My Dometic RV fridge is sucking my batteries dry and I can't determine why?!

[sunshine_eggo]

Well, now I definitely can't send this page to him, thanks a lot!!!

I think I can salvage what is here. It seems to be good equipment, just undersized. Hopefully, he and who he works for will stand behind his contention of adequate capacity. I won't throw boogers, but I'll let you know how the negotiations go...

I think I cleaned it all up. You might need to edit your posts where you quoted me.

?

 

[Petenebraska]

Cleansing activated...



It's not about surge protection. Wire size certainly matters to prevent excessive voltage drop and resulting current increase, but it's about DC powered 12V items that draw a big SURGE of juice when they start. The DC-DC MUST be able to handle this full current, or it will overload.

Fuses on DC items are not good indicators of the needed current. Fuses are sized for the run current + safety factor. Fuses can handle the brief surge without a problem. Surges for electric motors are commonly 5X their run currents.

"quality converter" may mean buying an expensive high amp converter to handle the surge. High current converters are not particularly efficient when operating at low current. You might find that a "90% efficient" converter really can be that efficient, BUT it might only be 75-80% at the lower continuous currents you actually use.

Ha! Thanks!!

I think I'll do some amperage draw testing for my dc appliances to see what will work. Shouldn't be too hard. My cousin has AN AWESOME set of tools!!! (Fast times at Ridgemont High reference, there.....for all of you youngsters...)

 

[sunshine_eggo]

Ha! Thanks!!

I think I'll do some amperage draw testing for my dc appliances to see what will work. Shouldn't be too hard. My cousin has AN AWESOME set of tools!!! (Fast times at Ridgemont High reference, there.....for all of you youngsters...)

Spicoli For The Win!

You'll need a quality clamp DC ammeter with a MAX function. They tend to fail to capture the true peak due to the sampling speed, but it's better than nothing.

 

[Petenebraska]

Spicoli For The Win!

You'll need a quality clamp DC ammeter with a MAX function. They tend to fail to capture the true peak due to the sampling speed, but it's better than nothing.

I was serious about my cousin. He's the Electrical superintendent for a major plastics manufacturing company here on the coast. He really does have or have access to a pretty awesome array of electrical tools. He's just not familiar with solar. (plus he deals with 24K hp electric motors and the electrical systems that keep them running.) . Now that I have this info, I'll get into his toolbox. Thanks!

 

[Jims94vmx]

Not sure if the install not looking good was for me? It isn't done. I am in an RV and need it to be secure. Will be working on trimming it out so nothing around the edges will be seen. I literally just re did the shelf because of the feet on the front extended past the original shelf.

Just trying to be helpful.

 

[sunshine_eggo]

Not sure if the install not looking good was for me? It isn't done. I am in an RV and need it to be secure. Will be working on trimming it out so nothing around the edges will be seen. I literally just re did the shelf because of the feet on the front extended past the original shelf.

Just trying to be helpful.

Took me a minute to figure out what you were talking about.

We were commenting on the install of the OP's inverter/battery system in the first post.

Was helpful. Please post your end result.

 

[chrisski]

@chrisski , how many hours/day of A/C use can you do with your setup?

Realistically at the equinox March and September when AC is needed in the day, 8-10 hours for a single AC Provided there is not a cloud in the sky. In the longest days of the year probably 14 hours. In the shortest days of the year, may be limited to 4-6 hours.

This Write up gives some stats of running AC.

-Count on an inverter pulling 1700 watts from a battery bank for a 15 k BTU unit.
-My production at equinox was 2100 watts max. My max I produced in a day was 18 kWh, and could have done more, I just did not produce more. I should max out around 20 kWh.
-My production at the shortest day of the year is 1500 watts. The most I produced in a day was 7 kWh, think I could get 10 kWh to 12 kWh.
-I am not sure of production at the longest days of the year. AZ temps are typically 110 F and a single 15 k BTU AC will not cool an RV. Two will, but i don’t have the power.
To run the AC on solar, there is 1650 watts of flat panels on the roof with 900 watts on the ground. This is really close to what Will said of filling up your roof and putting just as many on the ground.

