Bandsaw Blade and Drive Belt Tension

[Tom Trees]

So no contact of either upper or lower thrust guide due to inadaquete tension or tracking issues.
Could it be that the motor is configured to star/Y (high voltage) instead of Delta triangle (220v) ?

[John K Jordan]

I have no experience with large 3-phase motors but found this: "... motor control loads typically require more current when they are initially energized than under normal operating conditions.
This period of high current demand, referred to as inrush, may be as great as ten times the current required under steady state (normal) operating conditions, and can last up to 40 milliseconds."

The easiest thing to try might be to replace the breaker. Perhaps the existing one is defective or tripping too fast. If you have a storage oscilloscope you might rig it to watch the duration of the inrush current spike (across a shunt or with a current probe) to see if the time exceeds the breaker specs. If you do replace the breaker with a larger one, I assume you'll make sure the wire in the circuit properly sized for the breaker. (I didn't read all the details in the posts.)

As for sizing the breaker, I see lots of calculators and tables out there like this one, but some may be more appropriate than others:
http://wiresizecalculator.net/tables...emotordata.htm

If stumped, might call an electrician familiar with 3-phase industrial applications.

JKJ

[derek labian]

A good article on the topic.

https://www.jadelearning.com/blog/un...rticle-430-52/

John, yes upsize to 6/4 and a 60a breaker.

[derek labian]

I did some more testing on this. The draw is a solid 90A until it trips, about 3 seconds. I'm not sure a larger breaker will solve this issue because it will still be over the 60A for a period longer than 3 seconds. I could also not find breaker that has a longer curve, but 3 seconds seems pretty long already. The Phase Perfect has the capacity for this but I'd have to put in a much larger breaker, perhaps 100A. I couldn't find any details on the profile for the thermal characteristics, but if it is thermal load, the 60a would hand the 90a inrush better, right?

I researched the wire further, it's more or less a waste to put in 6 or 4 awg wire because the wire is rated to handle that inrush load for a short period. I found a number of calculators that show my cabling would be fine for much longer than I need that extended load. NEC accounts for this as well. The current cord is 10/4 SOOW, and the internal wiring on the saw is, at best, 10AWG, both of which should be fine even with the 90A inrush.

I suppose I could put a slow blow fuse inline with a 100a breaker behind it..

I'm open to any other suggestions.

[derek labian]

It seems like I could put a RK5 current limiting time delay fuse inline which are designed for motor starts/inrush. It should provide 60 seconds at 30A Fuse with peak current of ~600A. So I guess I could put in a 100A breaker and wire it to the fused saftey disconnect with RK5 30A slow blow fuses, and then run the existing 10/4 SOOW wire to the saw.

[Dan Friedrichs]

90A seems awfully high. You're putting the clamp meter around one leg of the 3phase supply?

How much current do you get with just the motor driving the bottom wheel (no blade)? You mentioned that without the blade, you can get it running - what does it draw for current once running (at speed)?

[Dan Friedrichs]

Oh, I missed that you had the 9.0HP, not the 4.8HP version. 90A still seems high but I suspect your breaker is just undersized. Breakers trip based on both the time and current, and if you look at the curve for a breaker, it will, for instance, tolerate 10s of 2x the rated current, or 5s of 3x the rated current, etc. So I think if you switch to a 40A or 60A breaker (along with appropriate wiring and receptacle), you'll be fine.

[derek labian]

90A seems awfully high. You're putting the clamp meter around one leg of the 3phase supply?

Yes.

How much current do you get with just the motor driving the bottom wheel (no blade)? You mentioned that without the blade, you can get it running - what does it draw for current once running (at speed)?

I don't know the current from no-blade/flywheel. From what I've been reading in my research, draw can be many times nominal load at startup for motors and transformers. These fuses are designed for motors startup. I could test again without the blade on to see though. Since these are Thermal MagCircuit Breakers, if the load was half at startup (1 flywheel), it would be 45A instead of 90A. All things being equal (and I know its a curve, but just for illustration), that might be 12 seconds of draw, and the saw spins up in about 5-6 seconds, thus it doesn't trip.

