TheSamba.com :: View topic - how long to kill a battery with fridge fan and 3w led light

Fri Jul 19, 2013 7:52 pm

hey now dont have a second batt(yet)
and when getting the fridge pre chilled on ac the fan comes on
its a muffin fan .25 amps
how much nrg will fan suck over a 24 hour period?
have a brand new 650 cold crank amp battery
also have 3watt led light bar

Fri Jul 19, 2013 8:15 pm

bdcain wrote: hey now dont have a second batt(yet)
and when getting the fridge pre chilled on ac the fan comes on
its a muffin fan .25 amps
how much nrg will fan suck over a 24 hour period?
have a brand new 650 cold crank amp battery
also have 3watt led light bar

Cold cranking amps are not important, you need to know the amp hour (AH) capacity of the battery, its likely around 80AH, you don't want to drop below %50 charge so you can use 40 AH IF it is a deep cycle battery, but it probably isn't so you shouldn't use more than 20 AH, if that, automotive batteries aren't really designed to get discharged any notable amount.

.25 amps for 24 hours is 6 AH, the dometic fridge pulls about 9 amps, so you really shouldn't use it on 12v because the amp draw is pretty excessive.

Fri Jul 19, 2013 8:34 pm

fridge will be on ac or propane
the fan comes on and draws 12v
i hope the fan would not run constantly
i have a second 12v fan back there that will run off of dc from ac transformer
which is ok for ac
but will only have propane with no ac while camping
thats why i asked
all's good as my wife now see's the need for a second battery system :D

Sat Jul 20, 2013 7:41 am

bdcain wrote:
all's good as my wife now see's the need for a second battery system :D

Sweet, it really is the way to go.

As for the 3 watt LED, it also pulls .25 amps.

Sat Jul 20, 2013 8:30 am

.25 amps is a lot for a muffin fan.

Here is one which uses 0.05 amps and moves 54 CFM very quietly:
http://www.noctua.at/main.php?show=productview&products_id=42&lng=en

I also had some fans claim higher consumption, like .25 amps, and found that was just the start up surge current and they settled back to .11 amps once at speed.

If you can access one of the fan's wires without too much effort and have a digital multimeter, you can check the true current draw easy enough.

Mon Jul 22, 2013 7:36 am

Running the Dometic fridge on propane and an LED light should not be an issue over a 24 hour period on the cranking battery, if that is what you are asking. The Dometic Fan, probably won't even run at night and you don't use the light during the day. That said, it will end up driving you nuts. No one wants to kill their cranking battery reading a book in the evening and listening to some tunes. Best to save up for an auxilary battery and get it installed. It does not need to be a monster. Just something to run your minor camping loads and give you peice of mind.

Mon Jul 22, 2013 8:21 am

With some kind of solar, you can then recharge your battery during the day, including when the fridge fan will be running the most.

Mon Jul 22, 2013 8:31 am

Weekend trips shouldn't be a problem with one battery and the use you describe.

An easy way to go is get an inexpensive second car battery (walmart) and just take it with you in the van. Charge it at home with a battery charger before you go and connect it to the main battery while you are camping. I did this for a couple years before installing a full set up. You only need some 10 ga. wire with and some allagator clips to connect it when camping. That will give you the peace of mind not to worry. Set it under the van when you are at camp and run the wires in the passenger or slider door. You can actually use any 12 volt battery like a lawnmower or motorcycle battery. Every little bit helps. Just don't forget it before you go!