Molding machine: 208V vs 240V 5

[badger2011]

Mechanical engineer here. I have 8 hydraulic molding presses in my facility for over-molding silicone. We're moving them to a new building that runs 208V power supply. These machines have a call out on the side that says "240V 60 AMP" Can these run safely/efficiently on 208 V or do I need an electrician to amplify this?

I tried contacting the manufacture but they are out of business I have a very basic manual, but there is not mention of this anywhere


Thanks in advance for any insight you can offer!

 

[ScusaMe]

I've made a very good living replacing 230v motors and such with 208-230 vac motors....
Also adding Boost tranformers to raise 208 to 230 ..
back in the days when SCE went to 208 v as their standard ....(claimed it saved them a few dollars.... cost their customers a bunch, though!)

One problem that's hidden is that the 208v supplies can sag to 190v when loaded ... further compounding the problem.

If it were me, I'd find an ACME Transformer (or similar) catalog and select the appropriate BOOST transformers to raise the 208 to 230vac.

 

[jraef]

I think that the point of sagging voltage is the main issue. TECHNICALLY, a lot of 230V rated motors can safely run at 208V, but what you are doing is dancing on the thin ice of the built in +-10% voltage tolerance. So if you use 208V, it is -0% and when it sags, and it will, your motor will overload. It's a safer bet to use a Buck-Boost transformer for the motors, or change them out to ones that say they are rated for 208V on the nameplate.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[cranky108]

Just guessing but it appears to me that you might also have heaters in this machine, not just motors. So the transformer idea is quick to boost the voltage. You may also want to add a capacitor bank to also rise the voltage a bit.

 

[itsmoked]

The heater issue could well drive you nuts with much slower heat-up and temperature sag during various injection phases. The heat output drops with the square of the voltage reduction.

You might consider a larger set of transformers to run all the machines.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[badger2011]

Thanks for the replies!

Yes, there are heaters. We already wait 1 hour for the presses to get hot, so I don't want to wait any longer.

These buck-booster, will I need one for each machine?

http://www.acmetransformerspro.com/acmebuckboosttransformers.htm

 

[pwrengrds]

Either one smaller three phase unit for each machine or 1 larger unit for all of the machines. It depends on how big your machines are and how they are fed as to what is the best choice.

 

[ScusaMe]

Contrary to Jeff's (jraef's) comment, NEMA MG-1 2011 and real world experience would disagree.

TECHNICALLY, a lot of 230V rated motors can safely run at 208V,....

NEMA MG-1 Section II, Part 14.35 - OPERATION OF 230-VOLT INDUCTION MOTORS ON 208-VOLT SYSTEMS

14.35.1 General
Induction motors intended for operation on 208-volt systems should be rated for 200 volts.

[COLOR=red yellow]Operation of a motor rated 230 volts on a 208-volt system is not recommended[/color] (except as described in 14.35.2) [COLOR=red yellow]because utilization voltages are commonly encountered below the -10 percent tolerance on the voltage rating for which the motor is designed. Such operation will generally result in overheating and serious reduction in torques.[/color]​

NOTE: For every 10 deg. C. rise in operating temperature above rated, insulation life is cut in half ! In like manner, bearing life is also reduced.

14.35.2 Nameplate Marking of Useable @ 200 V
Motors rated 230 volts, but capable of operating satisfactorily on 208 volt systems shall be permitted to be labeled "Useable at 200 volts." Motors so marked shall be suitable for operation at rated (1.0 service factor) horsepower at a utilization voltage of 200 volts at rated frequency, with a temperature rise not exceeding the values given in 12.44, item a.2., for the class of insulation system furnished. The service factor, horsepower, and corresponding value of current shall be marked on the nameplate; i.e. "Useable @ 200 V. __________hp, __________amps, 1.0 S.F."

14.35.3 Effects on Performance of Motor
When operated on a 208 volt system the motor slip will increase approximately 30% and the motor locked-rotor, pull-up and breakdown torque values will be reduced by approximately 20-30%. Therefore, it should be determined that the motor will start and accelerate the connected load without injurious heating and that the breakdown toerque is adequate for the application.

NOTE—Utilization voltage tolerance is 200 minus 5% (190 volts) - Ref. ANSI C84.1 "Voltage Range A." Performance within this voltage tolerance will not necessarily be in accordance with that stated in 14.35.2​

Jeff, without knowing the specifics of the given motor(s) design, that's a rather dangerous statement to make.

 

[ScusaMe]

Badger2011

Here is a link to a PDF file published by ACME Transformer. It contains a treasury of information about Buck-Boost transformers and their application.

I think you'll find the information you need when considering them as a remedy for your situation.

http://www.acmepowerdist.com/pdf/Page_104-109.pdf

itsmoked and pwrengrds both raised good points to consider.

Regarding itsmoked's comment .... I'd suggest you do a COST - BENEFIT analysis to determine whether or not a new distribution transformer is a better solution than a Buck-Boost transformer for each machine. Your analysis should include not only materials, but cost of installation as well. Also, as you read through the ACME Transformer PDF file linked above, you'll become aware of not only the advantages of the Buck-Boost solution but also the disadvantages as well.



Kind regards,

 

[waross]

I think that jraef said something quite similar.

because utilization voltages are commonly encountered below the -10 percent tolerance on the voltage rating for which the motor is designed.

TECHNICALLY, a lot of 230V rated motors can safely run at 208V, but what you are doing is dancing on the thin ice of the built in +-10% voltage tolerance. So if you use 208V, it is -0% and when it sags, and it will, your motor will overload.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScusaMe]

Bill,

go back to my post and you will see that I took umbrage ONLY with jraef's statement : TECHNICALLY, a lot of 230V rated motors can safely run at 208V,

which I placed in Quotes .... I have no quarrel with the remainder of his post; only with that statement which I, and NEMA disagree completely with.

His statement lacks foundation and appears to be opinion based as opposed to FACT based.

Do you believe that "Technically" a lot of 230 volt motors can SAFELY run at 208V ?

That's what he said; that's what I challenged; and NEMA concurs : "Operation of a motor rated 230 volts on a 208-volt system is not recommended..."

NEMA did NOT say: "Technically a lot of 230 volt motors can SAFELY run at 208V."; that's what Jeff said, and it's simply not true.

 

[waross]

NEMA did NOT say: "

Technically a lot of 230 volt motors can SAFELY run at 208V.

that's what Jeff said, and it's simply not true.

Actually, NEMA mentions the -10% lower limit for motor voltage. That works out to 207 Volts.
Many of us disagree with your statement that "it's simply not true."
230 Volt motors should be capable of operation on 208 volts according to NEMA.
That's the voltage at the motor.
On a 208 Volt SYSTEM the voltage at the motor may be below 208 Volts and that is why both jraef and NEMA recommend that 230 Volt rated motors NOT be used on 208 Volt SYSTEMS.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

On a 208 Volt SYSTEM the voltage at the motor may be below 208 Volts and that is why both jraef and NEMA recommend that 230 Volt rated motors NOT be used on 208 Volt SYSTEMS.

Yes, thank you, exactly and hence my use of the word "TECHNICALLY" plus a detailed explanation as to how it does NOT really work that way.

Sheesh...



"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376