off with soap and water for graffiti vandals to use?
>
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300076 is a reply to message #300054] |
Tue, 03 May 2016 05:54 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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On May 2, 2016, at 7:00 PM, A. wrote:
>
> If the fridge actually pulls 5A at 120VAC (600W), the inverter will have to suck more than 50A at 12VDC. I guess that might be right for an absorption
> type fridge(?). You will have to upgrade your alternator if running that inverter while under way.
And don’t forget about the I-squared-R resistance loss in the wires (and connectors) between the battery and the inverter - with 50 amps of load and just a tenth of an ohm of wire resistance you’d have 50 x 50 x 0.1 = 250 watts of loss and a corresponding voltage drop at the inverter’s input terminals. This means over 850W of power being drawn from the battery in order to power a 600W fridge.
This calculation becomes even more striking for those who are intending to run their 1000W microwaves with an inverter: 83 amps at 12 Volts means 83 x 83 x 0.1 = 690 Watts lost across that 0.1 ohm of resistance.
Good engineering practice dictates that the inverter be situated as close as possible to the battery that is powering it - and use the largest diameter wires that will fit into the inverter’s input terminals in order to reduce I^2R losses as described above. Pay particular attention to the connectors at the battery and the input terminals on the inverter as these can easily account for more loss than the wire itself.
Unfortunately many people do not realize the limitations of inverters and this means they are being installed in wholly inappropriate ways. I^2R loss is one of the primary reasons that the companies that operate the nation’s power grid go to a lot of trouble to step up power into the kilovolt (and sometimes megavolt) range for distribution.
—Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300077 is a reply to message #300075] |
Tue, 03 May 2016 06:16 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Let's talk about energy efficiency.
It takes a given of heat to operate an absorption type refrigerator. I do not know that value in BTUs but I an estimating it at around 2100 BTU/hr. That BTU value will not change. It takes x amount of BTUs to run the refrigerator. All you are discussing is the source of that heat.
1. Is by burning some propane.
or
2. Is by electrically heat the unit with with 120 volts AC which someone stated is around 600 watts. This means you will consume around 5 amps.
or
3. If by heating with 12-14 volts DC. We can assume the amount of heat will also be 600 around watts. So 12 Volts DC applied directly to the heating element that would be around 50 amps.
The problem with this proposed scenario with the inverter is:
1. We are burning gasoline in a poor efficiency engine to create mechanical energy.
2. Mechanical energy is then used to generate 12-14 volts DC which is also not 100% efficient.
3. We take that 12 volts DC and convert it to 120 volts AC using an inverter which is probably 80 to 85 % efficient
4. Finally we convert that 120 volt energy back to heat to run the refrigerator.
Wouldn't it make more sense to just burn some fuel and heat the refrigeration directly and eliminate all of the conversion losses in the above process?
I do not know the temperature of the heat required by the absorption cooling unit but if you wanted to look at energy efficiency we ought to look at heating the cooling unit with excess heat from the engine coolant or engine exhaust. Now that would be free since you are discarding that heat anyway.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300083 is a reply to message #300076] |
Tue, 03 May 2016 08:29 |
Justin Brady
Messages: 769
Registered: April 2015
Location: Bell Buckle, TN
Karma: 11
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What everyone is saying is all semi sound, however everyone seems to take a sky is falling kind of approach.
Upgrade to a 100 amp alternator and a 1000 watt+ inverter and this would not be an issue. 50 Amps is a big number but certainly not nearly unheard of when using 12V batteries. It's a pretty low number in that sense actually.
Jim makes the point of power loss, and IsquaredR, which is valid but the number are pretty exaggerated. With your inverter near your batteries (say 4 ft) using 4Awg wire your resistance is closer to .001 ohms not .1. Which reduces your losses by a factor of 100. 2.5 watts power loss is a lot more reasonable.
With such a small battery bank I'm sure this would not have particularly good effects on your batteries.
Your biggest issue would be forgetting to switch it back when you shut the engine down. It wouldn't take but an hour or so to murder your batteries.
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300088 is a reply to message #300083] |
Tue, 03 May 2016 08:51 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Bob is already convinced. He is on to some other problem. This inverter
talk is interesting to some. Just remember, there is no free lunch.
