Refrigerator on battery while in transit, pit stops?

Jay_and_Kat

Some co-workers today made a comment about towing with a fridge running on 12V and stops, suggesting not to do this as it'll drain the tow vehicles battery.  Well, we're heading north with a 4-5hr drive (said time includes a stop for breakfast) and I'm wondering if when we stop we should either disconnect the camper from the TV while we eat, or go in the camper and turn off the fridge so we don't have to ask for a jump start to get back on the road.

Or, once again, am I over-thinking things and the camper batteries and the solar will be more than enough to keep the fridge running without draining my Jeeps battery while we have breakfast?

johnfconway

If there is sun hitting the panels, you are highly likely OK. If not, the Norcold 3-way on 12V is a notorious power hog. But it's breakfast... how long could it take?!

Jay_and_Kat

Well, it's July 4th weekend, so...
1hr wait for a table, 1.5hrs to get the meal...  

Nah, wouldn't be that bad, (I hope) probably an hour-ish or so.  But it sounds like if it looks like it might take "a while" we'd be safer either shutting the fridge off while we're there or disconnecting the camper from the TV electric.

pthomas745

Tell us what exact fridge you have...if it is just the two way fridge, drive with it on.  If it is the 3 way, the newer 3 way fridges need ...wait for it...16 amps...continuously, to run.   The two way fridge uses about 1.5 amps per hour (depending) and as long as the solar/vehicle can keep up with that, (you have a large battery setup in the 400), then drive along with it on.

The dreaded "unplug the trailer from the vehicle because it will drain the battery issue." I'm not sure, but I think this is an "old camper" sort of thing that was common back in the day, but not so much with modern vehicles.  (I'm assuming a lot, here.)

Don't take anyone's word for it: test for yourself if your vehicle has an "Isolation Relay" that prevents power from being drained from the battery. Find the "Mouseketab" comment in this thread, there is a very simple procedure to test your setup.

https://tab-rv.vanillacommunity.com/discussion/comment/138756/#Comment_138756

Jay_and_Kat

@pthomas745 it is the NorCold 3-way, so it's going to be the hog...

And I think I'll also give that electrical test a try when we hitch up tomorrow to bring it home.

pthomas745

I want to say "most modern vehicles should" have an isolation relay, but it is better to test for yourself. Same thing with the fridge on 12V while driving.  Some owners swear their beast mode cars do it without a problem.  It is something you can test with the Victron app.

Denny16

Jay, your best bet is to pre-cool the fridge at home on AC, then freeze some 1qt or 1/2 gallon jugs to put in the fridge for the transit and run with the fridge off..  When you arrive, switch the fridge to AC or Propane depending on shore power availability.  The Gladiator alternator puts out max power a low RPMs, no high RPMs like older trucks do.  So you are not going to get a lot of charging power out the 7-pin whilst running higher RPMs towing the TaB.  It is adequate for the small load of the small 2-way fridge in our TaB400, but I would not run the large 3-way fridge on DC for any length of time, an hour or two or would work.  

Also, the 7-pin remains powered with the engine shut off.  For short stops of an hour or less, I just leave the TaB plugged in.  For overnight, I would unplug the TaB from the Jeep.  

 Cheers 

Jay_and_Kat

Hmm, sounds like we might be having to do a bit of re-thinking of our plans than.  We were going to pre-cool the fridge tomorrow into Friday morning with both AC and some gallon ice jugs we've used in our freezer, while the groceries sat in our house fridge getting cold.  So might now set up to use our big Yeti cooler (which WAS going to be staying home) to carry the groceries in the Jeep.

Our campsite will have a 30A shore hookup, which would be running the fridge on-site.

bergger

We pre-chill the fridge and if space allows put in some freezer packs.  If not just pack the fridge with cold food.  While traveling we turn the fridge on 12v.  Yes it is a power hog on the batteries but with the solar set up and the 200 amp alternator it keeps up fairly well.  It does draw down the trailer batteries but not too bad.  Of course this depends on the sunshine too.  When the our truck is turned off the trailer does not draw power from out staring battery.  It just draws down the trailer batteries.  

