Re-wire/re-motor band saw

[G-ManBart]

Hey all, I'm getting ready to attempt my first re-motor project and thought it would be smart to get a little expert advice before I start. I'll say up front that I'm no electrician, but I'm familiar enough with Ohm's law to keep from hurting myself

I bought a clean Wells horizontal bandsaw that was set up for 3-phase power. I have the correct single-phase replacement motor ready to install, and it currently has the leads set for 240V service. The motor shows a max of 4.4A current draw at 240V.

Since the saw was three-phase it has a magnetic starter switch, which shouldn't be necessary for single-phase, correct? The saw also has an automatic shutoff switch wired to the start/stop control box.

What I was thinking of doing was essentially bypassing the current wiring setup, adding a service disconnect with midget 5amp fuses, and then running a simple heavy duty on/off switch....essentially leave all the old stuff in place other than the wires to the motor and the automatic shutoff relay (guessing it's a relay, but I haven't taken it apart to look).

Am I missing anything obvious, or is this a dumb plan?


I've heard/read that some folks have retained the original wiring and used it to power the replacement single-phase motor, but that seems overly complicated for no reason (unless I'm missing something). This page covers a magnetic starter to a single-phase motor:
http://wiki.vintagemachinery.org/motor starter wiring diagrams.ashx

I'll post a couple of pictures of the current setup for reference.

 

[jakemac]

Can't help with the wiring, but I'm pretty sure that you'll be blowing fuses if you limit yourself to 5a. The 4.4a rating is for the run draw. It doesn't take into account the amps drawn at startup. You might want to use 7 or 10 amp fuses.

 

[bmwrd0]

Can't help with the wiring, but I'm pretty sure that you'll be blowing fuses if you limit yourself to 5a. The 4.4a rating is for the run draw. It doesn't take into account the amps drawn at startup. You might want to use 7 or 10 amp fuses.

Yeah, you need to have an idea of LRA before sizing a fuse, its not something I would go to a slow blow fuse on. Certainly no need for a mag starter.

How much HP are you talking?

 

[G-ManBart]

Yeah, you need to have an idea of LRA before sizing a fuse, its not something I would go to a slow blow fuse on. Certainly no need for a mag starter.

How much HP are you talking?

It's a 3/4hp Baldor. I was wrong...it shows 4.2A as the high voltage full load. I was sort of thinking 5A might be a bit too low.

http://www.baldor.com/catalog/L3507

 

[bmwrd0]

Starting Amps are listed (for that motor) as 24.7 under the performance tab. So, the fuse needs to be sized for that AT STARTUP. With just 3/4hp, I would just run it at 115v probably with a slow blow (I was thinking a bigger moter cause 240v) through a common motor starter switch. That way, you can run it off a regular plug if you need to move it around. They list it as 8.4 at 115v, so a 10a slow blow should do it. This should do for a switch: http://www.amazon.com/dp/B00CONEYIA/?tag=atomicindus08-20

But I haven't delt with this since trade school, and would defer to others. Also, call Baldor and get a recomend from them.

 

[454ragtop]

Starting Amps are listed (for that motor) as 24.7 under the performance tab. So, the fuse needs to be sized for that AT STARTUP. With just 3/4hp, I would just run it at 115v probably with a slow blow (I was thinking a bigger moter cause 240v) through a common motor starter switch. That way, you can run it off a regular plug if you need to move it around. They list it as 8.4 at 115v, so a 10a slow blow should do it. This should do for a switch: http://www.amazon.com/dp/B00CONEYIA/?tag=atomicindus08-20

But I haven't delt with this since trade school, and would defer to others. Also, call Baldor and get a recomend from them.

X2, I'd run it on 115 volt as well. If you're going to be the only one running it, I'd just run it off a good quality switch, that's what I do on my own saw. If you'd rather have a protective switch like linked to above, I probably have one in my stash I'd sell a lot more reasonably.
Jim

 

[G-ManBart]

Starting Amps are listed (for that motor) as 24.7 under the performance tab. So, the fuse needs to be sized for that AT STARTUP. With just 3/4hp, I would just run it at 115v probably with a slow blow (I was thinking a bigger moter cause 240v) through a common motor starter switch. That way, you can run it off a regular plug if you need to move it around. They list it as 8.4 at 115v, so a 10a slow blow should do it. This should do for a switch: http://www.amazon.com/dp/B00CONEYIA/?tag=atomicindus08-20

But I haven't delt with this since trade school, and would defer to others. Also, call Baldor and get a recomend from them.

