Constant 14.4V not OK for charging LiFePo4 batts with internal BMS?

[KS_Kampers]

The charger dropping from 13.6V to13.2V is a non-event. The charger doesn't allow a higher voltage battery to discharge into itself, so the only thing that happens is current stops flowing into the battery, the battery holds whatever its resting voltage is until the battery eventually drops to 13.2V, and starts accepting current from the charger.

I found my 9855 to discharge the battery. I ran a bench test over the course of about 3 days. I don't have a data logger, so I would go out and check the voltage at the terminals every few hours or so. For the first ~two days, the voltage ranged from 13.59V to 13.7V. After the first 44 hours was where I was really interested... sure enough, the charger folded back, and when I went into my shop the next morning I found the battery terminal voltage was then 13.2V. I pulled the converter from the battery, let things settle for a few hours, and measured..... 13.2V.

Re-attached converter, powered it back up, and let things charge for 24 hours. Disconnected, and let the battery settle overnight. Existing voltage on terminals is 13.57V.

So in this instance, the WFCO 9800 series charger did remove much of the battery charge when it is allowed to remain powered on after 44 hours.

For those who are aware that they have the non-AD version (9800 family as opposed to 9800-AD) of the WFCO converter, they can work around continuous shore power issues by power cycling their converters such that it doesn't reach that 44 hour timeout. I read elsewhere that some folks use a simple appliance timer to do this.

I'm going to switch to a Progressive Dynamics lithium compatible converter and be done with it. I'll just use that WFCO on my bench for charging portables.

 

[sunshine_eggo]

That's not typical behavior. The only "draw" from the battery should be the voltage measurement.

 

[KS_Kampers]

That's not typical behavior. The only "draw" from the battery should be the voltage measurement.

Specifically for the WFCO98XX converters? What is your confidence level that they don't pull a load on the battery when they downshift to 13.2V? These dang things are very ubiquitous so it would be good for all of us to know for sure. I've got buddies with these in their rigs. I'll see if I can convince one of them to let me do a confirmation test.

 

[time2roll]

Specifically for the WFCO98XX converters? What is your confidence level that they don't pull a load on the battery when they downshift to 13.2V? These dang things are very ubiquitous so it would be good for all of us to know for sure. I've got buddies with these in their rigs. I'll see if I can convince one of them to let me do a confirmation test.

Easy to check with a clamp-on ammeter. Although if the converter drops to 13.2 I would expect the lead battery to rest to that level. Most RVs have other items drawing the battery down so even a lithium will slowly drop to 13.2 volts. To really check if the converter itself is pulling power out of the battery it would have to be isolated from the RV to test. Could be a couple mA but should be very small.

 

[sunshine_eggo]

Specifically for the WFCO98XX converters?

Specifically for any device claimed to charge a battery and to remain permanently connected to one. The WFCO is connected to the battery full time, no? Why would it have any need - besides the micro-amp trickle of current needed to measure voltage - to pull current from the battery?

What is your confidence level that they don't pull a load on the battery when they downshift to 13.2V? These dang things are very ubiquitous so it would be good for all of us to know for sure. I've got buddies with these in their rigs. I'll see if I can convince one of them to let me do a confirmation test.

I'm 1000% certain no battery charger should pull the battery down to 13.2V. ANY loads on the system will pull the battery down to 13.2V, but the charger shouldn't.

I literally have 60+ battery chargers, and not a single one of them draws any more current from the battery than is needed to measure voltage.

 

[KS_Kampers]

I hear you, and I agree that the charger *should* not do that. I'm not disputing specification philosophy

I ended up calling WFCO and described my issue to them. They said that what I saw was not contrary to how that charger was designed to operate.

That charger applied 13.6V to the battery for 44 hours, then switched to 13.2V. After a lengthy delay, the connecting cables measured 13.2V at each end. Unless the battery had only reached the 13.2V (or less) state of charge by the time the charger dropped to 13.2V output, then the charger definitely functioned as a load and pulled charge off of the battery.

