Industrial Motors Theory

Thread Starter

cab12

Joined Dec 15, 2017
8
Hello,


I know rechargeable batteries can power homes and high power vehicles but my knowledge in the electrical side of engineering is limited so my question is, for example could an industrial 3 phase DC motor be powered with similar technology so it could run at a high RPM without being wired into the grid?


Craig.
 

LesJones

Joined Jan 8, 2017
4,174
A three phase supply is AC (NOT DC) The maximum speed an induction motor (Which I assume you are talking about.) can only run at just below synchronus speed. For a 2 pole motor (Which gives the highest speed.) synchrous speed is 3000 RPM for a 50 Hz supply or 3600 for a 60 Hz supply. Normal DC motors can run at a much higher speed than this and can be supplied directly from batteries.

Les.
 

Thread Starter

cab12

Joined Dec 15, 2017
8
Les,

Thanks for getting back to me all the information the better it really means a lot! I'm waiting on one of my old tradesman getting back to me on the specific details of the motors that were used in the place I served my apprenticeship. Like I said I'm mechanical biased so my electrical knowledge is very, very limited. Basically I'm working on a design project for my degree now and I'm wondering if industrial high RPM motors (like you said round about the 3000 RPM mark) could be powered by rechargeable batteries to allow units to be portable.

Craig.
 

dendad

Joined Feb 20, 2016
4,451
You really need to be a bit more specific.
What power do you need the motors to be, and the battery supply, and the run time...
It will most probably be easier to use Brushless D C motors (BLDC) with a driver, or you could just have brushed motors and PWM them.
A Variable Frequency Drive could run a 3 phase AC motor, but it all depends on what you want to do.
For small stuff, just think how battery drills run. But as you increase the power rating, the expense goes up pretty fast.
 

strantor

Joined Oct 3, 2010
6,782
A three phase supply is AC (NOT DC) The maximum speed an induction motor (Which I assume you are talking about.) can only run at just below synchronus speed. For a 2 pole motor (Which gives the highest speed.) synchrous speed is 3000 RPM for a 50 Hz supply or 3600 for a 60 Hz supply. Normal DC motors can run at a much higher speed than this and can be supplied directly from batteries.

Les.
I'm not sure if I'm disagreeing with you or just adding to your post. You left a lot of info out and made it seem like DC is the only option for vehicles.

That is absolutely not the case. Tesla uses induction motors, and I believe the Prius and most other hybrid or electric vehicles as well.

The key to making an A.C. motor operate from a DC supply is a VFD (variable frequency drive) AKA inverter. In A typical industrial setting, 240v or 480v AC 60hz single phase or 3 phase, is wired to a VFD, and inside the VFD it is rectified to DC. From there, the VFD chops up the DC into a new 3ph A.C. waveform. The VFD can create whatever waveform you want it to, at whatever frequency and whatever voltage. You send 60hz to the VFD and you can get 400+hz out of it. A.C. motor speed is dependent on frequency so you can absolutely get "high speed" out of them with a VFD.

Now for a vehicle, the VFD is actually simpler because it doesn't need an input rectifier. It simply chops up the battery voltage into A.C.

All that being said, NO, it's not advised to put an ordinary industrial ac motor in a vehicle. Why? Because they're heavy as hell, for the power they put out. A 75hp electric vehicle motor is about the same size and weighs about the same as a 15 or 20hp industrial motor. Industrial motors weigh more because weight usually isn't a concern for stationary machines so they can be made cheaply and effectively out of huge iron castings. All that iron is effective at dissipating heat. AC motors used in vehicles cost more. They are optimized for light weight. They are built more efficiently with better materials, and they generate less heat to be dissipated. That which is generated, is typically carried away with liquid cooling instead of a giant iron heat sink. Ev induction motors are also made with lower reluctance laminations to optimize them running at frequencies well in excess of the 60hz you get out of the wall plug.
 
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strantor

Joined Oct 3, 2010
6,782
Les,

Thanks for getting back to me all the information the better it really means a lot! I'm waiting on one of my old tradesman getting back to me on the specific details of the motors that were used in the place I served my apprenticeship. Like I said I'm mechanical biased so my electrical knowledge is very, very limited. Basically I'm working on a design project for my degree now and I'm wondering if industrial high RPM motors (like you said round about the 3000 RPM mark) could be powered by rechargeable batteries to allow units to be portable.

Craig.
The answer is yes, they can be powered from a battery bank (with a VFD) but it doesn't sound economical at all. Your best bet would be to rent a generator. I realize this is not a real-world scenario and you won't be needing an actual generator, but if you're going to be putting a lot of effort into the design of this for academic purposes, be aware that there is probably no real-world demand for it. Not sure if that matters or not.
 

Thread Starter

cab12

Joined Dec 15, 2017
8
Les,

Thanks for the feedback again. Should've made it clear that it isn't actually for a vehicle. The conceptual design/prototype is for heavy industry that use high pressure hydraulics.

Craig.
 

