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  1. #14
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    Quote Originally Posted by r22coolguy View Post
    You know, if it ends up being 'dirty' control voltage a transformer would clean it up.


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    How so?


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  2. #15
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    Quote Originally Posted by VanMan812 View Post
    How so?


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    Well, I'm thinking the later models probably drop the neutral requirement and just use a transformer to make 120v, similar to how Hoshizaki does it with their 3-phase machines. The output 120v is real clean (no voltage fluctuations). I'm still of the opinion that your problem is related to damage to the contactor coil with the probable cause due to voltage issues(maybe the neutral leg?) although that wouldn't explain why it only occurs when reversing.

    Anyway, I was just brainstorming.


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  3. #16
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    The 120v is still a product of the incoming voltage, I believe it will fluctuate as the supply voltage fluctuates. I like where your going though. The timer is what feeds the contactors the control voltage. I wonder if that's causing problems? Wait wait wait... one time I ran the unit with only one contactor and no timer for a day or two. I was sure it would run without issues, except for some uneven baking, but it cut out like it always does. So the voltage coming from the timer is probably ok. The 115v leg that feeds the timer comes directly off the power switch. So could I be getting goofy voltage from that?? I don't think so but at this point anything is possible.




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  4. #17
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    So this is fixed now. How you ask? I'm really not sure. I had been working on this for quite a while prior to my first post. There were 6 techs that had worked on it before I got a run at it. I couldn't figure out exactly what was causing the contactors to drop a leg. I had asked my service director to come with me on one visit. The guy is a marvel in this industry. He is the hardest working guy I know. He has an ingenuity about him that I only see in the best techs. I could go on and on about him. Anyway, after we go over the oven he tells me to change the fan wheel. It was slightly out of balance. I made note of it on my first visit and discussed it with the other lead tech working on it and we both thought it was so minor it didn't warrant replacing. But if the boss says jump... So I changed it out when I rewired the motor circuit. I wrote my first post on this oven two days later when they called and said it was down. Well, unbeknownst to me it wasn't "down". It was making a noise because I didn't secure some wiring well enough and it started rubbing against the cooling fan. I then went Blodgett for some training and when I got back I asked if I could go back and take another crack at it and my boss said it's been fixed for a week. It never lasted more than a day before!

    So did the rewire fix it or the wheel? I can't see why the wheel would fix it but I checked every single wire I replaced. I checked the connections before I took out each wire. I tugged on the wire to see it there was a weak spot and then I ohmed each wire out. Every one of them was fine. So unless I missed something it was the wheel that fixed it. But how is that possible? The motor actually ohmed higher after the wheel replacement but that was because the design of the wheel design had changed a bit.

    We'll see how long it works for but as of right now it's working great.

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  6. #18
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    This might be obvious but does the system have start/run capacitors installed on the motors (if the motors are AC which they probably are)??

  7. #19
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    No capacitors, it's a three phase motor.


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  8. #20
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    Quote Originally Posted by VanMan812 View Post
    No capacitors, it's a three phase motor.

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    Sorry about the capacitor reference.

    If it was me - I would look to make sure the proper contactors were specified and implemented.

    The number one reason for contactor failure is misapplication -- i.e. you do not want to use a contactor that was "designed" for turning lights on/off for a motor application. Likewise, you do not want to use a "normal operation" motor contactor for motor jogging duty. Contactors have specific designs for specific purposes. Typically "more expensive" is better. If you would supply the mfg/part number for the ones you are using -- we could go do some research for you and see if that is the issue.

    The contactor may not be sized properly as well. You might have one sized to run "steady state" for years. But -- if your motors are turning on/off periodically -- they may only last a few thousand cycles as they are right at the operational limit.

    If your contactor has failed - you can look at the active surface. Some minor pitting as well as a black oxide coating is normal, but severe pitting or any melting or deforming of the contact surface is a sure sign of misapplication.

    Finally -- operating voltages play a role. Coils can overheat if operating voltages are too low or too high. Coil insulation degrades quickly when it gets too hot. When it degrades, it will short out (and blow a fuse) or just open and stop operating. This sounds like your situation as well.

  9. #21
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    Thank you for the reply but if you look through the thread I covered most of all of that. The oven has been great so far. We'll see how it goes from here.


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  10. #22
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    I worked on a roll up door that wasn't reversing properly. The inertia of the door kept the motor turning the same direction despite a relay circuit that was trying to send it the other direction. The door was over running and bending the track. Installed a delay on reverse kit from the manufacturer and the problem was fixed. Maybe unrelated to your story maybe not. Electrical works in mysterious ways...


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  11. #23
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    It would be a good idea to check the amperage on your contractor coil. If your getting resistance from a switch or a wire It is possible your over amping your coil and the contact coil is swelling up

  12. #24
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    I have seen contactor coils fail like this when a three phase HVAC unit has lost a leg. I think voltage feeds back some how from one of the remaining lines trying to make it back to the lost phase. The coil fails, acting like a fuse. If your problem shows up again (which I hope it doesn't) you might look at the breaker and power distribution.

  13. #25
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    Thanks, we haven't had any problems in months but if it happens again it I'll take another look at the incoming power.


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  14. #26
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    Sure sounds like the coil is swelling and interfering with the operation of the contactor. Do you have any recording type meters?

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