Best Motor Type for Adjustable 1–24 RPM Clay Mixer: AC or DC, VFD or Gearbox?

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#1 21666676 21 Feb 2013 15:09

hadi makoui hadi makoui

Anonymous

Post #1
21666676 21 Feb 2013 15:09

Hi,
I need a motor to put it to work on a clay mixer. Rotational speed of the blender must be adjustable between 1 and 24 rpm.
Using a gearbox I can reduce 1420 rpm to 24 rpm but to reduce it up to 1 rpm I have to reduce motor speed without decrease of output power and torque of the gearbox. I have seen a video of a mixer in witch the operator just turns a switch to the right and left and easily that changes rotational speed of motor. any idea how can I do that? Should I use DC or AC motor to have a cheep,user friendly and simple system.
thanks.

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#2 21666677 21 Feb 2013 15:33

stephen Van Buskirk stephen Van Buskirk

Anonymous

Post #2
21666677 21 Feb 2013 15:33

That I know of AC speed control is done with fancy electronics, commonly variable frequency drives. They are expensive compared with DC h-bridge circuits until you get into big motors. 1 Hp is 750w. That is 62A at 12v or 6.2A at 120VAC. The decision is probably based on the horsepower you need in your application.

For AC power most VFDs can be controlled with a potentiometer dial. A good source for relatively cheap AC drives is Automation Direct on the internet. They have a good site and surprisingly good technical support.
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#3 21666678 21 Feb 2013 15:37

stephen Van Buskirk stephen Van Buskirk

Anonymous

Post #3
21666678 21 Feb 2013 15:37

I forgot to mention that you may be able to reduce your reduction based on the frequency range of the VFD, which might save some money.
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#4 21666679 21 Feb 2013 16:07

Sarah Harris Sarah Harris

Anonymous

Post #4
21666679 21 Feb 2013 16:07

I bought my husband one of these http://www.ebay.co.uk/itm/190726307679?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 to control his lathe and it works beautifully on single phase induction motors. far cheaper than making anything
#5 21666680 21 Feb 2013 16:21

stephen Van Buskirk stephen Van Buskirk

Anonymous

Post #5
21666680 21 Feb 2013 16:21

That looks like a good inexpensive unit for fractional horsepower motors (max just over 1/2 hp). It will probable be a bit load sensitive and might not work well at low rpms. Of course if you really want really good speed control you probably need to add an encoder to the motor - more money. With a speed range of 24:1 the slowest speed is 60 rpm which is fairly slow for a common AC motor.
#6 21666681 21 Feb 2013 17:04

Sarah Harris Sarah Harris

Anonymous

Post #6
21666681 21 Feb 2013 17:04

its good for 4ooow and runs a 3HP motor without issue
#7 21666682 21 Feb 2013 17:30

stephen Van Buskirk stephen Van Buskirk

Anonymous

Post #7
21666682 21 Feb 2013 17:30

Sorry, I misread it and thought it said 400. 4000 should be good for 5 hp. I also didn't consider whether this application was 120 or 240v. Of course we still have no idea how big a motor is needed for this application though a clay mixed does sound like a big application.
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#8 21666683 21 Feb 2013 20:29

Chuck Sydlo Chuck Sydlo

Anonymous

Post #8
21666683 21 Feb 2013 20:29

There has been some good info put out here. I'll just add that make sure you use a sealed motor. Clay could gum up the works in a hurry, and just remember that using a SCR means that torque will reduce with speed. That may be a problem in your application. I suggest you look at some commercially avaiable mixers and see what size motors they specify and see if they are using SCR speed control. To prevent excessive torque loss at low speed they may be using motors that are somewhat oversized, up to 100% over minimum torque requirement. Think somewhat oversized if you plan on using this on a daily basis as well. If you look up and build similar to a hobby type then use it every day in an industrial setting you should expect a shorter service life.
#9 21666684 21 Feb 2013 21:54

stephen Van Buskirk stephen Van Buskirk

Anonymous

Post #9
21666684 21 Feb 2013 21:54

One difference between VFD and SCR speed controllers is that an SCR turns off at zero crossing so for low speeds it will turn on at a low voltage. All the VFD drives that I know of make DC and switch it so the pulses are shorter but have a high peak voltage, which should reduce stalling. I know that works for DC motors.
#10 21666685 22 Feb 2013 12:04

