amp pull difference for 2S and 3S
 

hi
im wondering what difference in amp pull it would be for a brushless motor 3400Kv
with the current prop (30mm)i have on its pulling just enough to cut my ESC out! 40 amp peak for 10 secs
any smaller though and its not pushing the boat!
the lipo is a 3S 2200mah 20-30c so plenty of power but maybe to much

would dropping the volts to 2S -7.4v make a big difference?
if motor Kv is high enough 11.v is approx 37,000ish unloaded
7.4 gives approx 25,000 unloaded

would i still be able to use the same prop or would it then be able to take a larger prop

please help b4 i kill another esc!

i dont have a 7.4 pack to test with- if it would make the difference i will purchase one!

thanks
Graham

RE: amp pull difference for 2S and 3S
 

I would make a big difference. You can expect somewhere between 40 to 60 percent less current by using the 2s pack. Expect a big decrease in power also.

RE: amp pull difference for 2S and 3S
 

does dropping the volts just work out the same as only using 2/3rds throttle?? or is it not that simple?
if it is that simple then i will have to go the upgraded ESC and motor
its just that i see so many boats that seem to run on 6 or 7 cells(7.2-8.4v) and they dont seem to have a problem
maybe i just need to go up to 540 BL feigao motors and honking great big 120 amp ESC! lol
its the matching up of motor to boat size that seems to stump me!

RE: amp pull difference for 2S and 3S
 

According to the astroflight handbook 2/3 throttle will not nessarily drop the load at the motor. Using 2/3 of the cells is different though.

RE: amp pull difference for 2S and 3S
 

How big is the boat? a 2200mah battery even at 20c isnt a powerhouse for a large boat. a 7.4v battery would make a big difference in amp draw and probably run the boat better. What size motor is it?

RE: amp pull difference for 2S and 3S
 

i have 2 boats both with similar motors in them
one is a 19" deep vee-scaled from the gas mono plans- made from 1/16 ply- so quite light
the other was a depron rigger approx 16oz weight
the motors are decieving though -the size they staed was can size NOT stator size
measuring the stator gives me only a 20mm x 15mm
my limited knowledge -now!- thinks that is quite small even for the boats i have them in??
any help on prop sizes for motors that size would be handy!

cheers for the help so far!

speed 3-
mm. i do have a BIG 7.2 nicd brick pack i could try! if it doesnt sink the boat from the weight!!lol

RE: amp pull difference for 2S and 3S
 

i have a 14" depron rigger and run a 30A esc with a 3s lipo 20C rating. the motor is a 400df brushless pushing a 32mm de-tongued prop. handles well so far, i have had a smaller C rating batt in there & it couldn't hold max RPM for more than a few seconds before the prop dropped off RPM noticeably. i upped the C rating and it now holds RPM well, but that isn't the problem you had (reverse). this is in a 13 ounce rigger. so far i have been doing runs of about 2 - 3 minutes then bringing it in as i've just started setting it up, and temps have all been cool so far.

not sure if this helps, but i hope it does.

RE: amp pull difference for 2S and 3S
 

thanks Dicko - im guessing thats the renegade rigger you have?
im trying to find out what props i can run on mine!
i cant get ANY props from shops near me i have to order them all off of the net- can get expensive when you dont know where to start!
the octura plastic props only come in X431- thats my ideal size to start i think -only my shaft is 3/16! doh!!
im hoping if i drop the volts then i can size the prop up a bit- my mono seems to cavitate a long time b4 it moves and thats a 2035 cut down to 30mm
i think im gonna change the motor to a feigao 380 or similar size coz future boats will be a bit bigger than micro size
and then more people have the motors to offer advice on!:D
holiday time for me now! and then back to boats in a week!