Advice on Lithium BMS

[Bob Nodine]

My lithium battery bank is at 100 % SOC. I can't remember how that was determined with the Victron Shunt. Maybe I entered 100 Ah x 4 or something like that. The charger is in lithium mode and the voltage according to the Victron Shunt is 13.58 volts. Current flow into the batteries is near zero or slightly negative if some lights are on.

With the above as background consider this:

If I crank up the engine and allow the alternator to connect ( I can manually disconnect the two battery banks if desired) I will see current flow into the lithium house batteries on the order of 30 to 50 amps. I know this is because the alternator is putting out 14.5 volts but was under the impression that the BMS in the batteries would stop the current flow if the batteries were at 100 %.

This does not seem to be the case. My question is does this mean the batteries are not actually at 100 % or is the BMS not doing it's job? I am a little concerned at leaving the alternator connected for a prolong period of time but if the batteries are not actually at 100 % then maybe I should. It would seem that being on shore power for days the batteries should be at 100 % as the shunt says. Maybe I have input some values into the shunt incorrectly.

What do you all think?

 

[DavidEM]

Two things at work here I think:

One the batteries were not actually at 100%, 95% maybe.

Two the shorepower charger shuts off when the batteries see 14.2% but with the chassis alternator putting out 14.5%, the batteries will accept a little more current. You should see the alternator charging current taper off if you leave it running for a while.

David

 

[16ACE27]

13.6 VDC sounds like "float" voltage for a Li bank. Is your charger communicating with your Victron monitor?

I have a Renogy shunt monitor. I set the bank capacity in the settings and reset the SOC at 100% when I knew the bank was at 100% as determined by the BMS in each battery shutting off charging current. I have never reset this SOC since.

I agree that if the bank is truly fully charged then the BMS should not allow large charging current from the alternator. But even if discharged by a few % the BMS will allow a hefty charging current until the first cell reaches 100% voltage, then it shifts into finishing/balancing mode to bring the other cells to full voltage at a much lower current.

The fact that your Li charger allows the batteries to slightly discharge when the DC buss is loaded may be something to research. Is this normal for that charger?

In any case, I'd go through the procedure to reset your battery monitor to 100% SOC when you know for a fact the battery bank is at 100% SOC as determined by the BMS(s). Then see what the alternator current does.

 

[Chateau_Nomad]

Do you have direct Bluetooth connectivity to each battery? Battery SOC should be calculated by the voltage of each individual cell in the battery.

My shunt isn't Victron, but the most accurate method I found for deriving percent of capacity remaining is to COMPLETELY cycle the battery. Fully charge until the BMS cuts off charge (from all sources), then FULLY discharge until the BMS again disconnects.... which technically isn't zero, because most decent BMSs will cut out before that.

The shunt will record how many amps were drained - giving you true and accurate capacity. Once you tell the shunt that amp value, it SHOULD accurately calculate SOC and display as a percentage. Victron equipment sets the benchmark, so I'd definitely trust it.

My SOK batteries took a few cycles of charge/discharge to balance the cells within each battery. When I want to know EXACTLY how full each battery is I reference the cell voltage.

 

[Bob Nodine]

All good advice. I was concerned because research says the lithium batteries will be damaged if over charged. I will do some more testing and see if the BMS (there are actually 4 because there are 4 batteries in parallel) shuts off after additional charging.

I will admit that I have not gone thru the charge/discharge cycle to determine the actual SOC. I will put that on my list of things to do. Have been busy with other stuff like upgrading the solar, installing the extend-a-stay on the propane tank, and installing the Starlink.

The so called 12 gallon propane tank on our motorhome sucks. By design it will only hold 9.2 gallons of propane but in fact no matter where we go or who fills it the tank cuts off at 8.2 gallons. I purchased a new fill valves with the float but could not get the old one out of the tank. Emptied the tank and took it off the motorhome and still could not get the valve out. They used some kind of glue on the threads. I cannot find a propane service center anywhere that will work on the tank. So we decided to install the extend-a-stay so we could hook up an external tank in emergencies. Got stuck in 20 degree weather coming back from Florida two years ago. Propane was low and the vapor pressure was low due to the cold temps. The furnace would not work and the only thing that saved us was a small electric heater. Yes, when I got home I made a vapor pressure gauged and tested that we had 11 bars of vapor pressure from the regulator. Plugged it into the external propane connection for the grill.