hadi makoui hadi makoui

Anonymous

Post #10
21666685 22 Feb 2013 12:04

I consider using 1.5 hp 220v ac motor for my application. Normally commercially available mixers for my application use 1 hp 220v motors. It is not mentioned if it is ac or dc and I don't have access to any of those mixers. I'm planning to build it myself. Since I am a B.s of mechanical engineering, I don't have any experience in electronics. I think using oversized motor is a pretty good Idea and using one of dimmers that Sarah Harris suggested will work good. could you please give some info on SCR. Also how much is the percentage of motor torque at 60 rpm is compared to its nominal torque?
Thanks
#11 21666686 22 Feb 2013 12:53

Pothuganti Balaiah Pothuganti Balaiah

Anonymous

Post #11
21666686 22 Feb 2013 12:53

I think,a AC motor grinder,one that is used in floor mill for grinding wet rice for making dosa or
idle must be right choice for ur clay works..i think a light dimmer circuit can reduce the speed of
motor..
Dear experts what u say…
#12 21666687 22 Feb 2013 13:05

Pothuganti Balaiah Pothuganti Balaiah

Anonymous

Post #12
21666687 22 Feb 2013 13:05

by modifying this single phase wet grinding machine,i think it can be cheap and possible.. im attaching image.
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Topic summary

✨ For an adjustable 1–24 rpm clay mixer, motor speed control options include AC motors with Variable Frequency Drives (VFDs) or DC motors with H-bridge circuits. VFDs enable speed adjustment via potentiometer dials and can reduce the need for extensive mechanical gear reduction by varying frequency, but they tend to be more expensive than DC solutions for smaller horsepower motors. DC motors offer simpler and cheaper speed control but require higher current at low voltages. Using a gearbox to reduce from 1420 rpm to 24 rpm is common, but achieving 1 rpm output speed demands motor speed reduction without torque loss, which is challenging. SCR (Silicon Controlled Rectifier) dimmers are a low-cost option but cause torque reduction at low speeds and may be load sensitive. For industrial or daily use, an oversized sealed motor (up to 100% above minimum torque) is recommended to prevent premature wear and handle clay contamination. Commercial mixers typically use 1 hp, 220 V AC motors, but 1.5 hp motors may provide better performance. Encoder feedback can improve speed control precision but adds cost. Single-phase induction motors controlled by inexpensive VFD units are effective for fractional horsepower applications. Safety and durability considerations favor sealed motors to avoid clay ingress. Some users suggest modifying single-phase wet grinding motors with dimmer circuits for cost-effective speed control, though this may have limitations at very low speeds.

FAQ

TL;DR: For a 1–24 rpm clay mixer, use an AC induction motor with a gearbox and a VFD; “1 Hp is 750w.” [Elektroda, stephen Van Buskirk, post #21666677] Why it matters: You’ll get low-speed control with usable torque, safer operation, and simpler controls without overcomplicating the build.

Quick Facts

AC speed control uses Variable Frequency Drives (VFDs) and many accept a simple potentiometer dial input. [Elektroda, stephen Van Buskirk, post #21666677]
Oversize the motor up to ~100% when using SCR-type controllers to offset torque loss at low rpm. [Elektroda, Chuck Sydlo, post #21666683]
VFD frequency range can reduce required mechanical reduction, saving gearbox cost/complexity. [Elektroda, stephen Van Buskirk, post #21666678]
Use a sealed motor; clay ingress can shorten life dramatically. [Elektroda, Chuck Sydlo, post #21666683]
Users report a 4000 W single‑phase controller running a 3 Hp motor on a lathe. [Elektroda, Sarah Harris, post #21666681]

What’s the best motor type for a 1–24 rpm clay mixer: AC or DC?

Choose an AC induction motor with a gearbox plus a VFD. AC + VFD gives dial‑a‑speed control and robust torque. DC H-bridge is affordable for small motors but scales poorly in power. With AC, the VFD’s potentiometer input makes control simple. [Elektroda, stephen Van Buskirk, post #21666677]

How many horsepower do I need for a clay mixer?