I now have a shunt for measuring current, so I am going to re-test the WFCO charger. I'd be really surprised if it is operating differently than what they confirmed, but I've seen stranger things.

 

[SteveOOO]

Great conversation thread....

I started questioning my setup this morning after a long fight with a support tech from a test charger I was using in place of my BougeRV 40A. They insisted on my using their settings for Lithium batteries. (Bulk Charge: 13.6V /Absorption Charge: 14.4V / Float Charge: 0) That made no sense to me being most Lithium batteries can charge and discharge @ 100A with full charge being 14.6 and if one is running evecells as I am 2-560AH/200A JBD BMS batteries in my 5th wheel. Now for 3 yrs I have been running my charger @ (Bulk Charge: 14.4V /Absorption Charge: 13.34V / Float Charge: 0) Bulk kicks in again @ 13.27

I now found this was Battleborn's recommendation as well

Using a PowerMax AC to DC Converter Charger With Battle Born Batteries

The Powermax AC to DC converter charger works well with Battle Born LiFePO4 batteries and the voltage can be manually adjusted!

battlebornbatteries.com

I to agree constant 14.4 is a very bad Idea

​

If this is not health please tell me why?

Make It A Great Day Everyone
SteveOOO

 

[sunshine_eggo]

I have 3X PM-LK converters - PM3-100LK, PM3-55LK, PM4-100LK.

Works as a 3 phase charger or constant voltage power supply.

The bulk voltage is adjustable. When in power supply mode, the same pot adjusts the power supply voltage.

Absorption of 13.6V is enough to get a battery charged to 99%+ SoC given enough time.

Float of 13.2V allows significant discharge before the converter will contribute.

Holding at 14.4V is only warranted if extended balancing periods are required. IIRC, BB normally recommends 14.2V as a hold voltage. Forum members have held their BB at 14.2V for a week or two to correct horrific balance issues due to low voltage operation over three years (never charged into the balancing region). Capacity went from 53Ah to 90Ah+.

The voltage should only be as high as is necessary to provide balancing.

Many brand new batteries arrive out of balance due to the need to ship them at 30% SoC or lower and because it's likely 90+ days since they were last charged, so they will be out of balance, and they may need to be held at elevated voltage for hours or days to restore balance. Your typical passive BMS can only burn off about 1Ah/day.

 

[ericfx1984]

It's very important that you let all of the different safety measures work in concert with each other

Yes your BMS has a maximum pack voltage and a maximum cell voltage, But it's best to not be in a position where those are an issue in the first place

Generally what I do is choose a maximum charging voltage that should not cause any problems...

And then I choose a BMS cut off that is below the pack/cell maximum voltage specifications

So in theory lithium iron phosphate could be charged every single day to 3.65 volts per cell which works out to 14.6 volts on a 4S pack

But there's other things to keep in mind... How accurate is your BMS? Are you accounting for voltage losses and things like that?

I mean the BMS might read 3.65 volts but it might actually be 3.7... Probably not but you get the idea

It's always good to have a buffer in there

And it's always good to keep your charging voltage low enough that you're not overcharging cells if the BMS were to malfunction

In an ideal world cells would be so perfectly matched in connections would be so perfect that a BMS would be unnecessary... But in the real world all these different protection circuits are not enough on their own... I would even argue that even when they're all working perfectly that they require a little bit of human intervention from time to time

It would also be helpful to test the limits with a well trusted voltmeter

 

[ericfx1984]

I should also mention that I have a rather crazy setup compared to a lot of guys

I have a 4P4S 304ah(x4)battery with a 200 amp Jbd bms and a 5 amp active balancer... That's 1216 amp hours... As you can imagine it is helpful to have the active balancer with such a large battery bank... It certainly wouldn't be a problem at 304 amp hours... But at 1216 It's a bit much for the onboard one amp balancer

In addition I have a 2P4S 230 ah(x2) so that's 460 amp hours... It doesn't require a active balancer...

