Coils - Information (Duty Cycle)

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Ryan Rotary Performance
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Coils - Information (Duty Cycle)

Post by Ryan Rotary Performance » Wed Mar 06, 2019 11:11 am

Duty Cycle:

Recently a report about coils was posted on this forum, its output was to rank OEM and aftermarket coils available to the Rx8. One of elements mentioned when considering a new coil platform was “Duty Cycle” while this was mentioned it was never really explained and the author of the document seemed to have very limited knowledge on the subject.

Below is an abstract from the “Report” in question and it’s this area I’ll try and address in a bit more detail:

Report Abstract:

“The Okada Plasma Direct coils are at the top of the ranks, and with the experience and knowledge these guys have in manufacturing, they have the ability to manufacture these coils from the ground up. And they are designed to cope with the higher RPM, where others hope to be able to deal with the higher RPM, even though they’re not designed to cope. This is one of my main concerns with these other coils, as they were originally designed for trucks – and for that application they are bloody good. I'll try and explain non-NAME REMOVED like, so here goes: when making anything, you look at what it needs to do within its design parameters, and these truck coils would probably never see past 6000 rpm (redlining), and their peak power is, say, between 4200-5000 rpm. Therefore, these coils (even though some seem to cope) are not meant to live with the rev range of a rotary engine, nor are they designed to. My biggest concern is duty cycle with these truck-based coils, and I can only imagine that after 5000 rpm the duty cycle will drop as the RPM increases, and if the red line says max 6000 rpm their duty cycle will be maxed 40%, or somewhere around that. And the duty cycle after that is anyone’s guess!”

So it’s the last line in that where the author is “guessing” is what I’ll try and address and explain.

So what is Duty Cycle?

Duty Cycle of a coil is the relationship of how long the coil is working compared to its rest time. One cycle is the time taken to charge and dis-charge the coil. For example (and these are silly numbers) if a coil takes 3 seconds to charge and 2 seconds to dis-charge then one complete cycle takes 5 seconds. Now if the coil is required to fire every 10 seconds then the duty cycle in this example is 50%.

Below is a table which shows the duty cycle of the Stock Coil, the RRP coil and the D585 coils which has been configured for the RX8, the map used was not aggressive, I have seen far more aggressive maps for the D585 coils.
DC.png
DC.png (11.31 KiB) Viewed 658 times


The line called “firing interval” could also be labelled 100% Duty Cycle in ms (Milli-Seconds). The timings for these Duty Cycles can be seen below:
DC1.png
DC1.png (10.77 KiB) Viewed 658 times
Timings above are in ms and for the Stock and RRP coils are based on the stock Dwell settings, why they differ is that the stock coils takes 1.8ms to discharge reducing at 5K RPMS whereas the RRP MKII coils discharge over 2.2ms reducing from 5K RPMS. They are reducing as the charging time is reducing by how much this dis-charge time is reducing is an assumption (but a constant one)

The same logic has been applied to the D585 coils but the timings used are a conservative adjustment to the Dwell timings, the ideal for the D585 coil is 5.5ms of Dwell.

With this information we can see the stock coil Duty Cycle tops out 46%, the RRP at 50% and the D585 a whopping 78%.
At these setting the outputs will be (all reducing as the charge time does)

Stock: 45MJ (independent test)
RRP: 96MJ (Factory test)
D585: 70-100MJ (Online information)

So why not use stock dwell for the D585 coils? Well if you did the spark energy would fall to somewhere around 32-50MJ with a discharge time of 1.4ms. This will make it a lower performing coil than stock. Will that cause issues, no not all the time and on some cars not at all.

Conclusion:

The RRP coils are set at safe working load of 50% duty cycle (continuous) so it can be seen in the table that the coils are not being worked too hard for their specification type. The D585 coils are usually rated at 70% max continuous Duty Cycle so from 6K rpms you can see you are starting to push the coils over and above what they are designed for, this could be a factor to some coils failing especially those worked hard on track where they are in the 70% region for a long time.

I hope I’ve answered the original authors “anyone’s guess” comment and now Duty Cycle and its application in a Rotary is a little more clearer.

