DIY Motor Dyno/load?

Electric Motors and Controllers
Post Reply
shaman   1 kW

1 kW
Posts: 319
Joined: Dec 10 2018 7:03pm
Location: Fort Worth, TX, USA

DIY Motor Dyno/load?

Post by shaman » Oct 08 2019 8:11am

I'm looking to construct a crude motor dynamometer/load by utilizing a big cheap expendable motor or motor type thing (like a big converted alternator). I can control the braking force of the load motor with my controller that has variable active braking. The motor being tested will have a separate controller (also that is being tested) of which I can monitor power consumption from. The test motor is connected to the load motor by a chain or pulley. The idea isn't to be able to plot any torque or power curves. Just variable load testing.

Does this method make sense? Are there better ways of doing this? I'm looking for a quick and dirty solution.

Thecoco974   10 mW

10 mW
Posts: 26
Joined: Dec 07 2016 7:01am

Re: DIY Motor Dyno/load?

Post by Thecoco974 » Oct 08 2019 8:46am

If you just want to load your motor and don't need any power data, the quickest methode I can think of is simply braking it, either by using the brakes on the vehicule it's mounted on or putting some disks brakes on an axle. (May not work for long before overheating though)

Envoyé de mon Redmi Note 3 en utilisant Tapatalk


shaman   1 kW

1 kW
Posts: 319
Joined: Dec 10 2018 7:03pm
Location: Fort Worth, TX, USA

Re: DIY Motor Dyno/load?

Post by shaman » Oct 08 2019 5:27pm

Thecoco974 wrote:
Oct 08 2019 8:46am
(May not work for long before overheating though)
Yeah I'm trying to avoid friction based approaches for this reason. I need to be able to stress test my controller for a good duration. I've seen professional rigs that are essentially the idea I'm suggesting. I might just go ahead with the biggest beefiest alternator I can find, convert it to a motor and run it as a load.

Thecoco974   10 mW

10 mW
Posts: 26
Joined: Dec 07 2016 7:01am

Re: DIY Motor Dyno/load?

Post by Thecoco974 » Oct 08 2019 5:58pm

Yes, it's a good way of doing it. But might become expensive very quickly since the generator-controler combo must be a least capable of handling the max power of the motor tested.
If there is no need to control the load precisely, like you said an oversized industrial motor with a massive load is okay, you need to find a load that can sustain the power too !

Envoyé de mon Redmi Note 3 en utilisant Tapatalk


john61ct   1.21 GW

1.21 GW
Posts: 3793
Joined: Dec 18 2018 2:06pm

Re: DIY Motor Dyno/load?

Post by john61ct » Oct 08 2019 6:45pm

Big alternator, just add / remove electrical loads, headlights, hair driers, resistors in buckets etc

dustNbone   10 kW

10 kW
Posts: 948
Joined: Mar 13 2016 9:59pm
Location: Vancouver, BC

Re: DIY Motor Dyno/load?

Post by dustNbone » Oct 08 2019 6:52pm

john61ct wrote:
Oct 08 2019 6:45pm
resistors in buckets
This is probably the easiest, cheapest and least messy method available to the average person. As long as the water is kept below boiling point you can do this all day, with a pretty decent level of accuracy.

You can even just buy bulk nichrome wire and cut it to length to get the desired resistance.

shaman   1 kW

1 kW
Posts: 319
Joined: Dec 10 2018 7:03pm
Location: Fort Worth, TX, USA

Re: DIY Motor Dyno/load?

Post by shaman » Oct 08 2019 7:41pm

to be clear I'm not intending to use the alternator as an alternator. I would convert it to a motor that would then oppose the motor under test. I can make the alternator apply braking force via magnetism.

Basically adding resistive electrical loads to the alternator would just approach the same thing as shorting the alternator phase wires to each other. This does cause mechanical resistance but not enough I'm afraid.

john61ct   1.21 GW

1.21 GW
Posts: 3793
Joined: Dec 18 2018 2:06pm

Re: DIY Motor Dyno/load?

Post by john61ct » Oct 08 2019 7:50pm

Depends on the alt.

I've seen a 14kW unit off a Hummer requires a few horses

dustNbone   10 kW

10 kW
Posts: 948
Joined: Mar 13 2016 9:59pm
Location: Vancouver, BC

Re: DIY Motor Dyno/load?

Post by dustNbone » Oct 08 2019 8:47pm

Whatever you do is going to turn mechanical energy into heat at some point, you need to consider where that heat goes. The way you're suggesting seems like all the heat is going to need to be rejected through the windings of the alternator/motor, and I don't see that working well for long.

Moving most of that heat load to some external heat sink (bucket of water) will give you far more continuous power handling ability.

Punx0r   100 GW

100 GW
Posts: 5514
Joined: May 03 2012 8:16am
Location: England

Re: DIY Motor Dyno/load?

Post by Punx0r » Oct 09 2019 3:21am

Exactly. Not a great idea...

