Electrical modification (way non-aviation)

[rcaligan]

I'd like to get some advice on a project I have. I'm trying to modify a popcorn popper to roast coffee. An OTS popper runs the blower motor in series after passing the current through the heating coils. I'd like to control these separately so I can vary the temperature in the coils without changing the blower speed.

Any help at all would be appreciated. Thanks!

 

[Skip Miller]

I'd like to get some advice on a project I have. I'm trying to modify a popcorn popper to roast coffee. An OTS popper runs the blower motor in series after passing the current through the heating coils. I'd like to control these separately so I can vary the temperature in the coils without changing the blower speed.

Any help at all would be appreciated. Thanks!

More information needed.

First, why is the popper OTS? What doesn't work?

Second, are you sure that the motor and the heater are in series? If that is true, there will be a significant voltage drop across the heater so the blower motor is probably not 110V. See if you can find a voltage rating on the motor and heater coil.

-Skip

 

[rcaligan]

More information needed.

First, why is the popper OTS? What doesn't work?

Second, are you sure that the motor and the heater are in series? If that is true, there will be a significant voltage drop across the heater so the blower motor is probably not 110V. See if you can find a voltage rating on the motor and heater coil.

-Skip

Sorry...I meant OTS to be "off the shelf" not "out of service."

Yes, they are in series. I've done some research that the voltage to the motor possibly drops to 20V by passing the current through the heating coil, but no idea about amps. Googling the part # on the motor isn't turning up anything.

 

[Skip Miller]

Sorry...I meant OTS to be "off the shelf" not "out of service."

Yes, they are in series. I've done some research that the voltage to the motor possibly drops to 20V by passing the current through the heating coil, but no idea about amps. Googling the part # on the motor isn't turning up anything.

OK, let's measure the voltage across the motor while it is in operation. Do you have a VOM? Or just a voltmeter?

What you are going to need is a second resistance, equal to that of the heater, to put in series with the motor so that it runs without burning out. Then you are going to need a way to vary the voltage across the heater so you can control the heat output.

Alternatively you could blend in some cool air after the heater... but since your existing blower is undoubtedly on the cool side of the heater, you will need pressure to force cool air into the airstream after the heater. We are getting more and more complicated.

It seems like RonCo should make a $29.95 (+ $18 shipping and handling) roaster to do just what you need!

-Skip

 

[KennyFlys]

Looks like there numerous options. Among them...

http://www.sweetmarias.com/

More specifically...
http://www.sweetmarias.com/prod.freshroast.shtml

Does the appearance look familiar?

Personally, I'm waiting for microwaved coffee roasting. ​

 

[gismo]

I'd like to get some advice on a project I have. I'm trying to modify a popcorn popper to roast coffee. An OTS popper runs the blower motor in series after passing the current through the heating coils. I'd like to control these separately so I can vary the temperature in the coils without changing the blower speed.

Any help at all would be appreciated. Thanks!

First, I see a control/safety issue here. The blower is connected in series so that if anything obstructs the airflow the current through the heater drops off. Otherwise the heating element would just get real hot real fast. Your control mechanism should provide the same feedback somehow.

As far as the required current, the motor current and the heater current must equal the line current since all are in series, so you can take the dataplate wattage rating and determine the current (amps = watts/120).

With a voltmeter you can measure the drop across the motor and heater when it's running to determine what voltage is needed for each.

I think I also need to know what your intentions are WRT varying the motor speed and heater output. IOW do you want to reduce the heat while leaving the blower at full speed (good)? Or were you thinking of slowing down the motor while the heater runs at full power (bad).

 

[rcaligan]

The idea was to vary the temperature while keeping the fan at full speed.

My wife and I have visited the Sweet Maria's site a lot and ordered beans from there. They also have a lot of good links to commercial roasters and do-it-yourself varieties.

I appreciate everyone's help with this, but I think I'm going to hold off on the modification for now. I certainly don't want to burn our house down!

 

[gismo]

The idea was to vary the temperature while keeping the fan at full speed.

My wife and I have visited the Sweet Maria's site a lot and ordered beans from there. They also have a lot of good links to commercial roasters and do-it-yourself varieties.

I appreciate everyone's help with this, but I think I'm going to hold off on the modification for now. I certainly don't want to burn our house down!

You could probably accomplish this with a couple of incandescent light bulbs. You need to drop the voltage to the motor with one and the maximum voltage to the "speed" control (actually the heat control) with the other. If you really want to go there I can tell you how to pick the lamps, but this approach will definitely have the potential to overheat the heating element if the airflow gets blocked. There may be an overtemp cutoff (fixed thermostat) in there now which would probably prevent fires in such an occurrence. You can check for that by turning up the heat on the existing setup and blocking the fan. If the thing quits before catching fire, (should quit within seconds) then the cutoff is present.