Fridges, CPAPs, and Batteries, oh my!

[BigSwede]

I am mulling over a myriad of options for powering devices overnight, and would like some opinions. First of all, my situation: I use a CPAP "snorkel" for sleeping (sleep apnea). The CPAP company tells me the device uses about 1.3 amps. I have run this unit off of the vehicle many times overnight without noticeable effect on cranking at start in the morning.

I have a single yellow top battery series 35 rated at 48 amp-hours. The smallish battery is because I stole some of the battery tray for an ARB mini-compressor. It was an easy solution at the time, and has worked well up to this point.

Enter, the fridge. I am the proud owner of a new Engel MR040 fridge, and I am wondering if I need to beef up my power situation. Engel says "Typically, when maintaining temperature, the nominal draw of any Engel is under 1 Amp per hour." I am a little skeptical of this figure, but then again it doesn't run constantly like the CPAP, so maybe this is an accurate average. And I live in Minnesota, where overnight temps don't tend to be all that warm.

So if I apply these numbers to their typical use in an overnight camping situation, I come up with 1.3 ah * 8 hours for the CPAP, and 1 ah *~16 hours for the fridge. This adds up to 26.4 ah overnight (again, vs. a battery rated at 48 ah).

So question(s) #1 is: do I need an auxiliary power source of any kind? (And it's corollary: How many ah are needed left over in the morning to start a truck?)

It is also worth noting that I rarely travel alone...but I can't count on a jump start whenever needed.

If I do look at auxiliary power options, things get complicated. I could:

• Move the ARB mini-compressor and get a bigger battery, say a series 31. Not as easy as it sounds to move the compressor, but may be possible without rewiring and re-doing air lines. I would go from a 48 ah battery to a 75 ah battery, which seems like plenty on the face of it. The simplicity of this approach is appealing. A new series 31 AGM battery isn't cheap, though. Might be able to get something for my current battery, which is only a year old.
• Simply carry the means to jump start myself, such as those glovebox-size lithium jump starters. They seem to work, and run $80-150, but have little utility otherwise except to charge a cell phone and such. OTOH, they take up almost no room.
• Get a AGM battery jump pack and run the CPAP off of it overnight, thus relieving the vehicle battery of that burden, plus offering jump start backup capability. Takes up more room and weight than the little lithium jump packs, and are a similar price range.
• Dual battery system. I don't like this idea really, I think it is overkill. Quite expensive, heavy, and difficult to fit in the engine compartment. Possibly I could put another battery where the air box is and get a cone filter. I don't see this happening for less than $500 with a new battery and controls.
• Other auxiliary batteries...lithium or otherwise. I don't really know all the options here, but I know they exist.

So there are my thoughts so far. What are yours?

 

[lysol]

I would step up to a 31 series battery. When taking a battery past 50% SOC (State of Charge), it will shorten it's life. With a deep cycle, it won't affect it as much, but something to be aware of in how many times it's done. If you were to follow this rule and make the 50% mark your floor, that 48Ah battery becomes a 24Ah "useable" battery... Just something to think about. Also, dual batteries can make your life really comfortable.

 

[BigSwede]

Yeah, the problem with my current setup, as I see it, is that there is very little safety margin built in. It will probably make it through an overnight OK, but I will be pretty much required to start up the truck each morning and charge up for while, whether I want to or not. I don't really like that idea.

 

[wirenut]

If you run the items listed off your current battery it may work for a while. However, you're draining that battery fairly far down and the more you do that the shorter it's life.
The best solution is a dual battery set up. Keep the one you have and install a second deep cycle unit for your overnight draws. This isn't really that expensive. You could mount the second battery underneath the vehicle on a frame rail (some company makes a kit for that but I can't think who they are right now). Or, you could use an AGM battery and put it inside the vehicle. A group 24 would be just large enough at 75 Ah but I would go to a 27 or even 31 since the cost isn't much more. You'll need a voltage controlled relay like the Blue Sea ACR and some wire. There's no need for big heavy wire since your not drawing large amounts of power. #10 would probably be fine but I'd go up a size or two anyway. Don't forget fuses near each positive battery post.

