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Author Topic: Tachometer tech question  (Read 1172 times)
txjeff
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« on: October 08, 2010, 11:56:23 AM »

I installed a electronic tachometer in the bus. I connected the control wire from the tach to the alternator. When I started the engine the tach bounced around until I turned the clearance lights on, then it smooths out like it should. Has anyone else had anything like this with a tach? If so how did you remedy it?

jeff
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73 MC-7combo
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Tim Strommen
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« Reply #1 on: October 08, 2010, 12:11:22 PM »

The Alternator may not have enough load on it to display a stable voltage (which get filtered out by turning on the clearance lights).

Where does the tach get its signal - direct from the alternator?

-T
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luvrbus
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« Reply #2 on: October 08, 2010, 12:21:21 PM »

The tach hooks to the R terminal if you don't have the R terminal it hooks to the number 2 terminal

good luck
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txjeff
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« Reply #3 on: October 08, 2010, 12:51:39 PM »

I have it hooked to the R terminal from the alternator. I just found it odd that without the lights on it didnt work correctly.

jeff
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73 MC-7combo
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« Reply #4 on: October 08, 2010, 12:56:28 PM »

The R terminal is a relay terminal you probably have a relay that is not engaging till under a load 


good luck
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txjeff
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« Reply #5 on: October 08, 2010, 01:09:16 PM »

Would there be a better connection point other than the R terminal?

jeff
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73 MC-7combo
Brenham, Texas
luvrbus
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« Reply #6 on: October 08, 2010, 02:30:35 PM »

Jeff, 2 other ways to do it 

1 A sender generator off the tach drive

2 A transducer/magentic pickup screws into the bellhousing   
only other ways I know of


good luck
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eddiepotts
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« Reply #7 on: October 08, 2010, 03:36:58 PM »

Just throwing this out there but what about hooking some lights off the ignition switch that would turn on in the generator bay when the bus is running? Just to simulate the Clarence lights. Maybe some cheap red ones that would make it look like it's glowing red hot through the grill. It may be cheaper then buying something else but it may cause problems. It just sounds cool to me.
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Sean
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« Reply #8 on: October 08, 2010, 06:55:24 PM »

Your problem is very simple.

The R or Relay terminal on the alternator produces an output only when the alternator field is energized.  The field, in turn, is energized and de-energized by the regulator, based on need.  If the batteries need charging or there is a load of any kind, such as the clearance lights, then the field will essentially be energized all the time, and your tach will work fine.

If, however, the batteries are fully charged and there is no other load on the system, the regulator will be rapidly switching the field on and off.  It will probably not be "off" long enough at any time for the "Not Gen" or "Charge" light to come on, but it will wreak havoc on the tach reading.

The cure is simple:  Drive with your lights on.  I recommend this practice for safety anyway.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com
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luvrbus
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« Reply #9 on: October 08, 2010, 07:56:42 PM »

Yep a pulse  generator off a tach drive is the way to go they work all the time


good luck
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