All these changes we are making to the motorhome are in preparation for a trip to Newfoundland.

 

[dkoldman]

I know you have Victron Shunt, but not sure what type of DC2DC or LI-BIM?

I am interested in what you learn either way. To be honest, I don't see tangible value of BMS yet. It was great when I first got the Lithium battery to be able to see the display show SOC and voltage. But now after newness is gone, by 300ah Lithium is out of sight and out of mind.

My Orion XS allows for me to synchronize and re-calibrate as much as I like to 100% so I don't have to fool with all of that cycling. I figured my charging is controlled by the Lithium profile I bought with new Orion XS DC2DC and the new Progressive Dynamics converter. Both will only do Bulk / Absorption for some period of time deemed safe and adjust based on voltage. I can watch my Lithium be fully charged, start up the engine and I will see 48 amps or so but within 5 minutes it may be down to 15 amps of current depending on what is or is not running of the house bank.

I post a picture of my settings because there are a lot more settings I can control; and if I want more they have an Expert mode I ain't there yet. I have the manual but I have not got a round tuit.

Here is what I do know, I don't have anything temp related tied to my Victron so either my BMW works for that or it doesn't if it gets too cold. If my Lithium is damaged due to overcharging I will find fault with Progressive Dynamics and / or Victron. Ironically my Battery Mfg states 14.6vdc is preferred charge rate whereas by converter & DC2DC had 14.2vdc? I put the DC2DC at 14.4vdc to split the difference. I left the converter alone, because if I am on SP, I am never in hurry to quick charge. If I got somewhere to go, it will charge faster when I drive.

On a side note, since I have had the Victron Shunt, the lowest SOC I have seen was 71%. My genny's has never auto started for voltage not even close. It would have to down to 14%. I consume about 100ah/day running both fridges (inside fridge on propane)

Thus far I have always replenished in 2 hours or less due to the required running of ACs. This winter I expect, to go 2 full days before the AGS will kick to recharge, the downside is it might take 4 - 5 hours to get back up to 100% SOC?

 

[16ACE27]

I know you have Victron Shunt, but not sure what type of DC2DC or LI-BIM?

I am interested in what you learn either way. To be honest, I don't see tangible value of BMS yet. It was great when I first got the Lithium battery to be able to see the display show SOC and voltage. But now after newness is gone, by 300ah Lithium is out of sight and out of mind.

My Orion XS allows for me to synchronize and re-calibrate as much as I like to 100% so I don't have to fool with all of that cycling. I figured my charging is controlled by the Lithium profile I bought with new Orion XS DC2DC and the new Progressive Dynamics converter. Both will only do Bulk / Absorption for some period of time deemed safe and adjust based on voltage. I can watch my Lithium be fully charged, start up the engine and I will see 48 amps or so but within 5 minutes it may be down to 15 amps of current depending on what is or is not running of the house bank.

I post a picture of my settings because there are a lot more settings I can control; and if I want more they have an Expert mode I ain't there yet. I have the manual but I have not got a round tuit.

Here is what I do know, I don't have anything temp related tied to my Victron so either my BMW works for that or it doesn't if it gets too cold. If my Lithium is damaged due to overcharging I will find fault with Progressive Dynamics and / or Victron. Ironically my Battery Mfg states 14.6vdc is preferred charge rate whereas by converter & DC2DC had 14.2vdc? I put the DC2DC at 14.4vdc to split the difference. I left the converter alone, because if I am on SP, I am never in hurry to quick charge. If I got somewhere to go, it will charge faster when I drive.

On a side note, since I have had the Victron Shunt, the lowest SOC I have seen was 71%. My genny's has never auto started for voltage not even close. It would have to down to 14%. I consume about 100ah/day running both fridges (inside fridge on propane)

Thus far I have always replenished in 2 hours or less due to the required running of ACs. This winter I expect, to go 2 full days before the AGS will kick to recharge, the downside is it might take 4 - 5 hours to get back up to 100% SOC?

BMS is NOT the LCD display.

 

[Chateau_Nomad]

I know you have Victron Shunt, but not sure what type of DC2DC or LI-BIM?

I am interested in what you learn either way. To be honest, I don't see tangible value of BMS yet. It was great when I first got the Lithium battery to be able to see the display show SOC and voltage. But now after newness is gone, by 300ah Lithium is out of sight and out of mind.

