Charging lithium-ion trailer batteries while towing

[mtbikernate]

I camp in the woods and like to keep the trailer shaded under the trees. So I have my panels on portable mounts that I can move around the campsite to catch the sun wherever it strikes the ground.

You can have both. And depending on your willingness to climb on the roof, they could even be the same panels that you remove from the roof and set out in the sunshine when you get to camp.

I have a little squaredrop camper so reaching the roof is fairly easy. As such, I've begun building out my solar installation so that my panels can be either on the ground or on the roof. At the moment, they're just on-the-ground panels on a long extension cord. I'm currently collecting the parts to make roof mounts so the panels are removable.

Having one or more panels on the roof is going to generally give you really good charging while you're on the road with simpler wiring and electrical components (as compared to having a dc-to-dc charger esp in combination with a solar charge controller) since most roads generally are pretty exposed to the sun.

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[JonB]

You can have both. And depending on your willingness to climb on the roof, they could even be the same panels that you remove from the roof and set out in the sunshine when you get to camp.

I have a little squaredrop camper so reaching the roof is fairly easy. As such, I've begun building out my solar installation so that my panels can be either on the ground or on the roof. At the moment, they're just on-the-ground panels on a long extension cord. I'm currently collecting the parts to make roof mounts so the panels are removable.

Having one or more panels on the roof is going to generally give you really good charging while you're on the road with simpler wiring and electrical components (as compared to having a dc-to-dc charger esp in combination with a solar charge controller) since most roads generally are pretty exposed to the sun.

It's not easy getting on my roof, it's all ready full of vents, AC and, most importantly, I'm old. Thanks for the advice but I'm going to stick with having the panels portable for mounting on the ground.

 

[JonB]

UPDATE - First, thanks for all the comments and advice. Second, here's where we are now with the project:

TRAILER - The Rockwood trailer has a WFCO distribution panel/charger. It is not compatible with Li-On batteries. I have purchased WFCO's updated charger that senses the battery type and adjusts the charging accordingly. I've talked to their tech people. It's an easy switch and, once installed, will take care of charging the Li-On batteries when hooked up to shore power.

When boondocking I have a 200 watt solar system with an Epever 30A charge controller that I can set for different battery types. It will handle Li-On batteries.

TRUCK - With both solar and shore power charging taken care of, what's left is keeping the batteries charged while pulling the trailer. Reading through the responses above there are a number of different opinions on what to do. In all, I'm now thinking that a DC-DC adapter that will bump up the voltage to 14.4 volts is the way to go. I am digging into this and welcome further comments.

 

[JonB]

UPDATED UPDATE - Parts are arriving for the Li-Ion battery change-over. The new charger for the trailer is in, two Weize 100Ah LiFePO4 batteries have arrived and today the DC-DC charger/converter for the truck is due. It is a Victron Orion 30-amp unit. Next up is installing all of this stuff.

For those considering this I will post once the installation is complete with pictures. All is pretty straight forward except there are different opinions on wiring the Orion charger in the truck.

 

[JonB]

yes dc to dc

had 1 of these but didn't always go into charge mode but has wonderful features
https://www.amazon.com/Orion-Tr-12-30A-Isolated-Charger-Booster/dp/B07ZKG396Y/ref=sr_1_8?crid=2OYR5FY2CCJJW&keywords=dc+to+dc+charger&qid=1661096326&sprefix=dc+to+dc,aps,133&sr=8-8

ended up with a crappy renogy I got for free. setup up with a switch to turn off and on. not auto no/off with ignition.

I have this exact unit and am in the process of installing it. It is suppossed to sense when the truck is off and open the circuit to the trailer batteries. It can be tricky to get to work. I've read other posts where folks have had trouble getting the auto sensing on/off to work and have, instead, used the hard-wire option, hooking up the trigger line to a circuit that comes on only when the key is on.

I'll let you know how my install goes.

 

[kipkohl]

This is an old thread I know, but I have a question that I didn't see an answer to. Can the alternator be damaged by charging a LiFePO4 battery without a DC-DC charger while driving? I thought I had read somewhere that the battery would try and pull more power than the alternator can provide.
Not worried about being able to charge batteries while driving, more worried about possible damage to the alternator

 

[Skit hjälm]

The quick anser is yes.
Alternator can be damaged.
In general, lithium battery will accept as much current as available. This can overload an alternator and overheat the battery itself.
There needs to be a means to limit the charging current to a level whats safe for the alternator and limit current to prevent overheating the battery.
Usually thats done on alternator charging with a DC to DC converter which maintains suitable for lithium charging voltage and limits current to a level whats safe for the alternator and battery.

This is an old thread I know, but I have a question that I didn't see an answer to. Can the alternator be damaged by charging a LiFePO4 battery without a DC-DC charger while driving? I thought I had read somewhere that the battery would try and pull more power than the alternator can provide.
Not worried about being able to charge batteries while driving, more worried about possible damage to the alternator

 

[JesseS]

The quick anser is yes.
Alternator can be damaged.
In general, lithium battery will accept as much current as available. This can overload an alternator and overheat the battery itself.
There needs to be a means to limit the charging current to a level whats safe for the alternator and limit current to prevent overheating the battery.
Usually thats done on alternator charging with a DC to DC converter which maintains suitable for lithium charging voltage and limits current to a level whats safe for the alternator and battery.

Correct, but in my case my RV alternator is 200AH, and it has never supplied more than 45 AH to my 4X100AH Lithium batteries. Running the engine & generator at the same time will get the charge rate up to the mid 70's if the SOC is below 50% (almost never), have never seen the 100AH max allowed by the batteries BMS. My 700watts of solar will supply 30-35 AH on a summer day.

