Simple swap out lead acid -> LiFePo4

[JustAGuy101]

Ok so, here's the use case. 23 foot travel trailer, 2021 Jayco. Will be used almost exclusively for weekend (<3 days) boondocking.
Tow vehicle 2017 Tacoma, V6 with tow package.

The question is, if I were to simply replace the 12V/60Ah lead acid battery that sits on the tongue with a DIY 12V/206 AH LiFePo4 with
Overkill solar BMS, what would the possible consequences be?

Here's what I can think of:
Possible overload/damage from charging a LiFePo battery with the alternator while returning home.
Cables from battery to AC/DC distribution center may not be of sufficient size.
Stock converter will likely only charge the LiFePo to 50-60% SOC before the converter switches to float.

What am I missing?

Thanks

 

[snoobler]

You pretty much have it on the first two.

#2 typically CAUSES #3 and not be the fault of the inverter. Any converter you install will likely have the same result.
#3 may also suffer from the converter having a charge voltage higher than 14.6V or float voltage higher than 13.6V.

 

[Whinny]

IMHO....
Some sort of DC/DC charger for your alternator...
DC cabling in your Jayco is most likely #6-that is probably sufficient..
You may have a WFCO converter....If you find the Lithium doesn't charge fully (jury is out on that) try one of these...

WFCO Technologies - Innovating the Future of RV Power

WFCO Technologies is committed to simplifying, enhancing, and optimizing every RV owner’s experience through advanced power technology and proven support.

wfcoelectronics.com

I'm still concerned about the breakaway trailer brakes legality with a lithium battery and bms....

 

[HRTKD]

I'm still concerned about the breakaway trailer brakes legality with a lithium battery and bms....

It shouldn't be a problem, unless a DC-DC charger is installed using the 7-pin circuit and a return wire isn't implemented from the LiFePO4 battery to the breakaway system. The breakaway brakes are going to draw around 15 amps on a dual axle trailer.

 

[JustAGuy101]

IMHO....
Some sort of DC/DC charger for your alternator...
DC cabling in your Jayco is most likely #6-that is probably sufficient..
You may have a WFCO converter....If you find the Lithium doesn't charge fully (jury is out on that) try one of these...

WFCO Technologies - Innovating the Future of RV Power

WFCO Technologies is committed to simplifying, enhancing, and optimizing every RV owner’s experience through advanced power technology and proven support.

wfcoelectronics.com

I'm still concerned about the breakaway trailer brakes legality with a lithium battery and bms....

As far as chargers go, I'm seriously thinking about going with the Victron IP22 12/30 charger for the LiFePo4 battery and simply plugging that into my inverter generator if I want to top up the battery while we're out in the sticks. That way, I can also take my expensive charger home with me to use for other purposes. I can certainly understand why folks who will be spending more time hooked up to shore power or driveway surfing might want a more permanent or refined solution.

 

[sshibly]

Op,

1. The first thing you will realize that the battery in the front of the trailer will WALK, disappear if you keep a $$$$ Li battery there.

Please take steps to move it into the camper.

2. Get one of the 12v to 13.8v sealed converters like the one here
Not sure how long you drive to your camp spot, but I do 1000 miles for work and I have 15 hours to charge my cells .

 

[JustAGuy101]

Op,

1. The first thing you will realize that the battery in the front of the trailer will WALK, disappear if you keep a $$$$ Li battery there.

Please take steps to move it into the camper.

2. Get one of the 12v to 13.8v sealed converters like the one here
Not sure how long you drive to your camp spot, but I do 1000 miles for work and I have 15 hours to charge my cells .

Exactly! I'm balking at the thought of leaving easily removable $1000 pieces of equipment with the TT while it's in storage. Consequently, for now, I'm doing one of Will's milk crate assemblies so I can just set it in the equipment bay of the trailer when we arrive at camp and plug it in with Anderson connectors. Likewise when we pack up on Sunday.

 

[deeuubee]

1. I doubt you will be driving long enough to charge it back up.
You'll only get around 8amps from that skinny wire on the 7-pin from the truck.
Chances are the travelling load while will be close to that. (running lights, brakes, fridge, the bathroom fan you forgot to turn off )
Your alternator is only going to put out enough current to charge the battery and keep it charged as other loads drain it.

2. The wires on your RV were designed and fused for the load it came with.
Changing the battery will make no difference.

3. The stock converter will probably charge your battery to 85-90%, and using 90% down to 20% is still acceptable.
Depending on whose train of thought you follow.

 

[HRTKD]

1. I doubt you will be driving long enough to charge it back up.
You'll only get around 8amps from that skinny wire on the 7-pin from the truck.
Chances are the travelling load while will be close to that. (running lights, brakes, fridge, the bathroom fan you forgot to turn off )
Your alternator is only going to put out enough current to charge the battery and keep it charged as other loads drain it.

