Author Topic: LiPo Questions  (Read 483 times)

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Online jerryk

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LiPo Questions
« on: April 20, 2019, 04:54:43 am »
I have a Micro-Start XP-1 jump pack that was given to me after a pilot had it swell up when he was trying to jump start his airplane.  The photos below are the three LiPo cells that went through the stress event.  The cell on the right shows signs of swelling and there is a small amount of slack in the foil.  The other two cells are tight and look good to me.  The cell in the center has a little rounding in bottom of the cell but otherwise looks in perfect condition.

In a perfect world I would like to replace the swollen cell and save this jump pack.  The photos show all the identification marks on these cells but I cannot find anything on the net that leads me to a possible replacement.  Is there anything in these numbers that generically describe these cells?

Currently all cells have a charge and are balanced at close to 3.75V.  Is a visual inspection of LiPo cells a valid way to assess their condition?  I hate to waste good stuff but also understand caution is in order.

Jerry 

 

Online james_s

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Re: LiPo Questions
« Reply #1 on: April 20, 2019, 04:58:45 am »
Swelling is an indication of damage, but it doesn't necessarily mean the cell is bad or needs to be replaced. I have a load of LiPo packs I use in my RC aircraft and I've had a few that puffed a bit either due to manufacturing defect or abuse, provided it's minor I just keep using it. If a pack puffs up badly then it's time to retire it. I would not try to replace a single cell in a pack unless you *know* the protection circuitry is well designed. Discharging a cell below a certain point damages it, and over charging a cell much beyond 4.2V will cause it to burst into flame. IMO it's not worth the risk.
 
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Offline Audioguru

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Re: LiPo Questions
« Reply #2 on: April 20, 2019, 05:33:30 am »
There are new Li-PO cells now (Lithium Ferro Phosphate) that have iron in them instead of the original Cobalt and their voltage is lower.
Lithium Cobalt is fully charged at 4.20V, has a storage charge of 3.7V to 3.8V and is about 3.2V when its load should be disconnected.
The new lithium cells with ferrous might have a fully charged voltage of 3.6V.

Your puffed lithium cell is worn out or has been abused and all three cells are in series therefore have the same age or had the same abuse so the entire battery should be replaced. 
 
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Offline grizewald

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Re: LiPo Questions
« Reply #3 on: April 20, 2019, 05:56:44 am »
Damaged Li-Po cells are a liability and I wouldn't even entertain keeping those indoors. While it is rare, damaged cells can burst into flames all of their own accord. Once they start to burn, you can't put them out either.

Examine the top of the cells where the wires come out to see if they have a protection board or not. Then note the dimensions of the cells and look for replacements. The numbers on the cells often reveal nothing, but in the end, one Li-Po cell is much like another. They either have a protection board or they don't. If they do have a protection board, it prevents the cells from being either over, or under discharged. The fact that these cells became damaged in use tends to suggest that you won't find a protection board.

Just because some of the cells look OK is no reason to trust any of them. Dispose of them properly!

hobbyking.com is probably a good place to look for replacement cells, or even better, a replacement pack.

A replacement pack removes the need to work with soldering a pack together yourself. Even when the cells are at 3.7V storage charge, accidentally shorting one is something you won't forget! :D
 
 
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Online james_s

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Re: LiPo Questions
« Reply #4 on: April 20, 2019, 06:03:16 am »
While it is rare, pristine undamaged cells can burst into flames too, it's just the nature of the beast. My observation has been that the vast majority of LiPo fires occur during charging due to defective or improperly configured chargers that allow one or more cells to over charge. The next most common cause is crashes, a couple years ago I saw someone crash a large electric heli and it made an impressive fireball when it went in. Lots and lots of people fly slightly puffed cells without issue, it's a sign of degradation but doesn't mean a cell is finished.

I *never* store fully charged LiPo batteries no matter what their condition, and I never charge them indoors unsupervised. Normally I charge one set as I'm packing up my gear and then set up my charger at the field.
 
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Online jerryk

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Re: LiPo Questions
« Reply #5 on: April 20, 2019, 07:56:20 am »
I was surprised to see how this jump pack works.  These three LiPo cells are in series.  When you hook the pack up to the battery to your car, boat, plane or whatever, you have a direct connection to that battery with your LiPo pack and you can do a jump start  with no sort of over discharge protection on the jump pack itself.  I suppose the vehicle starter gives up at some point.

From what I'm reading here about similarities in LiPo cells I should be able to get any similar rated LiPo pack, make a direct connection to a car battery and jump away.

