7-pin power to trailer LiB while driving

[KootenayEV]

I am considering replacing the two 85Ah 12v AGM batteries on my travel trailer with one (or maybe two) "drop-in" 12v 100Ah lithium ion batteries (LiB, eg Renogy), but I have a question related to the 7-pin power from the truck.

Ideally I would maintain the ability to provide at least some juice to the batteries while towing, but I've heard that many tow vehicles are not really capable of providing any real power to LiB because their output voltage is too low. This post in a separate thread indicates the Rivian can at least temporarily put out quite a bit of voltage (near 14.5V).

I don't need it to ever charge the battery to full, just to pick up a few Ah while towing here and there, or in a pinch if I'm in a really shady site and can't get my rooftop 150W to do anything (I've already upgraded my solar charger and it is compatible with LiBs).

Edit: now for the actual question, phrased appropriately!

Will the Rivian onboard DC/DC adequately charge a LiB directly via the 7-pin harness? If not, do you recommend installation of a DC/DC charge controller?

Any other issues I should be concerned with? I've heard of some installing a diode to prevent draining the TV battery. Or I could just disconnect the power from the 7-pin...

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[mindstormsguy]

What’s the question? ?

 

[IGR]

What’s the question? ?

I am curious too now, all that buildup...

 

[MtnRiv]

I think when he says LiB’s, he is referring to “MAD Lib’s”. We have to fill in the blank.?

 

[Dark-Fx]

Trailer fuse is 35A, get a small smart DC->DC converter to charge the trailer batteries while plugged in (I personally wouldn't go bigger than 20A here). Make it only charge if input battery voltage is > 12.8V, should charge while the truck is "on" then.

 

[mindstormsguy]

Trailer fuse is 35A, get a small smart DC->DC converter to charge the trailer batteries while plugged in (I personally wouldn't go bigger than 20A here). Make it only charge if input battery voltage is > 12.8V, should charge while the truck is "on" then.

As an electrical engineer, that was my thought too. But I bought a trailer that simply connects the battery directly to the trailer plug, and it works fine. You can probably get away just fine without a real charge controller between the vehicle and the trailer battery.

Maybe a lithium battery is different.

 

[KootenayEV]

Thanks for replies thus far - I updated the original post with actual questions this time

 

[KootenayEV]

Trailer fuse is 35A, get a small smart DC->DC converter to charge the trailer batteries while plugged in (I personally wouldn't go bigger than 20A here). Make it only charge if input battery voltage is > 12.8V, should charge while the truck is "on" then.

Something like this?
https://www.renogy.com/12v-20a-dc-to-dc-on-board-battery-charger/

 

[IGR]

I would recommend DC-DC converter as well, Renogy is a good choice, company been around for a while.

Edit: unless you want to back-feed into the Rivian 12volt system to reduce vampire drain, lol jk don't do that.

 

[Dark-Fx]

Something like this?
https://www.renogy.com/12v-20a-dc-to-dc-on-board-battery-charger/

General idea, yeah. Rivian does seem to turn off the trailer 12V when the vehicle turns off, so even if you can't program the input voltage it should be pretty safe.

 

[KootenayEV]

General idea, yeah. Rivian does seem to turn off the trailer 12V when the vehicle turns off, so even if you can't program the input voltage it should be pretty safe.

Do you know what the wire gauge is to the 7-pin? Could I go higher than 20A up to below the 35A fuse?

 

[av8or]

I have a 100Ah lfp battery in my travel trailer and the truck recharges it fine. It’s always back to 100% by the end of the day when driving. At night I always unplug the seven pin plug even if staying hooked up. I’ve now tow the setup 3000 miles with no issues.

 

[KootenayEV]

I have a 100Ah lfp battery in my travel trailer and the truck recharges it fine. It’s always back to 100% by the end of the day when driving. At night I always unplug the seven pin plug even if staying hooked up. I’ve now tow the setup 3000 miles with no issues.

interesting! Do you have a voltmeter on your TT battery to see what it is pushing to the battery? I’ve read many ICE alternators can’t push sufficient voltage so the LiB doesn’t get full enough to balance.

 

[av8or]

interesting! Do you have a voltmeter on your TT battery to see what it is pushing to the battery? I’ve read many ICE alternators can’t push sufficient voltage so the LiB doesn’t get full enough to balance.

It reads between 13.4-13.7 volts. The R1T does a much better job of charging the battery than my Jeep. The Jeep uses a fuel saving strategy that basically shuts of the alternator when it senses the battery is full charge. The problem I’ve run into with the Jeep is when the Jeep battery is full the voltage is 12.6ish at the Jeep, but 13.6 at the trailer. It seems like the Jeep is actually pulling power from the trailer battery. When towing with the Jeep the battery gets lower throughout the day and with the Rivian it’s charged to 100% by the end of the day.

 

[Thedude]

I had no issues charging my trailer lithium batteries while towing. Usually saw about 13.6v and a 7-8AH charge going into the batteries.

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