how to measure amp draw of a fridge

[grntrdtaco]

my fridge is seemingly sucking down my group 31 die hard platinum battery in a real hurry these days and i am not sure if its the battery going bad (its not very old) or if its my ancient norcold fridge going out.

is there any kind of product that i can use that can measure the draw from the fridge?

i have also added a small adjustable 12v computer fan to cool the coils. unfortunately there is no cutoff on the fan and it will keep running until the battery is completely dead. is there a product that will shut off all accessories attached to a battery when it reaches a certain voltage?

i know i can plug it into a kill-a-watt but that will only measure AC draw i think and i run the fridge off of DC in the truck.

how do i test if a battery is going bad? the last time it went dead it took about 3 hours of driving/charging on the highway to get back up to 14v according to my scangauge (i am running the batteries with an isolator) and a 160amp alternator in my tacoma.

I am planning on adding a big solar panel to the mix but i need to get all of this figured out before i add that in just in case the battery is bad or the fridge is at the end of its life.


thanks

 

[MarcFJ60]

Well, you could use the kill-a-watt to test the fridge under AC power to see if it is working properly and then convert it to DC amperage.

I used a plotting multimeter to test mine over time. If you just have a plain-jane (fused) multimeter, you can do it too, but it will take some more work.

You need to set your multimeter in series with the power supply. In other words, run your positive wire from the battery to one of the leads, Then take your other lead and connect it to the positive feed for the fridge. I accomplished this by wiring in a fuse holder like this:

. Remove the fuse and stick a multimeter lead in each side of the fuse holder. (Make sure your wiring is ample and the connections are good.

At this point, all your really testing is static current draw - what it is drawing right now. But as we know, it draws next to nothing most of the time and when the compressor kicks on you get a decent draw. You need to figure out what it is doing over time. If your meter can't plot that, you will need to watch it over time to figure out how long the compressor runs each hour and what it is drawing.

You might quickly find a problem just measuring static amp draw at idle and when the compressor is running - i.e. draws 5 amps at idle (rather than a fraction) or 10 amps while the compressor is running (rather than about 4).

In the Edgestar thread, I think a member took pics of his set up when he tested it. On my Edgestar, I found it would run for about 15 minutes each hour and draw around 4 amps during that time (although briefly over 5 when the compressor starts up). While idle, it would only draw less than a tenth of an amp. Would think a Norcold would be at least that efficient.

 

[SoCal_80]

Try this: http://www.powerwerx.com/tools-meters/doc-wattson-meter-dc-inline.html

 

[dwh]

If it's a 3-way, it draws a lot of amps running on DC. I have a Norcold 323 (the smallest they make) and it draws 11.7a on DC, which is why I *never* run it on DC.

 

[ddog45]

I have a norcold 60l fridge that I run off of a yellow top. It seems to do best if I keep it in the shade with the rear windows cracked and our jackets laid over it to provide insulation. The longest I have left the truck parked is three days at that point my ibs battery monitor started to alarm. I also make sure to ask my friends if they have jumper cables if I begin to worry about killing my battery.

 

[Salue]

I read somewhere that if you drain it and just drive it to recharge, the alternator never gets the battery to 100%, just 80% or so. If possible, you should stick that battery on a trickle charger that's compatible with AGM batteries. Once it's fully charged, your battery will last a lot longer before being drained; that extra 20% capacity makes a big difference.
Here's a tool that you just connect to your battery and once it drains to a certain voltage, it disconnects your battery so you have juice to start it:

http://www.summitracing.com/search/brand/Battery-Brain/

They have different levels of the Battery Brain, so choose accordingly. If I didn't have dual batteries, I would invest in the cheapest model since it seems like good insurance.

Salue

 

[grntrdtaco]

The fridge runs pretty much all the time in the temps that I have been using it in lately. It's an ac/dc fridge from what looks like the early 80's. I got it for a hundred bucks about 5 years ago it had been on a boat before this. It's served very very well. It struggles to keep 40 degrees when it's over 100 but it's still better than soggy food.. I will try out the inline multimeter to get an idea of what is going on. I have another AGM die hard plat as a starter so it's not a disaster if it drains completely. My main is isolated so it never goes dead.

I do think that I will add the batt brains between my fuse boxes and the battery that looks like just what I need

Thanks for the tips

 

[goodtimes]

Try this: http://www.powerwerx.com/tools-meters/doc-wattson-meter-dc-inline.html

x2

Great little tools to have when you are troubleshooting problems like this. Just be sure that you use quality connections. A poor connection will drive the load through the roof (been there, done that).

 

[Herbie]

You can see how I did it here:
http://www.expeditionportal.com/for...lt-400-shipped?p=833347&highlight=#post833347

I used a precision shunt to measure the current using a voltmeter. In my case I did long-term tests, so I captured the data via RS-232 to a PC, but for instantaneous tests, you can just read the meter.

Precision shunts come in a variety of ratings, so make sure you understand what you're measuring. Here's one for less than $5: http://gb.suntekstore.com/DC-50A-75...auge-.html?&utm_source=gbus&utm_campaign=gbus

That one is 50A = 75mV, (or 1.5mV per amp), so you'll have to do a little math with the reading, but if you see 3mV across the terminals, you'll know the fridge is drawing 2A, etc.

 

[Frankspinz]

Add insulation (foil bubble wrap) and keep it out of the sun... That will surely help a bunch.

 

[grntrdtaco]

its fully insulated with a nylon cloth space blanket cover that i made with a 1/2" closed cell foam sleeping pad sewn into the middle of the space blankets. and i keep it in the cab of the truck behind the drivers seat. i am thinking the fridge needs a recharge or service, its very old.

this is kind of what it looks like (this one is for my mrft60) the other one is identical but for my mrft40 unit but i dont have any photos of it.