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These batts are giving me a headache!!

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Old 10-06-2009, 12:42 AM
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sweetrex
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Default These batts are giving me a headache!!

I need a battery pack for my GP to EP conversion. The plane is an 8lb scale model of a Lancair Legacy. I've got it all set up with a KMS motor (4120 .60 size equivilent), CC HV85 ESC and as of right now, I'm running an 8s 3200mAh pack (two 4s packs in series). When I static tested the system, the ESC was cutting out somewhere around 3/4 throttle. The manual says it could be a high current draw. So here I go again...I thought I had the total package with an incredible battery but as it turns out I think I'm screwed again. So what size pack is the answer? How can I know if the pack is too whimpy for my set up? Of course the motor's spinning at 100 mph and there's quite a pull on the plane. I think at even 1/2 throttle it's gonna move pretty good. Should I do a timed test at 1/2 throttle and see how much time I get from the packs and then if the time is sufficient just learn to fly at 1/2 throttle? or should I drop another $300-$400 on a brand new pack with more mAh? or can I go down to a 6s pack with more mAh and still see enough power to fly the plane? So many questions...
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Old 10-06-2009, 07:04 AM
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Default RE: These batts are giving me a headache!!

If your esc is cutting out you could be over amping it. Meaning your pulling more than 85 amps. The other issue you have is if your running 20C 3200's they are only good for 64 amps. I would say right now you need to invest in a watt meter to see what the motor is pulling for draw.

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Old 10-06-2009, 10:13 AM
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Default RE: These batts are giving me a headache!!

I do have a Watt meter. It's pulling somewhere around 60A when it cuts out so it makes sense since the batteries are only 20C. So what are my options in batteries? I don't want to go over 8s as I'm already over the manufacturers recommended 6s for the motor.
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Old 10-06-2009, 10:33 AM
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Default RE: These batts are giving me a headache!!

Well right there you have an issue. If your running 8 cells on a 6S rated motor you'll fry the motor eventually. Dropping to a lower volatge is going to increase amp draw as well. What is the max ratings on the motor you have? I like to use a pack that will surpass the max rates for a specific motor that way you have a little cushion to work with. In your case a pack that can handle at least 80 amps. So look at something like a 20C 4000 or higher, Here's our 4200 pack: http://www.maxamps.com/Lipo-4200-111-Flight-Pack.htm that pack is what I use in my 5S powered Hyperion Extra 260.

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Old 10-06-2009, 10:42 AM
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Default RE: These batts are giving me a headache!!

I'm not sue on the motor specs. I'll have to check the box when I get home. I think it was 6s max.
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Old 10-06-2009, 10:51 AM
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Default RE: These batts are giving me a headache!!

Jason, You said that a 20C pack can only handle about 65A max draw. What can a 30C pack handle and how do you figure that out?
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Old 10-06-2009, 11:00 AM
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Default RE: These batts are giving me a headache!!

take the mAh and multiply it by the C rate so 20C X 3200= 64 amps.

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