PLEASE HELP BMS / CHARGER SOLUTION ?

pig34

New Member
Joined
Jun 5, 2021
Messages
8
I have built a 4 cell 280ah lifepo4 battery, with an overkill solar BMS. Before installing it in my RV I charged and discharged it many times on my workbench, with a progressive dynamics charger and it works great. The problem arises when I charge with the inverter/charger in my RV ( Xantrex freedom xc 2000 ). The charger has a glitch which Xantrex says they would replace if it was under warranty. When the charger is set to charge at 14.4 volts it charges in bulk at full amps (80) until it hits about 14.4 volts then switches to absorb and continues at about 14.4 with the amps slowly dropping until the amps drop off rapidly. All is good until at this point the voltage spikes up to about 14.9 but only for a few seconds then drops back to 14.4 this trips my BMS over-voltage circuit. It does the same thing if set to charge at 14.0 volts. At 13.8 volt it does not trip the BMS but does not charge at full amps just due to the lower voltage.


The charger does the same thing with my old lead acid batteries so it is not the lifpo4. Xantrex thinks it has always done this I just never noticed it with lead-acid batteries. I only discharge and charge the batteries when dry camping about 25 days per year. The rest of the time the charger will be on shore power set to float at about 13.2 volts. Can I raise my BMS cell max limit to 3.8 volts and my battery max to 15.2 volts to accommodate the few-second voltage spike?


Thanks for your help.
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
2,184
Any chance there is an equalize function that can be turned off? Is this a custom setting... maybe use the GEL setting.
I would not increase the BMS above 14.6 and 3.650. I would sooner accept the 13.8 charge.
 

DLTooley

Solar Enthusiast
Joined
Jan 12, 2020
Messages
129
I’m thinking I’m just gonna set at 14 volts to keep things simple. Have you tried 13.9?How long are you in absorb at the different voltages?
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
2,184
I have my BMS set to 14.2 cap and cells to 3.60. Not installed in the RV yet but I plan to set the solar to 14.0 with a short absorption maybe 10 minutes. This should get me close to 95% or a bit more. Plenty for what I need.
 

Diysolar123

Solar Addict
Joined
Feb 28, 2021
Messages
642
The charger has a glitch which Xantrex says they would replace if it was under warranty. When the charger is set to charge at 14.4 volts it charges in bulk at full amps (80) until it hits about 14.4 volts then switches to absorb and continues at about 14.4 with the amps slowly dropping until the amps drop off rapidly. All is good until at this point the voltage spikes up to about 14.9 but only for a few seconds then drops back to 14.4 this trips my BMS over-voltage circuit. It does the same thing if set to charge at 14.0 volts. At 13.8 volt it does not trip the BMS but does not charge at full amps just due to the lower voltage.
well, chargers do not have "glitches"...if it is suddenly spiking above its advertised charging profile...
They can call that a "glitch", or a "feature", I think the right term is "defective".

as time2roll said try and make sure there is no equalize setting that you have enabled so you have the right charge profile for the battery chemistry.
Good thing you had a BMS doing the right thing and saving your batteries from what may be a defective charger. I would not recommend risking your batteries on a suspect charger until you are sure its not "glitching"...
 

pig34

New Member
Joined
Jun 5, 2021
Messages
8
There is no equalization function. I have used gel and lead-acid, as well as custom settings they all do the same thing. Xantrex says it its a glitch in the voltage ramp down so before ramping down it spikes for a second. I could set to a lower voltage but when camping i would like to charge as fast a possible. the lower voltages only charge at about 50 amp rather than 80. I have read numerous articals that say max voltage for lifepo4 prismatic cells is 4.2. I know this would not be good for prolonged use. But would 3.8 volts for a few seconds hurt? I really don't want to spend $1000 on a new charger inverter. Any other ideas ?
thanks for your help
 

Diysolar123

Solar Addict
Joined
Feb 28, 2021
Messages
642
well, I would have to say kudos to xantrex for admitting it; thaat is actually a good thing.
Now calling it a "glitch" when a charger suddenly pulses your batteries with an out of range voltage spike...yea.. I think I am going to stick with "its defective" on that one hehe
If they are willing to swap it, I would really try that path. if not, well, its still good for lead acid!

if you actually spent $1000USD on that, well, I am hurting for ya buddy!!
Even on amazon now its close to $700 so its no cheap clone; for the price you paid I would really try and work with the manufacturer for them to "fix the glitch" as a way to show their support for the product and demostrate their good will to DIY community (did that sound socialy weasely enough).
You really did pay a premium price and should get premium service.
 

pig34

New Member
Joined
Jun 5, 2021
Messages
8
Yes, Diysolar123 you are correct it is a defect. Xantrex had me power off for 24 hours to try and reset the software to no avail. it is the xc
inverter/charge so it is closer to $1000 but I overpay for everything. But my question remains, what harm would be done to hit 3.8 volts for a few seconds 25 times a year.
 

