Powering a 3-phase sawmill with single phase solar.

As several others have mentioned, I would look into using a rotary phase converter. It needs to be oversized, as mentioned, but it is a versatile piece of kit that you can use to power other 3-phase motors that you may acquire in the future.

Here is a video about someone in the UK building and using a RPC from their hybrid solar-wind generation. There is also a follow-up video with more info.



RPCs aren't cheap but they are relatively simple and durable contraptions.

tony uljee wrote:after seeing that clip ,now i want one of those , to add further complication to my already lengthy projects to do list, so anyone know the biggest horsepower electric motor that could be run on single phase , or in this case off the inverter ? Plus i am now starting to think of woodgas powered generator, too much ,too many distractions on this damn site, but i do hope some solution comes around

Yup... So many rabbit holes so little surfing time.

So a question as It keeps coming up, what exactly is "Leviathan" I am assuming some sort of large electrification push/system/project at the lab? Are we supposed to know yet? I am curious because this whole thread is 3 phase 3 phase 3 phase when it really seems like it would be a simpler solve with a small diesel or gas engine hence my question. There is obviously a bigger goal I don't understand. Feel free to tell me to temper my curiosity.
Cheers, David Baillie

The Solar Leviathan is linked in the first post. It is a large trailer with a unique walking axle design, solar panels, lead acid batteries, a solar charge controller, and I'm guessing an inverter in the one box I didn't see a direct picture for the insides. I can tell everything uses quality parts, but I'm uncertain of the specifications. To be honest, I heard about using this to power a swingarm sawmill several years ago and was under the impression it had already been done.

They've been running another, waaaaay smaller swing-blade off of it.

A brief history: https://permies.com/t/28678/permaculture-projects/solar-electric-sawmill

A recent picture:

source: https://permies.com/p/811736

I was trying to figure out a thing where we could upgrade the mill.  Not sure it's going to pan out, for lots of reasons, but this is still a worthwhile conversion, IMO.

i am one of the ---"i will give it try ,because i am to blissfully ignorant to know any otherwise "   gang  , so lets add some more mud into the puddle , how about hydraulics, going to need someone to correct me here , i built a 15 hp hydraulic motor powered mixer, this is low speed of course 400 rpm but its very small -- 4.5 inch dia by 9 inch long, perhaps a bigger one with a gearbox to power the saw ?. Could a suitable sized electric motor be powered from the panels and inverter to power the pump for a hydraulic 15/20hp ----- the long travel of the saw ---reminds of my telehandler  which has long attached hydraulic hoses on the boom.

The current sawmill there has a 4" cut.  How big is its motor and is it 110 or 220V?  Maybe we can upsize from there?  

For instance if a 2 hp motor can handle that, I'd think a 4 hp could do a 6" cut...

James Alun wrote:I would go with a slightly different rotary converter.

If you've got access to the battery system, then I would skip the single phase - inverter setup and run the 3phase motor-generator from a dc motor from a fork lift or milk float.

I would install the dc to 3 phase rotary converter as close as possible to the battery bank and then run 3 phase out to your workspace, as the higher voltage/lower current of the 3 phase line will reduce power losses.

YES. Thanks for that flash of brilliance. Duh! Skip the inverter entirely and dump your beautiful, raw DC straight into a motor that wants it and runs efficiently on it. Have that motor coupled to a 3-phase motor to act as your generator. Losses minimal, power output optimal.

Phil Stevens wrote:YES. Thanks for that flash of brilliance. Duh! Skip the inverter entirely and dump your beautiful, raw DC straight into a motor that wants it and runs efficiently on it. Have that motor coupled to a 3-phase motor to act as your generator. Losses minimal, power output optimal.

It's probably less efficient than a dedicated 3 phase inverter but it should be more robust and tolerant of abuse.

And those will be ideal sine waves coming from the motor, unlike the stepped approximation output by even the better inverters. Better match for inductive loads and I'd agree that it would be more tolerant of abuse.

So, more electrically advanced folks.. is it clearly advantageous to go from DC power to 3-phase AC for this application?

Big DC motors are around. Like the one proposed as the first step in this conversion to 3-phase..

One usual downside of DC is the wire size needed. But this could perhaps be kept to a pretty short run.. just over half the length of the mill worth of travel, if the power comes to the midpoint.. plus however much distance from the batteries as absolutely required...

Is the leviathan a 48v system? I have no idea whether it would make more sense to try and run the mill at 48v, or convert to 180v or some other common industrial voltage point...



PS; is there some discussion elsewhere of why the lab really wants swing blade vs bandsaw?

D Nikolls wrote:PS; is there some discussion elsewhere of why the lab really wants swing blade vs bandsaw?

