A question from a newbie

[Ricks2524]

I have a Johnson motor I want to use on a project. Can this motor be wired direct to A/C ? If not, can you give me a type of converter I would need ? I would also need to regulate the rpm's

Johnson 1.25 HP continuous duty Motor
Mod JM 15-001
Volts DC90V
RPM 5700
AMPS 10A S6 25%
Insul F
AMB 40 C

Thanks for your help

 

[spec]

I have a Johnson motor I want to use on a project. Can this motor be wired direct to A/C ? If not, can you give me a type of converter I would need ? I would also need to regulate the rpm's

Johnson 1.25 HP continuous duty Motor
Mod JM 15-001
Volts DC90V
RPM 5700
AMPS 10A S6 25%
Insul F
AMB 40 C

Thanks for your help

Hi Rick,
Can you give more data about your application and the motor. I have just been on the Johnson site but can't find a motor model JM 15-001.

You do not state where you live, so we do not know what your mains supply voltage is. Assuming you live in the US where the mains voltage is around 120V at 60Hz and making a few assumptions about your motor, it would be possible to use a bridge rectifier to convert the mains sine wave to a form of DC that may be suitable for driving a DC motor. If your mains supply voltage is different, say 230V you would then need a transformer. Another approach would be to use an off-line switch mode power supply, but to provide the equivalent of 1.25 horsepower you would need about a 1KW supply which would probably be quite big and expensive, at least that is my first thoughts. If you could point us to a data sheet for your motor on the Johnson web site, tell us what your mains supply is, and also tell us what your applications is we can probably be more definitive

 

[Ricks2524]

The motor is from a treadmill. I wanted to use it to make a tumbler for brass cleaning. The information above is all I have on it. Not sure of the age, probably no more than 8-10 years. Is this what I'm looking for?

 

[Les Jones]

You can't connect it to an AC supply as it says DC on the label. I suspect that it is a permanent magnet motor. If so and you connect it to AC yoy will probably demagnetise the magnets. This link to "KBLC" may help as they make speed controllers for DC motors.

Les.

 

[gophert]

Hi Rick,
Can you give more data about your application and the motor. I have just been on the Johnson site but can't find a motor model JM 15-001.

You do not state where you live, so we do not know what your mains supply voltage is. Assuming you live in the US where the mains voltage is around 120V at 60Hz and making a few assumptions about your motor, it would be possible to use a bridge rectifier to convert the mains sine wave to a form of DC that may be suitable for driving a DC motor. If your mains supply voltage is different, say 230V you would then need a transformer. Another approach would be to use an off-line switch mode power supply, but to provide the equivalent of 1.25 horsepower you would need about a 1KW supply which would probably be quite big and expensive, at least that is my first thoughts. If you could point us to a data sheet for your motor on the Johnson web site, tell us what your mains supply is, and also tell us what your applications is we can probably be more definitive

Suggesting a non-isolated (mains to bridge rectifier) to a person asking this question is dangerous. Either they know how to do something like this because they are knowledgable and experienced and wouldn't need to ask this question, or, they don't know much and shouldn't be use a non-isolated supply.

There are two hurdles for the OP's project.
1) converting your mains power to 90 V DC. That can deliver 10 amps. (This is best purchased). Lots of things can go wrong)

2) making a Pwm motor controller that can handle 10 amps and 90 V DC. It will take some big transistors and big heat sinks if you are trying to push big loads at less than full speed. Again, best to purchase if you have no experience and need something over a few 100 mA at 90 VDC. 900 watts is a lot to deal with for an amateur.

 

[gophert]

The motor is from a treadmill. I wanted to use it to make a tumbler for brass cleaning. The information above is all I have on it. Not sure of the age, probably no more than 8-10 years. Is this what I'm looking for?

