Running Fridge of inverter?

Thepips

Trade Member
Sep 26, 2007
493
1
Basingstoke
Funster No
441
MH
RV
Exp
6
I've been working on my Monaco Knight over the weekend and got to thinking about reducing the amount of LPG we get through. One of the biggest users seems to be the fridge. It's a big 4 door Dometic.
It's not on the inverter circuit but I can't think of a good reason why it shouldn't be. The fridge has a 5amp fuse so at 110volt can't be drawing more than 550watts which is a lot less than the microwave. The inverter is 3000 watts and I've 4 x 6 volt 125 a/h batteries. Ok I can see you wouldn't want to run it on inverter all the time but why not while driving? Or for a short time while on the ferry?
By my reckoning the batteries should last at least 3-4 hours. If I'm reading the manuals correctly the engine alternator puts out 100amps which charges all of the chassis and leisure batteries.
It could be quite sophisticated with a relay operated changeover switch so when the engine is running the fridge is powered by the inverter. Turn the engine off, the relay disengages and the fridge loses power so automatically switches to gas. Start the gennie or go onto hookup and the fridge would run of that.
Will it work? or I am missing something fundamental?

Cheers
Doug
 
Sep 23, 2007
1,381
714
Leicestershire
Funster No
347
MH
A Class
Exp
4 and many as a tugger
My own guess is that it is not connected to the existing circuit is as you have said, current draw. What hapens when you are driving at night, heater blower, lights, radio etc. I dont think the alternator will keep up.
 
OP
Thepips

Thepips

Trade Member
Sep 26, 2007
493
1
Basingstoke
Funster No
441
MH
RV
Exp
6
A very good point indeed.
Maybe I should consider a simpler solution. Just run a second power point into the fridge cabinet which is fed by the inverter. Plug into the inverter when I know the alternator would be able to cope. At all other times simply plug into the existing socket.

Thanks for input

Regards
Doug
 
Jul 29, 2007
4,777
9,251
Ipswich
Funster No
32
MH
RV
Exp
30 years
Hi that's what I can do with mine, when we are driving I sometimes have the inverter turned on, and it powers all the electrical circuits 110/230v so the fridge would automatically run on electric. I should remember to switch the battery charger off, but forget most of the time.::bigsmile:

Have be honest though, electric or gas its just as inefficient, if your not burning LPG, your burning petrol which is dearer. The 8.1 GM's have 140amp alternators, so plenty of power.

Olley
 

Geoff

Free Member
Nov 20, 2007
39
0
Evesham
Funster No
882
MH
C Class
Exp
on & off for 20 yrs
Hi Doug.
Couple of other factors to consider, electrical efficience (or inefficiency). Losses in the system mean draw from the alternator will be much greater than the rated input of the appliance. Also automotive alternators are rarely designed to output anywhere near thier rated value for any length of time, I wouldn't be happy running a standard type alternator at much more than 20-25% of max output continuously.

Regards Geoff.​
 

Keith and Debs

Free Member
Sep 25, 2007
46
0
In Our RV
Funster No
423
MH
Fifth Wheel
Exp
3 Years
Hi

Why do you need to run the fridge/freezer whilst driving.. We just turn ours off never had any probs with food thawing or freezer defrosting etc... It was even okay on the crossing from Bilboa to Portsmouth... saves a load of LPG..

Keith n Debs
 

pappajohn

LIFE MEMBER
Aug 26, 2007
36,097
24,162
Dark side of the moon
Funster No
172
Exp
Since 2005
I've been working on my Monaco Knight over the weekend and got to thinking about reducing the amount of LPG we get through. One of the biggest users seems to be the fridge. It's a big 4 door Dometic.
It's not on the inverter circuit but I can't think of a good reason why it shouldn't be. The fridge has a 5amp fuse so at 110volt can't be drawing more than 550watts which is a lot less than the microwave. The inverter is 3000 watts and I've 4 x 6 volt 125 a/h batteries. Ok I can see you wouldn't want to run it on inverter all the time but why not while driving? Or for a short time while on the ferry?
By my reckoning the batteries should last at least 3-4 hours. If I'm reading the manuals correctly the engine alternator puts out 100amps which charges all of the chassis and leisure batteries.
It could be quite sophisticated with a relay operated changeover switch so when the engine is running the fridge is powered by the inverter. Turn the engine off, the relay disengages and the fridge loses power so automatically switches to gas. Start the gennie or go onto hookup and the fridge would run of that.
Will it work? or I am missing something fundamental?

Cheers
Doug
if its an onboard genny then just switch off the charger and run that instead, or am i missing something :Doh: i dunno cos my kontiki fridge runs on 12v while travelling but then my fridge will fit inside yours.:ROFLMAO:

john.
 
OP
Thepips

Thepips

Trade Member
Sep 26, 2007
493
1
Basingstoke
Funster No
441
MH
RV
Exp
6
if its an onboard genny then just switch off the charger and run that instead, or am i missing something :Doh: i dunno cos my kontiki fridge runs on 12v while travelling but then my fridge will fit inside yours.:ROFLMAO:

john.
It just seemed daft to me to use LPG or diesel when driving. I know the alternator takes some power to drive it but that can't be as much as running the fridge/freezer on LPG can it? I then also got to thinking about how to keep the freezer on while on the ferry or going through the tunnel. Don't think they'd be too pleased if I ran the gennie:roflmto:

Thanks anyway
Doug
 
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