The Dometic CFX3 Mega Thread

You really shouldn’t discharge an AGM battery below 50% of its capacity. Determining state of charge based solely on voltage is a bit tricky and not all that accurate. At rest (hours of no load), at about 77°F, 11.8v is basically completely discharged. You can discharge it further and the voltage will continue to drop, but you’ve pretty much gotten all the power out by 11.8v. The tricky part is that the under load voltage can be much lower and the temperature affects the voltage measurement.

 

Aren’t deep cycle specifically meant to be discharged really low and recharged with no ill effect?

 

Ok that makes sense. And would explain why the unit is entering protection mode at the point that it is. However, it flies in the face of the heavy advertising @Dometic is putting forth on the CFX3s that they are efficient enough to run off a single battery since last weekend camping it was dead by 5AM after arriving in camp after 4PM.

 

I’m not a battery expert, but I think “deep” is relative. A typical starter battery isn’t meant to really be discharged much at all.

 

Thatswhatshesaid

 

Wow, that is much faster than I thought it would be. Would a typical lead acid be better than this though?

This has really got me thinking that a dual battery system needs to be a lot higher on my list...

 

Yea. That chart is slightly misleading:

https://marinehowto.com/under-load-battery-voltage-vs-soc/

The chart is probably referencing the voltage under 20-hour load.

So I’m still basically right.

 

I think it just takes longer for those numbers to get lower. I have a 27F and have no issues with my fridge running a couple day’s. I think it’s just your 34 being a lil small.

That’s a lot of words so I’m going to say you’re still wrong

 

Still sounds like something is a little off. Unless it was just stupidly hot or you cooled your fridge from ambient temp at camp, then I think you should have gotten a few more hours but not much.

 

The 75DZ is a power hungry beast. I get about a day from my 27F before I’m worried. I also don’t think my battery is fully charging, but even so I don’t think I’d get close to two day.

 

Nope. I cooled the fridge down to temp before leaving the house from AC, put only cold items in the fridge, then drove over 3.5 hours to camp at Rausch Creek so I know the battery was topped off, and temps were only in the high 70s at their highest.

 

Well since DOMETIC markets to “overlanders” they probably assume you are driving at least every 12 hrs.

 

Yea. You have to remember that the voltage drops while it’s running. So you might come back and see that the battery voltage is 11.8v but while the fridge was running it might have been 11.2v. Thought usually the voltage drop under just a few amps is a lot less than that. So I still think something is a little amiss here.

 

I wonder how much having the freezer section set and not double fridge sides comes into play?

Are you even an overlander if your trip is shorter than six months? Those are rookie numbers.

 

I really enjoy your bickering! Now, according to the internet JoeB is right and it makes sense.


Hate to be a troll and just repeat stuff I've read on the interwebs, but it is what it is
Randy your Northstar 27f had 92Ah capacity, wayyyy more than group 34 Oddysey, with your 2nd gen having capability to properly charge it every time, you will not have any issues with cfx355im. (I'm jumping into conclusions here big time, but do you actually have voltage booster?)

Myself, I was afraid that my undercharged 27f would not be able to power a 75dz (with a freezer) overnight, so I decided to run a dual setup.
I really hope @littlefish 's fridge is fine (since it's way cheeper and faster to replace the battery, than a fridge) I'm just wondering if battery voltage dropped too low when compressor kicked in, and battery didn't have a chance to recover in time (also 11.8V being discharged anyways)

 

All the voltage readings I took were while the compressor was running.

 

Im sure it plays a huge roll. The freezer consumes a lot of power.

 

I tried running a 75dz on a single 31 marine deep cycle battery for a while. I wasn’t happy with the run time so I installed another, after that in addition to 100w of solar it ran indefinitely for months.

 

First off, I missed a lot of the conversation between quoting ya'll and actually replying. My bad

OK. Not trying to split hair, and I'm really not trying to attract you and defend Dometic, or whatever. Probably I should stfu, just want to clear something up.
Even though our new fridges should be the newest engineering marvels, when a compressor kicks in, it draws more amperage VS when it's just running.
I might be completely wrong about stuff (happen like twice thia year ), and of course it's entirely possible that power saving mode could be too sensitive. At the end of the day, we don't want come back to a warm spoiled food while camping.

Really hope you get your issue resolved.

 

How bad was it on single 31m?