Battery Charging LiFePO4

[dcairns]

I have on older power converter (Progressive Dynamics PD9260C with Charge Wizard) that predates LiFePO4 batteries. I have two Dumfume 300Ah batteries installed several months ago. I also have a Honda generator and two 100 Watt solar panels with charge controller set to lithium. Ideally I should get a new converter (like a PD9360), but the specs on the PD9260C say :

BOOST MODE: If the voltage drops below a preset level the
output voltage is increased to approximately 14.4 VDC (28.8
VDC for 24 volt models) to rapidly recharge the battery. (Boost mode can be activated manually but reverts to Normal Mode after several hours

NORMAL MODE: Output voltage set at approximately 13.6
VDC (27.2 VDC for 24 volt models).

STORAGE MODE: If there is no significant battery usage
for 30 hours the output voltage reduces to 13.2 VDC for minimal water usage (lead acid battery). In storage
mode, the output voltage increases to 14.4 VDC for approximately 15 minutes every 21 hours
to help prevent sulfation of the battery plates.

This seems pretty close to that the LiFePO4 battery needs, other than not quite matching the 14.6 volts it can use for full charge and the "de-sulfation" jumps to 14.4 for 15 min a day. I do leave the trailer on shore power, batteries connected, in the driveway when not in use. Boost mode is activated manually but reverts to Normal Mode after several hours, so I have to hit the Boost Mode several times to give the batteries a chance to fully charge. Yes I realize the batteries have their own charge controllers, but don't charge above the input voltage, so applying the 14.4 for a while gets it close. I think I could live without the .2 volts difference I would gain by replacing the converter. But I was wondering if an simple 14.6 V charger would do the trick as well for $30ish dollars. I could plug it into shore power and the 12V side to the 12V buss on the power panel, before a trip and let it supply the extra voltage for a day or two. Charging two 300Ah with a 20A charger will, of course take longer, but that is ok as I can run it for days ahead of a trip, if needed.

 

[SargeW]

The biggest issue I see is that the charging source for the battery bank has to be strong enough to raise BOTH batteries to 100% charge and keep them there long enough to trigger the BMS in the batteries to balance the cells in both batteries. Without balancing the cells, the voltages can start to drift causing all kinds of strange behavior and affect the longevity of the cells themselves. The BMS in the batteries are not charge controllers, but rather "battery management systems" that control under charging, over charging, and balancing. They just monitor what ever power flows into the BMS, high or low.

There are many converter/chargers out there that are reasonably priced, and will handle all of the charging duties for you and easily maintain the new lithium batteries.

 

[John From Detroit]

I disagree with Sarge. If you are runnng two (or more) batteries in parallel they are balanced. IN fact so long as both are working properly, they MUST be balanced other than during initial install. Here is why.
Even though LiFePO4 batteries have a fairly "Flat" discharge chart (Mantan voltage with only a slight change from FUll to near empty) there is a slight change.

And as they discharge if one battery is even .01 volt higher than the other. The higher battery provides nearly all the current.

Likewise when charging if one battery is even 1% lower than the other. It sucks nearly all the charge current.. THus they self balance

NOW.. Within each batterries "Box" (The case) are cells as well.. THOSE are in series and balance may be an issue but the BMS should deal with that. if needed. To truly equalize those cells you put them in parallel and charge... This is a factory operation and you can't do it.

OVERChargng as you do with Lead Acid to equalize is not recommeded and may cause them to... Flame On.

In fact I charge mine here indoors to 80%

 

[Isaac-1]

Let me respond to this from practical hands on method, I have been running a PD9260 connected to a pair of 210AH LiFePo4 bluetooth enabled batteries (420AH total) for over 4 years, with Bluetooth I can monitor individual cell balance, etc. I also have solar on the roof, and store my coach with power in a enclosed shed. Overall it just works, though will go slightly out of balance after several months of storage floating on the PD9260, but this is quickly corrected by a few days of travel cycling the battery, and charging with solar / engine power through a DC-DC charger. I have thought about doing what the OP proposes, but just don't see the real world need.

