Rev counter for slow running diesels

[magnetman]

A simple digital rev-counter

 

If you want to accurately measure engine RPM and running hours on a slow running diesel the easiest way is to use a BICYCLE COMPUTER.

 

You can get one for about £5 (Ebay for example) just make sure it is designed to set wheel CIRCUMFERENCE in Millimetres or Centimetres.

 

What you do is this:

 

Set the 'wheel size' to 167cm or 1667mm.

 

Set the readout to display 'Km/h'.

 

Glue the small magnet to the flywheel.

 

Position the reed switch / sensor which normally goes on the front fork of the bike within 1/4" of this magnet, at a fixed point, ensuring the flywheel will rotate without fouling it.

 

Run the engine.

 

The cycle computer display will be 1/10th of the engine speed. E.G. 27.5km/h will be 275rpm. Some will go up to 100km/h (!) which is 1,000rpm obviously.

 

This isn't very good for fast running engines but is a very cheap way to display engine tickover speed. Some of the more expensive units (£10+) will also do average and maximum.

 

Its a good way to check correct governor operation by recording max and average at a set speedwheel position, you find out if the engine is 'hunting' ie speeding up and down.

 

The cycle computer is designed to stop its clock when the bike is stopped so actual engine rotation hours will be counted with no need for an alternator based hour meter. They do tend to reset after 12 hours however so daily recordings would be required if this was the only engine hour counter used for service intervals etc.

Edited December 22, 2006 by magnetman

[andywatson]

A simple digital rev-counter

 

If you want to accurately measure engine RPM and running hours on a slow running diesel the easiest way is to use a BICYCLE COMPUTER.

 

You can get one for about £5 (Ebay for example) just make sure it is designed to set wheel CIRCUMFERENCE in Millimetres or Centimetres.

 

What you do is this:

 

Set the 'wheel size' to 167cm or 1667mm.

 

Set the readout to display 'Km/h'.

 

Glue the small magnet to the flywheel.

 

Position the reed switch / sensor which normally goes on the front fork of the bike within 1/4" of this magnet, at a fixed point, ensuring the flywheel will rotate without fouling it.

 

Run the engine.

 

The cycle computer display will be 1/10th of the engine speed. E.G. 27.5km/h will be 275rpm. Some will go up to 100km/h (!) which is 1,000rpm obviously.

 

This isn't very good for fast running engines but is a very cheap way to display engine tickover speed. Some of the more expensive units (£10+) will also do average and maximum.

 

Its a good way to check correct governor operation by recording max and average at a set speedwheel position, you find out if the engine is 'hunting' ie speeding up and down.

 

The cycle computer is designed to stop its clock when the bike is stopped so actual engine rotation hours will be counted with no need for an alternator based hour meter. They do tend to reset after 12 hours however so daily recordings would be required if this was the only engine hour counter used for service intervals etc.

 

Brilliant.

Just nipping out to rob my bike.

[John Orentas]

.

Edited December 22, 2006 by John Orentas

[magnetman]

I have used reed switches in another life, it would be an interesting experiment to see just how fast these things will reliably function.

 

For those people who haven't come across them they comprise of what can only be described as a switch, either normally closed or normally open encapsulated in a glass envelope. When the magnet comes close it attracts one element of the switch causing it to change state. You need a magnifying glass the see the blades of the switch which are formed in such a way as to give a snap action. The units are capable only of switching only very tiny loads.

Best for slow engines I guess

Edited December 22, 2006 by magnetman

[Supermalc]

Excellent idea.

[DHutch]

This is exactly what we do on emilyanne, works very well for us, often in locks it the only indication that the engines actaully running!

- It also doubles as an hour counter and total-rev counter, using th "trip time" and "overall distance" readouts. And it tells the time for you too.

 

 

Daniel

[chris w]

The units are capable only of switching only very tiny loads.

 

Actually, you can get types that will switch 1 amp @ up to 200v DC. They are slow switching devices (electronicaly-speaking) at about 250 times (OFF-ON-OFF) per second. Certainly fast enough for narrowboat engines though as this equates to 15,000 rpm. They cost around 40p each typically.

 

Chris

 

[magnetman]

This is exactly what we do on emilyanne, works very well for us, often in locks it the only indication that the engines actaully running!

- It also doubles as an hour counter and total-rev counter, using th "trip time" and "overall distance" readouts. And it tells the time for you too.

Daniel

 

They are quite a bit cheaper than mobile phones.