The rev counter is very bouncy on my mini, I have looked on the internet and it seems a filter my help, i found this guide http://bikephotos.se/home/58-guages/51-mak...ach-filter.html
I can see the black wire goes to earth and the blue to the revcounter but which side of the coil does the other wire go to (-ve??) and also how are the 270 ohm, 1/2 watt resister, a 1 ufd electrolytic capacitor connected, it looks like rev counter to resistor, resistor to coil and the cap goes to resistor/counter?
Thanks
Alan

Rev Counter Filter (very Bouncy)
Started by
amarcd
, Jul 02 2011 06:59 AM
7 replies to this topic
#1
Posted 02 July 2011 - 06:59 AM
#2
Posted 02 July 2011 - 04:52 PM
If i'm honest i think they get bouncy with age as the parts in the circuit board go wrong, My origional one was bouncy, so i found and bought a genuine new one on ebay. Now this has gone the same way.
I think the capacitors on / inside the circuit board need replacing.
I think the capacitors on / inside the circuit board need replacing.
#3
Posted 02 July 2011 - 04:57 PM
The one i have got isn't that old but its a big one with shift light, I thought maybe it was just interference causing it to bounce. As its only couple of quid for the resister/cap i will try this and if it works i'll stick it on here. Maybe sell them pre built for a fiver lol

#4
Posted 02 July 2011 - 05:40 PM
For more information on what the guy is doing in the link, Google for "low-pass filters".
Succinctly, he is using the capacitor to route high-frequency noise and spikes to earth and only passing the low frequency pulses to the tach. All his wiring is based on modern negative earth wiring.
What he has is a 270 Ohm resistor connected to the coil (-) terminal. The other side of the resistor has two connections. The first connection is to earth (via his black wire). The second connection on the resistor (his blue wire) is for the tach sense wire (white/black in the case of the Mini).
I question his choice of 270 Ohms. I would think the 270 Ohms would be too low a value and might make it impossible for the coil to produce a spark. However, I defer to the poster's experience. The worst this could do to your car if the poster is wrong... is make it impossible to start your car until the earth connection is removed from the filter.
Succinctly, he is using the capacitor to route high-frequency noise and spikes to earth and only passing the low frequency pulses to the tach. All his wiring is based on modern negative earth wiring.
What he has is a 270 Ohm resistor connected to the coil (-) terminal. The other side of the resistor has two connections. The first connection is to earth (via his black wire). The second connection on the resistor (his blue wire) is for the tach sense wire (white/black in the case of the Mini).
I question his choice of 270 Ohms. I would think the 270 Ohms would be too low a value and might make it impossible for the coil to produce a spark. However, I defer to the poster's experience. The worst this could do to your car if the poster is wrong... is make it impossible to start your car until the earth connection is removed from the filter.
#5
Posted 02 July 2011 - 05:42 PM
What ohm would you recommend?
#6
Posted 02 July 2011 - 06:13 PM
I am not a "sparky" (a.k.a. electrical engineer).
The design of a low-pass filter is based on the values of both the capacitor and the resistor. My concern is that the 270 Ohms is so low that it may prevent the coil from switching on and off the way it needs to. However, as I said, I am not an electrical engineer so I don't know how I would need to tweak the capacitor value to achieve the same filter results when a higher Ohm resistor is used.
Like I said, you can certainly try the circuit exactly as shown in the link. The worst that would happen is the engine would refuse to start until you remove the filter earth connection.
The design of a low-pass filter is based on the values of both the capacitor and the resistor. My concern is that the 270 Ohms is so low that it may prevent the coil from switching on and off the way it needs to. However, as I said, I am not an electrical engineer so I don't know how I would need to tweak the capacitor value to achieve the same filter results when a higher Ohm resistor is used.
Like I said, you can certainly try the circuit exactly as shown in the link. The worst that would happen is the engine would refuse to start until you remove the filter earth connection.
#7
Posted 02 July 2011 - 06:15 PM
ok in that case i will try as is and update on this post
thank you so much
thank you so much
#8
Posted 02 July 2011 - 07:14 PM
Sparkies are electricians, not electrical engineers. Electrical engineers are corporate members of a professional institution such as the Institution of Engineering and Technology.
The bouncing around might be due to poor filtering allowing sherbert to get through and causing extra triggering. However, it might also be due to mechanical vibration causing resonance in the needle spring in the rev counter movement. Originally I had my rev counter mounted on the parcel shelf and this vibration made it bounce around all over the place. I now have it mounted on a stiff cardboard plate (covered with vinyl so you cannot really see it) placed on the parcel shelf. Without a fixed connection to the vibrating parcel shelf, there is no bouncing around at all.
The bouncing around might be due to poor filtering allowing sherbert to get through and causing extra triggering. However, it might also be due to mechanical vibration causing resonance in the needle spring in the rev counter movement. Originally I had my rev counter mounted on the parcel shelf and this vibration made it bounce around all over the place. I now have it mounted on a stiff cardboard plate (covered with vinyl so you cannot really see it) placed on the parcel shelf. Without a fixed connection to the vibrating parcel shelf, there is no bouncing around at all.
1 user(s) are reading this topic
0 members, 1 guests, 0 anonymous users