 

[sunshine_eggo]

Realistically at the equinox March and September when AC is needed in the day, 8-10 hours for a single AC Provided there is not a cloud in the sky. In the longest days of the year probably 14 hours. In the shortest days of the year, may be limited to 4-6 hours.

This Write up gives some stats of running AC.

-Count on an inverter pulling 1700 watts from a battery bank for a 15 k BTU unit.
-My production at equinox was 2100 watts max. My max I produced in a day was 18 kWh, and could have done more, I just did not produce more. I should max out around 20 kWh.
-My production at the shortest day of the year is 1500 watts. The most I produced in a day was 7 kWh, think I could get 10 kWh to 12 kWh.
-I am not sure of production at the longest days of the year. AZ temps are typically 110 F and a single 15 k BTU AC will not cool an RV. Two will, but i don’t have the power.View attachment 123944
To run the AC on solar, there is 1650 watts of flat panels on the roof with 900 watts on the ground. This is really close to what Will said of filling up your roof and putting just as many on the ground.

I was hoping you would demonstrate to the OP that the current system is inadequate for any major A/C demand, and you did it very nicely. Thank you!

I find similar numbers with my 3kW, but we're really sloppy about other power uses. Wife likes to dance around the RV turning high power shit on for fun. Brew coffee in the Keuri, let it get cold. Nuke it in the microwave. Airfry some taters for the breakfast burritos, run the panini press to toast the burritos, run the countertop dishwasher, etc. I just sit there nervously watching VRM to make sure we're not in overload. Since we're usually only there a couple nights, I can dip into the 23kWh of battery without concern as it will catch up after we leave.

Seriously though, she's actually pretty good, but we don't make major efforts to conserve unless it's cloudy and hot. 8-10 hours is a pretty reliable number, and it's usually me who's willing to run it a few hours afternoon/evening when we're paying for it with battery to help accelerate the evening cooldown.

 

[Johneb]

Those do look like a tank!!! But, if I were to purchase one, then it looks as though I'd have to buy an MPPT as well?? The one I have already has one integrated. It would have been nice to pass 240v on through though...

Idle draw in power saving mode 8w. In normal mode <30w.

 

[sunshine_eggo]

Idle draw in power saving mode 8w. In normal mode <30w.

Worth mentioning that power saving mode is worthless for anyone that needs AC loads 24/7, which is most folks.

 

[Cal]

I've been doing a lot of testing on my Norcold N611 absorption fridge. It operates on either propane or 300W ac. When operating on ac power, via a dedicated 500W inverter, the 12V battery is loaded with 25A. That a huge load for my 180Ah LiFePo4 battery. Therefore the fridge operates on ac only when the engine is operational. The 40A dc/dc, which is sourced from the alternator provides the charge to keep the battery from getting drained. I built my own BMS and can activate the 500W inverter from my iPad (via wifi).



This plot has battery current scale on left side (30A to -30A) and battery capacity in amp-hrs on the right (SOC description is in error). Time scale is in minutes, starting from 1150 minutes. The battery is near 100% charged when the fridge is turned on and also the engine is started. The current switches from 20A (dc/dc is on) to -25A (dc/dc off) multiple times while driving. The BMS turns the dc/dc and solar off when cell voltage reaches 3.41V. After ~10 minutes of driving the vehicle is turned off and current settles to around -20A. Solar provides about 6A. During this time the fridge is full on. Not until 1260 minutes does the fridge cycle off the first time. Charging current goes to 5.4A. At 1274 the fridge turns on again.

Fridge duty cycle = 31 minutes/45 minutes = 69% The duty cycle is dependent on ambient air temperature. If it's hot then fridge will be on 100% of time.