 

[BigSwede]

I have thought about the room underneath...there is room on the inner side of the passenger side frame rail (exhaust is driver side), if the fuel line that is also there can be accommodated. A kit would be nice, I don't have much for fab skillz.

 

[Corey]

Steve, have you thought about picking up the ArkPak as seen in this thread?
http://www.expeditionportal.com/for...-Portable-battery-boxes-and-where-to-buy-them
It has outlets for 110V and 12V.

I do run a dual battery setup in my FJ, but the second battery is mainly for backup in case I drain the factory battery from running my ARB fridge when camped.
I have tested the Toyota factory battery before in the past, and I have got near five days running the fridge without starting the rig once.
When it was time to start it, it was a little sluggish, hence why I went with a backup battery several years ago.

My ArkPak will be used for powering LED lights when camped, charging up camera batteries, etc.

I bought a group 31 AGM battery for it, plus this 100 watt solar panel.
W Solar 100 Watt Foldable 12 Volt Solar Panel
You can charge the ArkPak from your rigs 12V outlet while driving, and also charge it when camped via that 100 watt solar panel.

You can mount the ArkPak in the rear of your cargo area, and also take it off the mounts and run it outside under cover when camped.

 

[soul]

Steve, IMHO a dual battery setup will be the most useful here. I use LiFePO4 (3.2 x 100AH x 4) to run my ARB 50 fridge. The batteries get charged by the car alternator, but I have option of fitting 100W solar panel in future.
The setup is very compact/lightweight and size wise can fit in a laptop bag. Full details are on my thread http://www.expeditionportal.com/for...PO4-in-a-dual-battery-setup?highlight=LiFePO4

Few advantages, other than size/weight of LiFePO4 is the life (over 3000 cycles, versus 500 with Pb) and over 80% useful capacity. So the cost will balance out. In addition to running a 10gauge line from the battery, you will need DC-DC converter to step up voltage by few volts and a LiFePO4 Charger (easy to use Solar LFE charger, so a panel can be added later).

The ARB50 also is rated 1AH average (draw is about 4A, but it runs less than 1/4 duty cycle. Say 10mins run every hour). In California summer, a night draw is about 16AH but in winter it could go as low as 5AH in the night.
I easily get over 4 days of camping with this setup, and the main battery is never used. It takes about 2 hours of engine run to get additional 1 day of capacity, which unless stationary is easily achieved.

All the best!

 

[BigSwede]

Steve, have you thought about picking up the ArkPak as seen in this thread?
http://www.expeditionportal.com/for...-Portable-battery-boxes-and-where-to-buy-them
It has outlets for 110V and 12V.

Looks like a slick way to have a battery inside the cab (I know it is more than just that)...but the price - ouch! There's a reason I'm driving a 19 year old rig.

 

[BigSwede]

Steve, IMHO a dual battery setup will be the most useful here. I use LiFePO4 (3.2 x 100AH x 4) to run my ARB 50 fridge. The batteries get charged by the car alternator, but I have option of fitting 100W solar panel in future.
The setup is very compact/lightweight and size wise can fit in a laptop bag. Full details are on my thread http://www.expeditionportal.com/for...PO4-in-a-dual-battery-setup?highlight=LiFePO4

Few advantages, other than size/weight of LiFePO4 is the life (over 3000 cycles, versus 500 with Pb) and over 80% useful capacity. So the cost will balance out. In addition to running a 10gauge line from the battery, you will need DC-DC converter to step up voltage by few volts and a LiFePO4 Charger (easy to use Solar LFE charger, so a panel can be added later).

The ARB50 also is rated 1AH average (draw is about 4A, but it runs less than 1/4 duty cycle. Say 10mins run every hour). In California summer, a night draw is about 16AH but in winter it could go as low as 5AH in the night.
I easily get over 4 days of camping with this setup, and the main battery is never used. It takes about 2 hours of engine run to get additional 1 day of capacity, which unless stationary is easily achieved.

All the best!

