B52 LiFePO4 pack

Ok, not posted for a while..and yes, tell me I am beign a lazy b***ard.. cause I am .
Read the explanation and then a question at the bottom

Just had a Stealth B52 brought down to me...not charging. is battery shagged ?..etc.

not been charged for a while, Same old story etc.

So I pull the pack and strip..start checking cell voltages....yes all way too low..0.99 1.4 etc etc.

But for the hell of it, bypass the BMS and bulk charge with my trusty twin meanwell charger....all my packs have pretty much all been 20s Lipo.

So I charge it up to a point where the BMS charge line starts working...ahh great I think, so BMS is good...it is doing its job.

So I let it tick away and turn my attention to the charger that the present owner brought down with the bike...not an original Stealth Charger, some after market one.. Old one apparently had died

OK..so the OEM stealth pack appears to be 24S2P lipo 18Ah...that is what the label says..
Edit Sorry AmberWorlf..typo should have read LiFePO4

The charger they brought down is labelled at 87.6 volts ???hmmm

A brief Google says LiFePO4 charge voltage is 4.2 volts...hmmmm..odd i thought LiFEPO4 was lower than hobby type LiPo cells?

any way...24 series at 4.2 is 100 volts or so ..yet the charger I have here ..that actually only puts out 7 volts...yes it is shagged..is labelled at 87 .something volts.


So, some one tell me..I need to order a new charger...for 24 S LiFePO4 OEM Stealth pack.

What voltage do i need?

NeilP said:

So I pull the pack and strip..start checking cell voltages....yes all way too low..0.99 1.4 etc etc.

Click to expand...

Well, those cells are toast. I wouldn't recharge them, but since you've already done that, I wouldn't allow them near a building or anything else, especially if they actually are RC LiPo types. But even if they are the original Headway LiFePO4 cells...they're still overdischarged, and damaged.



Before we can recommend a charger, we would need to know what the pack you're going to replace this pack with is going to be. (because you don't want to keep using this one, if it was LiPo and that low, especially if it sat for a while it is a potential fire hazard. even if not, and is lifepo4, it is damaged and likely won't perform like it needs to).

A brief Google says liFePO4 charge voltage is 4.2 volts...hmmmm..odd i thought LiFEPO4 was lower than hobby type LiPo cells?

Click to expand...

Where does the LiFePo4 come in? You mention it for the charge voltage here and in the title, but not for the charger or for the battery, except for the last bit where you say it's the OEM pack...but which you said was a LiPo pack previously?

I'm trying to clarify, because the available info in your post is confusing, so far.

If you want to know what charger to use with the damaged pack, you would first need to be *sure* what that pack *actually* is. Is it really LiFePO4? Is it LiPo? Or something else? And for sure, how many series? You should verify on the cells or pack what they actually are--if they are the large cylindrical Headway cells, then they're LiFePO4.

Otherwise you risk overcharging it, compounding the problem of the already-damaged overdischarged cells, increasing the fire risk. (or just never charging it to even half-full, etc).

I tried to find the info on the stealth site, but they don't appear to have that info anywhere there (or really much of any technical detail about the bikes at all).

There are a handful of posts here on ES in a quick search that show that some early B52s did actually have a LiFePO4 pack, but I don't know if the one you have there is one of them.
https://endless-sphere.com/forums/search.php?keywords=stealth+b52+LiFePO4&terms=all&author=&sc=1&sf=all&sr=posts&sk=t&sd=d&st=0&ch=300&t=0&submit=Search


The supplied charger, 87.6v, would be just right for 24s LiFePO4, for 3.65v/cell full charge.

It's not quite high enough for typical 21s (should be 88.2v for 4.2v/cell full charge) and a little high for typical 20s (84v for 4.2v/cell full charge), in LiPo / etc,

yet the charger I have here ..that actually only puts out 7 volts...yes it is shagged

Click to expand...

I'll assume you've already tested it with a pack that's below the voltage it is supposed to put out, but not below the LVC for the pack, but in case you don't know this: Some chargers don't output anything (other than a low "leakage voltage") until they are connected to a battery pack that is between their minimum start-charge voltage (usually about the pack LVC) and their full charge voltage.

If not connected to anything, you wouldn't see much, if any, voltage output.




Without further data, my guess is the charger is fine, and the pack woudln't charge because the BMS shut off the input to prevent a potential fire, so the thing that needs to be replaced is all the cells, not the charger. If the charger is also dead, then you just need a whole new battery pack and charger as a set so you know they work together.

NeilP said:

Ok, not posted for a while..and yes, tell me I am beign a lazy b***ard.. cause I am .
Read the explanation and then a question at the bottom

Just had a Stealth B52 brought down to me...not charging. is battery shagged ?..etc.

not been charged for a while, Same old story etc.

