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 Battery charging question

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Samaj
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PostSubject: Battery charging question   Wed Feb 24, 2010 7:59 pm

Even though my new Lipo's will be here in the next one week. Dont want to give up on my New (we un-used) Ni-MH packs.

Pls see the attcahed scan highlighting what i believe to be the amp readout. (Correct me if iam wrong.)

http://i66.servimg.com/u/f66/14/26/26/91/charge10.jpg

I'am cycling the packs. Seem to have set all the parameters as well. The battery stops charging at the righ time & becomes warm- slightly over warm.

But when u actuall run the car it lasts for only 3-4 minutes. Been told that the more u cycle the packs the better the performance. Some sign of this is that with every cycle the charge time is increasing by average 8-10 minute or so.

So far the Tamiya 3600 mah pack charging at 2.2Am & 1.5 amp discharge. Threshold cutout set at 7mV/cell. Apprently finishes charging in 40 minutes & becomes slightly hot.

Should i continue on this path...?

Advise from the pundits welcome. Note These are new packs but never run since i bought them like 2 years ago.

Why go through the hastle when i'am getting Lipo. Answer......so i learn. Being avoiding this all this time.

Thanks in advace
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paul
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PostSubject: Re: Battery charging question   Wed Feb 24, 2010 8:18 pm

sam,

that is the mah count, but it wont read 3600 when you are done as you still have some charge in the battery before you charge.....depending on how flat the battery is you should be getting a reading there of 2500mah and up....

i think you may need to try and charge them at a higher amps..... try 3.6A....the battery should be pretty hot when finished charging
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Samaj
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PostSubject: Re: Battery charging question   Wed Feb 24, 2010 8:19 pm

When u say pretty hot...........55 degree celcius till it shuts of due to temp. over ride?
Just finished charging the 3600 battery. The mah reading touched 1284mh with 8.7V. Then it stopped charging after 40 minutes of charging.
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paul
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PostSubject: Re: Battery charging question   Wed Feb 24, 2010 8:46 pm

sam id say normal would be somewhere between 40-50degrees at the end of a charge, higher capacity batteries will get hotter at the end of a charge than lower capacity ones.

i reckon your batteries are false peaking and hence they are stopping after 40 mins...typical charging a flat 3600mah bat at 3.6 A should take 1 hour to reach full charge, so if you are charging at 2.2a it should take about 1hour 30 to charge up....

i think your bats may be done for:scratch:


Last edited by paul@play on Wed Feb 24, 2010 8:47 pm; edited 1 time in total
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mister-e
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PostSubject: Re: Battery charging question   Wed Feb 24, 2010 8:47 pm

During races, people are charging NiMh at even 2x it's capacity.
The higher the charge current, the higher the end voltage will be (stock racing) of the battery which equals to higher RPM on the electric motor, thus more speed.
When charging with low current (e.g. 3A), end voltage will be less high, however, you will get more run time (modified racing).

I'm charging the packs with 5 amps, which is a good averige between durability and performance. When charged, it's normal that the battery become "hot".
But I think the 55 Celsius is a bit high.
Maybe you can set the threshold cut-out at 4 instead of 7 mV/cell.

Before charging, actually you want to discharge each cell till 0,9V after usage.
When running it for only 4 minutes, then there is still some charge left in the pack.

Hope it helps!
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cathurga
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PostSubject: Re: Battery charging question   Wed Feb 24, 2010 9:57 pm

Mister-e, all good advise, but the delta peak cutoff should go HIGHER if it is cutting off too early...I would suggest increasing it to 10mv per cell.

Nimh do get hot, and yes they can be charged at higher than 1C, specifically for racing, but in this case where you are trying to rejuvenate the batteries, stay safer and keep it under 1C.
And when I say 1C, I mean, if it is a 3000mah battery, 1C would be 3A for one hour. If it is a 3600mah battery, 1C would be 3.6A for one hour.

If, as you say, they are being discharged to flat, and then recharged at less than 1C, and are cutting off at 40mins...it means the delta peak is too low...
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Samaj
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PostSubject: Re: Battery charging question   Wed Feb 24, 2010 11:15 pm

Thanks for all the advise guys. Will definately try it out tomorrow & posts results.
How many cycles is it safe to do per day? What gap should be there between cycle? Just let the batter y cool down...?

Thanks once again to all.!!
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cathurga
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PostSubject: Re: Battery charging question   Wed Feb 24, 2010 11:20 pm

I have heard people say that 2 - 3 cycles per day is the limit.....but I have never seen a NiMh battery wearing a watch, so I am not sure how the battery knows the difference....??!!

Letting them cool after discharging should be all thats needed...
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Samaj
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PostSubject: Re: Battery charging question   Thu Feb 25, 2010 4:07 pm

Ok guys some update

First pack Tamiya 3600 mAh

Charge rate 3am
Discharge rate 1.8am
Temp cut of 55 degree celcius
Peak Sensivity set at = 10mv/cell
Charge time = 34 minutes
Amp pumped till then = 1436amp
It seems to shut down charging due to the temp. cutof.

Do i raise the temp cut of from 55 to 60..? Degree celcius
---------------------------------------------------------------------

First pack Orion 3000 mAh

Charge rate 3am
Discharge rate 1.8am
Temp cut of 55 degree celcius
Peak Sensivity set at = 9mv/cell
Charge time = 33 minutes
Amp pumped till then = 1485amp
Apprently charger says full charge???

Bump up the sensivity threshold or the temp threshold.

