GWS ICS50 speed controller

[danielsmusic]

hi all, im back. i decided to come back into electronics, i don't think many will rember me.

but anyway, im making a model boat. a big boat, i have a big motor to put in it, i don't know the total specs of the motor but it is big and fast.

looking at it, it would easily draw about 20A (when starting) so its going to need a good speed controller. i had a look and couldn't afford a controller that ws prebuilt for this current. so i bought a GWS ICS50 speed controller, this can only controll small motors (2A@8-12V). i decided to use this to controll a transisor type circuit that would controll the motor. has anyone got and advice to what transistor to use/circuit for a soft start. i also want somesort of protection device that will activate a relay if the transistor is over-heating. i know how to do this already, but im sure it is easier than im thinking (voltage devider with a thermister, and a op-amp).

sorry, i just realized this is the wrong forum.

 

[dknguyen]

If it's brushless, I'm, not sure, but if it's brushed:

So you want to use a smaller speed controller to drive a larger home-built motor driver? You'd need to build an H-bridge first, with big transistors. Then you would definately need to pair up the 4 PWM H-bridge inputs so you only need two (since there are only two motor terminal outputs on the speed controller). For temperature control you would use put an AND gate at the each PWM input and feed the speed controller signal as well as a thermostat active-low temperature overload signal, so that the speed controller PWM would only reach the H-bridge if there was no temperature overload. Probably have some kind of silicon IC-based thermostat sitting next to or on the heatsink of the power transistors on the H-bridge.

All that aside, I don't think you will be able to do it the way you have planned. THe two inputs to an H-bridge require two independent PWM signals. The two motor terminal outputs on the speed controller are both on at the same time, all the time. I dont think you need the speed controller. I think what you need is a radio receiver. YOu can then feed these PWM outputs from the radio receiver into the H-bridge to do what you want. These radio receiver pulses though are probably too slow to drive a motor properly, so that would mean you would need a uC to read the receiver PWM and convert it to a higher frequency PWM to drive the H-bridge with. If the PWM is high enough frequency already, you just need some amplification transistors to step up the voltage so that it can drive the H-bridge FETs.

 

[Sceadwian]

An H-bridge is seldom required for a boat, boats almost never go in reverse and the circuit for a speed controller for forward only is incredibly simple compared to an h-bridge. Use say 4 TO-220 package 10amp logic level mosfets ganged to a common heat sink. You can feed the RC servo signal into a pulse stretcher (link bellow to a simple inverter pulse stretcher) and feed that directly to the mosfet drive line, the switching frequency will only be 50 hertz or so with an RC signal so you should have extremely low switching losses on the FET's, they should run very cool.

**broken link removed**
<Scroll to the bottom>

 

[dknguyen]

Ah true that. No reverse needed- forgot about that (was it you who said that to me last time when someone talked about a boat?). Then it's dead easy isnt it? Connect the - speed controller terminal to the source of a giant NMOS, connect the + motor terminal to the gate, and connect the drain to the - motor terminal. Isn't 50Hz too slow to drive a motor though without pulsations?

What do you mean by soft start though? Doesn't that just mean ease into the throttle when you drive it rather than going full blast?

 

[danielsmusic]

What do you mean by soft start though? Doesn't that just mean ease into the throttle when you drive it rather than going full blast?

so as the motor is starting, it doesn't suddenly make the transistors explode. hehe.

basicly, if you suddenly open the throttle it will stop the motor from drawing too much current by starting slower.

yes, it is a brushless motor. i really dont want to use a H-Bridge as it is too complicated. i wanted to just have a couple of transistors with the output from the speed controler switching them on and off. the speedcontroler uses pwm, but im not sure on the fequency

 

[dknguyen]

Okay, so if it's brushless and it's single direction, I think you still do the same thing. Except there are 3 wires. one MOSFET per wire...except for one which may be common. You want to use the signals from the speed controller to drive some MOSFETs which will make the same current flow in the same sequence through the windings. But don't brushless controllers require some position feedback to drive the brushless motor? This is something it can't get unless the wires go straight to the motor terminals.

 

[Sceadwian]

It's a boat... You don't need to worry about pulsation so much. Pulsation really only occurs under very high loads, and water doesn't create high loads.

 

[danielsmusic]

ok..schematic.

this is what i was thinking;

the thermister would attach to the heatsink.