LiFePO4 Charging

[Scott'n'Wendy]

Well...I bought a single 100ah LiFePO4 battery. I figure this will double the battery capacity that I have grown accustomed to and worked with for the last 2+ decades.
My question revolves around charging. Over the past year or two I have heard you can use the FLA charger and be fine, just a bit short on being fully charged.
I read you can max charge LiFePO4 at 14.6vdc. But, at that voltage you are hammering the cells. At 13.8-13.9 you will still get 100% charge, it will take a while, but is best for battery longevity.
I'm looking at the PowerMax converter/charger because of it's user adjustable o/p voltage...and wondering what the experienced LiFePO4 users on here have their chargers set at for charging voltage.

[Jlawles2]

Scott, refer to the mfg for max charge voltage. most likely the system is using a 4 cell setup and pushing the cells to 3.65V each. I run LiPO in RC and push the cells to 4.2V each.

Also remember that chargers push more voltage than the final charge to help drive the amps into the cells faster.

Again, refer to the MFG for proper charging amps and volts.

[Country Campers]

When I did my first battery upgrade I used the Powermax 100 amp, recommended by ncitro. It worked great and with the adjustable voltage one could tune it to the battery specs or whatever you wanted to charge at. I did have mine set to 14.6v as the Lion Energy battery specs stated this was the proper setting. I have read more recently that "over" charging Lithium batteries with high voltage like that "worked" the batteries harder and resulted in shorter life span, as you have already found the information for. With my new setup I have lowered my voltage to 13.8 to hopefully lengthen the battery life. What I am thinking is that if you deep draw the battery a lot and recharge a lot then at higher voltage then that may be what shortens the life, most lithiums have a 3000 to 5000 life cycles. If the batteries are not cycled a lot then the voltage may not have a large effect on them, maybe? I do keep my battery bank at about 50 to 60% charge when in long term storage, winter months, but this sometimes is not reached as I am doing projects on the RV thru the winter and they have been kept at full charge most of the time.

I would follow the battery manufacturer's instructions and you should be fine.

Brian

[Scott'n'Wendy]

Country Campers, how do you find the charge time at 13.8?
The manufacturer says you can max charge at 14.6, but recommends 14.2. But after reading a few web pages on lifepo4 charging, I am wondering if the manufacturers recommendations are modified a bit towards faster charging rather than lifespan for marketing purposes. Heck, battery technology could leap forward fast enough that lifespan isn't really a concern....maybe.

[Jlawles2]

Scott, On my RC LiPO the charger does funny things. Starts at high amperage with voltage not far above the battery, as the battery charges, the amperages goes down as voltage goes up. It's quite a thing to watch the volts and amps change during the charging process.

Depending on what Battery you chose, there is what they refer to as a Charge "C" and a Discharge "C". C is the multiplier for amp capacity to determine how many amps can be drawn from or added to the battery during cycling.

Take a 100A battery with a 10C discharge and a 1C charge. The battery can take a 1000 amp discharge rate but only a 50 amp charge rate (I think the math is correct there, but discharge rate may not be).

Based on how many amps were taken out of the battery will help estimate the charge time. Thus 50 amps out, 50 amp charge would mean about 1 hr charge time. This is just an estimate as the battery charge rate will drop as it reaches the end, so realistically it will probably take 1ht 15 min to charge and balance.

[Country Campers]

I went back and read my upgade thread here Replacing Lead Acid Battery with Lithium - Grand Design Owners Forums (gdrvowners.com) and I see that I charged the depleted batteries in about 3 hours, I believe at the time I had the charger set at 14.2 v. and was 2 batteries so 1 battery would be half the time or less. Although the Powermax had an output of 100 amps I think I only seen about 70 amps or so, this would be low because we were running the furnace and lights at the time of charge. With little or no dc draws while charging the charger will have more available output.

Also important to note not to exceed the battery specs for charging amps or voltage.

Brian

[Jkwilson]

Scott, On my RC LiPO the charger does funny things. Starts at high amperage with voltage not far above the battery, as the battery charges, the amperages goes down as voltage goes up. It's quite a thing to watch the volts and amps change during the charging process.

Depending on what Battery you chose, there is what they refer to as a Charge "C" and a Discharge "C". C is the multiplier for amp capacity to determine how many amps can be drawn from or added to the battery during cycling.

Take a 100A battery with a 10C discharge and a 1C charge. The battery can take a 1000 amp discharge rate but only a 50 amp charge rate (I think the math is correct there, but discharge rate may not be).

Based on how many amps were taken out of the battery will help estimate the charge time. Thus 50 amps out, 50 amp charge would mean about 1 hr charge time. This is just an estimate as the battery charge rate will drop as it reaches the end, so realistically it will probably take 1ht 15 min to charge and balance.

When battery load exceeds the output capacity of the charger, charger voltage will be very close to battery voltage. You have to understand that the charger never changes anything about it’s output. It never, ever adjusts its output. It’s a DC power supply, and very little more. If it’s a 100W charger, then it outputs 100W throughout the early charge process with voltage rising and current dropping as the battery charges. This voltage and current relationship is determined 100% by the battery.

[Country Campers]

I found this interesting and thought I would share, it may not be pertinent to your battery though.

This is from the Lion Energy faq pages.

"Lead acid batteries usually last a year or two and often come with a prorated warranty. The Safari UT 1300 has a limited life-time warranty. That means it can completely charge, discharge (use) and recharge 3500 times or cycles before the battery cells are depleted 20% (it still would have 80% of its capacity). This assumes you are charging one UT 1300 at a 1C rate or using a 90A charger for faster charging. If you use a .5C or 45A charger, the Safari UT 1300 can have up to 5,000 life cycle capacity. In simple terms – if you used all the energy in it every day and then recharged it using a 45A charger, the Safari UT 1300 will last for nearly 14 years. If you used it every other day, that’s 28 years, or every three day that’s 42 years and so on. Most people only use it for a few weeks at a time or for a season so the Safari UT 1300 can last a lifetime."

I found it interesting that if you use less amps at the charge cycle it will increase the life cycles, from 3500 to 5000. Although less amps will increase charge time it will also increase life time. A battery that will last 14 years on the 3500 cycles will more than likely outlast the camper and possibly the owners willingness to go camping.

Brian

[Guest]

Discharge load can also reduce the longevity of the lithium battery. Optimum usage is from 20%-80% SOC while keeping charge and discharge current at half the batteries max rating such as 1C. Its the heat generated in charging as well as discharging that reduces battery life. The cells of a battery will also deteriorate faster when the battery is held at its charged or discharged state for extreme durations. Its not always easy to do this but it is easy to charge to 100% SOC, begin use and to limit the discharge to no more than 20% SOC. Storage is best to be as far from these extremes as possible with is at 50% SOC.

Jim