Intermittent Tachometers

[GordMay]

See the:
VDO Gauge Installation and Troubleshooting Guides:
VDO Installation and Troubleshooting Guides - egauges.com

Specifically:
Electronic Tachometer with LCD Engine Hour Meter (0-515-012-037)
http://www.egauges.com/pdf/vdo/0-515-012-037.pdf

[S/V Antares]

Greg, No PHD but I did stay in a holiday inn last night.. just kidding. I worked for VDO for amost 20 years. "Retireing" in 2001 when Seimens bought them and t moved the US Marine biz to Allentown PA. (No water, no way). Unfortunatly I have forgotten a lot due in part to the cruising lifestyle!

If you have any issues downloadng Gords link (I did) I have a lot of tech stuff on a disc somewhere and will dig it up.

[GordMay]

Originally Posted by S/V Antares

... If you have any issues downloadng Gords link (I did) I have a lot of tech stuff on a disc somewhere and will dig it up.

The link [... egauges.com/pdf/vdo/0-515-012-037.pdf ] works for me, but I could print & Fax the Instructions (4 pages). Send me a PM /w a Fax number.

[svcattales]

Originally Posted by S/V Antares

Greg, No PHD but I did stay in a holiday inn last night.. just kidding. I worked for VDO for amost 20 years. "Retireing" in 2001 when Seimens bought them and t moved the US Marine biz to Allentown PA. (No water, no way). Unfortunatly I have forgotten a lot due in part to the cruising lifestyle!

If you have any issues downloadng Gords link (I did) I have a lot of tech stuff on a disc somewhere and will dig it up.

Will, I suspected you were a Holiday Inn guy based on your high level of expertise. The 20 yrs with VDO probably helped a little.

I downloaded & printed Gord's link OK. The wiring on my tach is different since I have only 4 wires going into the back rather than 8. I'm still trying to wrap my brain around calibrating the tachs. I apparently need to know the number of pulses per revolution coming out of my alternator. I'm going to mess with it tmw so I let you know what happens.

Gord, thanks for the link. That helps a great deal.

[GordMay]

See the Typical Wiring Diagram for 4-Wire Gauges at:

http://www.cruisersforum.com/gallery...p?i=4829&c=500

Not shown, the TACHOMETER “Sender” wire will be the Grey wire from the Alternator AC Tap to "S" on Tach'.
(or from the Hall-Effect Magnetic Pick-Up on Flywheel)

[svcattales]

Hey Will,

I did some testing on the bad tach and the good one using your advice and Gord's testing download.

On the bad tach, I pushed in the switch and turned on ignition switch and nothing appeared in lcd window. The tach needle did "twitch" once or twice when ignition switch was turned on. I also tried holding the switch in while I turned on ignition and started engine. Still nothing in the window and needle didn't move. Is there anything to be gained by opening it up? (Even a blind squirrel finds an acorn once in awhile.) I'm afraid it might be a dead duck.

On the good tach, I did the same tests. When I turned on ignition, the LCD window scrolled through parts of characters, but nothing I could decipher. I think the LCD display is hosed, although something was causing the display to scroll. I stopped this testing right away, because I was afraid to get into a gas engine calibration mode and never know which mode I was in. From what I read in the testing guide, the display must work in order to do the testing/calibration. After I stopped testing, I started the engine and needle moved to show RPMs so hopefully the tach is still working correctly in the "pulse" mode. I attached a couple pics of the tachs for you. Maybe you could take the pics to the Holiday Inn, hold them to your temple, and diagnose the problem!

[S/V Antares]

Greg, Give me the Diameter of the back of the Tach, (Hole size) It looks like the 75 mm units we made for Volvo. If so I have a few I would part with. cheap to a fellow cruiser. I am leaving for southern Lats next week so let me know

Will

[S/V Antares]

FYI The tachs shown in the Pix are not the same as the units Gord posted a link to. Some were set up for specific pulses and are not programable.

You may try Volvo in Chesapeake VA, or Sweden with the part number. . I will try some old contacts in Ruti Switzerland where they were built. PM me if interested in the scratch and dents I have. I will check them out tomorrow and see if they are the adjustable ones. ( Dif part number from yours)

[svcattales]

Originally Posted by S/V Antares

FYI The tachs shown in the Pix are not the same as the units Gord posted a link to. Some were set up for specific pulses and are not programable.

You may try Volvo in Chesapeake VA, or Sweden with the part number. . I will try some old contacts in Ruti Switzerland where they were built. PM me if interested in the scratch and dents I have. I will check them out tomorrow and see if they are the adjustable ones. ( Dif part number from yours)

Will,

Thanks again for all your help. The cutout size and the diameter of the black screw-on bezel is 87MM so it might be an odd ball version (Volvo part # 873992). I have found a few sources on-line with prices from $220 to $250. If you have "scratch & dents" that are compatible, I'm definitely interested. I'll send you a PM.

[svcattales]

Many thanks to Will on Antares for hooking me up with two working tachs/hour meters on Cat Tales.

I calibrated them to my engine idle speed of 800 RPM, but that maybe off a little. I would like to calibrate them closer to my cruise RPM @2200. Gord had an interesting post back in '05 about using a flourescent light to do calibration.

Here is a copy of that post:
"There is a way to check the accuracy of a tachometer using the highly accurate and stable frequency of AC power supplied from any source of commercial shore power. The concept is to use the AC line frequency as the measuring standard. The only tools needed for this calibration check are a piece of tape and a fluorescent lamp which operates from commercial AC line power.

