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Old Oct 16, 2003, 02:15 PM
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Braking in Nimh battery packs.

Just wondering what the procedure is and if you guys fly with brand new packs? I'm having a problem with the low volt cutoff killing the prop while the battery has plenty of juice left and am wondering if new batteries are the culpret?

-Dujara-
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Old Oct 16, 2003, 03:14 PM
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What size batteries do you have, and what current are you drawing from them? If your pack can't provide what your motor demands your 'voltage under load' will plummet to below the limits of your LVC and your ESC will quit.

Did you slow charge/cycle your pack [@ C/10] several times before using it in the plane?

Give us the info, and we may be able to pinpoint the cause of the problem.

Cheers, Phil
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Old Oct 16, 2003, 06:07 PM
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Quote:
Originally posted by Dr Kiwi
What size batteries do you have, and what current are you drawing from them? If your pack can't provide what your motor demands your 'voltage under load' will plummet to below the limits of your LVC and your ESC will quit.

Did you slow charge/cycle your pack [@ C/10] several times before using it in the plane?

Give us the info, and we may be able to pinpoint the cause of the problem.

Cheers, Phil
The batteries that I've had this happen with are 7.2V 230mah nicd, 8.4V 750mah nimh and a 9.6V 750 mah nimh and the motor is the standard 300, not 350, that comes with the Slow Stick.

No I didn't slow charge/cycle...I have the GWS MC-2002 charger and the peak charger that came with my Aerobird. C/10 is that 1/10 of an amp, dunno if my MC-2002 even goes that low? I'm not the sharpest knife when it comes to batteries and chargers.

Thanks much for your help!

-Dujara-
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Old Oct 16, 2003, 07:35 PM
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Hi Dujara

I think we have the answer! Your packs are way too small to provide the current draw your 300C is requesting.

I'll bet those 230's are AAA or smaller, and able to supply no more than 3-4A. The 750 NiMh are probably AAA too, and incapable of supplying any more than 6A. Under load they are quickly reaching the LVC limit of 4.7v or so.

What you need for a Slow Stick are 7-8 cell KAN 650/1050 NiMh packs which can readily deliver the 8-10A reqired by your 300C, for most of the potential pack capacity, without dropping their voltage anywhere near the LVC cut-off.

As far as C/10 goes - that is the recommended charge rate for "running-in" new packs (capacity in mAh divided by 10) for 10-14hrs [Charging is not 100% efficient, so it takes more than 10hrs to fill up the pack at C/10]. In the case of KAN 650's that is 65mA, for 1050's, 105mA and so on. Your MC 2002 isn't capable of supplying such low currents - you need an LiPoly capable GP Triton [to 50mA], FMA Supernova [to 100mA], or, best, an ACE DDVC [to 5mA] charger to provide these low break-in charges.

Good luck, Phil
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Old Oct 16, 2003, 07:51 PM
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An undercharged cell in a pack can make the pack un-useable. Say you get 7 cells that are 80% charged and one cell that is 10% charged. You put it on the charger and the 7 cells take 20% more energy bringing them up to 100% and then the charger see's enough of a peak to say "full". But the other cell is only 30% charged so it runs out of juice quickly and makes the pack look bad. That's why it is good practice to charge them at 1/10C for 16 hours prior to use. That should bring all cells up to 100% without hurting the high cells too much.

But like they have said, the KAN cells would work much better.
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Old Oct 16, 2003, 08:17 PM
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Where do you guys purchase your batteries?

-Dujara-
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Old Oct 16, 2003, 08:23 PM
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Eugene, Oregon, United States
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Quote:
Originally posted by Dujara
Where do you guys purchase your batteries?

-Dujara-
Try www.cheapbatterypacks.com
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Old Oct 16, 2003, 09:21 PM
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Quote:
Originally posted by Dr Kiwi
Hi Dujara

I think we have the answer! Your packs are way too small to provide the current draw your 300C is requesting.

I'll bet those 230's are AAA or smaller, and able to supply no more than 3-4A. The 750 NiMh are probably AAA too, and incapable of supplying any more than 6A. Under load they are quickly reaching the LVC limit of 4.7v or so.

What you need for a Slow Stick are 7-8 cell KAN 650/1050 NiMh packs which can readily deliver the 8-10A reqired by your 300C, for most of the potential pack capacity, without dropping their voltage anywhere near the LVC cut-off.

As far as C/10 goes - that is the recommended charge rate for "running-in" new packs (capacity in mAh divided by 10) for 10-14hrs [Charging is not 100% efficient, so it takes more than 10hrs to fill up the pack at C/10]. In the case of KAN 650's that is 65mA, for 1050's, 105mA and so on. Your MC 2002 isn't capable of supplying such low currents - you need an LiPoly capable GP Triton [to 50mA], FMA Supernova [to 100mA], or, best, an ACE DDVC [to 5mA] charger to provide these low break-in charges.

