lipo battery life

dolby

100 mW
Joined
Dec 8, 2012
Messages
46
Location
Melbourne, Australia
I am trying to work out why my 12s3p (48V 15000mAh) lipo pack is giving me such poor mileage. I am only able to achieve 17kms (10.2 miles) riding WOT (1KW conhismotor, max speed 48km/hr) before I reach 41.5 v LVC on my controller. This is slighly less than when I was running new packs with 12s2p (48V 10000mAh). I have charged them approximately 250 cycles. I have also accidentally mixed some turnigy and zippy packs together in my battery config. I parallel charge my 6s lipo packs on a parallel charging board and use a TURNIGY MEGA 400W V2 Lithium Polymer Battery Charger.
This problem seems to coincide when I fitted a larger 400w power supply for the charger. I then increased the charging current up to 17amp to reduce charging times. I have since now reduced this to 12amp but no improvement with mileage.
Is it possible that my Turnigy charger could be charging my packs up to the correct voltage (25.2 V) but not charging the cells to full capacity (mAh). So instead of having 15000mAh available, perhaps I have less.
Is my problem due to the fact that I charge my cells in lipo mode 4.2V/cell instead of charging in lilo mode 4.1V/cell, and now the batteries are worn?
Is this reduction in battery life typical for running 250 cycles?
help please :?
 
No, it's much less reduction in range than I'd expect. You get more voltage sag now too I bet. The cells are just getting old.
 
You need to IR test all the cells and/or measure voltage sag under high current draw.

The thing with aged RC Lipo is that some cells die earlier than others and if you wish to extend pack life you'll need to qualify them at cell level and be prepared to do the dangerous job of brick surgery.

Regularly charging to 4.2V/cell is a bad, bad idea for longevity. I'm still running Turnigy/Zippy cells that're 3 years old and well over 600 cycles but not without reworking some of the bricks (packs) to cull out the bad ones.
 
Quite possible that some, perhaps the zippies have gotten old faster than the others.

How many years old? Just 3 years on the shelf can wear them out, if stored hot and charged.
 
I would first measure the capacity of the battery. You need to know how many watt/hour that you really have available.
If your cells have lost a lot of capacity, then they are worn out and need to be replaced.
If your capacity is good but your bike is doing less mileage, then you have to find the current loss.
 
dolby said:
I am trying to work out why my 12s3p (48V 15000mAh) lipo pack is giving me such poor mileage. I am only able to achieve 17kms (10.2 miles) riding WOT (1KW conhismotor, max speed 48km/hr) before I reach 41.5 v LVC on my controller. This is slighly less than when I was running new packs with 12s2p (48V 10000mAh). I have charged them approximately 250 cycles. I have also accidentally mixed some turnigy and zippy packs together in my battery config. I parallel charge my 6s lipo packs on a parallel charging board and use a TURNIGY MEGA 400W V2 Lithium Polymer Battery Charger.
This problem seems to coincide when I fitted a larger 400w power supply for the charger. I then increased the charging current up to 17amp to reduce charging times. I have since now reduced this to 12amp but no improvement with mileage.
Is it possible that my Turnigy charger could be charging my packs up to the correct voltage (25.2 V) but not charging the cells to full capacity (mAh). So instead of having 15000mAh available, perhaps I have less.
Is my problem due to the fact that I charge my cells in lipo mode 4.2V/cell instead of charging in lilo mode 4.1V/cell, and now the batteries are worn?
Is this reduction in battery life typical for running 250 cycles?
help please :?

are you bulk charging this pack or is this a balancing charger? if you have no BMS how many times in the 250 cycles do you think one of the cells dropped under 2.7V without you knowing about it? the only protection you have is the controller LVC? i would expect with just the controller for LVC you might have been over discharged at least one cell more than few times.
 
Couple of issues with what you are doing with your Lipo... some already mentioned by others.

1) Charging to 4.2V per cell is a sure way to kill you Lipo battery fast. I am surprised your battery didn't lose more capacity than you did @ 250 cycles. Just from experience, I have the nanotech and @ 306 cycles, I have about 85%-90% of the original capacity. This is after 306 cycles of babying the battery from 3.6V to 4.1V.

2) Are you bulk charging? If so, are you using CCCV? If you bulk charge and stop right when it hits the 4.2V per cell voltage, then your Lipo is NOT fully charged. The voltage will drop quickly even if you leave your bike idle. The CV part of the charging is what fully charges your battery.

3) Charging at 17A is > 1C. This can reduce life cycles if you are using 1C max charge rate battery. Reducing the charging rate to 12A now would not help because the damage might have been done.

4) You stated you have the Turnigy charger. I would using a multi-meter to verify the charger is indeed charging your Lipo to the right voltage. Sometime these cheap charger can have their voltage reporting way lower later down its operation lifetime.

5) Have you monitor each cell during rides? It is very typical, especially at 250 cycles Lipo, to have weak/fast self-discharge cells. It might be the case you have 1 or 2 weak cells in the parallel and they are sagging more than others to bring the voltage down to the LVC of your controller. I had to remove 2 10s packs on my setup because they had 1 weak cells. Identify them using celllog during rides and remove them. Another way to split the packs all up into individual packs and leave them in storage at relatively high SOC (~4.1V) for a few days or so. You will see the high self-discharge cell dip faster than others. It is important you separate them because othewise, the strong cells in parallel will keep the weak cell stay charge longer.

