Hi all, I'm in the market for a water brake dyno. I can get a pretty good running start with brand new goodies for $10k from these guys. http://www.land-and-sea.com/dyno/dyno-price.htm Anyone know about anything used floating around out there? cheers, Sean
Check out www.racingjunk.com or the classified ads in the back of a National Dragster magazine. Depending on what you're planning on doing with it, beware of low priced dynos. They are not all created equal. For a reliable, repeatable, professional type, you'll be looking at 25k and up. The quality of the data acquisition unit is the main concern. Secondly is how well you 'drive' the dyno. Results can vary tremendously with different or 'bad' operators or cheap dynos were repeatability sucks. I have a Stuska/Depac with over 5000 pulls on it, I had an automatic water controller on it for a while, but found I can duplicate and control tests better with fully manual water control. (looks kinda like the Wizard of Oz behind the curtain, turning knobs and valves- but I like being in control).
Ryan Falconer built our LSR car motor and in one of our many meals together at Bonneville he said he was planning on getting rid of a couple of his. Might get in touch, I doubt he bought any junk. He has a good website that will have contact info. Have a look at the pictures of our car while you are there. His place is not far from Laguna Seca.
Hey all, Reading this thread got me all excited about building my own dyno from a 3 phase motor. I have access to that kind of hardware and it seems like it would work. But then these guys start talking about a brake retarder which I was not familiar with. I've done a bit of digging and can find one brand new for $4k which is good for 600 hp or something like that. It seems like they are installed on large trucks/buses etc. Seems like I should be able to find something like that surplus? Any thoughts on something like this? http://www.telmausa.com/TELMATECHWEB/parts.html Original thread... http://www.eng-tips.com/gviewthread....d/71/qid/84432 Hmmmm Make a eddy current dyno capable of holding 1100+lb ft of Tq A very easy way to build an eddy current brake is to just use any ac induction motor, and feed dc current through the windings. It only works for low power engines though, because the solid steel (squirrel cage) rotor does not dissipate heat well. But if you are experimenting at home with very small engines, it is a very practical ultra low cost way to do it. A three phase motor will have three terminals, just feed a dc current into any two terminals, and ignore the third. The rating plate will have a current rating for the motor, which should not be exceeded. Only a low dc voltage is required because the resistance of the windings will be quite low. Also the braking torque will be extremely high, even at currents far below the maximum on the nameplate. With a given braking current, the required torque to turn the motor increases very rapidly with speed. A given motor will brake full rated torque at its slip rate, which might be only 150 RPM. Just to explain this, if the mains frequency is 50Hz, the magnetic field inside the motor rotates at 50 x 60 = 3000 RPM. The motor speed might be rated at 2850 RPM, so the slip will be 150 RPM. If you try to spin it faster than 150 RPM with full field current, it will readily sink far more torque, so a small electric motor can easily hold almost internal combustion engine. But the big problem is heat buildup in the rotor. It will get very hot very fast, so that is what limits the power absorption, not torque sinking ability. So, a single or three phase induction motor would make a nice home chassis dyno for a cart or small bike, provided you were careful not to cook it. A large external blower or submerging the whole thing in oil might also work. It is all a bit Mickey Mouse, but some of us are not that wealthy. Short power runs are all you really need with long cool down periods for home use. Also, excessive RPM and heat might cause it to fly apart, so a bit of caution is required. Try it yourself, get a quarter horse or larger single phase motor, and while turning the shaft by hand, apply 12v dc and see what happens. The resistance in each coil is 0.945 ohms. There are 8 coils either side of the stator = 16 in total. Normally they are operated in 4 stages, 2 coils either side for stage 1 & 4 coils either side for stage 2 & so on. For the dyno i will wire all the coils together & apply power to all coils at once. Would a rotary motor controller,a high voltage potentiometer or a Rheostat do. Do they even make potentiometers that big or are these for AC power ????? The retarder can be wired to suit 12 or 24 volt DC, i have wiring diagrams-spec sheet. To keep it on 12 or 24 volt DC, i was going to use truck batteries unless there is a better way. Max current draw