LiFePo4 settings on Progressive Dynamics Converter

[757driver]

Originally Posted by craigav

All of the chargers I have seen that are Lifepo4 rated usually charge what is known as CV (constant voltage) at a preset value (some you can adjust) usually around ~14.5v. Think of it like a cruise control resume function, if you batteries are very low, the overall charge voltage will lag behind (lower) than the ~14.5v until the charge current is able to bring the battery voltage up to the set point (~14.5). Once the set voltage is obtained, then the charge circuit will maintain that voltage and constantly drop the charge amperage until another set point in the charger is hit (some are based on time, and some are based on current) (aka as constant voltage or CV).

In regards to floating, that is not really necessary although it does help in certain cases where you want the solar to keep the lifepo4 batteries fully charged for night time usage. In other words if your batteries were fully charged by 1pm (off of solar or other charger) and you turned off the charge and started discharging them, they may not ever get discharged to 13.2v during the afternoon but will not be at 100% when night time hits thereby wasting the solar charge available during the rest of the afternoon.

I personally would not recommend charging lifepo4 batteries to 14.5v (or 14.6v) unless you will be needing 100% of their capacity within a day or so. They will last a lot longer (based on mfgr reports) if you don't charge them to 100% and don't discharge them 100%. In fact, the low voltage cutoff in the BMS (for at least all lifepo4's I have looked at) is there for a safety and it is not recommended to run them down so low as to have the BMS shut off the battery (or charge them so high the BMS shuts off the current). When I don't plan to need the batteries at 100% I usually use the lead acid charge profile which on mine only charges them to about ~14v then I stop charging (depending on which charger I am using I set the float as low as possible). As others have mentioned, some lifepo4 batteries need the higher voltage to balance the batteries, the batteries I have don't require the high voltage to balance them. You should check with the mfgr of your batteries to be for sure. ~Craig

Craig,

You make some good points. I also see no reason to charge lithium to 14.5-14.6v as mine do not have balance boards. I charge mine to 14.2v and then a float of 13.5v if charging from solar. If from shore power 14.2v and then I stop charging altogether.

The difference in charging a lithium bank to 14.6v vs charging to 14.2v can be measured in seconds the amount of additional power you will obtain from the bank.

[CRV2]

Originally Posted by 757driver

Craig,

You make some good points. I also see no reason to charge lithium to 14.5-14.6v as mine do not have balance boards. I charge mine to 14.2v and then a float of 13.5v if charging from solar. If from shore power 14.2v and then I stop charging altogether.

The difference in charging a lithium bank to 14.6v vs charging to 14.2v can be measured in seconds the amount of additional power you will obtain from the bank.

Thanks, and as I think about it, even if I did have lifepo4's with balance boards that required ~14.5 volts (mine have a balance board but they don't require full voltage to balance them), I would probably only bring them up to that high of voltage maybe once or twice a month, as they shouldn't need to be re-balanced every day or even every week.

~CA

[757driver]

Originally Posted by craigav

Thanks, and as I think about it, even if I did have lifepo4's with balance boards that required ~14.5 volts (mine have a balance board but they don't require full voltage to balance them), I would probably only bring them up to that high of voltage maybe once or twice a month, as they shouldn't need to be re-balanced every day or even every week.

~CA

Craig,

I would agree 100%. I have read also that the more the lithium bank is balanced the more often it needs to be balanced. Good properly balanced cells can go for a year or more without going out of balance.

[Grump010]

I am running the PD 4655L and 2x 100ah Renogy Lifepo4 and I have had no issues. The Renogy battery has a BMS which manages the charging and balancing of the batteries. If you haven't already purchased the battery monitor I can recommend it. The BMS accepts the 14.6 but steps it down and manages the voltage and current to charge the cells. I also built a 105ah Lifepo4 power center for my trolling motor and around the campsite power needs and installed a very similar BMS into the case that I can access via bluetooth and modify parameters to fit the cell characteristics and use requirements. It is far more capable than a cell balancer that I use for my RC electric airplanes and drones.

[757driver]

Originally Posted by Grump010

I am running the PD 4655L and 2x 100ah Renogy Lifepo4 and I have had no issues. The Renogy battery has a BMS which manages the charging and balancing of the batteries. If you haven't already purchased the battery monitor I can recommend it. The BMS accepts the 14.6 but steps it down and manages the voltage and current to charge the cells.I also built a 105ah Lifepo4 power center for my trolling motor and around the campsite power needs and installed a very similar BMS into the case that I can access via bluetooth and modify parameters to fit the cell characteristics and use requirements. It is far more capable than a cell balancer that I use for my RC electric airplanes and drones.

Daryl,

Just curious, how does the internal BMS take 14.6v and step it down along with the current to charge the cells?