I haven't seen a discussion.  I heavily suspect it's more likely that having random boots operate a swing blade will work out better than a bandsaw mill.  And you can more easily sharpen a swing blade.  And it's less likely to break the blade.

This is just my guess but I'd put $20 on it

D Nikolls wrote:So, more electrically advanced folks.. is it clearly advantageous to go from DC power to 3-phase AC for this application?

The 3 phase motors are cheaper, more robust (less maintenance), and higher voltage means lower amperage for the same power meaning smaller (cheaper) wires. I don't know anything about the forklift motors. If they are brushed motors then they would need maintenance. If they are BLDC (BrushLess Direct Current) then those are effectively 3 phase motors.

Adding in extra conversions creates efficiency loss. However, if you have the option between some obscure expensive device to convert directly from DC to 3-phase AC, then that may be less ideal than to use more common parts that may be cheaper, easier to assemble, and possibly source used parts that would otherwise be scrapped. Part of the difficulty here is figuring out what will work well when assembled by people on hand. It would be much easier for some people to connect A to B to C than to reinvent the wheel going from A to C. For other people, they may have a mechanical background where making a new motor mount and swapping gears or pulleys would be a typical afternoon. Others still might have no issue with the electrical side, but not know the first thing about welding and drilling a custom motor mount. Cost is also a factor where some people might have cheaper access to different parts.

That's the great thing with this thread - there are lots of different ideas coming from different points of view. No matter which direction gets chosen, the other ideas and questions asked and answered are still valid for people to learn from.

Hi Beau,

Before you get too deep in the weeds on phase converters, etc., the 15HP motor that draws 11kW is probably not going to run on that Outback Radian system since it's only rated 8kW. The 8kW Radian will provide surge current of up to almost 17kW for up to 0.1 second which also will fall far short of the motor's starting (inrush) power.

You can put more than one Radian system in parallel to increase the output power but then you need to beef up the battery system required to run it. For an 11kW load on a 48V nominal battery system (usually around 52V actual) the battery current will be around 11,000W / 52V = 211A. The starting surge will be probably at least double. A 422A surge will require some 4/0 wiring to each parallel inverter at >$5/ft * 2 (positive and negative) and multiple batteries in parallel wired up with at least 2/0 cable.

The couple with the YouTube channel Ambition Strikes have a crazy system with 60kW of LiFePO4 battery storage, 20kW of inverters (2 10kW units with total 40kW surge). 10.5kW of panels and 2 charge controllers between the panels and the batteries / inverters. They spent $50k and they can run a CNC plasma cutter with its compressor (13kW load). They also chose an incinerating toilet that takes 2kWh per flush. They could run the Turbosaw if they had a phase converter.

As a phase converter alternative, you can connect 3 of the Schneider XW6848 inverters to directly generate 3 phase power at about $3500 each. Plus batteries, etc.

You might get away spending a little less, but a gas or diesel motor for the sawmill will be a much more affordable option in most cases.

---

Daniel commented on pure sine inverters and inductive loads. The portable power systems shown in the video are not the same as Outback, Schneider, Victron or similar off grid power systems. These high end inverters deliver solid power and will run heavy loads without issues. I'm typing this on a PC powered by a Schneider XW6048 6kW inverter. It has no problem starting a 3HP tablesaw or running any other items in our off grid home.

I've made several rotary converters and had a couple saw mills.
For a converter you need a 3 phase motor that has a larger amp draw than the motor you want to run. The existing 2 legs of 110v are wired to 2 of the 3 legs of 3 phase. and the sawmill motor is wired to all 3 legs of the converter. To start, wrap a chord around the shaft and start it like a lawn mower. There is a kit that will wire in and start the sawmill motor when power is applied. Probably on ebay. Also a good place to buy a used 3 phase motor.
If it was me, I'd buy a gas or diesel engine. Saw blades take a lot of power, and weak motors will make ragged cuts. You need to keep your blades sharp, too. Another way is to use a tractor's PTO.

In UK I had the same problem to power a briquette press but just installed a hybrid inverter to obtain the 3 phase. Would mean a rewire of your existing solar but is neat solution if you have sufficient solar panels to run it.

This is four months since this topic was up and i'm wondering if it went anywhere...

This is definitely a case that I personally would want to get some diesel military generator and use that to run the equipment.  I wouldn't even try to run it off solar.

