Alternator mod for rev counter signal?

[steve_d]

I have seen, but can't now find, a wiring diagram and description of how to wire an alternator to give a rev counter output.

The rev counter on my RRC uses this but apparently any alternator can be modified if you know how.

Can anyone help?

I have searched here and tech archive to no avail but now fully expect to be bombarded with clickies to threads in both the above.

Thanks in advance

Steve

[LandyManLuke]

you need to tap off one of the three windings, before the diode pack.

[discojmz]

so that takes into account one revolution of the alternator correct? so im guessing the rev counter works off say 4 pulses per rpm or whatever?

so by the same reckoning fitting an alternator with wrong sized pulley would cause incorrect rev counter reading?

jim

[LandyManLuke]

A diesel rev counter will normally have a set of switches and a tuning pot to set up the correct reading, as apposed to a petrol (coil) driven rev counter where you just set the number of sparkplugs/cylinders/ignition events

[western]

but now fully expect to be bombarded with clickies to threads in both the above.

These threads will help you fit a rev counter ------------

http://forums.lr4x4.com/index.php?showtopic=3026&hl=

http://forums.lr4x4.com/index.php?showtopic=7152&hl=

http://forums.lr4x4.com/index.php?showtopic=9408&hl=

[steve_d]

Thanks very much guys.

Will pass the info on.

Steve

[JimAttrill]

so that takes into account one revolution of the alternator correct? so im guessing the rev counter works off say 4 pulses per rpm or whatever?

so by the same reckoning fitting an alternator with wrong sized pulley would cause incorrect rev counter reading?

jim

My 300tdi Defender came as standard with a rev counter that underread badly, for example I hit the governor at an indicated 3400 rpm. It is a VDO, but unlike later ones it is not adjustable in any way. My alternator had the early big pulley, the one that needs the longer ERR3287 (I think) fan belt. Later Tdis use ERR5911 which is shorter as the pulley is smaller. I fitted the smaller pulley, found one somewhere, and the rev counter is now correct.

How do I know? - this is what you do.

1) use tipp-ex or paint to mark the crank pulley on the Tdi

2) get a petrol car with an accurate rev counter and couple up a timing light.

3) Get someone to hold the car at, say, 1000 rpm

4) point the timing light at the Tdi pulley, and operate the throttle until the light is stationary

5) Check the reading of the Tdi rev-counter.

Unfortunately this needs three people

Oh, and the alternator will go around a bit quicker, which should help the charging.

[LandyManLuke]

I've set mine by trial and error, using max RPM and tick-over, i really should do it properly one day.

[simonb]

so that takes into account one revolution of the alternator correct? so im guessing the rev counter works off say 4 pulses per rpm or whatever?

so by the same reckoning fitting an alternator with wrong sized pulley would cause incorrect rev counter reading?

jim

Nope faster engine goes, faster the ac frequency of the alternator. Tacho meaures the ac frequency. Its all relative for pulley sizes. You set the tacho to give the right rpm at idle - it will then be correct across all speed ranges - ac frequency increase is linear with engine speed.

[Carloz]

What about this: I changed my RRC 2.4 VM Diesel to a carburated 3,5 V8 some time ago.

I thought I could get away by just connecting the wire from the diesel alternator to the petrol ignition coil... but it does just nothing..

Anybody a idea how to get the original diesel rev counter working on the V8? :-)

 

[Bowie69]

If there is a W terminal on the alternator then just connect it there, and job done

[Carloz]

6 hours ago, Bowie69 said:

If there is a W terminal on the alternator then just connect it there, and job done

Well... the Diesel engine (and alternator) is gone.. There is now a petrol V8 instead.. It has to be triggered from te ignition coil now.. and that causes the rev counter doesn't work...

[Bowie69]

Yeah I understand that, but some 'petrol' alternators have the W terminal as well.... My 1991 RRC V8 included...

It doesn't have to be from the ignition coil just because it is a petrol, nor is there any real difference between petrol and diesel alternators

[Carloz]

Ah, in that way.. Thanks! :-)

I am going to check if my ancient alternator has a W-terminal..

Although I prefer a signal from the ignition because it is more accurate (does not depend on the pully ratio, slip etc.). But I understand now that a Diesel rev counter needs an other signal than a petrol rev counter.. So let's see if I can get it running at least in the "diesel-way".

Edited September 17, 2017 by Carloz

[Bowie69]

Yep good plan

If you look at the back of the tachometer, there may be an adjustment screw, or even in some cases a set of dipswitches to change how they work... VDO gauges work this way and can run from a coil or alternator, no idea on the standard RRC one... So try the W way first

Btw, W = winding, it's the pre-rectified AC signal from the alternator

[HoSS]

If it was me rather than mod the alternator, i would just fit a magnetic pickup on the crank pulley. Or possibly take a feed from the CPS or starter ring gear.

That way you know you have true RPM and its probably easier.
e.g.
This one would need a little circuit to convert NPN trasistor output to 12v pulses. http://www.ebay.co.uk/itm/Hall-Effect-Sensor-Proximity-Switch-NPN-3-wires-Normally-Open-With-Magnet-/172213773664?hash=item2818bda560:g:CRUAAOSwbPxXPtTz

or something like this, which seems to have a direct pulse output (but ad is not clear) http://www.ebay.co.uk/itm/NEW-Magnetic-Rotate-Speed-Sensor-3-8-24UNF-Thread/222595424069?_trkparms=ao%3D1%26asc%3D20170912102017%26meid%3Dbc15d211df304517b1e5ff60f821015b%26pid%3D100706%26rk%3D1%26rkt%3D1%26&_trksid=p2045573.c100706.m4781

[88 Especial]

Hello,

New to the forum, first post.

For what it is worth, I installed a tachometer from a Kenworth tractor in my SIII diesel several years ago.

I added a wire from a stator winding output, where it connected to the diode pack/rectifier.

Counted the number of poles on the rotor. I have a Delco-Remy alternator and it has 14 poles. I believe the Lucas has 12.

Measured the diameter of the alternator and crankshaft pulleys. Don't remember the sizes, but it was 2 +/-  revolutions of the alternator for each revolution of the crank.

My multimeter has a frequency function, used this to measure the signal from the alternator.

I used the formula:  f=p/2 X r/60.

Where:  f is the signal frequency in cycles per second,    p is the number of poles, and r is the speed of the rotor in revolutions per minute.

Knowing the frequency and number of poles, manipulate the formula to get the rotor speed. r=120 x f/p.

The tachometer had a number of dip switches, adjusted these till the reading on the tachometer was as close as possible to the calculated speed.

I lost most of my data in a hard drive failure, the attached spreadsheet has some data..Calculated speed.xls

This was almost 10 years ago, so I may have forgotten something. Also I am retired so this project was something to pass the time.

 

Cheers from Central America!

Edited September 20, 2017 by 88 Especial
spelling

[Carloz]

Thx for posting. :-)

Found out that my Lucas alternator doesn't have a "W"-terminal. And figured out that I don't want to go the diesel-rev-counter-route because: to much of a hassle AND a big chance that it doesn't give the right reading on the original rev counter. So it will be: sourcing a petrol rev counter or just stick without a functional rev counter. :-)

 

[Troll Hunter]

88 Especial, welcome to the forum.  It's members like you who make this forum what it is - a really good source of technical information.  I must admit that you are a little unusual, as most first posts are asking for help, and here you are offering help.  You obviously have significant experience and I hope you stay around.

Mike