Q&A Forum
Having issues with getting a clean rpm signal. This is on a water brake engine dyno. The engine I am trying to test is a GM 350 with an HEI distributor.
I bought this opto coupler: https://www.amazon.com/gp/product/B07YJL3MQQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Then wired it like outlined in the wiki page across the positive and negative coil wires.
When I go to run a test from 2500rpm to 4000rpm it starts the test, begins to load the engine then says done well before getting to 4k rpm. When I take a video of the screen you can see some spikes in rpm which goes over 4k and that's why it's ending the test.
My question is why? Is there a different opto coupler I need to use?
Thanks in advance. This is the last thing I need to figure out in order to make some actual power runs!!!
Hi, you need a trigger wheel and a proper RPM sensor. See https://yourdyno.com/YourDynoHelp/brake-rpm-sensors/
Since you run an engine dyno and probably have turned off the "Compensate for inertia effects during acceleration"-option you can strictly get a way with not running a trigger wheel and only have 1 pulse per revolution. But chances are the signal from the coil is noisy either directly or through induced currents in the wires from the ignition. You probably need to take a look in with an oscilloscope to be sure what is going on there. Do you have a shielded cable?
I really recommend running an RPM sensor and a trigger wheel.
To check the raw data you can do a run then open the raw log file in excel like this: Data->Get external data from->From Text->(open the .log file)->Delimited->":" in Other->Finish. Then plot column C (which is the inverse of RPM times some factor). It shall be smooth.
@admin it is not a shielded cable. But if this is not going to work I'm not going to keep working on this option.
In my setup the problem with a trigger wheel is getting enough pulses. The drive on the back of the dyno is very small and then to do 20 to 30 pulses I need a good size wheel, which the drive won't support. I've already been down that path and it didn't work.
@james-meyers for an engine dyno you don't need as many pulses as a roller based dyno. For example 6 pulses gives 200 samples per second at 2000RPM.
@admin would 4 pulses per rev be suitable? I think I can make that work as I had that same thing on my previous dyno and it seemed to give smooth results with the speed sensor I used.
Thanks again for the help, I really just want to start making some power, lol!!
Yes, go for that!
@admin Did a little machining last night and got my sensor and tone wheel mounted. This is the exact setup I used on my previous homemade waterbrake.
As of now I still have the erratic signal, it's a little better but not great. The only thing is I didn't have any shielded cable to connect this with so I'm wondering if that is part of my issue right now???
Thanks
@james-meyers, yes cable must be shielded. Also make sure the trigger wheel is very accurately made, because the time between each pulse is measured. If you do a run and send me the raw log file I can take a look at the signal.
@admin I just ordered a speed sensor from you so will wait for that and see what happens. Trying to update the firmware and software while I wait and struggling with getting it to find the driver file that I downloaded. Unfortunately I don't have WiFi in the shop area to do this online.
Each time I go to look for the file it says no driver file is found. But I can see the file in the folder. Any suggestions?
@james-meyers, I will ship the RPM sensor ASAP.
As for the driver, do you mean the USB driver (if you use Windows 7)? If you are able to connect via your phone or something then software is a snap!
@admin Yes the USB Driver using Windows 7 is what I am trying to do. However, it went through the first part of updating the driver and now shows that the YourDyno box is not connected at all times and won't find the new driver that I have downloaded.
I went and got my hotspot from work and tried to update the firmware online but again with no USB driver installed it won't connect to the YourDyno box. Below is what the status shows when trying to update the firmware online and also the message I get when trying to update the USB Driver.
Any help would be appreciated. Seems that I currently have an $800 paper weight to stare at. Thanks
OK, yes for Win7 you need a driver. Here are the instructions:
USB Driver:
Windows 10 installs the driver automatically. For Windows 7 and Windows 8 you need to manually install the driver.
To install the driver for Windows 7 and 8: Plug the YourDyno box into the computer, Open Device Manager, find “Ports (COM & LPT)”. You should see an entry there called USB Serial port or Cypress USBSer or similar. Right-click and choose “Update driver software”. Choose the .inf file you download here: Download driver.
The driver you download is a .zip file that you need to unzip to a location (it will be an .inf file), then choose it when updating as explained above.
If you are still struggling I can log in remotely and get it going.
@admin That is the process I was following. It doesn't let me manually choose the file, only the folder that it is in. But it still says that it cant find the file in the folder.
Let me know if there is anything else that I should try. Or let me know when you could remote in. Thanks again
Pretty much does the exact same thing. The log is attached. These two runs were supposed to go to 4k rpm.