Running trailer fridge on DC while towing

Sorry about the lengthy post, but I want to describe this situation completely…

I have a 2014 Tacoma 2-wheel drive with the factory tow package. I tow a 2014 16 ft Casita travel trailer equipped with a Dometic brand small fridge, which can run on Alternating Current (AC), DC, or propane. I recently (for the first time) ran the refrigerator on DC while traveling for a couple of hours. So far, I have always hooked up to electricity when camping, and had never run the fridge on DC. I have a battery minder in the trailer to monitor the trailer battery. According to Dometic, the fridge uses 9.58 amps per hour running on DC.

Here is the sequence of events which seems to indicate either a bad battery, something wrong with the DC operation of the fridge, or something else:
1. Leaving the campsite, I unhooked the AC power (battery showed fully charged – 13.79 volts before AC disconnected), switched the operation of the fridge from AC to DC, hitched up the trailer and plugged the trailer electric into the truck.
2. I drove for about an hour, then stopped for a break, and battery showed around 10 volts (too low!)
3. I unhooked the trailer electric connection to the truck, turned off the fridge completely, and went for lunch.
4. I returned about 90 minutes later, and trailer battery showed 9.79 volts (yikes)
5. I reconnected truck to trailer, turned on fridge (DC), and the battery immediately went to 12.07 volts.
6. Reached destination a couple of hours later, unhitched/unplugged trailer from truck, hooked up trailer to AC and switched the fridge to AC operation. Battery immediately went to 13.79 volts (typical when using AC for everything).
7. Some time later, to experiment, I disconnected the AC, and I watched the battery condition without anything turned on (no lights, no fridge, just the propane detector). Within one hour, the battery went from 12.97 to 12.64. Talking to another trailer owner, this appears to be an excessively fast decline in voltage with no load, perhaps indicating a bad battery.
8. I kept the trailer on AC, and did not have anything running in the trailer overnight.
9. The next day, I disconnected the AC, and with nothing turned on in the trailer, I hooked up the trailer to the truck. I started the truck and the trailer battery stayed above 13 volts
10. With the truck running, I turned the fridge on to DC, and the trailer voltage immediately dropped to 12.61, and within one or two minutes, it had dropped to 12.39
11. Wanting to compare using my truck with using a friend’s truck (2012 Tacoma), I hooked the trailer to the 2012 Taco. With nothing turned on in the trailer, the trailer battery voltage went from 12.67 volts before starting the truck, to 13.16 volts immediately after starting the truck. Within one or two minutes, the trailer battery voltage had risen to 13.42 volts.
12. With the friend’s truck running, I turned the fridge on to DC, and immediately the trailer voltage dropped to 12.7, and continued to drop to about 12.5 volts, with the truck running. I turned off this truck, disconnected trailer, and turned the fridge off.

Observations: The behavior of the trailer battery seems to be the same with both trucks when nothing is turned on in the trailer (trailer voltage holds above 13 volts), and also when the fridge is turned on to DC (trailer voltage drops below 12.5 volts very quickly)

I took the trailer battery in (it was under warranty, only 6 months old). They gave me a new battery, but did not say what was wrong with it, just that it was bad. I asked if it had a bad cell, and they said “no, it’s just bad”. They did not seem interested in discussing whether the problem came from my use of the battery or a defect in the battery.

Now that I have a new battery, I want to make sure that I am not doing anything wrong. On a Casita forum, a similar situation is described, and one contributor says that the truck wiring may be too small a gage. If that is the case, it seems that both trucks might have the same problem.

I would like to check with other Tacoma owners (especially 2014 with the factory towing package) to see if this seems to be a likely problem.

Would the tow package wiring requirements be different for a truck towing a small travel trailer like mine, equipped with things like this little refrigerator, trailer brakes and a 120 volt trailer battery, compared to a truck towing a work trailer with just trailer brakes and brake/signal lights? In my situation, I am towing a fairly light load, but have devices requiring power. This seems different from a heavily loaded work trailer that has the trailer brakes and lights, but no other electric devices.

Thanks for any input.

kathryn

 

Did you check to see if the battery was full? When they get low on eletrolight, they can display your symptoms?

Secondly, did you check these voltage with a multimeter, or just use the onboard gauge?

Lastly, there is a relay under the hood in the fuse box that feeds the trailer lights. I've had mine fail after I hooked up a trailer that was wired wrong. cheap to replace.

 

Thanks for the reply.

1. yes, the battery was full.