I can get the idea of wanting to use electric equipment - our reasons might not be the same, but i'm aware some used 400-480v 3 phase stuff thats more powerful can go for cheaper than 240volt stuff because the latter is more used in home garages and the 400-stuff almost never so there's less buyers.  I'd hoped/wanted to buy up a bunch of 4xx volt machine tools and such for a large workshop in the future when I found good deals...  but I expect to be deeply rural and off grid/unfeasible to run a big powerline i'd think without $$$.  So my plan was to just use a big diesel generator and run the tools off that instead - I wouldn't be using the equipment so much that a few gallons diesel would bother me...  I want tools for capability not nonstop industrial machining, so the intermittent power of a genset would work fine.  (or so I think)

Brian Shaw wrote:This is four months since this topic was up and i'm wondering if it went anywhere...

This is definitely a case that I personally would want to get some diesel military generator and use that to run the equipment.  I wouldn't even try to run it off solar.

I can get the idea of wanting to use electric equipment - our reasons might not be the same, but i'm aware some used 400-480v 3 phase stuff thats more powerful can go for cheaper than 240volt stuff because the latter is more used in home garages and the 400-stuff almost never so there's less buyers.  I'd hoped/wanted to buy up a bunch of 4xx volt machine tools and such for a large workshop in the future when I found good deals...  but I expect to be deeply rural and off grid/unfeasible to run a big powerline i'd think without $$$.  So my plan was to just use a big diesel generator and run the tools off that instead - I wouldn't be using the equipment so much that a few gallons diesel would bother me...  I want tools for capability not nonstop industrial machining, so the intermittent power of a genset would work fine.  (or so I think)

You dont sound as if you have had much experience of  large 3 phase motors. The problem with large 3 phase motors is the initial start up current required to get the motor going. Dont whatever you do buy a 15kw generator to run a 15kw motor as you will be disappointed. If your clever you can work out the maths or let the generator supplier know what the maximum size motor is that you want to run and they will spec the generator. Simple rule I was told was to size generator 3 times larger than largest motor so 15kw motor would require 45kw generator.  Dont have this problem with solar and batteries as the batteries can handle the temporary surge so long as the battery bank and controls a strong enough for the job.

Something that I noticed, in watching the video of the electric mill, and another of a gas powered one:
In the electric version, the motor swings with the blade. Therefore that electric motor needs to fit in the space available, so concerns about larger single phase motors may be valid. On the other hand, motor mounting seems dead easy, 3 bolts through motor base and ample real estate to drill new holes if needed in the frame.
In the gas/ICE version, the motor is kept level (by necessity) and there is some sort of right angle drive in the swing mechanism. The ICE could be replaced with ANY kind of MOTOR (and an appropriate belt) since it is above and away from everything.

r john wrote:

Brian Shaw wrote:This is four months since this topic was up and i'm wondering if it went anywhere...

This is definitely a case that I personally would want to get some diesel military generator and use that to run the equipment.

You dont sound as if you have had much experience of  large 3 phase motors. The problem with large 3 phase motors is the initial start up current required to get the motor going. Dont whatever you do buy a 15kw generator to run a 15kw motor as you will be disappointed. If your clever you can work out the maths or let the generator supplier know what the maximum size motor is that you want to run and they will spec the generator. Simple rule I was told was to size generator 3 times larger than largest motor so 15kw motor would require 45kw generator.  Dont have this problem with solar and batteries as the batteries can handle the temporary surge so long as the battery bank and controls a strong enough for the job.

Nope, no experience at all.    I'm here to learn.  I know they have surge current just like A/C, but was wondering if there would be other ways to help provide that capacity... oversizing the genset is certainly one way but I was wondering if there were others.  I'm not sure what would be the best use of money - having a 3x larger generator head, having some kind of motor/generator flywheel (like they use to provide power stability - tho I assume a powerhead for 30kw of surge wont be way cheaper than a bigger generator) or having a bank of batteries.  In a world of junkyards and vehicle-sourced parts my attitude a diesel with 3x the power costs no more than a small one so it's all about the power generating head or battery bank then.  (and the latter might not even have to be deep cycle, how long is a startup surge at the worst anyways?)

In this example I still couldn't see 15kw of solar panels (providing full power only during full sun) or batteries that can sustain a 15kw outgoing load for 1+ hours of work being more affordable than a diesel generator, and the battery power to take however many seconds of surge is required.

John F Dean wrote:OK, I am really going out in left field with this because I was a special case.  And I am pretty sure you are committed to solar.  I commented in my earlier post about bringing in commercial 3 phase.  That was in the late 80s.  I did it for “free”.   I contacted a beer company that was willing to pay for the lines to be brought in IF I agreed to do aluminum can recycling and IF I was willing to have a semi trailer parked on my property with their logo on it to receive those cans.  When the contract ran out, the trailer and recycling equipment vanished and I kept the 3 phase.

