Hello everyone, I need a little help. I have a friend who opened a pizza shop and has a Hobart 2HP 3 phase dough mixer (building has 240V Single phase 100 amp service) which is on a 3hp phase converter (which is what phase converter manufacturer suggested). Now when he starts it on speed 1 it works fine but when the speed is increased and it's mixing dough under load it trips breaker. When it's run on any speed and no dough thus no load it runs fine. I'm a little green with the phase converters....am I missing something or could it be perhaps an issue with motor or converter??:-? I should mention the phase converter has a 30A disconnect fused at 15A which is fed from panel on 15A breaker. Never blows fuses. Thanks in advance for your help!!
Phase Converter Help
- Thread starter awc
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The 15a fuses are obviously to handle short-term high current better than the breaker, which isn't surprising since, while the motor itself only needs about 7a at 3ph, the line current at 1ph will be quite a bit higher.
Is the motor 240v or 108v? Are the 15a fuses on the input to the converter or between the converter and the mixer? You may try raising the breaker size a bit. What size are the wires between the breaker and the converter?
Is the motor 240v or 108v? Are the 15a fuses on the input to the converter or between the converter and the mixer? You may try raising the breaker size a bit. What size are the wires between the breaker and the converter?
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
091122-2341 EST
On the surface if you assumed 1000 VA per HP, then 3000 VA are required from the 240 supply, or steady state 12.5 A. Phase converters are not very efficient, and may not provide a very balanced voltage to the load. It is also possible that under the heavy dough load that the motor is loaded heavier than 3 HP. Thus, supply load current may be higher than 15 A.
Is the phase converter rotary or just some capacitors?
Do some current and voltage measurements on the mixer motor under as heavy a load as possible without tripping the breaker. Also make sure it is not a 208 motor.
A better solution might be a VFD because you could limit torque and/or speed. I believe there are some 5 HP VFDs with enough capacitors to operate from single phase. Obviously if you limit torque and the load is too high the speed will automatically be less which might also be 0.
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On the surface if you assumed 1000 VA per HP, then 3000 VA are required from the 240 supply, or steady state 12.5 A. Phase converters are not very efficient, and may not provide a very balanced voltage to the load. It is also possible that under the heavy dough load that the motor is loaded heavier than 3 HP. Thus, supply load current may be higher than 15 A.
Is the phase converter rotary or just some capacitors?
Do some current and voltage measurements on the mixer motor under as heavy a load as possible without tripping the breaker. Also make sure it is not a 208 motor.
A better solution might be a VFD because you could limit torque and/or speed. I believe there are some 5 HP VFDs with enough capacitors to operate from single phase. Obviously if you limit torque and the load is too high the speed will automatically be less which might also be 0.
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mthead
Senior Member
- Location
- Long Beach,NY
Phase Converter Help
so to summarize what was just said-
[and to beat The Dead Horse also known as listing info and manufacturers instructions]..,
On the Dough Mixer mfg.stamped plate on the side of the unit;
1]What is the FLA max and min brkr size and conductor size for the unit when 208 /3ph
2]What is RLA max and min when 208/3ph
Now this is the better question...,
1]FLA brkr and conductor size if unit is installed 110/1ph and same question for RLA and has the unit been designed for that conversion possibility at all.
Now there's the rub..,for while we all know that the installation of a phase converter may make something possible..,
well you may also be finding out why the manufacturer never suggested using the machine in any fashion other than it's original design.
Unless this mixer is really old[which of course could set up a host of additional problems]I would bet there would be specs for the motor to be used as you want to now[i.e.-adapting to 1ph 110 via the employment of a phase converter which I'm also sure you checked to make sure is wired for correct rotational,right--cause we all know that mistake has been known to pop up when using a phase converter and going backwards thru dough..., well my breaker would pop to,'ya know what I'm sayin'.
so to summarize what was just said-
[and to beat The Dead Horse also known as listing info and manufacturers instructions]..,
On the Dough Mixer mfg.stamped plate on the side of the unit;
1]What is the FLA max and min brkr size and conductor size for the unit when 208 /3ph
2]What is RLA max and min when 208/3ph
Now this is the better question...,
1]FLA brkr and conductor size if unit is installed 110/1ph and same question for RLA and has the unit been designed for that conversion possibility at all.
Now there's the rub..,for while we all know that the installation of a phase converter may make something possible..,
well you may also be finding out why the manufacturer never suggested using the machine in any fashion other than it's original design.
Unless this mixer is really old[which of course could set up a host of additional problems]I would bet there would be specs for the motor to be used as you want to now[i.e.-adapting to 1ph 110 via the employment of a phase converter which I'm also sure you checked to make sure is wired for correct rotational,right--cause we all know that mistake has been known to pop up when using a phase converter and going backwards thru dough..., well my breaker would pop to,'ya know what I'm sayin'.
Rick Christopherson
Senior Member
From your description, I am betting it is a static converter. You need to get rid of it, as all it is doing is getting the motor spinning and then leaving the motor to single-phase from there on. The circuit breaker is tripping because the converter start relay is not cutting out with the heavier load.
For a motor this small, the most economical solution is a VFD, and you can find them starting at about $150.
For a motor this small, the most economical solution is a VFD, and you can find them starting at about $150.
240V motor. Fuses are on input to converter. #10 Wire.
Sorry, I forgot to mention it's a rotary converter. Going to try and get over there tonight to get some readings etc, I can then also get some more info to hopefully answer some of the other questions posted. Thank all of you so much for your help!!
Sorry but didn't get over there to look at it until tonight. Ok, I went all thru this thing and found nothing electrically wrong. Took several readings all over, plus I also found that it functions on every speed fine but speed 2 (has 4 total) thus I believe it to be something internal, perhaps gearing. These industrial dough mixers are rather complex I must admit. He is going to get a service tech to come look at the unit. Thanks to all of you for your help, you guys are great and have a Happy Thanksgiving!
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Logansport, just out of curiosity where in portage did you install? Was it a pizza shop? A friend of mine grew up in that area and refers to a pizza place by the name of J & J's................just curious if by some weird chance?????
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Thats funny, I do work for the store in Portage, and I wired the owners home, and I love there stuffed everything but the kitchen sink pizza, it's so full of meat and vegie's 2 pieces is a meal.
But no the mixer was at PePe's of South Haven, just to the south east of me.
Small world sometimes
I've yet to have a pizza from there but someday when I get up that way I plan on it.
Well, that takes you out of the loop.
Happy Turkey Day!
Thanks for your help Larry! Have a good one.
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