Website Home | Info & Posts | Club Membership | Eagle History | Contact Us

Doing the refregerator math

This is a public forum to discuss Eagle related technical issues. If you are having a problem with your Eagle, this is the place to find help.
Doing the refregerator math
Fri Apr 24, 2009 3:39 pm


In looking at the energy ratings of a new fridge, it uses 555kwh per year on the energy guide comparison... that's roughly 1.6kw per day on 365 days. So what's the battery bank capacity required to run on an inverter? I'm figuring 70% efficiency on the volts/amps converted (inverted from 12 to 110 volts)... but can't get to the storage amps required to be consumed from the battery bank (I assume the fridge would only run 1/2 of the total time)

Thanks,

dg
User avatar
TexasBorderDude
Club Member
Club Member
 
Posts: 148
Joined: Wed Jan 21, 2009 5:18 pm


Re: Doing the refregerator math
Sat Apr 25, 2009 6:38 am


Doyle, I am not an expert on this subject, but no one has jumped in, so I thought I would give you a couple of thoughts.

Trying to size a battery bank from refrigerator manufacturers data can be a bit frustrating, since there are lots of variables. I looked at my fridge and the rating tag is long gone. It was rated well for it's type and the time (about 5 years ago). It is a side by side with water dispenser, so not as efficient as some.

The interesting approach my fridge uses to be "efficient" is a small compressor that runs longer. It drive me crazy to hear it running so much, but that is the nature of beast. When it is running, I can't see the draw on my 120V ammeter. I do look at my rather accurate Trimetric battery meter and I think it draws about 20 - 30 amps on 12V. It is hard to isolate the fridge current, since we have a bunch of electronic equipment running most of the time.

While my compressor is supposedly small, it has a pretty good surge that really dims the lights for a second or two. I was very worried that this surge load would damage my inverter long term, but after 3 years of 100% on time it just plugs along. It does, however, point out the need for a good inverter (should be full sine wave) that has good surge rating.

Speaking of inverters, a modified sine wave inverter will not provide full heating on microwaves, so you need to run it longer (more battery bank). I mention this because the inverter characteristics have a significant impact of battery bank capacity requirement.

Since you seem to be working on sizing the battery bank, let me make an observation. We have 8 golf cart batteries. I work very hard not to let them get below 50% of state of charge (as measured by the Trimetric). With reasonably conservative use of lighting, my batteries will only give me about 1/2 - 3/4 day of usage. The fridge is a significant draw, but there are lots of other consumers. The inverter itself has some current draw. As I mentioned, we have a lot of electronic stuff running (DVR, TV, Motosat/internet modem, up to 4 laptops, printer, etc) running at any given time. Then there are the normal kitchen appliances. The coffee maker can use about 5 amps AC and the microwave is at least 10 amps as I recall.

So, the fridge is probably less than 30 - 40% of our load.

One of the things that folks preach is to disable the defrost function. Most fridges use a heat strip in the door and that can consume a fair amount of power. Some of us have played with this, but modern fridges are "computer" controlled and trying to disable the heat stip can cause control problems. I finally gave up and just live with the problem.

Not sure any of this rambling helps, but at least you got a reply :D

Jim
Jim Shepherd
Evergreen, CO
'85 Eagle 10 with Series 60 & Eaton AutoShift 10 speed transmission - not at all fancy, but fully functional
Bus Project pages: http://beltguy.com/Bus_Project/busproject.htm
Blog: http://beltguy.com/blog/
Email: jim@eaglesinternational.net (Please email me rather than use the PM process)
User avatar
beltguy
Moderator
Moderator
 
Posts: 2071
Joined: Wed Oct 08, 2008 4:39 am
Location: Evergreen, CO


Re: Doing the refregerator math
Sat Apr 25, 2009 1:37 pm


Doyle, forget about a house type fridge when we get back to AZ we will go to Prescott and look at the Millers propane( Amish made) and the SunFrost 12v or 24 volt fridges they will work best for you I think good luck

Clifford
User avatar
luvrbus
Club Member
Club Member
 
Posts: 2921
Joined: Mon Oct 13, 2008 12:50 pm


Re: Doing the refregerator math
Sat Apr 25, 2009 8:49 pm


Ahhhhh Clifford! You are the best ever!!!! Hadda great birthday party with the grand daughter... see you in a couple of days.

Best,

dg
User avatar
TexasBorderDude
Club Member
Club Member
 
Posts: 148
Joined: Wed Jan 21, 2009 5:18 pm



Return to Eagle Tech

Who is online

Users browsing this forum: Google [Bot] and 2 guests



cron