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Old 04-24-2008, 10:17 AM   #601
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Originally Posted by ta_man View Post
I got 3 new SMC 4000 hard case packs today. I checked the cell voltages before doing anything. All were unbalanced:

Pack#1
Cell#1: 3.20V
Cell#2: 3.35V

Pack#2
Cell#1: 3.36V
Cell#2: 3.24V

Pack#3
Cell#1: 3.31V
Cell#2: 3.41V

Is this typical, or should I be concerned?
Those voltages on discharged cells are normal and you should not be concerned. It's best to balance during charge and not do a passive balance (ie match voltages prior to charge).

As you discharge a 2 cell pack, the voltages will start to deviate. The more you discharge, the more it deviates. I've posted this on another thread before and I'll cut and past the response again.

-------------------------------------------------------
I once got into a discussion about cell balancing with the Engineers at a battery manufacturer. They were saying that most of the cell balancers for the RC market do not work correctly. I didn't understand what they meant at first, but after spending months trying to understand how commercial cell balancing chips work - I think I finally get it.

Let's say you have a two cell pack where both cells are fully charged 100%. Even though the manufacturer matches the cells prior to assembly, no two cells are exactly alike. Assume you partially discharge the pack by taking out 1.0 Ah out the pack. Both cells with the same initial voltage will probably be at slightly different voltages during and after the discharge. If you charge and put 1.0 Ah back into the both cells - they both reach 100% charge and 4.20V perfectly.

Now assume the same scenario, where you start with both cells 100% charged and you once again take out 1.0 Ah. This time you attach a balancer that bleeds off current from the higher cell and now the voltages are matched. Now you remove the balancer and recharge the pack. The cell that was brought down by the balancer is now not fully charged and the cell that was at a lower voltage during balancing is now overcharged. The cell balancer actually created a cell mismatch!

The bottom line is that passively balancing cells by forcing a matched voltage of partially charged pack is actually useless.

The balancer should only be used when fully charging the pack. It's meant to bleed off current to specific cell only when any cell reaches over 4.20V/cell. This ensures each cell gets a full charge and no cell gets overcharged.

Checking for cells in/out of balance with a multimeter should only be done when the pack is fully charged.
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Old 04-24-2008, 11:30 AM   #602
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Hello Danny,

Is it ok to discharge the 5000mAh lipo at 30amps. I have an Indi Reactor 30 http://www.integy.com/cgi-bin/webc.cgi/st_sresults.html

can I use this or should I look into something so I can discharge at 35amps.

I just want to stay as close to your methods as possible.

cheerz.

Last edited by Obsidian; 04-24-2008 at 12:02 PM.
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Old 04-24-2008, 10:00 PM   #603
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Originally Posted by linger View Post
Those voltages on discharged cells are normal and you should not be concerned. It's best to balance during charge and not do a passive balance (ie match voltages prior to charge).

As you discharge a 2 cell pack, the voltages will start to deviate. The more you discharge, the more it deviates. I've posted this on another thread before and I'll cut and past the response again.

-------------------------------------------------------
I once got into a discussion about cell balancing with the Engineers at a battery manufacturer. They were saying that most of the cell balancers for the RC market do not work correctly. I didn't understand what they meant at first, but after spending months trying to understand how commercial cell balancing chips work - I think I finally get it.

Let's say you have a two cell pack where both cells are fully charged 100%. Even though the manufacturer matches the cells prior to assembly, no two cells are exactly alike. Assume you partially discharge the pack by taking out 1.0 Ah out the pack. Both cells with the same initial voltage will probably be at slightly different voltages during and after the discharge. If you charge and put 1.0 Ah back into the both cells - they both reach 100% charge and 4.20V perfectly.

Now assume the same scenario, where you start with both cells 100% charged and you once again take out 1.0 Ah. This time you attach a balancer that bleeds off current from the higher cell and now the voltages are matched. Now you remove the balancer and recharge the pack. The cell that was brought down by the balancer is now not fully charged and the cell that was at a lower voltage during balancing is now overcharged. The cell balancer actually created a cell mismatch!

The bottom line is that passively balancing cells by forcing a matched voltage of partially charged pack is actually useless.

The balancer should only be used when fully charging the pack. It's meant to bleed off current to specific cell only when any cell reaches over 4.20V/cell. This ensures each cell gets a full charge and no cell gets overcharged.

Checking for cells in/out of balance with a multimeter should only be done when the pack is fully charged.
Thank you for the excellent explanation.

Do you know of balancers that work the way you describe as "proper"? I have a standalone Hyperion balancer and Hyperion charger with a balancer and they seem to be balancing as the pack is being charged (all throughout the charge process), at least according to the LEDs and the display.
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Old 04-27-2008, 08:56 PM   #604
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Okay, I did a cycle tonight. I raced Saturday. So the packs sat for a day or two without touching them. Pack 1 IR went up as expected. But Pack 2 went down. I'll cycle again tomorrow night and Pack 1 IR should drop back to normal. But I'm curious as to what Pack 2 will do. I do notice run time slowing going down. But that might be due to me charging at 12 amps. I'm gonna go to 8amp charge for racing and see what happens. Plus now I'm starting to heat up my packs after charging. Of course all my cycles are 1C at 4000mAh or 4amps. 35amp discharge with 180seconds cool down for the cycle. Packs are discharged down to 6v before cycle starts. Here's the history so far. Each packs usually get 3 runs on race day. 1~2 cycles during the week. So about 4 or 5 charges a week for each pack.

