Are you running a SawStop on an *off-grid* PV system?

[David Strip]

I just bought a Sawstop (3HP Professional) and it won't run on my off-grid system (2 x Outback VFX3524 inverters). The inverters can provide enough power for similar sized tools, but the Sawstop is sensitive to the voltage drop caused by the sarting tsurge and shuts down. I'd like to find out if anyone is successfully running this saw on their off-grid inverters and what brand and configuration you're running.

[Jack Frederick]

Interested in what you find as i am considering batteries for my 7.5kwh solar install. What has SS said? Have they offered any suggestions?

[Joe Jensen]

Instantaneous start currents are high on single phase motors, really high. One solution would be a 3 phase machine with a VFD programmed for soft start. A possible solution could be a much larger start capacitor. This is a brainstorm to look into and not a known solution.

[Joe Jensen]

This actually looks perfect. Electronic soft start for a single phase motor. I would still contact Sawstop to make sure their saw is ok with this.

https://www.raymondinnovations.com/collections/240v-north-america/products/gt20

[David Strip]

I've had extensive discussions with tech support at SawStop. Everyone I've talked to is really knowledgeable about the saw and it's inner workings. Responding to comments in turn:
Jack - even with batteries, it you remain grid-tied you won't run into problems.
Joe - yes, starting currents are huge. The SawStop pulls about 47A for 100ms, which is within the rated capacity of the inverters, but the voltage drop is the issue. SawStop is familiar with the problem and recommends not buying the saw if you are on off-grid solar or rely on anything other than a substantial generator. I thought about a larger start capacitor until a friend explained how it functions and it's not really a starting boost in the sense you might think. Motors with a starting capacitor have two sets of coils - run coils and start coils. The capacitor (start or run) provides the phase shift between coils, it's not stored power.

The SawStop is a much more sophisticated system than your run-of-the mill saw. Your generic saw just has an on/off switch (maybe "magnetic"), but still a simple on/off switch. You can replace the motor at your whim. Not so with the SawStop. The motor is integrated with the rest of the system. For example, there's a rotation sensor that is used to detect that the saw is still coasting after shutting off, so the brake system doesn't disengage until the blade has stopped. The same sensor is used to check if the blade has spun up fast enough. If not, the saw shuts down. A third party soft-start would fail this test. SawStop could, of course, build an integrated slow-start, but even then I couldn't retrofit it on my saw.

[Joe Jensen]

As an electrical engineer, a large enough capacitor would prevent voltage drop. Simple calc to figure out how many farads would be needed. I'd calculate and double or triple it. Sawstop is doing what we would at work. Non-standard is not recommended. Anything more increases their liability.

[Stephen White]

David, what about the contractors sawsstop? I use this one on a heavy duty mobile base and like it. I assume you bought the SS because of the blade brake and this keeps you in that world if it won't run into the same voltage drop issue.

[Frank Pratt]

This actually looks perfect. Electronic soft start for a single phase motor. I would still contact Sawstop to make sure their saw is ok with this.

https://www.raymondinnovations.com/collections/240v-north-america/products/gt20

That would have to go in the circuit after the electronics, but I can't see why it wouldn't work. I doubt if SawStop would sign off on it though.

[Erik Loza]

I know little to nothing about this stuff but will add that, over the years, have talked to a few folks who tried to run bandsaws or smaller machines (say, less than 5hp) in these off-the-grid type situations with generators, etc. Every one of them reported back that the machine was ultimately unusable. As others mentioned, the startup amp draw seems to be too high for these types of setups. To the OP, if you do manage to figure out a capacitor-based solution, please share with us. :)

Erik

[David Strip]

David, what about the contractors sawsstop? I use this one on a heavy duty mobile base and like it. I assume you bought the SS because of the blade brake and this keeps you in that world if it won't run into the same voltage drop issue.

Besides the brake, the SawStop is a superbly designed saw incorporating features the other vendors have yet to copy. The blade lift mechanism has air-springs to counter-balance the weight, making movement easy in both directions. The tilt is balanced to that movement is easy in both directions. The contractor saw would be a step down from the Delta Cabinet saw I replaced.

[ChrisA Edwards]

Could you step down to the 110V 1.75HP motor and controller?

