P-Mag and VM1000
 

Ok guys, I have done a lot of research (including search function) and have talked to several people offline. A lot of great advice and I appreciate it.

I am very close to pulling the trigger on upgrading to dual P-Mags and my only concern is the tach signal from the P-Mag communicating with my VM1000 (NOT the 'C' model).

P-Mag: I know the P-Mag has the ability to send out tach signal in 12v and 5v (with supplied jumper) and can be programmed via EICAD to push 1 or 2 pulses per revolution.

VM1000: Accepts 5v tach signal. Some DPU versions have a jumper (JP2) inside the DPU that cuts tach output in half (presumably for 2 pulse per revolution systems).


So here is my question:
1) Has anyone made the P-Mag tach signal successfully communicate with VM1000? (If so, what was involved)
2) The jumper inside the DPU, is it necessary to change the tach output in the DPU if I can reduce the P-Mag tach signal from 2 pulses to 1 pulse per revolution?

Just looking for some clarification before I pull the trigger!

Thanks

Dan

Dan,

Have you talked to the techs at PMag about this? I believe they have already worked out the details for interface with the VM1000's, I thought it had been posted here on VAF but could not find it when I ran a search.

The function of the RPM selection jumper also depends on the engine you are using, for example on a Lyc 6 cylinder with mags, the VM1000 looks for 3 pulses per 2 RPM vs. 1 pulse per 1 RPM on Lyc 4 cylinder mags.

Reggie

Short answer: Yes
 

Hey Reggie,
Yes I have talked to Brad on several occasions regarding the VM1000 issue. They do not have a resolution that they "endorse", but rather put me in contact with a few individuals who have successfully installed the P-Mag with VM hardware. Here is the kicker, most have the VM800 series, and none of them have completely integrated the two, but rather found solutions that "they could live with"

I am hoping to find someone here who has or who knows someone who has successfully integrated the two.

Dan

Well, I don't have PMags and I'm not real familiar with them. But, I'm pretty familiar with the EPI-800 and VM1000 architecture.

The VMS tach input looks for a 5V square wave with a pulse count/frequency proportional to the engine RPM, this typically comes from a hall effect sensor in the magneto vent port. Most DPUs are setup for magneto type ignition which usually (but not always depending on type of mag & ignition setup) means 2 pulses for 3 RPM on 6 cylinder engines and 1 pulse per RPM on 4 cylinder engines.

The VM1000 manual (2001 version) discusses integration with an EI very succintly saying "If you are connecting to an Electronic Ignition that does not use magnetos, the RPM transducer is not installed. Instead, connect the manufacturers ?tach signal output? in place of the RPM transducers White signal wire. No ground connection should be needed between the ignition and RPM cable, if the electronic ignition is very well grounded. In case you did not originally order the instrument system for electronic ignition, contact the factory if, as the configuration may need to be changed. Note that we cannot guarantee compatibility with electronic ignition systems as they are designed and revised without our control." Earlier versions of the manual (1995) also state "If you are connecting to an Electronic lgnition, only connect the manufacturers 'tach signal output' to J4 -12 and install blocking diode (such as 1N914) in series with cathode (bar) going to ignition side."

Another option is to use the mechanical tachometer drive off your engine's accessory case to a rotary style RPM transducer bypassing the PMags all together. This was the configuration of the original 1st generation EPI-800 systems of the late 1980's vintage but was later dropped in favor of the hall effect sensor.

Reggie

Ok Great info!

Now the P-Mag install manual says
So I am wondering if the issue has been resolved with the development of the new series P-Mag (114)?

If the VMS looks for 5v signal and I can convert P-Mag signal from 12v to 5v by installing the supplied diode from pin 1 to 6 on the P-Mag. And using EICAD, change pulse signal from 2ppr to 1ppr that the VMS is expecting. Is there any reason this won't work?

Am I missing something else? Surely someone has installed a series 114 P-Mag and VM1000.

Dan

Your theory is sound, seems like it should work just fine.

Dan,

I have the exact same situation... have you ordered your P-Mags?
Looking for a trail blazer...

Good timing!
 

Ernie,
They arrived this afternoon as I was waiting on the front porch like a kid waiting for Santa. :D

I can't install them until Monday as I am flying to the Chino airshow this weekend! I will update with my success or troubles after the install.

Dan

Dan,

Definitely interested in your results, like you said there's probably a number of people either in your situation or will soon be as more folks convert from Slick/Bendix mags to P-Mags plus it will just be good info for me to have in doing the VMS repairs & installation help.

Reggie

Success!
 

Reggie/Earnie,
First let me apologize for not updating sooner. The dual P-Mag installation took longer than I was expecting. Not due to the P-Mags at all, but rather my OCD wouldn't let me install the new mags without fixing some other gripes that came up when the old system came out. I will post my experience with P-Mags and the installation in a more appropriate thread.

As for the P-Mag (114 series) to VM1000 (Older version, non-"C" model) tachometer question:

1) I used EICAD and changed the tach signal on the left P-Mag from 2 PPR (default) to 1 PPR
2) Installed the provided diode from input 1 (GND) to input 6 (Tach) on the P-Mag connector
3) Ran an 18 gauge unshielded wire from input 6 (Tach) on the left P-Mag to the DPU J4-12.

The RPM works GREAT!

If you have any questions, give me a shout!

Hope this helps!

Dan