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Use a drill batery for RC boat?

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Use a drill batery for RC boat?

Old 06-15-2017, 06:00 AM
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Originally Posted by mathieu2400
The maximum current I can draw is 10C * 5000mAh = 50 Ampere.
(that is higher than the 42 Amps my motor can draw max, but wouldn't it break the motor?
No. Batteries don't determine the current draw, they only provide voltage and the load determines the current draw. If the load tries to draw more current than the battery is rated for, that can damage the battery. 10C is a pretty low rating though, I'd imagine pretty much any 3S pack with a worthwhile capacity should easily meet the requirements.
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Old 06-15-2017, 06:24 AM
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Originally Posted by gigaplex
No. Batteries don't determine the current draw, they only provide voltage and the load determines the current draw. If the load tries to draw more current than the battery is rated for, that can damage the battery. 10C is a pretty low rating though, I'd imagine pretty much any 3S pack with a worthwhile capacity should easily meet the requirements.
Oh I see, thanks. More and more information from the depths of my brain from school is coming to my mind.. Sorry for the eventual stupid questions.

The way I see it: the ESC is the component that decides what my load will be and how much Amps is going to go through my motor.

Do you know how other RC hobbyists make sure the ESC doesn't try to draw more current than the battery is rated for (suppose the C-value is low) and also make sure that the drawed current doesn't go above a specific Amps I want to set manually?

Suppose I have a battery with a specific load and can support a maximum draw of current X.
If I wanted the ESC to only draw current between a range of 0 Amps and X/2 Amps, how do I manage that with my ESC? Is it programmable to set those limits ?

If that's possible, I could be careful and try the drill battery and try out a low currentdraw.

Last edited by mathieu2400; 06-15-2017 at 06:39 AM.
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Old 06-15-2017, 09:10 AM
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Can you even get 10C Lipo's any longer? With that said I ran a 29" deep-vee fast electric on 5s2P LiFe cells out of a Dewalt drill pack or 5000mah 4S Lipo's. Even with the extra cell the A123 cells did not have the punch of the lipo's but other then the slightly lower performance they worked great. LiFe cells are pretty darn bullet proof and not a bad way to go.

Cheers,
Jim
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Old 06-15-2017, 09:21 AM
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Originally Posted by mathieu2400
Oh I see, thanks. More and more information from the depths of my brain from school is coming to my mind.. Sorry for the eventual stupid questions.

The way I see it: the ESC is the component that decides what my load will be and how much Amps is going to go through my motor.

Do you know how other RC hobbyists make sure the ESC doesn't try to draw more current than the battery is rated for (suppose the C-value is low) and also make sure that the drawed current doesn't go above a specific Amps I want to set manually?

Suppose I have a battery with a specific load and can support a maximum draw of current X.
If I wanted the ESC to only draw current between a range of 0 Amps and X/2 Amps, how do I manage that with my ESC? Is it programmable to set those limits ?

If that's possible, I could be careful and try the drill battery and try out a low currentdraw.
Someone can correct me if I'm wrong, but I believe ESCs are very high tech voltage regulators. The motor is the consumer of electricity and where the amp draw comes from. At wide open the ESC is essentially allowing the motor to take all it wants from the battery. If the motor tries to draw more than the ESC or battery can handle the one or the other fails, sometimes spectacularly. For land based RCs, gearing up or down will increase or decrease the load as well. I believe altering the propeller pitch for boats will have the same impact unless there is a transmission in boats too.

As for restricting or saving electronics and wiring from too much current, that is the job of fuses or circuit breakers which aren't usually used in RC land.
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Old 06-15-2017, 11:11 AM
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@jkaetz

Ok I get it
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Old 06-15-2017, 11:22 AM
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Originally Posted by jkaetz
Someone can correct me if I'm wrong, but I believe ESCs are very high tech voltage regulators. The motor is the consumer of electricity and where the amp draw comes from. At wide open the ESC is essentially allowing the motor to take all it wants from the battery. If the motor tries to draw more than the ESC or battery can handle the one or the other fails, sometimes spectacularly. For land based RCs, gearing up or down will increase or decrease the load as well. I believe altering the propeller pitch for boats will have the same impact unless there is a transmission in boats too.

As for restricting or saving electronics and wiring from too much current, that is the job of fuses or circuit breakers which aren't usually used in RC land.
One question more:

I'm a little bit confused about the Specs of my motor.
Here are the specs:
Max Voltage: 13v
Max current: 42 amps
Watts: 550
Resistance: 0.0155 Ohms

Which says that the ESC can allow a maximum voltage of 13V over the motor.
But the resistance of the motor is 0.0155 Ohms, and if I put 13V over the motor, the current through the motor is 838 Amps, how come that the maximum Amps in the specs is 42 Amps ??