You strike a favorable bargain, John.  You think if we park a Turbosaw trailer somewhere in view of the highway, they'd consider making us a mill with a motor to our spec?

I seriously doubt it, but it never hurts to ask.

Beau,

Let’s do some quick math. We need to calculate the watts and HP and see what’s what. For single phase AC and DC we use:

Watts = volts x amps

For example, we have 120 vac and 20 amp (common breaker size).

120 x 20 = 2,400 watts = 2.4 kW

Now we can convert that to HP:

2.4 x 1.341 = 3.2 HP

To size the wire, use this resource:

https://www.omnicalculator.com/physics/wire-size

Filling in the voltage of 120, amps of 20, loss of 3% (just take the default) and distance of 100 ft, we would need 8 gauge wire.

If we use 3 phase, we need to introduce power factor and the square root of 3. Power factor is like efficiency and the square root of 3 is because of how three phase works.

Watts = volts x amps x power_factor x sqrt(3)

Let’s assume 240 vac and 20 amp:

240 x 20 x 0.85 x 1.732 = 7,067 watts = 7.1 kW

Now we can convert that to HP:

7.1 x 1.341 = 9.5 HP

For the same 100 ft wire run, the wire size for each phase is now 12 gauge because of the higher voltage.

Now we have the relationship between HP, watts, volts, amps, and wire size based on distance.

I have some rhetorical questions:

1) What kind of wood are you milling?
2) What size of wood?
3) How fast must you mill?
4) Do you have time to mill it slowly?

If you have time to go slowly, and the wood isn’t too large or too hard, you may be able to use a band saw with a small motor. Why use a band saw? Because the thinner the blade, the less width of fibers you’ll be cutting through, so the less power it will take.

If we wanted to design a band saw, the speed of the blade would need to be around 200 FPM from:

https://www.sawblade.com/band-saw-blade-speed-and-feed-chart.cfm

If we assume an 18” diameter wheel, then we can calculate the RPM of the wheel like this:

200 x 12 / PI / 18 = 42.44 RPM

Where 12 is just 12”/ft (need to convert everything to like labels. Inches, ft, etc.).

Standard motors run around 1,750 or 1,800 RPM depending on the manufacturer. Let’s use 1,800. We’ll also use our 3.2 HP from before for a single phase (or DC) system. Horsepower through a system is constant, but torque can change based on mechanical advantage. Torque (ft lbs) is governed by this equation:

https://calculator.academy/hp-to-torque-calculator/
Torque = HP / RPM x 5,252

So plugging in our numbers, we get:

3.2 / 1800 x 5252 = 9.34 ft-lbs

This would be the torque of the motor shaft presumably. The actual torque provided would be part of the motor specs. We now know our motor RPM and our wheel RPM, so we can calculate the mechanical advantage.

1800 / 42.44 x 9.34 = 396.5 ft-lbs

Not that the “reducer” is 42.45:1 (1800 / 42.44). This is normally done through a set of v-belt pulleys but can also be done through a gear reducer.

The drive wheel is 18” diameter, so 9” radius. We convert the radius from inches to feet to get 0.75 ft. Now we can calculate the “force” being applied to the wood.

396.5 ft-lbs / 0.75 ft = 529 lbs.

Is 529 lbs a lot of force to pull a blade through wood? I would think it’s quite light. Keeping that blade razor sharp might go a long way! Remember, this was only 3.2 HP! Since nothing has a squared function anywhere, if you double the HP of the motor, you double the force on the wood.

It’s also obvious that a thinner blade would be much more efficient than a thicker one. The less width of wood fibers the saw had to cut, the more efficient.

But your original post was about converting solar power to 3-phase power and using that run a mill.

If you insist on using 3 phase AC, just know that about 40% of the energy consumed goes into powering up the windings. This is why many folks use VFDs (Variable Frequency Drives). A VFD cuts way back on the energy consumed by spinning the motor at only the speed needed to do the job, whatevery it might be. A great, great video explaining how a VFD works can be seen here:

https://www.youtube.com/watch?v=yEPe7RDtkgo

IF you have adequate time and IF you’re not milling anything overly large, I would suggest something different.

DC motors are unique creatures. They can run on practically any voltage from nameplate +10% down to zero. Their speed and torque will vary as the volts and amps vary. You can get DC brushed, permanent magnet motors from Worldwide.

https://worldwideelectric.com/product/wpmdc2-18-180v-145tcb/

This is a 180 vdc motor spec’d at 9.8 amps. It’s not going to light the world on fire, but you can run this directly off of solar panels with nothing in between except a disconnect switch. Some call this “daylight drive.” If you have 30v panels at 8 amps each, wire 6 of them in series and you’ll generate 180 vdc @ 8 amps in full sun. If you wire a second set of six and wire the two groups in parallel, you’ll generate 180 vdc @ 16 amps.