Even with the PD9260 in 13.2V Storage mode after several hours it will get the LiFePo4 battery up to about 75-80% SOC, so in my case I don't need to bump it back into 14.4VDC boost mode to top off my 420AH battery bank more than once. (Charge wizard button will put it back into boost mode for 4 hours, so about an extra 240AH worth of charging).

My typical routine is to let the PD9260 do its own thing, sit in storage mode when the coach is in storage then put the PD9260 into boost mode a day or to before I leave on a trip to fully top off the batteries.

 

[dcairns]

Isaac- Thank you for that info. Essentially what I have been doing, except I was getting a bit over enthusiastic about the pre-trip Boost Mode. I still am gaining experience with the $8 volt meter that I have installed and the "state of charge" charts for LiFePO4 batteries. So I was low on trust for the volt meter and it's idea of percentages. I really should toss it and get one with a shunt for a better idea of what my battery percentage really is.

I was rummaging around on the Progressive Dynamics website and found some info on the PD9360. In Lithium mode, the Charge Profile it offers to the battery

Boost Mode of 14.4 V 8 hours or current draw less than 3 amps for more than an hour
Storage Mode 13.6
Refresh Mode 14.4 After 21 days in Storage mode, 1hour of Refresh mode

Page 7 in the PDF shows the chart of the above.
https://www.progressivedyn.com/wp-content/uploads/Support/manuals/PD9300/PD9300-Manual-English.pdf


The 21 day storage mode of the PD9360 does sound better for the battery than the PD9260C Lead Acid Charge Profile. On the other hand, the Boost Mode voltage is the same between them. I suppose long term I should be upgrading the Converter, but probably not much harm done using the old PD9260C.

 

[DonTom]

I disagree with Sarge. If you are runnng two (or more) batteries in parallel they are balanced.

That doesn't balance the cells inside each battery--which was what Sarge was referring to.

I can check the "cell balance" of my single battery EV motorcycle with a Smartphone. It should be within a few MVs.

What "cell balancing" does is to make sure no cell has more voltage than the weakest cell. This helps the battery last a lot longer. Cell balancing is normally only done at 100% SOC--when at full charge. It delays the charge time to get the full charge completed. But there are other methods of cell balancing. Tesla uses a different method which can balance the batteries at any SOC. since they recommend not charging above 80% too often. But their method adds to battery drain when not being used--so they also recommend keeping the car plugged in when not in in use for a long time, such as mine right now. I do NOT keep my Chevy Bolt plugged in and it does not lose anything after a couple of months sitting, unlike the Tesla, which would, if it were not plugged in. Every few nights, it will charge for perhaps 3 minutes or so at 80% SOC.

-Don- Douglas, AZ

 

[dcairns]

Dumfume claims that my batteries have:

200A Built-in BMS – Multiple protections with auto cell balancing above 14.1V.
Dumfume® 12V 300Ah LiFePO4 Deep Cycle Battery for RV & Solar

So either power converter meets the 14.1V requirement to allow cells to be balanced.
I see that Dumfume also sells a small stand alone AC charger (10Amp) that puts out 14.6V.

Dumfume 14.6V 10A LiFePO4 Battery Charger | Fast & Safe Charging

Which would imply that 14.4V to 14.6V is sufficient for the BMS to reach full charge. Perhaps I am worried about nothing other than the better long term charging behavior of the PD9360 which is made for Lithum as opposed to my old converter made for Lead Acid.

 

[Isaac-1]

Actually the lowest voltage that is above the BMS balance voltage transition is the best voltage for top balancing as it maximizes the time spent balancing which is the typical limiting factor for the BMS's used in these sorts of LiFePo4 batteries. In other words floating at 14.2VDC would be better than at 14.6VDC for top balancing a battery whose BMS is programmed to start balancing at 14.1VDC. The catch here is not all brands of batteries have their BMS set to start balancing at the same voltage, therefore from a charger manufacturer point of view, you get better compatibility with more brands of batteries if you float at 14.4VDC or 14.6VDC even if it is not best for the individual brand of battery.

 

[Lou Schneider]

The only difference between a "lithium" converter and a non-lithium converter is the lithium version puts out a constant 14.6 volts while a lead acid converter puts out anywhere from 13.5 to 14.1 volts depending on which charging mode is active.