My Orion XS allows for me to synchronize and re-calibrate as much as I like to 100% so I don't have to fool with all of that cycling. I figured my charging is controlled by the Lithium profile I bought with new Orion XS DC2DC and the new Progressive Dynamics converter. Both will only do Bulk / Absorption for some period of time deemed safe and adjust based on voltage. I can watch my Lithium be fully charged, start up the engine and I will see 48 amps or so but within 5 minutes it may be down to 15 amps of current depending on what is or is not running of the house bank.

I post a picture of my settings because there are a lot more settings I can control; and if I want more they have an Expert mode I ain't there yet. I have the manual but I have not got a round tuit.

Here is what I do know, I don't have anything temp related tied to my Victron so either my BMW works for that or it doesn't if it gets too cold. If my Lithium is damaged due to overcharging I will find fault with Progressive Dynamics and / or Victron. Ironically my Battery Mfg states 14.6vdc is preferred charge rate whereas by converter & DC2DC had 14.2vdc? I put the DC2DC at 14.4vdc to split the difference. I left the converter alone, because if I am on SP, I am never in hurry to quick charge. If I got somewhere to go, it will charge faster when I drive.

On a side note, since I have had the Victron Shunt, the lowest SOC I have seen was 71%. My genny's has never auto started for voltage not even close. It would have to down to 14%. I consume about 100ah/day running both fridges (inside fridge on propane)

Thus far I have always replenished in 2 hours or less due to the required running of ACs. This winter I expect, to go 2 full days before the AGS will kick to recharge, the downside is it might take 4 - 5 hours to get back up to 100% SOC?

You probably should read up on the importance of a LiFePO4 BMS, and it's functions... most importantly it's role in cell balancing. No third party device can do internal cell balancing. There's four cells in your battery, and not monitoring/controlling voltages of those individual cells can be catastrophic... drastically shortening the battery's life, or worst case killing the battery.

 

[Mark54]

My lithium battery bank is at 100 % SOC. I can't remember how that was determined with the Victron Shunt. Maybe I entered 100 Ah x 4 or something like that. The charger is in lithium mode and the voltage according to the Victron Shunt is 13.58 volts. Current flow into the batteries is near zero or slightly negative if some lights are on.

With the above as background consider this:

If I crank up the engine and allow the alternator to connect ( I can manually disconnect the two battery banks if desired) I will see current flow into the lithium house batteries on the order of 30 to 50 amps. I know this is because the alternator is putting out 14.5 volts but was under the impression that the BMS in the batteries would stop the current flow if the batteries were at 100 %.

This does not seem to be the case. My question is does this mean the batteries are not actually at 100 % or is the BMS not doing it's job? I am a little concerned at leaving the alternator connected for a prolong period of time but if the batteries are not actually at 100 % then maybe I should. It would seem that being on shore power for days the batteries should be at 100 % as the shunt says. Maybe I have input some values into the shunt incorrectly.

What do you all think?

BMS is designed to shut off if too cold or hot, reverse polarity, or anything that might threaten the battery, except humans...

LFP batteries are 100% SOC at 13.6VDC, so best way is to have a multimeter and check voltage on each battery to see what it really is.
Charge rate is 14.6Vdc for discharged or weak batteries, 1VDC higher than wet-cell charge rate. So be sure it is set for LFP and correct battery amperage (as you seem to have already done)

UHG will float charge at anything below that to maintain SOC.
I use my Balmar app and gateway to 'see' what the UHG is actually doing- so if you have that for the Victron, it helps a little.
There should also be a regulator to prevent overcharging. Find it, if present, and read the manual to make sure it is connected and operating properly.
Thor mis-wired my MC-618 by reversing polarity on the battery temp and UHG temp sensors. I checked my app and all seems ok after I 'corrected it'. I did replace the battery sender as they had modified it and was too short after I moved my batteries.
I checked the connections at the UHG and seems ok. Also made sure the belt was not being cut as many have had happen.

Also UHG (Balmar one) can be 170A or 260A output type, depending on battery bank size and wiring.
Boat yards are one of the best places to go to, as you may find a tech there that knows a lot more than any RV place, b/c that's where it all started...

Good luck!!

 

[dkoldman]

BMS is NOT the LCD display.

I assumed it was a display from the BMS board?

