I thought going to LiFePO4 batteries would be easy.

To go along with the dc compressor upgrade for the rv fridge, a 200ah LiFePO4 battery was ordered from Aliexpress. It's shows as being shipped. Using our agm's in the mean time.
Then I started doing charging research. My 1 year old Magnum inverter/charger doesn't have the newest firmware update to optimally charge them as a battery type setting. The board with the 2.0 version is virtually unobtainable from what I've found. I finally found a YouTube video produced by a very experienced full time rv-er with some very serious battery knowledge. He explains how to use the cc/cv mode. So ok that's covered. 
Now the issue of alternator charging, which I didn't expect to be an issue.  The LiFePO4 batteries have such low internal resistance they can & will pull max current of the BMS. This one has a 150 amp BMS. Then when the BMS disconnects, this can damage the alternator also. It looks like the Cummins alternator stock is 130 amps. So that's a problem. Even on higher output alternators at low idle rpms, the alternator isn't spinning fast enough to cool & the alternator over heats, starts smoking & burns up. 
So options are a higher amperage alternator or a dc to dc charger between the alternator & LiFePO4. The dc to dc charger looks much cheaper. Now it looks like I get to know the charging wiring intimately just like the fridge. 
 

In reply to mdshaw :

I've been doing some casual learning on this subject, as we'll probably be upgrading our RV's electrical system next year. We'd like to have enough solar & battery capacity to be comfortable off-grid for a few days without needing to rely 100% on the generator. 
 

I still have quite a bit to learn myself, especially regarding the batteries & their management. 

In reply to Pete Gossett (Forum Supporter) :

I wasn't really researching solar, but may want it in the future. Some dc2dc chargers have a solar input plus the isolated battery outputs from the alternator. Looks easy to add solar with one.

In reply to mdshaw :

I have seen those, especially the one from renogy, but for now I have a 20a dc-dc charger for driving. Just need to add the higher amp supply to the 7 pin connector. 

Yes not a cheap conversion.  When I do it the plan is to get a portable power supply, everything in one unit and then it can move on to the next camper.  EcoFlow, Jackery,  can't pick which one yet.

In reply to porschenut :

I'm planning the same thing. Portable solar panels with a solar generator that has flow through ability so I can change the generator and the trailers batteries at the same time. At night the solar generator will help keep the trailers batteries up when we use the furnace and lights, and also will let us watch a movie.

In reply to porschenut :

If I can find one powerful enough to run my unit, that would be cool. But the 30a units are few and expensive. 

What are you trying to pull 30A with/from?  Thats a lot of nut for most things.  

Ive gone from limping my starting battery along to a Goal Zero 500x, then an Anker Powerhouse 800, and now a Goal Zero 1000x just running my fridge and topping off some other items for a few days, and its the bees knees.  I used to think they were sort of stupid, all in one, pre-engineered, and I could do better.  I was wrong.  They are an awesome engineered solution. The GZ1000X is the very bottom of their high end range, 1500 watt inverter, linkable, the whole Mary Ann, as they say.  

My recommendation would be to buy the GZ setup instead of trying to build something - its that nice. 

Ihave looked at lithium for the fossil and it seems like an awful lot for not much. Although my frame of reference for such things is a little skewed.

In reply to 93gsxturbo :

My camper is 30a and it's easy to hit it   

Very timely post as I just bought a new battery for my camper van. it came with two flooded lead acid batteries in the cabin that don't charge quickly and off gas. I ultimately decided not to go lithium because I don't also want to have to get the dc-dc converter to replace the battery isolater, and a new solar charge controller.
 

Ended up getting a Renogy AGM 12v with 200 amp hours. I would have loved to get the lifepo, but the price (I've bought cars for less!) and the above factors were just too much for me. The agm will charge faster than flooded and not off gas so much, but I will miss the big weight reduction and even more charge of lithium.

I imagine you won't iver charge as long as you get the dc-dc converter... but my knowledge is limited.
 

I ordered the Renogy DCC50S that has solar input also. Looks like it basically replaces the Trombetta isolator.  
That got me tracing down wires & checking on the alternator. The alternator is a DR 22SI which is only 130amp & is at least 13 years old & doesn't have remote sensing.  Replacing it with a DR 28SI 200amp which does have remote sensing.

mdshaw said:

 Even on higher output alternators at low idle rpms, the alternator isn't spinning fast enough to cool & the alternator over heats, starts smoking & burns up. 

This has me concerned now, I just bought a 160a alternator for my car because the stock-type 80a unit overheats at idle with the lights and fans on and stops charging to 14v unless it has time to cool off.

We sure appreciate you dealing with the learning curve for us.

Ya these 130a alternators were not really enough output when new on this motorhome I'm learning.  At idle a new 130a alternator only outputs @50-60a. It only has 1 internal fan also. If the chassis/starting batteries are low & you idle for a while, the alternator overheats because it isn't spinning fast enough, then it shuts off & cools down, then the chassis batteries discharge more. Even at 1500-1600 rpms which is common in the 5.9 Cummins/6 speed Allison, the output when new was probably 90-100a. Driving at night with the cab a/c on or in the rain, the chassis V demands are really high. 
So the bigger the alternator the better & with remote sense is even better. I almost got a 40SI alternator which is 300a but it's 4x the cost, need a longer serpentine belt & make a bracket for it. 
Adding a solar panel can reduce this initial low starter battery issue also. 

In reply to CyberEric :

But even a 200ah AGM is only 100ah usable since it's still basically a SLA.  We've got 2 AGM 50ah's & even before installing the dc fridge cooler, by morning on propane the fridge would be saying low dc V.  Looking forward to the 200ah LFP.  
I've limped this along for 13 years, now time for good dc V.

Installed the Renogy DCC50S with an 80A breaker for the alt supply & a 60A breaker from the Renogy to the coach batteries. Disconnected the ignition wires from the Trompetta battery isolator & just using it as a junction point to go to the Renogy with the alt connection then back from the Renogy to the coach batteries. Turned it all on & it's working as the manual says. Still using agm coach batteries. When the LFP battery arrives, I'll switch Renogy to LFP.  

In reply to mdshaw :

Indeed. I totally get the desire to switch to lithium. I just couldn't justify it.

with the new AGM I am able to power an ARB fridge, instant pot, LED lights, and a fan with two 100 watt panels. I do have to be careful with the instant pot though on cloudy days. I can probably only use it twice safely without issue.

Glad things seem to be working so far. Do you have a battery monitor?

My buddy put the (edit) LiPo battery for his RC boat on the charger and went out to dinner. He didn't get to eat. Neighbor called to tell him his shed was on fire. he got home a couple minutes before the fire truck arrived.

he didn't win.

In reply to AngryCorvair (Forum Supporter) :

That's kind of an odd choice for remote control vehicles- most use LiPo in packs.  Which do heat up and can become flammable.  LiPo packs have a really high discharge rate, which makes them really popular for RC applications, but LiFePO4 can't be discharged all that quickly relative to their charge amounts.

In reply to alfadriver :

My bad, I went back and read his text again:

Only thing I can think of is leaving a rc truck lipo battery on the shelf, while making repairs to the truck.   Then forgetting to grab the battery and put it in its fireproof bag in the garage.