Phase converters

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KP2

Senior Member
Location
New Milford, CT
I need to install a 3 phase converter on a 240v single phase residential service. I was expecting to pay a few hundred dollars for an static inverter.

I spoke to a tech rep and he claims that because the load is for a refrigerated box truck with a 5 HP motor @ 230 volts Y connected 3 Phase and the other 2 motors run on 12 volts that I need to use a rotory phase converter to get full power.

Can anyone confirm this the rotory unit is $1400.00
 

mxslick

Senior Member
Location
SE Idaho
Yes, generally speaking you need a rotary converter for anything other than a single motor load.

Has to do with how the static converter makes the third "phase" and the fact that static converters behave differently when starting and then running a motor.

Attempting to use a static converter in your application will result in the release of the magic smoke from the converter, your load or both.
 

dbuckley

Senior Member
Theres a difference between a static converter, and a static inverter; one is a superb low cost bodge, and the other is a UPS without batteries.

Give the guys at http://www.50hz.com a call - they may have a static inverter that'll convert 240 single phase to three phase and they'll have advice and back their product.

The little rotary converters are cheaper but they are mechanical and have losses, so an inverter may save money over the longer term, if this needs to run a lot.
 

jminer99er

Member
Location
Sacramento, CA
Yeah you dont want use a static converter. If I remember correctly, you only get 2/3 of the hp from the motor your trying to run when using a static phase converter.

There is a guy on here named Jraef who really knows about this subject, he could point you in the right direction.

I think 1400 is to high, but Im not the expert.


I built a really nice 10hp rotary phase converter for my dads mills and lathes, If you cant find the info you are seeking here, there is a website specifically for this topic its on practical machinist forum, and under tranformers, vfd, and rpc (rotary phase converters)

they can tell you the best deals and who to buy from so you're not getting ripped off!

James
 

KP2

Senior Member
Location
New Milford, CT
Theres a difference between a static converter, and a static inverter; one is a superb low cost bodge, and the other is a UPS without batteries.

Give the guys at http://www.50hz.com a call - they may have a static inverter that'll convert 240 single phase to three phase and they'll have advice and back their product.

The little rotary converters are cheaper but they are mechanical and have losses, so an inverter may save money over the longer term, if this needs to run a lot.

I'm waiting to here back from them.

someone has a 5 hp converter for 300$ on craigs list in scranton-wilkes-barre,pa area

I can't trust something from the list because to much money in product would be lost the first time it failed. I know most people have good luck there but I can't risk it but thanks for looking it up I'm greatful the help.

I did find another one for 1,000.

This job is going to be costly.
 

wasasparky

Senior Member
...and the other 2 motors run on 12 volts that I need to use a rotory phase converter to get full power...

12V or 120V?
Can the loads be segregated such that the converter dives only the three phase motor? 120V is readily available...
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
12V or 120V?
Can the loads be segregated such that the converter dives only the three phase motor? 120V is readily available...
I agree, please clarify if this was a typo or your other loads are really 12V. If they are, then a 12V power supply is not going to care much where it gets powered from.

If you meant 120V, I would just carefully route power to them from the original incoming 240V 1 phase supply and then deal with a phase converter separately for just the 3 phase going to that one motor if you can. I personally would use a VFD to power it, but I'm like that. There are plenty of good rotary units that would cost a lot less than $1400.00 or even $1000.00! Here's one.
 

KP2

Senior Member
Location
New Milford, CT
I agree, please clarify if this was a typo or your other loads are really 12V. If they are, then a 12V power supply is not going to care much where it gets powered from.

If you meant 120V, I would just carefully route power to them from the original incoming 240V 1 phase supply and then deal with a phase converter separately for just the 3 phase going to that one motor if you can. I personally would use a VFD to power it, but I'm like that. There are plenty of good rotary units that would cost a lot less than $1400.00 or even $1000.00! Here's one.
That is the company I think I'm going to use. The rep said to use the 6500- 11kVA. The list price is under 1k.

And yes the other 2 fans 12 volts DC. They normaly run off the trucks power and the truck power.
 

kwired

Electron manager
Location
NE Nebraska
Is the three phase motor a general purpose motor or a hermatic compressor? Even a Hermatic compressor may be in similar price range to switch to single phase. VF drive is still good possibility for using as phase converter but will have to be oversized if not specifically designed for single phase input and this will get you into the $1000+ range also.

BTW are you making this truck box something permantly connected or does the owner drive this truck and wish to power it while parked at his home?
 

KP2

Senior Member
Location
New Milford, CT
Is the three phase motor a general purpose motor?

BTW are you making this truck box something permantly connected or does the owner drive this truck and wish to power it while parked at his home?

Yes it a general motor turning a belt driven comp.

And yes the owner (my father inlaw) drives the truck during the day.

He got a good price on the truck and didn't realize the truck was 3 phase. Now that it is warming up in CT he needs to plug it in at night and over the weekend.
 

kwired

Electron manager
Location
NE Nebraska
Yes it a general motor turning a belt driven comp.

And yes the owner (my father inlaw) drives the truck during the day.

He got a good price on the truck and didn't realize the truck was 3 phase. Now that it is warming up in CT he needs to plug it in at night and over the weekend.

Unless there is a good reason to leave the three phase motor change it to single phase motor, instead of messing with the expense and other potential problems with phase conversion.
 

KP2

Senior Member
Location
New Milford, CT
Unless there is a good reason to leave the three phase motor change it to single phase motor, instead of messing with the expense and other potential problems with phase conversion.

That was my first respons when I was asked to do this job. It was easier for my father-in law to ask me to do the work. Then the price went up and up.

So over the holiday he said he's going to change the motor now.

what conserns me is that the guy he is using is a commercial kitchen DIY guy. He does it all when it comes to appliances and referigeration equipment. He is not an electrician. His respons to the rotory phase converter was that it was overkill and the static converter would have been fine.

His intent is to just change the motor as well. The entire control system needs to be rewired as well. Thier are other loads that need to be sorted out. His remark of "just change the motor, it's easy", has me woried.
 
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