Many years ago I added external voltage control to my PD9160 converter by just varying the DC voltage on one pin of the 3 wire Charge Wizard socket.

When I got three surplus Iota converters to charge my 36 volt golf cart I did the same thing using an internal trim pot until I got the 14,6 volts I wanted. Then I placed all 3 converters in series and it worked fine.

I don't know, but strongly suspect the same voltage control may be true for any PD 91xx converter without needing to invest in a charge wizard or make any other modifications.

 

[dcairns]

Lou- The thing that has me moving towards upgrading the power converter is the storage cycling that is geared for LiFePO4 to help extend life of the batteries. The batteries are a $600 investment, I may as well treat them right.

Thank you all for your input. It has clarified that the best route forward is to "bite the $300 bullet" and get the PD93060 Power Converter that is intended for LiFePO4 batteries.

 

[Isaac-1]

dcairns, let me ask, in what way do you see the charge profile of the PD93060 to be "geared to help extend the life" of a LiFePo4 battery compared to the charge profile of the PD9260? Personally I like the lower 13.2VDC "storage" voltage of the 9260 when, well storing my coach during the off season, as lower SOC tends to increase the service life of LiFePo4 batteries. Though of course this comes at the price of potential top balancing drift.

 

[dcairns]

The PD9360 for LiFePO4 has a 21 day cycle in storage mode. The PD9260C had a daily cycle in storage mode. That is the main reason.

 

[Isaac-1]

Ok, but what do you consider the advantage of a 21 day cycle storage mode to be with the way you use your RV?

 

[Lou Schneider]

Lithium batteries aren't harmed by being stored at less than full charge, in fact some studies say it's beneficial because maintaining a full charge makes the positive anode more brittle over time.

You do need to raise the charging voltage over 14.1 volts every once in a while so the BMS can balance the cells, though. This is handled by the equalizing cycle in a lead acid multistage charger.

 

[dcairns]

Isaac- Given the info here and my trust for Progressive Dynamics knowing what they are doing, the PD9360 for LiFePO4 seems ideally suited. Left to itself, the converter will spend 21 days at 13.6v, letting the batteries self discharge some, not sure if that amount of time gets it down to 13.6v. Then the Refresh of 14.4v every 21 days bumps things up again.

Boost Mode of 14.4 V Manually activated. 8 hours or current draw less than 3 amps for more than an hour
Storage Mode 13.6
Refresh Mode 14.4 After 21 days in Storage mode, 1hour of Refresh mode

We usually use the trailer one to two times a year, but that may be changing now that the wife has retired and frees up our schedule. The rest of the time the trailer sits in the driveway plugged into shore power. Letting the Converter do it's thing to keep the batteries healthy is ideal.

I have already ordered the PD9360 from etrailer.
In the mean time I have installed a battery disconnect switch and Renogy battery monitor (with shunt). I already like it after a short test of 3 hrs to see how much power all the lights use (unplugged from shore power of course). It is 3.7Ah per Hour if your are curious. It is nice having an idea how much I am using at the moment and an accurate reading of percentage used.

 

[Isaac-1]

I guess I have a lot less trust for PD designing a LiFePo4 charger, given the way they completely screwed up their first generation Lithium Converter which basically acted at a 14.4VDC constant power supply.

Having said that I don't have a problem with the PD9360, it seems to be a good LiFePo4 charger, particularly for those that want their RV to be ready to go at a moments notice. If I were buying a new converter anyway, I might get one, I just don't see it as a significant upgrade over the PD9260 in any real way. In certain circumstances it may actually shorten the service life of the batteries, in others it probably helps a little with proper balancing, it just depends on how you use the RV.

 

[klook]

From what I have been reading, the proper way to store your battery is to discharge it to between 30/50% and unplug it and leave it alone.

 

[Isaac-1]

Unplugging it and leaving it alone works if you don't have parasitic loads, but floating works better if you do. In our case we run refrigerator, etc. year round as the RV doubles as our hurricane bug out vehicle. This is part of why I like the 13.2VDC storage mode on the PD9260 as that equates to around 70%SOC

 

[klook]

I under stand, many also say that not charging to a full charge is better as well. I don't charge my phone battery past 8o% with an app.