That is a bridge but connecting that directly to your 120v AC mains will give you 170 volts DC if you filter the output to make DC. Without filters, you will get a rectified AC signal (a series of camel humps with 170 v leaks. See above: don't connect your mains power to a bridge rectifier. Use a transformer, or, better, buy a pre-built power supply.

The motor will not survive the 170 V from rectified mains.

 

[spec]

The motor is from a treadmill. I wanted to use it to make a tumbler for brass cleaning. The information above is all I have on it. Not sure of the age, probably no more than 8-10 years. Is this what I'm looking for?

As I say in my previous post, we need more data about the motor before deciding what can be done with your motor in terms of bridge rectifiers because that will requires some specialist design work and also investigations of the safety aspects. On the other hand, an isolated off line switch mode power supply with an output voltage adjustment would probably be your best approach.

 

[Ricks2524]

Thanks everyone. looks like a bad deal. I think finding a used electric motor will be easier and cheaper. Thanks again

 

[spec]

Thanks everyone. looks like a bad deal. I think finding a used electric motor will be easier and cheaper. Thanks again

Very wise, that is the best move.

 

[gophert]

Thanks everyone. looks like a bad deal. I think finding a used electric motor will be easier and cheaper. Thanks again

A board from a used treadmill might have everything you need.

 

[spec]

That is a bridge but connecting that directly to your 120v AC mains will give you 170 volts DC if you filter the output to make DC. Without filters, you will get a rectified AC signal (a series of camel humps with 170 v leaks. See above: don't connect your mains power to a bridge rectifier. Use a transformer, or, better, buy a pre-built power supply.

The motor will not survive the 170 V from rectified mains.

You don't know what the motor will survive, or have you seen the data sheet? 170V camel humps as you call it is 120V RMS which is not that far from 90V DC. If you look at other data sheets for similar motors on the Johnson site you will see that the motors have quite a wide input voltage range. By the way, by the time you have taken into account the VF of the bridge the peak voltage of the humps will be 168V.

It is quite common to use a DC motor with camel humps.

 

[spec]

Suggesting a non-isolated (mains to bridge rectifier) to a person asking this question is dangerous. Either they know how to do something like this because they are knowledgable and experienced and wouldn't need to ask this question, or, they don't know much and shouldn't be use a non-isolated supply.

There are two hurdles for the OP's project.
1) converting your mains power to 90 V DC. That can deliver 10 amps. (This is best purchased). Lots of things can go wrong)

2) making a Pwm motor controller that can handle 10 amps and 90 V DC. It will take some big transistors and big heat sinks if you are trying to push big loads at less than full speed. Again, best to purchase if you have no experience and need something over a few 100 mA at 90 VDC. 900 watts is a lot to deal with for an amateur.

I can do without the lecture thank you

Your opening argument is illogical and circular- if someone knew about a subject they would hardly be asking a question on ETO in the first place.

I am not suggesting that anybody do anything and well you know it from my post. The whole theme of my post is that further information is required before a move could be considered. Your post is melodramatic and obstructive at the best. Saying lots of things can go wrong is also melodramatic, cryptic and without value.

 

[audioguru]

Wouldn't the DC motor vibrate like crazy when running on low frequency camel humps? The motor will probably also smell as bad and make as much noise as a camel.

 

[spec]

Wouldn't the DC motor vibrate like crazy when running on low frequency camel humps?

Quite possibly- we do not know. On the other hand, the inductance of the motor may just integrate the whole thing out. A capacitor might also help. The scientific approach would have been to get the data sheet for the motor and to contact Johnson to find out what can be done. That would also include the safety aspects. This thread is now closed anyway because the OP has, very wisely, decided to investigate an alternative approach.

The motor will probably also smell as bad and make as much noise as a camel.

Nice to end on a humorous note after the aroma of all the BS.