[derek labian]

Oh, I missed that you had the 9.0HP, not the 4.8HP version. 90A still seems high but I suspect your breaker is just undersized. Breakers trip based on both the time and current, and if you look at the curve for a breaker, it will, for instance, tolerate 10s of 2x the rated current, or 5s of 3x the rated current, etc. So I think if you switch to a 40A or 60A breaker (along with appropriate wiring and receptacle), you'll be fine.

Hi Dan,

I failed to find the curve specs for the Siemens QP series breakers.

Edit: I looked again. All the spec/datasheets I could find don't have trip curve data. In any event, I don't have a lot of choice in breaker selection that will fit this panel. Unless the 22KAIC breaker has a longer curve...

[John K Jordan]

...

I'm open to any other suggestions.

For peace of mind I'd take the motor to a local motor shop and ask them to test it.
It might not make sense to design around the symptoms if a problem exists in the motor itself.
Might ask if they would test the switch at the same time.

The times I've taken a local motor to a motor shop for inspection or repair they were quick and reasonably priced. Also, I like to buy switches for motors from them to save me the effort of verifying the claims of those I find online. Some lie.

JKJ

[derek labian]

For peace of mind I'd take the motor to a local motor shop and ask them to test it.
It might not make sense to design around the symptoms if a problem exists in the motor itself.
Might ask if they would test the switch at the same time.

The times I've taken a local motor to a motor shop for inspection or repair they were quick and reasonably priced. Also, I like to buy switches for motors from them to save me the effort of verifying the claims of those I find online. Some lie.

JKJ

its brand new, if its got a problem, i should contact the manufacturer, from what ive read this is not abnormal. Once its running st spead, if nominal load doesnt drop to 22a, ill contact the manufacturer.

[Malcolm McLeod]

Might have missed a detail or 6, as I didn’t read this all, but did read the OP…

Didn’t see anyone state the obvious, but when starting with no blade, the motor only has to overcome its internal inertia and that of the lower wheel (plus some friction). Adding the blade will (nearly) double the inertia. I don’t know what your wheels weigh, but I’d bet its a lot.

FWIW, I’d estimate my 18” BS takes at least 3-4 seconds to spin up to ~85%(?) with a blade, but <1 second without. (Never had issues, so never tried to get more precise).

A larger CB may be the only reasonable solution (with wire to match). Other options could be:

• a VFD to slow the accel and so inrush current;
• a soft start (Wye-Delta dual starter setup);

[Dan Friedrichs]

This seems specific to air compressors, but it shows needing a 40A breaker for a 3ph, 240V, 10HP motor: https://eatoncompressor.com/wp-conte.../Amp-draws.pdf

I think this is the curve for your Siemens QP breaker: https://assets.new.siemens.com/sieme...-15-70a-1p.pdf

So if you're using a 30A breaker, your 90A load is drawing 3x the rated breaker load, which the breaker should be able to handle for a minimum of 4.5 seconds.

If you switched to a 40A breaker, you'd get at least 15 seconds; a 60A breaker, at least 50 seconds.

[derek labian]

This seems specific to air compressors, but it shows needing a 40A breaker for a 3ph, 240V, 10HP motor: https://eatoncompressor.com/wp-conte.../Amp-draws.pdf

I think this is the curve for your Siemens QP breaker: https://assets.new.siemens.com/sieme...-15-70a-1p.pdf

So if you're using a 30A breaker, your 90A load is drawing 3x the rated breaker load, which the breaker should be able to handle for a minimum of 4.5 seconds.

If you switched to a 40A breaker, you'd get at least 15 seconds; a 60A breaker, at least 50 seconds.

awesome, i have a 40, 50, 60, and 100 on the way, along with the slow blow RK5’s. Ill start with the 40! Thanks Dan!

[derek labian]

Didn’t see anyone state the obvious, but when starting with no blade, the motor only has to overcome its internal inertia and that of the lower wheel (plus some friction). Adding the blade will (nearly) double the inertia. I don’t know what your wheels weigh, but I’d bet its a lot.

Correct.

A larger CB may be the only reasonable solution (with wire to match). Other options could be:

• a VFD to slow the accel and so inrush current;
• a soft start (Wye-Delta dual starter setup);

Or the slow blow fuse I mentioned. It seems the larger breaker is the obvious answer however I don't see a need to change the wire. The 10/4 SOOW i'm using, in my configuration is rated at 39a, at least, in my application. I will check the thermals on it though once I get it up and working. The wire in the saw is also 10awg.