Good luck, Phil
For a foam plain using a GWS-300C and 12 x 6 prop what KAN packs do I get? Cheapbatterypacks shows

6 cell, 7 cell, and 8 cell KAN all 1050, but increasing voltage, and weight. :-(

KAN 1050 7- 2/3A Cells. (8.4volts) 5.6 oz.

KAN 1050 8- 2/3A Cells. (9.6volts) 6.4 oz.

Which one do I really want? I was looking at 8x720mah nimh but I cannot find a posted weight on the 8x720.

Thanks,

Scott
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Old Oct 16, 2003, 09:32 PM
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Eugene, Oregon, United States
Joined Sep 2001
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Quote:
Originally posted by dreslism
For a foam plain using a GWS-300C and 12 x 6 prop what KAN packs do I get? Cheapbatterypacks shows

6 cell, 7 cell, and 8 cell KAN all 1050, but increasing voltage, and weight. :-(

KAN 1050 7- 2/3A Cells. (8.4volts) 5.6 oz.

KAN 1050 8- 2/3A Cells. (9.6volts) 6.4 oz.

Which one do I really want? I was looking at 8x720mah nimh but I cannot find a posted weight on the 8x720.

Thanks,

Scott
Scott,
You want the 1050 7 cell packs as the 8 cell packs will burn out the motor much quicker as the KAN's produce so much power! The 6 cell packs are too wimpy! The SS won't even know they are on there weight wise!
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Old Oct 16, 2003, 09:37 PM
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Weight of 8x720AAA is 104g. 8x800 5/4AAA is 112g, 7x1050KAN is 158g, 8x1050KAN is 180g. From various posts I've seen from guys using the 12x6, it seems you can use the 8-cell 1050KAN without unduly shortening motor life [obviously your motor will be less stressed on 7-cells, but your power will be down a bit] - your choice!

Cheers, Phil
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Old Oct 16, 2003, 09:44 PM
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Eugene, Oregon, United States
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Quote:
Originally posted by Dr Kiwi
Weight of 8x720AAA is 104g. 8x800 5/4AAA is 112g, 7x1050KAN is 158g, 8x1050KAN is 180g. From various posts I've seen from guys using the 12x6, it seems you can use the 8-cell 1050KAN without unduly shortening motor life [obviously your motor will be less stressed on 7-cells, but your power will be down a bit] - your choice!

Cheers, Phil
Phil,
There have been several posts that the 8 cell KAN packs have burned out the 300s quickly! The 800's and 720 8 cell packs can not come close to producing the amps the KAN's do and the reason you can (and I have) gotten away with using the 8 cell 720 and 800 packs is the voltage with the 12 X 6 prop drops off rapidly and the motor isn't as stressed however the battery packs have shorter lives as they get very hot (over the recommended 104 degrees)
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Old Oct 16, 2003, 10:14 PM
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Elk Grove, CA
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boomer is right again.

I got many flights on the stock motor out of 7-cell 750 mAh GDH (unknown maker green colored cells) packs. As soon as I went to the 8 cell 1050 KAN's and 8 cell CheapBatteryPack.com 1800's, even with a heat sink on the motor, I started smoking 300C's left and right. The SS flys real well on 8 cells, but the motors don't last (like 4 hours max). I am going to try a new 350C since that should last longer, at least long enough for Santa to bring me a brushless .

FoamCrusher
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Old Oct 16, 2003, 10:41 PM
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I bow to the voices of experience - the only KAN cells I've dared use on my SS are 7-cell KAN 950, but I had thought others had got away with 8!

Cheers, Phil
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Old Oct 17, 2003, 10:02 AM
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The CBP 650 2/3rds AA's are a nice combo of hi power in a light package. they can handle 9~10 amp draws without dropping voltage and also stay cool doing it. They do have a shorter duration though.
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Old Oct 17, 2003, 12:20 PM
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Quote:
Originally posted by FoamCrusher
boomer is right again.

I got many flights on the stock motor out of 7-cell 750 mAh GDH (unknown maker green colored cells) packs. As soon as I went to the 8 cell 1050 KAN's and 8 cell CheapBatteryPack.com 1800's, even with a heat sink on the motor, I started smoking 300C's left and right. The SS flys real well on 8 cells, but the motors don't last (like 4 hours max). I am going to try a new 350C since that should last longer, at least long enough for Santa to bring me a brushless .

FoamCrusher
I'm really interested in finding out how the 350 handles the 8 cell packs....keep us posted ok?

-Dujara-
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