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Author: Subject: Home built engine dynoís
mark chandler

posted on 10/5/21 at 03:11 PM Reply With Quote
Home built engine dynoís

Has anyone here built an engine dyno?

Having a google eddy brake systems come up every now and then, I have just purchased one from a Mercedes sprinter that is designed to stop 370ft/lb at 5000 rpm so will be giving it a go.

For the controls I plan to keep it simple, run the brake with a couple of high powered alternators so 100amp each and a battery so itís self powered - well by the engine.

Not go for anything complex to run it software wise, just switch in coils so I can add load, then map the engine around these points, being more advanced would require controlling the current.

By measuring the load I will be able to sort out the advance curves and lambda sensor for mixtures, not perfect but ample for my new project car that will be running SU carbs, an old Riley Brooklands in pieces?

Cheers

Mark

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coyoteboy

posted on 10/5/21 at 07:04 PM Reply With Quote
I was involved in a project to do this about a decade ago, but it got mothballed due to H&S concerns in the institution we were in.

It's relatively simple, but you do need some hefty welded fixtures for mounting it and some sort of cage to ensure that any overspeed won't cause a burst. On top of that, you need temp monitoring - in active duty the brake won't ever overheat as it has more mass than is required to stop the vehicle, and the friction brakes to help. However you'll be operating it hot for a long duration - how are you actively cooling it, what overspeed and overheat protection are you integrating and how do you plan to control the reaction torque finely enough to map cells? We were planning a smoothed PWM drive from a very high current PSU.

Very easy to calibrate and instrument, and not have the endless guestimations of drivetrain loss.

I think we got ours from a bus, for about £250.

[Edited on 10/5/21 by coyoteboy]





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mark chandler

posted on 10/5/21 at 09:32 PM Reply With Quote
It cost £600 delivered so you are well ahead of me!

I have not got into the details yet, itís a 12v item, my plan was to switch in coils to add load, having had a few cars on rolling roads the best tune I have had was from Dale @ Bailey performance and he was not sitting hammering the car at high RPM for prolonged periods so I plan to emulate that to control heat - no reason not to face it with a fan or sort out some water cooling I guess.

I will of course have to make a substantial frame, probably start off with an RSJ chassis bolted to the floor.

Have you got any info on a PWM controller, staying at 12v is attractive as I can use it to generate safe power, others have re-wired from parallel to series running at 200v which I do not fancy.

Thanks for the tips, this will no doubt grow in complexity.

Cheers

Mark

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SteveWalker

posted on 10/5/21 at 10:39 PM Reply With Quote
When working in industry and using a dyno to measure the output of a 4500hp (at 300 rpm), 250l, 2 stroke, turbocharged, V12, gas engine, we simply drove a pump, pumping water out of and back into a tank, restricted the pump outlet (with a valve) and measured the rotation of the pump body against a spring to get the torque. Simple, effective and safe.

They were beasts of an engine - 120 tons and only 4500HP, but due to the low speed and low stresses, they'd be expected to run 24 hours a day, with little maintenance, for 20-odd years or more.

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coyoteboy

posted on 10/5/21 at 10:40 PM Reply With Quote
On ours (24v) the coils were in different series combos for different torque levels, via an input plate. 3 were broken so we had to do some simple repairs first but you could wire them individually if you can get access.

Careful working up to speed/load would keep you safe. Maybe with an IR pyrometer. Just follow basic safety processes like not standing beside it 😂

PWM controller was our own design, we had free access to some monster switching components so it was a super simple microprocessor based controller with a huge output stage from what I remember. I don't have the schems anymore I don't think, or you could have them.





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coyoteboy

posted on 10/5/21 at 10:42 PM Reply With Quote
quote:
Originally posted by SteveWalker
When working in industry and using a dyno to measure the output of a 4500hp (at 300 rpm), 250l, 2 stroke, turbocharged, V12, gas engine, we simply drove a pump, pumping water out of and back into a tank, restricted the pump outlet (with a valve) and measured the rotation of the pump body against a spring to get the torque. Simple, effective and safe.

