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Old 09-27-2021, 08:36 PM   #1
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WFCO 8735(non lithium) Performance with Lithium Batteries

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.
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Old 09-28-2021, 12:02 PM   #2
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Good info.
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Old 09-28-2021, 06:35 PM   #3
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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.
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Old 09-28-2021, 08:21 PM   #4
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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.
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Old 09-28-2021, 10:22 PM   #5
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Originally Posted by Tyler-98-W68 View Post
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.
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Old 09-28-2021, 10:27 PM   #6
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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?
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Old 09-28-2021, 11:23 PM   #7
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Originally Posted by Tyler-98-W68 View Post
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.
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Old 09-29-2021, 09:12 AM   #8
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Originally Posted by TitanMike View Post
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?
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Old 09-29-2021, 09:58 AM   #9
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When you say turn off, are you simply turning the breaker to the converter off, then on 30 seconds later?
Yes.
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Old 09-29-2021, 08:07 PM   #10
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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.
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Old 09-29-2021, 09:36 PM   #11
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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.
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Old 09-30-2021, 04:41 AM   #12
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Quote:
Originally Posted by TitanMike View Post
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?
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