Hi Cam/Sporti Coils wondering if Stick Coils Feasible?

[Weegie]

So I'm starting to get into my new to me BMW R9T ready to start doing a little service work and noticed that it has stick coils. A while back I was thinking of replacing the standard coils on my HiCam with stick coils and just looking at the BMW coils and placing them into the HiCam thought they might fit reasonably well. The main reason was/is to get rid of the conventional coils as I'd like to install a larger cooler and the coils and fuel pump are the 2 items that would need relocating (the coils especially being a PIA where they are currently sited).

I had looked at this before and it's still just idle musings for now.

One thing I read after doing a bit of Googling was how older bikes just left the coils to charge/saturate during the time they are not required to generate a spark, but that might burn out stick coils as they are usually a far lower primary resistance. Burning out the ECU was also mentioned if the coil resistance was too low as well, due to taking a larger currrent than it could handle.

However the Marelli 850 coils installed on the HiCam/Sporti and possibly V11s have a very low resistance, around 0.6 Ohm, compare that to any of the older models which usually have coils cirica 5 Ohms. It got me to wondering if unlike the earlier bikes the charging/saturation times on the Marelli 850 coils is controlled by the ECU in so much as the ECU actually switches them on and off as opposed to just leaving them live when a spark isn't required. If that's not the case why install coils with such a low primary?

As I said it's pie in the sky right now but just a thought and if it was possible and stick coils could be identified that were suitable, might help others as the Marelli coils can sometimes be hard to source.

I wonder if @Meinolf knows if the ECU switches the coils on and off and what the saturation times are, pretty sure he must have some sort of clue as he's done extensive research on the workings with the ECU and built simulators to mimic its functions on a running bike.

Idle musings for now

John

[Meinolf]

Hi John,

On 1/6/2022 at 10:53 AM, Weegie said:

I wonder if @Meinolf knows if the ECU switches the coils on and off and what the saturation times are,

I can probably contribute something, but need to know which ECU you are referring to.

Cheers
Meinolf

[Weegie]

1 hour ago, Meinolf said:

Hi John,

I can probably contribute something, but need to know which ECU you are referring to.

Cheers
Meinolf

 

Hi Meinolf

The specific bike I'm referring to runs a 15M ECU and it's a 4v/v per cylinder Hi Cam engine (the model would be a Daytona RS). I think the Sport 1100 injection and the early V11s also had the 15M (not that I know anything about ECUs)

Looking at the wiring diagram for a Centauro, which is almost identical, it's obvious that the coil has a positive supply to it all of the time, it's fed from the power relay.

Does the ECU vary the period it opens the circuit to the coils (or is it a fixed period regardless of any other parameters), prior to grounding it again?

I'm wondering if the circuit to each coil was left open by the ECU for a period longer than required to discharge the coils, then grounds the coils to charge them.

If that was the case then the coil charge period would be controlled by the ECU on the negative side, when it was open the coil wouldn't charge and when it was grounded it would.

Many Thanks for posting up and responding, very much appreciated.

If you require more information on the ECU or if it's unclear what I'm trying to explain, just let me know.

John

[Meinolf]

3 hours ago, Weegie said:

Does the ECU vary the period it opens the circuit to the coils (or is it a fixed period regardless of any other parameters), prior to grounding it again?

Hi John,

the  procedure as I understand it is as follows. The ECU goes thru an initial process to determine the engines rotational status. Eg, which cylinder is where and in which state, compression or emptying the bucket. This is governed by the toothed wheel attached to the camshaft and the engine position sensor and takes several engine rotations.

After the status has been established and verified the fuel phase table takes over. This table contains rotational degree values which are the starting point for the calculation of coil discharge and injector opening time. They are used in a backward calculation.

Which makes sense if one considers that the behaviour of any coil is depended on voltage (and coil design characteristics) and the logarithmic charging characteristics. So the tooth wheel and the missing teeth provide the starting point for the capcom-ops in the code which do the pulse-counting. This starting point (from a rotational point of view it's behind TDC) is in fact the point at which the circuits are opened again. Meaning, the point at which the discharge of the coil or the opening of the injector end.

So the calc looks like this:

Endpoint (fuel phase table value) + coil charging time/injector opening time = coil discharge start/injector opening

The code also contains a trim table to take care of the voltage dependencies. Eg, lower voltage requires a longer coil charging time/injector opening time to achieve the same effect due to the slower coil saturation.

So, the answer to your question "Does the ECU vary the period it opens" is yes, it does.

Based on the terrific analysis of the components used in the 5AM ECU done by John Th. we know that the current draw is used as another factor in the 5AM (and presumably later generations). I don't know if this current draw was already used in the 15M/RC.

Cheers
Meinolf

[Weegie]

@Meinolf

Wow that's a fantasitc piece of work and terrific explanation, thank you so much.

I'll need to read it a few times to take in, in its entirety.

The ECU is doing even more than I imagnied, I knew it was complex before, but that's even way more advanced.

So if I'm reading your explanation correctly (still taking it all in) then the ECU has control over coil saturation times and can and does vary them dependent on various external factors.

If that is the case then obtaining a stick coil to suit is a possibilty, not for now, it's very useful to have some rudimetary understanding (not you're explantion of course, more my limited intellect.)

That's given me an insight into an area of the ECU that I just had no clue about

I am most grateful

John

[Lucky Phil]

7 hours ago, Weegie said:

 

Hi Meinolf

The specific bike I'm referring to runs a 15M ECU and it's a 4v/v per cylinder Hi Cam engine (the model would be a Daytona RS). I think the Sport 1100 injection and the early V11s also had the 15M (not that I know anything about ECUs)

Looking at the wiring diagram for a Centauro, which is almost identical, it's obvious that the coil has a positive supply to it all of the time, it's fed from the power relay.

Does the ECU vary the period it opens the circuit to the coils (or is it a fixed period regardless of any other parameters), prior to grounding it again?

I'm wondering if the circuit to each coil was left open by the ECU for a period longer than required to discharge the coils, then grounds the coils to charge them.

If that was the case then the coil charge period would be controlled by the ECU on the negative side, when it was open the coil wouldn't charge and when it was grounded it would.

Many Thanks for posting up and responding, very much appreciated.

If you require more information on the ECU or if it's unclear what I'm trying to explain, just let me know.

John

No Hi Cam engine has ever used the 15M ecu as standard John. It was either the P7/8 or the 16M.

Ciao 

[Weegie]

10 minutes ago, Lucky Phil said:

No Hi Cam engine has ever used the 15M ecu as standard John. It was either the P8 or the 16M.

Ciao 

Damm Thanks Phil it's a 16M

Reckon the principal still holds true, that the ECU does control the saturation time for the coils, that being the case if I managed to determine a stick coil with a similar primary or even slightly higher resistance, it would be a canditate for use in place of the Marelli 850s.

It's not something I'm going to looking at anytime soon though, just installed some NGK racing leads to replace the original HT leads which were suffering badly from lying on the heads

John

[Lucky Phil]

3 minutes ago, Weegie said:

Damm Thanks Phil it's a 16M

Reckon the principal still holds true, that the ECU does control the saturation time for the coils, that being the case if I managed to determine a stick coil with a similar primary or even slightly higher resistance, it would be a canditate for use in place of the Marelli 850s.

It's not something I'm going to looking at anytime soon though, just installed some NGK racing leads to replace the original HT leads which were suffering badly from lying on the heads

John

Of course I have 15M maps for the hi cam engine if you need one John. Coilovers wouldn't look to special on a hi cam engine I don't think either.

Ciao