If you have 40v panels, wire four or five in series and you’ll get 160 or 200 vdc respectively. This works for basically any brushed motor. I’ve done it for corded power tools.

https://www.facebook.com/1463805713/videos/3120196448244247/

To learn more about daylight drive, check out the videos from Living Energy Farm.

https://www.youtube.com/@livingenergyfarm1912/videos

I hope this helps at least somewhat.

Eric Tyira wrote:
1) What kind of wood are you milling?
2) What size of wood?
3) How fast must you mill?
4) Do you have time to mill it slowly?

1) Softwoods, mostly pine, fir, larch.
2) Varies.  But we're mostly pulling off 3/8x6 up to 6x6 dimensional.  Perks of the swingblade is it does not know or care how big your log is.
3) Slower the better, as our millers are not very experienced and a slow pace helps them move carefully, avoiding mistakes, damage to equipment, and injury.
4) see 3, above.

If you have time to go slowly, and the wood isn’t too large or too hard, you may be able to use a band saw with a small motor. Why use a band saw? Because the thinner the blade, the less width of fibers you’ll be cutting through, so the less power it will take.

We want to stick with a swing blade, for the above reasons.  Also (I may not be 100% clear here) it is my understanding that our swingblade (and most, for that matter) are quite energy efficient because, while it may have a wider kerf than a bandsaw, it also only has two teeth.  That means only one tooth is doing work at any given time, which means it can run well on less power.  It also means our blades last a very long time, and we can easily and quickly sharpen them ourselves.

DC motors are unique creatures. They can run on practically any voltage from nameplate +10% down to zero. Their speed and torque will vary as the volts and amps vary. You can get DC brushed, permanent magnet motors from Worldwide.

https://worldwideelectric.com/product/wpmdc2-18-180v-145tcb/

This is a 180 vdc motor spec’d at 9.8 amps. It’s not going to light the world on fire, but you can run this directly off of solar panels with nothing in between except a disconnect switch. Some call this “daylight drive.” If you have 30v panels at 8 amps each, wire 6 of them in series and you’ll generate 180 vdc @ 8 amps in full sun. If you wire a second set of six and wire the two groups in parallel, you’ll generate 180 vdc @ 16 amps.

If you have 40v panels, wire four or five in series and you’ll get 160 or 200 vdc respectively. This works for basically any brushed motor. I’ve done it for corded power tools.

https://www.facebook.com/1463805713/videos/3120196448244247/

To learn more about daylight drive, check out the videos from Living Energy Farm.

https://www.youtube.com/@livingenergyfarm1912/videos

I hope this helps at least somewhat.

This is all very interesting.  Thanks for your contribution!

As you know, folks usually go with a gas engine or grid-tie. Off-grid electric isn’t impossible but it seems it would take a big system, at a price, and not sure how plug-and-play it would be.

Tough design problem. Sorry I don’t have an ideal answer.  Often batteries are the most expensive part, so a “daylight drive” or partial makes some sense, at least if passing clouds weren’t a nuisance.  In theory it’s cheapest to run a 3 phase motor on 1 phase power with a static phase converter.  But it’s hard on the motor. Not recommend for continuous duty, and it’s only 2/3 power (10 hp out of a 15 hp motor).  Rotary phase converter could be expensive?  A phase converting vfd might not be available at that high of a power.  You could install a single phase induction motor but as you said it could have to be a custom fit. Same for a PMDC motor. The PMDC motor has more low-end torque, so less nuisance stalls.

Maybe you can get a 48V DC Motor and so you can run it directly from the solar panel/battery bank. A 11kw motor like the ones they use in electric cars and electric motorcycle.
https://www.electricmotorsport.com/me1507-sevcon-gen4-48v-450a-motor-drive-system.html

11,000W motor =240V * 46A = 11KW+ Inverter = 11,000W battery bank  discharge rate  = 48V * 229A (the battery bank should probably be 4x that aka 900AH @ 48V)
I recommend getting this inverter/charge controller. https://unboundsolar.com/10000210/sol-ark/solar-inverters-electrical/15k-120v-240v-208v-solar-hybrid

Here is a inverter that does 480V 3-phase and thus you wouldn't have to make any changes to the mill.
https://unboundsolar.com/2950182/sma/solar-inverters-electrical/sunny-tripower-core1-stp-33-us-41

I saw this VFD listed for $600-$700.

https://www.google.com/search?q=ato+15+hp+11+kw+three+phase+vfd