Motor wiring 2

[jyman]

Hello - I'm a new user of this site and have some very simple questions regarding wiriing of motors (I have limited knowledge of this subject).

My situation: I have an opportunity to purchase a used machine with a motor that runs a hydraulic pump (at a very attractive price). The motor is currently set up to run on 3phase 460 volt power source. My location has 3phase 208 Volt source. The motor does not have the plate on it that would show how to wire it for lower voltages.

My questions: 1.Is there any way that I can find out if the motor will be able to be wired to run on lower voltage? If so, how does one do this?

Thanks in advance for any help.

 

[sreid]

If there is a wiring box on the motor you could see how many wires go to the motor. If there are three wires only, then it's a single voltage motor. If there are a lot of wires then it is multivoltage (but you won't know what they are). If the horsepower is not too big then your simplest fix might be to use a three phase step-up transformer.

 

[SteveKW]

Even with just three wires from the motor, any electric motor shop can bring out leads to make it 230 volts. Of course, you will have to derate the HP based on the lower voltage.

 

[ScottyUK]

Derate it? Why? The winding currents are still the same, but the line currents are higher at the lower voltage. The delivered power should be the same whether the connection is star or delta provided that the voltages measured at the winding are the same.



----------------------------------

If we learn from our mistakes,
I'm getting a great education!

 

[jyman]

Thanks for the info.
The machine is an injection molder, so the 460V power is also used for the heater bands. New heater bands would be placed on the machine. The controls and all other electric componnets run off two internal transformers. The manual shows the necessary connections for lower voltages, so they can be easily modified to run on the lower supply voltage.

There are multiple wires in the motor wiring box. As sreid said "but you won't know what they are". That is my question - are there any techniques to determine what wires would be put together for lower voltages?

About how much would a step up transformer cost that would work?
The machine is set up to use 460V, total rated current=26.6A and total apparent power=21.2 kVA (so @ 208V = total rated current=58.8A)

 

[jraef]

Try checking with the motor manufacturer for lead connections. There are industry standards that SHOULD have been followed, but that is not guarnteed, especially if the motor is an off-brand. And without ANY markings whatsoever, it will be very difficult for the average person, even electrically adept at normal tasks, to determine which ones go where.

Something to look for however is that the motor lead markings might be printed directly to the wire insulation itself. Most manufacturers of small motors do that, as opposed to nice clear heat-shrink plastic tags or terminal blocks that you may be used to. They are often difficult to see if the motor is old, but with some patience and a big magnifying glass I would bet you can find them.

Better yet, take it to a good motor shop and pay them for an hour of shop time to figure it out, clean it and check the motor over for any other latent problems. The peace of mind will be worth it in the long run IMHO.

"Venditori de oleum-vipera non vigere excordis populi"

 

[busbar]

 
Get a vendor quote on {30kVA grounded-Y 480V} something like

http://www.acmepowerdist.com/pdf/Page 14.pdf

 

[SteveKW]

Derate it? Why? The winding currents are still the same, but the line currents are higher at the lower voltage.


Hmmm. Well, I just didnt assume he had load that was less than his rated HP!

 

[aolalde]

