550 volt motor on 480
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  1. #1
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    Default 550 volt motor on 480

    I just got a grinder(pedestal grinder) that turns out to be 550 volt machine. I was comparing the sound to another grinder I have that IS 480 volt machine. The 550 grinder has smaller wheels and spins up slower than the other grinder, it seems to run at a bit lower speed? There is a 2 leg starter/ overload that is working with a 550 coil.

    The voltage here is near 490 generally.

    Any issues or mitigation short of a transformer? It is not going to be used 8 hours a day, a few 5 minute bursts is about the workload expected.

    Steve

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    The torque generated by the motor is proportional to the square of the ratio of the difference in voltage.

    As long as the motor doesn't overheat and burn up, you're good, likely, no where close to getting it hot.

    it will run a bit slower.. like say 1700 rpm instead of 1750, under load, due to the lower voltage, but it doesn't matter.

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    Maybe a transformer?
    something like this?
    https://www.ebay.com/sch/i.html?_fro...9698+&_sacat=0

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    so your 550v grinder actually wants 600 volts, the difference is voltage drop and accounts for line voltage varying. most motors state 220 or 230 on the nameplate, even though line voltages are 240 just about everywhere nation wide.

    most 240v motors (230 on the nameplate) of service factor 1.25 also state "useable on 208". what they don't mention is that it uses up that extra .25 service factor. other motors give line amps for 208 and temperature rise. its higher for both. maybe 55C temp rise instead of 40 and the line amps like say, 15 instead of 13.

    a 5hp service factor 1.25 is safe to deliver 6.25hp without burning up on actual 230v line.
    it will safely deliver 5hp at 208 line voltage (which could be as low as 200) without burning up.

    as long as your grinder delivers the hp you need, i wouldn't waste any more time.

    cheapest method to add 120 volts to your 480v delta is very likely to buy 2, 240/480v:120/240v transformers and wire them like this:
    20211201_222112.jpg

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    I agree the two single phase would work. Two things concern me, first this is an old machine early 1950's so 600 volts is pushing it. Second I am guessing that I need 3~4 Kva, over 1Kva single phase boxes get expensive. A 208/240 backfed on 480 would give me 554 volts or ? Is the 208/240 not up to the high voltage? They should hi test to 1500?

    That ebay link is the best price in 3Kva I could find.

    Steve

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    i couldn't make out for sure what that ebay link is.


    again if the motor doesn't overheat, its not a problem. add a thermal fuse in series with the 120v coil that runs the motor overload/contactor.

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    Boost-buck formers will give you 10% pretty cheap, what do ya think ?

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    Quote Originally Posted by EmanuelGoldstein View Post
    Boost-buck formers will give you 10% pretty cheap, what do ya think ?
    Define "cheap" the boost formers I have seen are well over 500 for the Kva needed.

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    Quote Originally Posted by Steve in SoCal View Post
    Define "cheap" the boost formers I have seen are well over 500 for the Kva needed.

    KVA only has to be what is "added" by the transformer. So the voltage and current in the boost transformer.... not the entire kVA number. If you add 10% voltage at the same current, all you need is 10% of the new total VA figure.

    Actually, go by current..... if you have 100A, then any B-B transformer that handles 100A on the LV side will automatically have the VA rating corresponding to its LV side voltage.

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    The ebay link to the Transformer Fanuc A800L- 0026- 0003 is a good option.

    The primary would be connected in Y according to the diagram, 480v line applied to terminals 2,10,18 and terminals 8-16-24 connected together but not connected to anything else (unless your 480v is supplied as 277/480)

    output taken at terminals 1,9,17.

    So because this is a Y connection, and because you probably don't have Y power available with a neutral (thus you cannot connect the neutral to anything), any difference in current line to line would cause the transformer to saturate. However, the secondary is Delta and thus prevents this from happening.

    you should be able to get a good bit more than 5KVA out of that transformer without overheating it, because the secondary (which normally makes up half of the copper losses) is not being used. (except to pass the difference in current from one line to the other)

    it may be you can safely pull 7kva of 550v out.

    if you have 210 available anywhere, you can certainly use the transformer backwards to get 550v at 5kva.

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    I do have delta service with high leg delta on my 240 side so no 208 or 210.