2. To watch the trailer voltage I am using an Inova device that plugs into the 12V outlet inside the trailer. It shows the voltage to 2 decimals, and has an icon that indicates the level of charge visually (so you know if you are at 50%, 70% etc).

3. The trailer lights and signals have always worked when I checked before each trip. I hope to not add to my worries.

kathryn

 

The only othere thing is there may be short in that trailer wiring system. Gonna take some hunting. Wish I could offer more.

 

truck only supplies a trickle charge.not enough to support the fridge running.around here everyone runs there propane while traveling.

 

Thanks!

 

On the Casita forums, the issue of using propane while travelling (I'm originally from Canada) seems to be whole other can of worms (problems keeping it lit, etc. ). But I don't want to change the subject. Right now, my fridge won't run on propane and I'm getting that fixed - which is why I tried the DC. Thanks for alerting me to the issue of small charge from the truck.

kathryn

 

the newer fridges are a lot more dependable with electronic starters.pilot lites aren't as dependable.still truck won't support battery.a catch 22

 

Thanks. I hope to get the propane operation working this week - I know it's the most efficient.

 

I think I'll have to research wiring. But I'm also thinking the battery might have been bad. It seems odd that if I was not towing the trailer, the trailer battery should have easily operated this little fridge for the duration of the trip. The Dometic people told me that the trailer battery should operate the fridge for approx. 3 days if other things weren't running. So I'm puzzled why the fact of towing would make a difference. And if towing does make a difference, then the wiring must be a factor. And that is something I need to learn about.

Thanks to all for all the input.

Kathryn

 

3 days running a fridge on battery power alone, seems really unrealistic unless the battery is huge. I was in the mountains last month with a new battery. Just running the lights at night, they were noticeably dim by day 3. It was COLD that week, 20 below some nights, but the little bulbs draw a lot less than 10a.

A basic car battery carries between 40-60 amp/hours of charge. At a 10a/hour draw (more or less) you've got 6 hours. The basic wiring between the tow rig and the trailer is *maybe* 5 amps, not enough to keep up with a heavy draw. It's designed keep a battery topped off. You can get more by really upsizing the wiring. You just need to be aware if you stay hooked up with a heavy draw you can end up with a dead trailer battery and a dead car battery.

A 12v battery at rest should be in the 12.4 to 12.6v range. If you drained it to 9v and were still drawing on it, you can kill a battery. So the battery may have been good when you isntaled it, you killed it, and got a replacement. Hard to say. If it had a bad cell it wouldn't have charged to 12+, figure on about 2v per cell capacity.

In summary, I think your fridge people lied to you.

 

To add to Indy's response. Your old battery might have been partially sulfated and not accepting a full charge or undercharged. Lead-acid batteries are perishable and you need to maintain them at a full charge when not in use. The drop from 12.97 VDC to 12.64 VDC after it is disconnected from a 14.4+ VDC charging source is the plate "surface charge" bleeding off and is normal. Temperature and parasitic load affect the amount of time it takes to lose its surface charge. The next time have the trailer connected and the engine running at fast idle, measure the voltage across the terminals of a fully charged house battery without a load. Compare that reading with the voltage you measure across the terminals of your vehicle's starting battery. That will give you the best case charging voltage and voltage drop across the trailer wiring and connector. You should expect approximately 14.2 or more VDC on the house battery at 77 degrees F ambient. Now apply a load on your house battery. If it drops below 13.6 VDC, then the voltage drop the trailer wiring is to great or vehicle's charging system is possibly undersized. I am assuming both the starting and house battery are healthy.

IMHO, OEM trailer wiring and connector is undersized for recharging house batteries or heavy trailer electrical loads. If possible, my recommendation is to try and fully recharge your house battery from a smart battery charger on "shore" power before departing and not run the refrigerator on DC while enroute. This will keep allow the vehicle's charging system to "top off" your house battery while enroute, so you will have a fully charged battery for dry camping. At 77 degrees F, the [absorption] charging voltage needs to be 14.4 VDC for a wet lead-acid battery and 14.8 VDC for a wet "Maintenance Free" or AGM lead-acid battery to full charge them. Undercharging causes a gradual buildup of lead sulfate reducing the AH capacity or CCA performance of the battery.

For more information, please see Section 9 in the "Car and Deep Cycle Battery FAQ" on www.batteryfaq.org.

 

Easiest method is to run the fridge before you leave, put some frozen water bottles in there and don't worry about running the fridge while you're driving. Run the propane when you get where you're going. Your food will be fine.