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brush less motor as eddy current eng Dino

brush less motor as eddy current eng Dino

brush less motor as eddy current eng Dino

(OP)
I am trying to use a small brush less AC motor to load a eng.
What options are ther to make a field to load the rotor.

David

RE: brush less motor as eddy current eng Dino

(OP)
http://www.tppower.com/sort.asp?class_id=4&new...
Here is a link to the motor that I will be using.
I will turn this motor with a nitro powered 1 CID Eng that will run at 28000rpm to test the power out put.
the motor will be in a rotating cradle with a load cell attached to get ft.lbs. readings.
There are various ways to load the field just what is the best way?
Feed DC voltage to the winding on two poles.
Invert the 3 Ph out put and load with Resistance bank?
Feed AC to the windings?
Any help would be much appreciated.

David

RE: brush less motor as eddy current eng Dino

Your PMDC motor used this way is just a PM synchronous generator.
Just attach a variable three-phase resistive load.

Benta.

RE: brush less motor as eddy current eng Dino

So, you have an (internal combustion, IC) motor that drives the brushless motor at the mentioned rotating speed. The brushless motor acts as a generator in order to load the IC-motor. You want to measure the torque (and rotating speed) in order to get the power of the IC-motor. Did I get this right?

The simplest way to load the generator is to connect equal resistors in each of the wire-pairs of the generator. That is, three resistors connected in a triangle, and the generator wires connected to each corner of the triangle. There are some problems with this approach, however: the size of the resistors in Ohms, and in terms of the power they can handle.

You do not mention the power of the IC-motor, but the data of the brushless motor indicates that several kW are available. The resistors should be "powerful" enough to handle this. In addition, cooling of the resistors is needed with a fan or water, for example.

The second problem is that the resistors (the value in Ohms) very much determine the loading. This means that you should have a set of resistors in order to find the maximum power. You are after the maximum power, aren't you?




RE: brush less motor as eddy current eng Dino

I'm impressed. I was all set to talk about the problems taking a typical motor and running it at 28K. Who knew something this esoteric existed in the hobby world.

RE: brush less motor as eddy current eng Dino

Probably the the cheapest way will be to buy replacement elements for a clothes drier to use as resistance. These are coils of nichrome wire that you may cut or tap for the values you need.
Your power dissipation will depend on the square of the voltage which will depend on the speed. You should plan on some instrumentation to indicate the power produced. Don't forget to add the internal loses of the motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: brush less motor as eddy current eng Dino

I don't see enough data on those motors to really be able to predict what the expected voltage and current would be under load.

If doing it starting with nothing, I would rectify the 3-phase output into DC and then feed a PWM controller dumping into a resistor. The only issue with this idea which might cause issues is that the DC voltage will vary with rpm. However, it might be possible to get a pwm controller with input voltage compensation. In other words, the controller will automatically vary the PWM duty cycle to maintain a constant power output even when the input voltage varies. You might also find you want the load to increase as the rpm increases and this really isn't an issue.

First, I would investigate if a RC controller could be used. I'm sure there must be one that does regen braking. You could just connect it to a big battery and it'd dump the energy into the battery. Switch a big load onto the battery to dump the energy.

RE: brush less motor as eddy current eng Dino

LionelHutz, the idea with rectifying and PWM modulating into a load is really nice.

A non-isolated step-down converter would probably be simplest. If the efficiency curve of the converter is nicely smooth and horizontal (is it not at low load, but who cares in this application), output power into the resistive load would be proportional to the input power coming from the BLDC generator.
Using heating elements for the load is the way to go.

I like it.

Benta

RE: brush less motor as eddy current eng Dino

(OP)
I have explored the Scenario of rectifying the AC to DC then resistors for the load.
Looked at kiln heater coils and also a custom made salt water resistor.
The problem is adaptability over a span of different RPM ranges and load conditions.
the voltage will change a lot with a 780Kv motor. All the different loads and RPM's will make it hard to have one size fits all. this will be a test stand so You do not really know what you will have till you run it.
I am interested in trying to put a DC current to the field coils on two legs of the Y wind or isolating the polls and running DC to all of them in a series parallel circuit.
The load dose not need to be measured the load cell will do that.
But the load dose have to be adjustable over a span of RPM ranges and different loads.
Dose any one have any thoughts on putting a DC current to the stator to load the rotor?

