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Is AMR 1912 suitable for a 200tdi defender?


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picked it up and have tested it seems to work fine.

turned out the guy only lived 10 miles away

get them while there hot....

Can you stick a quick guide up on how to connect it when you get time? Going to purchase mine now then as i reckon they will be gone soon!

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Can you stick a quick guide up on how to connect it when you get time? Going to purchase mine now then as i reckon they will be gone soon!

I can do but I am a little busy at the moment and im going away this weekend. It really is ever so simple. 3 cables needed, 12 volt, earth and one from the 'G' on the gauge to the back of the alternator which should have a terminal marked with a 'W' at the base of it (was on the right hand side near the bottom when looking down on the alternator from the front on mine).

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I can do but I am a little busy at the moment and im going away this weekend. It really is ever so simple. 3 cables needed, 12 volt, earth and one from the 'G' on the gauge to the back of the alternator which should have a terminal marked with a 'W' at the base of it (was on the right hand side near the bottom when looking down on the alternator from the front on mine).

Cheers. Thats all i needed.

I take it yours accurately represents the engine speed with a conventional size pulley?

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it was saying just a bit over 750 at idle which i beleive is correct and when the engine was reved it seemed to be going up at the right rate, didnt disproportionatly sky rocket at all so i believe it was working well

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  • 3 months later...

Long time since i bought this, but thought i would update the thread. I fitted the tacho to my defender 200tdi, but i beleive it is under reading by 1/3 all of the time. So at idle it reads 500rpm, but should be more like 750. At full revs, it reads at just under 3000rpm, but should be nearer 3800 i beleive. No adjustment on the one that i bought, so looks like an AMR1912 might be for sale soon! At least the wiring is there for the correct one when i get it fitted!

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I havent permanently fitted mine yet. never got round to it but i will soon when i rebuild it on to a new chassis :D . When i tested it mine worked fine. ill report back when i have it in full time....

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  • 4 months later...

Hello all,

(This is my first post on here so go easy on me)

I bought one of these and am only just getting around to fitting it (always seems to be something else I'm 'supposed' to be doing). Anyway I remembered this thread to I hooked it up temporarily first and saw the idle speed was showing a little over 500rpm. Now from what I've read the idle speed should be around 750rpm, so do I believe the guage?

I've noticed there is no adjustment on the guage (you can't even take it apart, unless you want to damage the surround) but I did notice a sticker saying 12V/1800HZ, does anyone with an accurate guage also have a sticker indicating HZ?

I wanted to see what the 1800hz corresponded to so I set up a test with a frequency generator and an oscilloscope and took some readings for various indicated rpms.

250 rpm = 106hz

500 rpm = 163hz

750 rpm = 228hz

1000 rpm = 260hz

2000 rpm = 570hz

3000 rpm = 870hz

4000 rpm = 1170hz

5000 rpm = 1435hz

6000 rpm = 1726hz

So it looks like the 1800HZ is supposed to represent full needle deflection.

Does anyone know what frequency the alternator should produce for a given engine rpm?

Sorry for all the questions on what is now an old thread (makes mental note to get off backside quicker in future)

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Sorry for all the replies

Looks like there are two different alternator pulley sizes available for the 300tdi :- (from http://forums.lr4x4.com/index.php?showtopic=7336)

49mm From VIN TA969103------Pt No STC3202

61mm To VIN MA969102----------Pt No STC1796

Mine has the 61mm pulley which would mean it will read about 20% slower than the 49mm

The crank pulley is 160mm (measured from a spare engine, hope there is only one size) so the relative step ups of the two pulleys are (I hope my maths is correct :-S)

160/61 = 2.6

160/49 = 3.25

Now representing RPM in hz (cycles per second) choose an arbitary engine speed of 1000rpm

1000rpm/60 = 16.66 hz

Multiply by 2.6 (for 61mm) to give alternator speed

16.66 hz * 2.6 = 43.33 hz

Multiply by 3.25 (for 49mm) to give alternator speed

16.66 hz * 3.25 = 54.15 hz

From my measurements in previous post (assuming it got approved)

to show 1000rpm on an AMR1912 we need 260hz at the W terminal.

There is obviously some multiplier affect within the alternator, if we knew the correct amount we could work out which alternator pulley (if any) is the correct one for the AMR1912 to read the correct RPM.

Effective multiplier of alternator for 61mm pulley to be correct would be...

260hz/43.33hz = 6

Effective multiplier of alternator for 49mm pulley to be correct would be...

260hz/51.45hz = 4.8

The multiplying effect in an alternator is a product of the number of poles it has, basically a 12 pole alternator has a multiplier of 6 and a 10 has a multiplier of 5. from wikipedia (http://en.wikipedia.org/wiki/Alternator)

So the question boils down to is the alternator on my 300 tdi a 12 pole alternator?