 

[Les Jones]

Just a couple of points. It is quite common for speed controllers for permanent magnet motors to use raw rectified AC. (I.E. No reservoir capacitor.) The speed control is achieved using phase angle control or PWM. the phase angle control is normaly done using two diodes and two SCRs in a bridge. The 90 volt motor is about right for use with a speed controller running from 120 volt mains. The motor on my Seig x3 milling machine is rated at 180 volts and has a speed controller running from 240 volt mains. This is the schematic of the speed controller on my X3. The other point is that I think a tumbler would be a machine that is left running for many hours so a brushed motor would require the brushes changing often. I think a three phase induction motor in conjunction with a VFD (Variable frequency drive.) would be a better solution. I agree with the warning about someone that does not know what they are doing playing round with high voltage.

Les.

 

[gophert]

I can do without the lecture thank you

Your opening argument is illogical and circular- if someone knew about a subject they would hardly be asking a question on ETO in the first place.

I am not suggesting that anybody do anything and well you know it from my post. The whole theme of my post is that further information is required before a move could be considered. Your post is melodramatic and obstructive at the best. Saying lots of things can go wrong is also melodramatic, cryptic and without value.

I didn't think it was circular at all. It pointed to only one conclusion - the OP was new and should not be connecting mains to a bridge. Also, your suggestion of a bridge to mains would not get the OP the 90V that the motor specified.

And, if I have to choose, I would prefer you to be unhappy, insulted or mis-understood than the OP ending up dead.

audioguru
Yes, I didn't like the suggestion of the bridge and no mention of filter capacitors.

 

[gophert]

Just a couple of points. It is quite common for speed controllers for permanent magnet motors to use raw rectified AC. (I.E. No reservoir capacitor.) The speed control is achieved using phase angle control or PWM. the phase angle control is normaly done using two diodes and two SCRs in a bridge. The 90 volt motor is about right for use with a speed controller running from 120 volt mains. The motor on my Seig x3 milling machine is rated at 180 volts and has a speed controller running from 240 volt mains. This is the schematic of the speed controller on my X3. The other point is that I think a tumbler would be a machine that is left running for many hours so a brushed motor would require the brushes changing often. I think a three phase induction motor in conjunction with a VFD (Variable frequency drive.) would be a better solution. I agree with the warning about someone that does not know what they are doing playing round with high voltage.

Les.

I know it is done, I just don't think it is a project for a noob - especially when the recommendation starts out by suggestion a bridge rectifier before any SCR or suggestion to use an SCR bridge.

 

[spec]

I didn't think it was circular at all. It pointed to only one conclusion - the OP was new and should not be connecting mains to a bridge. Also, your suggestion of a bridge to mains would not get the OP the 90V that the motor specified.

And, if I have to choose, I would prefer you to be unhappy, insulted or mis-understood than the OP ending up dead.

audioguru
Yes, I didn't like the suggestion of the bridge and no mention of filter capacitors.

You have totally ignored what I have said? Who cares what you would chose. As I say you are being melodramatic.

Just a couple of points a DC motor has AC in its coils- that is what a commutator is for. The original motor was 90V DC which is a dangerous voltage anyway so I can't understand all these so called worries about rectified 120V are all about. I am not suggesting that the OP have any live wires exposed anyway.

 

[gophert]

You have totally ignored what I have said? Who cares what you would chose. As I say you are being melodramatic.

Just a couple of points a DC motor has AC in its coils- that is what a commutator is for. The original motor was 90V DC which is a dangerous voltage anyway so I can't understand all these so called worries about rectified 120V are all about. I am not suggesting that the OP have any live wires exposed anyway.

Yes, that is my point. I am concerned because you do not understand the benefit that comes with isolation from a transformer when dealing with mains power.

As for the commutation, listen to Audioguru - you will have lots of vibration if you commutation does not match the frequency of your 120Hz rectified AC.

 

[Tony Stewart]

A large flywheel can smoothen the vibration, but half-wave rectification of 120Vac is around 90Vdc avg.

An SCR can give variable speed with current handling for start surge.

Pulley speed reduction will be necessary to reduce the 5700 RPM down to desired tumble rate.