Batteries are ALWAYS HEAVY AND IT TAKES A LOT OF THEM TO DO ANY SERIOUS
WORK. Intermittent use or short term they are fine and dandy, also in low
current drain applications. With wattages in the range of 1000 or higher,
not so much.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On May 3, 2016 6:30 AM, "Justin Brady" wrote:
> What everyone is saying is all semi sound, however everyone seems to take
> a sky is falling kind of approach.
>
> Upgrade to a 100 amp alternator and a 1000 watt+ inverter and this would
> not be an issue. 50 Amps is a big number but certainly not nearly unheard of
> when using 12V batteries. It's a pretty low number in that sense actually.
> Jim makes the point of power loss, and IsquaredR, which is valid but the
> number are pretty exaggerated. With your inverter near your batteries (say 4
> ft) using 4Awg wire your resistance is closer to .001 ohms not .1. Which
> reduces your losses by a factor of 100. 2.5 watts power loss is a lot more
> reasonable.
> With such a small battery bank I'm sure this would not have particularly
> good effects on your batteries.
>
> Your biggest issue would be forgetting to switch it back when you shut the
> engine down. It wouldn't take but an hour or so to murder your batteries.
> --
> Justin Brady
> http://www.thegmcrv.com/
> 1976 Palm Beach 455
>
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300092 is a reply to message #300045] |
Tue, 03 May 2016 09:15 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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In some decades of situations where AC loss could not be tolerated, I used an inverter sized for the minimum load we could get away with, but with only a few minutes capacity - time required to start the genset. I take the same approach in the coach, where the load is only the icebox and whatever lights/pump/fan I need. The house battery keeps them up directly, andneeds to do so only long enough to stop for lunch or while parking and hooking to shore power. If it's a long lunch, fire off the genset. This approach, coupled with a set of solar panels and a smart charger, aloows me to use a small (read cheap) marine bvattery for the house battery. Saves weight and money.
Note: If you're a boondocker, this approach won't work very well.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300098 is a reply to message #300088] |
Tue, 03 May 2016 10:15 |
Justin Brady
Messages: 769
Registered: April 2015
Location: Bell Buckle, TN
Karma: 11
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Senior Member |
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True enough Jim.
I was posting really for reference is someone decided to search for something similar later.
I don't like having threads around with incorrect/misleading/one sided information. It makes it very difficult for people to find a straight answer when searching.
The answer to Bob's initial question is yes you can do that no problem, it just has to be done correctly, and a stock setup coach probably isn't going to cut it.
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300105 is a reply to message #300045] |
Tue, 03 May 2016 12:31 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Spring for a pure sine wave inverter. Her charger may be damaged by square wave AC being that her charger is probably some sort of switching PSU and or has smart tech inside. The reffer idea is best to scrap as it would use 2/3 if the 80 alt continuous draw. Not enough headroom for me.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Restoration. Invertor to power the frig while on the road. [message #300114 is a reply to message #300083] |
Tue, 03 May 2016 21:01 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On May 3, 2016, at 9:29 AM, Justin Brady wrote:
>
> What everyone is saying is all semi sound, however everyone seems to take a sky is falling kind of approach.
What I and several of the other people on GMCnet are saying WRT inverters is perfectly sound and is backed up by the laws of physics - there’s nothing “semi-sound” about it. We have had close to 75 GMCs through the work rallies that my family has hosted over the years and some of the inverter installations that we’ve seen are downright scary. GMC owners that attempt such installations need to understand _all_ the factors involved and one of the greatest shortcomings is based on a clear misunderstanding of what is happening on the DC side of the system.
> Jim makes the point of power loss, and IsquaredR, which is valid but the number are pretty exaggerated. With your inverter near your batteries (say 4
> ft) using 4Awg wire your resistance is closer to .001 ohms not .1. Which reduces your losses by a factor of 100. 2.5 watts power loss is a lot more
> reasonable.
The resistance number in my example is exaggerated in the case of a brand new 4 foot length of 4 AWG as you described but it is not so exaggerated when you consider a coach with its house batteries in front and the inverter in the back - using a 4 AWG cable whose connectors have 40 years of corrosion on them and coupled with a chassis return for the negative side of the circuit through multiple rusty frame rail joints. Yes, I’ve seen such an installation in person and the resistance was much *larger* than I used in my example.
At no time did I say that 0.1 ohm was representative of what might be experienced in the general case - I only used it as an example to illustrate the magnitude of I2R loss and how a miniscule amount of resistance can result in a massive power loss when dealing with realistic amounts of supply current.
--Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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