 

[JonB]

I started this post and promised to let folks know when I finished the installation. It’s done -

Two 100 Ah Weize LiFePO4 batteries in the trailer are charged from the tow vehicle by a 30 amp Victron DC-DC charger. It’s wired with 6 ga from the battery. The WFCO AC to DC “smart” charger in the trailer that was supposed to sense the LiFePO4 batteries never did, even after a firmware update. So it was replaced by a Progressive Dynamics charger dedicated to LiFePO4 batteries. It works fine.

Now, as for the necessity of the DC-DC charger, yes you should use it. I’m on forums for my trailer and solar systems and no one has ever reported or seen damage to a charging system without the DC-DC charger, but that doesn’t mean it’s not a good idea. I’m in Quartzsite, AZ and attended the RV show and listened to several seminars. The speakers all agreed that a DC-DC charger is a good and necessary thing.

 

[kipkohl]

Ok then, that sounds like good advice. Thanks

 

[JonB]

I recommend the Victron, though there are others out there that work fine. The Victron has an app that lets you monitor and control the charger. It also has a “smart” voltage feature that monitors when the vehicle is on or off by the voltage on the line and switches off (disconnects the tailer’s batter from the two vehicle) when the voltage drops. I did not use this feature and instead have a manual on/off switch.

 

[JGF]

I started this post and promised to let folks know when I finished the installation. It’s done -

Two 100 Ah Weize LiFePO4 batteries in the trailer are charged from the tow vehicle by a 30 amp Victron DC-DC charger. It’s wired with 6 ga from the battery. The WFCO AC to DC “smart” charger in the trailer that was supposed to sense the LiFePO4 batteries never did, even after a firmware update. So it was replaced by a Progressive Dynamics charger dedicated to LiFePO4 batteries. It works fine.

Now, as for the necessity of the DC-DC charger, yes you should use it. I’m on forums for my trailer and solar systems and no one has ever reported or seen damage to a charging system without the DC-DC charger, but that doesn’t mean it’s not a good idea. I’m in Quartzsite, AZ and attended the RV show and listened to several seminars. The speakers all agreed that a DC-DC charger is a good and necessary thing.

Thank you for keeping us all up to date on your installation. I tow a 16ft travel trailer with a 2020 Ranger Lariat. I'm in the process of swapping my two 100 amp Weize AGM's for LiFePo4 batteries as well. I've got 400 watts of solar, 200 on the roof & 200 portable. I've disabled my WFCO AC to DC converter and charge through a 2500 watt Aims inverter/charger.

I'm most concerned about my alternator. My batteries are mostly fully charged before I drive anywhere so not sure how that would play into the alternator issue? But sometime when breaking camp (We mostly boondock) I may not be fully charged if overcast before driving. Will I damage the alternative then?

Some say the 7 pin only charges via a #10 charge wire and that will limit the load on the alternator. Any truth to that?

 

[JonB]

I'm most concerned about my alternator. My batteries are mostly fully charged before I drive anywhere so not sure how that would play into the alternator issue? But sometime when breaking camp (We mostly boondock) I may not be fully charged if overcast before driving. Will I damage the alternative then?

Some say the 7 pin only charges via a #10 charge wire and that will limit the load on the alternator. Any truth to that?

As stated above, although the potential exists for damaging the alternator I have never heard of it happening.

The only way a wire limits a load is by its resistance to the current flow. Enough resistance (pushing more amps than the wire can handle) results in the wire burning up. One way to limit current flow but not the recommended method. A better way is to have the DC-DC charger control the charging current.

The 7-connector wire to the trailer provides only a trickle charge - 3-4 amps. If the batteries are fully charged this may be enough. If not, the DC-DC charger, wired properly, will provide up to its rated capacity. In my case, 30 amps.

Remember also your vehicle's charging system is designed to keep its battery charged. LiFePO4 batteries charge at a higher voltage. Again, a DC-DC charger will step up the voltage from the vehicle to properly, and completely, charge the trailer's batteries.

Hope this helps.

 

[Dgc333]

TRUCK - With both solar and shore power charging taken care of, what's left is keeping the batteries charged while pulling the trailer. Reading through the responses above there are a number of different opinions on what to do. In all, I'm now thinking that a DC-DC adapter that will bump up the voltage to 14.4 volts is the way to go. I am digging into this and welcome further comments.

The charging system in the Ranger runs between 14.4 and 15.0 volts. It will drop down to the low 13s when it senses a fully charged battery to improve fuel economy by not loading the engine as much. Not sure how this plays into charging the battery(s) on your trailer.

 

[JonB]

The charging system in the Ranger runs between 14.4 and 15.0 volts. It will drop down to the low 13s when it senses a fully charged battery to improve fuel economy by not loading the engine as much. Not sure how this plays into charging the battery(s) on your trailer.

While this is true, the Ranger’s charging system is designed to charge the vehicle’s battery and nothing else. Adding the LiFePO4 batteries into the equitation presents a number of issues:
1. The LiFePO4 batteries have a much lower internal resistance than the lead-acid battery in the truck. As such, the charging system will see them as an additional load and try to compensate.
2. LiFePO4 have a two phase charging procedure; lead acid have three.
3. While the truck’s charging system will generate voltages to 15 VDC it is not designed to maintain the 14.-14.6 volts needed to charge LiFePO4 batteries.
4. The resting voltage of a lead acid batteries is 12.4-12.8. It’s 13.5 for a LiFePO4 battery.

There are enough differences between the battery in the truck and the trailer’s batteries to make have the DC-DC charger a requirement.

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