Charging Camper LiFePo4 Battery From Truck

FlyboyTR · 03-08-2023, 04:55 PM

This subject has been tapped on a bit...but I still have concerns. My new CHINS Smart battery is doing well as is the new Progressive Dynamics converter. Thanks again to all that helped me with that decision.

Now...back to charging/maintaining the Lithium battery while driving the truck. Some folks (on various forums & Facebook pages) say a DC to DC converter is REQUIRED...or life as we know it will come to an end as well as it will kill my alternator.

I believe on this forum someone had said that a DC to DC converter is NOT needed. So......................??? My concern is not a lack of electrical knowledge...but still a very limited knowledge base with the lithium iron battery!

I have pondered over this at great length. Our drive times after DRY camping will be typically 4-6 hours. It appears with a 10 amp load on the HOT terminal of my 7 pin connector on the truck, I am seeing about 13.8 volts. I was shocked at that. That said........

Will I harm the lithium battery OR the truck alternator by just connecting and hitting the road; without a DC to DC converter?

As always...you input is appreciated!

Travis

**ShrimpBurrito** · 03-08-2023, 08:18 PM

I use one, but I also had it with lead acid batteries.

But if you don't care about charging your TM batteries while underway, you would always just disconnect the charge line so they are not connected to the alternator....

Dave

FlyboyTR · 03-09-2023, 07:49 AM

Quote:

Originally Posted by ShrimpBurrito

I use one, but I also had it with lead acid batteries.

But if you don't care about charging your TM batteries while underway, you would always just disconnect the charge line so they are not connected to the alternator....

Dave

Thanks,
That is certainly a consideration.

**ShrimpBurrito** · 03-09-2023, 11:40 AM

Also, you said:

"It appears with a 10 amp load on the HOT terminal of my 7 pin connector on the truck, I am seeing about 13.8 volts."

A 10 amp load where? In the TM or TV?

What I think you really want to do is have the fridge on DC in the TM, connect the TM to the TV, ideally with the batteries having been discharged some, and then measure the voltage drop from the TV battery post to the TM battery post. The voltage at the TM batteries is what matters. And if your 3023 has its batteries in the front, as it comes from the factory, the voltage drop will very likely be MORE than it would be on units where the batteries in the back. That's because the wires from the TV go all the way back to the converter/DC distribution panel FIRST, and THEN go to the batteries, so the run on a 3023 will be substantially longer, and the wire gauge for those runs is typically woefully undersized.

If the concern is overcharging your lithium batteries while underway with the fridge on DC for 4-6 hours after dry camping, when those batteries will have significant discharge, my guess is that you probably don't have anything to worry about. I put a DC-DC battery charger because the voltage at my flooded lead acid batteries (which charge at a lower voltage vs. lithium) was too low, and so the problem would be even worse with lithium (and so, charging even less). But you'll need to take some measurements first.

Dave

FlyboyTR · 03-09-2023, 12:58 PM

I put a 10 amp load on the 7 pin connector on the truck...trailer was not connected...and with the 10 amp load I had 13.8 volts at the connector (engine running).

When I installed the lithium battery, I moved it from the front to the rear. I don't run the fridge on DC; either AC or LP.

I will follow your suggestion and see what the voltages are looking like while connected.

If I have been on shore power, the new Lithium will be at 100%. I could easily pull the fuse on the circuit feeding the panel/battery from the truck. If I have been dry camping for a night or two with a lower % of SOC, the allowing the truck to provide power to the trailer/battery should not cause a problem. Did I get that right? Thanks!

**rich2468** · 03-09-2023, 01:27 PM

Hey Travis,
I have Lithium Ion Phosphate batteries in my TM and have towed for two years without a DC-to-DC charger. My tow vehicle (TV) has a "smart" alternator and my TrailManor batteries are located at the rear storage of my 2922KB....so the Lithium batteries work out to be about 36-38 feet from my TV battery. (considering the routing through the tow vehicle, over the Bargman wiring, connecting through the TrailManor's power converter, the Lithium battery shunt, then finally to the Lithium battery bank).

