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Author Topic: LiPo C Rating  (Read 2025 times)

Offline Shadow

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LiPo C Rating
« on: November 05, 2011, 08:41:42 PM »
What's the recommended C-rating/Amp Discharge rate for a LiPo to pull a M120 spring?

I've noted that even on a full charge, my 7.4v 1100Mah 20C LiPo doesn't seem to have enough juice to pull the spring.  The motor is fine (Systema Magnum) and acts as if the battery is dead (slight whir/click) and the battery heats up very quickly.

So it's either a bad battery or a weak battery...
« Last Edit: November 05, 2011, 08:51:10 PM by TPA_shadow »
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Offline ThatGuy

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Re: LiPo C Rating
« Reply #1 on: November 05, 2011, 09:47:33 PM »
If the battery is getting hot and there is no short in the wiring the battery does not have enough output.

Try a 2000mah 20c/30c burst   should work fine.

I use 3300 mah 25c/50c burst in my gun runs all day
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Offline axisofoil

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Re: LiPo C Rating
« Reply #2 on: November 05, 2011, 10:12:15 PM »
If you can hit 60 amp peak rates, you should be fine for whatever airsoft needs you have.
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Offline -MAD- SARGE

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Re: LiPo C Rating
« Reply #3 on: November 05, 2011, 10:27:06 PM »
Your battery has a constant discharge rate of 22amps, sounds like the motor requires more amps to pull the gears and spring than the battery can provide.

Are you sure you shimmed it correctly? Also are you using deans connectors or the standard plastic tamiya connector? The standard tamiya connector is only rated for 10amps and they heat up badly and cause a lot of resistance.  I have shot several m120s with my 20C 1200mah wired for deans.   

You can use this formula to figure out what the constant amp discharge rate of batteries should be. 
(C-rating x MAH)/1000 = Amp discharge rate
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Offline Shadow

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Re: LiPo C Rating
« Reply #4 on: November 06, 2011, 09:40:24 AM »
It's a Systema Turbo gearbox with a M120 spring and the Magnum motor.  I'm pretty sure it's shimmed correctly, but I will triple-check just to make sure.

Sounds like I need to pull a Scotty and give it more powa, Capn!
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Offline SLINKEY

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Re: LiPo C Rating
« Reply #5 on: November 06, 2011, 10:35:51 AM »
Magnum motors can short out when they get to certin amperage rates.. I would simply try tossing some rubber washers Under the two allen head screws on the End Bell area. (part with the Bushes, and were the wires connect)

sounds to me like the classic, systema Magnum motor short.

Expeshally if its a Older generation of the magnum motor.

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Offline XavierMace

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Re: LiPo C Rating
« Reply #6 on: November 06, 2011, 11:29:16 PM »
The Magnum can also pull like 60a under load.  That's a pretty low powered battery to be running a Magnum.  I'd also agree on checking for shorts though.
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Offline Shadow

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Re: LiPo C Rating
« Reply #7 on: November 07, 2011, 08:45:29 AM »
Thanks for the info, guys.  Surprisingly, that battery has run the Magnum about 90% of the time.  It's only lately that it hasn't, which means I probably killed the battery in the process.
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Offline Shadow

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Re: LiPo C Rating
« Reply #8 on: November 07, 2011, 12:50:16 PM »
Thoughts on this one?  That's a 55amp output...

http://www.hobbypartz.com/98p-25c-2200-2s1p-2222.html
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Offline deathbydanish

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Re: LiPo C Rating
« Reply #9 on: November 07, 2011, 03:48:51 PM »
How about this one?

http://www.onlybatterypacks.com/showitem.asp?ItemID=12406.78

I've been using that in my L85 and its using a M120 spring as well, the response is very crisp and on full auto it'll empty a mid cap in less than 3 seconds. The only problem is it has a tendency to fry fuses, it shouldn't be a problem if you don't have a fusebox.
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Offline Shadow

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Re: LiPo C Rating
« Reply #10 on: November 07, 2011, 03:51:59 PM »
Quote from: deathbydanish on November 07, 2011, 03:48:51 PM
The only problem is it has a tendency to fry fuses, it shouldn't be a problem if you don't have a fusebox.

I've got an AB mosfet, so it shouldn't be much of an issue.
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Offline ThatGuy

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Re: LiPo C Rating
« Reply #11 on: November 07, 2011, 03:56:26 PM »
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Offline Shadow

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Re: LiPo C Rating
« Reply #12 on: November 07, 2011, 04:06:56 PM »
Thanks, all.  New batteries are on the way and should be here in time for CB2 :)
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