dumb battery consumption question.

[oldbernie]

We have a Chevy 3500 van with two of whatever size house batteries that Sportsmobile installs.(Was that a properly constructed sentence?) Anyhow, we are usually campground campers but this trip we are going to Chaco Canyon for two nights. Also, we have the 3.6 cf fridge 12/120 and I couldn't find the consumption specs for it. So a couple of questions. Assuming that I arrive at Chaco with full batteries and the fridge runs for 10-12 hours off of battery will I be able to use my single Shot Kuerig which draws 1425 watts for morning coffee without killing my batteries? If not I can set up the single burner propane and boil water. Secondly, given that the fridge has been running all night will I get enough of a charge back into the batteries just driving around Chaco all day or will I need to sit and idle for some period? I'm pretty good with AC house stuff but this battery consumption thing throws me for a loop. Thanks for any help you can provide.

[daveb]

It all depends on what type/size battery they installed and how old they are. If they are in fairly good shape, I don't see any issues with running a standard 12vDC fridge while set up in camp and throughout the night. The coffee maker is a different issue. Running high amp items will deplete a smaller battery system really fast. I'm not saying it won't work but the best way is to experiment at home. A plug in voltmeter can be used to check the resting voltage to see where your batteries stand.

Driving the vehicle will normally recharge the house batteries w/i a few hours but it also depends on how low the batteries were taken and what the alternator puts out. The van should have a separator/isolator that protects the starting battery from being drained but if you're not sure just run the engine while the coffee maker is working.

[oldbernie]

Thanks. Kind of what I was hoping to hear. The batteries are only a couple of years old and they've always handled the fridge well. I was concerned that with the mileages around the Chaco site that The batteries wouldn't get a chance to adequately recharge enough to carry the fridge through a second night. I might have to drive the tour road a couple of times to make sure. Running the engine during coffee making(coffee is important right?) sounds like a viable option as long as I don't disturb anyone else. Thanks again for your help.

[arctictraveller]

There are simply too many variables to accurately answer your questions with out a lot of additional information. The current draw of your loads, the ampacity of your batterys, the age of your batterys, the number of hours the refer and all other loads run, the size of your alternator, the percentage of recharge from driving, how far your willing to discharge your batterys, even the charging losses in your cables will be factors in determining the time between charges. The best way to get the answers you want is to install a battery monitor that will let you see and track voltage and amps in and out. 1500W is a pretty big load for even fully charged batterys. In the morning, with somewhat discharged batterys, it will be even bigger in terms of the amp draw required. Probably the most important thing to realize is that the further you discharge your batterys, the shorter their lifespan. Deep discharge will cause premature failure, so at a minimum an accurate voltmeter will help determine the state of charge. I highly recomend this book if you want to get a better understanding of 12V theory and systems. It's slanted to boats but he does an outstanding job explaining things in plain english....Boatowners Mechanical and Electrical Manual 4/E by Nigel Calder | 9780071790338 | Hardcover | Barnes & Noble

[oldbernie]

Thanks. At the least I need a better battery monitor.

[daveb]

Originally Posted by oldbernie

Thanks. Kind of what I was hoping to hear. The batteries are only a couple of years old and they've always handled the fridge well. I was concerned that with the mileages around the Chaco site that The batteries wouldn't get a chance to adequately recharge enough to carry the fridge through a second night. I might have to drive the tour road a couple of times to make sure. Running the engine during coffee making(coffee is important right?) sounds like a viable option as long as I don't disturb anyone else. Thanks again for your help.

Yeah a lot depends on what you have and the shape they're in. I wouldn't assume they are at 100% just because they're 2 years old. A simple voltmeter can tell you a lot. I'd hate to have you depend on them if you haven't used them lately. To test your batteries, charge em up to fully charged state, turn off the charger, and make sure most of the load has been shed by turning everything off (don't worry about the CO/Propane detectors) and test the voltage 4 hours later. Voltages around 12.8 are considered a fully charged battery.

You can always fire up your fridge at home on the highest setting and let it sit overnight after fully charging the batteries. Test the voltage in the morning then give your coffee maker a try. The voltage will seem low but after things are turned off for a few hours the voltage will creep back up and where it stops is the batteries resting state. I wouldn't worry about running them flat during the test. If they can't hold enough energy to supply the needs you're stating, it's time for a new and/or bigger battery system.
Here is a diagram that might help:

[1der]

One thing not mentioned here is temperature of the batteries. Amp hour ratings are typically done at 75F (25c). The real eye opener is how what is loss as the temperature goes down. The factor is 1% for every one Celcius degree change. Does not seem like a lot, right?

Well, 32F is 0C, that means a 25% drop in available amp hours just due to temperature drop from 75 to 32f overnight. Having a temperature compensating monitor makes for an interesting study.

[TexGX]

I just picked up an old school coffee percolator. It makes the best coffee and you would not have to worry about battery use. I also have a 100w portable folding solar panel with controller that I put out if sitting all day ($160). Another option would be a 12v coffee maker. It would use much less battery.

TexGX

[moorefc]

Typically they put in 2 group 27 batteries if they are marine type and vehicle shape. Are they lead acid, agm or?. They also put in the super large agms that weigh about 100# each. You really need to look at the batteries, measure the dimensions and their labels. \then you can define their capacities. The 3.6 they used for years was a Norcold DE541, draws about 4A with maybe a 60% duty cycle depending on temps. We get about 4 days/3 nights in warmer conditions before the 2 90AH batts get seriously drained (below 12v)....YMMV. Your electric coffee would kill the batts without the engine running, and with it running about 100A while it is on...Your alternator probably wouldn't keep up at idle.....How bout a stovetop moka pot for some espresso? Also driving around all day is what, 4 hours? That should be pretty good. You need to bring a voltmeter and monitor it but if you are talking only 2 nights with driving during the middle day (assuming 90AH good condition batts) you should be fine if you run your engine while doing coffee...........Also you should find out the capacity of your alternator, the assumption here is you have ~130a alternator....
Have a great trip!

[BrianW]

Carry your Keurig over to the toilet building in the Chaco campground and use it there. If I recall correctly, they have electric outlets there. If a ranger or maintenance person comes by and complains (which I'm sure they won't), just offer them a free cup of coffee! Insure wouldn't use it on van battery power through, at least for more than one cup, and only with the engine running if so.

If it's hot during the day, keep the shades closed to keep the interior as cool as possible to keep the frig from cycling too much. And it gets reasonably cold there at night, so that not an issue.