As we travel down the road we check occasionally check the battery level with our Victron battery app.  This is convenient and if I see the battery get into the mid to low 80% range I will turn off the fridge at a gas stop or lunch break, drive for a while to recharge the battery then turn in on again.  On long trips, say 7-10 hours of driving I will usually turn the fridge off and back on a few times just to be safe.  When we stop for an extended break, lunch or whatever, I will also turn it off as I do not feel the performance of the 12v power is worth the draw down on the battery.  Keep the fridge closed during your trip and keep an eye on your battery and you'll be fine.  But on long stops I'd turn it off.   If all is cold inside it will maintain cold temps for a while.  Or if it's gonna be a few hours of stopping you can always turn on the propane during your stop.  

VictoriaP

@Jay_and_Kat
Some recommendations:
- Freeze multiple smaller bottles or ice packs, put them in the pre-chilled fridge along with your pre-chilled food. The fridge makes an excellent cooler.
- I’ve seen a couple of people recommend alternating the fridge on or off for every hour or so of driving if you’re dealing with a long drive. In other words, stop to stretch your legs every hour, and switch the fridge on 12v from on to off (or vice versa) when you do so. While this does use a fair bit of power still, it’s half what it could use if you simply left it on. Since in this case, you’ll have power when you arrive, if you want to try this, I’d probably only run it for an hour in the middle of your drive; it will stay plenty cold in between for a couple hours if you have some ice packs in there too.
- Two items you should always have in your Jeep: a 12v tire inflator, and a self contained battery pack capable of jumping your own battery. Especially on a holiday weekend, when roadside assistance will take absolutely forever!

Denny16

Jay, if you pre-chill the fridge and food, add the cold packs or frozen jugs, then you should be good for four hours or so, depending the the temp.  We carry the Yeti in the back of the jeep with critical foods, like meat, milk, and a few drinks.  The produce, cheese, eggs, etc we carry in the pre chilled fridge.  Even if the fridge warms up to 45 or so for a short time, these items will not be affected.

How you go, depends on the drive time, and outside temps.  For longer drives, you could run the fridge on DC for n hour or so, every three hours, and the Jeep should maintain the charge driving with the fridge off for two or more hours.
It is very situational, and there are too many variables for any hard and fast rule or approach.
 Cheers 

Yoshi_TAB

pthomas745 said:

I want to say "most modern vehicles should" have an isolation relay, but it is better to test for yourself. 

...I also would think so...but my 2021 Jeep GC does not.  Easy to test on a vehicle.   I have stopped up to 3-4 hours to site see w/o unplugging and have not had a problem with the frige running on setting 2-4.  

Jay_and_Kat

So when I was hitching up to bring the camper home, I followed the steps to check for an isolation relay.

The '22 Gladiator Sport doesn't have one.

The camper is at home now, in AC with ice jugs in it and a remote thermometer, so we'll see if it cools down, considering I had to put it in the drive with the vents for the fridge facing the sun and it's touching 90F already outside...

pthomas745

Well, thank you for the updates on your isolation relays.    Another "assumption" bites the dust!

Denny16

The new Jeeps have relays, but the 7-pin battery charge connection is left on whilst the Jeep is turned off.  Their is a relay between the small Stop and Go battery and the main battery, which on the Gladiator is 75AH AGM starting/house type combo battery, which is connected to the 7-pin.  The smaller Start/Stop battery is disconnected when the engine is off, and will start the Jeep, if the big battery is run down, from what I understand.  So the answer is battereis are isolated, but main battery is left connected to the 7-pin.
 Cheers 

Jay_and_Kat

Well one piece of good news so far, the fridge is cooling down nicely, the last time I was in and checked the thermometer about an hour or so ago, it was getting ready to cross out of the 40s into the 30s.  We bought a small cooler, big enough for a couple 4lb ice packs, a gallon of milk and some other items so we don't have to drag along our big Yeti 105...

bergger

Good news.  Enjoy the trip and the trailer!

