Higher discharge rate for small lipo ?

[martoediefroets]

I noticed that my mini is stalling after a couple of minutes of crawling. This happens every time I use my 350mah lipos. I have 3 of these and it happend to all of them. They loose power at about 7,8V.
When I use a 800mah lipo the problem is gone and it performs well until the cutoff kicks in at 6.6V.
Both the 350mah and 800mah lipos are 25C discharge rated.
As setup I run a Sidewinder micro with an Insane 370 motor.
All on 2S.
Could it be that it needs a higher discharge rate when using small lipos?

[T3rry]

did you measure the individual cells? i know i have had a couple small batts that would discharge only 1 of the 3 cells and then hit cutoff very prematurely.

[martoediefroets]

I did measure all the cells(3 lipopacks) and they are all evenly discharged.

[WAM]

The voltages you're mentioning are open-circuit volts with no current drawing. If you measured the battery voltage during the stall, you'd probably find it's down around the esc cut-off.

Battery capacity times discharge rate equals the max current that can be delivered (everything perfect). When you attempt to draw current close to max available, you get higher internal voltage drops. Small batteries deliver smaller amps, so yes...you probably need higher discharge rates. I've had no brown-outs with ThunderPower 325/65C and others have had good luck with TP 325/45C.

Other possibility is servo is drawing so much power from your esc bec (if that's what you're using) that not enough is left over to run the truck. An external bec might help that.

FWIW, I've been playing with two 350/20C batteries in parallel. They're really tiny so package nicely. Together they act like a 700mah battery.

[Charlie-III]

Originally Posted by WAM

The voltages you're mentioning are open-circuit volts with no current drawing. If you measured the battery voltage during the stall, you'd probably find it's down around the esc cut-off.

Battery capacity times discharge rate equals the max current that can be delivered (everything perfect). When you attempt to draw current close to max available, you get higher internal voltage drops. Small batteries deliver smaller amps, so yes...you probably need higher discharge rates. I've had no brown-outs with ThunderPower 325/65C and others have had good luck with TP 325/45C.

Other possibility is servo is drawing so much power from your esc bec (if that's what you're using) that not enough is left over to run the truck. An external bec might help that.

FWIW, I've been playing with two 350/20C batteries in parallel. They're really tiny so package nicely. Together they act like a 700mah battery.

+1.

The lower the mah, the higher the "C" to get the same power without brownout/hitting LVC.

Some people running 5000mah packs in scalers/bashers can get away with 20C packs.....not the same for 325mah packs.
Since your larger mah packs are more than double the capacity of your smaller packs, they have a lot more power they can produce, thus no issue even though they have the same "C" rating.
I believe ThunderPower makes a 65C rated pack in the same mah......CheapBatteryPacks - Thunder Power 325mah 2s/7.4v 65C G6. CheapBatteryPacks carries ThunderPower.

[martoediefroets]

Originally Posted by WAM

The voltages you're mentioning are open-circuit volts with no current drawing. If you measured the battery voltage during the stall, you'd probably find it's down around the esc cut-off.

Battery capacity times discharge rate equals the max current that can be delivered (everything perfect). When you attempt to draw current close to max available, you get higher internal voltage drops. Small batteries deliver smaller amps, so yes...you probably need higher discharge rates. I've had no brown-outs with ThunderPower 325/65C and others have had good luck with TP 325/45C.

Other possibility is servo is drawing so much power from your esc bec (if that's what you're using) that not enough is left over to run the truck. An external bec might help that.

FWIW, I've been playing with two 350/20C batteries in parallel. They're really tiny so package nicely. Together they act like a 700mah battery.

Very clear and helpfull
I will get some lipo with higher rating and set the old ones up in a parallel pack.