Rev limiter

ollyc98

ollyc98

Ex. Club Member
The k10 doesn't have a limiter (or I haven't hit it yet) so I was thinking of getting one from microdynamics, it goes on the ignition not the fuel pump to limit so I can't see any problems in fitting.

So does anyone know something on this subject that I may have missed.

Or is there a cheaper alternative as I'm looking at quite a bit of money.

Another idea I was thinking of was a shift light where the output goes to a relay to cut off the coil when it hits a certain level of revs.
 
Well if you sit on the line waiting for a green light you rev it until you go when you drop the clutch, now if you haven't got a limiter you can damage the engine. On the limiter you don't have to worry and you can floor it til you go. Plus if a limiter cuts the spark you can have an exhaust flamer on the redline cos of the extra fuel in the exhaust.
 
To be fair the K10 doesn't have enough power to kill itself on a 'launch'.
 
Jesus christ, you sit there red lining!
A rev limiter wont help in saving your engine, near standard k10's have very low torque and the top of the revs and finally thats a useless method on a n/a engine, its used by people with a lot of turbo lag and not many brain cells!
 
Ok but I do love the sound of a car hitting the limiter, and no I don't sit there red lining cos I'm worried about damaging my engine.

My above example of needing a limiter was on a track of course, not the road.
 
Ed said:
Care to elaborate?
Click to expand...

basically, take the pulse off of the distributer, (where u connect ur rev counter), feed it into an LM2917 (frequency to voltage convertor), set up to give about 0.5volts per 1000rpm, then feed that into an lm741 set up as a comparator with an adjustable referance by using a pot, the on the output of the 741 to a highish power transistor such as a 2n3055, then use that to turn on a relay and connect the coil to a NC contact of the relay so when the frequency reaches say 6000rpm the voltage will be about 3 volts, the referance on the comparator is set at 3 via the pot, so at 6k the comparator o/p will switch on which will turn on the transistor which will then turn on the relay disconnectiong the coil, thus creating an adjustable rev limiter.

alternatively to using the transistor and the relay, get an ecc coil and power transistor and use the output of the comparator to drive the power transistor just like the ecc unit would, however this would require pins 2 and 3 of the 741 to be reversed so that the output went low when it was limmiting.

costs
lm2917 = £3 ish
lm741 = £0.50
2n3055 = £1
pot = £1
few other resistors = few pence
nice box to put it in = £2
wire and anything else = £<1

total = no more than £8.50, even less as i have already got everything i need off of the list that i had left over from my led rev counter project.

elaborate enough? lol
 
Ok the theory is sound. How do you intend to protect the LM2917 from the EMF breakdown from the coil?
 
You mean EMF caused by the inductance of the coil?
Edit: Hmm, I was thinking more an inductor arrangement. Another method would be a rotational sensor (of some description-Contact, non contact). Anyway, a connection to the low tension side of things (with diode) should be fine, although my usual disclaimer applies.
 
Ed said:
Ok the theory is sound. How do you intend to protect the LM2917 from the EMF breakdown from the coil?
Click to expand...

well to be honest i lied a little, when i did my led rev counter i usea a comparator on the front of the system to square up the pulse, so therefore it shouldnt affect the lm2917, and i had my led rev counter in for months and it never went down.

and zanes, if i was making a 1 off it would be on veroboard, but depending on demand it may be time to dig out me uv exposure unit and bubble etch tank.

wot i may do over the next week or so is make 1 up and check the performance, depending on how that goes i may see if people would want them making.
 
If we were being really pedantic, a diode may help.
Ed and Others: I'll reference this up to the hilt if needs be, but I really don't want to. There is no theory here, this is sound electronics.
 
I know my electronics. I write assembler for microchip pics etc and have done for companies like Wizards of Nos etc..

I am asking you if you connected your circuit directly to an ignition coil on a car and found it worked successfully... Rather than say a frequency generator as a proof of concept. And theory does not always follow fact with electronics. I designed high power RF amplifiers etc for years and things don't always work as expected.

Personally I wouldn't use a frequency to voltage converter. I'd sample the pulses and work out the RPM from that and then use that to cut the spark to the coil using a small micro.
 
