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Old 05-06-2006, 07:18 AM   #1
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Default My last battery in pack dies on me... why?

Hiya,

I've been experiencing a weird phenomenon lately. I have 2 packs of batteries: el-cheapo 1900 mAh (desoldered stick pack) and Team Orion VMAX used to be top-of-the-line (3600 Sanyo cells) whatever you like to call it.

Now here is the problem: it concerns the orion pack
The problem is that the last cell (positive side, the one to which I hook up the ESC) is always discharged as the first. I measured this with a digital multi meter, the positive side cell reads 0.180V, all the other cells read 1.3V. Now, because of this last cell (I think its the reason), my car "stutters" after like 30 seconds of runtime.

So, these are batteries from a friend, and he never had problems with them... they come from a boat (he used them to race). He gave me six cells, I soldered them together, and this is what happens.

Yesterday, I called him up, I said that I have a faulty cell. He said alright, come down here, I'll give you some more. He very kindly gave me 3 more cells (1 Team orion, and 2 Peak racing, both are Sanyo cells) and some brushes (which work great!). I took out the cell that I thought was faulty, and replaced it with the Team orion one. Then I placed the whole pack on a LRP conditioning tray. Today, I charged the pack, and went out to drive. The el-cheapo 1900mAh pack ran fine, I used it to warm up my tires. Next, I hooked up the Team Orion pack, which I hoped to be fixed. The car just ran amazingly well... I thought that the problem was solved. I got at least 15 minutes runtime. Then, I lifted up my car, pulled the trigger hard a few times, placed the car back on the blacktop, and the stuttering appeared So I'm like oh well, I drove home. Now I checked all the cells with a multimeter, and the one that I replaced again showes a very low voltage (0. something) while the others show 1.3. I'm completely baffled...

Now, I'm saying, its the first time I've ran the new pack, so the cell might be OK (have to charge the pack). But what could be causing this? Or moreover, is this normal? I don't want to be freaking out over something that is normal, but this does NOT seem normal...

Any help GREATLY appreciated.
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Old 05-06-2006, 07:44 AM   #2
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You got 15 minutes runtime before the pack went flat. That sounds alright to me.

Charge the pack again before making a final judgement. It could be that your car is shorting out that 6th cell due to poor wiring or exposed chassis.
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Old 05-06-2006, 07:52 AM   #3
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im not sure if it is the pos or neg side but one will go down lower then the rest.. All of my cells go out at diff time on the tray,, thats why they call a tray an equalizer.. it gets the cells more equal before the charge.. If the pack ran fine, and you got 15 minutes out of it i woulnt call that a problem.. 15 minutes is way more runtime then most people use..
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Old 05-06-2006, 07:55 AM   #4
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Quote:
Originally Posted by sosidge
You got 15 minutes runtime before the pack went flat. That sounds alright to me.

Charge the pack again before making a final judgement. It could be that your car is shorting out that 6th cell due to poor wiring or exposed chassis.
I'll give it a shot...

to be more precise, the last cell reads 0.07V, the others read 1.2V after being in the discharge tray.

The thing is, this time I did get 15 minutes, but then the car started stuttering... with my El-cheapo pack, it barely stutters, it just goes slower as the pack is discharged.
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Old 05-06-2006, 10:29 AM   #5
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Ok, I charged an ran both packs.

Here is a summary:

El Cheapo runs great, does not stutter when nearly empty, just gradually looses power (only faint stuttering). All cells discharge equally (all cells read 1.2 or thereabouts on the DMM)

Team orion ran great for about 2 minutes, then stuttering appeared. The last cell was completely discharged, the others still full. Also, the last cell ("faulty cell") was hot, the others were quite cool.

I also placed the pack in the chassis, and measured various points, all showed 00. (I wanted to see if perhaps the cell was shorted somehow)

Now, what can we deduce from this?
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Old 05-06-2006, 12:06 PM   #6
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More info:

I tried charging the defective cell separately, and it only got to around 1000mAh before it temp cut (45C).

Is this a sign of a defective battery?

I was using the following on my Cell Master:
Number of cells:1
Temp cut:45
Capacity:3900
Current:4.5A
Delta Peak 06
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Old 05-06-2006, 12:12 PM   #7
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If it was fully discharged before, then peaking at 1000mAh would show that it was damaged.

