NOVICE4EVER

Hi fellow racers!
What is the right way to check which battery is dead on a stick pack?

Ray Lan

iTrader: (4)

Good question.

I'm not so sure of the RIGHT way myself. But I'll share what I do, hope someone can enlighten me.

Charge the pack, then discharge the pack using about 20 AMPs or more, this is to stress the cells to allow the weaker cell to show up more obviously..

IMMEDIATELY after it dumps, use voltmeter to record each single cell voltage and note down. If the cell is really gone, it will show up having the least voltage and has the largest voltage difference from the other cells. After 5~10mins, check all cells again. The weakest cell is the cell that takes the longest time to recover to nominal voltage of about 1.2volts. Just to confirm, check again after another 10~20mins. If the other 5 cells are at 1.2volts already while the dead cell is still struggling to recover from its discharged voltage. Usually a healthy pack will "spring back" to nominal pack voltage of about 7.2 to 7.8 volts per pack.

This "spring back" effect after a discharge cycle shows the INTERNAL RESISTANCE of a battery cell.

Healthy cells can recover fast due to LOW internal cell resistance, they have more voltage output thoughout the discharge curve and is simply shows up on your car as faster and punchier, when they dump, they dump suddenly.
Feels like drinking water from a cup, can take big gulps, shiok, and finish the water faster.

Weak or damaged cells recover slowly due to HIGH internal cell resistance, they have lower voltage output thoughout the discharge cycle, car feels slower, low punch, BUT may last very long becos its running very slow.
Feels like drinking water thru Yakult straw, very little water go into your mouth, and take longer to finish than when you drink from a cup.

There ARE proper R/C dischargers that can give you this reading when using side-by-side packs, but since these equipment is expensive and I'm using stick packs, this is the method I use.

INTERNAL RESISTANCE is a good indicator of cell health according to my readings. "Nipple" in this forum has got good knowledge on this topic, maybe he can shed some light on this issue.

You can read more HERE:
http://www.batteryuniversity.com/

Maikaitan

iTrader: (2)

good one Ray!!! i think he covers almost all areas... easy to understand and easy to follow...

Nipple

iTrader: (1)

Wah lau, I see my name.
Erh.... I passed the "Picture Book" to another racer, he say beri boring to read lei.

And bcos of copyright stuffs etc, sorry but I think I can't upload it for pple to download.

What ray mentioned is a good way to test.

But 1 thing to add, Cell deterioration can take two forms:
1. Oxidation of the negative active material and electrolyte dry-out leading to
increase in cell internal resistance.
2. The positive active material deteriorate resulting in less active material
available for reaction thus capacity reduces.

So higher internal resistance may be a indication of dying cell, but not all dying cell has higher internal resistance.

Lastly, batteryuniversity is not a bad website to readup for more "general info" on batts.

Just my 2cents. But seriously, I dun noe how many pple will trust my words...

Ray Lan

iTrader: (4)

Bro, you got PM.

NOVICE4EVER

First of all just want to say thank you for all the information you shared.
Now, I'm wondering how many cycles can a battery last for both 3700 GP and 4200 IB?
Measuring the voltage of each batteries after each procedure mentioned (charging and discharging), I found out that there is no dead cells in the batteries as all the readings are the same.
The batteries had been charged for 5 to 7 times, when the problem shows up.
Now the reading are as follows: 1.20 for 3700 GP and 2.7 for the 4200 IB base on my charger.

Ray Lan

iTrader: (4)

Hi,
Its important to be specific when you use internet forums, if not you either get a wrong answer or no answer.

When you say 1.2V is it PER CELL or ENTIRE pack? If per cell, normal, if per pack... pretty dead.

2.7 cannot be per cell, each cell should at most go to 1.6 volt/cell at peak. 2.7 per pack is also... pretty dead. Try charging, with low amp say 2~3amps and monitor temperture, there has been exploding cells recently, you can't be too careful when it comes to such incidents. Take each cell reading again. If still 2.7 per pack... time for new packs. Dispose battery safely.

Try not to use charger for voltage readings.
There are electronic circuitry inside the charger that may drop voltage and give wrong readings(too low).
Or if the charger is trickle charging(automatically for some chargers) the cell while not fast charging, it may give another wrong reading(too high).
Use a dedicated digital voltmeter(10 bucks from sim lim tower) with the battery pack disconnected from everything. Only then can you be sure the readings you took are accurate.

