The Start of My Coal Forge

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For general information, an electric motor is an electric motor, is an electric motor.  What matters is the electricity getting to the motor.  Reduce the amount of electricity going to the electric motor and it slows down.  Try using a light dimmer switch to turn on the motor.  Those can be picked up at any Home Depot or Lowes, or instal and adjustable restate between your switch and the motor to control the amount of electricity to the motor.  I use to teach troubleshooting and repair of mobile electric generators which used electric motors.

[the iron dwarf]

altering the frequency of the ac is the best way, feeding a 240 volt 50 hz ac motor with 110v  will stall it under even slight load.

most motors I work on are 415 volt and I can vary the frequency from 25 hz to 300 on some if the motor can take it

[Marc1]

Some motors can take speed variation others don't. The main concern is usually overheating. 

Best way to change the airflow is with a gate. if you don't, not only you will go through tons of coal, you will burn the edge of the firepot very quickly

However for the OP, the problem you will have with that forge is not the blower, that is easily fixed or altered, but with the way you built your firepot. It will get blocked with clinker all the time. Been there done that. Build a proper clinker breaker with a rotating triangular block of steel or similar. 

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1. Standard frequency for house current in the US is 60Hz.  50Hz is used overseas in Europe. One actually needs a converter to make electrical equipment functional overseas.  Hz (Hertz), Frequency or Cycles will effect performance only because equipment is designed for a specific frequency or cycle.  But reducing a voltage does not change the frequency of the voltage.  Take a motor that runs off 115/120 volts for instance and its rpms is 100, dropping the voltage will only make it run slower.  Unless there are internal solid state electronics that require 115/120 volts to function.  

Marc it sounds like we are on the same page for variable and constant speed motors but I really like your info on burning the edges of the fire pot and just changing airflow with a gate.  

Iron Dwarf, you work with some heavy duty motors.  I've worked with electric motors that could be configured for 440 VAC or 220 VAC.  Cycles remained the same at 400 Hz due to the naval aircraft they serviced.  It sounds like the system your motors are plugged into are designed to accept various cycles.  That is a whole different can of worms.

[Marc1]

Actually, when all of that 110/220 and 50/60 is all correct, for all practical purposes, there is a manufacturer in the US called Dayton that makes a string of different blowers very reasonably priced that work on 220/240V and 50 or 60 HZ irrespectively, making it the choice for anyone wanting to build a solid fuel forge either in the US, Europe or Australia. 

Using a 220V 60 Hz motor on 220-240V 50 Hz would normally mean losing power and overheating, this light motors work irrespective of that variation in frequency because being so small they rely on the load to regulate the speed and can take it no problem. Dayton actually specifies this on their technical data. They are also way quieter than those monstrous jumping castle blowers. 

Of course a 3 phase motor or 3 phase + neutral motor works on different principles and is better suited to speed variations by electronic means. 

[the iron dwarf]

the frequency determins how many of the motor poles  pass per second, change the frequency and you change the speed, keep the frequency the same and lower the voltage and the motor will try to run at the same speed but with much less power so can stall or overheat.

here 2 or 4 pole motors are most common but you also can get others meaning the most common motor speeds are about 2850 and 1425 rpm, it the us 2 and 4 pole motors will run faster so your common speeds will probably be more like 3300 and 1750 at a guess.

with DC shunt motors you vary voltage to vary speed

run a motor expecting 60 hz on 50 hz as long as voltage is correct motor will run a bit slower.

the magnetic field in the motor rotates at a speed determined by the frequency and that frequency is not determined by the load, if the motor cannot turn that fast due to the load on it it will get hot

[Marc1]

Explanation given to me by an engineer:

Looking at the specs for that motor, It appears that when driven with 60 Hz, the fan load increases and limits the speed to not much more than the 50 Hz speed.
eg: 
50 Hz speed: 2700 slip = 300 RPM
60 Hz speed: 2880 slip = 720 RPM.

So it appears that they are running the motor near the motor torque limit and letting the fan load limit the speed.
With an integral HP motor this would be wasteful and inefficient.
To use an integral motor in this fashion, The current may be 200% of normal running current. This can be done if the wire gauge is increased to carry the greater current without overheating.
But that means a larger core, which means more wire again.
In practice you could design the motor for about 340 or 350 Volts and then run it on 230 Volts. Same result.
Possible but prohibitively wasteful.
But this is a 1/30 HP motor. In a motor this small, it is not costly to allow the load torque to limit the speed and use very high slip frequencies.
Consider: A 1760 RPM motor has about 2.2% slip.
This motor has 10% slip at 50 Hz and 20% slip at 60 Hz.
You can use such a design easily at 1/30 HP, but not at higher HPs.

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Though I am new here, I have a vast base of technology and you've put together a great forge here.  Well designed.  Thanks for posting this thread.

I am planning my first forge and expect it to be similar to your's.  I may have to wait a while to tackle this project because I'm preparing to move soon.  I'm going to learn all I can and build my forge at my next location.  I'm moving from Florida to Texas.  I just hope I shrivel up and die from a lack of water out there.

 

[ThomasPowers]

Where in Texas?  I can see El Paso from my front porch and most of my team is in Austin...(and kinfolk in Katy...)

[ShortMagPirate]

All this talk of motors and frequencies and voltages makes my head hurt. And this is what I do for a living (E&I Supervisor at a major gold mine (currently)...)
There is actually a lot of good and in-depth technical info in this thread... but for all intents and purposes, it's really overkill for what we need. 
The bottom line is that the best, safest and most efficent way to vary the airflow output of a small single speed AC motor driven fan or blower is mechanical.
IE: via an air gate as Marc1 suggests below. Sure, you probably can get away with using a dimmer switch for a while, using such a small motor, but a valve or gate is a relatively simple thing to incorporate. I may be new to the intricacies of forging, but the principles are the same whether applied to combustion (coal boilers, stoves, incinerators, etc.) cooling, dust suppression, ventilation or anything else requiring controlled air flow. I have a 1/4 turn ball valve on my forge set up, as well as the ability to simply redirect the blower nozzle away from the inlet pipe, but there are plenty of other designs that I have seen, all of which would work just fine.

This thread is actually one of the ones that originally brought me to this forum, so I've been watching this build with interest...

On 4/7/2018 at 3:37 PM, Marc1 said:

Some motors can take speed variation others don't. The main concern is usually overheating. 

Best way to change the airflow is with a gate. if you don't, not only you will go through tons of coal, you will burn the edge of the firepot very quickly

However for the OP, the problem you will have with that forge is not the blower, that is easily fixed or altered, but with the way you built your firepot. It will get blocked with clinker all the time. Been there done that. Build a proper clinker breaker with a rotating triangular block of steel or similar. 

 

14 hours ago, ThomasPowers said:

Where in Texas?  I can see El Paso from my front porch and most of my team is in Austin...(and kinfolk in Katy...)

TP: my son's girlfriend is from Katy, and I have a friend who up until very recently worked in a salt mine just a few miles north of there... such a small world we live in.