OT: Motor control circuit
- Thread starter laserhawk64
- Start date
The number on the end indicates forward voltage not maximum current. Higher current diodes are much bigger and have really fat leads and they are not necessary for this.Resistor value will be fine in this circuit - the 1N4004 is probably way over spec (4Amps) but a diode is needed for each motor (you could probably use a 1N4001)
On average a 1/4 watt resistor is standard unless otherwise quoted, but any watt resistor will do in this case.
R3 can be 5K6 and may have been a typo error from me.
The 10K pot should be a linear (B) pot or can be trimpot if you wanted, bit harder to adjust though.
A 0.4 watt zener is all that is needed, but a 1 watt zener will work just as well.
As both motors are driven together a single 1N4004 or 1N4001 will do, or you can put a diode across each motor if you wanted too.
R3 can be 5K6 and may have been a typo error from me.
The 10K pot should be a linear (B) pot or can be trimpot if you wanted, bit harder to adjust though.
A 0.4 watt zener is all that is needed, but a 1 watt zener will work just as well.
As both motors are driven together a single 1N4004 or 1N4001 will do, or you can put a diode across each motor if you wanted too.
JimPerry
Senior Member
My mistake - but 400V is still over the top!
westaust55
Moderator
For the 1N400x range of diodes, the rating is given as the peak repetitive reverse voltage.
1N4001 ==> 50 Vpeak ==> * 0.636 = 31 Vrms
The originally mentioned
1N4004 ==> 400 Vpeak ==> 254 Vrms
So for single phase mains (which many here should not be touching) a 1N4004 would be the minimum for rectifier duty and for free wheeling diodes across coils/motors/etc a higher rating agin is required.
1N4001 ==> 50 Vpeak ==> * 0.636 = 31 Vrms
The originally mentioned
1N4004 ==> 400 Vpeak ==> 254 Vrms
So for single phase mains (which many here should not be touching) a 1N4004 would be the minimum for rectifier duty and for free wheeling diodes across coils/motors/etc a higher rating agin is required.
Hi,
After nearly 50 posts, perhaps it's time to reprise the design targets and current proposals (preferably with an up-to-date circuit diagram). If I've followed the thread (please correct me if I'm wrong), simplicity and power efficiency are particular aims, the power supply is to be 4 x Primary (non-rechargeable) cells, the output transistor is a "Darlington (pair)" and the two motors are to be reversed with a DPDT (mechanical) switch. Note that if a diode is connected literally "across the motor terminals" then it can only rotate in one direction.
To make even moderately good use of the the energy in alkaline cells (don't even think about the "heavy duty" carbon types for 1 Amp) then the circuit should work down to 1.25 volt per cell, and preferably to 1.0 volt. That "safety" diode in the supply rail is unlikely to drop less than 750mV and similarly the Darlington transistor, so the motor(s) may not see much more than 3 volts. Also, Darlingtons tend to make poor high-speed switches (because there is usually no mechanism to draw charge out of their base) so you might find nearly as much power being dissipated in the semiconductors as in the motor(s). With so many unknowns (e.g. the PWM frequency and its effect on dissipation and acoustic noise, etc.) a "paper" design is probably impossible, and breadboarding essential. However, I'd proceed as follows:
With partly discharged cells, the zener is not going to "see" 5.1 volts so won't regulate (when it's potentially most needed). In any case, 5.1 volt zeners have a poor "knee" compared with the original 9.1 volt device, and zeners below 5.1 are even worse. So I'd just throw out the zener and increase the value of the decoupling capacitor (which now only needs to be 10 volt rated, of course). Also, it's probable that the power transistor can survive reversed battery connections (but the 555 will not) so I'd move the series diode next to the filter resistor (R1), where it won't dissipate the motor current and only needs to be a 1N 4148 type.
Then measure a breadboard at various PWM frequencies to determine which (if any) give acceptable results.
Cheers, Alan.
After nearly 50 posts, perhaps it's time to reprise the design targets and current proposals (preferably with an up-to-date circuit diagram). If I've followed the thread (please correct me if I'm wrong), simplicity and power efficiency are particular aims, the power supply is to be 4 x Primary (non-rechargeable) cells, the output transistor is a "Darlington (pair)" and the two motors are to be reversed with a DPDT (mechanical) switch. Note that if a diode is connected literally "across the motor terminals" then it can only rotate in one direction.
To make even moderately good use of the the energy in alkaline cells (don't even think about the "heavy duty" carbon types for 1 Amp) then the circuit should work down to 1.25 volt per cell, and preferably to 1.0 volt. That "safety" diode in the supply rail is unlikely to drop less than 750mV and similarly the Darlington transistor, so the motor(s) may not see much more than 3 volts. Also, Darlingtons tend to make poor high-speed switches (because there is usually no mechanism to draw charge out of their base) so you might find nearly as much power being dissipated in the semiconductors as in the motor(s). With so many unknowns (e.g. the PWM frequency and its effect on dissipation and acoustic noise, etc.) a "paper" design is probably impossible, and breadboarding essential. However, I'd proceed as follows:
With partly discharged cells, the zener is not going to "see" 5.1 volts so won't regulate (when it's potentially most needed). In any case, 5.1 volt zeners have a poor "knee" compared with the original 9.1 volt device, and zeners below 5.1 are even worse. So I'd just throw out the zener and increase the value of the decoupling capacitor (which now only needs to be 10 volt rated, of course). Also, it's probable that the power transistor can survive reversed battery connections (but the 555 will not) so I'd move the series diode next to the filter resistor (R1), where it won't dissipate the motor current and only needs to be a 1N 4148 type.
Then measure a breadboard at various PWM frequencies to determine which (if any) give acceptable results.
Cheers, Alan.
laserhawk64
Senior Member
Hate to say it after all this help... but I'm thinking that it might be a good idea to shelve this for a little while.
I'll be starting a new, on-topic post in a minute... something I can do pretty cheaply for sure.
I'll be starting a new, on-topic post in a minute... something I can do pretty cheaply for sure.