Assuming the motor has 9 leads. Test the nine leads for continuity to determine whether the motor is wye or delta connected. The star connected motor will have only one set of three leads with continuity between them, and three sets of two leads with continuity. The delta connected motor will have three sets of three leads with continuity between them
For “Star Connected Motor”, label the three leads with continuity, #7, #8, and #9.
Flash with a battery the #8 & #9 pair. Clip a DC voltmeter to each pair of leads with continuity between them, until you find a pair that produces minimum deflection when flashing. This pair of leads is #1 & #4.
Move the battery positive lead on the #7 lead and the negative lead to be used for flashing the #8 lead. When the voltmeter is so placed on the #1 & #4 pair that it measures a positive deflection on the "make" of the negative #8 lead, the voltmeter positive lead is the #1 motor lead, and the negative voltmeter is the #4 motor lead.
Move to #7 & #9 leads with the positive lead on the #9 motor lead, and the negative to flash the #7 lead. The positive voltmeter lead should match the #3 motor lead if it shows a positive kick and the negative lead should be on the #6 motor lead. Shift the battery to the #8 & #9 pair, with the positive battery lead on the #8 lead and the negative used for the flashing. An upscale kick will identify the #2 motor lead. The positive voltmeter lead will be found on the #2 lead, and the negative voltmeter lead will be the #5 lead.
For a Motor “Delta Connected”: Find the corner leads #1, #2, and #3. Using an ohmmeter, identify the leads that show the minimum resistance to the other two leads with continuity. The lead located halfway between the other two will thus be the corner lead of the delta. Repeat this for each group of leads, marking them #1, #2 and #3.
The other two leads of each group must be: #4 & #9 in the group of #1; #5 & #7 in the group of #2; #6 & #8 in the group of #3.
Next, use the inductive kick test method to identify the proper markings for the other two leads of each group. The flux produced by #3 & #6 and #3 & #8 combined, will be perpendicular to the axis of #1 & #4 and #2 & #7. Opening and closing a switch in this circuit will produce a kick in coils #1 & #9 and #2 & #5, but no kick in #1 & #4 and #2 & #7.
Therefore, if the battery is connected from #3 & #6 and #3 & #8, opening and closing the battery circuit, the voltmeter will identify leads #1, #4, and #9 and can be distinguished by noting the magnitude rather than the polarity. The voltmeter can then be connected to terminal #2 for determination of the leads #5 & #7. Leads #2 to #7 which will give little or no deflection, and leads #2 to #5 will give a substantial deflection.
The battery is then transferred to the corner of #1. Tie the battery between leads #1 & #4 & #9. Making and breaking the circuit will be perpendicular to #3 & #8 and #2 & #5, resulting in no deflection. However, there will be a deflection from leads #2 & #7 and #3 & #6.
Finally place the battery on the #2 & #5 and #2 & #7 leads which are perpendicular to #1 & #9 and #3 & #6 leads, therefore creating no deflection on them. Leads #1 & #4 and #3 & #8 will have a deflection.

 

[humbleuser]

aolalde:

Thanks so much for your very informative reply. I, just like jyman, have an injection molder with a motor whose face plate is missing. Fortunately, the wires are all marked. I checked for continuity and determined that the motor is star (wye) connected with leads 7, 8 & 9 showing continuity. The other sets of wires are the same as you described.

My questions is this:

I am rewiring for a lower voltage (230V). Do I connect the single speed motor using the following?:

L1, 1, 7 (join)

L2, 2, 8 (join)

L3, 3, 9 (join)

4, 5, 6 (join)

I look forward to hearing from you. Again, thanks alot.

HU

 

[aolalde]

Yes, you are wright.

That is a 2 Wye connection regularly for 230 V 60 HZ.
1 Wye will be for 460 Volts.

 

[humbleuser]

Thank you.

 

[jyman]

aolalde

WOW! very detailed reply! However the first sentence of the reply states "Assuming the motor has 9 leads". After looking closely, this motor only has 6 leads coming form it. Your post at least helped out humbleuser.

So, can I follow a similar type of procedure with only 6 leads? Or (I know very little about motor wiring) does 6 leads mean I am out of luck?

Thanks again for the previous replies.

 

[aolalde]

A STD motor with six leads is made for wye or delta connection. You will find three pairs of leads. Continuity will show between 1&4, 2&5, 3&6.
For Delta connection the Voltage is 460/1.732 =265.6 Volts. Connect L1 to 1&6; L2 to 2&4; L3 to 3&5
For 208 V the voltage is short, only 78.3% and the motor will be very weak. If the load is not that tight to the motor it could work. Make a test with the load and measure the current and motor shaft rpm. If those are close to the nameplate values it will work.
Let me know if the numbers from the leads are lost. A similar procedure as detailed above will identify the leads.