I retrofitted my 1.75HP PCS to the 3HP 240v.

So I have a spare motor (110v) and controller doing nothing.

[David Strip]

That would have to go in the circuit after the electronics, but I can't see why it wouldn't work. I doubt if SawStop would sign off on it though.


as I wrote above, the Sawstop controls require the blade to come up to speed within about 1.5 seconds. If the slow start fails to achieve this, the saw will shut down.

[David Strip]

I know little to nothing about this stuff but will add that, over the years, have talked to a few folks who tried to run bandsaws or smaller machines (say, less than 5hp) in these off-the-grid type situations with generators, etc. Every one of them reported back that the machine was ultimately unusable. As others mentioned, the startup amp draw seems to be too high for these types of setups. To the OP, if you do manage to figure out a capacitor-based solution, please share with us. :)

Erik

I've been running my shop on off-grid solar for 15 years now. Prior to the Sawstop the largest motor was 2HP on my Rikon bandsaw. Curiously enough, it's starting surge is HIGHER than the 3HP sawstop. However, it is a "dumb" motor, so it doesn't care about the voltage sag. I've never had problems with any other tools. Of course, not all solar installations are equal. The inverters have to be large enough to provide the require current, as do the batteries. Also, some early inverters (and current cheapo ones) produce really crappy waveforms; in some cases it's just a square wave. It's not surprising that tools won't like that.

Same situation holds for generators. If you have a portable 3kW generator you probably shouldn't expect it to provide the starting current for a large power tool. On the other hand, if you have a large, stationary generator capable of powering a house through a blackout, it will handle the tools with ease. Mine is rated 15kW continuous load, capable of running for days at a time. It runs the SawStop without breaking a sweat.

[Frank Pratt]

as I wrote above, the Sawstop controls require the blade to come up to speed within about 1.5 seconds. If the slow start fails to achieve this, the saw will shut down.

Sorry, I completely missed that. But 1.5 sec is quite a long time. I just timed mine & it takes roughly 1/3 sec to come up to speed. Of course, that would be longer with a full dado stack.

[David Strip]

Sorry, I completely missed that. But 1.5 sec is quite a long time. I just timed mine & it takes roughly 1/3 sec to come up to speed. Of course, that would be longer with a full dado stack.

Is that with a soft-start?

[Doug Garson]

Just a shot in the dark by someone who knows nothing about the topic but is the 1.5 sec part of a software setting that can be edited to a higher number?

[Christopher Charles]

Curious-does it start in bypass mode?

[David Strip]

Curious-does it start in bypass mode?

No. According to SawStop tech support, the contactor drops out when the voltage drops below 200V. As a result it clatters in and out - pulling the voltage down, dropping out, then re-engaging. Repeat.

[Mike King]

I'm completely ignorant of the electrical issues here, but would a battery solution fix the issue? Something like this?

https://www.festool.com/products/systainer-and-transport-systems/sys-powerstation/205721---sys-pst-1500-li-hp

[Paul F Franklin]

I wonder if beefing up the wiring between inverter and saw (and perhaps between batteries and inverters) might reduce the voltage drop just enough for you to get by? Given the large inrush currents, you could have quite a drop across the wiring during the startup surge.

[Alan Lightstone]

Not sure if this helps at all, but I've got a very large photovoltaic system (30kW) and a 5HP ICS. It runs through a 10HP Phase Perfect.

I am on the grid, so perhaps when I start the SawStop ICS the surge comes from the grid. Or else the Phase Perfect handles it (which would be my guess, but just a guess). But the solar panels produce way more electricity than the ICS needs, so maybe it's all coming from them.

Never had an issue with the ICS starting.

[Frank Pratt]

Is that with a soft-start?

No, full voltage.

[Frank Pratt]

I'm completely ignorant of the electrical issues here, but would a battery solution fix the issue? Something like this?

https://www.festool.com/products/systainer-and-transport-systems/sys-powerstation/205721---sys-pst-1500-li-hp

I doubt very much if that would work. Its maximum peak output is 11,000W at 230V, which is less than 48A. Peak starting current on that saw is probably in the range of 100A.

I hate to think of what the price is for that unit. I bet it's more than the SawStop.

