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Discussion Starter · #1 · (Edited)
There has always been talk about the charging power you can get from the 7 pin tow connector on vehicles. The general consensus is that its not good for much of a charge. My Grand Cherokee has the factory tow package and 220a alternator. I run a 100ah lithium battery in my Travel trailer and was curious just how much current I could get from the 7 pin connector. The answer is anywhere from 0-22 amps of charging current.
I got my battery 100% fully charged and put it in the trailer and had the fridge running for a while before I got to hooking my vehicle up. When I hooked the trailer to my jeep I was getting 6-7 amps of current with the battery at 94-95%. As I drove the voltage slowly rose to 14.2v and current down to almost nothing basically charging my battery right back to 100% again.




That kind of current isn’t anything special as anything under 10amps is to be expected, I purposely drained my lithium battery down this morning and started with 12.53v at the battery prior to hooking it up to my jeep. With the jeep running as soon as I connected the trailer I was getting between 15-17amps and this continued while the jeep was running.


I then drained the battery down to almost nothing (11.3v). When I first connected them to the Jeep without it running I was getting 5-6 amp charge current. Once I started the Jeep up the charge current immediately spiked to almost 23amps and the current stayed between 21-23amps.



To check and see if that was as much as it was going to pull I turned the inverter on in the trailer and put a 350w space heater on which is about a 30amp draw. Initially it showed a draw from the battery of 16 amps but then dropped back to a draw of about 7 amps from the battery.


Basically, showing that the 7 pin connector on my Jeep is able to give 23 amps of current to a very dead battery, or able to run 23 amps of appliances in the trailer while driving down the road without having to worry about drawing the batteries down.

I was pleasantly surprised how much power could actually be drawn from the hitch wiring considering most the posts online say it's a terrible way to charge batteries. I agree it's not the most idea but it does work quite well on the WK2. Since 23amps is about the limit that makes sense as the tow fuse is 30amps
 

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Hi, I know this is an old post but it's real good information. It sounds like the lithium battery can be charged without a DC/DC charge controller.

I've read that damage to the alternator can occur or even worse melted wires from too much current being pulled. Does this test eliminate that concern? Can you just pull the 30 amp 12V fuse that powers the 7 pin to be sure? Thank you
 

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Discussion Starter · #4 ·
While I no longer have the vehicle, I know have a Wrangler Rubicon 4xe, with tow package, behavior is exactly the same. Up to 23 amps, What would pulling the 30amp fuse do? It would then not power anything through the 7 pin unless I misunderstand what you mean?

If you want fast charging a DC/DC charger will work fine, but the factory 7 pin and charge at a decent rate without anything extra. With the amount of solar on the roof of my TT I don't really expect much from the 7 pin charging wise.

There are better options out there for charging but the 7 pin method does work.
 

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, What would pulling the 30amp fuse do? It would then not power anything through the 7 pin unless I misunderstand what you mean?
Hi, The reason for pulling the fuse is because I plan to install and use two Li batteries before I install a DC to DC charger. I've read in many places damage to the alternator or wires can take place because of the current draw. Don't know if this is a urban legond or not. But do read it over and over...although I've never read of it actually happening.
 

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Discussion Starter · #6 ·
Urban legand, I had lithium batteries in my TT, the only "negative" was if my vehicle was off, and the trailer was connected, the trailer lithium batteries would try to charge the AGM in the jeep.
 

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Hi, I ran the same test today with the lead acid batteries I have in my TT. Thank you for the insight of how to use the smart shunt app. to get the data.

If I follow you, if after changing out I don't exceed 30 amps on that circuit, everything will be good? If anything exceeds 30 amps, the fuse should blow before anything bad happens? Correct.
 

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Discussion Starter · #8 ·
Correct, but the factory programming in the jeep isn't going to allow anything much more than 23 amps going to the battery to charge, in order to get the 23amp current my TT battery had to be extremely low, it was usually around the 10-15 amp range when it was almost fully charged.
 

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Discussion Starter · #10 ·
23 amps was the max, whether that was when the batteries were deeply discharged, or I put a heavy load on them and measured the 23 amps going into the batteries from the 7 pin connector
 

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Discussion Starter · #12 ·

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Hi ,

Sorry to bug you, but you seem very knowelgable on this issue.

1. I measured the voltage at my battery (and 7 pin) with the engine cold at 14.8 V. Let the vehicle idle for about 45 minutes (everything off) and there was no change in voltage, same 14.7V. Does that mean it is not a "smart alternator?

2. What devices do you have to get the above data. It intriques me?

Thank you,
 

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Discussion Starter · #14 ·
Hi ,

Sorry to bug you, but you seem very knowelgable on this issue.

1. I measured the voltage at my battery (and 7 pin) with the engine cold at 14.8 V. Let the vehicle idle for about 45 minutes (everything off) and there was no change in voltage, same 14.7V. Does that mean it is not a "smart alternator?

2. What devices do you have to get the above data. It intriques me?

Thank you,
Sorry for the late reply,
I use the OBD adapter
OBDlink MX+ Along with the included OBDlink Software.

When you say "cold" how cold was the ambient temperature. Colder temperatures = higher voltage coming from the alternator. What year is your WK2 it shouldn't charge any different than my Grand Cherokee
 
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