Tach and W terminal questions - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• Tach and W terminal questions by BellCityDubber on 03 Jun, 2006 16:28
• well as some of you may noticed my v-belt/alt thread....
  
  I swapped the alternator and now I have no tach.... the W terminal is there and all, and I'm charging.. but no tach...
  
  does anyone happen to have an explainaiton for what's going on with my tach/W terminal?
  
  TIA
• #1 by akrallysport on 04 Jun, 2006 10:48
• Interested as well... I've been breaking alt-to-starter cables, the last time involved rewiring the voltage regulator plug... now I have no tach, batt light is on and oil light flashing.
• #2 by BellCityDubber on 04 Jun, 2006 11:16
• well, mine's not that bad, my charge light works, my oil light works... just my tach doesn't work anymore...
  
  I've used a multimeter on the battery.. it's 12v when off, and 14 when on, so it's charging...  but I just dont have a tach signal....
  
  I think this alternator I picked up is from an earlier car.... anyone have any ideas?
• #3 by tylernt on 04 Jun, 2006 17:12
• I wonder if this alt came from the factory on a car that did not have an upshift light or tach or dynamic oil pressure buzzer and the terminal is simply not hooked up to anything inside the alt. If you talke to TurboniumHillfolk on VWVortex, I think he has rebuilt these things so might have an answer for you.
• #4 by BellCityDubber on 04 Jun, 2006 18:24
• Quote from: tylernt

  I wonder if this alt came from the factory on a car that did not have an upshift light or tach or dynamic oil pressure buzzer and the terminal is simply not hooked up to anything inside the alt. If you talke to TurboniumHillfolk on VWVortex, I think he has rebuilt these things so might have an answer for you.

  
  
  Hmm, possibly... I wouldnt be surprised, that makes a lot of sence now that you mention that.
  
  I run into the hillfolk on the tex a few times... Very knowledgeable dude.
• #5 by akrallysport on 04 Jun, 2006 20:24
• OK, did a bit of troubleshooting today... I had to do emergency repairs on my return Toronto to Montreal last week. I guess I found out that reversing the D+ and W will kill the tach, trigger the oil pressure and batt lights. :oops: Now knowing this, I'd say in your case something isn't hooked up right, as it's not setting off the lights. When one of the voltage reg wires was letting go, my tach would flicker...
• #6 by BellCityDubber on 04 Jun, 2006 23:43
• well the alternator that was on there was replaced...  the old one worked perfect until it started to die....
  
  the new one just doesnt work with the tach... everything else works great.
  
  but as far as reversing the D and W terminals.. that couldnt have happened because I have the original VAG white plastic cover on the W terminal and that went to the W terminal on the new alternator... <it>....
  
  I'm putting money on it being from a car that didnt have a tach/upshift light...
• #7 by akrallysport on 05 Jun, 2006 07:24
• I understand that in your case you couldn't have reversed the wires... I guess I should've been more clear. I was just using my 'reversing' situation to narrow down the possibilities to the wires or the pickup (or lack thereof) in the alt.
• #8 by regcheeseman on 05 Jun, 2006 07:40
• Have you actually put the wire on the w terminal ? It not unheard of for the w terminal to bend out ogf the way of the housing.
  
  If the terminal is there, it will be hooked up. If it isn't connected or the connection is broken then repair it.
  
  Could be that a winding is down on your alt, the winding thatalso feeds the W terminal.
  
  You would still measure 14 volts with this fault existing.
  
  Can you hyrid the two alts?
• #9 by BellCityDubber on 05 Jun, 2006 10:52
• regcheeseman
  
  yes, I've installed the alternator properly with the W wire on the W terminal.... (it's not THAT hard, playing rubicks cube proves more difficult.... damn those stupid coloured squares)
  
  anywho, I believe your explaination to be quite valid as well....
  
  I took my original alternator into the starter/alternator shop to be repaired. they said it would be ready midweek.
  
  as for making a hybrid alternator.. I'd like to keep the original as original as I can and maybe muck around with the temp replacement I picked up at the junkyard
  
  maybe I'll talk to the starter/alternator shop guys and get the temp replacement one wound up to 90 amps like the original one, and see if they can fix the W terminal or something.
  
  
  Thanks for the advice, I really appriciate it..
• #10 by Mark(The Miser)UK on 05 Jun, 2006 14:45
• If you can get hold of a oscilliscope you can check the output...
   IIRC a very spikey 20V or so hence kills attempts to stick on a gasser tach 99 times out of 100  :shock:
• #11 by regcheeseman on 06 Jun, 2006 04:46
• Quote

  as for making a hybrid alternator.. I'd like to keep the original as original as I can and maybe muck around with the temp replacement I picked up at the junkyard
  
  maybe I'll talk to the starter/alternator shop guys and get the temp replacement one wound up to 90 amps like the original one, and see if they can fix the W terminal or something.

  
  
  A 'hybrid' would be as original as the original one but not broken.  :wink:
  
  Take the 90A  w term assy,rotor and windings from the 90A alt add a blend of the temp replacements doide pack, brushes and voltage reg and fit into the original case.
  
  When I said hybrid maybe it was misleading... basically I meant repair the original alt using bits from the new alt.
  
  Repairing alts is no black art, they are as lego-like as the rest of the car.  :lol:
• #12 by BellCityDubber on 06 Jun, 2006 08:56
• already sent it out for repair at the local starter/alternator shop...
  
  maybe I'll send the temp one there so they could figure out how to get the W Terminal working
• #13 by hillfolk'r on 06 Jun, 2006 16:24
• a good fluke meter that reads hz is all thats needed for checking the tach w lead,actually the tach lead is ac power before it is rectified by the diodes,so you can check for ac or hz
  the lead could be broken in the case,,not letting the ac power to the w lead to give the tach its signal
  i would say that if the w lead was still good,but you didnt have any  ac on that lead,then you wouldnt be sending ac to one of the 3 diodes,and charging would be reduced,red light would/should be dim
  i bet something is funny with that w lead,like its not reallya w lead
  wheni first got my tach i called 2 alternator shops,asking how do i get a w lead to run my tach,they said" w lead? an  alternator putting out ac? never heard of that"
  i got a fax from vdo that told me how to mod a stock alternator..
  alternators ,well ours are "3 phase", so lose a phase,especially the one with the w lead,well it wont work fer crap ....
  
  ......those guys in most of those places  just fix stuff,they dont know the theory behind how it works(except for a few old timers,that save these guys butts when they are scratching their heads)
  that was before i went to tech school,and learned all about it
  i never tried it,but put your meter on ohms,it should read some kinda resistance on the w lead  to the main charge lead lugs ,,its reading thru a diode though,,i may have to "test"my good one for ya.....
• #14 by BellCityDubber on 06 Jun, 2006 17:41
• .... thanks dude.. that clears up a lot....
  
  it's as clear as...
  erm
  good coffee at the moment