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Older Servo Speed Control - New Motor

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Older Servo Speed Control - New Motor

Old 01-31-2005, 05:15 PM
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Default Older Servo Speed Control - New Motor

I have a quick question about older servo controlled speed controls.

I have salvaged an older spped control from a friend and I am trying to use it for speed control on a salvaged 16.8v Cordless drill motor.
It seems to work but I have noticed that just playing with the control for a few minutes on my bench, a ceramic block gets VERY hot.
This is connected to the speed control and I beleive this control was used on a 6 volt motor.

the ratings on the ceramic block ( I am not sure if it is a resistor or some other choke or something ) are as follows 7 Watt 0.3 ohms x 2 . It looks like it may have been made by some company name JAMS or something.

I am looking at maybe changing the block if possible to something that would be compatible for the 16.8 v motor I am going to use.

any ideas or suggestions would be appreicated , other than go buy an ESC I have thought of that but I would like to use some salvaged parts to put into my first sratch built boat.
Old 01-31-2005, 05:45 PM
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Default RE: Older Servo Speed Control - New Motor

yes it does sound like it's drawing too much current, for the speed controll to keep up with. Im not an electronics expert, but i would say it is worth trying to change the block. WTH?
Old 01-31-2005, 06:07 PM
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Default RE: Older Servo Speed Control - New Motor

yes , that is a ceramic /epoxy coiled resistor . the numbers are for the resistance and allowable wattage . And that motor that you are using most defitately draws more than 7 watts .
The voltage , is more than likely acceptable .
Gotta remember ... increase voltage , decrease amperage ( wattage ) . Increase amperage , decrease voltage .
Again , it not the voltage that is heating the resistor up , but the wattage ( amperage ) draw.
Think of it this way ...
Take the batteries you use for your TX ... 12 volts .. take those and stick them to your tongue ... you might feel a tingle or so . Now , take the same voltage , your cars battery ( I mean , in your real car ) rated at aprox 500 amps . Stick those terminal connections to your tongue and your dead .

So , see , its the same with the resistor . Too high of a draw .
Just a shot in the dark guess , but I would say that the old drill motor should have a draw of aprox 35 or so watts ( and thats being conservative . )
Those style resistors can also be found on the older Chrysler cars ( Dodge , Plymouth ,Chrysler ) on the firewall .
get yourself one , or two of those ran parallel , and then you should be good to go .

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