Delay motor start

Thread Starter

djsfantasi

Joined Apr 11, 2010
7,561
I’ve bought a delayed start relay module for my problem, but was wondering since my application is so simple if there was an equally simple alternative.

I have a DC (geared) motor that is turned on with an SPST switch. I want the motor to be delayed less than a second (to a second or two) after the switch is toggled.

The toggle switches +6V to the motor. Can I place a cap between the switched power and ground to delay the motor?
 

nsaspook

Joined Aug 27, 2009
8,168
RC delays would not be my first choice.

The problem with direct DC motor RC time delays is the current requirements require components that would cost in the same range as a simple hobby type delay relay module with anything more than the tiniest motor. At instant zero of the delay cycle the motor is a DC resistance that likely is much lower (no back-emf) than the normal run impedance of the motor. You need to supply that DC load in addition to the cap until the motor starts to slowly spin-up as the rotation field builds. What you have is a slow start instead of a delay start.
 

Thread Starter

djsfantasi

Joined Apr 11, 2010
7,561
RC delays would not be my first choice.

The problem with direct DC motor RC time delays is the current requirements require components that would cost in the same range as a simple hobby type delay relay module with anything more than the tiniest motor. At instant zero of the delay cycle the motor is a DC resistance that likely is much lower (no back-emf) than the normal run impedance of the motor. You need to supply that DC load in addition to the cap until the motor starts to slowly spin-up as the rotation field builds. What you have is a slow start instead of a delay start.
I had considered that as well. Slow start is a design benefit!

I’m doing this to retrofit a poorly designed useless box. The hand shuts it off almost before you can remove your finger.
 

MisterBill2

Joined Jan 23, 2018
8,230
How accurate a delay do you need, and do you really need to have an electrical delay.
NO, connecting a capacitor will not work that way, although if yo use a relay then an RC time constant delay for the relay operation can work. You did not mention how much current the motor draws.
 

Thread Starter

djsfantasi

Joined Apr 11, 2010
7,561
How accurate a delay do you need, and do you really need to have an electrical delay.
NO, connecting a capacitor will not work that way, although if yo use a relay then an RC time constant delay for the relay operation can work. You did not mention how much current the motor draws.
Delay accuracy is not critical. I need to turn on an electrical switch and have the motor actuation be delayed.

Why would an RC time delay work for a relay and not a simple DC perm mag motor?
 

sghioto

Joined Dec 31, 2017
2,272
I think the most reliable method is to use a low voltage low current relay for the delay or just use the module.
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Last edited:

nsaspook

Joined Aug 27, 2009
8,168
The motor is a motion transducer with a large number of possible electromechnical reactive power states between stopped with no load and full speed at full load during a slow ramp up/down. Full-on from full-off and back switching simplifies those states without motion feedback.The relay/modules electromechincal state is much simpler and the mechanical job (work) at a lower level within normal operating parameters.
 

Thread Starter

djsfantasi

Joined Apr 11, 2010
7,561
That doesn't seem correct. Below is the wiring for the Useless Box.
View attachment 232247
I’ll have to check the wiring again.

The motor is a motion transducer with a large number of possible electromechnical reactive power states between stopped with no load and full speed at full load during a slow ramp up/down. Full-on from full-off and back switching simplifies those states without motion feedback.The relay/modules electromechincal state is much simpler and the mechanical job (work) at a lower level within normal operating parameters.
So you’re saying that I DONT want an electro mechanical relay?
 
Last edited:

nsaspook

Joined Aug 27, 2009
8,168
I’ll have to check the wiring again.



So you’re saying that I DONT want an electro mechanical relay?
How consistent and predictable is up to you and your requirements. A electro mechanical with a RC coil delay is better than a direct RC motor windings delay. A delayed start relay module (that you already have) would likely be even better.
 

MisterBill2

Joined Jan 23, 2018
8,230
It is not useful to delay the motor directly with an RC time constant, first, because the motor will gradually start turning as the voltage rises, and to get enough delay to be useful the capacitor will need to be electrically BIG, also physically big. But the relay is a binary device, either off or on, and so it will stay completely off until all at once it switches completely ON. I hope that explanation is adequate.
 

Thread Starter

djsfantasi

Joined Apr 11, 2010
7,561
How consistent and predictable is up to you and your requirements. A electro mechanical with a RC coil delay is better than a direct RC motor windings delay. A delayed start relay module (that you already have) would likely be even better.
I’d like a random start delay. But also want a simple solution. If a particular simple solution is unpredictable, whoa, I’ve hit the jackpot

A simple circuit or module that gives an unpredictable result is preferred. You guys sometimes are so focused on the perfect answer, you miss that sometimes the imperfect answer is the perfect answer.
 

MisterBill2

Joined Jan 23, 2018
8,230
OK, and the application should have been stated at the start.If a random delay is desired, that can be arranged. Otherwise you get guesses.
 
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