Lipo getting hot quickly

[Pewpewpetie]

Hi all, have an upgraded classic army scarab. It has 13:1 gears, AOE corrected, shimmed very nicely (bevel to pinion), new airnozzle and shs high speed motor, Gun cycles lovely, problem is if I use an 11.1v (has built in mosfet /ETS) the battery gets warm very quickly, be it full auto or semi. Wiring doesn't appear to get hot nor the grip. I've checked for shorts and can't find any. The battery is a nuprol 1450mah 11.1v 30c , when I use a 2000mah 7.4v 25c, battery only gets slightly warm. Problem is, I can't fit the 7.4v 2000mah in the foregrip as it's too big.. anyone have any thoughts on why this is happening

[Adolf Hamster]

the 11.1v has a continuous current rating of 43.5A and the 7.4v is rated for 50A, burst currents might be higher admittedly.

 

bearing in mind the 11.1 will also be getting more draw from the motor, sounds like you might be over-drawing on the 11.1 which isn't good.

 

only fix for that is a bigger (capacity) battery, higher C rating or a gun that draws less juice (slower motor/lower gear ratio)

 

 

what sort of rps are you getting? i'm assuming pretty damn fast to the point that slowing it down a tad might not be the worst plan anyway.

[Asomodai]

SHS high speed is not a good choice for 13:1 gears. That might not be helping with the heat aspect of things. Change over to a high torque. 

Edited August 28, 2021 by Asomodai

[Pewpewpetie]

49 minutes ago, Adolf Hamster said:

the 11.1v has a continuous current rating of 43.5A and the 7.4v is rated for 50A, burst currents might be higher admittedly.

 

bearing in mind the 11.1 will also be getting more draw from the motor, sounds like you might be over-drawing on the 11.1 which isn't good.

 

only fix for that is a bigger (capacity) battery, higher C rating or a gun that draws less juice (slower motor/lower gear ratio)

 

 

what sort of rps are you getting? i'm assuming pretty damn fast to the point that slowing it down a tad might not be the worst plan anyway.

Rps is is around 30, very rarely use full auto as it's set to 3 round burst. I can't really put any other sector gears in it as it has a magnet inside it for the mosfet to detect sector position . Any other way to slow down?

[concretesnail]

As Hamster mentions, it sounds like you are pulling too many amps for that particular battery.

If your battery compartment isn't big enough for the 2000mah 7.5v then you can either change the motor for a higher torque, fewer revs and pull less juice from the pack or use higher c batteries which are smaller but use more of them over the course of the day.

[Adolf Hamster]

6 minutes ago, Pewpewpetie said:

Rps is is around 30, very rarely use full auto as it's set to 3 round burst. I can't really put any other sector gears in it as it has a magnet inside it for the mosfet to detect sector position . Any other way to slow down?

 

pretty much as asomodai says, switch to the ht motor.

[Pewpewpetie]

9 minutes ago, concretesnail said:

As Hamster mentions, it sounds like you are pulling too many amps for that particular battery.

If your battery compartment isn't big enough for the 2000mah 7.5v then you can either change the motor for a higher torque, fewer revs and pull less juice from the pack or use higher c batteries which are smaller but use more of them over the course of the day.

Tomorrow I will put the high torque classic army motor that came with it and see if it stops the battery heat. I'll update tomorrow morning once swapped.

10 minutes ago, concretesnail said:

As Hamster mentions, it sounds like you are pulling too many amps for that particular battery.

If your battery compartment isn't big enough for the 2000mah 7.5v then you can either change the motor for a higher torque, fewer revs and pull less juice from the pack or use higher c batteries which are smaller but use more of them over the course of the day.

The 11.1 is a 30c though, are you suggesting going higher than that

[Adolf Hamster]

27 minutes ago, Pewpewpetie said:

The 11.1 is a 30c though, are you suggesting going higher than that

 

Mah and C rating are both ratings where there's no such thing as overkill.

