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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Solid State relay kills induction motor fans
I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects. These are inexpensive 20 inch box fans with induction motors. I have tried several brands and styles of fans. The latest was a Home Depot unit that only lasted 2 months.
Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK. Thanks for any ideas. I am going to switch over to a mechanical relay. Dean |
#2
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Solid State relay kills induction motor fans
On 07/27/2015 7:06 PM, Deane Williams wrote:
I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects. These are inexpensive 20 inch box fans with induction motors. I have tried several brands and styles of fans. The latest was a Home Depot unit that only lasted 2 months. Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK. Thanks for any ideas. I am going to switch over to a mechanical relay. Dean Have you had any other fans of the same make/model running on just 115VAC to see if they run any longer? They could be just cheap fans whose oil dries up. Hard to see where a SS AC Relay could hurt an induction motor if the motor isn't overheating. Does the fan still spin? Is there continuity in the winding? John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
#3
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Solid State relay kills induction motor fans
On 28/07/2015 03:06, Deane Williams wrote:
I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects. These are inexpensive 20 inch box fans with induction motors. I have tried several brands and styles of fans. The latest was a Home Depot unit that only lasted 2 months. Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK. Thanks for any ideas. I am going to switch over to a mechanical relay. Dean Do you do TIG/MIG welding in this garage? |
#4
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Solid State relay kills induction motor fans
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#5
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Solid State relay kills induction motor fans
On Tuesday, July 28, 2015 at 7:47:17 AM UTC-4, wrote:
http://www.bcae1.com/relays.htm https://goo.gl/TCo6MH |
#6
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Solid State relay kills induction motor fans
Hard to see where a SS AC Relay could hurt an induction motor if the motor isn't overheating. Does the fan still spin? Is there continuity in the winding? John :-#)# The motor still spins easily. There is no DC continuity from the power plug but I beleive this is normal for induction motors? Perhaps the overheat sensor has opened permenently. Home Depot gave me a replacement so I will try it again. These fans typically last for many years when plugged directly into a wall socket. This is a real mystery to me. Perhaps SS relays generate some large spikes on their output? I should check it with a scope. Thanks for the comments. |
#7
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Solid State relay kills induction motor fans
On Tuesday, July 28, 2015 at 3:15:20 AM UTC-4, N_Cook wrote:
On 28/07/2015 03:06, Deane Williams wrote: I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects. These are inexpensive 20 inch box fans with induction motors. I have tried several brands and styles of fans. The latest was a Home Depot unit that only lasted 2 months. Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK.. Thanks for any ideas. I am going to switch over to a mechanical relay. Dean Do you do TIG/MIG welding in this garage? No. I don't own a TIG/MIG welder. |
#8
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Solid State relay kills induction motor fans
On Tuesday, July 28, 2015 at 7:47:17 AM UTC-4, wrote:
http://www.bcae1.com/relays.htm Thanks for the detailed treatise on mechanical relays. But I am using a solid state relay (SSR). |
#9
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Solid State relay kills induction motor fans
On Wed, 29 Jul 2015 08:12:51 -0700 (PDT), Deane Williams
wrote: Hard to see where a SS AC Relay could hurt an induction motor if the motor isn't overheating. Does the fan still spin? Is there continuity in the winding? John :-#)# The motor still spins easily. There is no DC continuity from the power plug but I beleive this is normal for induction motors? Perhaps the overheat sensor has opened permenently. Home Depot gave me a replacement so I will try it again. These fans typically last for many years when plugged directly into a wall socket. This is a real mystery to me. Perhaps SS relays generate some large spikes on their output? I should check it with a scope. Thanks for the comments. You have an interesting problem. I hope you figure it out. I have never used SS relays, but I can't image they cause spikes and other anomolies that would kill a simple AC motor. Is the relay rated for inductive loads? By the way, I have a similar fan I purchased years ago. I just measured its DC resistance and found it to be about 18 ohms on its high setting. Clearly, that number is no indication of its impedance at 60 Hz while in operation, but it definitely conducts DC. My best guess is something is causing the motor windings to overheat and eventually open. Unfortunately, I can't think of any way to explain why that would happen. Pat |
#10
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Solid State relay kills induction motor fans
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#11
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Solid State relay kills induction motor fans
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#12
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Solid State relay kills induction motor fans
On Wed, 29 Jul 2015 19:32:06 +0100, MJC
wrote: In article , says... On Wed, 29 Jul 2015 08:12:51 -0700 (PDT), Deane Williams wrote: You have an interesting problem. I hope you figure it out. I have never used SS relays, but I can't image they cause spikes and other anomolies that would kill a simple AC motor. Is the relay rated for inductive loads? I can't be bothered to study SSRs so I just speculate... Could it be that the ones you use just deliver one polarity of AC instead of both, like a rectifier? Resulting in a DC component which the fans do not like... Mike. That's an interesting thought. Even if most SSRs handle full AC, maybe this particular one is faulty and only passes one polarity. That would certainly make the fan motor unhappy. Pat |