An automotive disc brake is pretty compact and simple and can dissipate a fair amount (few kW) continuously but may not be that linear due to CoF changing with temperature.

Another alternative is driving a hydraulic pump through a restriction and an oil cooler. Non-linearity would also be likely as fluid viscosity reduces with temperature.

A noisy but effective option is driving a propellar - cheap, simple, doesn't heat up.

Or an alternator/generator powering a resistive element in a bucket of water :wink:

peters   1 kW

1 kW
Posts: 303
Joined: Oct 20 2012 11:46pm
Location: Hungary

Re: DIY Motor Dyno/load?

Post by peters » Oct 09 2019 4:04am

You could use 2 identical motors and controllers, one in drive and the other in regen mode, or the second one also in drive mode with lower torque, that would rotate backwards, and powered from the same battery. Then most of the energy would be dumped back onto the battery, if the rpm is not close to 0.

User avatar
DogDipstick   1 kW

1 kW
Posts: 464
Joined: Aug 19 2018 12:39pm
Location: Fleetwood Pa

Re: DIY Motor Dyno/load?

Post by DogDipstick » Oct 09 2019 6:25am

Yeah just use two brushless motors end to end.
Allota Watts @ 83.1v of raw QS power takes me everywhere on my Ironhorse DW link XC... :) Powered by Chevy. :D Broke 10 horses the other day. ( BTW; ...don't get hurt... :? )... (Currently building a battery datalogger.). :roll: Playin with (24) IRFB4115s now. :wink:

Thecoco974   10 mW

10 mW
Posts: 26
Joined: Dec 07 2016 7:01am

Re: DIY Motor Dyno/load?

Post by Thecoco974 » Oct 09 2019 8:12am


shaman wrote:to be clear I'm not intending to use the alternator as an alternator. I would convert it to a motor that would then oppose the motor under test.
That's what I call a generator or alternator :P. Same hardware, positive energy.
Of course the best is to dump back the energy in the battery.
If you're planning this for stress testing your New Serious focer, why not strapping an other one as load and stress test it in regen mode at the same Time ? :)



Envoyé de mon Redmi Note 3 en utilisant Tapatalk


shaman   1 kW

1 kW
Posts: 319
Joined: Dec 10 2018 7:03pm
Location: Fort Worth, TX, USA

Re: DIY Motor Dyno/load?

Post by shaman » Oct 09 2019 11:49am

This is all good feedback here. My concern is that regen braking alone won't produce enough opposing torque and active braking will be needed. This is fine since any VESC based controller can do this. Also using a big 100A alternator should tank the current and heat pretty well.

My initial approach will probably be something like @peters is talking about. It allows for a lot of control. If for some reason that doesn't work out, then it will be time to create dummy resistive loads and submerge them in water.
Thecoco974 wrote:
Oct 09 2019 8:12am
If you're planning this for stress testing your New Serious focer, why not strapping an other one as load and stress test it in regen mode at the same Time ?
Cause it's not a proven design. The load needs to be controlled by something I know works. I can eventually throw in a Serious FOCer after I've validated it.

dustNbone   10 kW

10 kW
Posts: 948
Joined: Mar 13 2016 9:59pm
Location: Vancouver, BC

Re: DIY Motor Dyno/load?

Post by dustNbone » Oct 09 2019 4:33pm

It's pretty easy to size an alternator as a load. A 10Kw one will be able to convert 10Kw of mechanical energy to electrical energy, it's literally what they're made to do.

If you can't get it to do that, you either need to turn it faster or put a more appropriate electrical load.

An ebike controller running in regen mode will probably not be as efficient, and more expensive.

Thecoco974   10 mW

10 mW
Posts: 26
Joined: Dec 07 2016 7:01am

Re: DIY Motor Dyno/load?

Post by Thecoco974 » Oct 09 2019 9:59pm

shaman I just dont understand when you and Peter are saying : "the second one also in drive mode with lower torque, that would rotate backwards"
For me BLDC being synchrnous motor (and it apply to other motor technology) you cannot just run it in opposite direction of the driving motor, either they are both stalled or one is running and the other one lost sync and isn't producing torque anymore.
I may just miss something here :confused:
For me it works like this guy is doing :
one in drive the other in regen

peters   1 kW

1 kW
Posts: 303
Joined: Oct 20 2012 11:46pm
Location: Hungary

Re: DIY Motor Dyno/load?

Post by peters » Oct 10 2019 12:34am

Thecoco974: yeah, in this setup the direction is the same physically, but it is all about the 4 quadrants of the drives:
https://en.wikipedia.org/wiki/Variable- ... _operation
Image

The driving motor works in quadrant I, and the braking motor+controller can be either in quadrant II or IV from the point of view of the software, depending on the setup (sequence of phase and hall wires):
quadrant II: positive direction with negative torque (negative current setpoint)
quadrant IV: opposite direction with positive torque

The advantage of this active braking is that the high torque operation can be tested at low or 0 speed, and also reversing the motion at high torque if the controller is capable of seamless 4 quadrant operation. It depends on the software and I don't know enough about VESC, but certainly it can run at least in quadrant I and II.