On the box,
Pack 1;
415 seconds 7.34v
4034 mAh 7.1 IR

Pack 2;
409 seconds 7.35v
3976 mAh 7.2 IR

4/8/08
Pack 1;
422 seconds 7.32v
4102 mAh 7.5 IR

Pack 2;
416 seconds 7.33v
4044 mAh 7.5 IR

4/9/08
Pack 1;
420 seconds 7.34v
4083 mAh 7.2 IR

Pack 2;
416 seconds 7.33v
4044 mAh 7.2 IR

4/13/08
Pack 1;
417 seconds 7.35v
4054 mAh 7.2 IR

Pack 2;
413 seconds 7.35v
4015 mAh 7.1 IR

4/22/08
Pack 1;
416 seconds 7.34v
4044 mAh 7.5 IR

Pack 2;
410 seconds 7.35v
3986 mAh 6.9 IR
Okay, here is tonights cycle after yesterdays trophy race in Arkansas at the Roar Nats track. I ran both packs all day long through practice and the qualifiers and main. Charged mainly at 8amps. But I did do some 12amp charges to get the packs done faster so I could try and heat them up under the sun and some warmers. I would say each pack maybe had 4 or 5 charges yesterday. Of course the cycle was done as normal 4amp or 4000mah rate. 35amp discharge with 180 second cool down. Blah blah blah...

4/27/08
Pack 1;
416 seconds 7.37v
4044 mAh 6.8 IR

Pack 2;
410 seconds 7.36v
3986 mAh 6.9 IR
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Old 04-27-2008, 10:39 PM   #605
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Mile your car did look fast Saturday at the ark race.
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Old 04-28-2008, 12:46 AM   #606
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[QUOTE=JimmyMac;4393907]....Charged mainly at 8amps. But I did do some 12amp charges to get the packs done faster so I could try and heat them up under the sun and some warmers. I would say each pack maybe had 4 or 5 charges yesterday. Of course the cycle was done as normal 4amp or 4000mah rate. 35amp discharge with 180 second cool down. Blah blah blah...


Jimmy what charger you use?
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Old 04-28-2008, 02:17 AM   #607
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Jimmy what charger you use?
GFX.
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Old 04-28-2008, 06:51 AM   #608
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Is there any word on a saddle pack smc lipo ?

cheers
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Old 04-28-2008, 07:06 AM   #609
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JimmyMac...... or anybody
Could you tell me what balancer works with the updated GFX ????
Thank you

Last edited by Lazer Guy; 04-28-2008 at 07:24 AM.
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Old 04-28-2008, 10:26 AM   #610
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Hello Danny,

Is it ok to discharge the 5000mAh lipo at 30amps. I have an Indi Reactor 30 http://www.integy.com/cgi-bin/webc.cgi/st_sresults.html

can I use this or should I look into something so I can discharge at 35amps.

I just want to stay as close to your methods as possible.

cheerz.

Yes you can discharge at 30 amps but make sure to stop the discharge at 6 volts as the Reactor 30 has a 5.4 volt cutoff. An easy way to do this is to hook a voltmeter up while discharging and then unplug the pack when it gets close to 6 volts.
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Old 04-28-2008, 10:31 AM   #611
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Is there any word on a saddle pack smc lipo ?

cheers
Waiting on the prototype to come in and if all looks good we will go to production. The approximate size will in millimeters will be 26H x 46W x 68L.

Originally the capacity was going to be 5200 but the pack would of been over 30mm in height so we decided to retool and make the pack not as tall so it fits under all the topdecks of the current offroad cars. So now the pack will be a 5000/28C.
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Old 04-28-2008, 11:14 AM   #612
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Yes you can discharge at 30 amps but make sure to stop the discharge at 6 volts as the Reactor 30 has a 5.4 volt cutoff. An easy way to do this is to hook a voltmeter up while discharging and then unplug the pack when it gets close to 6 volts.
Danny FYI....you can adjust the cut off on the Reactor 30....inside the case there is an adjustment pot that you can turn up to adjust the voltage cutoff just above 6v and down to about 4.8v from what I have seen with my Reactor 30.....also some of them dont come 100% calibrated to 5.4v and they should be checked if you are using one.
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Old 05-05-2008, 02:04 AM   #613
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i just purchased your 5000 pack.im looking for balancer is the new max amps method balancer any good?
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Old 05-10-2008, 03:59 PM   #614
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anybody out there??
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Old 05-10-2008, 04:03 PM   #615
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i just purchased your 5000 pack.im looking for balancer is the new max amps method balancer any good?
iv just purchased 6 x 4000 smc lipos and a GT Power charger and it works a treat. here is the site http://www.hobbycity.com/hobbycity/s...dProduct=6443#
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