Subaru Ascent Forum banner
1 - 20 of 28 Posts

·
Registered
Joined
·
107 Posts
Discussion Starter · #1 ·
Does anyone know the maximum safe current that can be supplied through the 7 pin plug to a trailer? I have a 3 way refrigerator in our trailer that will draw 17 amps when running on 12V and wonder if the Ascent wiring as well as fusing is adequate to keep the trailer battery charged when running the fridge while traveling.
 

·
Administrator
Joined
·
11,108 Posts
Fuse #28: "Trail" 15a
SBF-4: Slow Blow Fuse in the Engine Bay 40a.
 

·
Registered
Joined
·
107 Posts
Discussion Starter · #3 ·
I found Fuse 28 but not SBF-4 in the engine bay (or is this one of the resettable circuit breakers?). Which one feeds the 12 Volt for charging the trailer battery - I believe this is pin 4 of the 7 pin connector. If it's the 40A then there should be no problem but if it's the 15A then I would think it would blow the fuse if I am drawing 17A.
 

·
Administrator
Joined
·
11,108 Posts
I believe SBF4 is for braking, meaning "Trail" #28 is for power/charging, but I have not tested to make sure. Pulling the fuses and doing a continuity test may confirm my suspicion, but, I do not have the time today (or probably this week).

So, my suspicions are you're 2a too low. But, if you get a chance to test before this weekend, let me know.

SBF4 is 2nd from the right in this diagram. It is a "S"low "B"low "F"use (hence the designation).
4950
 

·
Read Only
Joined
·
0 Posts
So, my suspicions are you're 2a too low. But, if you get a chance to test before this weekend, let me know.
More like 8a too low.

I'd fuse that circuit for at least 25a, possibly even more due it being a refrigeration load with a possibly large start up demand. My usual target is <75% of a fuse capacity for circuit load, so 17a on a 25a is 68%. You could do 17a on a 20a but that's 85%, too high for my liking. Circuit breakers (IIRC) are designed for 80% rated capacity 125% ampacity of the wire, so there's also that route.
 

·
Read Only
Joined
·
0 Posts
Fuse 28 does feed Pin 4 of the 7 Pin plug. 15A seems low for charging the RV battery.
There is not start up as its only a heater as it's an absorption refrigerator - no moving parts.
Like a peltier device? I'd look at the manufacturer recommended feed wire / fusing requirements or amp it out in normal running and heat-saturated start up states before I fused it.
 

·
Read Only
Joined
·
0 Posts
You should not just change a fuse size because you need more amps. The fuse is to protect the wire from melting in case of a short and starting a fire.
Correct, i was not advocating for replacing the fuse, I should have been more deliberate in my post to advocate for a supplemental wire run of appropriate rated wiring.
 

·
Administrator
Joined
·
11,108 Posts
You should not run LP while moving After you are parked and level, light it up. But while engine is running, use the 12V.

I would run it on LP while traveling. You will most likely drain your battery running it on 12v power. We turn ours on the day before we plan on leaving then run it off LP for the trip there.
Most fridges (eg: Dometic's line) will not use LP if not level. So, while most places don't seem to recommend against it for safety reasons, the problem is that many fridges will shut off as soon as the trailer isn't level, then try to turn back on, and then repeat. Some are pretty sensitive.
 

·
Registered
2019 Ascent Premium
Joined
·
366 Posts
I believe SBF4 is for braking, meaning "Trail" #28 is for power/charging, but I have not tested to make sure. Pulling the fuses and doing a continuity test may confirm my suspicion, but, I do not have the time today (or probably this week).

So, my suspicions are you're 2a too low. But, if you get a chance to test before this weekend, let me know.

SBF4 is 2nd from the right in this diagram. It is a "S"low "B"low "F"use (hence the designation).
View attachment 4950
FYI this 40A fuse is the fuse that blew and cut the power to my brake controller, unbeknownst to me. I would have thought the inline 20A fuse would have failed first. Took the dealership just a short period of time to locate this fuse as the issue causing no power to the Tekonsha controller. Up until then I'd never heard the term "slow burn/blow" fuse before.
 

·
Registered
2019 Ascent Premium
Joined
·
366 Posts
I would run it on LP while traveling. You will most likely drain your battery running it on 12v power. We turn ours on the day before we plan on leaving then run it off LP for the trip there.
This is a topic that generates lots of passionate discussion in RV forums. Some people say they've done it for years without an issue, and an equal number take the opposite view. My understanding if you do travel with the propane on that there are places where the propane must be turned off, such as tunnels and gas stations, but there may very well be differences by state. I for one have put 6000 miles on my trailer behind my Ascent with the Dometic refrigerator turned off, up to ten hours at a time, and never had an issue with spoilage/thawing upon arriving at my destination. Of course I precool the fridge, freeze a half gallon container of water to help keep things cool, and pack the freezer section with lots of frozen food.
 

·
Registered
Joined
·
609 Posts
Most fridges (eg: Dometic's line) will not use LP if not level. So, while most places don't seem to recommend against it for safety reasons, the problem is that many fridges will shut off as soon as the trailer isn't level, then try to turn back on, and then repeat. Some are pretty sensitive.
The fridge must be level to work correctly, but it will still work. Most of our towing is flat and level.

I would also agree with just running without power to the CG if you are concerned about safety. It would have to be a really long trip to spoil most food. And there is always the ice chest option.
 

·
Administrator
Joined
·
11,108 Posts
The fridge must be level to work correctly, but it will still work. Most of our towing is flat and level.
That's a generalization that's incorrect as such. For instance, the Dometic series in the Heartland Edge M18 and M21 will either (a) shut off, or (b) try to switch to DC or AC power, depending on if it's in LP mode or Auto mode (respectively).

So, what I am trying to say is that it's fridge specific. As I said, multiple models will shut off if set to LP and the vehicle is driven and sets off the level sensors while driving. Not all, but quite a number of them.
 

·
Registered
Joined
·
609 Posts
Any modern vehicle that has provisions for towing should be able to support that load whilst the engine is running. It's usually only super-economy minded vehicles that are designed to account for every last amp under the guise of efficiency that cant.
Which is pretty much every vehicle produced today. Even f150s only put out 5 to 10 amps at the 7 pin connector according to some rv forums I frequent.
 
1 - 20 of 28 Posts
Top