WFCO 8735(non lithium) Performance with Lithium Batteries

[Tyler-98-W68]

There have been lots of questions on whether or not the factory WFCO 8735 converter that doesn’t “support” lithium batteries is capable of charging them sufficiently.

I have a 2021 Geo Pro with a 100ah Screampower Lithium Battery and the WFCO 8735 non lithium converter. Prior to having a battery shunt my limited testing showed the converter is capable of charging lithium batteries, but not to 100% and usually very slowly. After getting my Victron Smart Shunt this past weekend I can confirm the behavior I saw earlier.

Before I get very long winded, the WFCO 8735 is completely capable of charging a lithium battery up to at least 90% and sometimes 100% but the key is that the battery has to be at an extremely low state of charge to do so.

After drawing down my battery to 13.0v I plugged the trailer in to shore power. I observed a 17amp spike of current that progressively went down and down but was mostly around 4-6 amps. Charging at a painfully slow speed. After 16.5 hours The battery was at 96% and zero current going through the battery. The previous 3.5 hours I wasn’t able to check (I was sleeping) but the converter likely charged the battery up to 100% and then the voltage started to drift down as the converter likes to stay right around 13.5v. So in this test we have the converter basically charging the battery up 100%.








In order to make sure it wasn’t a false recharge reading I put a bunch of draw from some small space heaters I have until I kept hitting the inverter cut off (10.5v, my battery will actually function down as low as 10.1v) I was able to measure 100ah of energy drawn, indicating I did in fact get a full charge.






Next was to plug in to shore power from a very low voltage (11.0v) and observe the charging current and speed. As soon as I plugged in to shore power the converter charge current spiked to 33amps, and gradually dropped over 3.5 hours to a low point of 17 amps before turning off because the battery was fully charged. After 30 minutes of being nearly fully charged the state of charge started to drop down (just like it did when I started a recharge from 13v indicating the converter does draw the battery down when not actively charging)








So it took almost 14 hours to charge my lithium battery from a starting voltage of 13.0v, or 3.5 hours from a starting voltage of 11.0v using the factory non lithium WFCO 8735 converter. Once fully charged though if the converter is left on the battery does get drawn down






The method of charging, high current and voltage slowly rising with the converter charging is the exact same behavior that my 10amp lithium specific charger that came with my battery came with.
So if someone did not want to swap out their converter to a lithium specific one there are a few “issues” to deal with

1. You need to turn the converter off from charging once it decides its done charging, which is between 90-100% soc.

2. You need to have your battery at a very low state of charge. In my case 11.0v works (My BMS cuts off at 10v)

3. Not an issue but if you have the Go Power solar set to LFP mode it will finish off the charge for you.

[Adirondack_Camper]

Good info.

[TitanMike]

Definitely good info. Proves that one CAN charge LiFePo4 batteries with a conventional converter/Charger (even a WFCO).

The downside is the amount of time it takes. Can be a non-issue if returning to a shore power connection after a long weekend but not the greatest if having to rely on a generator for recharging.

To offer a comparison, if my two Battleborn 100 ah batteries are discharged to 20% (deepest discharge for me to date) it takes just over 3 hours to reach 100% charge (including cell balance) using my PD9100 ALV (lithium capable) Converter. For me it's only a half gallon of gas (or so) and a lot less generator run time.

If one does a lot of driving between sites after stays that don't totally deplete the batteries a DC-DC charger is really a GREAT addition if one is going to "fly" with the stock Converter (WFCO 8955 in this case).

A side note. It's really important to periodically charge LiFePo4 batteries to a full 14.2-14.6 volts in order to balance the cells. If not, any cell that is depleted to a lower capacity than the rest will severely limit the batteries total capacity. Unlike Lead Acid batteries you can't force power through a low cell in order to balance it. It takes the cell balancing circuitry in a BMS to accomplish this and they typically require charging voltages over 14 volts. On that note, any PD Converter with Charge Wizard allows one to force converter into Bulk/Boost mode which satisfies this requirement.

[Tyler-98-W68]

I agree about the 14v charging to top them up, which my solar does. But I also have my 10A lithium specific charger mounted in my battery box and use that to fully charge it up once I get back from my camping trips, or if I don't want to run my generator I use one of my lithium battery packs to run the 10a charger.

I have been thinking about getting the PD9160AL and putting that in my battery box for quick charging duties.

[TitanMike]

Originally Posted by Tyler-98-W68

I agree about the 14v charging to top them up, which my solar does. But I also have my 10A lithium specific charger mounted in my battery box and use that to fully charge it up once I get back from my camping trips, or if I don't want to run my generator I use one of my lithium battery packs to run the 10a charger.

