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Project that was working, but then stopped

Andy 1066

Jan 31, 2018
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I have a problem with a project, and needs some advice.

A brief description of the component involved. There is a 230 volt AC to 24 volt DC converter, which connects to a 24 volt speed controller, which is connects to a 24 volt D.C Motor.

Did a test run of the above set up, everything worked O.K

Then attached a belt to a pulley on the motor, to a pulley on a drive shaft, on this shaft is a flywheel.

I spun the flywheel (so that the motor did not have its dead weight to contend with when it started spinning) Then did a test run, at a quarter speed for five minutes, everything worked O.K

But when I did the next test run, at half speed, (spinning the flywheel as I did before), everything worked O.K for four minutes. Then everything started to slow down and stopped, (the flywheel on this test was really moving quite fast). The reason why I mention this, is because, I tested the motor, and the converter and they working O.K

The on and off speed control switch has developed a fault, it seem. I did a separate test of the speed controller, and the motor using a 24volt battery set up. When I turned the power on, with the speed controller switch in the off position, the power bye passes the switch, because the motor started spinning.

I was wonder whether the flywheel momentum could have build up, so that it ended up spinning faster than the speed controller, was set at, for the electric motor to rotate at. So that the electric motor was forced to spin faster, than it should, relating to the setting on the speed controller, this is hypothesising on my part.

Any suggestion on what might have caused the damaging to the speed controller, would be greatly appreciated, and also how to stop this happening.
 

kellys_eye

Jun 25, 2010
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The motor will be generating it's own voltage in opposition to the driving voltage. This may well have caused an over-current situation. I'm assuming the circuitry has back-emf protection fitted?
 

dragon

Oct 31, 2022
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get rid of the speed controller and see if it works without it.
 

Andy 1066

Jan 31, 2018
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The motor will be generating it's own voltage in opposition to the driving voltage. This may well have caused an over-current situation. I'm assuming the circuitry has back-emf protection fitted?
Thank you for your reply to my posting. I have to say firstly that I have a basic knowledge of electronics. So I can't say defiantly that the circuitry does have back-emf protection. I presume you mean on the speed controller circuitry?. I would guess not, because thinking logically, speed controller's are designed to drive something that would not have the potential to increase its speed, like say a conveyor belt. So how would I go about protecting the speed controller from this over-current situation that might be causing the problem?.
 

Andy 1066

Jan 31, 2018
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get rid of the speed controller and see if it works without it.
Thank you for your reply to my posting. I did do a test with out the speed controller, with the converter wired directly to the motor, and it work O.K
 

dragon

Oct 31, 2022
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Youd think a speed controller wouldnt be bothered by back emf if its designed to be connected to dc motors.

All you really need for one, is just a powerful transistor connected to an ordinary potentiometre going to the base, with a back going diode at the motor terminals for the back emf protection. That would work, they are pretty easy to make.
 

Martaine2005

May 12, 2015
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What are the specs of the DC converter?.
Don’t forget that a motor can draw up to 10 times it’s running current when starting or stalling. Maybe the speed controller and motor is just too much for the converter?.

Martin
 

Andy 1066

Jan 31, 2018
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What are the specs of the DC converter?.
Don’t forget that a motor can draw up to 10 times it’s running current when starting or stalling. Maybe the speed controller and motor is just too much for the converter?.

Martin
Thank you for your reply to my posting here are the details of the complete set up. The project consists of a 600W AC to DC converter 230V TO 24V 25-30A power switch transformer. A 10-50V 40A DC Motor Speed control PWM HHO RC controller 12V 24V, and a 350W 24 volt D.C motor, rated current 18.7A. Just to say again, that all was working perfectly until the finale test.
 

Andy 1066

Jan 31, 2018
27
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Youd think a speed controller wouldnt be bothered by back emf if its designed to be connected to dc motors.

All you really need for one, is just a powerful transistor connected to an ordinary potentiometre going to the base, with a back going diode at the motor terminals for the back emf protection. That would work, they are pretty easy to make.
Thank you for your reply to my posting. Your knowledge of electronic I expect is greater than mine, all the electronics parts you mentioned I know what they look like, and what there function is in a electronic circuit. But what values the different parts would need to be, that I would need to purchase, and how to connect them together, is beyond my knowledge. The project I under take are from books with electronic projects, with all the information you need, diagrams, part lists.
Regarding the speed controller I am using it in a totally different situation than the norm, where it might be used to power a conveyer belt that would stop, and start, speed up, slow down, with out building up speed. But the flywheel on the shaft is a completely different thing too have to cope with.
 

dragon

Oct 31, 2022
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Heres a schematic of a diy motor speed controller, i was going to add the BEMF diode but then I thought nah it wont work so its not there.

msc.png

the pot is easy enough to get any value for just about, but the transistor needs to be NPN for this circuit and u need to support 24 volts and the amps of the motor, which u can get from just running it by itself with the battery shorting into it.
 

Andy 1066

Jan 31, 2018
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Thank you for your reply to my posting, and the schematic drawing of the diy speed controller.
 

danadak

Feb 19, 2021
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Heres a schematic of a diy motor speed controller, i was going to add the BEMF diode but then I thought nah it wont work so its not there.

View attachment 58044

the pot is easy enough to get any value for just about, but the transistor needs to be NPN for this circuit and u need to support 24 volts and the amps of the motor, which u can get from just running it by itself with the battery shorting into it.

That circuit is a recipie for disaster. First of all the pot can become 0 ohms
and tie the base to a 1 V supply causing high current and hose the transistor.
You can put a R in series with pot to limit max base current.

With no R in series with motor you can possibly burn out the transistor, and
cause it to short taking out the motor. Again a R to limit current in series with
motor needed.


And you have to calculate the power rating needed for those resistors and the
pot. And heat sink with proper sized heatsink.

Regards, Dana
 

dragon

Oct 31, 2022
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Its good cause its simple. Maybe theres problems in using it, maybe DanaDak's suggestions are good to use to advance it whilst increasing the parts.
 

Andy 1066

Jan 31, 2018
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That pot and transistor idea is direct from another continent that swamps YouTube.

Martin
Thank you for your thoughts on the DIY speed controller, and where it came from. I am not in a hurry, so I am contacting other Forums, and looking for information on the internet.
 

Andy 1066

Jan 31, 2018
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Its good cause its simple. Maybe theres problems in using it, maybe DanaDak's suggestions are good to use to advance it whilst increasing the parts.
Thank you for your thoughts, on the DIY speed controller
 
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