David

RE: brush less motor as eddy current eng Dino

(OP)
The Eng's I will be testing will be any where from 5 to 10HP.
I will be testing different size IC Eng with this setup. So it has to be flexible with its load adjustment.
I am using this small motor to keep the power absorption from the rotors inertia to a minimum.

David

RE: brush less motor as eddy current eng Dino

dwilfong
1) The problem is adaptability over a span of different RPM ranges and load conditions. All the different loads and RPM's will make it hard to have one size fits all.

2)I am interested in trying to put a DC current to the field coils
Dose any one have any thoughts on putting a DC current to the stator to load the rotor?

David


David, did you post wrong link to your motor? why do you insist on trying to supply a field when the link showed non?? You posted a link to a low voltage high current PERMANENT MAGNET FIELD motor. 3 wires coming out. so why the consistent talk about a field winding if you have none?

your link describes a typical pmdc V & I rating for GOLF CARTS. Google golf cart controllers and check your options there; I paid like $ 175 for 400 amp 36v pwm drive for my modified GE Electrac riding lawn mower with pmdc motor. You can then set torque level to value to match the load on your dyno at any time.

RE: brush less motor as eddy current eng Dino

(OP)
Will the winding in the stator become a opposing field when energized with DC current?
That is the Question I am posing.
If I use the speed controller from say a golf cart. how will this load the motor by back feeding to a battery? Or just using the breaking circuit in the controller?
then you need a programmer to adjust it?

RE: brush less motor as eddy current eng Dino

put dc into the motor and you make a humpy torque as each magnet goes by. being hi speed, i assume these are 2 pole motors so put dc in and you make a steady magnetic field that will attract both magnets as they go past; 2 humps of torque per rev; in between the humps = no torque. not much of a dyno....

there are ac model gold cart drives that operate in 4 quadrant mode; meaning yes, you dial in how much torque you want and if the motor is in generator quadrant it puts it back in batteries. w/o a drive i do not see simple way to make a pure resistive infinitely variable resistor capable of multiple kw load.

when we build kw dynos for servo motor load testing, we have supplied sophisticated VFD drives and run induction motors. control of dyno is our world has always simply been analog speed command potentiometer dialing up 0 - max torque load. Controller is the mn standing there changing the pot. More sophistication then is plc or controller using some other feedback to modulate it if that is appropriate.

RE: brush less motor as eddy current eng Dino

You may buy two identical motors. Connect the leads from one to the other. Now when one motor is turned the other will lock on and turn with it. Put an aluminum disk on the second motor and use a DC coil to make an easily controlled eddy current brake on the disk. The second motor and disk may be located a safe distance away.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: brush less motor as eddy current eng Dino

You can't put DC into the motor. Even if it would produce a load (which it won't), applying DC to the motor would mean all the test motor power (10hp = 7.4kW) would be dissipated into this electric motor which would most likely quickly burn it up. This is why you need a controller and a load - so the power gets safely dissipated into the load bank.

I still think investigating a suitable controller capable of regen or 4 quadrant operation is the first thing you should do.

I didn't think about this last post but there are dump controllers for wind renewable energy applications. This is a module you basically connect across your battery bank and the module begins to dump energy into a resistive load when the battery voltage reaches a certain level. the basic theory of operation for small wind RE is that wind turbines can't be unloaded so once the wind turbine has charged the battery bank the generated energy gets dumped as heat instead. Use a motor controller into a battery with a dump controller to prevent over-charging.

The controller requirements shouldn't be that big a deal. 780kV or 780rpm/V isn't listed for any of those motors you linked. Still, you're looking at 36V give or take or 3 x 12V batteries in series. There should be a RC controller and dump load controller available for 36V.

