PWM Signal

[Sh1ine]

We are running a 6 CIM Drive for the first time this year. We want the security of running each speed controller to a separate PWM port on the DSC but we don't have 6 to spare. Can we create a 3 way splitter cable to attach to each speed controller, and on the other end wire two PWM connectors in Parallel and attach it to 2 PWM ports? This photo should help clarify. That way we save 2 PWM ports and we have some redundancy in the electronics.

Is this a good, or horrible idea?

[Dale]

Teams do that all the time. AndyMark even sells a Y cable for doing two at a time. I'm sure doing three Talons would be fine as well.

[Ether]

Originally Posted by Dale

Teams do that all the time. AndyMark even sells a Y cable for doing two at a time. I'm sure doing three Talons would be fine as well.

Did you notice that he is proposing to connect the two DSC outputs together?

see attached sketch

[Kevin Selavko]

Find it highly unlikely that only one port on your sidecar will fail and in a way that it would not interfere with the signal from a second. I also don't know how well the controllers would like having two signals sent to it all the time, Im guessing that the signals would not be exactly the same. Also I think it to be more likely for your pwm y cable to fail more than any port on the DSC, and adding to the number of pwms connected to each other will increase the probability of a connection coming loose.

[Dale]

I didn't catch that you were connecting multiple outputs of the DSC together. Just run the three Talons from a single DSC output and you'll be fine,.

[Ether]

Originally Posted by Dale

Just run the three Talons from a single DSC output and you'll be fine,.

I think you're probably right Dale. But this post by EricVanWyk from 4 years ago does seem to suggest that the number that can be supported is different for different models of controller.

Maybe Mike Copioli could weigh in here and let us know if he believes that 3 Talons will be OK being driven off one DSC PWM port.

[Dale]

It's feeding into an optoisolator in each Talon out of a 330 ohm resistor in the DSC. The PWM output can source or sink 15ma. Most optoisolators turn on around 1.6ma. We've driven three Talons before with no issue but Mike might have thoughts about whether it's likely to be on the hairy edge.

[Ether]

Originally Posted by Dale

It's feeding into an optoisolator in each Talon

Most likely so*. If there's a schematic, I haven't been able to find it.

out of a 330 ohm resistor in the DSC

Yes. There's a schematic for this.

The PWM output can source or sink 15ma.

With a dead short, yes.

Most optoisolators turn on around 1.6ma

The spec is available for the Jag, and it is guaranteed to turn on with 1.6 ma.. Since there's a 150ohm series resistance and a voltage drop across the LED, it requires about 1 volt to push that 1.6 ma through the LED.

So if you drive 3 Jaguars being driven by one DSC PWM port:

5 - 330*i - (150/3)*i - 0.7 = 0 . . . => .. i=11ma .. => .. 3.8ma per Jag

So it should work for 3 Jags... but I'm not sure about that 0.7 number; couldn't find a spec.

We've driven three Talons before with no issue but Mike might have thoughts about whether it's likely to be on the hairy edge.

If you're reading this Mike, any info you'd be willing to provide would be appreciated. Don't want to speculate.


* http://www.chiefdelphi.com/forums/showpost.php?p=1127215&postcount=3

[tStano]

With this fix, you're using 2 slots anyway, so why don't you just use a y-cable and a normal PWM for each side? As mentioned above, I can't see one port failing and not the other, although I'm sure its possible; just not likely enough really to worry about.

That is, If you don't just want to run the three PWMs off one port, which probably would work just fine, as discussed above.

[DonRotolo]

Originally Posted by tStano

That is, If you don't just want to run the three PWMs off one port, which probably would work just fine, as discussed above.

I agree.
IF YOU DO run 3 off a single port, PLEASE post your results here so everyone else will know whether this will work or not. Thanks!

[Sh1ine]

Currently we are running three off of one port. It is working fine, I hope that it continues to work fine. We will post an update later in the season.

Thanks all.

[Ether]

Originally Posted by Sh1ine

Currently we are running three off of one port. It is working fine, I hope that it continues to work fine.

My guess is that it will.

Does your team have access to an oscilloscope? If you want to be on the safe side, you can measure the voltage waveform (and magnitude) on the signal line in your PWM cable. It can give you some assurance that you've got adequate operating margin.

FWIW, I just found this note in the spec for the H11L1M optocoupler used in the Jaguar.

[dvanvoorst]

We've been running three Talons from one cable this season and haven't noticed anything unusual. It would be good to know if we're living on the edge, or are well within the normal operating capabilities.

[Ether]

Originally Posted by dvanvoorst

We've been running three Talons from one cable this season and haven't noticed anything unusual. It would be good to know if we're living on the edge, or are well within the normal operating capabilities.

The evidence is starting to mount that doing this should be OK, but yes you are wise to want to confirm that. I will trying sending a PM to Mike Copioli to alert him to this thread and see if he can help.