 

pretty much the only downside to having both numbers as high as possible is the cost, and physical size, of the battery pack.

 

 

[Pewpewpetie]

18 minutes ago, Adolf Hamster said:

 

Mah and C rating are both ratings where there's no such thing as overkill.

 

pretty much the only downside to having both numbers as high as possible is the cost, and physical size, of the battery pack.

 

 

Sorry not great with all the numbers shouldn't the 11.1 1450mah 30c be better then , rather then the 7.4 2000mah 25c?  Sorry if that sounds stupid

[Pewpewpetie]

40 minutes ago, Adolf Hamster said:

 

Mah and C rating are both ratings where there's no such thing as overkill.

 

pretty much the only downside to having both numbers as high as possible is the cost, and physical size, of the battery pack.

 

 

So something like this would be more efficient

[Adolf Hamster]

20 minutes ago, Pewpewpetie said:

Sorry not great with all the numbers shouldn't the 11.1 1450mah 30c be better then , rather then the 7.4 2000mah 25c?  Sorry if that sounds stupid

 

nope, the rated continuous current is the mah divided by 1000, then multiplied by the C rating.

 

1450/1000=1.45*30=43.5A

2000/1000=2*25=50A

 

now often batteries can sustain more in short bursts, sometimes it's even stated (if you see 2 C ratings on a pack that's what it means) but it's a general guide.

 

1 minute ago, Pewpewpetie said:

So something like this would be more efficient

 

 

that's a pretty good example, taking the ratings at face value at least. notice how it even specifies a 100C burst current.

 

however also look at the dimensions- its a literal big battery and has the size to match. needless to say this is a problem if, like your gun, battery compartment space is at a premium. wether or not you're happy to run a fake peq box, or change the stock or some other modification to allow you to run a larger battery is up to you.

 

 

bearing in mind that the overdraw premise is based on the assumption there's nothing wrong with the 2 battery packs you're currently using, you may wish to test in a different gun just to be sure that's not the problem.

 

 

tbh, given you say you're mostly dealing in 3 round burst rather than auto, it would probably be better to simply change the motor to a ht (slower and less amp draw) then make up for any loss in trigger response (aka lock time) with a mosfet that allows precocking (not sure if the existing one does or not)

[Pewpewpetie]

2 minutes ago, Adolf Hamster said:

 

nope, the rated continuous current is the mah divided by 1000, then multiplied by the C rating.

 

1450/1000=1.45*30=43.5A

2000/1000=2*25=50A

 

now often batteries can sustain more in short bursts, sometimes it's even stated (if you see 2 C ratings on a pack that's what it means) but it's a general guide.

 

 

 

that's a pretty good example, taking the ratings at face value at least. notice how it even specifies a 100C burst current.

 

however also look at the dimensions- its a literal big battery and has the size to match. needless to say this is a problem if, like your gun, battery compartment space is at a premium. wether or not you're happy to run a fake peq box, or change the stock or some other modification to allow you to run a larger battery is up to you.

 

 

bearing in mind that the overdraw premise is based on the assumption there's nothing wrong with the 2 battery packs you're currently using, you may wish to test in a different gun just to be sure that's not the problem.

 

 

tbh, given you say you're mostly dealing in 3 round burst rather than auto, it would probably be better to simply change the motor to a ht (slower and less amp draw) then make up for any loss in trigger response (aka lock time) with a mosfet that allows precocking (not sure if the existing one does or not)no mosfet 

No mosfet doesn't have Precocking , I'll order one of the xt high torque 22tpa motors from ak2m4. Hopefully will help. Many thanks. I'll report back tomorrow with outcome of using the classic army high torque( not sure if it really is but that's what's on the sticker)

[Pewpewpetie]

Just updating this thread, I replaced the motor with a rocket 22tpa (with cooling fan) and issue seems to have been resolved. Thanks all for helping