Shift light.

[bigbadbob76]

While doing my tacho and dash PCB upgrades I noticed that relay 4 position in a late fusebox has a tacho feed.
I wondered why until I realised the fusebox is a CE1 used in several other models of the same era.
Relay 4 is for a light that comes on at about 2krpm when you're not in top gear and are accelerating.
This was to encourage you to drive economically and was called the "upshift lamp"

I figured it wouldn't be too hard to raise the rpm trigger point to something sensible like 4kRPM and add a shift light to my array of leds in the dash.
The relay is actually an upshift control module, marked with a No.5, pt No. 171919091
I ordered one on e-bay from Latvia and it arrived promptly so I drew out the circuit.



it's very similar to the dops circuit and I just had to ground the vacuum switch input and add an LED in order to test it.
I also changed the values of a capacitor and a couple of resistors to increase the RPM trigger point to 4K.
took it for a spin last night with the "relay" in position 4 and it works just fine.
Now I just need to get a wire from the back of the fusebox to a LED on Chris's dash PCB and we're good to go.

4k rpm seems like a good trigger point but I could recalculate the resistors for peak power at 4600RPM (on a DG),
Or 70MPH in top gear as a "speeding" warning.
Going much lower than 4K would be annoying as it would be on in top gear on the motorway, we don't have the top gear switch in our gearboxes that disables the light.



And the improved version with a 100k trimmer to allow RPM adjustment.
I've bench calibrated mine to 3700RPM which is 70MPH with 185/85R-14 tyres and my DU gearbox.



And wired into terminal A3 on the fuse box.

[kevtherev]

Brilliant!
Very usefull!
I drove 6 miles in third on a motorway

[bigbadbob76]

Cheers Kev.
It started as a poohs n giggles experiment but sounds like it would be usefull.
I managed to get a crimp terminal into fusebox terminal A3 which is unused on our vans and connects to the L terminal on the "relay" and run a wire to the dash PCB.
I did a test run tonight and 3700RPM is not 70MPH on my van.
Either my DU box has been re-built with different ratios or my calculations are wrong.
Even an "indicated" 70 is nearer 4000RPM.
So I wound the trimmer up a bit to a 4KRPM trigger point.
I'll have to get out on the local airstrip to get it up to a real 70MPH.
It's not physically possible on our local roads. (and not legal either obviously).
Or wait till i'm next down south.

[937carrera]

My model says 3798 rpm for 70 mph on standard tyres with a DU box

[bigbadbob76]

Cheers Carrera.
I guess my DU box has lower ratio's than standard then, or my tyres have shrunk in the wet.
looking at this- http://rjes.com/html/gearbox_types.html
I either have diesel ratios or a 4 speed with 5 speed ratios.
I've never found it to be a problem.

[937carrera]

What's 3 rpm between friends

I think you have a final drive from a diesel or 1.6 air cooled, 38:7 which makes 4096 rpm at 70

Have you ever tried for 5th

[ajsimmo]

Could you add a switch in the lever housing under the floor, front left, that would switch when selecting top gear? Should be straightforward to make a suitable bracket.

Sent from my B1-830 using Tapatalk

[CJH]

Brilliant!
Very usefull!
I drove 6 miles in third on a motorway

I've forgotten about 4th gear a couple of times too - in the general cacophony with the windows open, radio turned up, it's quite easy to do.

I did a test run tonight and 3700RPM is not 70MPH on my van.
Either my DU box has been re-built with different ratios or my calculations are wrong.
Even an "indicated" 70 is nearer 4000RPM.

Bob, how are you measuring speed? Your speedo is likely to have a significant error (they all do), so GPS is the best way.

[bigbadbob76]

Thanks for the interest in this guys.
By GPS, my speedo reads about 10% high so an "indicated" 70MPH is more like 63/64.

Yes, I could add a 4th gear switch but I'd like the light to come on at true 70MPH in 4th as a speeding warning.

I havn't tried for 5th... maybe I should...

This brings up an interesting point about tacho calibration though.
I set the shift light to trigger at 3750RPM on the bench and the led came on at (as close as I could tell) 3750 on my tacho when I put it in the van, but I wasn't doing 70MPH.
The tacho in the van I calibrated with my clip on digital meter at 3000 RPM, I need to check it at 4000 to make sure it's not my tacho that's giving me errors.
But If you calibrate your tacho or shift light on the bench with square or sine wave signals that are 50% duty cycle, it might be inaccurate as the ignition pulses are not 50%.
Anyone know the dwell angle for a late DG? say 50 degrees? that would be just over 13% duty cycle.

I tried a spare 52mm tacho on the bench with square wave pulses at 50% duty and it reads up to 10% low. are they really that crap? or is it the duty cycle?

So now I've set my shift light to 3800 according to that tacho rather than to the true frequency, we'll see what happens when I plug it back in the van.

Ideally I'd go for a drive down the motorway and hold a steady GPS 70MPH while a mate adjusts the shift light but It's a wee bit far away.
This is getting interesting.

[937carrera]

Test the mechanical side first ?

Van in high gear, plugs out, chalk mark on the bottom of a tyre and floor, engine at TDC.

Push the van forward a certain number of engine revolutions and measure the distance along the ground. You can then confirm the gearing / final drive you have fitted.

It's a bit physical and you ideally need somewhere level and smooth, but you can push a T25 on your own, or at least I have.

More empirical than electrickery

[CJH]

But If you calibrate your tacho or shift light on the bench with square or sine wave signals that are 50% duty cycle, it might be inaccurate as the ignition pulses are not 50%.
Anyone know the dwell angle for a late DG? say 50 degrees? that would be just over 13% duty cycle.

I tried a spare 52mm tacho on the bench with square wave pulses at 50% duty and it reads up to 10% low. are they really that crap? or is it the duty cycle?

My £20 signal generator doesn't have any duty cycle adjustment, but it does have a selection of different waveforms (sine, square, triangle, sawtooth, reverse sawtooth), and my tacho read exactly the same with all of them. I think the 'frequency-to-current' converter chips (e.g. SAK215) aren't affected by duty cycle - they're just measuring frequency. So I think your spare tacho needs its trim pot adjusting.

I would even say that a bench-calibrated tacho may be a more reliable indicator of vehicle speed than a tired old speedo, when you know your gear ratios and wheel circumference - the sum of the errors in that approach could well end up being less than the typical 10% speedo error.

[bigbadbob76]

Sounds like a plan.
I do need to confirm my ratios.

I just set this up on the bench-


With this sig gen I can set the duty cycle.
It proves that the tacho is frequency dependent and duty cycle independent.
But my shift light circuit depends on both as it works by pulse width.
So I know I can calibrate my tacho on the bench.
Now I need to measure dwell angle at 3750 rpm so I can set my shift light on the bench without having to do 70mph.


Sent from my iPhone using Tapatalk

[bigbadbob76]

Push the van forward....

Surely I can jack it up and count wheel revs vs engine revs?

[937carrera]

You could do that too, I did think of that just worried about the diff interfering in some way, but can't argue why it should if one wheel is on the ground.

[ajsimmo]

I've forgotten the point of all this...

Sent from my ONEPLUS A3003 using Tapatalk