Strangely, I also write PIC assembler, although admittedly at the minute it is only the relatively crude 16F54 and 57 for me.
Surely using the low tension side would be fine (although a connection to the high tension side would be pretty amusing), although I suppose I would use the revcounter connection on the ECU. A PIC for purely rev limiting purposes would be slightly over engineered IMO (although maybe something like the 12F508 wouldn't be (ignoring certain pats of Microchips app notes iirc)), but I suppose it comes down to what you are comfortable using and whether you intend any further development.
Surprisingly, I'm not trying to cause a fight here, and I understand what you're saying in your stickies this morning, but we mustn't stifle innovation. Perhaps the forums need a re org?
 
I take it from the above you have not actually tried it then? I can tell you without some decent protection it would not work. When the field on the primary winding brakes down it induces a current in the secondary, and thus its repeated in the primary until the energy is sufficient that it causes a spark thus dissipating the energy in the coil. This ringing causes a back emf of in excess of a few hundred volts in the primary winding. Any logic you attach to that will be completely destroyed. Analogue electronics for such a device are typically inaccurate and due to temperature changes would cause the rpm limit to change etc, and would be subject to massive amounts of noise, making them further inaccurate.

Just a thought for you if you intend to try this.
 
I think you're talking about inductance causing a backward EMF. That is exactly what happens when a relay, motor or other inductance is turned off. A diode connected similar to the one's in the link below will safely dissapate this EMF (It's been used in robotics for years) and there are plenty of diodes in existance that will easily deal with this situation.
http://www.robotroom.com/BipolarHBridge.html

I'm not sure why temperature would be an issue, as the electronics would not necessarily be installed in the engine bay (apart from possibly a sensor, depending on which approach was to be taken) and it could be disadvantageous installing them there.

Again, I'm not trying to start a fight, so please do not take it as I am, and disagreements like this are what makes a forum! (so please don't hate me!!)

From wikipedia, http://en.wikipedia.org/wiki/Relay#Operation;
"If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a spike of voltage and might cause damage to circuit components. Some automotive relays already include that diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle"

I know that refers to a relay, but the principle I am trying to illustrate is the same. No I have not tried it, but I do not believe that disqualifies me from talking about it (although it would disqualify me from providing exact schematics). I can see why you may disagree with that.
Perhaps I came across as a little confrontational during my last few posts, but that was not my intention.

Again Ed, I can appreciate you getting frustrated with some of the recent forum activity (heck, I think we all have been) but it is important to make the distinction between asking stupid, repetitive questions and exploring alternative approaches (however fine that distinction may be). I also strongly believe that this kind of thing is what makes forums interesting.
I repeat my earlier comment that a forum re organisation may be in order, perhaps with a free forum (where anything goes) and another section (possibly members only) where we discuss only proven, verified things.
 
zanes said:
I think you're talking about inductance causing a backward EMF. That is exactly what happens when a relay, motor or other inductance is turned off. A diode connected similar to the one's in the link below will safely dissapate this EMF (It's been used in robotics for years) and there are plenty of diodes in existance that will easily deal with this situation.
http://www.robotroom.com/BipolarHBridge.html
Click to expand...
I'm a bit confused why you think the above is relevant. The last thing you want to do is short the stored energy out within the ignition coil upon field collapse with a diode. Ill let you figure out why, but I did briefly mention it above. Also the H bridge has nothing to do with this application and in fact nothing in the diagram above would be of any use at all in this application.
It turns out that if you look at the lm2917 datasheet all the info is given for you, including appropriate input filtering to the lm2917.

I'm not sure why temperature would be an issue, as the electronics would not necessarily be installed in the engine bay (apart from possibly a sensor, depending on which approach was to be taken) and it could be disadvantageous installing them there.
Click to expand...
Your measuring frequency, and quite a low one at that, depending on how accurate you want to be temperature errors may cause a problem. I have frequency generation equipment which has crystal 'ovens' to help ensure that the clocks remain very stable, generally the slower the signal is that your measuring the bigger the problems you may get with errors. Try making a really slow 555 based timer of a few minutes or more. The errors can be huge.

Again, I'm not trying to start a fight, so please do not take it as I am, and disagreements like this are what makes a forum! (so please don't hate me!!)