The engine is started at 1447 minutes. The 40A dc/dc turns on and battery current changes from -23A to 17A.

BTW, the current has a downward curvature. That's the effect of the sun dropping elevation and reducing solar output.


I've added a temperature sensor on the fridge boiler. The BMS monitors the temperature and shuts down the fridge in case of a thermal runaway.



This is a plot of fridge boiler temperature in deg.C. Taking the second cycle in the plot, the propane heater turns on at 1068 min. (124C), has a peak at 1085 min. (212C), turns off at 1103 min. (166C) and turns back on at 1120min. (123C). The duty cycle is: 35min. / 52min. = 67%.

 

[RoadTurtle]

I'm in way over my head here, but there was something that caught my attention, keeping the existing 12v intact.

Here's a really stupid question, is the original converter/charger still in the system and is receiving 120V from the battery bank to run the charger off the inverter, creating a never ending loop?

I originally missed this when I first put in my inverter to run the entire trailer off of batteries. It killed the batteries in a matter of hours.

 

[sunshine_eggo]

I'm in way over my head here, but there was something that caught my attention, keeping the existing 12v intact.

Here's a really stupid question, is the original converter/charger still in the system and is receiving 120V from the battery bank to run the charger off the inverter, creating a never ending loop?

I originally missed this when I first put in my inverter to run the entire trailer off of batteries. It killed the batteries in a matter of hours.

Nope.

The inverter is powered by a completely separate 48V battery bank. Think of it as on board shore power.

 

[chrisski]

Here's a really stupid question, is the original converter/charger still in the system and is receiving 120V from the battery bank to run the charger off the inverter, creating a never ending loop?

Depends on how the inverter is wired.

I shut the circuit breaker off to the converter. If I don’t, it keeps the loop you talk of.

In my case, I plug my inverter to shore power on the RV. That’s why I get the loop.

If you don’t have a dedicated circuit breaker, things get harder.

RV with Tito has a video on using a contractor relay to shut off the converter so this doesn’t happen. I opted not to build that.

 

[Checkthisout]

I'm in way over my head here, but there was something that caught my attention, keeping the existing 12v intact.

Here's a really stupid question, is the original converter/charger still in the system and is receiving 120V from the battery bank to run the charger off the inverter, creating a never ending loop?

I originally missed this when I first put in my inverter to run the entire trailer off of batteries. It killed the batteries in a matter of hours.

No, you should start a YouTube channel and market this as an overunity product and save the world!

Also, some inverter/chargers have an output that is only live if a/c power is hooked to it. This is a perfect use for that output.

 

[Bobert]

My wife and I now live fulltime in our 34' fifth wheel. We are currently in TX. In October, we went to Hawaii for a month and while we were there, I contracted with a company in Idaho to install a solar system. I now have 18 - 100w panels, a 6000w inverter/charge controller, 2 100ah/ 48v LiFePo rack batteries and a battery monitor (SOC reader). I started having troubles with it immediately but was assured that it was an exceptionally robust system and would accommodate our lifestyle of travelling and following the weather (not running the A/C units "all the time".) Through many conversations with the installer (who is great, by the way) we are leaning in the direction that the Dometic RV fridge (absorption style) is sucking too much juice. It pulls 400 - 500w for most of the day. It's very rarely pulling less than 350w. Well, that doesn't pencil out and my installer says that his research suggests that RV fridges are supposed to be MORE efficient than residential, so he can't imagine how it's pulling so much.
When the system was installed, the installer decided to leave the whole 12v system (12v lead acid battery, 12v charger/converter, wiring, fuses, etc) intact and just bypass all of that and wire directly from the new 6000w inverter to the breaker panel. Initially, I thought that sounded like a good idea, but my continuing problems make me think that wasn't the best design?
Does anyone have any suggestions about A.) Should we have pulled the existing 12v system out of the trailer prior to installing the new system and installing a DC to DC converter?
B.)Have you ever heard of an RV fridge pulling this much juice and do you know of a "fix". I'm considering buying a new, small residential fridge to replace this one and just plug into the 110v outlet in the fridge cabinet and letting the 48v batteries handle it without the added complications of the 12v DC and propane inputs.