#13
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Solid State relay kills induction motor fans
On 07/29/2015 11:40 AM, Pat wrote:
On Wed, 29 Jul 2015 19:32:06 +0100, MJC wrote: In article , says... On Wed, 29 Jul 2015 08:12:51 -0700 (PDT), Deane Williams wrote: You have an interesting problem. I hope you figure it out. I have never used SS relays, but I can't image they cause spikes and other anomolies that would kill a simple AC motor. Is the relay rated for inductive loads? I can't be bothered to study SSRs so I just speculate... Could it be that the ones you use just deliver one polarity of AC instead of both, like a rectifier? Resulting in a DC component which the fans do not like... Mike. That's an interesting thought. Even if most SSRs handle full AC, maybe this particular one is faulty and only passes one polarity. That would certainly make the fan motor unhappy. Pat The motor would run at half speed at best. The motor won't overheat though unless it stalls/is jammed and can't self cool. It is more likely that the motors are just of a cheap quality construction (for example are the UL or CSA rated?) and fail far too easily. A SS AC modular relay is simply a high current TRIAC and these are used on many fans around the world - what do you think a motor speed control is? A moments research pulled up this PDF: http://www.omron.com/ecb/products/pd...utions_ssr.pdf (quote) The following will demonstrate the process to determine the effective ratings of non-motor control rated Solid State Relays for use in motor control applications: Example question: “Can I use a standard Solid State Relay (which is not included in the Crydom Motion Control Brochure and therefore without HP or KW Motor rating) to control the start/stop of a motor?” The answer: Yes, you need only to consider the motor nominal current value (FLA), inrush current value (LRA), motor power factor (typically 0.1 to 0.9) to select the appropriate turn-on switching type (zero-crossing or random) and possible need for SSR transient protection to select an appropriate Solid State Relay. (end quote) John :-#(# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
#14
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Solid State relay kills induction motor fans
On Monday, July 27, 2015 at 7:06:47 PM UTC-7, Deane Williams wrote:
I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects.,,, there is no smoke smell, no visible damage and if there is a capacitor it tests OK. Three possibilities: your thermostat could be chattering (sending a bouncy-switch signal to the SSR) and that is causing rectification. Your SSR could be a zero-crossing type, which is exactly the most stressful motor-start situation (and an inexpensive motor might take a magnetization at turn-off, then saturate at turn-on, and melt its fusible protector). Third, the SSR might be susceptible to some other signal than your thermostat (RF or maybe even input/output feedback oscillation). If you use an AC relay, it cannot operate fast enough to rectify; if you feed that AC relay with a triac-output optoisolator, with a smallish capacitor shunting the input terminals (1 uF?), there ought to be no drive-side problems. |
#15
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Solid State relay kills induction motor fans
"Deane Williams" wrote in message
... I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects. These are inexpensive 20 inch box fans with induction motors. I have tried several brands and styles of fans. The latest was a Home Depot unit that only lasted 2 months. Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK. Thanks for any ideas. I am going to switch over to a mechanical relay. Dean Some induction motors will have a thermal fuse incorporated onto the main winding. In the absense of a thermal fuse, this is my amateur speculation: The switching of the SSR creates voltage spikes. Normally these are easily absorbed by the induction motor. With enough time and heat, the lacquer insulation on the motor windings gets brittle, thermal cycling compromises its ability to insulate, then the voltage spikes begin jumping across high potential areas (between winding ends or where wire leads are tied to windings). If there is a capacitor involved, the arc is that much more spectacular, and the motor's demise quicker. Scott |
#16
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Solid State relay kills induction motor fans
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#17
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Solid State relay kills induction motor fans
diode the relay
use the resistor use 2 Tyco/Bosch mechanical relays with diodes for relays and inputs |
#18
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Solid State relay kills induction motor fans
On Wednesday, July 29, 2015 at 1:27:35 PM UTC-4, Pat wrote:
On Wed, 29 Jul 2015 08:12:51 -0700 (PDT), Deane Williams wrote: Hard to see where a SS AC Relay could hurt an induction motor if the motor isn't overheating. Does the fan still spin? Is there continuity in the winding? John :-#)# The motor still spins easily. There is no DC continuity from the power plug but I beleive this is normal for induction motors? Perhaps the overheat sensor has opened permenently. Home Depot gave me a replacement so I will try it again. These fans typically last for many years when plugged directly into a wall socket. This is a real mystery to me. Perhaps SS relays generate some large spikes on their output? I should check it with a scope. Thanks for the comments. You have an interesting problem. I hope you figure it out. I have never used SS relays, but I can't image they cause spikes and other anomolies that would kill a simple AC motor. Is the relay rated for inductive loads? By the way, I have a similar fan I purchased years ago. I just measured its DC resistance and found it to be about 18 ohms on its high setting. Clearly, that number is no indication of its impedance at 60 Hz while in operation, but it definitely conducts DC. My best guess is something is causing the motor windings to overheat and eventually open. Unfortunately, I can't think of any way to explain why that would happen. Pat the thermometer rapidly operates relay on and off circuitry passing something of this to the fans who are confused square one without dioding separating the systems unbalanced properties. |
