Static phase converter too big?

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butter

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Hi all,

Just picked up a new to me 1980 Webb 2s.

Motor tag shows 3 phase, 2amp. Shop I bought it from had 3 phase, but previously had it running on a static phase converter. Looks to be the original Taiwan motor, tag is super hard to read, so I won’t post a pic

Shop threw the static phase converter in for free. It’s a Phase-a-matic heavy duty PAM-900-HD. It shows a rating of 4HP min and 8HP max.


Is this converter too big to safely run the 2hp motor?

While I’d love to get a VFD, I was hoping to run it for a bit before more investment
 

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butter said:
Hi all,

Just picked up a new to me 1980 Webb 2s.

Motor tag shows 3 phase, 2amp. Shop I bought it from had 3 phase, but previously had it running on a static phase converter. Looks to be the original Taiwan motor, tag is super hard to read, so I won’t post a pic

Shop threw the static phase converter in for free. It’s a Phase-a-matic heavy duty PAM-900-HD. It shows a rating of 4HP min and 8HP max.


Is this converter too big to safely run the 2hp motor?

While I’d love to get a VFD, I was hoping to run it for a bit before more investment
Click to expand...
Motor will only pull amps it can use. Shouldn’t be any problem running the phase converter, especially since it was running that way before.

John
 
Thanks. That was my initial assumption.

Only nagging concern is they were also selling a lathe, which is rated at 5HP. I’m beginning to think they swapped the Phase-a-matic on me, plus it’s marked as “lathe”…
 
Throw on an idler motor (wire it so it is running anytime the static phase converter is running), then you can treat it like a rotary phase converter and it will be able to supply pretty well any 3 phase motor up to the capacity of the converter). Ideally you would find a 4hp motor, but 2 or 3 hp would still give real benefit (very cheap to do, because you can use most any surplus motor, you don’t care about shaft size or mounting details) and you won’t need to do any mods to you machine electrics (ie. with a VFD you have to move all the motor control functions to the VFD, that isn’t a big deal, lots of folks here to help you with that - but what you have is pretty well ready to go).
 
That is what I did, used the phase o Matic and a 7.5 HP motor for an idler, best to also add some oil filled capacitors to partially balance the voltage to the manufactured leg.
 
the major problem can be the starting capacitance.
generally speaking it only requires between 50 and 150Uf of capacitance per HP to start a 3 phase motor on single phase supply
that being said, at worst case your 2 hp motor would need a 300 Uf capacitor
if the static converter is rated for 8 HP, it is likely to have capacitance upwards of 600 to 800 Uf
at best case you'd be putting 2X the required capacitance to the windings of your 2HP motor, which is not a good thing...

Compounding the problem is the potential relay found in most static converters.
the potential relay will be called into action of dumping the start capacitors charge through the potential relay to the motor winding.

that's all well and fine if the workload doesn't take much power.
but as soon as the line voltage dips below somewhere around 165V, the start capacitor's charge is dumped by way of the potential relay into the motors windings, ad infinitum, until either the load is reduced, the cap blows up, the potential relay fails, motor windings fail, or the motor voltage is otherwise cut off.

a quick get around to the potential relay issue is the installation of a normally open momentary switch to the generated leg of the static converter.
the momentary switch would block unwanted winding activation, past the initial starting operation
the motor would last longer, provided that long periods of heavy loads were not demanded or necessary.

my advise would be to have a look at the starting capacitor inside the static converter and reduce the starting capacitance to somewhere around 300Uf, and install the normally open switch before i'd go any further

start capacitors are about $20
a momentary switch could be around $35

good luck on which ever road you travel
 
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The higher capacitance of the larger static converter will push more current through the windings during start up shortening their life.
 
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Thanks all for the feedback. I’ll look into the VFD, cap/momentary start and slave motor options.
 
Yeah, don't use it- it or the motor will overheat
It probably wasn't being used on the Webb in the first place if they just "threw it in"
It says min 4 HP for a reason
 
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