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Charging lithium batteries in travel trailer without solar?

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OffRoadRN

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Jan 12, 2021
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Hello everyone, first post here. I am planning on building the minimalist system in the near future for my travel trailer. My problem is I need new batteries now, but I'm not quite ready to plunge into a solar system for a few months.

I plan on buying two 100ah SOK's now. How can I safely charge these with my trucks alternator (F250 with 240 amp alternator)? Is the renogy dc to dc charger my best bet? Can I safely charge the sok's with a propane generator hooked up to my trailers 30 amp cable after some modifications? If so, what do I need to do?

Ultimately I would like to get a victron multiplus to power my entire ac system with 400ish watts of panels on the roof, but I'm not quite ready to spend that much money.

Thanks!
 
Yes, a DC-DC charger is recommended to charge LiFePO4 from an alternator. For a minimalist install, you would use the circuit that is coming through the 7-pin cable. That circuit will not produce more than 30 amps, usually closer to 20. Because of that, you should get a DC-DC charger in that amp range. Less is OK, more might tax the circuit and cause you to blow a fuse.

If you need more than ~20 amps of charging from the alternator, then you're no longer in minimalist territory. You would need to run a dedicated set of cables from the tow vehicle's battery to the rear bumper where you would have a quick connect. The trailer would have a similar cable and quick connect. That cable would go ONLY to the DC-DC charger, which could be sized maybe as big as 50 amps, but it depends on how large the dedicated cable is.

To charge from the generator, a AC-DC converter that has a LiFePO4 charge profile is needed.
 
Plan exactly what you want to end up with, that way you don’t buy equipment twice or are missing good things because you got this piece instead of that one.

For example, on my MotorHome I decided I really liked the info that Victron’s CCGX provided.
so first item - BMV712- battery monitor.
and I built from there. Later SmartSolar chargers and panels. When I got the inverter I got the CCGX at that time (became you need a control panel to operate the Multiplus).

you will need a dc-dc charger to charge off of your truck alternator.
Needing to charge the batteries- this will eventually be done by the Multiplus- Do you want to buy a lithium charger now? How will the converter in your trailer work with the lithium batteries?
sometimes one item snowballs into several at once.
 
HRTKD said:
Yes, a DC-DC charger is recommended to charge LiFePO4 from an alternator. For a minimalist install, you would use the circuit that is coming through the 7-pin cable. That circuit will not produce more than 30 amps, usually closer to 20. Because of that, you should get a DC-DC charger in that amp range. Less is OK, more might tax the circuit and cause you to blow a fuse.

If you need more than ~20 amps of charging from the alternator, then you're no longer in minimalist territory. You would need to run a dedicated set of cables from the tow vehicle's battery to the rear bumper where you would have a quick connect. The trailer would have a similar cable and quick connect. That cable would go ONLY to the DC-DC charger, which could be sized maybe as big as 50 amps, but it depends on how large the dedicated cable is.

To charge from the generator, a AC-DC converter that has a LiFePO4 charge profile is needed.
Click to expand...

Is 20 amps sufficient to charge 200ah of LiFePO4? Will it take 10 hours of driving to charge a dead battery (10 hr x 20 amp from the alternator). For the ac-dc converter, where in the system does that get installed? Can you recommend a good unit?
 
It would indeed take a long time to charge that battery. Most of us don't rely on the alternator. 99% of my charge comes from solar. 1% from generator. I don't even have the alternator circuit connected.

Consider a suitcase solar panel or something like that. Just a couple of solar panels you can deploy on the ground and tilt toward the sun can go a long ways towards getting your batteries charged. If you buy the right panels, they could eventually be the ones you put on the roof.
 
OffRoadRN said:
... My problem is I need new batteries now, but I'm not quite ready to plunge into a solar system for a few months.

... I plan on buying two 100ah SOK's now. ...
Click to expand...
SOK is subject to shipping delays in California ports. You may be ready to plunge into solar before your new batteries are delivered. If the need for replacement is urgent, correspond with Min (sales@sokbattery.com) about expected delivery dates before placing your order.
 