So I pull the pack and strip..start checking cell voltages....yes all way too low..0.99 1.4 etc etc.

But for the hell of it, bypass the BMS and bulk charge with my trusty twin meanwell charger....all my beks ahve pretty much all been 20s Lipo.

So i charge it up to a point where the BMS charge line starts working...ahh great I think, so BMS is good...it is doing its job.

So i let it tick away and turn my attention ot the charge that the present owner brought down with the bike...not an original Stealth Charger, some after market one.. Old one apparently had died

OK..so the OEM stealth pack appears to be 24S2P lipo 18Ah...that is what the label says..

The charger they brought down is labelled at 87.6 volts ???hmmm

A brief Google says liFePO4 charge voltage is 4.2 volts...hmmmm..odd i thought LiFEPO4 was lower than hobby type LiPo cells?

any way...24 series at 4.2 is 100 volts or so ..yet the charger I have here ..that actually only puts out 7 volts...yes it is shagged..is labelled at 87 . somethignh volts.


So, some one tell me..I need to order a new charger...for 24 S LiFePO4 OEM Stealth pack.

What voltage do i need?

Click to expand...

amberwolf said:

NeilP said:

So I pull the pack and strip..start checking cell voltages....yes all way too low..0.99 1.4 etc etc.

Click to expand...

Well, those cells are toast. I wouldn't recharge them, but since you've already done that, I wouldn't allow them near a building or anything else, especially if they actually are RC LiPo types. But even if they are the original Headway LiFePO4 cells...they're still overdischarged, and damaged.

Click to expand...

Low recovery current at about 0.2 amps for couple of hours.. Yes I know they are toast, no puffed pouches. Current situation with COVID etc..living on the island of Jersey, could be 3-4 months before we could get a new pack.. You know me AmberWolf, I have been here long enough to know about the danger of lithium.

amberwolf said:

Before we can recommend a charger, we would need to know what the pack you're going to replace this pack with is going to be. (because you don't want to keep using this one, if it was LiPo and that low, especially if it sat for a while it is a potential fire hazard. even if not, and is lifepo4, it is damaged and likely won't perform like it needs to).

Click to expand...

Sorry my bad, I should not have given an explanation...I should have just asked a straight question...but then if I had done that..I'd have got questioned asking what it was about. The same old story with asking a good question on a forum. Don't give all the info and people ask you more questions, but give too much and the question is hidden and things get side tracked!

I don't need a charger to be recommended.

All I need to know is the terminal max charge voltage per cell, recommended for Stealth LiFePO4 Pouch Cells as built in the OEM pack

amberwolf said:

A brief Google says LiFePO4 charge voltage is 4.2 volts...hmmmm..odd i thought LiFePO4 was lower than hobby type LiPo cells?

Click to expand...

Where does the LiFePo4 come in? You mention it for the charge voltage here and in the title, but not for the charger or for the battery, except for the last bit where you say it's the OEM pack...but which you said was a LiPo pack previously?

Click to expand...

Sorry my bad again ..typing on the workshop computer at about 2000 hours I think, after having been at the farm since 0630, typing on the workshop computer, standing at the computer in the dark.....

It is the OEM LiFePO4 pouch cell pack 24s 2p 18Ah. But not the original charger

amberwolf said:

I'm trying to clarify, because the available info in your post is confusing, so far.

Click to expand...

Yea, sorry ...

amberwolf said:

If you want to know what charger to use with the damaged pack, you would first need to be *sure* what that pack *actually* is. Is it really LiFePO4? Is it LiPo? Or something else? And for sure, how many series? You should verify on the cells or pack what they actually are--if they are the large cylindrical Headway cells, then they're LiFePO4.

Click to expand...

This is where I was confused too...Most definitely NOT headway cells..I know Headway cylindrical cells , have used them many many times on customer build bikes. Most definitely pouch cells, Most deficiently labelled LiFePO4 and most deficiently 24 series...counted the balance wires 25 of them...and counted the pouches. I can't remember seeing LiFePO4 Pouch cells before, but I do not doubt they exist.

amberwolf said:

I tried to find the info on the stealth site, but they don't appear to have that info anywhere there (or really much of any technical detail about the bikes at all).

Click to expand...

Yes, i searched briefly too the Stealth site..and e-mailed them..but no reply yet, then I thought, shot in the dark (like my typing! ) I'd try a post here.

amberwolf said:

There are a handful of posts here on ES in a quick search that show that some early B52s did actually have a LiFePO4 pack, but I don't know if the one you have there is one of them.
https://endless-sphere.com/forums/search.php?keywords=stealth+b52+LiFePO4&terms=all&author=&sc=1&sf=all&sr=posts&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

Click to expand...

