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diy solar

Convert from FLA to LiFePo

elewis33

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Feb 13, 2020
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My little teardrop trailer has one 12 volt deep cycle SLA battery and has a very modest power draw. I'd like to replace the battery with LiFePo and worried about the charging provided by the trailer's built-in charger. It's got an "all in one" AC panel, DC panel, charging package. Of course, LiFePo wasn't really much of a thing back in 2010 when this was built so I suspect the charger isn't up to the task of charging LiFePo batteries with the proper charging profile.

I'd like to keep the AC/DC combination panel and remove/replace the charger with something appropriate to LiFePo. I'm not planning on installing a solar system right away so I'm looking for a charger that takes 120 volts from the shore power and charges the battery via AC.

I bought the Victron IP 67 for charging my SOK 12v100 at home and wondering if something like this would be a good fit for the trailer too?

Victron Energy Blue Smart IP67 12/24-Volt 5-25 amp Battery Charger (Bluetooth)
 
Not to be argumentative, but the different chemistry between lead/acid and LiFePo4 requires different charging characteristics. I haven't heard of lithium batteries being "drop-in" replacements without changing out the shore power AC-DC charger and changing settings on the solar charge controller, but I'm relatively new to all of this so please correct me if I'm wrong.

But this brings up a good topic to discuss. If someone was to simply replace their travel trailer's lead/acid battery with an LFP battery and use their existing lead/acid AC-DC charger and the tow vehicle's alternator to replenish the trailer's battery on camping trips, and then rely on their solar charge controller and an external lithium battery charger at home to bring their battery back to peak freshness between camping trips, would that be an acceptable option? Or is the lithium chemistry so sensitive to any charging voltages that this would still shorten the battery's lifespan to not "properly" recharge the battery every single time?

I'm sure this "shortcut" isn't the optimal setup, but it's awfully expensive to upgrade an entire trailer's electrical system to use the optimal equipment. So for folks who aren't living out of their trailer full-time and have the opportunity to regularly return home and give their lithium battery a "proper" charge between trips with a proper lithium battery charger, perhaps this would be an acceptable "drop-in" battery solution?
 
Not to be argumentative, but the different chemistry between lead/acid and LiFePo4 requires different charging characteristics. I haven't heard of lithium batteries being "drop-in" replacements without changing out the shore power AC-DC charger and changing settings on the solar charge controller, but I'm relatively new to all of this so please correct me if I'm wrong.

You're mostly wrong. It's mostly about voltages. Often canned AGM settings work great for LFP.

If a 12V charger is capable of 14.2-14.4V absorption and float not higher than 13.6V, it's good to go.

The above is pretty much it.

Note how Battleborn doesn't indicate a LFP charger is necessary:


I leave it to you to determine if Battleborn or you know better. ;)
 
That's encouraging news because I've been trying to figure out a parts list to upgrade my travel trailer from twin 6V FLA golf cart batteries to a single big LiFePo4 battery. This will greatly simplify and reduce the cost of the project if what you say is true. :)(y) The last thing I'd want to do is kill $1-2k worth of lithium by improperly charging it.
 
Even if you keep an FLA only converter/charger that bulks @ 13.6V, you can still just drop in a LiFePO4 with a good BMS. The BMS does all the work. Sure, it's better to have LiFePO4 specific parameters from all chargers, but not required.
 
Not all FLA converters will work of course..BB keeps a list of those that don’t. So you might just give them a call with your model numbers to confirm. My FIL bought two BBS and found his OEM converter would not charge them very well. Getting a lithium capable charger works Much better
 
Who, several questions here...
Most battery charger agm settings will work fine for lfp... however, using the tow vehicle alternator for a house battery charging is unwise without a dedicated dc to dc charger installed.
 
Who, several questions here...
Most battery charger agm settings will work fine for lfp... however, using the tow vehicle alternator for a house battery charging is unwise without a dedicated dc to dc charger installed.
I'm not doing alternator charging on this, so that helps simplify things.
 
FWIW to anyone that might be following along, these older WFCO all-in-one panels with converter/charger aren't capable of charging at 14.4 volts. I haven't been able to find out where that cutoff point might be in terms of the different models or year of production, but mine isn't going to work for my brand new battery and I'm not going to risk "trying it". I'll be investing in a modern capable charger so I can get the most out of my battery investment.
 
