The Dometic CFX3 Mega Thread

No, drinks on the fridge side and three large, previously frozen water bottles on the freezer side. Also, the fridge stays in the bed of my truck, but under the tonneau cover, no direct sunlight.

 

That’s interesting. Mine has been plugged up to ac since it arrived and it’s been holding at 2 degrees on the freezer side and 37 on the fridge side since. I am swapping it to the truck today once I finish the slide. I know you said deep cycle but what’s the amp hours on the battery?

 

This doesn't sound like its very efficient but I want to ask a couple of questions because I have been looking at this same model. I currently run a Whynter 45 - mostly as a fridge but on longer trips I run it as a freezer to support a cooler that I use as the fridge. I'm thinking of switching to this model because of the dual mode but I'm also suspicious of the current draw/efficiency of the Whynter and I'm hoping this will be better. Its pretty apparent there are some issues (like won't go below 9°F ?) but I just want to ask about the power some more.

One word of caution: Some of the chargers are notoriously fickle so the batteries could certainly be salvageable. Try to boost them another way and see if the charger will take them after that. Or check the manual and see if you can adjust the minimal acceptable pre-charge level.

- What was the ambient temperature outside and under the tonneau? My buddys tonneau makes an over of his bed and its been hot AF in Texas lately.
- Did you bring the unit to desired temps (using the 120v or whatever) before hooking it to the batteries or was it starting from ambient each time?
- You already confirmed you had stuff it it but it sounds like it maybe half full, correct? Were those items cooled before going onto battery power?
- Can you confirm that on the second battery you did 12 hours first (and it dropped to 12.3v) and then went for another 12 hours (where your changer says is toast)? Not sure I read that right. If so, what is the voltage left at the end?
- What size battery was used on the second test? Ah?
- A post on the first page (#18) about the PLB40 gives some expected run times at 75°F for the 40Ah of that unit (https://www.tacomaworld.com/threads/the-dometic-cfx3-mega-thread.647777/#post-22592777). Based on you using both fridge and freezer temps you might land in the middle of the estimates - maybe 24-30 hours. If its hotter than 75 then it would be less.

Thanks for any answers. Hope this gets resolved to your satisfaction.

 

Plugged into ac mine isn’t even drawing at 1 amp/hr

 

see my post above about my current amperage draw on ac I will update with dc later this after noon

 

On AC, the current is much lower (10x lower in fact). On 12v, the 75DZ pulls about 6 amps when it's running. But it usually averages about 1.75Ah/h (internal temp at about 32°F), meaning I'll get about 24hrs from a 40Ah PLB-40 (about the same from an 80Ah AGM battery).

 

They don't show it while plugged in to AC power. Ah draw/usage is only shown while connected to DC (it should have been specified in the manual, but I haven't seen it. Maybe I missed it)

 

The outside temps are awful, with very high humidity. In saying that, it was when I got home that I dropped the temp to 5(on AC power). After 12hrs, it dropped from 12 to 9....and that’s it. Parked inside my shop, in the open bed of my truck. Everything that I put in it was cold or frozen before. Infact, the first day I had it , at the voltage dropped to 12.2, the temp on the fridge side kept climbing...to 81!!!! Something is not right. The fridge was initially cooled on AC. The second battery went down to 12.3v in under 12hrs, then I got home, switched to AC power and put the battery on the charge. This is the 3 month old battery that I used on the second day. https://www.academy.com/shop/pdp/in...ne-cranking-amp-battery#repChildCatid=6570502

 

Thanks for the response.

That's an 80Ah battery so about as good as can be expected. I does sound like there are some issues with your fridge. I would get on phone with Dometic and see if they can help troubleshoot and if that fails swap it out for a replacement. It may help to just focus on one issue - like the nothing below 9° issue - for better customer service. Try to save that one battery too if you can. I have heard of charger issues with batteries that aren't really faulty, just too low for the default charge.