My suggestion is to do a charge/discharge cycle using your lipo charger to see what capacity you actually get. Set it to the normal 3.0V to 4.2V. I suspect you have damaged your Lipo battery by doing the 1-5 I stated above. Also do what others are saying. Check the internal resistance of the battery. If it's high, it means your pack is at its end of life.
 
Thanks for your help guys. Much appreciated :D
I have tested my batteries with my battery medic to identify weak cells. Here are my results
all 6 packs connected in parallel, pack 1, pack 2, pack 3, pack 4, pack 5, pack 6
cell 1- 4.11, 4.11, 4.11, 4.11, 4.11, 4.11, 4.11
cell 2- 4.18, 4.18, 4.18, 4.17, 4.17, 4.17, 4.17
cell 3- 4.13, 4.13, 4.13, 4.13, 4.12, 4.13, 4.13
cell 4- 4.13, 4.13, 4.13, 4.13, 4.13, 4.13, 4.13
cell 5- 4.18, 4.18, 4.18, 4.18, 4.18, 4.18, 4.18
cell 6- 4.14, 4.14, 4.14, 4.14, 4.14, 4.14, 4.14

All packs appear to have nearly identical cell voltages at full charge. Would this suggest that I do not have any weak cells? I only a week ago balance charged each pack separately. I seem to have always got this variation between cell voltages even after balance charging each pack.
Am i better to measure all cell voltages after a discharge to see variation between cell voltages? Maybe that may highlight weak cells. Any thoughts would be appreciated. :wink:
 
With all in parallel each cell group should read identical voltage as most of yours do. One problem yo8u have is they aren't balanced real good from 4.11 to 4.18 is terrible if you did a balance charge. When I balance charged 6 4s packs in parallel, they were all within .003V. Yours are .070V spread. Looks like you have some weak cells. Balance each pack one at a time to find the bad cells.
 
Those fully charged numbers are fine but do not tell you anything really.
you must be able to see your cell voltages under load to see if one cell sags and triggers your low voltage cutoff or if ( more likely) you have diminished capacity on the old packs. Do they get hot with discharge?

I used a cellog 8 the one that goes for about $ 27 to test cells

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9282

this Celllog can track voltages of individual cells so you can see when thecells hit 3.60 they are dead, and I bet if you have a watt meter ( if you do not, you need one) you will see what the capacity of the pack is. Capacity may be greatly reduced.
Is that clear?
For example, I had several 2-3 year old six series packs I ran as 12 series one paraell. I use the same excellent charger that you have.
I found by testing the cells by hooking up a light or by riding the bike with cell log and watt merter , my cells hit 3.60 after only 3 amp hours delivered. to me I consider that pack toast. I found half of my packs deliverd 2.2-3 amphours while the others contiued to deliver 3.5-4.3 amp hours.
hope that helps.
I think you need to figure out the good packs from the taoted ones and use those to ride. good luck.
 
Yes, you have to find out with a discharge test which cells have higher internal resistance, and or lower capacity. They all charge to full, but using the water analogy one might be a full gallon while another is only a full quart.

Bet they all are pretty similar, just wearing out.
 
BikeFanatic said:
Those fully charged numbers are fine but do not tell you anything really.
you must be able to see your cell voltages under load to see if one cell sags and triggers your low voltage cutoff or if ( more likely) you have diminished capacity on the old packs. Do they get hot with discharge?

I used a cellog 8 the one that goes for about $ 27 to test cells

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9282

this Celllog can track voltages of individual cells so you can see when thecells hit 3.60 they are dead, and I bet if you have a watt meter ( if you do not, you need one) you will see what the capacity of the pack is. Capacity may be greatly reduced.
Is that clear?
For example, I had several 2-3 year old six series packs I ran as 12 series one paraell. I use the same excellent charger that you have.
I found by testing the cells by hooking up a light or by riding the bike with cell log and watt merter , my cells hit 3.60 after only 3 amp hours delivered. to me I consider that pack toast. I found half of my packs deliverd 2.2-3 amphours while the others contiued to deliver 3.5-4.3 amp hours.
hope that helps.
I think you need to figure out the good packs from the taoted ones and use those to ride. good luck.

The packs do not get hot after use. I have one of these cell monitors.
http://www.hobbyking.com/hobbyking/store/__10328__Hobby_King_Battery_Medic_System_6S.html
I do have a watt meter on my bike. So all I need to do is connect my packs as 12s1p, connect my battery medic to each battery with some load on the hub motor wheel and observe the voltage sag across the 6 cells in each pack. The cells with the greatest sag are responsible for my reduced mileage?
So the other option is that I can run the bike with a 12s1p config and observe the watthrs used on the watt meter before dropping to say 44volts? Try this and alternate different packs to see which packs provide the lowest capacity.
 
I tend to drag this thread up once or twice per month for RC Lipo IR cell testing:

http://endless-sphere.com/forums/viewtopic.php?f=14&t=48739&p=718933&hilit=celllog#p718933

Maybe it should be stickied/wiki'd? More and more old RC Lipo out there with each day....
 
have a watt meter on my bike. So all I need to do is connect my packs as 12s1p, connect my battery medic to each battery with some load on the hub motor wheel and observe the voltage sag across the 6 cells in each pack. The cells with the greatest sag are responsible for my reduced mileage?
So the other option is that I can run the bike with a 12s1p config and observe the watthrs used on the watt meter before dropping to say 44volts? Try this and alternate different packs to see which packs provide the lowest capacity.

Yes ,it would be nice if you just had one weak cell and you could just replace it. Calculating IR IS another test also .
 
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