SOHC.co.uk Forums > CB500/550
Electronic ignition
deltarider:
The best instructive vids about our SOHC Fours are made by Marco, a member of the German forum. With his soft, modest voice he demonstrates restaurations in detail, explains all his findings, etc. Although it's in German, I like to honour him and present a link to his tutorial on the CB350F ignition system which is ofcourse very similar to ours. Although the video is worth watching as a whole, I'd like to point at the section where he summarizes all data on paper: 26:52 - 35:26 and - more in particular - where it is about Sättigung (saturation) in 28:41 - 29:12. New to me was, that there's a standard formula for inductance and that at max rpm in Honda's stock set up, our coils become saturated for only two thirds. Actually partial saturation begins at around 6500 rpm. TEC has ofcourse dimensioned the coils thus, that they are adequate.
For convenience I've made a copy in translation, which you find below. If you need more translation, feel free to ask. If you can shoot holes in his explanation, you're invited ofcourse. He is a friendly person and always open to criticism.
https://www.youtube.com/watch?v=HBJY8705gdc&t=1747s
HONDA CB350F IGNITION Specifications and Settings
COILS TEC FL703-12V
Primary resistance ~ 4,5Ω
Secundary resistance ~ 14,7kΩ
Turns primary 420
Turns secundary 13.000
Voltage secundary @ 10001/~14kV @10.0001/~11kV
Inductance ~ 14mH
Saturation (see 28:41-29:12 for explanation) Ï„ = L/Rp = 3,1ms (63,2%) Ï„ x 3 = 9,3ms
Charge time @ 1.000 rpm and 55% Dwell* 1 revolution = 0,06s > 33ms
Charge time @ 10.000rpm and 55% Dwell* 1 revolution = 0,006s > 3,3ms
CONDENSERS
Capacity 0,22 μF +/- 10%
courtesy Gruzzel
* Actually it is 55% Duty Cycle which equals 49,5o Dwell (4 cyl scale) which is a tad narrower than a 0,3 mm gap. Personally I'd chose a somewhat wider opening as the gap tends to narrow over time (Deltarider).
allankelly1:
Hi all
Been following this thread with some real interest
Like it had been said the original Honda design is up to the task and I am not making any claims I understand any of the electronic stuff, but for me personally if you are going to add any electronic control to a ignition system it make more sense (for me) just to replace the lot rather than have a modified /hybrid system
Modern Electronic ignition systems are well proven and with a system such a Boyer Brandsen you remove all the mechanical switches and the mechanical ignition advance and simplify everything, and for me it’s knowing that the complete ignition system is as good as new (if it needs replacing) even if it is a bit of an expense at the time.
(The full system included magnetic pick up CDI and two micro coils was only £237 which I felt was good value for a complete electronic ignition system when you look at how much we spend on our toys)
This is not a criticism of this thread or anybody here as I can see there are some real electronic gurus and wish I did understand it but I am more of a mechanical engineer and is just a personal point of view
Best wishes to you all Al
Sent from my iPhone using Tapatalk
Sesman:
Totally agree oddjob. But of course if your points and condensers are near to end of life then the Velleman self build makes good sense when considering the cost of good quality points and condensers. Unless somebody can supply me with a source at a reasonable cost….reasonable to me that is.
Does the Hondaman kit utilise the original capacitors? If so then the buyer could be in for some unforeseen additional costs if his condensers are fooled.
I really don’t know. The Ashmac solution (mainly Ash) is just an inexpensive experiment rather than a contender.
K2-K6:
"Does the Hondaman kit utilise the original capacitors? If so then the buyer could be in for some unforeseen additional costs if his condensers are fooled."
As I understand it, no his system doesn't use them. He leaves them in place but disconnected such that IF his electronics were to fail, then you can hook them back in circuit at roadside in reverting to straight points ignition to not leave you stranded.
Essentially the switching transistor takes all of the load itself with no need of condenser to mitigate. The "fault" side of the points that the condensers are there to control doesn't go away (as are most things in physics) it just comes out as heat from that transistor which has to be adequately dispersed to avoid failure of that component. Two different sides of a square in carrying out the same task effectively.
deltarider:
I could have left out my condensers. They are not needed for the power transistor, because it switches full yes or full no. Without the condensers, the benefit would be an even steeper rise time, which is fine. However, breakerpoints are not as perfect in switching as transistors, so there is a chance, if the points are 'hesitating', so to speak, in their opening and closing, they may cause the power transistor to switch multiple times. For the transistor itself that would be no problem. I could experiment with it to see if this really does happen. My electronic tach/dwell meter would tell me by showing funny readings. But I am satisfied with the rise time as it is now, so I kept the condensers. Whether these are the Honda ones or the ones that came with the kit, is the same.
Also, IIRC Hondaman at first had condensers built in, like in my module, then left them out, then later, after some customers had experienced irregularities, advised to use condensers again, but now the OEM ones that are at the base plate. Smart choice as this makes returning to OEM, in case of failure, even easier. Also this makes his modules cheaper to make, condensers being the second component in price after the power transistor.
Those of you that have studied the data in reply #170, will now understand that where the stock ignition cannot saturate the coils completely in the higher rpms, my module can, thanks to that shorter rise time it provides. As predicted by Bosch and Steinbuch, the gain is in the low and in the high rpms.
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