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Startrite 352 conversion

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spearojosh

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Hi all,
I recently acquired a 3 phase 352. I've taken out the old three-phase, 1hp motor and ordered a new 1.5hp, single phase motor. Can anyone tell me if the old switches (pictured) built into the machine will still work?

Thanks
Josh
 

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Fitzroy

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Unlikely. I’ve just moved a three phase Startrite 352 to single phase, via a VFD rather than motor conversion, and the relay under those switches was 400V not 240V. It would hold shut if I closed it with a stick but the coil didn’t have enough guts to pull itself closed with only 240v.

If you take the cover off and look at the coil behind those switches you can see its voltage. Make sure it’s unplugged when you take the cover off!

Fitz.
 

spearojosh

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Hi fitz, how would you recommend going about remedying this issue? A whole new switch or can you replace the coil alone?
 

Fitzroy

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I like to try and keep things original so would personally be installing a new contactor. I did some research when changing mine and it’s possible to buy a 240v original Danfoss unit but they were about £60. A new contactor will be about £10.

This will however require some degree of electrical competence to wire in, you’ll be using the original switch behind the start/stop buttons to close/open the coil circuit but the new contactor for the motor circuit.

I’m an engineer by degree with a fair degree of electrical knowledge due to experience through 20years in the oil/gas industry. However I’m not an electrician. Just my little disclaimer ;)

Regards.

Fitz
 

jimmy_s

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The existing contactor overload will be a three phase job so the unit will not be able to take the running current of the single phase motor. If the overload was suitably rated you could have run the single phase live through the three sets of contacts in series and that would have allowed the power side of the contactor to operate. The other issue is that the coil will probably be a 415v coil designed to operate between 2 phases and will not work wired to single phase. So unless you can find a 240v coil and a suitable overload then no its not going to be suitable.
 

Fitzroy

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The contactor in my saw is similar but not identical. I think mine is older.

The green starter button on your contactor is the metal strip on mine. The stop button on both our machines pushes on the mechanical interlock and breaks the circuit via the red stop on the contactor below the metal bit.

943D7C98-BDF0-471F-AFFD-4C11E7EDA747.jpeg

502A13FE-1671-4D2E-B982-F0CC7647E092.jpeg


There is a good post on wood haven showing the bits of a 352 contactor. It also describes why the Startrite approach is flawed as they’ve mounted the parts in a non dust proof enclosure, ie the saw box.
http://www.thewoodhaven2.co.uk/viewtopi ... 4&start=25

If you look at my second photo you can see a relay I’ve installed in addition to the original contactor. I am using the on switch, and off/ interlock cut out, in the coil circuit for this relay. The relay just sends a run signal to the VFD on the saw, ie very low power.

If you want to maintain the original start stop switch you’ll need to mount an additional new contactor inside the original housing and incorporate the start and stop from the original into the coil circuit on the new.

Fitz.
 

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