Denny16

Yes, have fun Jay and Kat, be safe…
cheers

Chopin

We have the isotherm 12v fridge and routinely tow with it cranked up to 6 or 7. It seems to mostly run off the solar while towing. If it’s pulling from the car battery it’s nothing we notice. Note: if we’re making short pit stops I leave the 7-pin plugged in but if it’s anything longer I disconnect the 7-pin to stop it drawing from the car battery when the engine is not running. Done this on 14 trips, some as long as 6 hours with no problem. We also took a 4 hour ferry ride once. I disconnected the 7-pin and dialed the fridge down. It ran off the battery fine. 

hustoncs

@Jay_and_Kat We have the three way fridge and we do this.

Bring the trailer home from storage and run the fridge for 24-48 hours to cool down off shore power. Then we load it up with what we are bringing that needs to be refrigerated.

While we are driving we do run the fridge off battery and monitor the batteries with the Victron app. We also dial down the temp a bit as well and we monitor  the inside temp.

At stops greater than a gas fill-up we turn off the fridge.

At the campsite we turnoff the fridge until we are on shore power or on propane.So far this has worked well for us Cheers

JDRotz

A question for those saying to use the Victron app to monitor the battery SoC.  Are you using a Smart Shunt, or something similar to get an accurate indication of the battery condition?  Without that, I was under the impression that the Victron MPPT controller information on battery SoC wasn't really accurate due to current draws that aren't accounted for. 

As an aside, just did a 5 week trip through the Pacific Northwest, and was very impressed with the 12V Isotherm in my '21 T@B 400.  Kept frozen stuff frozen on the #5 setting, and had enough room for (just) me.  I was concerned about the parasitic draw on the TV battery ('13 F150), but on a couple occasions I left it hooked up/plugged in overnight while off-grid, and didn't notice any issues when starting the truck in the morning.   Since I wasn't measuring battery voltages or draw with the engine off, those results don't really mean much.

Is it confirmed that the trailer battery charging function on the 7-pin connector will allow the TV battery to be drained?  I'd think the charge controller wouldn't let that happen.

Denny16

You can install either a Smart Shunt or the original display model of the shunt battery monitor, and it will report to the Victron App corrected SoC as well as current DC battery energy being used and charge status.  The App can network the Shunt and Solar controller to work together.
 Cheers 

pthomas745

@JDRotz If you have a lead acid battery, the battery state of charge will always be inaccurate on any voltage measuring device if the battery is being charged, or if the battery is "in use", or being discharged. ("False Capacity").  The "most accurate" voltage readouts are achieved if the battery is allowed to "rest".  Turn the battery switch off, and turn off or disconnect any chargers (solar or shore power).  Depending on how much is running in the trailer if you try to read the Victron with the battery switch on, the difference in voltage compared to a "rested" battery can be significant.

The thread linked above has a procedure to check if your vehicle has an "isolation relay" that would prevent the vehicle battery from providing power to the trailer if the vehicle is "off".

rcarlson1957

I drive with my 3 way fridge on 12v in my 2018 320S. But I also put in a 100 a/h lithium battery and use a Victron Smart Shunt and Victron App to watch battery charge and also an Engbird frig monitor and app to monitor frig temp. With stock battery, my battery would be dead by time I got on site. Now it's never a problem. 

bergger

@JDRotz we have the smart shunt installed and use that app while traveling to monitor our battery.  And yes, as @pthomas745 said it is not completely accurate as it is having a discharge and charge.  However it is no different than checking your battery state while camping.  While camping the battery is discharging and charging as well and not at rest.  We have found that using the smart shunt to monitor the battery has worked well for us.  If the battery gets down to 85% or so we will turn off the fridge at our next stop and charge it back up for a while then turn the fridge back on.   We have the stock dual 6v batteries and this has worked well for us with the factory solar and the 200 amp alternator on our truck.  We've never even come close to running our batteries down while driving or while camping.