Thread Starter

cab12

Joined Dec 15, 2017
8
Folks,

Just to be clear the motor I'm talking about would actually be something along the lines of an industrial induction motor (operating around 3000 RPM) used to rotate a variable displacement hydraulic pump, sorry for the initial confusion. I'm not looking for prices or if it would economically possible. I'm just wondering if it WOULD be possible to run a motor of similar capacity on a rechargeable battery rather than being wired into the grid. I hope I've now made my idea a little bit more transparent.

Craig.
 

strantor

Joined Oct 3, 2010
6,782
Folks,

Just to be clear the motor I'm talking about would actually be something along the lines of an industrial induction motor (operating around 3000 RPM) used to rotate a variable displacement hydraulic pump, sorry for the initial confusion. I'm not looking for prices or if it would economically possible. I'm just wondering if it WOULD be possible to run a motor of similar capacity on a rechargeable battery rather than being wired into the grid. I hope I've now made my idea a little bit more transparent.

Craig.
Yes, it's possible. But again, nowhere near economical or practical. Diesel generator to electric HPU beats battery power HPU, and Diesel HPU beats diesel Generator to electric HPU.
Hopefully your design is specified for applications that require a short run time or else you're going to need a diesel generator to charge your battery powered HPU, which is completely pointless and is the worst of the worst scenario.
 

Thread Starter

cab12

Joined Dec 15, 2017
8
The motor that's in question would be operating a variable displacement hydraulic pump that supplies high pressure fluid to rotating, lifting and linear equipment. It's more of a short term (few hours???) replacement in the instance the main power pack breaks down. So they could operate the manufacturing line while the main power pack is being repaired.

Craig.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
I agree with @strantor it is hardly practical, but if the DC supply is there of sufficient capacity a off the shelf VFD on DC without modification could be used with a 3 phase motor.
But the supply capacity would have to sustain the load.
Max.
 

strantor

Joined Oct 3, 2010
6,782
The motor that's in question would be operating a variable displacement hydraulic pump that supplies high pressure fluid to rotating, lifting and linear equipment. It's more of a short term (few hours???) replacement in the instance the main power pack breaks down. So they could operate the manufacturing line while the main power pack is being repaired.

Craig.
Manufacturing? OK, now you're on to something.
You said "Portable" and I assumed "roadworthy" - like a trailer-mounted unit designed for transport to remote locations.
Now that we're talking about a manufacturing setting, there is a little more validity to it.
In the place I used to work they made cables for subsea use, several miles long. They need wires with absolutely perfect insulation, zero defects, 20,000ft long. If an extruder shuts down in the middle of an operation, the wire has to be scrapped. That company scrapped millions per year in cables or wires that had a hiccup in extrusion at some point in it due to a power outage.

They found it economically sensible to purchase and install a locomotive-sized battery-backup UPS for the entire plant. And along-side it, another locomotive-sized diesel generator. If the plant experienced an outage, the machines would continue to operate without missing a single AC cycle as the UPS picked up the slack. The UPS was good for a few minutes until someone got the generator on-line.

The point is, some manufacturing processes could benefit from having a battery backup if they cannot tolerate an outage, but Diesel is still king.
If your process experiences an outage and you need to get it back online, a diesel generator in the parking lot is still more economical than a battery powered HPU sitting in the plant.
 

Thread Starter

cab12

Joined Dec 15, 2017
8
I agree with @strantor it is hardly practical, but if the DC supply is there of sufficient capacity a off the shelf VFD on DC without modification could be used with a 3 phase motor.
But the supply capacity would have to sustain the load.
Max.
@MaxHeadRoom

Ok thanks for the feedback, like I said I'm mechanically biased so my knowledge is very limited. It doesn't need to be DC, I just worded it very poorly to begin with, apologies. My thinking was if Tesla can have a battery that runs the motor in their fully electric models, couldn't this be achieved for an induction motor that drives a variable displacement hydraulic pump?

Craig.
 

Thread Starter

cab12

Joined Dec 15, 2017
8
@strantor

Magic! Sorry for how I've worded my previous comments could've been more clear just didn't want to write an essay on the project in case I rambled on. Exactly, the point of the unit is just a short time emergency response to supply the part of the manufacturing line that's down. I was thinking it's not really emergency response if you have to wire the units motor into the grid so was just checking to see if battery power could possible be achievable.

Craig.
 

strantor

Joined Oct 3, 2010
6,782
@MaxHeadRoom

Ok thanks for the feedback, like I said I'm mechanically biased so my knowledge is very limited. It doesn't need to be DC, I just worded it very poorly to begin with, apologies. My thinking was if Tesla can have a battery that runs the motor in their fully electric models, couldn't this be achieved for an induction motor that drives a variable displacement hydraulic pump?

Craig.
Tesla has invested billions of their dollars, your dollars, and my dollars, into developing proprietary battery and motor technology that is safe, efficient, compact, and light weight. You can do what you are seeking to do, but I'm seeing in my mind's eye a bank of lead acid batteries that weighs more than a truck, to power a 30hp HPU for a couple of hours.
 

strantor

Joined Oct 3, 2010
6,782
Hence the 'Hardly Practical' comment!;)
Max.
yeah, I mean how long does does a battery-operated scissor lift or fork-lift weigh, and how long can it operate at max capacity?
Because hydraulic pumps are not typically optimized for efficiency. They run constantly, and in the case of fixed displacement pumps they run at max load all the time, bypassing over a relief valve, even when no work is being done.