[Mike King]

I doubt very much if that would work. Its maximum peak output is 11,000W at 230V, which is less than 48A. Peak starting current on that saw is probably in the range of 100A.

I hate to think of what the price is for that unit. I bet it's more than the SawStop.

It's 48amps, which is about what was quoted above as the starting current.

The Festool product is designed to allow folk to use machinery without connection to the mains. I wouldn't be surprised if it would work. But I also suspect you would have to buy it from Germany to find out...

Mike

[Frank Pratt]

It's 48amps, which is about what was quoted above as the starting current.

The Festool product is designed to allow folk to use machinery without connection to the mains. I wouldn't be surprised if it would work. But I also suspect you would have to buy it from Germany to find out...

Mike

I wouldn't count on it putting out even a tiny bit more than 48A. That spec is not its rated output, but its peak. Festool is not known for understating the power of its products.

[Eric Arnsdorff]

If the issue is the contactor/motor starter dropping out due to the voltage sag then there are a number of solutions that would work. If it is the coil of the contactor dropping out then there are ways to address that aren't terrible.

I saw a soft start was suggested previously and should work. VFD's were mentioned but would be both changing the motor and adding the drive.

One additional thought is to change the contactor/motor starter.

You could change this to a manual motor starter. Often a design with a manual motor starter will include an UVT (under-voltage trip) to turn the saw off when power is lost so that it won't start when power returns unexpectedly but would actuate on a voltage sag as well. However, holding the manual actuator (holding the start button or equiv.) during the voltage sag caused by the inrush would allow the motor to start. I haven't looked at the wiring diagram for a sawstop but this could be possible within the same enclosure that is on the saw.
Another version of this would be to change it out for one that uses a 24VDC coil and add a 24VDC power supply. The power supply design contains capacitors which keep the DC voltage up during such sags and can hold the contactor closed during the start. This would allow a short button press and not require holding the button during startup.
Basically, changing out the contactor for one that would ride through the motor start. If you do this you do want to make sure you include the overload for the motor and these are very standard items and are basically what makes up a motor starter (contactor and overloads).

An example of a manual motor starter is: https://www.automationdirect.com/adc/shopping/catalog/motor_controls/iec_manual_motor_protectors/manual_motor_protectors_(01_to_63_amp)/mpw40-3-u020
The starter costs $58 from AutomationDirect.
The UVT that would go with is: https://www.automationdirect.com/adc/shopping/catalog/motor_controls/iec_manual_motor_protectors/spare_parts_-a-_accessories/shunt_trip_-a-_undervoltage_release_devices/urmpv18
The UVT costs $21.

There are current limiters as well that may work for you.
I see AutomationDirect has added a current limiter. I haven't used it and don't see the specs to understand if it alone may solve your problem. However, it would definitely be worth a call to them to see. It's $39.
https://www.automationdirect.com/adc/shopping/catalog/motor_controls/iec_manual_motor_protectors/spare_parts_-a-_accessories/mounting_-a-_connection_accessories/clt32mpw40

There are other ways to provide the inrush as well. Unless you're looking for a full shop solution then likely doing something for just the saw would be easier and more economical.

If this is of interest I'd be glad to look up the diagram for your saw and make a quick sketch of how to re-wire it for an alternate motor starter solution.

[Eric Arnsdorff]

463397
I looked up the wiring diagram for the Sawstop PCS. It does appear this design is subject to a voltage sag causing the coil to drop out. Changing this to a design that would allow a voltage sag would get your saw started reliably.

[Eric Arnsdorff]

My apologies - I skimmed this thread but didn't read all of the OP's investigation with this saw.
If it is that the saw has a startup timer of 1.5 sec or it opens the contactor then an even simpler solution would be to over-ride this.
I'm not sure how interested you are in modifying this aspect.
I did see another suggestion was to add a capacitor to provide the inrush current. This sounds like a good solution external to the saw.

[mreza Salav]

What are the batteries rated in your off-grid system? I supposed adding a few batteries would help. A good 12V 800CCA battery should (theoretically) provide that many amps at minimum 7.2V for 30 seconds. So 8 of them in a system should provide 100amp at 230V for that period.