Yes, early, Chassis Number 094

amberwolf said:

The supplied charger, 87.6v, would be just right for 24s LiFePO4, for 3.65v/cell full charge.

It's not quite high enough for typical 21s (should be 88.2v for 4.2v/cell full charge) and a little high for typical 20s (84v for 4.2v/cell full charge), in LiPo / etc,

Click to expand...

Yes I thought much lower than 4.2v ..hence my question...This is my bad once again..the danger of posting when tired...I did a LiFePO4 Charge voltage google search and came up with this ..screen grab...4.2 volts... That is what prompted my post I was confused that there was info saying LiFePO4 charge voltage was 4.2..not lower. I should have followed the link and read the small print! Doh!

https://www.evworks.com.au/page/technical-information/lifepo4-care-guide-looking-after-your-lithium-batt/

amberwolf said:

yet the charger I have here ..that actually only puts out 7 volts...yes it is shagged

Click to expand...

I'll assume you've already tested it with a pack that's below the voltage it is supposed to put out, but not below the LVC for the pack, but in case you don't know this: Some chargers don't output anything (other than a low "leakage voltage") until they are connected to a battery pack that is between their minimum start-charge voltage (usually about the pack LVC) and their full charge voltage.

If not connected to anything, you wouldn't see much, if any, voltage output.

Click to expand...

yes did all the usual, opened it up to check for obvious burnt parts, etc, rigged up a series string of Nano Tech Lipo, to give about 68 volts... No relay click in, no fans, no voltage rise...the charger is shagged..

amberwolf said:

Without further data, my guess is the charger is fine, and the pack woudln't charge because the BMS shut off the input to prevent a potential fire, so the thing that needs to be replaced is all the cells, not the charger. If the charger is also dead, then you just need a whole new battery pack and charger as a set so you know they work together.

Click to expand...

That was my thought at first, that the BMS was preventing charge.
So I stripped the end off the pack accessed the BMS, and set about measuring cell voltages.
many low but none zero...told owner it was toast..but we could try slow current recovery for a bit.

While that was happening , dug out a selection of my other LiPo bulk chargers all set at from 84 up to about 135 volts.

After a while I gave the pack an attempted charge with a spare charger of mine, via the BMS charge port and it started charging fine once the cell voltages had been brought up.

Tried the charger the owner had...no go.
Charger stuffed
BMS good
Cells suspect. but the best we have for now. COVID etc could be months before we got a new pack delivered












You can just see the pouch cells here.

So , yea, thanks AmberW

to Sum up..by bad..posting when tired. and being lazy..I already admitted that

Yes LiFePO4 pouch cells, 24 series and 3.65 volt per cell gives the 87.6 as on the charger.

So all good.


As long as the pack does not pop.

He know he has to buy new pack and charger...

LFP maximum has been reduced over the years.

3.33 - 3.35Vpc at rest is Full

There are hundreds of charge profiles that will get you there.

Going over 3.45 - 3.50Vpc termination voltage is not conducive to long lifespan.

The vendor data sheet maximum is a **maximum**, stressful, to be avoided, not to be considered a charge spec.

Holding that top Absorb voltage until amps trail to say 0.05C - CV stage - gives precision if needed for benchmarking.

Charging to and stop, or CC-only profile

you could go a bit higher, say 3.6Vpc

but the resulting SoC% (capacity utilisation)

will vary be CC stage (Bulk) current rate.

Low & slow under 0.4C is healthier and gets you higher.

In fact you can **overcharge** in CV stage, even at 3.4Vpc, if your charge rate is under that above endAmps spec of 0.05C

Note that once over 3.35Vpc at rest, you are not really storing usefully any added current input, just harmfully heating the chemicals, "stirring the pot".

AKA "surface charge", just remove 0.001% of the mAh and resting voltage drops down to the usual 3.33-3.35V.

Also, even more important for longevity, besides going too high

is how long you sit at high SoC.

Best to reduce to storage voltage, 40-60% SoC until discharging is required, and charge up just before needed.

Ok thanks
Will see what the owner decides to do
I will e-mail him the link to this thread so he can read up on it all and decide.

He may just ask Stealth to send new battery and charger or we may build new pack ourselves....Angus.... over to you and Oz to decide... new pack needed .... what you want to do is your choice

NeilP said:

You know me AmberWolf, I have been here long enough to know about the danger of lithium.

Click to expand...

I do, but I also "speak" for all those reading that *don't* know the potential dangers.