Thanks!
Pete

My small dometic fridge uses 450 ish watts of power while on ac power and calling for cooling. Yours is in a slide and needs circulating fans in order to work properly. Because you have no roof vent for natural convection this adds to the power consumption. If spacing or the vent fans are incorrect the fridge will run nearly continuously even in moderate weather. I didn’t get a chance to thoroughly read all the other responses but here’s a few ideas for you.

If you want tor run the fridge off electric only a compressor fridge is the best option. Absorption fridges are designed to use lp for off grid applications and save gas when connected to “free” campground power. They are inefficient on electric power. Improperly installed they are very inefficient.

If you use a lithium battery for the 12v side of your rv you can reduce the losses associated with charging and discharging a lead acid battery and still maintain the additional redundancy of a separate 12v system.

A 48v to 12v converter is an efficiency improvement over the standard converter charger by has 2 drawbacks that I know of. It reduces redundancy by not having battery backup should the converter fail or if your 48v bank becomes exhausted. The other potential drawback is that 48 to 12 volt converters have been reported outputting 48v under certain conditions when they fail.

One solution is to simply use lp to run the fridge off grid. That is what we do.

 

[Checkthisout]

One solution is to simply use lp to run the fridge off grid. That is what we do.

Which still sucks because they don't have auto defrost.

You have to shut it down and clear the ice.

 

[Petenebraska]

I was hoping you would demonstrate to the OP that the current system is inadequate for any major A/C demand, and you did it very nicely. Thank you!

I find similar numbers with my 3kW, but we're really sloppy about other power uses. Wife likes to dance around the RV turning high power shit on for fun. Brew coffee in the Keuri, let it get cold. Nuke it in the microwave. Airfry some taters for the breakfast burritos, run the panini press to toast the burritos, run the countertop dishwasher, etc. I just sit there nervously watching VRM to make sure we're not in overload. Since we're usually only there a couple nights, I can dip into the 23kWh of battery without concern as it will catch up after we leave.

Seriously though, she's actually pretty good, but we don't make major efforts to conserve unless it's cloudy and hot. 8-10 hours is a pretty reliable number, and it's usually me who's willing to run it a few hours afternoon/evening when we're paying for it with battery to help accelerate the evening cooldown.

I think the installer and I need to have a serious discussion about his calculations and assumptions. I haven't yet, but I'm going to send this page to him. It's very informational, thank you all!

I just went to Home Depot and bought a residential fridge. It gets delivered on Fri so after some reconstructive surgery to the cavity, I'll have an energy efficient fridge, at least (and I'm looking forward to the project...I'm a little bored...don't tell my wife!!). Anyone want/need a perfectly adequate Dometic RV fridge??

 

[Checkthisout]

I think the installer and I need to have a serious discussion about his calculations and assumptions. I haven't yet, but I'm going to send this page to him. It's very informational, thank you all!

I just went to Home Depot and bought a residential fridge. It gets delivered on Fri so after some reconstructive surgery to the cavity, I'll have an energy efficient fridge, at least (and I'm looking forward to the project...I'm a little bored...don't tell my wife!!). Anyone want/need a perfectly adequate Dometic RV fridge??

I'll take it off your hands

 

[Petenebraska]

Nope.

The inverter is powered by a completely separate 48V battery bank. Think of it as on board shore power.

Isn't that what RoadTurtle is asking? I think he's right. The 12v inverter is receiving 120v from the new 48v inverter and batteries via the breaker/fuse panel as if the rig is hooked up to shore power. So I see his description of a "Loop" but it's just a charging loop to power the 12v system of the camper. You've already addressed that and the efficiency of it still being in the system.