I have been thinking about getting the PD9160AL and putting that in my battery box for quick charging duties.

Have you tried restarting the WFCO concerter once battery current drops to zero?

Ustally this forces the converter jnto bulk mode and due to the charging curve of the LiFePo4 batteries, it should remain there for a while, adding more to storage.

This is actually a "hack" recommended by lead acid battery mfr's to force an equalization charge with only 3 stage converter chargers.

[Tyler-98-W68]

Originally Posted by TitanMike

Have you tried restarting the WFCO concerter once battery current drops to zero?

Ustally this forces the converter jnto bulk mode and due to the charging curve of the LiFePo4 batteries, it should remain there for a while, adding more to storage.

This is actually a "hack" recommended by lead acid battery mfr's to force an equalization charge with only 3 stage converter chargers.

Once the battery is fully charged and the current is zero, when left plugged in there is a draw showing on the battery of a few amps and the voltage goes down to 13.5-13.6. Is that what you mean?

[TitanMike]

Originally Posted by Tyler-98-W68

Once the battery is fully charged and the current is zero, when left plugged in there is a draw showing on the battery of a few amps and the voltage goes down to 13.5-13.6. Is that what you mean?

At that point try turning off converter for 30 seconds then turn on. Current should then resume and continue for a while with voltage approaching 14+ volts.

Eventually it will drop down to ~13.8 v and current flow will drop to zero again. You can "goose" the charge by repeating the off/on process if you want.

[Rolland]

Originally Posted by TitanMike

At that point try turning off converter for 30 seconds then turn on. Current should then resume and continue for a while with voltage approaching 14+ volts.

Eventually it will drop down to ~13.8 v and current flow will drop to zero again. You can "goose" the charge by repeating the off/on process if you want.

When you say turn off, are you simply turning the breaker to the converter off, then on 30 seconds later?

[TitanMike]

Originally Posted by Rolland

When you say turn off, are you simply turning the breaker to the converter off, then on 30 seconds later?

Yes.

[KelleyTexas]

Very good info, and it seems to support what the people in the vendor tent at the FROG Rally last month told me about this same converter (same exact model as mine on the R-POD). So, that might solve one half of my puzzle. The other half is deciding if I should be concerned about the gauge of wiring in my trailer for use with lithium batteries. Do the wires that connect to the battery match up with the gauge wire used throughout the trailer (i.e., can I determine the gauge of wire by looking at the wires where they attach to the battery)? Or can it vary? Sorry if that is a dumb question. I meant to ask this question while I was in Elkhart. I'm pretty sure I read somewhere that lithium batteries are higher voltage, so the gauge of wire can be important, unless it's probable that my R-POD is good to go. Just getting started with researching all of this.

[Tyler-98-W68]

There really isn't much higher voltage going through the wiring, my Geo Pro has a 1000w inverter, my lithium battery is rated at 100c continuous discharge current which is over the 1000w inverter output, and since the trailer was wired to run 1000w from the inverter there is no need to do any additional wiring. If I was to add a second 100ah lithium battery and a larger inverter then I would want to upgrade the wiring.

[DouglasReid]

Originally Posted by TitanMike

PD Converter with Charge Wizard allows one to force converter into Bulk/Boost mode which satisfies this requirement.

I do have a PD converter with Charge Wizard, a 9280 if memory serves. It is buried behind my load center.

What must be done to force the converter into Bulk/Boost mode or is is automatically done in the PD's circuitry?

[Tyler-98-W68]

Just wanted to provide a small update. I no long have my Geo Pro however my new "trailer" 2022 Keystone Retreat Loft has a WFCO 9855-AD Model converter. This new lithium compatible converter has been showing up (WFCO 8735-AD) in some of the new Geo Pros.

I'm quite disappointed in it's performance. It performs EXACTLY as the non lithium specific converters. Meaning that unless the battery is drawn down extremely low, its not going to charge the battery very fast. The only difference is that no matter what state of charge your lithium battery is in. It will charge up to 100% without any solar needed to top off, so really in my opinion its not a converter to upgrade to or spend money on.

What I did to get the bulk charging to start was to create a large draw on the battery and then flip the converter on, and you can see the bulk charging happens



This is the charging it normally gives if the voltage isn't really low



When it doesn't go into bulk charging mode (voltage has to be below 12v) it takes forever to charge up, not a big deal if time isn't of the essence but if you are looking for a quick charge converter the AD models from WFCO really aren't much better than the "old" ones especially if you have factory solar and switch it to the lithium setting.