RE: brush less motor as eddy current eng Dino

Won't you need a couple of caps on the motor to get it to gen before you rectify it.

RE: brush less motor as eddy current eng Dino

(OP)
The motors are 6 poll design. as far as heat the motor will be in a water cooling jacket to take the heat out of the motor.
http://kershawdesigns.com/TPPower.htm
This is the motor I am thinking of using.
There are many motor to choose from any KV and polls you can think of.
Most of the high end motors are very expensive $700 or more.
I am trying to keep the cost down on this build for the first tests to see what is what.
That is why I was thinking of the DC system. easy to build and simple in design over a wide range of RPM and loads.
At 20000+ RPM I don't think the notching will be a concern.
Was thinking of a square wave generator as in a model train transformer to energize the coils.
I have worked on self propelled personnel lifts for 30 years. Have maintained and repaired many DC drive systems in the lifts. the first ones where SCAR rectifiers with GE EV-10 modules in them. the newer ones are like the golf carts and need programmer to adjust them. thy do not have much adjustment as thy are designed for each application.
Need a easy adjustable system to change the load as I am running the ICC Eng in testing.
Not looking for a preset load that can not be changed while running the test.
Need to adjust the load at RPM to see what the Eng can run.
I know this is not the norm as most systems are made to do just one thing.
That is my reason for posting here to get some input from a different perspective.
I am a mechanic with many years of electric over hydraulic power system experience not a engineer. I know my limitations.
I thank you all for your interest and input it is all good.


David

RE: brush less motor as eddy current eng Dino

That motor will not create a load if you apply DC to the windings. You need another solution. Try something already posted.

RE: brush less motor as eddy current eng Dino

A single phase load on a delta generator will safely load it to 2/3 of the generator three phase capacity. How about an auto-transformer on two leads with a resistor bank on the secondary. You can base load with fixed resistors and trim the final part of the load with the auto-transformer.
Opera, these motors have permanent magnet rotors. No need for caps.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: brush less motor as eddy current eng Dino

Further to waross's idea, dispense with the two linked motors and just fit an aluminum disk to a jackshaft, and brake it with a DC coil.

http://en.wikipedia.org/wiki/Eddy_current_brake


Mike Halloran
Pembroke Pines, FL, USA

RE: brush less motor as eddy current eng Dino

(OP)
There are some trying to use disks from a hard drive with the permint mag in the drive to build a load. moving the mags in and out on the disk will change the load.
Inertia is the reason for not using a large mass on the rotating assembly as this mass will absorb the power. A low mass rotating assembly will replicate the conditions the Eng will see when used in the application it is intended for.
The Eng are used in RC boat racing. We race at speeds close to 100MPH on a course that will fit in side a foot ball field. the boats turn 180deg in a span of 50' or less at speeds of 75+ mph and entry speeds close to 100 MPH.
We burn 50 to 65% nitromethan mix in the Eng for racing. a 1 CID can make 8+ HP at 28000RPM depending on the tune.
The high RPM is the problem with testing this in a Dino. what ever you use has to handle the High RPM at a load.
the smaller Eng .45cid will turn 30000RPM and the .21 cid eng will rev 35000rpm.producing 3.5+ hp.
Waross can you explain you idea a little more?
Delta wind is a option when specking these motors.
Auto-transformer? single phase load?