If doing a battery powered HPU, I think it would make a lot of sense to use a fixed displacement pump with no pressure relief vale (a safety relief valve of course, but not one designed for constant bypass of pressure) and use a pressure transducer to control the pump motor at variable speed. It only turns as fast as the flow demand, and if the demand is <0>, then the motor doesn't turn, or it turns very slowly to maintain the pressure setpoint as pressure bleeds past seals & such. This would be a much more efficient HPU design and could decrease the battery requirement drastically, compared to slapping an off-the-shelf, typically inefficient standard HPU setup on a skid with S-load of batteries.
 

strantor

Joined Oct 3, 2010
6,782
Greenlee have managed to create a battery powered pump (https://www.youtube.com/watch?time_continue=108&v=Gem5cTQptE0) that can produce 10000 PSI, An 18V lithium ion (Li-ion) battery. Why couldn't something with more juice operate and run a motor connected to a pump similar to this one https://www.flowfitonline.com/hydra...8NpOpghl9s8e_0eZiK1u9jeWpHZeTiUaAp9oEALw_wcB?
upload_2017-12-15_11-27-13.png


Greenlee pump:
0.3 l/min * 700bar / 600 = 0.35kW


KOMPASS HYDRAULIC PISTON PUMP: @1800RPM
32l/min * 245bar / 600 = 13.07kW

13.07kW / 0.35kW = 37.34

Kompass pump requires 37.34 times more power than Greenlee pump.

Greenlee specifies no discharge time, but specifies a charging time of 30min.
Since battery-operated tools under constant/non-stop use (as an HPU would be) typically deplete twice (or more) as fast as they charge, I will estimate that the Greenlee pump battery will drain after 15min of non-stop pumping.

Let's say you wanted this battery-powered HPU to last for 2 hours:
the pump requires 37.34 times as much power, and you want it to run for 8 times longer than the greenlee pump:
37.34 * 8 = 298.72

So your battery powered HPU will need 300X the battery bank as the Greenlee pump.
The greenlee pump retails for $3,500. How much of that is the battery and how much of that is the pump? I don't know.
Let's use Dewalt 18V cordless tool battery packs for a reference instead, since I assume the greenlee 18V pack is similar:
The best deal I can find on the DeWalt packs is $50/ea.
So $50 * 300 = $15,000 for the battery bank.
(and there's still no way to charge that many DeWalt batteries)

In order to be able to charge this battery bank safely, it would probably require lead acid batteries. Now multiply the weight of your 300 DeWalt batteries by 5X or more.

You get my point?
Possible?-yes
Practical?-no
Affordable?-no

The only reason electric cars are economically viable is because the government funds half of their production expenses and then gives you tax credits for buying them.
 

strantor

Joined Oct 3, 2010
6,782
I don't know why, but this thread snagged my brain and I couldn't let it go. The deWalt battery pack wasn't good enough; I decided to do a real-world evaluation of what it would take to power this HPU from batteries.



The math for doing this with lead-acid deep-cycle batteries:

http://batteryuniversity.com/learn/article/lead_based_batteries

upload_2017-12-15_12-47-52.png

We want to use Deep cycle batteries and not discharge them more than 30%, (70% remaining) in the interest of longevity.
I am not talking about 70% of battery voltage remaining. I am talking about 70% of capacity (amp*hours) remaining.
A dead 12V battery (0% remaining) is still 10.5V, not 0V.

Supposing we use a 240V motor and VFD, the VFD is going to expect (3*240*√2)/ ∏ or 324V DC fed into its DC bus (+/-10%, typically).
We'll go for the upper 10% to account for voltage droop so 110% of 324 is 356V

That means (29) 12V deep cycle batteries in series (348VDC).


Pump efficiency:

upload_2017-12-15_12-20-22.png

At max pressure (around 210bar) efficiency of the pump is about 88% per the curve.
For 13kw hydraulic output you would need 13kW*(1/.88) = 14.77kW electric motor.
Round up to 15kW - this should cover inefficiencies in the motor, which are usually negligible.

running for 2 hours is 30kwH.

with a 348V DC bank, 30,000kwH / 348V = 86AH (amp-hours)

This is actually not that bad. See typical deep cycle battery AH below.
But we only want to use 30% of that in 2 hours. So we should shoot for a 287AH bank.

The motor will be drawing (15kW / 348V = 43A) amps

https://www.solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html

upload_2017-12-15_13-16-46.png

We need to find a battery that can give us 43A while maintaining a discharge rate of 287AH

This looks like a good fit @ $256/ea.

upload_2017-12-15_15-26-7.png

The 5-hour discharge rate is 271, meaning 54.2A for 5 hours (54.2*5=217)
This is just above the 43A we want, so should be good.

They're only 6V each, so we'll need 58 of them instead of 29.
$14,848 + shipping.
at 96lbs /ea, they're going to weigh in at about 5,600lbs, so shipping isn't going to be free.
 
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