Thanks Simon, that certainly sounds logical.
E: Engine BTH magneto
- Thread starter Sakura
- Start date
Ian is certainly right in that electronic ignition cannot 'advance' it can only retard from a known reference point.
I can't seem to find the advance curve graph mentioned but the website states analogue, non-programmable electronic advance I think that Simon's explanation is how we would like it to work but I don't believe it actually does. Any of the programming/ delay systems fall down when you are dealing with kickstarting a bike. You want it to spark on the very first compression so there is no time to calculate the required delay based on measured cranking speed.
When building an experimental ignition system for myself I used a second trigger point that is only used for starting. I set this to spark at tdc so there is no chance of it kicking back if you run out of kick just before the piston goes over the top. I imagine - but don't know - that this is how bth does it.
Many analogue advance systems simply rely on the rise rate of the signal to the inductive pickup as a measure of engine speed. That is why they seem to reach full advance so early.
It would be nice to get one of these magnetos on a test rig and find out what we are actually talking about.
I can't seem to find the advance curve graph mentioned but the website states analogue, non-programmable electronic advance I think that Simon's explanation is how we would like it to work but I don't believe it actually does. Any of the programming/ delay systems fall down when you are dealing with kickstarting a bike. You want it to spark on the very first compression so there is no time to calculate the required delay based on measured cranking speed.
When building an experimental ignition system for myself I used a second trigger point that is only used for starting. I set this to spark at tdc so there is no chance of it kicking back if you run out of kick just before the piston goes over the top. I imagine - but don't know - that this is how bth does it.
Many analogue advance systems simply rely on the rise rate of the signal to the inductive pickup as a measure of engine speed. That is why they seem to reach full advance so early.
It would be nice to get one of these magnetos on a test rig and find out what we are actually talking about.
Simon's post #12 above is on the right track.
In the old magnetos the armature has the low tension generating coils wound on the armature. The high tension windings were wound over the top of the generator windings. When the points open the field in the LT indings collapses and a high voltage is induced in the HT windings and fed to the plugs. Most old magnetos were classed as rotating armature with the magnets static, built into the magneto body. Some magnetos were rotating magnet with (you've guessed it) the magnet going round and the coils static. I guess that most people know the above. (Anyone still awake?)
O.K. I am not an electronics expert (or an expert of any sort come to that) but in very simplistic terms the new BT-H, like any magneto has a low tension generator section. In this instance the magnets are rotating. The HT winding section is the HT coil or coils mounted external to the body. Between the LT section and the HT section there are some electronics involved to rectify this output and charge capacitors to output maybe 400 Volts. (The elctronics are encapsulated and are inside the BT-H body or sometimes mounted externally.) There is a rotating magnet on an arm that passes over a coil to produce a trigger pulse. This pulse is fed to an RC circuit. (RC time circuit is a capacitor being charged through a resistor. The more pulses the sooner it charges to a given voltage.) When the voltage in the RC circuit reaches a threshold voltage a circuit dumps the 400 Volt charge stored in the capacitors mentioned earlier through the HT coils.
Phew!
Re: "mechanical maintenance in a Nuclear Power Station" I know very little about nuclear power stations. The closest I got was over 50 years ago when I worked for a company where we made a few stainless steel parts for Hinkley Point (B?) power station. Youngest daughter works for the Nuclear Decommissioning Agency in Cumbria. She probably knows more than me.
Re: "Every day's a school day". Late in my working life I moved from engineering to teaching. For 10 years I certainly learnt something every day. Not sure if the kids learnt much.
Pass me my "D" Distributor !!. Cheers Bill.Simon's post #12 above is on the right track.
In the old magnetos the armature has the low tension generating coils wound on the armature. The high tension windings were wound over the top of the generator windings. When the points open the field in the LT indings collapses and a high voltage is induced in the HT windings and fed to the plugs. Most old magnetos were classed as rotating armature with the magnets static, built into the magneto body. Some magnetos were rotating magnet with (you've guessed it) the magnet going round and the coils static. I guess that most people know the above. (Anyone still awake?)
O.K. I am not an electronics expert (or an expert of any sort come to that) but in very simplistic terms the new BT-H, like any magneto has a low tension generator section. In this instance the magnets are rotating. The HT winding section is the HT coil or coils mounted external to the body. Between the LT section and the HT section there are some electronics involved to rectify this output and charge capacitors to output maybe 400 Volts. (The elctronics are encapsulated and are inside the BT-H body or sometimes mounted externally.) There is a rotating magnet on an arm that passes over a coil to produce a trigger pulse. This pulse is fed to an RC circuit. (RC time circuit is a capacitor being charged through a resistor. The more pulses the sooner it charges to a given voltage.) When the voltage in the RC circuit reaches a threshold voltage a circuit dumps the 400 Volt charge stored in the capacitors mentioned earlier through the HT coils.
Phew!
Re: "mechanical maintenance in a Nuclear Power Station" I know very little about nuclear power stations. The closest I got was over 50 years ago when I worked for a company where we made a few stainless steel parts for Hinkley Point (B?) power station. Youngest daughter works for the Nuclear Decommissioning Agency in Cumbria. She probably knows more than me.
Re: "Every day's a school day". Late in my working life I moved from engineering to teaching. For 10 years I certainly learnt something every day. Not sure if the kids learnt much.
Dear Bill,
Perhaps I made most of that up.
It is actually all done by smoke and mirrors.Nuclear Power Stations. I worked in a Magnox Station. The nuclear side was just another way to boil the kettle. A good mechanical fitter from the beginning of the 20th century would have felt at home with much of our work on the conventional plant. Lapping steam valves, overhauling pumps, scraping white metal bearings, turning, milling, welding etc. Very little straight assembly work, most plant and equipment had to be fitted up - pretty much like a Vincent!
I have a BT-H on a B Rapide with 7.3:1 MK1's and 1 1/16 carbs. The only issue I have ever had with it was trying to run NGK 7 plugs. They are really hard starting especially if it is cool out. Put 6's in and the starting was transformed. We also have a big bore Comet around here that has a BT-H and also a real pig to start on a 7 but is fine with a 6.
When I was a mobile car mechanic, Long time ago, I bought a kit with points/Condensers/Distributor caps, Which would repair most cars used on the road, It was very cheap.
I remember my Volvo, Which would not start, Electric ignition, We was going to a wedding, I told the Wife I was in trouble, And she carried on loading the car !!, No chance !!.
I borrowed Ron/Lin's car, But got there as they where coming out of the wedding.
I have been in trouble ever since !!. Cheers Bill.
I remember my Volvo, Which would not start, Electric ignition, We was going to a wedding, I told the Wife I was in trouble, And she carried on loading the car !!, No chance !!.
I borrowed Ron/Lin's car, But got there as they where coming out of the wedding.
I have been in trouble ever since !!. Cheers Bill.
The only trouble I've had with my BT-H is the lead pulling out as the early coils only had a spike not a screw.