David

RE: brush less motor as eddy current eng Dino

Yes David I can describe it, then tell us if it will fit your plans.
Assume an 8 KW generator/load.
Build some resistor banks from nichrome heating elements. say 1 KW, 1 KW, 2 KW, and 4 KW. Arrange these to be switch connected.
Now add an auto transformer and load of about 2 KW. On single phase,this will generate the same heat and take the same generator capacity as a 3 KW three phase load. Pre-set the base load and fine tune it by adding load with the auto-transformer.
I see a problem here and a possible solution. Many electrical and quite a few mechanical breaking schemes are speed dependent. As the speed drops, the generated voltage will drop and the dissipated energy will drop be a square factor.
As an example, we want to look at the performance of a motor at 10,000 RPM and 28,000 RPM
Calculate the resistance needed to load the motor at 28,000 RPM and set up a resistor bank and auto-transformer setting combination that will match power output at 28,000 rpm.
Do the same for 10,000 RPM, but subtract the amount of resistance in place for 28,000 RPM.
Now, with the motor running and loaded at 28,000 RPM, switch in the resistance block for 10,000 RPM. This will create an overload condition which will slow the motor until the speed and load stabilize at around 10,000 RPM.
Switch out the added resistance and the motor can be expected to accelerate to 28,000 RPM.
You may use an auto-transformer for each speed, or if time constraints permit, use the auto-transformer to determine the resistance required and make a fixed resistance for that setting. Ni-chrome elements are easy to to connect and tap.
Of course this may end up pricing above controllers, but if you don't do the numbers you don't know.
If it fits your plans and you are testing a group of similar motors, consider a fixed setting and reporting both HP and speed.
One motor may be reported at 6 HP at 28,000 RPM and the next motor reported at 6.3 HP at 30,000 RPM
Stated another way, you may set the test for a given HP at a given RPM and then see if the motor under test meets or exceeds the test points.
Reporting both over HP and over speed may be a more accurate description of the motors expected performance, or maybe not. You tell me. grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: brush less motor as eddy current eng Dino

(OP)
What you explained is how I had it planned at the on set. but I was running the 3 ph AC thew a bridge to change it to DC. your plain eliminates the need for a bridge. Great idea!
I have done all the calculations for resistance to make the loads with varying voltages as the RPM change with rotor speed already.
I am a little fuzzy on the way to wire the load system this way.
Lets say the 3 wires coming out of the motor are referenced a1,a2,a3 this is three leads coming from a Delta wind motor.
Make a load bank of whatever connecting a1 and a2. now make a variable load from a2 to a3 ?
I have looked in to making water resistor dummy loads from vinyl tubing with copper lug at each end using copper sulfate as the restive medium in the tube.
Then coiling the tube in a 5 gal bucket and running water thew the bucket to keep the heat under control.
Then for the fine tuning using a large Biddle rheostat or a jagabi carbon pile rheostat.

RE: brush less motor as eddy current eng Dino

(OP)
One more question what would the calculation be to figure the load on one ph at the lower voltages that the motor will produce.
Say a 15a 120v auto trans would build how many watts at only say 40v?

RE: brush less motor as eddy current eng Dino

Are you sure about the quoted RPM figures?
I'd believe that a small piston engine could go 14,000 rpm, but 28,000 rpm is a bit less believable.
Did someone perhaps measure the exhaust frequency and assume they're 4-strokes, not 2-strokes?

Mike Halloran
Pembroke Pines, FL, USA

RE: brush less motor as eddy current eng Dino

(OP)
http://www.hobbysupplies.com.au/CMB%20Engines.HTM
Here is a link to one suppler that shows specks on the Eng I run in stock form.
I do all the modification to my own Eng and thy make more than the stock figures. also the stock HP and Rpm ratings are on 20% nitromethain not modified eng running 60% nitromethain.
Theses eng are the cutting edge of IC eng design. that is why I run RC boats.
To push the edge of the HP envelope.
I build different variants of these Eng from stock parts to gain even more HP.

RE: brush less motor as eddy current eng Dino

Examples.
You want 300 Watts load. Calculate the resistors for 100 Watts load. Make three resistors and connect one from a1 to a2, one from a2 to a3 and the third resistor from a3 to a1. Now you have a 300 Watt load. Now put a 100 Watt resistor on the auto-transformer and connect it across any two leads. a1 to a2 will be fine. Now you have a 300 Watt base load and and an additional 100 watt variable load. or 300 Watts to 400 Watts. The internal heating of the motor/generator will be the same as if a 450 Watt load was connected. The capacity of the generator must be calculated for 150% of a single phase load. That is the advantage of a three phase base load. If the entire 400 Watt load was connected single phase you would need 600 Watts generator capacity rather than 450 Watts.
More information later if you need it, but the 100 Watt resistor on the auto-transformer (set at 100%) will give you a 100 Watt load. AS you dial the AT down and reduce the voltage on the resistor to zero, the 100 Watt load will reduce to zero.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: brush less motor as eddy current eng Dino

(OP)
Bill
Can I use 3 transformers to change the lower voltage output of say 40v on each leg to 120v
and use a variac one pot on each transformer to adjust the load.
http://www.ebay.com/itm/181004336490?ssPageName=ST...
Here is the one I was looking at.