The distance from the tow vehicle's batteries via the Bargman to the area behind the Trailmanor's refrigerator where the two different (battery) direct current power sources (TV and TM) meet is probably around 26 to 28 feet from the tow vehicles's lead acid battery (over 10 guage wire). That mid-point connection also probably 10 feet from the Lithium battery bank after passing through the TM power center.

I use an OBDC bluetooth dongle to monitor various tow vehicle running parameters (engine & transmission temps along with charge voltage) and haven't noticed anything unusual in the tow vehicle alternator charge status due to having the TM Lithium batteries attached over the small wired Bargman connection (even when the TM battery bank has been discharged). I do see the tow vehicle alternator voltage jump up when turning on the TV's air conditioning systems (which is to be expected)....but I don't notice any unexpected behavior with the TrailManor connected. As previously stated I wired my power lead for the tow vehicle's Bargman connection with 10 guage wire.

I am in the middle of adding a DC-to-DC charger (with appropriate sized wiring and Anderson connections) as a separate connection from my tow vehicle to my TrailManor's
Lithium Ion Phosphate battery array due to the simple desire to keep my TM Dometic 3-way fridge running in DC mode while under tow for extended periods of time. The Victron Energy 18 amp DC-to-DC charger (with dedicated wiring and fusing) should allow me to arrive at all campsites with a cold fridge along with both my battery bank and propane tanks topped off.

Your situation is certainly different than mine-
Sounds like you're using propane for a refrigeration energy source under tow
I have no idea of you tow vehicle alternator/ vehicle capabilities
I don't know your budget constraints

If budget is not an issue, I'd suggest considering a DC-to-DC charger simply to allow you to potentially run your (stock) refrigerator via DC under tow and only worry about impacting your propane supply for boon docking refrigerator usage, water heating, and cooking (and supplemental heat if the diesel heater needs help).

I know that propane is cheap and that you're adding a diesel supplemental heater and I also think I recall that you're going to add solar. Solar is great (I have a kilowatt on my roof now), but solar won't add to your battery charge much on cloudy days or any at night. In my book DC-to-DC is a smart idea due to the limited weight and the ability to charge under any towing conditions. It also fits within my goal of not carrying along a generator and being able to perpetually boondock/ dry camp under reasonable conditions (even if those boondock campsites may only be in State and National Parks vs. BLM land).

Ironically, when I check the Amp rating of a small Honda (47lb) EU2200i inverter generator- I see that it's pretty identical to the Victron DC-to-DC charger that I'm installing. The generator is certainly more versatile at camp, but it won't help me while I'm under tow.

**ShrimpBurrito** · 03-09-2023, 01:38 PM

Quote:

Originally Posted by rich2468

Solar is great (I have a kilowatt on my roof now), but solar won't add to your battery charge much on cloudy days or any at night.

You have 1,000 watts of solar on your roof? Where? Do you have any photos? That's pretty impressive if they're all on the TM roof.

Dave

**rich2468** · 03-09-2023, 02:04 PM

Quote:

Originally Posted by ShrimpBurrito

You have 1,000 watts of solar on your roof? Where? Do you have any photos? That's pretty impressive if they're all on the TM roof.

Dave

Yes, I had 600 watts on my rear shell array and added 400 on the front last Fall.

I still have to complete the wiring for my DC-to-DC charger and some wire routing clean up, but I will be happy to share a "build out" post when I think it's presentable.

I'm attaching couple photos and will be happy to share more via PM if you have specific questions before my build-out post...but don't want to go further in a hijack of Travis' thread.

Rich and Lynn
2021 2922KB

**ShrimpBurrito** · 03-09-2023, 02:36 PM

Impressive!

Wavery · 03-09-2023, 02:39 PM

Quote:

Originally Posted by rich2468

Yes, I had 600 watts on my rear shell array and added 400 on the front last Fall.

I still have to complete the wiring for my DC-to-DC charger and some wire routing clean up, but I will be happy to share a "build out" post when I think it's presentable.

I'm attaching couple photos and will be happy to share more via PM if you have specific questions before my build-out post...but don't want to go further in a hijack of Travis' thread.

Rich and Lynn
2021 2922KB

WOW!!!!! I have a hard time lifting my front roof with 2, 100W panels (and air conditioner) on it. How in the heck do you lift your roof?