Either way, I don't know the fuss of BMS. I know it is a management system, but until this battery all my life I had batteries and none with a BMS. What's so special. Assume the temp sensor is any good, it will stop actual charging when freezing even though real current is being applied

I had a option to connect a temp sensor on my Victron, I passed in favor of allowing my Victron to monitor both Chassis & House banks.

And to think that Will Prowse guy belittled and tossed out so many otherwise good batteries because he did not think the temp sensor was accurate or had a Government Weapons Spec Certified Weld WS-6536E

 

[Bob Nodine]

Guess I was being a little paranoid about overcharging the batteries.

The motorhome is parked in the garage and the outside temps were in the thirties. I did not want to start the engine for a prolonged period in the garage so decided to use the 100 amp Converter/Charger I installed to reduce generator run time while boondocking. I installed this charger with an on/off switch and only planned to use it with the generator.

Got my phone connected to the Victron 500 amp shunt and verified the voltage was 13.6 volts and current flow was very low. Switched on the 100 charger and the current immediately jumped to well over 50 amps and the voltage was 14.6. Soon the current started to slowly drop off and after about 15 minutes was below 2 amps. Left and did some other stuff and came back in about an hour to find that the charger had dropped voltage to 13.6 and the current was zero.

I had upgraded our WFCO power center to the WF-8955-AD-MBA converter/charger with the auto-detect mode. After going back and reading the manual for that charger I now understand what is going on. The WF-8955-AD-MBA will only go into the Bulk mode if the batteries are drawing a significant charge current. When using this charger with Lithium batteries it is a 2 stage charger and does what the manual refers to as Charge Mode and Power Mode. In Charge Mode the voltage is 14.6 and in Power Mode the voltage is 13.6. After 4 hours the charger will drop into Power Mode. If the battery bank is greater than 200 Ah (I have 400 Ah) the power must be cycled to put the charger back into Charge Mode. It seems I had some serendipity by installing the 100 Amp Converter/Charger.

 

[dkoldman]

You probably should read up on the importance of a LiFePO4 BMS, and it's functions... most importantly it's role in cell balancing. No third party device can do internal cell balancing. There's four cells in your battery, and not monitoring/controlling voltages of those individual cells can be catastrophic... drastically shortening the battery's life, or worst case killing the battery.

Assume I read up further on BMS. What will I do differently? I have watched videos ad nauseum. My BMS is what it is and is hard tied with capabilities of Lithium battery I purchased. My role to protect the same was in my investment with new converter and DC2DC charger. My Home is protected by Smith & Wesson, my Lithium battery is protected by Progressive Dynamics and Victron I have no need to worry further.

FWIW, my Lithium Battery Mfg provided me with all of the Technical specifications, for those that applied they have been entered into my settings with Victron & Progressive Dynamics. And if for some reason my Lithium battery is damaged due to charging when temperatures are below freezing; then that means I had a defective battery to begin with because the BMS and/or temp sensor had failed. If that occurs, I will buy another Lithium of a different brand. But from little I know, I suspect that the only issue when freezing is that it cannot recharge, not be damaged by device attempting to charge. I worry more about when my day come to travel to the moon, if my rocket will hit one of those Starlink satellites trying to leave the earth's atmosphere.

 

[dkoldman]

Guess I was being a little paranoid about overcharging the batteries.

The motorhome is parked in the garage and the outside temps were in the thirties. I did not want to start the engine for a prolonged period in the garage so decided to use the 100 amp Converter/Charger I installed to reduce generator run time while boondocking. I installed this charger with an on/off switch and only planned to use it with the generator.

Got my phone connected to the Victron 500 amp shunt and verified the voltage was 13.6 volts and current flow was very low. Switched on the 100 charger and the current immediately jumped to well over 50 amps and the voltage was 14.6. Soon the current started to slowly drop off and after about 15 minutes was below 2 amps. Left and did some other stuff and came back in about an hour to find that the charger had dropped voltage to 13.6 and the current was zero.

I had upgraded our WFCO power center to the WF-8955-AD-MBA converter/charger with the auto-detect mode. After going back and reading the manual for that charger I now understand what is going on. The WF-8955-AD-MBA will only go into the Bulk mode if the batteries are drawing a significant charge current. When using this charger with Lithium batteries it is a 2 stage charger and does what the manual refers to as Charge Mode and Power Mode. In Charge Mode the voltage is 14.6 and in Power Mode the voltage is 13.6. After 4 hours the charger will drop into Power Mode. If the battery bank is greater than 200 Ah (I have 400 Ah) the power must be cycled to put the charger back into Charge Mode. It seems I had some serendipity by installing the 100 Amp Converter/Charger.