Diysolar123

Solar Addict
Joined
Feb 28, 2021
Messages
642
Yes, Diysolar123 you are correct it is a defect. Xantrex had me power off for 24 hours to try and reset the software to no avail. it is the xc
inverter/charge so it is closer to $1000 but I overpay for everything. But my question remains, what harm would be done to hit 3.8 volts for a few seconds 25 times a year.
well, have you actually gotten a scope on the glitch so you know its real limit (it could be some really high flyback voltage spike because somebody forgot diode somewhere...)
This is always the tricky part with "glitches", is the glitch the limit of what is wrong or is something else going to happen.

I hunted around (a few duckduckgo searches hehe) to try and find some studies on shorted lifepsan from short term voltage spikes past 3.65 and did not see anything. There are studies that show reduced lifespan if you keep going for that last few percent of capacity but nothing about "spikes". Also lifepo4 can survive higher voltage "oopsies" better than other lipo batteries.

Sadly I have have not found a clear answer on transient high voltage spikes.
here is a video of somebody putting 12V into a single lifepo4 cell which is just a tinnnyyyyy bit over the cell limit hehe
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
2,184
I still recommend keeping the battery voltage cut off at maybe 14.4 and charge at 14.2 volts. To make the best of the situation set the recovery voltage close at say 14.395 and just a few seconds for release so that once the inverter gets back to proper regulation the battery will be quickly back on and charging again. Same with the cell cut off, go to the top 3.650 and release at maybe 3.625 with 15 second delay. Give this a try and adjust a bit if needed. Post what you find works or fails. Either way the battery is protected.
 

pig34

New Member
Joined
Jun 5, 2021
Messages
8
Thank you guys for your help. I am trying not to trip the BMS. If I set the charge voltage to 14.2 it will spike at the end of the charge cycle to about 14.7 volts for a few seconds. If I set my BMS battery overvoltage protection to 14.8 volts and cell protection to 3.7volts this would eliminate the BMS tripping. from what I can determine these few seconds of 14.7 volts would not harm the battery. I am trying to verify this. Diysolar123 has a good point of is this glitch ( defect ) a consistent occurrence? from what I have observed it is consistent. But if not my BMS should protect my battery.
 

pig34

New Member
Joined
Jun 5, 2021
Messages
8
Also, I am not concerned with longevity. at 25 cycles per year even at only 1000 cycles that is 40 years. I plan to be dead long before that.
 

pig34

New Member
Joined
Jun 5, 2021
Messages
8
yes, I may have to do that. The only problem is when camping I charge the batteries from a generator. at 13.8 volts it takes much longer to charge than at 14.4 volts. about 50 amps vs 80 amps. I am trying to find out what the harm of 3.7 volts per cell for a few seconds would do.
 

JeepDaddy

Solar Addict
Joined
Feb 1, 2021
Messages
240
Location
Kent, WA
at 13.8 volts it takes much longer to charge than at 14.4 volts
It really shouldn't make that much difference unless you have a voltage drop between your charger and battery. What size and length are the charger to battery cables?

I do appreciate the effort to keep running a generator to a minimum.
 

pig34

New Member
Joined
Jun 5, 2021
Messages
8
From charger to the battery-- 3 feet #1 to 3 feet #2 total 6 feet. I will check again the amp difference between 13.8 and 14.4. tomorrow, as right now at Xantrex request I am powered down for 48 hours to see if the software will reflash correctly.
 

DLTooley

Solar Enthusiast
Joined
Jan 12, 2020
Messages
129
yes, I may have to do that. The only problem is when camping I charge the batteries from a generator. at 13.8 volts it takes much longer to charge than at 14.4 volts. about 50 amps vs 80 amps. I am trying to find out what the harm of 3.7 volts per cell for a few seconds would do.
A small solar system in conjunction with a generator isn’t a bad combo. Give the generator the bulk charge at high rate, then let the solar finish it off.
Also, a good way to start on the solar learning curve.
 
Top