There is a circuit board associated with the jump pack that provides various other outputs like 19V for laptops, a usb port, and a 12V jack for other things.  It also manages the charging function some status lights, and a flash light with various modes.  I don't see any direct protection on top of the battery and assume the only protection is in the main board on the charging end.  Nothing I can see would prevent a total discharge of this unit.

Jerry
 

Online james_s

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Re: LiPo Questions
« Reply #6 on: April 20, 2019, 08:04:54 am »
They don't have any protection because it would be impractical to implement a disconnect device capable of carrying the current necessary to start a car within the cost constraints of a cheap consumer device like this. They are disposable, you use them a few times and the LiPo pack inside is pretty much finished, then you go and buy another one. That's just the reality of this sort of thing, it's an emergency device meant to prevent you from getting stranded, not something you'd use regularly.
 
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Offline mikerj

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Re: LiPo Questions
« Reply #7 on: April 21, 2019, 07:43:50 pm »
I was surprised to see how this jump pack works.  These three LiPo cells are in series.  When you hook the pack up to the battery to your car, boat, plane or whatever, you have a direct connection to that battery with your LiPo pack and you can do a jump start  with no sort of over discharge protection on the jump pack itself.  I suppose the vehicle starter gives up at some point.

The protection circuitry is in the separate "dongle" that is attached to the alligator clips to attach to the vehicles battery.
 
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Online jerryk

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Re: LiPo Questions
« Reply #8 on: April 22, 2019, 02:17:57 am »
I was surprised to see how this jump pack works.  These three LiPo cells are in series.  When you hook the pack up to the battery to your car, boat, plane or whatever, you have a direct connection to that battery with your LiPo pack and you can do a jump start  with no sort of over discharge protection on the jump pack itself.  I suppose the vehicle starter gives up at some point.

The protection circuitry is in the separate "dongle" that is attached to the alligator clips to attach to the vehicles battery.

It's funny that I forgot about that dongle.  I'm going to see if my friend still has it so I can take a peek and see what's inside.   This all came about from trying to jump an airplane that had serious battery ground issues.

Thanks - Jerry
 

Offline MadScientist

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Re: LiPo Questions
« Reply #9 on: April 23, 2019, 04:43:22 pm »
There are new Li-PO cells now (Lithium Ferro Phosphate) that have iron in them instead of the original Cobalt and their voltage is lower.
Lithium Cobalt is fully charged at 4.20V, has a storage charge of 3.7V to 3.8V and is about 3.2V when its load should be disconnected.
The new lithium cells with ferrous might have a fully charged voltage of 3.6V.

Your puffed lithium cell is worn out or has been abused and all three cells are in series therefore have the same age or had the same abuse so the entire battery should be replaced.

Lithium-Iron , or more correctly LiFePO4 are not “ new”, they’ve been around awhile especially in large prismatic enclosures. They have a lower charge density then other forms of LiPO and lower terminal voltage, but have far less risk of thermal runaway , they are also a good bit more expensive wattH per wattH then other more common forms of LiPO .  They also can’t be charged quite as aggressively . Hence they tend not to be used in quick charge high energy applications , ( like jump starters , RC etc )
EE's: We use silicon to make things  smaller!
 

Online james_s

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Re: LiPo Questions
« Reply #10 on: April 24, 2019, 01:35:35 am »
The biggest advantage of lithium iron is that they don't seem to mind being stored fully charged. They would definitely be preferable for an application like this, but they cost more so I don't know if any of these jump starters actually use them.
 

Online jerryk

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Re: LiPo Questions
« Reply #11 on: April 24, 2019, 02:44:54 am »
The biggest advantage of lithium iron is that they don't seem to mind being stored fully charged. They would definitely be preferable for an application like this, but they cost more so I don't know if any of these jump starters actually use them.

There is only one that I know of by EarthX.  It's popular in the light aircraft world in part because EarthX batteries are being used in many aircraft in the experimental category.  EarthX now even has one of their batteries approved for certified aircraft.  All of the EarthX line is LiFePo4 chemistry.

The jump pack that I have apart is an older XP-1 Micro-Start from Antigravity Batteries and is lithium-ion (per their website) and assumed Lithium-Cobalt in chemistry from what I'm learning here.

I use both the XP-1 and XP-10HD in my flying hobby.  The XP-10 is used often, primarily to charge other electronic devices that I carry to the field but can also serve as a emergency backup jump pack incase the airplane fails to start.  The XP-1 primary mission is as a backup jump pack for the plane.  That's why I jumped at the chance to cut this XP-1 open when my friend abused it.  I figured I should learn a bit more about the technology I'm working with.

Jerry 
 


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