The general consensus of the web is that most alternators are 12 pole so that would mean after all that the AMR1912 will work fine on my 300 tdi defender..... I better go and wire it up properly this evening :-)

Please check my working out, I hope to be corrected if I am wrong.... thanks and sorry for my ramblings.

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I fitted mine and have left it fitted for now, BUT, as you say, it constantly underreads. My idle speed is the same on the gauge as yours (~500rpm), so about 1/3 less than it should be. If i max the revs out, i get nowhere near the 3600rpm that i think my tdi should top out at under load. The error doesnt seem to be linear. I contacted VDO about this and they said that the gauge cannot be adjusted. If you do find a way, i'd be keen to know how, as the thing is pretty useless to me as it is!

I think that this was fitted to the NAS spec v8 90 and the guys in the states also seem to suggest this:

http://www.d-90.com/forum/showthread.php?t=29315

(if anyone has a v8 and thinks this gauge will fit and wants one, PM me as i need to change it really!)

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So based on my guage, and poor maths....

Actual RPM Expected frequency on W terminal Indicated RPM

750 195hz 600 rpm ish

1000 260hz 1000 rpm

2000 520hz 1800 rpm

3000 780hz just over 2600 rpm

4000 1040hz just over 3500 rpm

For a list price of £140 odd punds you would expect a bit more accuracy than that I would have thought :-(

So it's not a particularly accurate guage but appears to be designed for the 160mm crank pulley with the 61mm alternator pulley ..... I wonder if anyone does a digital tacho???? (I'm sure the mrs doesn't really want that new cooker....)

reb78, hope these figures help with yours.... they seem to marry up with your experience of it.

PS I'm currently moderated so my responses take a while to show up ... hopefully they don't get too out of step.

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A smaller pulley would be the only way to get the reading (near) correct.

I thought that, but the one on there seems pretty tiny already, so i'm not sure i can go any smaller!

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Just playing with a few numbers and a multiplier of 3 would work best with my guage....

6000rpm would give 1800hz

5000rpm would give 1500hz

4000rpm would give 1200hz

3000rpm would give 900hz

2000rpm would give 600hz

1000rpm would give 300hz

750rpm would give 225hz

which if you compare with the actuals results from the test I did

6000 rpm = 1726hz

5000 rpm = 1435hz

4000 rpm = 1170hz

3000 rpm = 870hz

2000 rpm = 570hz

1000 rpm = 260hz

750 rpm = 228hz

500 rpm = 163hz

250 rpm = 106hz

They are really pretty close (trust me to have chosen 1000rpm for my other post which seems a bit of an anomoly)

That would mean I need a 53mm pulley on the alternator :-s ..... what's interesting is the outside lip on the 49mm pulley is 53mmm ..... I wonder if someone made a mistake somewhere along the lines? or maybe they just stuck it halfway between pulley sizes so it was about right?

(I really hope my posts all come out in order when the moderator reads them)

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The adjuster for it is hidden behind a white sticker on the side of the guage, about an inch bach from the front edge and at the bottom (behind where it says vdo)

Mine now indicates 750rpm with 196hz and 4000rpm with 1040hz

Have fun .... unfortunately I had to take mine apart to find it (stupid moment doh) SO I shall be trying to put mine back together nicely now :-S

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Just been out for a spin and all looking good :-)

Indicated RPM's went up to 3800 rpm before I chickened out as the engine sounded to be going as fast I was comfortable with (never rev'd it that much before based on the sound anyway)

When I got back idle tickover was pretty much 750 rpm.

I'm happy :-) sorry for all the posts but it helped a lot with the thought process, even though in the end I should have just peeled all the stickers off!! lol. Also working out the theory means I now feel like the guage is properly calibrated and can trust what it is saying.

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I got one as well and i am happy with what mine is reading. If the engine is cold the rpm is below 750 but after a bit of a run it idles happily at 750.....

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Mine is now doing the same as yours jad, little under 750rpm cold but 750rpm after a run. :-)

Out of interest Jad when you get a moment it would be interesting to know the diameter of your crank pulley and the diameter of your alternator pulley (measured at the top of the ribs).

Sounds like the tacho is right for your pulley combination, but it was under reading on mine and is under reading on reb78's. It's good to know it works as standard on at least some 200tdi's :-)

From what I have heard there are two different types of 200 tdi crank pulley, I don't know if they are different diameters but they have different locking tools.... maybe you have the older crank pulley (with the slots) and reb78 has the newer one with the threade holes like the 200tdi? that's pure guesswork but may be a plausible reason for the difference.

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