They were beasts of an engine - 120 tons and only 4500HP, but due to the low speed and low stresses, they'd be expected to run 24 hours a day, with little maintenance, for 20-odd years or more.


That works too if you have a big enough tank to cope with the heat. We had started with a water brake but it was old, too small for the engine we were using and leaked like a sieve !

[Edited on 11/5/21 by coyoteboy]





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Bluemoon

posted on 12/5/21 at 10:37 AM Reply With Quote
quote:
Originally posted by coyoteboy
quote:
Originally posted by SteveWalker
When working in industry and using a dyno to measure the output of a 4500hp (at 300 rpm), 250l, 2 stroke, turbocharged, V12, gas engine, we simply drove a pump, pumping water out of and back into a tank, restricted the pump outlet (with a valve) and measured the rotation of the pump body against a spring to get the torque. Simple, effective and safe.

They were beasts of an engine - 120 tons and only 4500HP, but due to the low speed and low stresses, they'd be expected to run 24 hours a day, with little maintenance, for 20-odd years or more.


That works too if you have a big enough tank to cope with the heat. We had started with a water brake but it was old, too small for the engine we were using and leaked like a sieve !

[Edited on 11/5/21 by coyoteboy]


Might be a good option for a home dyno, however.. you can dissipate a lot of heat in water - not so simple to do electrically, also the operational principle is easy to understand for the mechanically minded.

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coyoteboy

posted on 12/5/21 at 11:55 AM Reply With Quote
The cost of a suitable waterbrake is high though, too. They're not just plain ol' water pumps, of course.

You don't dissipate heat electrically, it's just a big disc brake with its own centrifugal heat transfer, it just needs suplemented if used for long duration.





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mark chandler

posted on 12/5/21 at 01:36 PM Reply With Quote
Iím not planning to hit it with constant high loads, simple maths says it will be generating the maybe 9kw of heat so will cook very quickly, however it should be fine used as basic load, much the same as an inertia dyno without the flywheel.

The engine will be an old Riley lump from 1929 - twin cam hemi but not as you would know it, two cams in the block feeding pushrods so maybe 60-70hp.

I also want to run up a 4.0litre jaguar engine, this would be over 300hp, if I am successful full with an engine dyno I may move to hub dynos.

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SteveWalker

posted on 12/5/21 at 02:43 PM Reply With Quote
quote:
Originally posted by Bluemoon
quote:
Originally posted by coyoteboy
quote:
Originally posted by SteveWalker
When working in industry and using a dyno to measure the output of a 4500hp (at 300 rpm), 250l, 2 stroke, turbocharged, V12, gas engine, we simply drove a pump, pumping water out of and back into a tank, restricted the pump outlet (with a valve) and measured the rotation of the pump body against a spring to get the torque. Simple, effective and safe.

They were beasts of an engine - 120 tons and only 4500HP, but due to the low speed and low stresses, they'd be expected to run 24 hours a day, with little maintenance, for 20-odd years or more.


That works too if you have a big enough tank to cope with the heat. We had started with a water brake but it was old, too small for the engine we were using and leaked like a sieve !

[Edited on 11/5/21 by coyoteboy]


Might be a good option for a home dyno, however.. you can dissipate a lot of heat in water - not so simple to do electrically, also the operational principle is easy to understand for the mechanically minded.


A simple and effective cooling system would be a few car or truck radiators and fans. They can dissipate a lot of heat.

Assuming that the dyno is only for occasional use (and hopefully that water is unmetered), simply continuously adding water to the loop and allowing the tank to overflow to drain provides a fair bit of cooling. I had to do similar, running water through a gas/water heat exchanger and to drain, to cool the recirculating gas of a compressor, under test, running at full load of 330kW (small for us - big ones used 8MW motors and some of the centrifugal ones used gas turbines rated at 23.1MW).

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