I'll be investing in a modern capable charger so I can get the most out of my battery investment.
Probably best imho
You mentioned victron which doesn’t even need discussion as to quality.
Just an FYI I believe there’s a small 15A ‘RV converter’ on amazone that claims LFP battery compliance for under US$100 if that interests you. Thats not a ‘here’s something cheaper’ suggestion, just a unit that might work and serve as a 100% duty power supply while accomplishing your charging goal without each-time-of-use effort.

(200W of solar could keep you going pretty well over longer ‘stays’ is another thought.)
 
FWIW to anyone that might be following along, these older WFCO all-in-one panels with converter/charger aren't capable of charging at 14.4 volts. I haven't been able to find out where that cutoff point might be in terms of the different models or year of production, but mine isn't going to work for my brand new battery and I'm not going to risk "trying it". I'll be investing in a modern capable charger so I can get the most out of my battery investment.

Beware of slick marketing. When people are trying to sell you something, you really need to question their info.

Most of the converter LFP implementations are marginal. I have yet to find one that I really like, and most converter installations are more of a problem than the converter.

Just because a charger can't supply 14.4V doesn't mean it's a problem. Just as important is HOW you're going to be using the charger. If you're using a generator or want the fastest possible charging, you want one option. If you want slow charging on shore power or maximize battery life, you want something else.

A fully programmable charger obviously gives you to the most options, but it may not be the best VALUE.
 
By visiting Internet Archive Wayback Machine you could find the parameters of your WFCO charger.

We purchased our camper in October 2018. Our WFCO 8955 states: 14.4 bulk for up to 4 hours, 13.6 absorption for up to 40 hours, and 13.2 float charge. It seems the WFCO 8900 series is in most smaller campers.

We also have a 100 watt Renogy portable and Zamp port, with three 15' sections of Zamp 10 awg cable, and a Victron 100/20 SCC next to the batteries. With all three 15' sections having a controller on the portable means that it's sending lower voltage to the batteries resulting in an unacceptable cable loss, that's why the SCC is next to the batteries.

The WFCO could probably keep your batteries at 80% or more (just an off-the-cuff estimate), while a portable could be used to keep your LFP batteries charged to 100% many days.

Food for thought,

Perry
 
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Nope. At 13.6 (3.4V/cell), LFP will slowly charge to about 95%.
Actually the answer would be "Yup." I stated "The WFCO could probably keep your batteries at 80% or more (just an off-the-cuff estimate)" Again, that was "80% or more" and 95% is simply "more."

and there's really no point in floating LFP to 100%.
Many charge to 100%, and for them it's a point, but I could care less if it's 95% (choose an upper point) or 100%.

Both points are merely hair-splitting.

Perry
 
Keep in mind actual output voltage and advertised specs don't always match, my Progressive Dynamics 9260 has a measured output of .06 VDC above spec, so when it is in 14.4 bulk mode it is really putting out 14.46,and 13.4 absorption mode is really 13.46 etc
 
Actually the answer would be "Yup." I stated "The WFCO could probably keep your batteries at 80% or more (just an off-the-cuff estimate)" Again, that was "80% or more" and 95% is simply "more."


Many charge to 100%, and for them it's a point, but I could care less if it's 95% (choose an upper point) or 100%.

Both points are merely hair-splitting.

Perry

"could probably keep your batteries at 80% or more"

Could you be more non-committal? You don't get to take credit for that amount of vague. :D

LFP WILL charge to 95% capacity at 3.4V/cell. It will take about 4-6 hours once 3.4V/cell is achieved assuming a 0.1-0.2C start current.

"hair splitting" implies you were not being vague. When you take a large locus of points and eliminate all the others and point at the one that's correct, that's not "hair-splitting," it's being accurate. :p
 
The issue here is a tenth of a volt variation at around 13.3-13.4VDC going into the battery can be the difference between eventually reaching 70% state of charge and eventually reaching 95% state of charge. This variation could come from the charger being out of spec, under sized battery cables, poor connection at the battery terminals, corrosion on the cable lugs, or a combination of all of the above.
 
The issue here is a tenth of a volt variation at around 13.3-13.4VDC going into the battery can be the difference between eventually reaching 70% state of charge and eventually reaching 95% state of charge. This variation could come from the charger being out of spec, under sized battery cables, poor connection at the battery terminals, corrosion on the cable lugs, or a combination of all of the above.
Agree. There are too many variables.

If I've learned one thing, theory and actual practice alter accuracy. :p

Enjoy,

Perry
 
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