Having said that with every cycle on both the batts. The overall charge time & the amps pupmed increase by approx 10-15%.
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paul
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PostSubject: Re: Battery charging question   Thu Feb 25, 2010 6:50 pm

it sounds positive that you getting more charge in them each time...

have you tried to run them in the car again sam?

if so,are you get longer run times yet?

how many times have you cycled the batteries now?
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Samaj
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PostSubject: Re: Battery charging question   Thu Feb 25, 2010 7:57 pm

Yup with each cycle more time to charge & more amps are going in.
Finished about 5-7 cycles so far.

Last time i barely got 2-4 minutes of actual runtime in the car.
Will have to c.
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paul
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PostSubject: Re: Battery charging question   Thu Feb 25, 2010 8:01 pm

samaj, try and run them and see how much runtime you will get now, last time you tried was on the weeknd right?

i reckon if you dont have them close to normal by about 10-12 cycles - you may need to scrap them!
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Samaj
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PostSubject: Re: Battery charging question   Thu Feb 25, 2010 9:06 pm

I reckon as well. I still have some hope as i have reached about 5-7 cycles with positive results. As u said 10-12 & they still dont work. Will bin them.

I have gone crazy this time. I'am cycling them at work. So i have the charger set up next to my workstation. I have an excel sheet where i mark up all the progress etc. Fun actually..... rolling eyes
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paul
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PostSubject: Re: Battery charging question   Thu Feb 25, 2010 9:37 pm

Samaj wrote:
I have gone crazy this time. I'am cycling them at work. So i have the charger set up next to my workstation. I have an excel sheet where i mark up all the progress etc. Fun actually..... rolling eyes

okay you making me nervous now! shocked lol

no thats good at least you can track the progress!

i give you credit i wouldnt have persevered for so long, would have binned them by now....

anyway hopefully you get lucky and they come back to full power bounce
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mister-e
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PostSubject: Re: Battery charging question   Fri Feb 26, 2010 3:18 am

"the delta peak cutoff should go HIGHER if it is cutting off too early...I would suggest increasing it to 10mv per cell."

As result: "It seems to shut down charging due to the temp. cutof."

=> That's what I was trying to say, the delta peak cut off is too high. Try a lower value.


Also battery could be false peaking. Was it a matched pack?
Try to balance the battery, discharge each cell individually till 0,9V the charge them again.
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cathurga
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PostSubject: Re: Battery charging question   Fri Feb 26, 2010 1:23 pm

Mister-e, sorry but you are wrong on the delta peak setting. There are a number of things to consider here, but I am trying not to confuse Sam.

As you increase the Amps, you should lower the delta-peak, so you are right there, but at the moment, Sam is BELOW 1C and increasing slowly.
The difference between slow/trickle charging (1/10C) and fast charging (1C or higher) is that the lower the charge rate, the smaller the voltage drop (delta) when charged so you need the detection smaller. When it is fast charging the voltage will suddenly drop by a large amount, and that is the drop you want the charger to detect. Detection of the smaller drops will result in a 'false peak'.

Sam doesnt have the tools to discharge each cell, it ia a standard tamiya stick pack and as such, yes it is balance, but he cannot discharge each cell.

Sam, your next step is to make the amps 1C, set the delta a7 7m/v, run the battery in the car and see how long it runs, when it is cool, try charging it at 5A ...same delta.

Alternatively, dispose of them, and wait for your Lipo
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Samaj
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PostSubject: Re: Battery charging question   Fri Feb 26, 2010 3:37 pm

Thanks guys............progress under progress. very happy
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Samaj
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PostSubject: Re: Battery charging question   Sun Feb 28, 2010 2:45 pm

Ok have managed to pump in the 2000am rate today (on the 3000 Ni-MH). That real good news. Considering i started with only 800 amp odd going into the batterries. So after 8 cycle or so the batter seem to be coming alive.

Only thing is now it seems to prematuely stop charging because of the temp. threshold. As stated on the LCD screen when it stops charging.

Currently the temp. threshold is set at 55degree celcius & the delta peak sensitivity at 9mV/cell.

So it can take more charge but shut down because of the temp.

Hhmmm.......?
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cathurga
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PostSubject: Re: Battery charging question   Sun Feb 28, 2010 2:50 pm

drop the delta-peak to 7m/v and see what happens....I would suggest taking the temp higher but I suspect that would be dangerous....
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gerg
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PostSubject: Re: Battery charging question   Sun Feb 28, 2010 3:08 pm

It is also a good idea to see if you can detect if any one cell is getting hotter than others. Sometimes you may just have one bad cell (out of the 6) and that could mess with your charging routine.
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Samaj
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PostSubject: Re: Battery charging question   Sun Feb 28, 2010 7:43 pm

All my four packs are prebuilt & heat shrink wrapped. There is no way of knowing which is the bad cell.
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PostSubject: Re: Battery charging question   Sun Feb 28, 2010 8:04 pm

Sam, the normally start heating up from the plug lead side....in other words, the one closest to the plug gets warmest first....but if there is a dud, it normally gets considerably hotter than the others..
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PostSubject: Re: Battery charging question   Wed Mar 03, 2010 8:50 pm

How many amps should be pumped into a 3600 & 3000 Ni-MH to be considerd a full charge?
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PostSubject: Re: Battery charging question   Wed Mar 03, 2010 9:19 pm

sam

it depends how empty the battery is.....but pretty close to 3600 or 3000....a better way to judge it is through time, 3600 bat should take an hour to charge at 3.6A charge rate
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Samaj
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PostSubject: Re: Battery charging question   Wed Mar 03, 2010 10:12 pm

Today i managed 50 minutes of charge for the 3000 map Ni-MH which pupped 2200 amps then shut down at 55 degree celcius.
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