I run into some issues where the smaller battery will reach full charge before the larger battery. Part of this is that I will oftentimes charge at 150 amps or more

If I were charging at a much smaller rate everything would probably stay pretty balanced... What's interesting is as a smaller battery gets closer to a full charge it will start to slow down and the power that was going to that smaller battery will now be going to the larger battery

Even if I don't finish my charge cycle by the time the large battery is done, the small battery will push power over to the large battery which causes them to balance out

So this would be an instance of me relying on the battery management system to shut off charge at a certain point... There's also somewhat of a natural change in charging potential of the battery itself as it gets higher in voltage

Anyway it works but it's certainly not ideal and in order to do this I'm giving up one of the potential safety mechanisms for a period of time... It hasn't been a problem for me, but I know at any given time it could be...

So from time to time I will simply watch the end of the charge cycle just to see that nothing is running away overcharging or any other weird activities... But you see if I didn't have to do it this way I would have a much simpler charge cycle

 

[KS_Kampers]

And BTW, I can't rule out that both of my batteries are acting in a way I consider oddly. I started another thread about BMS operation. I'm thinking that neither of my batteries charge to a SoC which would reflect more than a 13.2V resting voltage. So what happened with that WFCO was that at some point the BMS does a disconnect prior to full charge, then stays disconnected during the 13.6V phase, and internally leaks down to below 13.2V which is why I thought that the WFCO was pulling charge off.

Instead, the battery never had a remotely full charge due to the BMS.

My measurement tools are limited... I only have a Fluke voltmeter, and a Victron smart shunt. I really wish I had a decent load... I may have to rig something up with auto bulbs and see what happens over a long discharge using my Victron app.

I'm working to characterize what I am seeing now, and will post a summary shortly. Thank you to all for the attention. I'm new to LiFePo4 stuff.

 

[sunshine_eggo]

Disconnect the positive from the lead acid, and jumper cable it to your car. Turn your car Key-ON, Engine-OFF. Should pull about 10-20A, and you can turn on headlights, blower, rear defroster, etc., for extra drain.

 

[KS_Kampers]

Many brand new batteries arrive out of balance due to the need to ship them at 30% SoC or lower and because it's likely 90+ days since they were last charged, so they will be out of balance, and they may need to be held at elevated voltage for hours or days to restore balance. Your typical passive BMS can only burn off about 1Ah/day.

^^^^ Hmmmmmmmm. Unfortunately what I am seeing on both of my batteries, is that when I apply 14.38V, I see an initial charging current of 55A, which quickly drops. Once it hits 3A, the change in charging current slows down, but still dropping. Then it hits 1.4A, and immediately goes to zero and stays there while the charger is happily holding 14.38V. That all takes about 60 seconds. One hour later it drops to 13.6V, and still zero amps are taken. After the time that the charge current goes to zero, no measurable current (via Victron smartshunt measurement) is going into or out of the battery regardless of applied charging voltage.

Just to make matters more interesting, both batteries behave somewhat differently. Grrrrr..... (more on that later)

data posted once I get done collecting. Assuming I don't get frustrated and jump out the window.

 

[sunshine_eggo]

^^^^ Hmmmmmmmm. Unfortunately what I am seeing on both of my batteries, is that when I apply 14.38V, I see an initial charging current of 55A, which quickly drops. Once it hits 3A, the change in charging current slows down, but still dropping. Then it hits 1.4A, and immediately goes to zero and stays there while the charger is happily holding 14.38V. That all takes about 60 seconds. One hour later it drops to 13.6V, and still zero amps are taken. After the time that the charge current goes to zero, no measurable current (via Victron smartshunt measurement) is going into or out of the battery regardless of applied charging voltage.

Just to make matters more interesting, both batteries behave somewhat differently. Grrrrr..... (more on that later)

data posted once I get done collecting. Assuming I don't get frustrated and jump out the window.

You're likely over-charging. LFP cells are full at 3.65V and 0.05C (5A for 100Ah battery). At 3A or 1.4A on a 100Ah battery, you're not imparting usable charge.

I would regard those batteries as balanced well-enough.

 

[KS_Kampers]

Thanks... I'm going to switch over to my BMS question thread, as I'm starting to push my own thread drift