#19
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Solid State relay kills induction motor fans
AC relay with a triac-output optoisolator, with a smallish capacitor shunting
the input terminals (1 uF?), there ought to be no drive-side problems. /////////// they're mating http://goo.gl/Dj00S9 |
#20
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Solid State relay kills induction motor fans
Deane Williams writes:
The motor still spins easily. There is no DC continuity from the power p= lug but I beleive this is normal for induction motors? Perhaps the overheat= sensor has opened permenently. You got it. As they age the bearing dry and they pull more current. Eventually they open the Microtemp protecter within.... -- A host is a host from coast to & no one will talk to a host that's close.......................... Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 |
#21
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Solid State relay kills induction motor fans
David Lesher wrote:
Deane Williams writes: The motor still spins easily. There is no DC continuity from the power p= lug but I beleive this is normal for induction motors? Perhaps the overheat= sensor has opened permenently. You got it. As they age the bearing dry and they pull more current. Eventually they open the Microtemp protecter within.... ** "The motor still spins easily" contradicts that idea. Seen a few cheap Chinese fans with tight/stuck bearings - takes a fair bit of solvent to get them spinning again. The OP has no so far bothered to open a fan a check the motor wiring for continuity. .... Phil |
#22
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Solid State relay kills induction motor fans
Deane:
What relay are you using? What is the the motor? Some SSR bricks designed for this purpose have 3-32 V for an input and no series resistor is required. A heat sink with the appropriate thermal grease is. They have to be triac or back to back SCR's. Some offer to switch at zero current. It should be random. Some require series resistors. Some SSR's are triacs, dual SCR's, SCR's (won;t work) or MOSFETS (won;t work). |
#23
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Solid State relay kills induction motor fans
On Tuesday, July 28, 2015 at 10:06:47 AM UTC+8, Deane Williams wrote:
I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects. These are inexpensive 20 inch box fans with induction motors. I have tried several brands and styles of fans. The latest was a Home Depot unit that only lasted 2 months. Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK. Thanks for any ideas. I am going to switch over to a mechanical relay. Dean If you need the thermal fuse, please feel free to contact . We are thermal fuse, MOV and thermal protected MOV manufacturer in China. Any question, please do not hesitate to inform us. Best Regards Leo |
#24
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Solid State relay kills induction motor fans
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#25
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Solid State relay kills induction motor fans
Deane Williams wrote in
: I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects. These are inexpensive 20 inch box fans with induction motors. I have tried several brands and styles of fans. The latest was a Home Depot unit that only lasted 2 months. Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK. Thanks for any ideas. I am going to switch over to a mechanical relay. Dean So you blew some fans. But what about the SSR? Is it suited for diving these motors? Some properties are as important as properties of a mechanical relay and even with the right specs it may be defective. Then, what about the signal diving the SSR? If it comes from a mechanical switch, the contactbounce can damage or destroy the SSR which in turn can blow the motor(s). SSRs like to be driven by clean signals and tend to be much more unforgiving them their mechanical couterparts. petrus bitbyter |
#26
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Solid State relay kills induction motor fans
M Philbrook wrote:
" The motor still spins easily. There is no DC continuity from the power plug but I beleive this is normal for induction motors? " The OP has no so far bothered to open a fan a check the motor wiring for continuity. Yes he did, There is no continuity.. ** ".. from the power plug ... ". Box fans typically have timers, 3 way speed controls and tilt switches, any of which could be the real problem. Which means it's been operating hot! ** Not likely with perfectly free bearing and no damage. ..... Phil |
#27
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Solid State relay kills induction motor fans
On 07/31/2015 7:42 PM, Phil Allison wrote:
M Philbrook wrote: " The motor still spins easily. There is no DC continuity from the power plug but I beleive this is normal for induction motors?" The OP has no so far bothered to open a fan a check the motor wiring for continuity. Yes he did, There is no continuity.. ** ".. from the power plug ... ". Box fans typically have timers, 3 way speed controls and tilt switches, any of which could be the real problem. Which means it's been operating hot! ** Not likely with perfectly free bearing and no damage. ..... Phil Hi Phil, I don't think anyone read my quote (July 29) from a SSR (Omron) manufacturers' FAQ PDF about using non-motor rated SSRs with induction motors. As they said, as long as the SSR has sufficient rating to handle the start up current (etc.) there will be no problems for the SSR. The only thing folks haven't considered is a voltage surge - that could take out the fan without harming the SSR. The wiring may have problems where the neutral fails in a sub-box leading to 240VAC going to a motor designed for 120 - the motor would not last long, yet wouldn't give obvious signs of failure as the internal overheat fuse would open quickly... I have no other ideas unless he isn't giving the house elves enough food and clothing. John :-#(# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
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