Thecoco974   10 mW

10 mW
Posts: 26
Joined: Dec 07 2016 7:01am

Re: DIY Motor Dyno/load?

Post by Thecoco974 » Oct 10 2019 8:30am

I know the 4 quadrant of motor operation, It appears I havent' understand it as well as you did ^^
For me when torque and rotation are in opposite direction it mean that the motor is producing negative work or generating power. But you tell me that the controler can actively drive the phases 90 degres after the magnet field instead of in advance .
That's make sence to me now since bldc controlers uses a full bridge it is possible but I'm not sure it's actually programmed . I may look more into it that's interesting :)


Envoyé de mon Redmi Note 3 en utilisant Tapatalk


shaman   1 kW

1 kW
Posts: 319
Joined: Dec 10 2018 7:03pm
Location: Fort Worth, TX, USA

Re: DIY Motor Dyno/load?

Post by shaman » Feb 17 2020 9:51am

coupling.JPG
coupling.JPG (73.64 KiB) Viewed 571 times
Ok so I threw something together with scrap wood and some cheap outrunners for proof of concept. It works. I'm able to control load torque with one motor/controller and then control driving torque with the other motor/controller. Makes for some decent testing of various conditions with load. The limitations now are the thermal capability of the motors. They get hot and I can't test under load for the amount of current I want for as long as I want. Ideally I want at least 100A phase current for 1 hour.

To scale this up for the current and duration I want, I'm thinking of course larger motors, metal mounts/assembly, and submerging the motors in tech grade mineral oil. I'm looking at some goldenmotor 3 or 5kw motors but I'm open to suggestions. What do yall think?

User avatar
Okami   10 W

10 W
Posts: 84
Joined: Jun 02 2016 3:00am

Re: DIY Motor Dyno/load?

Post by Okami » Feb 17 2020 3:22pm

Nice to see some progress on dyno.

I suppose with golden motor ones u mean these ones right:

https://www.goldenmotor.com/frame-bldcmotor.htm

They do seem fine, though I might look into some non branded ones as I think Golden Motors are putting some margin on them.

Seems like gocarts are using them, so should be ple nty beefy in that respect

shaman   1 kW

1 kW
Posts: 319
Joined: Dec 10 2018 7:03pm
Location: Fort Worth, TX, USA

Re: DIY Motor Dyno/load?

Post by shaman » Feb 18 2020 12:16am

The QS 3000W motor might be a good candidate too. I would buy 2, mount them side by side, and couple them together with a belt or chain. It’s all still tentative and I’ll be shopping a bit.

flat tire   1 MW

1 MW
Posts: 1881
Joined: Feb 26 2014 12:20am

Re: DIY Motor Dyno/load?

Post by flat tire » Feb 18 2020 12:24am

Intertial might be better.

A few people have made simple inertial dynos with scrap electrical motors weighing hundreds of lbs.


Cheap solution for higher power (for ebikes) dynos and relatively straightforward. Add a tach and look at rate of change, compare to baseline or previously run motor of known output.

User avatar
DogDipstick   1 kW

1 kW
Posts: 464
Joined: Aug 19 2018 12:39pm
Location: Fleetwood Pa

Re: DIY Motor Dyno/load?

Post by DogDipstick » Feb 18 2020 3:18am

All this complexity and a Prony brake wont work here? Seems like alot of labor for a little work payoff.
Allota Watts @ 83.1v of raw QS power takes me everywhere on my Ironhorse DW link XC... :) Powered by Chevy. :D Broke 10 horses the other day. ( BTW; ...don't get hurt... :? )... (Currently building a battery datalogger.). :roll: Playin with (24) IRFB4115s now. :wink:

shaman   1 kW

1 kW
Posts: 319
Joined: Dec 10 2018 7:03pm
Location: Fort Worth, TX, USA

Re: DIY Motor Dyno/load?

Post by shaman » Feb 18 2020 7:40am

flat tire wrote:
Feb 18 2020 12:24am
Intertial might be better.
DogDipstick wrote:
Feb 18 2020 3:18am
a Prony brake wont work here?
The goal is to have a highly adjustable load that also run a test script through the VESC tool. A prony brake doesn’t give the flexibility of an electronically controlled load and its harder to keep cool. An inertial load doesn’t like it would actively resist the motor providing positive torque and I wouldn’t be able to have it run any load profile

shaman   1 kW

1 kW
Posts: 319
Joined: Dec 10 2018 7:03pm
Location: Fort Worth, TX, USA

Re: DIY Motor Dyno/load?

Post by shaman » Feb 22 2020 9:01am

I've had several suggest just to use distilled water. Its cheap, easy cleanup, and I can flush it periodically to void impurity build up. Guess that's what I'll do. Maybe I can even make ice from distilled water to further cool the test setup.

I will be using two of those QS 3000W mid drives. I think i'll do a side-by-side orientation an couple them with a belt or chain. Just gotta figure out the mounting brackets and hardware

Post Reply