Commercial mixers in this class often use about 1 Hp at 220 V. If your mix is heavy or you expect continuous use, stepping to 1.5 Hp offers headroom. This aligns with the original builder’s plan after surveying available mixers. [Elektroda, hadi makoui, post #21666685]

Do I need a sealed motor for clay mixing?

Yes. Clay dust and slurry rapidly foul open frames. A sealed motor helps prevent contamination, reduces downtime, and extends life in daily use. “Clay could gum up the works in a hurry,” as one expert warned. [Elektroda, Chuck Sydlo, post #21666683]

Can I use a light dimmer or SCR controller on an induction motor?

It can spin the motor, but torque drops hard as speed falls. That’s risky for a mixer that must not stall when loaded. If you insist on SCR, oversize the motor significantly to compensate. [Elektroda, Chuck Sydlo, post #21666683]

What is a VFD and why use it here?

A Variable Frequency Drive converts AC to DC, then synthesizes variable‑frequency AC to control speed. Many VFDs accept a simple potentiometer for user‑friendly speed dialing and reduce need for extreme gearing. [Elektroda, stephen Van Buskirk, post #21666677]

Will a VFD help me reduce gearbox size?

Yes. Extending the motor’s frequency range trims required mechanical reduction. You can keep torque with a proper gearbox but avoid excessive ratios, lowering cost and complexity. [Elektroda, stephen Van Buskirk, post #21666678]

How stable is speed at very low rpm?

VFDs switch high‑peak pulses after rectifying to DC, which helps resist stalling at low speed. SCR controllers fire near zero crossing and can bog down under load. Add an encoder only if you need tight closed‑loop control. [Elektroda, stephen Van Buskirk, post #21666684]

What is an SCR controller?

An SCR controller uses silicon‑controlled rectifiers to chop AC voltage, reducing effective voltage to the motor. It’s simple and cheap but reduces torque at low rpm, a key drawback for mixers. [Elektroda, Chuck Sydlo, post #21666683]

Is 1 Hp really 750 W? How does that help sizing?

Yes—1 Hp ≈ 750 W. Use it to estimate current and thermal load. Example: 750 W at 120 VAC is about 6.2 A, guiding wiring and controller selection. “1 Hp is 750w.” [Elektroda, stephen Van Buskirk, post #21666677]

Could a 4000 W controller run a 3 Hp motor?

A user reported a 4000 W single‑phase controller running a 3 Hp lathe motor. Treat this as anecdotal and validate with your motor’s datasheet and duty cycle. [Elektroda, Sarah Harris, post #21666681]

Do I need to oversize the motor for daily, heavy use?

Yes, plan for an oversized motor, especially with SCR control. This prevents excessive torque loss and extends service life in an industrial‑like duty cycle. [Elektroda, Chuck Sydlo, post #21666683]

What is an H‑bridge?

An H‑bridge is a circuit that drives DC motors forward or reverse by switching current direction. It’s mentioned because DC solutions can be cheaper at small sizes but are less attractive at higher power. [Elektroda, stephen Van Buskirk, post #21666677]

How do I wire a simple VFD speed control with a dial?

Select a VFD sized for your motor’s Hp and voltage.
Wire the motor to the VFD per its terminal diagram.
Connect a potentiometer to the VFD’s speed input and set min/max frequency. “Most VFDs can be controlled with a potentiometer dial.” [Elektroda, stephen Van Buskirk, post #21666677]

Can I rely on frequency range instead of extreme gearing?

Partly. Use VFD range to trim ratios, but still include a gearbox to deliver mixer torque at 1–24 rpm. This balances efficiency, cost, and stall resistance. [Elektroda, stephen Van Buskirk, post #21666678]

Any edge cases where low rpm still fails?

Yes. SCR‑driven induction motors may stall under sudden load at very low rpm. Plan for oversizing or switch to a VFD to mitigate this failure. [Elektroda, Chuck Sydlo, post #21666683]

Do single‑phase induction motors work with these controls?

Yes. Users reported success on lathes with single‑phase induction motors and aftermarket controllers. Verify controller rating, motor Hp, and duty cycle before use. [Elektroda, Sarah Harris, post #21666679]