Powering a 10kW motor, 3-phase 230V 14A

[sawmiller]

Hello from Sweden!
I am about to set up a small bandsaw mill in an old barn that has no electricity. The main motor is rated at 14A input with 3-phase power at 230V AC, i.e. 10kW, see image below. I was thinking about a small stack (4-5ish) of those 48V 100AH server-rack batteries which should last for a working day, since the motor won't run at full power most of the time.

Serveral questions, apart from the obvious one whether this is a good idea at all.

• Inverter. I seem to have a hard time finding a ~20kW inverter from 48V DC to 3-phase 230V AC, any tips would be appreciated.
• Starting current. Induction motors can draw a lot of current for the first fraction of a second. The mill has star-delta soft start, but still I am unsure if a margin of 2x is enough to not immediately trip the inverter. Any experience with running large-ish motors from batteries welcome.
• Recharging would be from existing solar or grid, a quarter mile away. First idea is to mount the rack on a pallet, build a simple roof around them, and just use my small wheel loader for the back-and-forth. Any caveats apart from potentiual drop damage?

cheers, Thomas

 

[Norwasian]

I don't have one, so cannot recommend it from personal experience, nor can I verify that it would be applicable to your full specifications, but if I were in the situation you describe, I would be taking a serious look at this option, from a brand that comes well-recommended by many on this forum:

Three Phase Inverter Charger – Sigineer Power

sigineer.com

 

[timselectric]

If the Pic is of the correct motor tag. That's not a 230v motor.
Which would be a very expensive mistake, if you purchase the wrong inverter.
You need a 400v 3-phase inverter setup.

 

[sawmiller]

If the Pic is of the correct motor tag. That's not a 230v motor.
Which would be a very expensive mistake, if you purchase the wrong inverter.
You need a 400v 3-phase inverter setup.

Normal european grid 3-phase power is often written as 400V, since you get that between any two of the phases. Each phase has 230V against neutral.

 

[timselectric]

Normal european grid 3-phase power is often written as 400V, since you get that between any two of the phases. Each phase has 230V against neutral.

Correct.
Make sure that you are shopping for the correct 400v 3-phase.
A 230v 3-phase inverter won't work.

 

[rogerdw]

First off, I would consider a decent sized 48v forklift battery. Robust and forgiving in harsh conditions.

I have no idea what 3-phase 48v inverters are available with the grunt you'd need to start and run the motor.

I recently bought some gear at auction and it would come close to doing what you need. A Trumpf TruConvert AC3025 unit which is a 3-phase 25kVA inverter. The only problem with it is that the DC input required is between 750-950v !!!

To provide that, you'd need two or three of their DC1010 dc-dc converters (10kW ea) which operate from 48v and convert up to the 750-950v required for the inverter.

The AC3025 25 kVA ... 25% overload for 10 minutes - 50% overload for 1 minute

Mains voltage range (3 phases) - 380 V -10 % … 480 V +10 %

They're not sold in Australia and I haven't been able to find prices for them anywhere yet. Made in Germany by Trumpf.

See my thread about them here ...

 

[Farm Boy]

In my experience with a saw mill and 3 phase table saw, id consider converting to a twin 22-25hp gas or diesel engine.
You could get by with a 3 phase converter I have on my table saw. Its a 7.5hp with additional 220v motor attached to the side of the unit which you start first with 220 or 230 to created the 3rd phase, with motor starter and heaters it may start on the second try with 60amps minimum and 10 second duration it comes alive spinning up with the 14" blade 1" arbor. Not sure on the inrush but its a lot. No inverter here will start it. Once it on, it uses little power. I use gas for my sawmill but it is used outside.

 

[sawmiller]

Thanks, this confirms my suspicion that this kind of motor is no good match for the kind of inverters that I had in mind.

 

[Norwasian]

Thanks, this confirms my suspicion that this kind of motor is no good match for the kind of inverters that I had in mind.

LF inverters are better at starting motors. The Sigineer I linked is of this sort, with large transformers in its architecture. You will notice they say "They are great to drive 3-ph motor, A/C, cooling fans, compressors, water pump, etc to meet the high power demand for off grid, commercial or residential systems."--all of these examples touted being motors, because the HF inverters are not as capable with these inductive loads.

It's my understanding that the Sigineer is also capable of matching your voltage requirements. You might wish to inquire for more specifics from the manufacturer before purchasing, however, to be sure.

 

[Hedges]

3-phase 380 to 420 delta.

3-phase 220/380Y to 240/420Y also works, just doesn't need neutral connected.