My F-350 is rated to provide 30 amps at the 7-pin. Real world, it's a bit lower, but that's a dedicated wire for that 30 amp circuit. Brakes and running lights are a different wire and the power for that comes from the truck also, so those are not draining the house battery, unlike the refrigerator or bathroom fan.

I would have no qualms about installing a 15 amp DC-DC charger that is powered from the tow vehicle's 7-pin circuit. For RV owners with minimal roof space for solar, this may be a good solution, even if it's just enough to maintain the battery state of charge while traveling.

 

[deeuubee]

I've been doing a lot of suppozin Based on what I know.
Admittedly, I know little about the ECU charging profile in my Ram 2500.
Other than what I observed, a-la a beer, a book, and a meter today, playing with the charging system.

The 30 amp fuse is there to protect the 10 awg wire based on the current restriction of the wire.
As a result you know you can put a maximum of 30 amps through it.
You could put the same 30 amp fuse on 4/0 wire rated for much more.
In that case you are using the fuse to limit the current to 30 amps.

The main reason I don't believe you'll see more than 8-9 amps available at the 7-pin plug is by factory design.
I can't verify this until next week when I get to my trailer and hook it up.
If any one has done this, let me know what you got.

The manufacturers don't know what size Ah battery you will be using, so I think that they would program the ECU charge profile for the smallest battery that you would expect on a trailer which I believe would be a 12Ah battery used for the brake disconnect.
Even though that 8-9 amps would be way over the .3C recommended charge rate.

This whole discussion has set me to find out what's what...I'll be back.

 

[HRTKD]

A guy on the Ford forum did a similar test on a recent F-350 and, as I recall, saw no more than 20 amps at the 7-pin connection. There is a 30 amp fuse as well as a 30 amp relay.

 

[hour]

i just opted to disconnect my battery before driving, latest improvement being a battery switch so I don’t have to touch the 50 amp powerpole style plug I made to go between trailer and battery. I guess this doesn’t work well for trailers with brakes.

I charge up at home and use solar when camped. If I need I can power a 600w 24v power supply with my generator and pipe that in as PV to my charge controller.

Not sure what would happen if trailer was plugged in to shore power, but the only chance of that happening is if I croak and someone buys it at the estate sale.

I’m not impressed with any onboard converter-chargers, even the ones with lithium profiles. Saw a vidya on youpube of a guy replacing his converter with dumb power supply in to a MPPT. Doesn’t sound like an awful solution. I’d pull the trailer power fuse on the tow vehicle

 

[HRTKD]

i just opted to disconnect my battery before driving, latest improvement being a battery switch so I don’t have to touch the 50 amp powerpole style plug I made to go between trailer and battery. I guess this doesn’t work well for trailers with brakes.

I charge up at home and use solar when camped. If I need I can power a 600w 24v power supply with my generator and pipe that in as PV to my charge controller.

Not sure what would happen if trailer was plugged in to shore power, but the only chance of that happening is if I croak and someone buys it at the estate sale.

I’m not impressed with any onboard converter-chargers, even the ones with lithium profiles. Saw a vidya on youpube of a guy replacing his converter with dumb power supply in to a MPPT. Doesn’t sound like an awful solution. I’d pull the trailer power fuse on the tow vehicle

The breakaway system doesn't work if you disconnect the battery. The regular brakes will work. Those are powered by the tow vehicle.

There's a lot of disappointment with quite a few of the common converters. I'm not thrilled with mine, but it simply doesn't get used enough for me to worry about it. PV is what I use 99% of the time.

 

[JustAGuy101]

I think I've settled on a solution that will work for us. I believe I will retain the lead battery on the tongue
to run the brakes while en route. I'll also add my 206AH DIY LiFePo4 pack to the trailer by way of a 3 position
switch and a couple of bus bars. That way, when we get to camp, I can simply switch to the big battery for the
weekend, switch back to the lead battery for the trip to storage and then disconnect while IN storage. I've ordered
a Victron 30 amp, single output charger for which I will make up one pigtail for each battery. Then, if we should somehow
find a way to use more than 200AH of lithium power and 30+AH of lead power, I can top up the lead battery for the trip home and take
the lithium to the house to charge it up there.

Oh, and I finally completed the capacity test on my new cells with the Overkill BMS. Couldn't be happier. The cells achieved
218AH (according to the load tester) over ~15.5 hrs at 14 amps. Couldn't be happier. That Overkill BMS is pretty
slick. Now looking for just the right box to put the battery in.

 

[rootusrootus]

Congrats on your X213. We had a 2016 X213 before we traded up to a bigger TT a couple weeks ago. Great little trailer, we stuffed it into many places that weren't really meant for a trailer to be .

I'm not entirely clear on the outcome of this discussion, and I have essentially the same question. I am building a DIY LFP battery with 272Ah cells (and I will probably build a second), and I'd like to just replace the FLA batteries with mine and not change much else. I'm using a Victron MPPT charge controller, but still have the stock WFCO converter.