[Grump010]

Originally Posted by 757driver

Daryl,

Just curious, how does the internal BMS take 14.6v and step it down along with the current to charge the cells?

Your question although perhaps legitimate is far beyond the OP's initial question to which my response was directed. If you're actually searching for an answer to your question, perhaps Google would be a potential route. Also, Will Prouse has a webpage with other links and videos that could assist with information that may answer to your question but a further research dive will be required to fully answer your question.

[Itinerant1]

Originally Posted by Grump010

Your question although perhaps legitimate is far beyond the OP's initial question to which my response was directed. If you're actually searching for an answer to your question, perhaps Google would be a potential route. Also, Will Prouse has a webpage with other links and videos that could assist with information that may answer to your question but a further research dive will be required to fully answer your question.

It's a fair question, you made a statement that the BMS steps voltage down and looking at their manual it doesn't say that. What their's and most every other BMS does is protect the battery/ cells.

It's the chargers that charge at x amount not the interal bms.

[757driver]

Originally Posted by Grump010

Your question although perhaps legitimate is far beyond the OP's initial question to which my response was directed. If you're actually searching for an answer to your question, perhaps Google would be a potential route. Also, Will Prouse has a webpage with other links and videos that could assist with information that may answer to your question but a further research dive will be required to fully answer your question.

Had a chance to read through the Renogy manual this morning. The BMS will NOT take 14.6v and reduce it or restrict it in any way. The BMS is there to protect the batteries and cells from over voltage over current and several other safe guards.

The Renogy BMS will not restrict voltage or current going to the batteries until it reaches 14.8v and the current is 100A or greater.

Renogy lithium batteries require a max charge voltage of 14.4v and a max charge current of 50A so there is room for potential abuse from the operator in either voltage or current prior to the BMS stepping in to shut things down.

A PD charger that puts out 14.6v may do long term harm IF that full voltage gets through to the Renogy batteries instead of the recommended 14.4v. The line loss with your setup (length and size of wire from your charger to the batteries) may look after that 0.2v difference but for others it may not.

Glad your system is performing well for you.

[Jerry Burks]

So I ordered that 300Ah CHINS battery 6 days ago and was told it should arrive sometime mid to end of the month. And what...it showed up today at my door.

Had not really planned for it but I will try to install it tomorrow before we leave for our next trip the day after. Fortunately the 2/0 wiring for the inverter, disconnect switch, bus bars and other small stuff also arrived today. I am planning to mount all that on a strip of phenolic Garolite on top of the battery.

[hclarkx]

Originally Posted by 757driver

Whether being used daily or in storage I see no need for floating lithium batteries at any voltage. Perhaps a case could be made for a low float voltage of 13.1-13.2v but a float voltage of 13.8v is absolutely absurd.

I agree. I float at 13.4 (100% SOC) when the RV is in use. This keeps us prepared for inclement weather (solar is our only charge source). When the RV is in storage, it's in my yard and I'm in and out of it several times per week, often at night. I also often have an exhaust fan running on hot days and then there's that parasitic load. Since I need power so often when its in storage, I keep the battery connected and I float it at 13.2V (roughly 50% SOC in my Lifeblue) for long life.

[hclarkx]

Originally Posted by 757driver

It depends on the use and charge source. For me floating at 13.6v while on shore power would keep the bank at 80-90% SOC. If I am not using the batteries I like to treat it as a storage situation therefore store at about 50% SOC. Floating at 13.6v while boondocking and using solar for the charge source makes perfect sense. If your battery bank is full early afternoon then a float of 13.5-13.6v would be desirable to keep the bank at a higher SOC for the coming night when it will inevitably drop by the next morning.

You've finally said something I don't agree with (a very rare event!).

A LiFePO4 "12V" battery will charge to 100% SOC with any voltage above about 13.34V applied. Hence floating a battery above 13.34V will get it to 100%. It just takes longer at 13.6V than at a higher voltage because charge current will be lower.

The typical curves (see image below) that show voltage rising to about 14.4V and indicating 100% SOC at that point apply to the usual charge process where the constant current bulk stage of a charger is applied until voltage hits 14.4V. These curves show the battery passing through 13.6V at around 80-90% SOC. Indeed, if you stopped this charging process at 13.6V and removed the charger, you would have an 80-90% SOC. If you simply stopped the voltage rise when it hit 13.6V, the battery would continue to charge and get to 100% after, say, an hour instead of another 20 minutes (at 14.4V). Ditto for floating at 13.6V.

Hence, these curves belie the fact that a LiFePO4 will charge to 100% at any voltage over 13.34V and so will charge to 100% when floated at any voltage above 13.34V.

[757driver]

Originally Posted by hclarkx

You've finally said something I don't agree with (a very rare event!).

