Can someone explain to me, an aging imbecile, how one might construct a functional DC filter choke to be used on a 130 VDC, 3 HP treadmill motor?

I'll be using a cheap Amazon sourced SCR speed controller to a bridge rectifier. I expect the maximum motor current to be =<20A.

I have a shelf full of various sized torroid / common mode chokes, miscellaneous salvaged PCB components, commercial rectifiers (24 & 48V DC), a few transformers of various sizes, etc. I just don't know what would actually be required to achieve the intended purpose of a store bought filter choke...and I would rather use something I have or make something...because that's what old retired cheapskates do.

Anyway, if someone is willing to help, I appreciate it. Again, I can buy one...I don't want to.

Thanks!!

 

The Johnson range of motors use two ferrite toroid's , Three turns of the DC supply through one, the other in the GND conductor .
Each are 30mm in dia 18mm internal with a depth of 15mm.
That is for PWM, of course, if Triac controlled then the Laminated steel choke is used.

 

Thanks.

I've seen a guy on Youtube repurpose a transformer frame to make one but as much as I like repurposing stuff, it seemed a bit much...and huge.

I have several machines in my shop converted to DC motors using g KB SCR (KBIC-225) controllers, none of which use any external filtering, so I was assuming that something within those circuits achieved the necessary filtering and I may be able to cobble something usable myself out of components to work with the cheap controller I'm using for this one.

Thanks again.

 

No, the KB controllers do not have any motor filters, it has to be done externally, the better kind is the common mode choke, see here for explanation. https://www.doeeet.com/content/eee-...solution-for-brush-dc-motor-emc-requirements/
the polarity of each winding must be observed, a small transformer can be re-purposed for them, just remove all windings and wind on a few turns for each winding of sufficient gauge enamel wire .

 

I have a bunch of common mode chokes of various sizes and access to more that can be removed from the commercial rectifiers I have for parts. Some with a single lead, some with two. I'm guessing it would be better to use one with two leads and windings large enough to handle the anticipated current, placed between the bridge rectifier and motor lead...or closer to the motor?

I was reading about using a capacitor in parallel on the DC side to smooth out the AC ripple, but even using online calculators, I haven't determined what value might be best. I get different results using different calculators for some reason.

The motor voltage is 130 VDC, 120V / 60HZ AC supply to the SCR, and allowable voltage drop should be =< 10V...or whatever is realistic to expect. The voltage to the motor isn't super critical as I I'm going to set the machine speed with belt pulleys.

I have a 30A AC EMI filter that I plan to use on the line in, if that matters.

And thanks for the info on the KB controllers. I had no idea that they had no DC smoothing / filter feature, so I'll be adding same once I figure out what works well enough.

Thanks again for your time and input. Very much appreciated.

 

No, the KB controllers do not have any motor filters, it has to be done externally, the better kind is the common mode choke, see here for explanation. https://www.doeeet.com/content/eee-...solution-for-brush-dc-motor-emc-requirements/
the polarity of each winding must be observed, a small transformer can be re-purposed for them, just remove all windings and wind on a few turns for each winding of sufficient gauge enamel wire .

 

I was reading about using a capacitor in parallel on the DC side to smooth out the AC ripple, but even using online calculators, I haven't determined what value might be best. I get different results using different calculators for some reason.
The motor voltage is 130 VDC, 120V / 60HZ AC supply to the SCR, and allowable voltage drop should be =< 10V...or whatever is realistic to expect. The voltage to the motor isn't super critical as I I'm going to set the machine speed with belt pulleys.
I have a 30A AC EMI filter that I plan to use on the line in, if that matters.
And thanks for the info on the KB controllers. I had no idea that they had no DC smoothing / filter feature, so I'll be adding same once I figure out what works well enough.

You may upset the feedback control circuit if you decide to smooth the DC , what is the reason for doing it?

 

Can someone explain to me, an aging imbecile, how one might construct a functional DC filter choke to be used on a 130 VDC, 3 HP treadmill motor?

I'll be using a cheap Amazon sourced SCR speed controller to a bridge rectifier. I expect the maximum motor current to be =<20A.

I have a shelf full of various sized torroid / common mode chokes, miscellaneous salvaged PCB components, commercial rectifiers (24 & 48V DC), a few transformers of various sizes, etc. I just don't know what would actually be required to achieve the intended purpose of a store bought filter choke...and I would rather use something I have or make something...because that's what old retired cheapskates do.

Anyway, if someone is willing to help, I appreciate it. Again, I can buy one...I don't want to.

Thanks!!

Regarding the filter choke. We need to consider the purpose of the choke in these motor drive circuits. It's my understanding that the common mode filter is used for noise suppression. Which is a valid use with these brush type motors that act like spark transmitters. However the output choke in these circuits is not for EMI. It is used to smooth the pulsating DC. Low cost simple drives are very similar to an incandescent light dimmer control. They only pass a portion of the AC sine wave depending on the potentiometer position, less on low setting and up to the full wave on maximum setting. This output is fed through a rectifier to produce DC for the load. As you can imagine this DC is very dirty and pulsating badly at 120 Hz. This is fine to power a light filament or resistive heater, but bad for a motor.The purpose of the series choke in these circuits is to remove some of the pulsations so that the motor operates smoothly and with less arcing on the brushes. An inductor (the choke) opposes change, the magnetic core of the choke stores and then supplies energy, smoothing the power to the motor. Considering the low frequency and high current it is understandable that this choke requires an adequate amount of mass in its iron core and a wire gauge capable of carrying 15 amps. Regarding the use of a filter capacitor. I would be careful with that and would use it after a filter choke. A high value capacitor directly on the output would cause a large surge current, if you try one, start it with the control all the way down and turn it slowly. It will also affect the response time of speed changes.
A full output 15 amp current would require about 100,000 microfarads @ 200vdc , a very large cap, to reduce ripple to about 12 volts. That would be an intolerable amount of ripple for most power supplies, but probably okay to drive that motor. The primary winding of a microwave transformer could act as a choke but it will have a larger voltage drop and also be careful about the secondary; it could produce 2500vac so you must short or remove it first. Not sure about shorting for long term use, the winding may overheat. You could cut the winding with a hacksaw and remove it. A treadmill choke I measured was 6.5mh and a MW transformer primary was 37mh with the secondary open and 17mh with the secondary shorted. The inductive reactance (XL) of 6.5mh at 120 HZ is approximately 5 ohms and 37mh is 28 ohms, so the voltage drop will be much higher with the transformer. Also the increased resistance makes speed fluctuation under load worse . Removing some wire from a MW oven transformer primary winding will reduce the XL and the voltage drop and improve performance.

 

However the output choke in these circuits is not for EMI. It is used to smooth the pulsating DC. Low cost simple drives are very similar to an incandescent light dimmer control.

It all depends on the technology of the controller, There are typically two types in popular use, the Cheaper, 'Noisy' SCR bridge, and the preferred, higher frequency PWM version.
The former uses the LF 120hz choke version, the latter, the HF noise suppressor.