David A Cherry Posted May 14, 2022 Share Posted May 14, 2022 So I have a Racine ring cage, The motor says AC/DC.. after running for an hour or so the motor was warm but not overly warm but it got me to thinking what if I run a bridge rectifier would it run cooler or not.. So after hooking it up it took off like gangbusters.. Without measuring it sounded like a double the speed on high and then on low maybe only half again more speed than the AC.. But still noticeably faster.. It didn’t run any cooler if anything it got hotter faster.. didn’t want to burn anything up so I disconnected it and went back to alternating current.. can anyone explain what happened and why it ran so fast.. is there a possibility that the bridge rectifier increase the voltage.. Quote Link to comment Share on other sites More sharing options...
Russ Huber Posted May 14, 2022 Share Posted May 14, 2022 Do you have a digital strobe to clock blade speed? If so, clock your Racine blade speed on AC current. Next, clock your blade speed using rectified DC current. Not sure if you already installed a full wave bridge rectifier in your fan or not? If you did, use a variable transformer (Variac) to reduce your wall voltage to your fan checking blade speed to roughly match the blade speed your fan ran at on AC current. Then check the temp of your motor. Universal motors are known to run faster on DC current. Quote Link to comment Share on other sites More sharing options...
Russ Huber Posted May 14, 2022 Share Posted May 14, 2022 The R&M 8" list 3500 with universal motor has resistance wire in the base switch for the DC position to slow down the excessive DC current RPM. Quote Link to comment Share on other sites More sharing options...
Bill Dunlap Posted May 14, 2022 Share Posted May 14, 2022 An AC/DC motor is in reality just a DC motor. When AC is applied to the field coils, the properties of inductance actually converts the AC roughly to DC at the armature. It's not very efficient, but it works. When pure DC is applied to the motor, it becomes much more efficient and motor just loves it. You may need to throttle down the speed when using DC, but typically the motor will run smoother and faster than with AC and probably produce less heat. Cheers, Bill 2 Quote Link to comment Share on other sites More sharing options...
Russ Huber Posted May 14, 2022 Share Posted May 14, 2022 (edited) 32 minutes ago, Bill Dunlap said: An AC/DC motor is in reality just a DC motor. This brushed motor fan will only operate properly with speed fluctuation on alternating current despite a laminated stator. It will run on AC 120 VAC wall current with speed fluctuation. I tried juicing it with rectified DC current through a variable transformer and the motor was racing at roughly 35 to 40 volts and offered little to no speed fluctuation. The only way to reason the operation of this motor based on its simplicity is the manner in which the armature is wound. Edited May 14, 2022 by Russ Huber Quote Link to comment Share on other sites More sharing options...
David A Cherry Posted May 15, 2022 Author Share Posted May 15, 2022 On 5/14/2022 at 1:19 PM, Bill Dunlap said: An AC/DC motor is in reality just a DC motor. When AC is applied to the field coils, the properties of inductance actually converts the AC roughly to DC at the armature. It's not very efficient, but it works. When pure DC is applied to the motor, it becomes much more efficient and motor just loves it. You may need to throttle down the speed when using DC, but typically the motor will run smoother and faster than with AC and probably produce less heat. Cheers, Bill thanks Bill.. it all really makes perfect sense.. it runs like gangbusters on DC.. so much so that I thought it was some sort of voltage spike.. Glad to hear it will be OK.. Quote Link to comment Share on other sites More sharing options...
Russ Huber Posted May 15, 2022 Share Posted May 15, 2022 (edited) On 5/13/2022 at 11:15 PM, David A Cherry said: So I have a Racine ring cage, The motor says AC/DC.. after running for an hour or so the motor was warm but not overly warm but it got me to thinking what if I run a bridge rectifier would it run cooler or not.. So after hooking it up it took off like gangbusters.. Without measuring it sounded like a double the speed on high and then on low maybe only half again more speed than the AC.. But still noticeably faster.. It didn’t run any cooler if anything it got hotter faster. So what did you do to to get it to run gang busters on DC, David? Reduce your AC voltage with a variable transformer through the bridge rectifier? I just figured being you used a bridge rectifier you don't have pure DC source. But, I really don't think between the 2 DC sources it would make much difference in your fans operation. Edited May 15, 2022 by Russ Huber Quote Link to comment Share on other sites More sharing options...
Russ Huber Posted May 15, 2022 Share Posted May 15, 2022 I felt the same way Bill Dunlap did about universal motors, or brushed armature laminated stator fans at one time. I thought any of them would be compatible or operate much the same with DC or AC current. The unknown fan gave me a heads up that there are some exceptions. Quote Link to comment Share on other sites More sharing options...
Bill Dunlap Posted May 16, 2022 Share Posted May 16, 2022 I've done up a number of Northwinds with bridge rectifiers. I rewind the speed coils to give more desirable speeds. It takes a bit more resistance to keep the speeds reasonable, even with radiused wings and more pitch as well. Being more efficient, the wattage drops considerably, too. Quote Link to comment Share on other sites More sharing options...
David A Cherry Posted May 16, 2022 Author Share Posted May 16, 2022 5 hours ago, Russ Huber said: So what did you do to to get it to run gang busters on DC, David? Reduce your AC voltage with a variable transformer through the bridge rectifier? I just figured being you used a bridge rectifier you don't have pure DC source. But, I really don't think between the 2 DC sources it would make much difference in your fans operation. Russ I just used a bridge rectifier so it’s not clean direct current.. I didn’t use a variable transformer.. just straight 110 into a bridge rectifier and then to the fan.. I’m not sure what the speed is but it sounds like it’s doubling between AC and DC.. Then when I put it on slow speed it knocks it way down but it is still faster on DC.. anyway it kind of makes sense that it would speed up if it’s basically a DC motor to begin with.. I’m pretty happy with it on low speed running on The bridge rectifier.. I was just curious as to why it sped up considerably more than AC... Racine fan motors are very powerful for their size.. they also seem to be ozone generators.. You can smell some sort of electric ozone smell.. It might be from the oil from the bearing getting on to the brush commutator and burning off.. I kind of remember the same smell from my train set as a kid.. Brings back memories.. Quote Link to comment Share on other sites More sharing options...
Russ Huber Posted May 16, 2022 Share Posted May 16, 2022 1 hour ago, David A Cherry said: Russ I just used a bridge rectifier so it’s not clean direct current.. I didn’t use a variable transformer.. just straight 110 into a bridge rectifier and then to the fan.. I’m not sure what the speed is but it sounds like it’s doubling between AC and DC.. Then when I put it on slow speed it knocks it way down but it is still faster on DC.. anyway it kind of makes sense that it would speed up if it’s basically a DC motor to begin with.. I’m pretty happy with it on low speed running on The bridge rectifier.. I was just curious as to why it sped up considerably more than AC... Racine fan motors are very powerful for their size.. they also seem to be ozone generators.. You can smell some sort of electric ozone smell.. It might be from the oil from the bearing getting on to the brush commutator and burning off.. I kind of remember the same smell from my train set as a kid.. Brings back memories.. David, my bad. I misinterpreted your return message to Bill above with your DC operation. If you have your bridge rectifier inline on your power cord, you can slow the animal down on high speed using a variable transformer(if you have one) if you dig the way it runs on DC over AC. The variac is an easy fix for voltage control, and they are handy as h ell. 🙂 Quote Link to comment Share on other sites More sharing options...
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