Maybe the resistance isn't accurate or isn't the resistance of the motor itself?
hobbyking.com/en_us/turnigy-trackstar-1-10-10t-3900kv-brushless.html?___store=en_us
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Old 06-15-2017, 02:46 PM
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Originally Posted by mathieu2400
One question more:

I'm a little bit confused about the Specs of my motor.
Here are the specs:
Max Voltage: 13v
Max current: 42 amps
Watts: 550
Resistance: 0.0155 Ohms

Which says that the ESC can allow a maximum voltage of 13V over the motor.
But the resistance of the motor is 0.0155 Ohms, and if I put 13V over the motor, the current through the motor is 838 Amps, how come that the maximum Amps in the specs is 42 Amps ??

Maybe the resistance isn't accurate or isn't the resistance of the motor itself?
hobbyking.com/en_us/turnigy-trackstar-1-10-10t-3900kv-brushless.html?___store=en_us
When the motor spins it generates a back EMF. This will reduce the current that flows through it. You can't think of them as an ohmic load. That resistance rating is just the properties of the stator.
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Old 06-16-2017, 12:56 AM
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Originally Posted by gigaplex
When the motor spins it generates a back EMF. This will reduce the current that flows through it. You can't think of them as an ohmic load. That resistance rating is just the properties of the stator.
Ah yes, I see, totally forgot about it.

Than how do I interpret these max Voltage and max current values of 13V and 42 Amps?

I found this information on this website: http://fpvlab.com/forums/showthread....-rating/page2&

I think this is good information:

"it's not all technical. i think the max is probably more of a recommendation so that the guys that don't really know what they're doing can't get into too much trouble with the props that are typically used for that motor. sure you can use really high voltage as long as you put a small enough prop to keep the amps down. but as Bruno suggested this only works to a certain point, and eventually even at no load, the high rpm will just destroy the bearings or throw a magnet. the typical user probably won't bother to check to make sure he's still below the max wattage. the motor manufacturer is just trying to cover their ass, and they can easily do that by specifying a "max voltage." you can certainly go over that if you know what you're doing.

add to this the fact that some of the online retailers (especially chinese ebay sellers) just regurgitate the text they found somewhere and don't even know what it means."

Last edited by mathieu2400; 06-16-2017 at 01:18 AM.
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Old 06-16-2017, 01:31 AM
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Originally Posted by mathieu2400
Ah yes, I see, totally forgot about it.

Than how do I interpret these max Voltage and max current values of 13V and 42 Amps?

I found this information on this website: Why do brushless motors have a max voltage rating? - Page 2

I think this is good information:

"it's not all technical. i think the max is probably more of a recommendation so that the guys that don't really know what they're doing can't get into too much trouble with the props that are typically used for that motor. sure you can use really high voltage as long as you put a small enough prop to keep the amps down. but as Bruno suggested this only works to a certain point, and eventually even at no load, the high rpm will just destroy the bearings or throw a magnet. the typical user probably won't bother to check to make sure he's still below the max wattage. the motor manufacturer is just trying to cover their ass, and they can easily do that by specifying a "max voltage." you can certainly go over that if you know what you're doing.

add to this the fact that some of the online retailers (especially chinese ebay sellers) just regurgitate the text they found somewhere and don't even know what it means."
You've already used the voltage rating to select an appropriate battery voltage. For current... again that's basically that's just a rough guideline to ensure you select an appropriate battery. Your load, in this case propeller size/type/pitch, is going to be the determining factor of what your actual load will be, and thus what current will actually be drawn. Try to forget about the ratings at this point, and just monitor the temperatures.
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Old 06-16-2017, 02:19 AM
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Originally Posted by gigaplex
You've already used the voltage rating to select an appropriate battery voltage. For current... again that's basically that's just a rough guideline to ensure you select an appropriate battery. Your load, in this case propeller size/type/pitch, is going to be the determining factor of what your actual load will be, and thus what current will actually be drawn. Try to forget about the ratings at this point, and just monitor the temperatures.
Thanks, I think I know enough know to finish the project !

Indeed, I am going to use a 3S LiPo cell, thus I've selected the battery voltage I will use.

So first thing I'm gonna do is experiment with different prop sizes in the water and see what the currentdraw will be and experiment with acceptable currentdraws and temperatures of the motor.

Thank you for the answers and this lovely community !
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