A fluorescent lamp is actually a gas-discharge lamp with the interior of the glass envelope coated with a light-emitting phosphor. When the gas within the lamp is ionized by alternating current it emits pulses of energy. One pulse occurs for each of the voltage excursions of the AC waveform. For the 60-Hz power common in North America, there will be 120 such flashes per second, 60 positive and 60 negative. The pulses of energy created within the lamp excite the phosphor coating, which in turn emits visible light. Because the energy driving the lamp is not continuous, the light emitted is not continuous. The fluorescent lamp emits 120 pulses of light per second, but the human eye's persistence of vision makes us think the light is always on. We can use the pulsing light output of the fluorescent light as a very accurate measuring tool with which to check the calibration of the engine tachometer.


First, obtain access to the front of the engine. Place one piece of white tape on the face of the large pulley mounted on the engine's crankshaft (usually this is the largest pulley in sight). Illuminate the front of the engine with light from the fluorescent lamp. Run the engine at 1,800 rpm, as shown on the tachometer. If the tachometer is accurate, four stationery, or very slowly moving, white marks will appear on the face of the pulley where the tape was placed. If the tachometer is inaccurate, the tape marks may be rotating in either direction. Adjust the throttle until the four tape marks appear to stand still. Note the tachometer reading. If the difference between the reading and 1,800 rpm is at all significant, look for a small adjustment screw on the back or within the body of the tachometer. Turning this screw slightly should make the indicator needle move to exactly 1,800 rpm. If the speed range of the engine permits, increase the engine speed to 3,600 rpm. At this speed, only two tape marks should be visible on the crankshaft pulley. Repeat the check of the tachometer reading and, if necessary, readjust the tach. The basis of this stroboscopic speed calibration is quite simple. At 1,800 rpm, the engine is turning at 30 revolutions per second. The lamp is flashing at 120 flashes per second, or four flashes per engine revolution. Therefore, if the engine is turning at exactly 30 revolutions per second the tape mark will appear four times, with each apparent tape position 1/120 of a second or 1/4 revolution apart. When the engine runs at 3,600 rpm there will be only two light flashes per engine revolution. If the boat is in a country where the standard AC power frequency is 50 Hz, the check speeds would have to be 1,500 and 3,000 rpm since the light would flash 100 times per second."

Has anyone had success doing this "Mr Wizard" experiment? I tried it and didn't see the tapes stand still. All I saw was a white blur regardless of the engine speed. I used a cold flourescent (pig's tale) bulb for my light. Would using a flourescent tube make a difference?

[GordMay]

Originally Posted by svcattales

...I used a cold flourescent (pig's tale) bulb for my light. Would using a flourescent tube make a difference?

Yes, a fluorescent lamp with a Magnetic ballast will work.

The Stroboscopic Effect (Flicker) is an artifact of the frequency at which the lamp is driven, and will only be present with old fashioned Magnetic Ballasts. These older magnetic ballasts operate on 60 cycles per second (60 Hz), and the lamps actually flicker on and off 120 times per second.

The new Electronic Ballasts, and Cold Cathode Fluorescent Lamp (CCFL) Drivers operate at much higher (than 50/60 Hz) frequencies.

For more information on Stroboscopic Speed Calibration see “Speed Calibration” at:
Spindle and Surface Speed Measurement

[svcattales]

Originally Posted by GordMay

Yes, a fluorescent lamp with a Magnetic ballast will work.

The Stroboscopic Effect (Flicker) is an artifact of the frequency at which the lamp is driven, and will only be present with old fashioned Magnetic Ballasts. These older magnetic ballasts operate on 60 cycles per second (60 Hz), and the lamps actually flicker on and off 120 times per second.

The new Electronic Ballasts, and Cold Cathode Fluorescent Lamp (CCFL) Drivers operate at much higher (than 50/60 Hz) frequencies.

For more information on Stroboscopic Speed Calibration see “Speed Calibration” at:
Spindle and Surface Speed Measurement

Thanks again Gord. I'll have to figure out how to get that six foot shop light from my garage into the bilge..ha..ha. I'll have to do some shopping to find an old style tube light that is small and portable.

[svcattales]

My tachs were working well thanks to Will on Antares until I took my first cruise. After many hours of motoring one tach quit and then the other. I checked the alternator A/C output and it was zero. Once again my voltage regulators were sabotaging my tachometers like white blood cells on an infection.

After months of more frustration, I asked for help on the Cruiseheimers SSB Tech Net. One of the cruisers asked if I had solar panels which I did. He suggested I shut them off and see what happens. I installed on/off swithces for each panel. Yesterday, I went daysailing with fully charged batts. Sure enough the stbd tach quit after an hour of motoring. I shut off all the solar panels and the tach started working again right away. Apparently the solar panels were handling all the electrical loads which made the voltage regs shut down the alternators. When I shut off the panels, the loads from radio, autopilot, stereo etc. caused the voltage regs to re-energize the alternators and the tachs came back. Hopefully, this is the last step in solving this problem. YEAH!

[Jeannius]

I know it's been a long time since this thread was last updated but, I have a problem with Volvo tachs and am appalled by the replacement cost.

Does anyone know the VDO part number that equates to Volvo part 873992?

[svcattales]

Originally Posted by Jeannius

I know it's been a long time since this thread was last updated but, I have a problem with Volvo tachs and am appalled by the replacement cost.

Does anyone know the VDO part number that equates to Volvo part 873992?

I replaced both tachs with used ones, but I'm still not happy with them being driven by alternators. Even when I turn off wind & solar panels, I still have intermittent tachs when batteries are fully charged and external voltage regulators turn off alternators. Also, the hour meter died on one of the new tachs and both of the old ones. If I replace them again, I would look at a non-Volvo/VDO tach that senses RPM off flywheel or crankshaft. I would guess that you can adapt an "after market" tach that will work better and be a lot cheaper. I replaced one of the hour meters with a simple counter and that was less than 10 bucks on Ebay and it fit nicely on the engine panel. Good luck.