Question on max current through the 7-pin

[Michael_EE]

Originally Posted by bigb56

Yes, this is what I said as well.

Indeed you did

Originally Posted by bigb56

Being that you are an EE can you show an example calculation where the resistance of the #10 wire is enough to keep the current in check for some of the non-believers? I worked in the residential wiring trade and I don't think most folks realize what a huge impact VD has when the voltage is only around 12 volts.
(SNIP)

Better than that, I'll try to model this tonight or tomorrow morning which will be more visual than what we've been trying to describe.

[ArtJoyce]

Originally Posted by darrellr

The first part of the statement is true for sure. However, the statement about #10 wire is wrong. My 2021 Ram is #10 to the 7-pin, from the factory. Edited to add it is fused at 30A.

What wire size did the trailer come from the factory with?

[MarkSaxton]

I'll try to model this tonight or tomorrow morning

Very nice! :-)

[darrellr]

Originally Posted by ArtJoyce

What wire size did the trailer come from the factory with?

I haven't been back out to the trailer to check yet. It is at a storage place and I am on the road right now for work.

[Steve 716]

You can pull enough current through the coil cord to run a battery maintainer wired to your toad battery. The 12 volt fuse in my coach for the this line is 20 amps. A maintainer will pull 12 amps max if your battery is very low but generally just pulls enough for a trickle charge.

[Tomahawk]

Originally Posted by 4x4ord

I don’t know what limits the current through the 7 pin connector hot wire but it is not the fuse or the resistance of a 10 AWG wire. If the rv battery was dead (12 volts) and the truck alternator is putting out 14.5 bolts there would be a 2.5 volt gradient between the truck and rv circuits. The resistance on 25 feet of 10 AWG wire is about .025 ohms. If current were allowed to run unrestricted through that wire there would be 100 amps going to the RV …. the 30 amp fuse would blow immediately (2.5 volts/.025 ohms = 100 amps). There is going to be resistance in the dead battery …. It will only accept a charge of 20 amps or so. I suspect the truck and RV might both have some kind of regulators in their circuitry as well to prevent a heavy amp draw through the wire. I’ve had low batteries in my RV and even with 4 dead golf cart batteries I’ve never had the fuse blow on my truck.

I am not an EE. My guess is combination of wire resistance, internal battery resistance, and actual V differential. For the wire you need the round trip length, at least 50ft. So more like .05 Ohm. A LiFePo4 is 12.8V at 20% SOC and the Alternator is probably around 13.6V. More like .8V differential. Internal resistance of the LiFePo4 depends, a quick google search says .002 to .02 Ohms. Let's call it .01 then the current would be around 13A (.8/.06). If the LiFePo4 is closer to 50% SOC then delta V would be .6V resulting in 10A. This makes sense with people reporting 7A as the LiFePo4 is probably closer to 13.1V or 13.2V. I'd guess if the battery was ran down to 10V (near zero SOC) you could blow a fuse.

[corn18]

I canceled my order for the Orion XS. Wasn't going to ship until the end of May and I really don't need it. 1600W of solar has me spoiled.

[MarkSaxton]

@Corn18 That is an impressive amount of solar. This isn't the trailer forum, I know, but I am curious what your setup is - what panels / batteries / controller?

[corn18]

Originally Posted by MarkSaxton

@Corn18 That is an impressive amount of solar. This isn't the trailer forum, I know, but I am curious what your setup is - what panels / batteries / controller?

8x200W panels mounted on unit strut. 2x Victron 10050 MPPT controllers. 3xSOK 206Ah 12V batteries.

[darrellr]

Originally Posted by ArtJoyce

What wire size did the trailer come from the factory with?

Sorry, just looping back to this. The power and ground were both 10 gauge in the 7-pin cable on the trailer.

[xc-mark]

depending on how long the truck is with s 10 AWG wire your only going to get 5~10 amps at 12.6 volts DC + back at the trailer , at that point your trailer batterys will be suppling most of the power. My DC to DC Victron charger see about 10 volts DC back at the trailer while drawing 25~27 amps off the truck. My victron is the 18 amp output version, I don't think you can run any bigger charger off the stock truck wireing and trailer plug.