Motors typically have starting surge "LRA" 5x the current "FLA" of full running load. Could last about 1 second.
The star-delta switch will provide a nice current reduction. Sometimes transformers are used to drop voltage lower.

I use Sunny Island. The European model is 220V 50Hz, and three of them can be configured WYE.
That would be 18kW continuous, 33kW surge for 3 seconds.
It might be challenged with 5x 10kW starting surge, but the WYE configuration of motor should make the difference.

In the US, SolArk has 3-phase inverter, but it uses HV battery.
Maybe some other Deye models would meet your needs, or other Chinesium inverters.
Victron I think also supports 3-phase. And Schneider, if they come in your voltage.

You should be able to use VFD to slowly ramp up and run the motor. But the PWM of VFD can damage motors not designed for inverter drive.
If you had a way to series connect batteries for suitable DC voltage, VFD would take that directly.
Easier said than done if using LV lithium batteries. Need HV BMS. Trivial with lead-acid; many UPS are built that way.
VFD can also be fed AC; that is normal application. But typically only up to a couple kVA recommended for single phase, 3-phase input preferred at high wattage to reduce ripple.

 

[sawmiller]

Indeed, the Sigineer TPH 18KW explicity claims to be able to start an 18hp motor. Alas it seems to be an Americas-only company.

But SMA is German and three of their Sunny Island 8.0H look indeed like they would fit the bill. The split inverters woild have the added flexibility in case of emergency or other future single-phase applications. I'll try to get a quite for these or find a reseller.

 

[bolek_bolek]

Having a star - delta contactor for softer startup makes start easier, but it depends on how long it takes, so the inverter does not sense overload even after delta is coupled, see if there is some delay adjustment to increase it. If it's mechanical it may still be too fast.

 

[sawmiller]

Adding a star - delta contactor for softer startup can make your life easier, if you have access to the connection box of the motor coils and if you are ok with rewiring them. Careful about polarity, it can spin backwards if wired wrong.

Loading…

eepower.com

Yes, star-delta soft start is already present, see first post.

 

[Norwasian]

Having a star - delta contactor for softer startup makes start easier, but it depends on how long it takes, so the inverter does not sense overload even after delta is coupled, see if there is some delay adjustment to increase it. If it's mechanical it may still be too fast.

Most of the talk about soft-start devices seems to come from the folk with HF inverters which are not best suited to heavy inductive loads. I do not recall seeing anyone with an LF inverter claiming to need a soft-start device. Perhaps someone can enlighten me if in this I am mistaken, but I think the surge ability of the LF inverters makes a soft start unnecessary.

 

[timselectric]

Most of the talk about soft-start devices seems to come from the folk with HF inverters which are not best suited to heavy inductive loads. I do not recall seeing anyone with an LF inverter claiming to need a soft-start device. Perhaps someone can enlighten me if in this I am mistaken, but I think the surge ability of the LF inverters makes a soft start unnecessary.

It doesn't matter if it's an inverter, generator, or other power source.
You have to size the source large enough for the surge expected.
A soft start reduces the surge, and allows the source to be sized smaller.
In the past, LF inverters had a higher surge capacity than HF inverters, compared to the continuous run capacity. That is becoming less of a difference every day. HF inverters are being designed with higher and higher surge capacity. (The market demands it)
But you still have to size a large enough source, whatever that source is.

 

[Norwasian]

A soft start reduces the surge, and allows the source to be sized smaller.

I am interested in understanding this better. Doesn't a "soft start" device essentially buffer the current draw by sucking up the full output of the source via capacitors while not sending it fully to the load until those capacitors are sufficiently charged and able to provide the "surge" that the source was otherwise incapable of supplying? That is, at least, how I have imagined the soft start to work. I'd be happy to learn more if I'm mistaken.

 

[timselectric]

I am interested in understanding this better. Doesn't a "soft start" device essentially buffer the current draw by sucking up the full output of the source via capacitors while not sending it fully to the load until those capacitors are sufficiently charged and able to provide the "surge" that the source was otherwise incapable of supplying? That is, at least, how I have imagined the soft start to work. I'd be happy to learn more if I'm mistaken.

The older types used large capacitors.
The newer smaller ones reduce the voltage, I believe.
I really don't know exactly how the newer ones work. But they slow down the start up. Which lowers the initial surge, and spreads it out over more time (seconds).
It's slowly ramped up, instead of just slammed on.

I would compare it to a clutch in a vehicle.
Letting it out too fast, stalls the engine. But Letting it out slowly doesn't.

 

[Norwasian]

The older types used large capacitors.
The newer smaller ones reduce the voltage, I believe.
I really don't know exactly how the newer ones work. But they slow down the start up. Which lowers the initial surge, and spreads it out over more time (seconds).
It's slowly ramped up, instead of just slammed on.