(don't want completely inexperienced people looking to fix their zero-volt pack to just connect up the charger to the cells and walk away, cuz they read that "someone else did it just fine"....and come back to a pile of charcoal and rubble. Even if it's a low-probability result, it is a very bad outcome when it does happen.)

I don't need a charger to be recommended.

All I need to know is the terminal max charge voltage per cell, recommended for Stealth LiFePO4 Pouch Cells as built in the OEM pack

Click to expand...

Ok.

Then 3.65v would be the most common LiFePO4 voltage for that, and is almost certainly what the BMS is set to balance to. All the cells I've dealt with personally, and those I've helped others with, used that. That's what I would use for them, without specific information to the contrary, because the BMS is not going to balance them otherwise, if it's setup for that (which is almost certain, given the age of the bike and pack).

But if it is important to know exactly what it is, we'd have to know which actual cell they used, and see if anyone has a spec sheet for it somewhere on the web...but I couldn't find anything other than Headway cylindrical cells in the little stuff here on ES about Stealth LiFePO4 OEM packs (no pouch cells). So I don't know which cell or BMS they used.

If it's not important, than that 87.6v charger that was with the bike would be the right voltage to get 3.65v per cell @ 24s, so that's what I would use.

This is where I was confused too...Most definitely NOT headway cells..I know Headway cylindrical cells , have used them many many times on customer build bikes. Most definitely pouch cells, Most deficiently labelled LiFePO4 and most deficiently 24 series...counted the balance wires 25 of them...and counted the pouches. I can't remember seeing LiFePO4 Pouch cells before, but I do not doubt they exist.

Click to expand...

They definitely exist. If nothing else, Ping packs have always been made of pouch LiFePO4 cells, AFAIK. A123 20Ah LiFePO4 are pouch cells, too. Others I can't recall ATM. Hobbyking has sold a few kinds of LiFePO4 bricks, made of pouch cells, over the years.

Yes I thought much lower than 4.2v ..hence my question...This is my bad once again..the danger of posting when tired...I did a LiFePO4 Charge voltage google search and came up with this ..screen grab...4.2 volts... That is what prompted my post I was confused that there was info saying LiFePO4 charge voltage was 4.2..not lower. I should have followed the link and read the small print! Doh!

https://www.evworks.com.au/page/technical-information/lifepo4-care-guide-looking-after-your-lithium-batt/

Screen Shot 2020-05-23 at 06.54.44.jpg

Click to expand...

FWIW, some of the large-format LiFePO4 cells (like those from thundersky, winston, calb, etc) have a 4.2v charge voltage in their spec sheets or other documentation. But what they don't say (or at least, not in plain english) is that this is a "Formation charge", only done at the factory, and not intended to be done by the end user. So there *are* places that quote this documentation's voltage, but none of the other info...occasionally leading to people damaging cells/etc by always charging to this voltage.

Hey Neil get on your boat and go to London https://endless-sphere.com/forums/viewtopic.php?f=31&t=102908

Yes of course if a pack has a non-adjustable BMS whose "start-balance voltage" **requires** going higher than 3.45Vpc

then you have to choose between letting a crappy BMS dictate your charging profile at the price of reducing pack longevity, or

replace the BMS, or

use something else to do your balancing.

999zip999 said:

Hey Neil get on your boat and go to London https://endless-sphere.com/forums/viewtopic.php?f=31&t=102908

Click to expand...

Thanks... interesting...

john61ct said:

Yes of course if a pack has a non-adjustable BMS whose "start-balance voltage" **requires** going higher than 3.45Vpc

then you have to choose between letting a crappy BMS dictate your charging profile at the price of reducing pack longevity, or

replace the BMS, or

use something else to do your balancing.

Click to expand...

Yes, for my own use I never bother with BMS... just a decent multipole plug out the pa k and check and balance charge when needed.

Bulk charging my 20Ah 20s LiPo at 20 Amps to to about 4.05 volts was my usual way.

But for non tech person ... has to be BMS.
Need to wait for their decision

AW, cheers.
Yes understand your points,
Interesting about Ping packs...
Is he still about ?

If I get the Steslth pack here and open again, I’ll photo the BMS and read label on cells

Mr Ping
http://www.pingbattery.com

A Ping in a stealth ping has been using better cellsbut his packs are pretty big for the power they put out. Those EIG cells bolt together are a little smaller and zero used them. I noticed a stealth store opened up the next city over I don't know I guess I would have to make contact and arrangements for an appointment it's just can't walk in nowadays.

Yes LFP has lower energy density (Ah capacity per volume and weight).

But much longer cycle life

My lifepo4 A123 7yrs big and heavy 24,000miles 24s20 ah pouches. Oh 1,490 cycles. No BMS as 20ah