for 12 volt is 196 amps & for 24 volt is 98 amps. Braking torque is 1450 Nm or 1066ft/lbs. Would AC power make the retarder vibrate or chatter because of cycles per min?. As i take it DC is smooth & AC comes in cycles, correct me if i'm wrong. I mentioned before we have a 250 amp AC/DC converter that i use for tig welding can this be used instead of batteries?? I know a little about eddy currents about 8 yrs ago i built a retarder ,wound the coils & used cast iron brake disc rotors that i machined to suit. It was an experimental project,it works good for small engines but it has to much resistance per coil, wire to small for better engines. I controlled this--playing-- through a 10 amp AC rotary controller that i use for honing into a stick welder wound up full & then through the AC/ DC converter. Basically all i proved is, that it's easy to MAGNETIZE an entire workshop full of tools in one fowl swoop not to mention still having to comb my hair down every 10 mins. The Telma retarders I have seen are used on heavy trucks, and are rated to sink 1,000 Ft/lb torque, and some up to 4,000 Ft/lb torque, according to their website. They do this at truck type tailshaft speeds, so in a truck, I don't know but maybe 1,500 RPM or something might be typical in a mid gear going down a hill? Now with an eddy current brake, the faster you try to turn it, the more torque it takes. What I am trying to say is you might not need to sink 4,000 Ft/lb of torque continuously at 1,500 RPM in your application. You might not actually require anywhere near the 196 Amps at twelve volts. It might be more like 19.6 amps at 400 Ft lb at 1,500 RPM, and even less current at higher RPM to hold the same torque. The way I would do it, would be to find myself an old style heavy duty industrial battery charger. It could be 12v, 24v, or 48v. something with plenty of grunt. It will come in an earthed metal box with an ammeter, and would be ideal. These things are used for recharging electric forklifts, and telecom applications an so on. You might get lucky at a machinery junkyard or in the Trading Post. The sixteen coils can be connected in a variety of ways to suit any suitable operating voltage. I have no idea what voltage your TIG runs at, or how happy it would be running at a continuously high dc current, but it might well be o/k. Once you have a suitable transformer and rectifier, you will need to control the output. The easiest way is with a VARIAC. These are a continuously adjustable output transformer where you can adjust the output voltage from zero up to full mains voltage by turning a large knob through about 270 degrees of rotation. You just connect the variac up to 240 volts, and run your battery charger from the output. In this way the dc output of the battery charger can be adjusted from zero up to full rated output at the turn of a knob. Variacs are rated by current and come in many sizes, so you can get for example, a 2.5 amp variac, or a 20 amp variac and so on. How big it needs to be, really be depends on how much power your battery charger draws. The rating plate on the back will tell you. So get the battery charger first. I am in Melbourne by the way, and my e-mail is: [email protected]
The obvious search term is "eddy current brake" and I've heard of eddy brake dynos but always thought they were stupid expensive. I thought they were big generators and you needed a huge resistor bank or something to absorb the energy but it's nothing like that. You "use" energy to create the braking force vs. just creating and absorbing it but the amperage required is nothing like I was imagining. One big drawback I read of these setups can be the inertia of the system. Oil rigs, etc. use them ... saw one for $45k but don't need something that big LOL. cheers
This bit is a lot to sort thru, but to summup not the brightest idea to use electric motors as they are not intended by back feeding current into them. exploding wires and armatures is beyond dangerous. not to mention the calcs needed to figure the heat loss and saturation of the core along with current load to figure your power, it gives me a headache thinking about it. I'm going to agree with rifedriver here and say your best option is finding someone trying to sell there used,old or outa business model. it's easier to 'upgrade' an existing dyno then fiddle with a custom unit. If this is just for tuning and consistent results why not use a PM mag flywheel and torque tube separating them, then with an optical sensor you can measure the deflection and calculate the torque from twist at speed. also the PM mag flywheel can feed a vari/resistor cap bank and you can get some useful 'generator' electricity out of it. HD PM mag are lethal but not overly expensive. It always come down to calculations though and a fair amount of them when going down the EM route.