[nvs4602]

I bought the WF-8950L2-MBA lithium compatible converter. In the manual it states that it will bulk charge at 14.6v for 4hrs. Then it switches to float charge at 13.6v no mater what % charge the battery is at. You have to cycle the converter off and on to go back to bulk. I have 245ah so if I really discharge it 4hrs at bulk isn't long enough.

Most if not all lifepo4 batteries will charge to 14.6v or 3.65v per cell. When you take them off charge they will rest at 13.6v or 3.4v per cell. That's why a lithium charger will float at 13.6v because it's a good resting voltage.

[PhilFromMaine]

Originally Posted by KelleyTexas

Very good info, and it seems to support what the people in the vendor tent at the FROG Rally last month told me about this same converter (same exact model as mine on the R-POD). So, that might solve one half of my puzzle. The other half is deciding if I should be concerned about the gauge of wiring in my trailer for use with lithium batteries. Do the wires that connect to the battery match up with the gauge wire used throughout the trailer (i.e., can I determine the gauge of wire by looking at the wires where they attach to the battery)? Or can it vary? Sorry if that is a dumb question. I meant to ask this question while I was in Elkhart. I'm pretty sure I read somewhere that lithium batteries are higher voltage, so the gauge of wire can be important, unless it's probable that my R-POD is good to go. Just getting started with researching all of this.

It is very easy to over think this subject. Your wiring will be more than adequate for any reasonable upgrade you could do.

The determinate of wire size is how much amperage will flow through the wire and the length of the run. The only place in your RV that would be an issue would be from the battery to the inverter (if you even have one).

All the other wiring in an RV is engineered by electrical engineers to meet all applicable codes and the equipment the wires service. So your upgrading to lithium (lifepo4) batteries is nothing to be concerned about.

The Scientists tell us that it is best to only discharge lithium batteries to 20 percent and to charge them to 80 percent for the optimum health of the battery. Of course you can discharge them more and charge them more is you like.

[Hclarkx]

Originally Posted by TitanMike

A side note. It's really important to periodically charge LiFePo4 batteries to a full 14.2-14.6 volts in order to balance the cells. If not, any cell that is depleted to a lower capacity than the rest will severely limit the batteries total capacity. Unlike Lead Acid batteries you can't force power through a low cell in order to balance it. It takes the cell balancing circuitry in a BMS to accomplish this and they typically require charging voltages over 14 volts. On that note, any PD Converter with Charge Wizard allows one to force converter into Bulk/Boost mode which satisfies this requirement.

Indeed! And, that trip up to 14.4 also resets the SOC monitor which will drift away from actual SOC (typically overstating actual SOC) if it does not see that assumed 100% SOC that occurs at 14.4V occasionally.

[Hclarkx]

Originally Posted by Tyler-98-W68

What I did to get the bulk charging to start was to create a large draw on the battery and then flip the converter on, and you can see the bulk charging happens

I wonder if the new converter has trim pots on it that could fix this. My old WFCO 8955 (removed years ago) has three trim pots, one of which might be the bulk engagement setting. I know one of them is the float voltage and one is the current limiter. I use these when using the retired unit as a bench supply (the current limit works in float mode as well as bulk mode). The other one might be the bulk engagement trigger voltage. I've never tested it. If your new unit has trim pots, one of them just might be the bulk trigger voltage level.

[Tyler-98-W68]

I want to update this post (Again) and state that the issues I was having have been resolved. Turns out my converter was in lead acid mode and not lithium mode. I ended up draining the battery cycling the breaker on the converter and then got it in to lithium mode (glowing blue light, before it was yellow)

It now charges quickly from any state of charge. Only issue is that sometimes it requires a cycle of the breaker to get it back into the bulk charging mode, but not all the time.

I initially didn't have my screen recorder app when I did the first test and it went in to bulk mode no problem. I then turned the breaker off started the screen recording and it wouldn't go into bulk mode, once I cycled the breaker again, it charged as it should.

https://www.youtube.com/watch?v=88b15oRLDzw

[Hclarkx]

Thanks. Interesting. It seems the auto-detect circuitry isn't ready for prime time. I wonder if load on the battery confuses it. Hopefully it will stay in Lithium mode or will get there more easily in the future.

[DonBr]

Originally Posted by Tyler-98-W68

Turns out my converter was in lead acid mode and not lithium mode.

I'm quite curious how that works. AD reviews generally fall into one of two categories, 5-star that say "It looks good but I haven't installed it yet" and one or 2-star that say "After talking to WFCO support I had to trick it into Lithium mode." The latter often say it reverts back to lead-acid.


Is your situation one where you had to trick it, and if so how?