I would compare it to a clutch in a vehicle.
Letting it out too fast, stalls the engine. But Letting it out slowly doesn't.

But if the inductive load (motor) gets a slowly-ramped-up voltage, wouldn't that be hard on it? It draws more at startup because it needs more at start up. Sure, one can keep the inverter from shutting down by shielding it from that draw surge, but it just robs the motor to pay the inverter.

I think this is why I have seen people posting about lower motor life with HF inverters. Nevermind the longevity of the inverter itself, it's the motors at stake, too. Motors don't take well to brownout conditions--they tend to burn out.

 

[rogerdw]

It's slowly ramped up, instead of just slammed on.

I would compare it to a clutch in a vehicle.
Letting it out too fast, stalls the engine. But Letting it out slowly doesn't.

That's pretty much my understanding too. I fitted one to a large ducted aircon compressor and it reduced the startup current from ~100A down to ~44A.

It is not all that physically large a device and certainly no additional large capacitors involved.

Unfortunately it seems that the compressor has failed since then ... so I'm up for a new system ... but it is 20 years old so it was always a risk.

 

[timselectric]

But if the inductive load (motor) gets a slowly-ramped-up voltage, wouldn't that be hard on it? It draws more at startup because it needs more at start up. Sure, one can keep the inverter from shutting down by shielding it from that draw surge, but it just robs the motor to pay the inverter.

I think this is why I have seen people posting about lower motor life with HF inverters. Nevermind the longevity of the inverter itself, it's the motors at stake, too. Motors don't take well to brownout conditions--they tend to burn out.

A soft start (if correctly sized) lessons the stress on the source and the motor. They aren't just used with inverters and generators.
They have been used for many years to keep the lights from dimming, on houses with large central air units.

 

[jharrell]

But if the inductive load (motor) gets a slowly-ramped-up voltage, wouldn't that be hard on it? It draws more at startup because it needs more at start up. Sure, one can keep the inverter from shutting down by shielding it from that draw surge, but it just robs the motor to pay the inverter.

Soft-starts use semiconductors to slowly ramp up voltage and current rather dumping huge current limited only by winding resistance at motor start.

Motor soft starter - Wikipedia

en.wikipedia.org

This reduces both electrical and physical stresses on the motor during startup which can increase life. This also reduces voltage sag on the rest of the electrical system (no dimming of lights) and allows for inverters and generators to more easily start the load with less stress on them as well.

People use soft-starts on LF inverters all the time, I did on my Magnum 3000w in my RV because occasionally it would trip overload when starting the 15k btu rooftop A/C it was pushing the surge ability and if the inverter can do it its very hard on the mosfets over time, the large transformer in a LF does nothing for surge its magnetic field can't even buffer a cycle and motor start is around 30 cycles.

The reason a LF's typically have longer surge compared to a HF is because the surge support comes directly from the battery through the high current low voltage mosfet bank while a HF has to go through the DC-DC to get battery current so large HF designs will have a large cap bank on the HVDC to buffer short inductive surges.

 

[timselectric]

That's pretty much my understanding too. I fitted one to a large ducted aircon compressor and it reduced the startup current from ~100A down to ~44A.

It is not all that physically large a device and certainly no additional large capacitors involved.

Unfortunately it seems that the compressor has failed since then ... so I'm up for a new system ... but it is 20 years old so it was always a risk.

I added one to my 3 ton unit.
My system had no problem starting it without the soft start, but I wanted to remove the stress on everything.

 

[Hedges]

Soft-start (I think, haven't used) are actually VFD, using starting winding of single phase induction motor as 3rd phase.
Running at lower frequency would be even higher current, so PWM to reduce current.

The Sunny Island 8.0-H has had a bunch of sub-varieties. Some having internal relay for grid, some controlling external relay.
So research it carefully before selecting.

In the US, ours are only one model, except for wattage. In fact ~ 20 year old models take same firmware and have same functionality as newest.

 

[sawmiller]

I recognize this is no longer "DIY solar", but I wonder what the chances are an electric car will be able to power the above motor? For example, the small new Renault R5 has a 52kWh battery and promises 11kW 3-phase as vehicle-to-load/home. Again, I expect the starting current to be the issue, but I have no idea what kind of surge capacity a car has. I am not a little tempted to test-drive it and simply try plugging it in.

 

[Hedges]

Get a VFD and it should work fine.

But yeah, maybe you get lucky and it has enough surge. No harm in trying (with the dealer's car). Are rentals available? No watchful eye of salesman, who would know you were the one who killed it.