Hump Battery Discharge Current / Servo Running & Stall Current

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RicoBanderez

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Hi all,

I'm trying to understand what battery I should pair to the servo's I'm planning on purchasing.

The servos I'm looking to run in my losi 8ight 4.0 are Savox 1270/1271.
  • Running Current (no load): 150mA @7.4V
  • Stall Current (at locked): 6800mA @7.4V

The battery that I'm planning to run is a Dynamite 7.4V 2000mAh 2S 5C LiPo
  • Maximum Continuous Discharge Current: 10A
  • Normal/Standard Charge Current: 2A

The thing that I can't understand is the servo's mention a "running and stall" current while the battery as a max. continuous discharge and standard discharge current but I can't make sense of it .. will the battery be to powerful for the servos and just blow them? In my (simple) mind, the voltages work so that's good I don't want to buy servo's that draw too much (or too little) current and end up draining the battery in 5 minutes or blowing up.

I'm don't really understand the electrical side much so I'm just looking to gain some confidence that this battery and servo pairing is going to work well.

The battery has been chosen as it sits nicely into the battery compartment of my car, the servo's have been chosen because they are within (ish) budget and are 7.4 v.

I was originally looking at a 6v NiMH hump pack and 1258 savox servos but I've not been able to find any 6v battery that'll fit into the compartment and being the stubborn person I am, I would like it all to fit nicely together.

Looking forward to feedback thanks all

Rich
 
looking at the numbers, it would be .150 amps at running current, that's its draw normally, and the stall current should be when its fully to one side up against the mechanical stopping device in the gears, and given that it is no longer moving the current goes straight through, sort of like a lightbulb. so it is quite a bit higher, why it is 6.8 Amps draw.
that battery being a 5 amp continuous with a spike rating of 10 Amp in my mind would be safe to not try to over-draw the battery current.
i would really like to have someone reinforce/confirm this though.
 
For what it's worth, a battery doesn't "push" anything. Current is pulled out. A device will only pull as much as it possibly can. If the battery doesn't have enough, then it will die/fail.

Stall current is when the servo is physically stopped anywhere along the path of travel. It means the motor cannot spin any further and it's pulling as many amps as it ever would. Something you should be mindful of when setting up EPA's. You never want a servo to be stopped mechanically by the linkage. With the tires in the air, the EPA's should be set so that the servo can move them from side to side as far as they can go before they stop due to contact with something on the chassis.

If your running two of those servos, then you are going to possibly pull 13.6 amps at some point. Braking pulls a lot of amps as it's putting a heavy load on the servo. A lot of times, when racing, your going to be leaning on the brakes while turning into a corner, which means both servos are going to be asking for a lot of current at the same time. It may not be the full 6.8A, but odds are, it will be close to 10A for a few seconds at a time. I would assume you would want something that has a nominal current of at least 10A with a peak that's 20A to be on the safe side.

Something like this may be better:
https://www.venompower.com/collecti...v-receiver-transmitter-flat-pack-lipo-battery

Continuous, 5C (12.4 Amps), max burst 10C (24 Amps).

Or this:
https://www.venompower.com/collecti...v-receiver-transmitter-hump-pack-lipo-battery

11 Amps continuous, 21 Amps max burst.

EDIT:
Man, I'm an idiot. I read your initial comment that it was max burst at 10A, not max continuous.

Carry on. You should be fine with that.
 
Last edited:
thank you for clarifying that Olds, i need to understand this kind of stuff better o_O
 
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