A LiFePO4 "12V" battery will charge to 100% SOC with any voltage above about 13.34V applied. Hence floating a battery above 13.34V will get it to 100%. It just takes longer at 13.6V than at a higher voltage because charge current will be lower.

The typical curves (see image below) that show voltage rising to about 14.4V and indicating 100% SOC at that point apply to the usual charge process where the constant current bulk stage of a charger is applied until voltage hits 14.4V. These curves show the battery passing through 13.6V at around 80-90% SOC. Indeed, if you stopped this charging process at 13.6V and removed the charger, you would have an 80-90% SOC. If you simply stopped the voltage rise when it hit 13.6V, the battery would continue to charge and get to 100% after, say, an hour instead of another 20 minutes (at 14.4V). Ditto for floating at 13.6V.

Hence, these curves belie the fact that a LiFePO4 will charge to 100% at any voltage over 13.34V and so will charge to 100% when floated at any voltage above 13.34V.

Attachment 331313

Not a problem. I guess we have different sources for our information. Mine comes from here: https://marinehowto.com/lifepo4-batteries-on-boats/

My sources list a voltage as low as 3.42vpc (13.68v) can eventually fully charge a lithium battery. So would 13.6v be 80%, or 90% or a little higher after an extended period of charge time is subjective and may depend on type of lithium cells and construction methods.

My experience thus far with my bank does NOT show an eventual full charge with a charge voltage as low as 13.34v. YMMV

[hclarkx]

Originally Posted by 757driver

Not a problem. I guess we have different sources for our information. Mine comes from here: https://marinehowto.com/lifepo4-batteries-on-boats/

My sources list a voltage as low as 3.42vpc (13.68v) can eventually fully charge a lithium battery. So would 13.6v be 80%, or 90% or a little higher after an extended period of charge time is subjective and may depend on type of lithium cells and construction methods.

My experience thus far with my bank does NOT show an eventual full charge with a charge voltage as low as 13.34v. YMMV

Yes, theoretically 13.34 would take forever. Allow for about 10 mv drop in the BMS and in fact one might not get above 99%. But, 13.6 doesn't take so long. I've experimented with my 280 Ah Eve banks and my Lifeblue 300 Ah. If you set the solar controller at 13.6V and watch it (starting from less than a 100% charged battery) the current takes a while to go to zero (fully charged). If you then remove the charger and let the battery sit long enough, the voltage will get down to a bit over 13.3V which is the usual full-charge resting voltage of virtually all LiFePO4 batteries. You can reduce the time to get from 13.6 down to 13.3 by putting a 100 ma load on for an hour or two.

The site you mention is one of the best I've found. Better than Battery University. It was updated late last year, but there's a lot of info in it that was speculative when it was written and could be made more definite now.

They say this about floating at close to the resting voltage:

"Please understand that any voltage below the 100% SoC point, of the LFP battery, would not be considered “floating” it. If using a standby voltage at say 3.35V per cell, the current into the battery will end up at 0A and be slightly below the 100% SoC point."

Note that 3.35 per cell is 13.4V. In the context of their corresponding discussion, "slightly below" means about 99%.

Ergo they are saying that floating at or above 13.4V is effectively floating at 100% SOC.

[757driver]

Originally Posted by hclarkx

Yes, theoretically 13.34 would take forever. Allow for about 10 mv drop in the BMS and in fact one might not get above 99%. But, 13.6 doesn't take so long. I've experimented with my 280 Ah Eve banks and my Lifeblue 300 Ah. If you set the solar controller at 13.6V and watch it (starting from less than a 100% charged battery) the current takes a while to go to zero (fully charged). If you then remove the charger and let the battery sit long enough, the voltage will get down to a bit over 13.3V which is the usual full-charge resting voltage of virtually all LiFePO4 batteries. You can reduce the time to get from 13.6 down to 13.3 by putting a 100 ma load on for an hour or two.

The site you mention is one of the best I've found. Better than Battery University. It was updated late last year, but there's a lot of info in it that was speculative when it was written and could be made more definite now.

They say this about floating at close to the resting voltage:

"Please understand that any voltage below the 100% SoC point, of the LFP battery, would not be considered “floating” it. If using a standby voltage at say 3.35V per cell, the current into the battery will end up at 0A and be slightly below the 100% SoC point."

Note that 3.35 per cell is 13.4V. In the context of their corresponding discussion, "slightly below" means about 99%.

Ergo they are saying that floating at or above 13.4V is effectively floating at 100% SOC.

It is always interesting to go back and reread through that white paper.

My take on it is a lithium battery can be charged to 100% SOC as low as 3.42vpc (13.68v) as mentioned in the paper a few sections above where you quoted. The difference with 3.35vpc (13.4v) is this voltage will hold a “fully charged” lithium battery at or near 100% SOC, but I don’t think it will charge a discharged lithium battery to 100% at that voltage. The two are not the same.