Thanks...I looked at the performance tab and totally missed the starting amperage.

I think running it 115 makes a lot of sense, and it's easy enough to change the pre-wired configuration.

 

[G-ManBart]

X2, I'd run it on 115 volt as well. If you're going to be the only one running it, I'd just run it off a good quality switch, that's what I do on my own saw. If you'd rather have a protective switch like linked to above, I probably have one in my stash I'd sell a lot more reasonably.
Jim

I'll be the only one using it, so that part makes things easier. I was thinking maybe a protective might be a bit of overkill, but figured it was worth asking the question.

 

[foghorn1966]

Myself, looking at your starter pic. I would leave your motor wired for 240V, change the primary taps on the control transformer to 240/250 Volts, and buy two properly sized overload heaters for your starter. You would only use two phases on the contactor. Your existing control switches should work fine.

 

[G-ManBart]

Myself, looking at your starter pic. I would leave your motor wired for 240V, change the primary taps on the control transformer to 240/250 Volts, and buy two properly sized overload heaters for your starter. You would only use two phases on the contactor. Your existing control switches should work fine.

Okay, I think I'm tracking with you, but just to be sure, I've got a couple of questions.

First, going off the markings on the control transformer all I would need to do would be to jumper H2 to H4, right? That way H2 and H4 would look the same as H1 and H3 do now?

Does it matter which phase/leg I leave off of the contactor? I'm guessing just leave off L3, but I'd rather not guess

 

[ddawg16]

Can you post a pic of the motor name plate?

I'm inclined to agree with going the 120Vac route. Just assume it's going to be running off one of your 20A wall ckts. There should be enough time delay in your breaker for it to start up. No extra fusing needed.

I'd pull the contactor and transformer and sell them on Ebay.

 

[Doug Arthurs]

I would use the original wiring and as mentioned set the transformer to 240v and run the motor from 240v. This leaves all the controls as original. You will have a blade that stops at the end of the cut and a safe magnetic motor starter. Plus you won't have to replace anything except for fuses and the overload heater.

 

[G-ManBart]

I would use the original wiring and as mentioned set the transformer to 240v and run the motor from 240v. This leaves all the controls as original. You will have a blade that stops at the end of the cut and a safe magnetic motor starter. Plus you won't have to replace anything except for fuses and the overload heater.

Does it matter which leg gets left off?

 

[foghorn1966]

It looks like the control transformer is wired for 240V input right now & the primary is on L1 & L2. So leave L3 off. Remove the fuse on the secondary on the control transformer & measure the voltage across the open fuse holder. If you get aprox 120 V you are good to go once you replace the fuse. Post back the voltage reading.

 

[foghorn1966]

Also check the full load amps at 240 V on your motor nameplate along with the service factor number. Then consult the chart on the inside of the electrical cabinet door. I suspect even the overload heaters will be close to the required size. You might have to wire it up like the diagram in your original vintage machinery link if that overload block needs to sense current in the three legs. ( I forgot about that possibility.)

 

[G-ManBart]

It looks like the control transformer is wired for 240V input right now & the primary is on L1 & L2. So leave L3 off. Remove the fuse on the secondary on the control transformer & measure the voltage across the open fuse holder. If you get aprox 120 V you are good to go once you replace the fuse. Post back the voltage reading.

You were right....got 126V across the open fuse holder which is what I routinely see in my barn and house (off the same transformer). At that point I wired the motor according to the diagram and it works like a charm! I still have to check the heaters, but that's an easy fix if they need to be swapped out. I made one test cut on a piece of 2.5" angle and it ran smooth, and the motor didn't even get warm. The switches all work and the automatic cutoff functions properly, so that's a bonus.

I tried to make a quick video, but had technical difficulties....pushed the button at the wrong time! I'll redo that just because everybody loves videos.

You guys ROCK!

 

[foghorn1966]

Glad to help! Always like a low $ fix!

 

[G-ManBart]

Here's a video of it working....finally got it to upload correctly!

 

[G-ManBart]

Here's a quick video of it cutting...seems to run pretty smooth:

 

[454ragtop]

Effing photobucket ***** donkey balls