So, is the consensus that the converter needs to be replaced? I thought I might just let it charge to 70% and then the solar can top it off.

And I hadn't considered the 7-pin from the truck. My TV is a '19 F250. Something else I have to find a solution for?

I don't want to do what you're doing, with a switch, I want to make it a fairly transparent drop-in solution.

 

[HRTKD]

Congrats on your X213. We had a 2016 X213 before we traded up to a bigger TT a couple weeks ago. Great little trailer, we stuffed it into many places that weren't really meant for a trailer to be .

I'm not entirely clear on the outcome of this discussion, and I have essentially the same question. I am building a DIY LFP battery with 272Ah cells (and I will probably build a second), and I'd like to just replace the FLA batteries with mine and not change much else. I'm using a Victron MPPT charge controller, but still have the stock WFCO converter.

So, is the consensus that the converter needs to be replaced? I thought I might just let it charge to 70% and then the solar can top it off.

And I hadn't considered the 7-pin from the truck. My TV is a '19 F250. Something else I have to find a solution for?

I don't want to do what you're doing, with a switch, I want to make it a fairly transparent drop-in solution.

In my case, I chose to not use a converter that uses a lead acid charge profile (and never a four stage profile!), nor the 7-pin charge. I tried to put in a system that required no manual intervention. If I left on a trail ride for the day, I didn't want my wife to have to read instructions for using the system.

If you're good with manually managing the system, then the existing converter is OK. The 7-pin circuit is a bit iffy because you're not in the trailer to actively manage it.

 

[JustAGuy101]

Congrats on your X213. We had a 2016 X213 before we traded up to a bigger TT a couple weeks ago. Great little trailer, we stuffed it into many places that weren't really meant for a trailer to be .

I'm not entirely clear on the outcome of this discussion, and I have essentially the same question. I am building a DIY LFP battery with 272Ah cells (and I will probably build a second), and I'd like to just replace the FLA batteries with mine and not change much else. I'm using a Victron MPPT charge controller, but still have the stock WFCO converter.

So, is the consensus that the converter needs to be replaced? I thought I might just let it charge to 70% and then the solar can top it off.

And I hadn't considered the 7-pin from the truck. My TV is a '19 F250. Something else I have to find a solution for?

I don't want to do what you're doing, with a switch, I want to make it a fairly transparent drop-in solution.

Just about the time you posted this, I "finished" my basic diagram for my additions. Not sure if it's right yet since I haven't had several days to look at it and doubt myself. For my use case I think this is the PITA factor I'm willing to put up with....i.e., putting the battery and Victron in the cargo area before each trip and removing it after. However, I think it completely obviates the need to change anything having to do with alternator to house battery charging of a LFP. The stuff in green is the new equipment.

 

[HaldorEE]

There's a lot of disappointment with quite a few of the common converters. I'm not thrilled with mine, but it simply doesn't get used enough for me to worry about it. PV is what I use 99% of the time.

Please expound more. I am in the market for a DC-DC alternator charger controller and this is of great interest to me.

The rest of my system is all Victron (except for the battery):

• Multiplus 24/2000-50
• MPPT Smart 100/20
• BMV-712
• Battery Protect 12/24-65
• DIY 8S LiFePO4 battery
  • Linshen 280 AH cells
  • Heltec BMS
  • QNBBM Active Cell Balancer

Top candidate so far is the Orion-TR Smart Isolated, but it seems to me that Victron got a little lazy with the Orion-TR Smart. It lacks the some of the connectivity of the MPPT Smart.

 

[HRTKD]

HaldorEE, my post was in reference to the AC-DC converters, not the DC-DC chargers.

 

[deeuubee]

@JustAGuy101 -

My opinion: Install both batteries connected to a marine "1-2-both" disconnect switch.
1 - Lead (travel/shore power/storage), 2-LiFePO (camping)

When in "1" travel/shore power, it's just no drama. No worries about charge profiles, 7-pin charging, stolen battery, etc.
It's just the way it was designed.

When in "2" camping, no drama there either. if the LiFePO runs low, charge it it from the generator with the existing converter. Until you actually do it, you won't know if it charges to 90-80-70-60%. Either way, it's enough to finish the weekend. Your not running the generator long enough to be concerned with bulk, absorption, float charge.

If you're plugged into shore power, well, you're not using the battery anyway, so leave it in "1".

Use your LiFePO charger as a portable charger. Top off the LiFePO at home or camping.

You're supposed to have a set-up/disconnect check list.
First thing on the set-up list, "switch battery to camp" mode. Last thing on the disconnect list, "switch battery to travel" mode.
In the event that you replace the lead with another LiFePO, just leave the switch in "both" for the additional capacity.

You could have all these things done automatically; you just have to decide how much you want to pay.

Oh, and I would buy the 280Ah instead of the 206Ah.