I tested my Whynter-45G at 38°F on battery, but indoors at 72°F. I got around 15 hours before the battery cutoff kicked in at 11.3v (i think). I didn't check the pre-voltage but I think it was fully charged. In usage, I have had some issues sustaining overnight but there have been variables. Originally I only had a single 100w panel and when the weather was rainy it never really fully recharged during the day. Once the sun came out for full days then I was able to make it to morning sun again but just barely. This was running at 38° with ambient around 80° at mid day with the fridge about 2/3 full. I now run 2x100w panels and on a recent longer trip I ran the unit at 0°F with days from 60-80° and the unit from full to 2/3 full. We had two days of rain (wife was thrilled) and I had issues on the third morning. Everything stayed rock solid frozen but the battery cutoff kicked in at some point in the night and the display said it was 28° inside. Not sure where the sensor is located but it was still very deep frozen at the bottom.

My auxiliary battery is only rated at 65 Ah (dual 25/35 setup) so I actually think its doing pretty good. I really want to go to a split unit as I like having a freezer for longer trips. Right now on long trips I'm running the 45G as a freezer, a RTIC-45 as a fridge (fed with ice-packs/frozen bottles from the freezer), and a RTIC-20 as veggie cooler. With the 75DZ I was hoping to get rid of the RTIC-45 since the freezer and RTIC are actually only about half full each with real contents - water bottles are used as space filler/ice packs. (I'm keeping the separate veggie cooler though - that's been a big improvement not having the veggies getting half frozen or abused every time I have to dig under them in the fridge cooler. Stuff was getting too bruised and mushy before.)

Good luck with this.

 

Well, the fridge was plugged into AC, inside my shop(on the floor) all night, and it only got down to 12(set at 0). Also, I replace my battery with the same replacement. Now I’ll call @Dometic.

 

So I dropped off my fridge with a local RV shop, after talking to dometic. My question now is, should I run in on 24v(two 35ah 12v in series) or a 109ah 12v? It uses a lot less amps at 24v, but I’ve never dealt with 24v stuff. What’s the major difference in the two?

 

the 12v option has more energy capacity. I’d go that route.

Watt-Hours = Amp hours x Voltage

109Ah x 12v = 1308 Wh

35Ah x 24v = 840 Wh

 

Thanks. I’m just trying to figure out what I’m doing wrong, and to set it up the right way. I don’t completely understand all this electrical gizmo’s....but what make the jackery 1000 keep a fridge running for 3-4 days? I can’t find an AH spec on it.

 

Man, you gotta name your fridge something fun!

 

It won’t keep a 75DZ running for 4 days set at the temps you are.

The Jackery 1000 is 1000Wh. I get about 1 day from 500Wh running my 75DZ at 32° on both sides.

 

This power stuff always makes my head spin. The basic calculations are pretty straightforward but the variables in application always messes up the numbers.
According to an online calculator, 80Ah calculates to approximately 1000Wh. Considering the application, and the low voltage cutoff, is an 80Ah battery still a legitimate comparison to a 1000Wh Jackery? I guess what I'm asking is if you think the Jackery design gets more out of 1000Wh than I would having it a 80Ah as a dedicated fridge battery?

 

Yes, the jackery is getting more out of the 1000Wh because it’s lithium ion. So it can be drained to 0% repeatedly without much degradation. A typical lead acid or AGM battery should only be cycled to 50%. So an 80Ah AGM only has about 40Ah useable. So you’d really need a 160Ah battery to match up to the Jackery. Now you could just go with the 80Ah and run it down to 0% but you’ll be replacing it more often. How often? I really can’t say for sure.

 

Oh yeah, I forgot the Jackery was lithium ion. Big difference. Also $1k for the 1002Wh

 

Yea, it's a bit pricey. The Dometic PLB40 is about $850 for only 512Wh. It's a nicely built unit, but with a few less "features". Trade offs I suppose.

 

So... I have read this entire thread twice and my wife had read it as well. While I think I understand some of it I guess I’m still a bit lost at the end here. If we run a Cfx 75 dual zone and run one to keep snickers ice cream bars frozen so 5 degrees I guess, will we have enough run time over night on the standard battery in our first gen or even an ungraded one like the yellow top ultima or is a dual battery pretty much mandatory for frozen stuff? Assuming we are on the road each morning driving around 9 and at camp around 6 each evening. Some of what I read says we should be good, but other stuff makes my simple stupid brain think all my yummies will be melted.