RE: brush less motor as eddy current eng Dino

I'm a little tired just now so please forgive any foolish typos.
For illustration, and to make it easy to grasp lets take a motor/generator which develops 50 Volts at 50,000 RPM.
At 28,000 RPM it will develop 28 Volts.
At 14,000 RPM it will develop 14 Volts.
Sizing a transformer: The winding will have to be capable of carrying the full current, Voltage and frequency is more flexible.
A six pole motor looks like an 1800 rpm @ 60 Hz motor. At 18,000 a 12 volt winding will take 120 Volts without saturating. (A 6 Volt winding would be better if available. So, over-voltage is not a problem as far as saturation is concerned.
Example: we want to dissipate 5100 Watts at 14,000 RPM. The voltage will be 14 Volts.
The current per phase will be: 5100W/1.73/14V=210 Amps.
A 12 volt winding to handle 210 Amps will be rated at 210A x 12 Volts = 2500 VARs.
The secondary will put out 14V x 10 = 140 Volts
At 28,000 RPM the voltage will be 28V and the 120 Volt secondary will be putting out 280 Volts.
When you look at the price of dry type transformers (figure 3 x 5 KVA or 3 x 7.5 KVA) you may want to go with resistors sized for the out-put voltage and forget about transformers (except for the auto-transformer).
Time for bed, more tomorrow.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: brush less motor as eddy current eng Dino

Everyone always says, I just want this. But really you are going to want a lot more capabilities
than just a simple load. This is an engineering forum and we should be going for more. You seem
competent enough for what I am about to propose.

Three phase rectify the output from the motor and filter that voltage with several large electrolytics,
say three 4700uF 63V. Monitor the voltage with an Arduino UNO ans drive three or more FETs with the PWM
output pins. Each FET will have its own load resistor. Load resistors are easy to make if you don't go
commercial. An adjustable resistor into one of the A/D inputs. Isolated ACS712 current sense boards are
only about $4 that will deed directly into another A/D input if you want to calculate power too. The UNO
has nice monitoring capabilities. You can skip exotic LCD programming by just using the USB port of a
laptop. A copycat version of the UNO is less than $15 and the development system is FREE to download and
try. "Conversational logic", if this and if that is straightforward and easy enough for anyone to understand.
Map functions easily convert data into engineering units. Standard PWM outputs operate at 490Hz which makes
driving a FET straightforward. With all this capability you can capture peak events, monitor temperature and
have a nice record of the test. There are lots of dump load discussions at fieldlines.com where this voltage
and much higher currents are common. Many of these logic functions have been discussed there. You could always
wimp out and use a GHURD controller and TURNIGY 130A to collect data. I think you would like using the UNO.
There would be interest in this dump project at fieldlines and you would get help there.

RE: brush less motor as eddy current eng Dino

(OP)
I have a Arduino Nano that I was planing on using as a eng control system for theses eng.
That is the reason for building this Dino to run simulation on the bench.
I have a data acquisition system http://www.eagletreesystems.com/# that I use now to log the RPM, head Temp and GPS speed in the boat as it is running on the water.
I have also logged EGT with this system.
This is what I am planing on using to run the Dino.
There is a analog to digital inter face card made for this system to gather the load cell info.
Every thing will be logged on one graft and also in Excel spread sheet form.
I can log RPM,HEAD TEMP,EGT(exhaust gas temp) and load cell readings at the same time.
That is why I am looking at a easy cheep fully adjustable load system for this motor.
I need to start some where before I jump into the Arduino system.
I am not very proficient at code writing or under standing the logic circuits involved with the Nano.
I need to walk before I can run.

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