Yeah but seems to me an eddy brake is the device used on some electric dynos. Agree about the heat generation using "any" 3 phase motor. You just use a tq arm to calculate power like any other dyno either way. Tell me more about this PM flywheel. I don't understand what you're describing. cheers
BTW what I pasted is all the links parsed togther by someone else. If you follow that link you can see the discussion evolve a bit. Bottom line is the eddy current brake is a device that is meant to be fed current and provide braking action for large vehicles and they specifically talk about the dangers of using just any 3 phase motor ... that's petty much off the table after reading about the power requirements of a proper eddy brake. And as I said they are the device that is used in an "eddy brake dyno". Any thoughts? cheers
sure, it can be a trip down 'crazy' lane but there are lots of PM (permament magnet) flywheel designs by the OU (overunity) guys. It's mostly amusing to read what lengths they go to, however they have spent an enormous amount of time simply re-inventing the wheel on mag motors. Lots to pick and sort thru but the basic concept here would be to use the PM flywheel to generate an electrical load and if for say you have an arrangement where the mag moves thru a coil field you can use the lorentz force to 'brake' the mag movement. there are a few types of coil windings that would work better for increasing the effect than whats in a motor as that is usually wound to reduce that effect as much as possible. the basics would be a flywheel with PM that pass thru a coil field, applied current to the field to induce a magnetic field to hold the PM's. the force needed is simply the current needed to generate a T# high enough to brake it or less to hold it. if you alternate the coil arrangement you can have one bank generating a current and the other receiving it, there will be losses but you'd only need to supply a small percentage of power to hit 100%. heat will always be an issue in current transformation. my only concern would be cost of materials as that's going to be a fair amount of copper! but would have a real turn of the century industrial look to it. thinking off the cuff here, if you feed the power back into the 'braking' coils via a varicap you can get fine adjustment of the LC tank circuit. I've got a copy of a grad textbook on HVDC power transmission laying around here somewhere that may have more info on 'outside' the box thinking with this. as with all HV make sure you don't over do it on the ozone, nasty side effects there. got overexposed a couple months ago on another project - not fun.
Brake retarder seems to be an Aussie term. If I was an Aussie there's no doubt I'd have one of these things in one of my randomly abandoned vehicles "in the yard" ... or they might be too new of a feature for that. Any big rig mechanics here? cheers
approach it from the stand point of using the engine as one part of the generator. and on the generator side will increase the reactive load to put a 'load' on the engine so it has to work to match the 'load' applied. if the engine is used to generate current thru a bank of variable coils then the load can be from 0 to ~
No that's the my technical description of one, eddy current is a lorentz force transformation. what's crazy is the improper use of a 3phase motor do that.
yep. So what about these brake retarders that are used on bigger vehicles? Is looking for one of those like looking for a cheap F1 pump for a 355 ? They might not be used that much? cheers
probably, but that systems also used in trains. might be some scrapyard for that stuff around your neck of the woods.
Been searching around. Found this brand new: PRECISION RACING (ESP) PDA- 250 DYNO, NEW. Anyone familiar with this brand? It's an eddy current dyno that uses the brake retarder thingy I was looking for. I expected I could find a surplus retarder for cheap from an automotive/truck application but it's not looking that way. $6000 brand new. It's a chassis dyno but making bits to use it as an engine dyno wouldn't be the end of the world and then I'll have both . The guy is a machinery dealer and not local and that was a number he threw out. If he was a closer I'd probably drive over with some cash and make him an offer. cheers
The other hill billy suggestion I saw was to use an entire automatic transmission. If I had zero electronic skills I think I'd give this a try. Just wanted to share that thought and here the major pit falls to it. I've personally tq braked cars for a very long time and these cars had no provision for cooling the tranny ... they made it back to the car lot just fine . cheers
Just had to be scraped off the ceiling ... $35-$40k for a water cooled eddy current brake capable of handling 300 hp ... that was for a used one the guy 'splained me . That one I listed above isn't water cooled. Anyone real world experience? cheers
