PLC dyno?

G'day guys!

A mate of mine wants a dyno for testing cars and bikes. He can not find a commercial unit that will do both, he can easily build the mechanical parts of the project himself, so I am thinking a SLC 5/03 I already have and an analogue card would easily do the trick. Having said that I am not up to analogue in my course yet and am usure how you would actually go about it.

For starters would you use a voltage or current input and what would you use to drive the input? The horsepower/ KW reading does not have to be super accurate all we would be looking for is the change before/after modification.

Once we had it working some sort of SCADA setup or a panelview would be a nice touch, for that professional look.

Thanks in advance for your ideas, Richard.

Nice topic for a project. So, horsepower/KW need to be measured from a transducer that can produce an output, either voltage or current. Now, finding a transducer for this purpose may indeed be difficult. There are many such devices out there for industrial uses but for a dynamo, not sure. Now on the mechanical end, if your mate can build that part easily, he and you must know that to read power from this rig, you must have a way to load the engine under test. You will need a way to control the loading and of course that can be tricky. With a PLC it will be a lot easier and a fairly simple loading mechanism could be a DC generator driven by the dynamo and in turn the generator would produce energy that could be absorbed by a sufficiently large resistor bank. Not your little circuit board size resistors, very low resistor values, but high wattage such as those used in electric heat applications. The sensor to drive your analog input would be measuring the DC power being supplied by the dyno and you are set to go. Just one method.

G'day Randy.

Loading it up is lookig a little more tricky than I first considered. It seemed like a regen set up to back feed the power grid would a good idea but unfortunately you would very quickly start generating more current than their consumer mains are rated for and also there are issues with making sure the supply is suitable.

It seems Dyno Dynamics use something called a retarder which looks like an electrically controled disk brake? Wonder if anyone has any ideas on these? They claim 675kW (900HP) with one unit and 1350kW (1800HP) with two. So far it is this loading that seems to be the major question that needs to be answered.

The DC generator is a good idea, but will get very large as the HP goes up! A few of the blokes who would have access to this setup own drag boats that are in the area of 1000HP. One thing we can be sure of, is that sooner or later one of those motors will end up in a car to "test out the dyno"!

Searching the net has come up with a few torque sensors that can be fitted with an optional indexing setup to give Horsepower aswell and come in 0 - 10v, 4 -20mA, RS232 or pretty much any setup you'd like. So getting the data looks like it's the easy although expensive part of the equation.

Any thoughts or ideas would be appriciated. Thanks, Richard.

Why not a good old prony brake? Just use a strain gauge and amplifier on the torque arm, and use a prox into a high speed counter input for rpm.

Richard,
It is a little more clear now what your intentions are. The high horsepower will definitely make the electric heat loading a bit of a bother. However, the mechanical breaking mechanism is going to generate a lot of heat that will have to be dissipated by some means. I suppose cooling water flow of sufficient rate would take care of that. So, the breaking idea may well be the best one of the lot, so far. Others will doubtless have some input on this topic. If I run across any good links or ideas, I will post it here. Good luck!

Tom Jenkins said:

Why not a good old prony brake? Just use a strain gauge and amplifier on the torque arm, and use a prox into a high speed counter input for rpm.

Click to expand...

I wasn't directly involved, but this is how we built our dyno back in college. It worked well and served our purpose (before-after comparison) for many years. I think that dyno is still in use today.

Tom Jenkins said:

Why not a good old prony brake? Just use a strain gauge and amplifier on the torque arm, and use a prox into a high speed counter input for rpm.

Click to expand...

Tom, what is a prony brake anyway?

It is essentially a band brake that allows measurement of the torque. If torque and rpm are known, horsepower can be calculated. The "b" in "bhp" stands for brake, since this was the standard method of testing engine output for generations.

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

http://www.me.utexas.edu/~epfahren/me244L/labs/pmdc/pronybrake.html

I worked on a Dyno for high performance race car engines. We used a water brake to control the torque on the engines. We used a SLC503 with 8 analog ins and 6 analog outs. The SLC controlled and ran the tests and after each test, the data was then sent to the PC for graphing and saving.

Thanks for the info on the prony brake, I knew the rest of the stuff but never had heard of that particular device. The link to wikipedia was a lot of help too. It this a great place or what?

mates got a dyno at his hipo car workshop.

The rollers pretty much are a water pump with a series of goyen water solenoid valves controlling the load.

its about 30 years old but works a treat.

recently upgraded it to AWD too (same method)

We have both chassis rolls and a flywheel (bobtail) dynos, both use water brake technology.


We buy SuperFlow absorbers and we have our own controland monitoring system. Look for SuperFlow on the web, has a lot of good info.

Thanks to everybody for their reply's! I think my biggest problem has been expecting the worst (ie 1000HP)! I think I need to scale down get something that works with a bike, say no more then 200KW for heaps of head room and then apply the knowledge gained. I have a habit of over engineering! Baby steps is probably the way to go here, thanks to all for taking the time to respond, it should be an interesting project.