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For years we have wanted a PTO dyno on the farm but have never been able to find a used one in our price range that wasn't 1,000 miles away. Now that winter seems to be here we are thinking about building one. With the advent of cheap load cells like the one below, measuring the force produced by the resistance of the dyno is easy.


https://www.amazon.com/Prime-Scales-1000lb-Industrial-Hanging/dp/B007M4CMMG


Creating the resistance and keeping it cool is the problem. We would like it to be able to handle 250 HP from 1000 RPM PTO. Our initial thought was to use a 20K pound truck axle with the differential locked together and use the brakes to create the resistance. If we were to drive it from the end of a hub so the brake drums (or discs) were turning 1000 RPM, the brakes would easily hold 1300 ft lbs, wouldn't they?


The problem is, if each drum weighs 100 lbs, it would take about 14 seconds at 250 HP to take the drums from 80° to 180° F if my math is correct.



How could I keep them cool for even a minute long pull? I don't think the drums have enough surface area to keep them cool by hosing them with water, do they? It would take about 10 GPM of 55° water to maintain temperature...


Thoughts?
 

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They used water to cool the drums for years back in the days of real log hauling off road. Was water tanks built into the front of the log bunk rigging on the truck and some trailers had tanks too. Problem isn't keep drums cool, its the shoes, once you cook them they turn to glass and won't hold nothing.
Many a truck shop does testing using the "bendix dyno", good way to test trannys jumping out of gear, driveline vibrations and those dam peanuts in a Mack power divider lol, have to admit was more than once I often wondered just how fast I'd launch myself thru the door if the overhead hoist let go lol.
But when doing it, you only load up the brakes for seconds at a time, kind of like a duty cycle on a welder. Once you start to smell them, time to let it cool down.

You like messing around, why not turn an old engine into a compressor and go that route.
 

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The factory built dynos are water cooled.
They have sealed brake drums that run about 1/2 submerged in the cooling tank.
Its been a while like 25 years ago since we overhauled one at work.
There are usually no hot deals on used factory ones because if I remember correctly core value on a non functioning unit was $2000 if it was sent back to A&W for rebuilding.
* there was some kind of oil inside the shoe and drum assembly also on those that probably did some heat transfer also.
 

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We have a Taylor engine dyno we are looking to sell.
PM me with contact information if you are intrested
 

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Discussion Starter #5
They used water to cool the drums for years back in the days of real log hauling off road. Was water tanks built into the front of the log bunk rigging on the truck and some trailers had tanks too. Problem isn't keep drums cool, its the shoes, once you cook them they turn to glass and won't hold nothing.

You like messing around, why not turn an old engine into a compressor and go that route.

Agreed on keeping the shoes cool - if I can keep the drums below 140° or so, I would think the shoes would stay cool enough not to glass over, wouldn't they? Even if they did eventually glaze over, it wouldn't be the end of the world to pull the drums every now and then and hit the shoes with a belt sander.


Have thought about a trying to rig a pump or even our generator (would only do 540 though) and a salt box, but the truck axle seems to me to be the simplest and most easily controllable/accurate option.
 

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Discussion Starter #6

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Discussion Starter #7
The factory built dynos are water cooled.
They have sealed brake drums that run about 1/2 submerged in the cooling tank.
Its been a while like 25 years ago since we overhauled one at work.

How large was the cooling tank?
 

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Here a newer version
Now there is no rocket science in how that thing works.
Inside the top blue box in this picture is the brake drum assembly.
Which the brakes are hydraulic applied and the sealed brake drums have oil inside them also that's separate from the cooling water surrounding it.
Oh yeah now its coming back to me.
What goes wrong is water leaks into the shoe/drum assembly with the oil and this buggers things up.
Wrecks the cast drum and shoes from what I remember.
Even with water being fed in continually that thing couldn't be run long on A MF 4900 tractor maybe 30 mins before the dyno would be overheated.
Ya know 25 years ago a long time to remember all this stuff.
 

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Yeah some cheap load cells and a set of heavy truck diffs would do the trick. Spray water into the drums while it’s loaded.

I’ve got a 2500hp Superflow I use for my sled puller and it’s an eddy brake. Fan cooled and that thing will sure start pumping the heat on a long pull.
 
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