    The amount of Kva required to boost the voltage with corner ground single phase transformers would be in the 1 Kva range then? That opens up a host of .5 to .75 Kva transformers with reasonable cost and form factors. I have a basic understanding of the process but this is a learning experience as much as anything.

    The grinder came from a remote sale by a seller who knew little of the machine. The photos showed a L61-30 plug and I never questioned the power requirements. The data plate was very corroded when i got the machine, some steel wool got the faint impressions of volts and amps. I have another grinder that is the same model that is 440.220 dual voltage machine. That grinder has new 14X3 wheels and spins up quicker and runs at a faster speed noticeable by casual observation.

    To sum up, I want to make this right and finding a solution that is both cost effective and well matched to the task is the goal. I appreciate the assistance/help in this. Regarding the Kva on a three phase transformer, do I need 4~5 or could a 1+ kva work. There are several of these at very attractive prices.

    Steve

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    Ok so we're talking about i'm guessing a 3 hp motor. not like a 1/2 hp bench grinder.

    The 120volt coil of the boost transformer is only passing the line amps of the motor, thats it.

    You can find two, 0.5KVA 120/240v : 240v/480v transformers and connect them in the open delta connection. this will get you 600 volts which will drop a bit under load. the motor can handle the voltage.

    alternatively even adding 48 volts might make a difference, which will open up your search options. this would get you 520 volts.

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    Quote Originally Posted by johansen View Post
    Ok so we're talking about i'm guessing a 3 hp motor. not like a 1/2 hp bench grinder.

    The 120volt coil of the boost transformer is only passing the line amps of the motor, thats it.

    You can find two, 0.5KVA 120/240v : 240v/480v transformers and connect them in the open delta connection. this will get you 600 volts which will drop a bit under load. the motor can handle the voltage.

    alternatively even adding 48 volts might make a difference, which will open up your search options. this would get you 520 volts.
    This IS a 3 HP grinder. So, I have 2X.500 Kva transformers 480/120. I wire the transformers open delta with H1- H4AndH1-H4 on the line side 480 volts. The load is connected to the X1- X2andX1-X2 to supply 600 volts. I need to ground the load side X2bridgeX1 lead. This then goes to the motor control/starter. What protection should be inline with the transformers?

    Steve

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    A 4hp motor overload upstream of the transformers would work fine.


    Not sure what you mean with grounding the load side. The open delta connection is by nature, not symetrical. Its ground referance is through the transformers.

    If you need 120 volts for the motor starter you can get it from one of the boost transformers but it will be floating at 240 to 3xx volts above ground

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    I read a thread regarding an open delta that used a ground on the high side? The starter on the machine is a full voltage starter, I may see what I have with a low voltage coil. I need some 120 for lights and a dust collector relay so a smaller control transformer off the 480 might be in order.

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    I have two .500 Kva 120-240/480 transformers a matched pair that I will use to boost the voltage. I just read a white paper on back feeding from ABB. The article states that when back feed the inrush current can be as high as 37 time the full load current. This means these have the potential to draw 44 amps of inrush current. The circuit powering the grinder is 30 amp 480 disconnect on a buss duct. I have a 30 amp fused disconnect and 10 gauge wire suppling the grinder.

    Based on the above is there a need to up the overcurrent protection and wiring to the grinder?

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    A .5kva 480v transformer inrush is just a few cycles, and by itself with no load, would probably not trip a 1 amp slow blow fuse.

    It will however increase the amps drawn by the motor from say, 48 amps, to 60 amps (because the voltage at the motor increased from 480 to 600)

    As for the motor overloads, take the line amps at the motor and add 25% to get the amps at the 480v line.

    https://documents.hammondpowersoluti...g-(HTP-16).pdf

    page 91 of the document, which is page 96 of the pdf.. connection diagram 8 is what you would use for a 120/240:240/480 transformer to boost or buck 480 into 600 or 600 into 480.

    h1-h4 being the 480v coil, the two 120v secondaries are in parallel.

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    The transformers I have only have taps for X-1 and X-2 externally. The diagram 8 on page 91 shows the H-1 low or line connected to the center leg and directly to the high side? The H-4 low or line side connected to X-1. Then X-2 connects to the motor on the two outer legs with the center leg only connecting to the H-1 and the motor?

    Steve

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    Can you post a photo of the nameplate of the transformers you have?


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