little help please with fe heat

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delowen

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Feb 22, 2018
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4
hi if I run two identical riggers one with 2150 kv motor with 6s and a 547 prop and the other with a 1650 kv 6s same prop can I expect one to pull more amps and run hot!!! (which one draws most ?) If I change the 2150kv to 4s will that draw less amps with same prop etc.. just as my ohms law tells me lower voltage means higher amps? but it seems to be higher kv motors run on less volts ? any views greatly welcomed ! thanks all
 

longballlumber

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Apr 17, 2003
Messages
1,376
Lots of variables in your questions, but generally speaking the answer is; yes. With all things being equal; your 2150kv motor will draw more amps than your 1650kv motor using the same 6S battery.

Your 1650kv motor is on the higher side of 6S voltage (for my liking). I would suggest 1200kv-1500kv range on 6S.

Your 2150kv motor is right in the sweet spot for 4S voltage. I typically suggest 1800kv-2200kv range for 4S.

2150kv on 25.2v = 54,180 unloaded rpm. That is WAY TOO HIGH
1650kv on 25.2v = 41,580 unloaded rpm. Still on the high side, but doable if you have a controller to handle it and your boat is set up correctly with the properly sized prop.

2150kv on 16.8v = 36,120 unloaded rpm
1650kv on 16.8v = 27,720 unloaded rpm

Again, generally speaking, HIGH RPM will increase amp draw. All of the setups you reference are high amp draw setups and will require a equally capable speed control.
 

delowen

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Feb 22, 2018
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4
Lots of variables in your questions, but generally speaking the answer is; yes. With all things being equal; your 2150kv motor will draw more amps than your 1650kv motor using the same 6S battery.

Your 1650kv motor is on the higher side of 6S voltage (for my liking). I would suggest 1200kv-1500kv range on 6S.

Your 2150kv motor is right in the sweet spot for 4S voltage. I typically suggest 1800kv-2200kv range for 4S.

2150kv on 25.2v = 54,180 unloaded rpm. That is WAY TOO HIGH
1650kv on 25.2v = 41,580 unloaded rpm. Still on the high side, but doable if you have a controller to handle it and your boat is set up correctly with the properly sized prop.

2150kv on 16.8v = 36,120 unloaded rpm
1650kv on 16.8v = 27,720 unloaded rpm

Again, generally speaking, HIGH RPM will increase amp draw. All of the setups you reference are high amp draw setups and will require a equally capable speed control.
many thanks for the reply I am using a ZTW 200a water cooled contol connections are all xt90 and 12awg wires. for both 4s and 6s motors are sss 4092 just for ref many thanks
 

HTV Boats

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Nov 8, 2006
Messages
2,445
I generally use lower volts for Kv to RPM no load. Looking at some save data logging a 4S started at 16.7v and during the 23 seconds of full throttle voltage was 13.8 to 14.1 under load. Even at that the actual RPM was about 20% lower. My 33000 no load was 27000 on Castle data.
RPM can vary with prop load.

As for heat it goes hand in hand with amps and amps are increase with prop load. If you went with 6S and switched from 2150 to 1650 kv using the same prop amps go way down as does speed. You could get the speed back with more prop but the amps and heat come back up. The trick here is find the prop that pushes the boat as you want and keeping the amps in check. Bear in mind attaining the same speed with higher KV's the prop pitch and diameter affect heat faster. Lower KV's allow a wider prop selection.

Now for a 6S rigger and 6 lap or general running I agree with Mike on lower KV 1200-1500 range. I have tested a lot of 6S riggers with 1250 to 2000 kv and I feel 1600 is too high for heat racing. Especially with a 4092. A 547 may work with 1650Kv but not 2150. The type of hull your using size and weight factor in. A large hull going down to 4S to may lose more speed than you want.
What kind of speeds and run times are you looking for? What size is your boat?
Mic
 

delowen

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Joined
Feb 22, 2018
Messages
4
HTV thanks for reply my rigger is around 37in long tub is tad under 4 in wide here is a video of it running with 2150 6s and m series 47mm dia 2 blade. I had no data but run was HOT and had melted one connection on a xt90 12awg connection no puffed battery or burnt out motor or speedy. thanks for your input (video is first time on the water)
 

HTV Boats

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Nov 8, 2006
Messages
2,445
Your xt90's are the fuse in your system. The melting is telling you something. I would suggest going to 5.5 or 6.5mm bullets. That won't cure the excess heat that will eventually show up elsewhere. Without a data logger your best bet is measure motor and ESC temps immediately after your run. Also check your cell voltages after a run. Try to stay above 3.75v per cell. Adjust your run times accordingly. A 200 amp controller is marginal with a 4092 size motor so reducing load with prop or less KV's which is kind of just lower gearing. The hard part of FE is matching components in the system. Test and monitor.
Your boat looks pretty good on the water so have fun with it.
Mic
 

J.J. Horvath

Active Member
Joined
May 29, 2019
Messages
30
The issue is the battery connectors (xt90’s) rated at 90A on a setup that can pull over 200A peak. Properly size motor connectors as well to reduce resistance.

I successfully race the TP 4092 -1650kv, seal 200A, on 6S, with ABC H-7 or 1914. Does low 70’s mph and only requires a single 6S -5000mah pack.

Just make short runs until you refine the boats setup, otherwise it will just get hot and pull extra current.
 

delowen

New Member
Joined
Feb 22, 2018
Messages
4
The issue is the battery connectors (xt90’s) rated at 90A on a setup that can pull over 200A peak. Properly size motor connectors as well to reduce resistance.

I successfully race the TP 4092 -1650kv, seal 200A, on 6S, with ABC H-7 or 1914. Does low 70’s mph and only requires a single 6S -5000mah pack.

Just make short runs until you refine the boats setup, otherwise it will just get hot and pull extra current.
what alternative to the xt90? thanks
 

Grimracer

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Joined
Dec 27, 2001
Messages
8,800
I (we) did a bunch of testing back in the Hobbico days and the best you can do.. if your connectors are yellow copper.. get the BIGGEST YOU CAN!

Because if your connectors are yellow copper its ALL ABOUT large surface area and heat dissipation..

Grim
 
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