Tabletop Engine Dyno *Build In Progress*

[adrian_sm]

Man your dyno looks beautiful. Wish I had access to your machine shop. Then my dyno and resistive load bank wouldn't look so dodgy.

Where did you find the big light bulbs? How much? Those would have saved me wasting an evening sucking solder fumes paralleling 35w 12V halogen bulbs.

Can you easily adjust the load your alternator applies via the field coil voltage or something? The ability to easily adjust the load would be the highest thing on my wish list for upgrades to my dyno. Then I could easily keep the torque load constant while playing with speed, controller voltage, motor, etc. At the moment with a resistive or regen load the load is very dependent on the motor speed.

Here is a post I made that characterised my various load options at the time.

Keep up the good work.

- Adrian

 

[circuit]

For me, having CNC and CAD practice, This is probably the sexiest build I've seen here. Subscribed.

 

[salty9]

Yay! The engineer porn is back.

 

[Arlo1]

Dude you build beautiful stuff

 

[fechter]

Can you easily adjust the load your alternator applies via the field coil voltage or something? The ability to easily adjust the load would be the highest thing on my wish list for upgrades to my dyno.

Yes, with a car alternator you can control the load by changing the field coil current. They usually max out at around 2A (14v). It should be fairly easy to make a control loop for that. You could do a manual adjustment by using a bench power supply.

 

[liveforphysics]

That load was a great choice. Be careful you don't set the wall on fire though, I remember my first fog light setup I made with aircraft landing lights, and the melted bumper cover it resulted in. lol Amazingly bright bulbs though, they make insane flashlights when combined with a nano-tech pack and over-volted by like 2-3v so they draw like 800w and are just burning white hot. I don't like incan lights much, but these are kinda an exception to that rule. lol And make great load banks.

 

[acuteaero]

A typical alternator can easily do way more than 12v. Most have diodes rated for 50-60v, so don't exceed that unless you know the exact ratings. If you run a higher voltage into the load, you can get much more power out of it for a given amount of heating. Pumping the power back into the pack driving the motor is not such a bad idea (as long as you stay below 48v or so). Since there are always losses in the system, you could never overcharge the pack running. If you wanted to run over 48v, you could get a different set of diodes for the alternator.

That is a good way of thinking about it. I had assumed I would just run the resistive load only on this project, and there are some cases when you would want to do that... say to test an entire battery/controller system- but for most cases simply dumping back into the source battery through a diode bridge and modulating the torque by automatically controlling the field would work just fine. I actually broke the three phase leads out of the alternator and the landing lights are currently wired in Delta... it would be easy enough to connectorize an alternator diode pack or a higher voltage set of diodes to substitute for the light bulbs- plug and play.

Thanks!

Where did you find the big light bulbs? How much? Those would have saved me wasting an evening sucking solder fumes paralleling 35w 12V halogen bulbs.

I bought the landing lights *used* on e-bay, they were like $12 each. The backup plan was is the sack of 50 chinese halogen headlight bulbs, the H-7 style. Those have an isolated mounting flange and two male fastons on the bottom. I was thinking I would tack weld them to a steel bar and hook them up with crimp faston terminals. This allows them to be mounted to the same piece and put in series or parallel. There are also ones where the flange is used as one of the electrical connections, where welding the flanges to a bar would facilitate parallel connection.

Can you easily adjust the load your alternator applies via the field coil voltage or something?

As Mr Fetcher said- indeed- the current through the field coil determines the strength of the field electromagnet, which determines the back EMF/ kV, which with a fixed resistive load determines the amount of current that flows through the load, which determines the torque. This is the major advantage of using an alternator for this application- I have thought that if I wanted to build a much bigger dyno I would use a golf-cart sized sep-ex motor for the same reason. 24v/300a alternators also exist for busses... I have a 15vdc SMPS and some very simple mosfet H-bridges sitting around that I was planning to piece together to achieve field control through the data acquisition system. Not because you need 15v (Like Fetcher said, it probably saturates a hair lower) or a H-bridge...

Thanks for the comments, guys! Check back in in a few more months, see if I've made any progress :wink: I'm enrolled in plenty of classes this upcoming semester... Got a couple other projects cooking too :wink:

 

[acuteaero]

That load was a great choice. Be careful you don't set the wall on fire though,.

I rather don't mind the idea of leaving some big scorch marks on the cube wall That way my coworkers can remember me after I leave to go back to university... On the plus side setting the wall on fire means everything else is working really well, right?

 

[liveforphysics]

That load was a great choice. Be careful you don't set the wall on fire though,.

I rather don't mind the idea of leaving some big scorch marks on the cube wall That way my coworkers can remember me after I leave to go back to university... On the plus side setting the wall on fire means everything else is working really well, right?

I stand corrected.

 

[pavlik1]

Hello acuteaero

Very nice mechanical design. I am curious to know:
- how much it the breaking torque your generator/brake can apply to the motor?
- type and rating of the generator?
- the generator rectifier is in use?
- direct short circuit or load?

I am using mine by shortening 3 phases , without diodes, controlling the braking force with the field winding.
So far I am not able to measure the torque.

cheers