Interesting. The potential for these new battery types is exciting. And I do have an underfloor compartment under the rear seats in my Trooper that might work for a setup like that. Those batteries cost dang near as much as my fridge, but hopefully prices will drop as with most new tech.

I have much to think about this winter (it's -16F here as I type this).

 

[soul]

The single cell is around $143, sometimes lower. Using cells makes it easy to configure the pack, either lay them flat or stack them based on available space. Also they are very safe, no liquids or spillages. Due to the blooming EV market the price should start getting lower. http://www.all-battery.com/32v100ahlifepo4lithiumironphosphaterechargeablebattery.aspx . A 4 pack weights just over 30lb (7.8lb each), while a comparable Lead-Acid will easily go above 70lb or more. This battery is equivalent to 160AH Lead-Acid in terms of useful capacity, so even a 60AH could work.

 

[Scoutn79]

"""It is also worth noting that I rarely travel alone...but I can't count on a jump start whenever needed."""" Are your travel companions not very helpful???

My friend uses a a CPAP with a heater in it and it will almost kill a battery on it's own overnight. It probably draws 5-6 amps at least. The ratings for the Engel are good for a rough idea of usage...there are many variables that will affect that. I figure mine on a 60 degree night in the camper runs 20 minutes or less per hour at a less than 2.5ah running.
I would get a second battery (or other power source) just for safeties sake.

Darrell

 

[BigSwede]

"""It is also worth noting that I rarely travel alone...but I can't count on a jump start whenever needed."""" Are your travel companions not very helpful???

They are very helpful, when they are around. I'm just saying I can't count on ALWAYS having someone around to jumpstart.

My friend uses a a CPAP with a heater in it and it will almost kill a battery on it's own overnight. It probably draws 5-6 amps at least.

Wow, that's a huge draw. Is he running if off an inverter or something?? Crazy. Fortunately I have never felt the need for a humidifier except sometimes during the dry winter air. I don't really notice any decrease in cranking speed when starting the morning after using my CPAP, never been a problem, so I think the manufacturers statement of 1.3 amps is probably correct.

 

[Scoutn79]

They are very helpful, when they are around. I'm just saying I can't count on ALWAYS having someone around to jumpstart.


Wow, that's a huge draw. Is he running if off an inverter or something?? Crazy. Fortunately I have never felt the need for a humidifier except sometimes during the dry winter air. I don't really notice any decrease in cranking speed when starting the morning after using my CPAP, never been a problem, so I think the manufacturers statement of 1.3 amps is probably correct.

Here in Colorado we have very low relative humidity so it is required or it will dry him out pretty bad and the heater portion is to keep the vapor from condensing in the tube on the way to the mask. He has a 12 volt plug for it so we can plug it into the campers electrical system.
Your system is much friendlier for use on a battery system. We spend a lot of time charging the batteries during elk season (25' hardside camper). Not sure what he would do if he camped in a tent...I guess just plug it into the truck....all of our trucks have separate battery systems, one for start and one everything else..

Darrell

 

[BigSwede]

Not sure what he would do if he camped in a tent...I guess just plug it into the truck....

Yep, I have a 25' 12V cord for power to a tent.

 

[BigSwede]

Well after much web time I have come full circle and decided I may as well just do the dual battery system after all. It actually won't cost that much more than the other options I was looking at. So I have ordered a Blue Sea Add-A-Battery kit (#7650) for great price off of eBay. Now I just need to figure out where the battery is going. I am leaning toward the air box location, but nothing is set yet. Too bad the Trooper is under a snow drift in below zero weather, I am itching to get started...a heap of wiring is in my future, between the dual battery, the fridge, and I was also going to re-do my auxiliary fuse panels and wiring, with one panel in the engine compartment and one in the passenger compartment.

Question: do all AGM batteries have similar charging characteristics? I definitely will get an AGM for the house battery, but the Optima 31 only has 75 ah vs. around 100 ah for more convention layout AGM batteries (probably due to the losses in internal volume from the spiral-wound geometry). That extra 25 ah would be nice.