 

[16ACE27]

Guess I was being a little paranoid about overcharging the batteries.

Yeah, a properly functioning BMS won't allow you to overcharge.

So to apply your Li capable converter terminology to my non-Li capable converter, I have:

Charge mode - 14.5 VDC - will charge the batteries to close to 100%
Power Mode - 13.6 VDC - will finish charging the batteries to 100%
Storage Mode - 13.1 VDC - allows the batteries to discharge to storage capacity of 60% to 70%

 

[dkoldman]

Yeah, a properly functioning BMS won't allow you to overcharge.

So to apply your Li capable converter terminology to my non-Li capable converter, I have:

Charge mode - 14.5 VDC - will charge the batteries to close to 100%
Power Mode - 13.6 VDC - will finish charging the batteries to 100%
Storage Mode - 13.1 VDC - allows the batteries to discharge to storage capacity of 60% to 70%

Looks like the only real difference is my Li Converter only has two stages. Charge (14.4 -14.6) and Idle(13.6)

I don't see how 13.6vdc could overcharge a Lithium Battery even if it were truly at 100%? Maybe I need to watch some more Will Prowse videos to see how to open up my battery and take the BMS out

 

[Chateau_Nomad]

Looks like the only real difference is my Li Converter only has two stages. Charge (14.4 -14.6) and Idle(13.6)

I don't see how 13.6vdc could overcharge a Lithium Battery even if it were truly at 100%? Maybe I need to watch some more Will Prowse videos to see how to open up my battery and take the BMS out

The BMS won't let it overcharge... but 100% might only be 93% when the BMS drops the voltage to 13.6... but hey... close enough for a bargain!

 

[dkoldman]

The BMS won't let it overcharge... but 100% might only be 93% when the BMS drops the voltage to 13.6... but hey... close enough for a bargain!

That is just it, for Lithium 13.6% can / will take it to 100% if not fully charged per the BMS.

The Victron allows you to say when SOC is 100%. You can synchronize or calibrate as many times as you like. But for me the real number to watch is Consumed AHs. If I see where I have consumed 246AHs, I know I am really low (not out / drained down), and my genny should be running.

So far I consume about 95ahs per day, so I will always have plenty of battery power, I can make 3 days with no SP, No genny and no Solar if I wanted to

 

[Bob Nodine]

Yeah, a properly functioning BMS won't allow you to overcharge.

So to apply your Li capable converter terminology to my non-Li capable converter, I have:

Charge mode - 14.5 VDC - will charge the batteries to close to 100%
Power Mode - 13.6 VDC - will finish charging the batteries to 100%
Storage Mode - 13.1 VDC - allows the batteries to discharge to storage capacity of 60% to 70%

By definition you have a 3-stage charger which is used for flooded/AGM batteries.

Bulk - 14.4 VDC
Absorption - 13.6 VDC
Float - 13.2 VDC

The Float mode is to keep the flooded battery from loosing excessive fluid while connected long term on a charger. Normally if you turn on a few lights, etc. the charger will switch back to Absorption mode.

It seems that Lithium batteries do not need the Float mode and can remain in the Absorption state forever. The manual for the WF-8955-AD-MBA refers to the Absorption state as the Power Mode. Their terminology, not mine. They refer to the Bulk mode as the Charge Mode. They have eliminated the Float mode as it is not required for Lithium batteries. Thus they call it a 2-Stage charger.

Some chargers are 4 stage and have an Equalization mode used to de-sulfate flooded batteries with vents. This mode overcharges the battery to make it boil. Obviously an outdated function and not something you would exptect to see in a modern battery charger.

 

[The Rookie]

I have seen various BMS amp ratings on LFP batteries. What is the difference and should one be looking for a higher rating?

 

[16ACE27]

I have seen various BMS amp ratings on LFP batteries. What is the difference and should one be looking for a higher rating?

The BMS rating is generally matched to the AH rating. Almost all 100 AH LFP batteries have a 100 amp BMS. When you get into the 200 and larger LFP batteries you will begin to see some variance in BMS ratings. All other things equal on two different 300 AH batteries, pick the one with the 300 amp BMS over the ones with a 250 or 280 amp BMS