It seems that two cells have now done this to you, either that is bad luck or their is something about your setup that is doing this.
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Old 05-06-2006, 02:10 PM   #8
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Quote:
Originally Posted by sosidge
If it was fully discharged before, then peaking at 1000mAh would show that it was damaged.

It seems that two cells have now done this to you, either that is bad luck or their is something about your setup that is doing this.
Ok, in my first post, I said that he gave me 3 cells. Now, I tried the Peak racing ones (they have better parameters than the Orion ones). The cell I tried charged to 3900mAh no problem... tomorrow I will try and solder it to the pack.
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Old 05-06-2006, 05:10 PM   #9
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be carefull not to overheat the cell while soldering. Make sure you have a REALLY HOT soldering iron so you can get the solder melted more quickly, so less heat goes into the cell. That kind of heat can really damage the cells.
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Old 05-06-2006, 07:14 PM   #10
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Check the shrink on the cell. It may have gotten cut against the chassis. If you have a carbon chassis it may be shorting.
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Old 05-12-2006, 01:48 AM   #11
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Ok, I'm back.

Here is what I did:

1) Desoldered old cell
2) Tested new cell, by soldering some wire to each end, and charging it with my Cell Master, everything was OK
3) Soldered the whole pack together
4) Placed insulation tape on the end of each cell, just to be sure that it isn't shorting
5) Gave the cells a few runs on my Cell Master (discharged & charged 5 times).

Now, during charging and discharging, I noticed that the cell closest to the positive side of the pack (not the one I replaced, but the one next to it) kept getting hot, and caused the charger to stop charging. It would always discharge first too... I bet you know where I'm heading.

I took the car for a drive yesterday, and yep, you guessed it, the cell that kept getting hot (not the one I replaced, that one works OK) died on me. I had about 10 minutes of runtime (I have to mention that the trigger was floored most of the time, or I was triving with a twitchy finger). Then the car started stuttering. I came home, placed the pack on my LRP tray, and watched - to my surprise, the one cell which kept getting hot was immediately discharged, while the others were more or less the same. I then measured the voltage on that cell, and Whoa! 0.3xxV. Next, I tried charging that cell individually with my Cell Master, but it gave me some sort of error a few seconds from the start (I just connected the leads to the bars coming to and from the battery). I left it overnight, woke up this morning, measured the voltage, and whatcha guess - 0.045....

So, why is this happening?

Before, the cell that looks dead now seemed to be OK, but the first one seemed to be bad, but it is now ok.....


Any help greatly appreciated.

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Old 05-12-2006, 07:24 AM   #12
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Quote:
Originally Posted by AdrianM
Check the shrink on the cell. It may have gotten cut against the chassis. If you have a carbon chassis it may be shorting.
This could be the problem. Also make sure you have good connections when charging or discahrging individual cells. And be sure the charger/discharger is actually doing what it is supposed to be doing.
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Old 05-12-2006, 07:30 AM   #13
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Quote:
Originally Posted by Rick Hohwart
This could be the problem. Also make sure you have good connections when charging or discahrging individual cells. And be sure the charger/discharger is actually doing what it is supposed to be doing.
I wrapped insulation tape around EACH cell, to make sure that it was not touching the graphite.

The charger charges my El Cheapo pack fine, so I see no reason why there should be anything wrong...

I set it up according to the manual.
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Old 05-12-2006, 07:48 AM   #14
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Quote:
Originally Posted by D_o_S
I wrapped insulation tape around EACH cell, to make sure that it was not touching the graphite.

The charger charges my El Cheapo pack fine, so I see no reason why there should be anything wrong...

I set it up according to the manual.
Check the LRP tray and make sure the cell cut-offs are all the same. If the one station is not discharging enough or too much, you can ruin that one cell in one cycle.
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Old 05-12-2006, 10:29 AM   #15
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Quote:
Originally Posted by Rick Hohwart
Check the LRP tray and make sure the cell cut-offs are all the same. If the one station is not discharging enough or too much, you can ruin that one cell in one cycle.
That might be it!!! I didn't realize that once, I placed a fully charged pack onto the tray, and it burnt/got really warm (the tray). It might be damaged...

Luckily, I have 1 cell left that I can swap out... I'll try that, and I won't discharge it on the tray

Oh yeah, and also, I bought a SMC Pack today - IB 3800. I hope it works great. Numbers are 409 seconds (lets not forget that its at 35A) and 1.205V, in case anyone's interested.
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