NOVICE4EVER

In my charger after indicating full charge its read 1.20mah (stick pack six cell)

discharge = 1amp
charge = 1amp

Then i checked the voltage of my battery, I'm using digital multimeter to measure the voltage of individual cell.

For individual cell its read 1.35
For six battery 8.10

discharge = 25amp
charge = 5.5amp

For individual cell = 1.33
for 1 pack of 6 cells = 7.98

after 8hrs i check again the voltage of individual cell , same reading 1.33 and 7.98 for six cells

as i said before this cell took 5 to 7 cycles (now after testing 10 cycles). Now I'm wondering
How many cycles can a battery take?

Ray Lan

iTrader: (4)

"For individual cell its read 1.35
For six battery 8.10

For individual cell = 1.33
for 1 pack of 6 cells = 7.98"

Your packs look pretty normal by voltage. If you really want to test a pack, you have to load it with something stressful, like 20Amps and look at the capacity avaliable.

You have not mentioned the type of battery you use. 6 cell is the normal. But what is the CAPACITY? is it 1600mAh, 2400mAh, 3300mAh, 3600mAh, 4200mAh...etc etc..?

Usually a healthy pack will show slighty less than its rated capacity(what the pack sticker says) when discharged at 20~30 Amps. This is normal.
Example, 3600 pack will give 3400~3500mAh, 4200 pack will give about 4000 mAh etc...

1.2 should be Ah = 1200mAh.
1Ah = 1000 mAh

If your pack really 1.2 mAh, then i think its spoilt.
How long did it take to charge at 1 amp? How long at 5.5 Amp?

Nipple

iTrader: (1)

It dpends on the made. Well for the Sub-C cells used in RC EP, GP cells seems to last longer then Intellect ones. But can't give you a absolute number. It depends on how u use/charge/maintain them.

But personal experience is, GP cells can last me more then 50 cycles with no dead cell, IB based, a few cells is dead after 5-6 cycles. "Hear-say" some drivers have expereince dead IB cells just after 1-2 cycles.

Well, although the cells such as GPs can last 50 and more cycles, but the performace will drop, in terms of capacity and voltage. Usually, the performance will drop after a few cycles (Also cannot give you a absolute number, but again, my personal experince is less then 7 cycles).

The drop in capacity and voltage is quite "chim". It's not just about internal resistance. It has to do with "Cell Deterioration" which i mentioned earlier and voltage depression. I will not explain in details here.

Nipple

iTrader: (1)

Sorry Ah Lan, but I think discharging the sub-c cells at 20-25amps with "accurate equipments" will not give you those numbers. It will be even lower.

Just a info, the rated capacity (what the pack sticker says) or nominal capacity is rated at a 0.2C discharge rate. That means for 3600mAh cell, the discharge rate is 720mA or 0.72A down to 1.0V.

And discharging cells with different load such as resisitor or motor with the same current will also give different results, cos cell perform differently under different load such as resistive (voltage and current are in phase) or capacitive (Voltage and current not in phase) load.

Just my 2cents.

NOVICE4EVER

Is the dean connector help to prevent the sudden drop of voltage in a battery?
What is the advantage of using dean connector than Tamiya plug?

Ray Lan

iTrader: (4)

You spoke.
Me listen, enlightened I am.
Thanks.

Deans Connectors/equivalent:
Lower resistance than tamiya plugs due to better connection in terms of surface area and material. results: Car runs faster, battery last longer.

NOTE:
When people say "Longer" "faster", it means the value of increase may be slight or great. even 0.0001 sec increase in run time is "longer" so when you read advertisments or hear other people talk, must judge for yourself whether its really significant enough for you to spend money and time, esp if you are on a tight budget.

In this case of Deans versus Tamiya plugs, so long as the rules allow you to change, use DEANs or other low loss connectors, you wont go wrong, worth the money. Charger and discharger must change as well.

Blueshark

Folks, check here for more info on NiMH Care.

http://www.rccaraction.com/ME2/dirmo...5272522C115271

Nipple

iTrader: (1)

I think it a good guide, but note, that was posted in year 2000. And Ni-MH batt back then and now has some differences in terms of performance and handling.

Just my 2 cents.