HRTKD said:
It would indeed take a long time to charge that battery. Most of us don't rely on the alternator. 99% of my charge comes from solar. 1% from generator. I don't even have the alternator circuit connected.

Consider a suitcase solar panel or something like that. Just a couple of solar panels you can deploy on the ground and tilt toward the sun can go a long ways towards getting your batteries charged. If you buy the right panels, they could eventually be the ones you put on the roof.
Click to expand...
One last question, how do I disable alternator charging?
 
SomebodyInGNV said:
SOK is subject to shipping delays in California ports. You may be ready to plunge into solar before your new batteries are delivered. If the need for replacement is urgent, correspond with Min (sales@sokbattery.com) about expected delivery dates before placing your order.
Click to expand...
Thanks, Min said they will be taking orders early February for shipment at the end of the month. That works for me.
 
OffRoadRN said:
One last question, how do I disable alternator charging?
Click to expand...

1. In your main distribution panel, there should be an incoming wire. Disconnect that from the panel, cap it off and secure it.
2. Or, find where that incoming wire originates under the trailer. There should be a distribution box near the tongue that the 7-pin goes into. Find the wire coming out of that box that goes into the trailer.

The wire that goes into the main distribution panel is probably going to need to be removed anyhow. You'll want to tie your new battery bank into the main distribution panel at that connection. On mine there was room for two positive cables to be connected.
 
HRTKD said:
1. In your main distribution panel, there should be an incoming wire. Disconnect that from the panel, cap it off and secure it.
2. Or, find where that incoming wire originates under the trailer. There should be a distribution box near the tongue that the 7-pin goes into. Find the wire coming out of that box that goes into the trailer.

The wire that goes into the main distribution panel is probably going to need to be removed anyhow. You'll want to tie your new battery bank into the main distribution panel at that connection. On mine there was room for two positive cables to be connected.
Click to expand...
Thanks!
 
My main distribution panel is made by WFCO. It's 15 years old, so if you have a more recent trailer, things may have changed.
 
HRTKD said:
Yes, a DC-DC charger is recommended to charge LiFePO4 from an alternator. For a minimalist install, you would use the circuit that is coming through the 7-pin cable.
Click to expand...
The voltage drop over the 7-pin cable is probably going to be brutal.
 
smoothJoey said:
How long is the cable and how much current are you drawing?
UPDATE: What is the voltage at source?
Click to expand...

From the engine compartment to the truck's 7-pin connection is about 23 feet, not taking into account wiring detours. From the trailer's 7-pin connection to the battery is maybe 10 feet. No idea what the voltage at the source is. Amperage allowed on the circuit by the truck is no more than 30 amps. I have no idea how many amps the trailer is drawing. The lead acid battery on the tongue doesn't get drawn down much so I doubt the 7-pin circuit is pressed hard.
 
I use a Renogy 20A DC-DC Charger and am pleased with it as I can charge while driving or from the converter. Here is my system wiring. The Renogy was simple to wire and inexpensive. They are a buck/boost circuit so they can operate from a higher or lower voltage than the storage battery.
 

Attachments

  • Renogy DC-DC Charger wiring diagram-compressed (2).pdf
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Last edited:
Jasgeer said:
I use a Renogy 20A DC-DC Charger and am pleased with it as I can charge while driving or from the converter. Here is my system wiring. The Renogy was simple to wire and inexpensive. They are a buck/boost circuit so they can operate from a higher or lower voltage than the storage battery.
Click to expand...
Hello Jasgeer, thanks for posting your wiring diagram. If I'm following correctly, based on your diagram I'm assuming your WFCO converter does NOT support lithium charging, and thus the switch behind the converter would be set to 'Batt 2' for charging when plugged into shore power, and set to 'Batt 1' when your trailer is drawing from the batteries? Assuming this is correct, what position is your switch set to when you are actively towing? I am guessing Batt 1 so the trailer is still drawing from its Li batteries, but this would also mean there is no direct power (charge) connection to your F250 (besides lights etc). Thanks!
 
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