From wikipedia, http://en.wikipedia.org/wiki/Relay#Operation;
"If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a spike of voltage and might cause damage to circuit components. Some automotive relays already include that diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle"

I know that refers to a relay, but the principle I am trying to illustrate is the same. No I have not tried it, but I do not believe that disqualifies me from talking about it (although it would disqualify me from providing exact schematics). I can see why you may disagree with that.
Perhaps I came across as a little confrontational during my last few posts, but that was not my intention.
Click to expand...
I'm not interested in arguments to be honest, however back to the point if you put a diode across an ignition coil to deal with EMF, the car will not run. Try it if you don't believe me! The whole point of the EMF is very fundamental to the operation of the coil. How do you think such high voltages are made from coil winding ratios that on the face of it simply don;t make sense. (around 50-100:1 iirc)

Ed
 
so ed if you dont think it will work on an op-amp or an lm2917 because of the induced emf and such like frying things, how would you overcome it, and how do u plan on connecting a micro to said coil which are even more delecate than a run of the mil 741.

on a side note, i have just started to learn pic assembly etc, ive just programmed one for my final year project.
 
Zanes, (edit) Care to elaborate on your reply? Or am I wasting my time?
 
I think we'll go round in circles, which I think you're trying to avoid with the forum atm :laugh: But if you want we could talk electronics for a long time? Maybe a new section :laugh:
SuperLS, where are you studying electronics?
 
superls said:
so ed if you dont think it will work on an op-amp or an lm2917 because of the induced emf and such like frying things, how would you overcome it, and how do u plan on connecting a micro to said coil which are even more delecate than a run of the mil 741.

on a side note, i have just started to learn pic assembly etc, ive just programmed one for my final year project.
Click to expand...

I think you need to read my latest post regarding the LM2917.

BTW its great that PIC ASM is now taught at college. When I did my couses years ago I learnt ASM on z80 cpus which pratically have no use to anyone, even then. You should have a look at some of the dsPIC MCUs they are pretty impressive...
 
PICs have been available for over 15 years... lol. Just college level education takes ages to catch on with this kind of technology.
 
zanes im doing it at hnd level at chesterfield college, u sound as though u no a bit are u studying it?

ed pic isnt being taught there i had to give myself a crash course in pic programming, this sight proved very helpfull
 
Ok, I walked into that. D'oh!
SuperLS, I'm studying a MEng in Electronics (with Space Tech) at a certain south-west university. ;)
We don't hit PIC programming until our second year (I suspect using C though :( ), I bought myself a PIC book and am teaching myself. Currently making a photovore (although exams have that on hold until next month....)
 
it was taught a couple of years ago but the lecturer that did it retired and no-one ever took it back up, unfortunately, its the same as we have a room set out at college fully equipped with allen bradley plc's, but no lecturers knows what there doing with it so the wont teach it to us, but u ask a question about a great big dirty induction motor there on the ball straight away, lol
 
Or something like this: http://www.mikroe.com/en/tools/dspicpro3/ this is my main bed for development now. They do loads of other ones too.

Anyway to avoid going too far from the topic, I think someone should have a go at the rev limiter idea. BTW you will need something like a BU941ZT to clamp the coil when the limiting is in use. Its a dedicated ignition coil driver transistor, and as you'll see its collector/emitter junction is protected and clamped to prevent self-destruction.
 
ed ive just read the lm2917 datasheet and it shows a typical application being connected to an ignition coil,, it is just filtered via a couple of resistors and a capacitor. ill look into the device u speak of though
 
Yep, pretty much. I bought this, but I don't use the demo board. I rigged up a programming cable, and put the PIC on some breadboard and program it that way. I don't know whether you can buy the PICkit (ie, the black thing and the cable) seperately, but that one is a nice complete package I feel. You can probably find it much cheaper online though,
The PICkit supports a few PICs; list
Although it's massively geeky, that board is seriously impressive ed! Should we start a PIC/electronics topic in general
 
thats a heafty list, my programmer only supports about a dozen, including the 16f84, i used the 16f628a for my project
 
superls said:
ed ive just read the lm2917 datasheet and it shows a typical application being connected to an ignition coil,, it is just filtered via a couple of resistors and a capacitor. ill look into the device u speak of though
Click to expand...

Exactly! Its a high impedance low pass filter. Protects the chip from too much current and also filters out the high harmonics ensuring a reliable signal. If you look at an ignition coil firing on a scope they are really quite noisy. If you can get sensitive electronics operating reliably under these conditions they will operate under pretty much any.
 
well to be honest with you i over looked a vital part, ive just checked my old documentation and i did actually use that filter arrengement on the front end of my led rev counter, so it may just work, like you said earlier, theory dosen't always match up with practical, so i feel the best thing to do is for me to build one and test it, then post up the results.
 

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