Happy to receive comments and Q’s below guys, hope it was informative and useful. :thumright:
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Re: Coils - Information (Duty Cycle)

Post by V8 Power » Wed Mar 06, 2019 11:34 am

That is excellent information and explanation.
Thanks Carl.
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Re: Coils - Information (Duty Cycle)

Post by bigpete8 » Wed Mar 06, 2019 12:00 pm

Very informative Carl, presumably these figures refer to your Mk2 Coils, do you have that info for the Mk1?
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Re: Coils - Information (Duty Cycle)

Post by qwakers » Wed Mar 06, 2019 12:06 pm

very clear, concise, well backed up and explained.

in short, very professional, as have been all your dealings with me and others ive seen on this forum (in some cases, way more restrained than i would have been!)


you're a credit to yourself and your company and the above points are why im entrusting my rebuild to you :)

edit :mrgreen: about my fee 8)
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Re: Coils - Information (Duty Cycle)

Post by 13Black » Wed Mar 06, 2019 12:17 pm

Not enough assumptions.
Too much data.
Too much punctuation.
Too much understanding.

2/10 Melons.
Would not recommend to a friend.
I prefer streams of half-conscious drivel, myself.
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Re: Coils - Information (Duty Cycle)

Post by Essex2Visuvesi » Wed Mar 06, 2019 1:04 pm

13Black wrote:
Wed Mar 06, 2019 12:17 pm
Not enough assumptions.
Too much data.
Too much punctuation.
Too much understanding.

2/10 Melons.
Would not recommend to a friend.
I prefer streams of half-conscious drivel, myself.
Behave [-X :lol:
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Re: Coils - Information (Duty Cycle)

Post by warpc0il » Wed Mar 06, 2019 1:09 pm

Ryan Rotary Performance wrote:
Wed Mar 06, 2019 11:11 am
So why not use stock dwell for the D585 coils? Well if you did the spark energy would fall to somewhere around 32-50MJ with a discharge time of 1.4ms. This will make it a lower performing coil than stock. Will that cause issues, no not all the time and on some cars not at all.

The D585 coils are usually rated at 70% max continuous Duty Cycle so from 6K rpms you can see you are starting to push the coils over and above what they are designed for, this could be a factor to some coils failing especially those worked hard on track where they are in the 70% region for a long time.
At last some evidence that supports my experience and assumptions regarding dwell changes for D585 coils.

1. While increasing the dwell should increase the spark energy, it's unlikely to make any noticeable difference to engine power. The combustion charge is either correctly ignited, or it isn't.
2. Increasing the dwell proportionality increases the workload of the coils and therefore the likelihood of load-related failures.
3. Not changing the dwell has little downside, a potential upside in reliability and allows you to replace any/all of the D585 coils for either OEM or RRP Mk2 without damage, whether this is a permanent change or just substitution for fault-finding.

Would that be a fair interpretation Carl?
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Re: Coils - Information (Duty Cycle)

Post by Ryan Rotary Performance » Wed Mar 06, 2019 3:00 pm

warpc0il wrote:
Wed Mar 06, 2019 1:09 pm
The D585 coils are usually rated at 70% max continuous Duty Cycle so from 6K rpms you can see you are starting to push the coils over and above what they are designed for, this could be a factor to some coils failing especially those worked hard on track where they are in the 70% region for a long time.

At last some evidence that supports my experience and assumptions regarding dwell changes for D585 coils.

1. While increasing the dwell should increase the spark energy, it's unlikely to make any noticeable difference to engine power. The combustion charge is either correctly ignited, or it isn't.
2. Increasing the dwell proportionality increases the workload of the coils and therefore the likelihood of load-related failures.
3. Not changing the dwell has little downside, a potential upside in reliability and allows you to replace any/all of the D585 coils for either OEM or RRP Mk2 without damage, whether this is a permanent change or just substitution for fault-finding.

Would that be a fair interpretation Carl?
Some cars experience no problems with no dwell and some do experience issues especially around idle and at 7K where the VDI opens, the latter being splutter which is most commonly solved by upping the Dwell on the D585s.

I think there is still benefit in upping the Dwell on the coils most road cars wont see prolonged periods in above 6K, on track though its a different story. My advice is definitely up the Dwell in the lower rev ranges as here there is scope to do so with no negative effects.

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Re: Coils - Information (Duty Cycle)

Post by Juey » Wed Mar 06, 2019 3:40 pm

"car feels better" vs Actual dyno results

"ill thought out polls, online circumstantial stories and assumptions" vs facts backed up with data.

Actual results, facts and data WINS :thumright:

Nice work Carl.

...part of me is still with Nick though. Can you make it a bit more woolly and contentious next time please 8)
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Re: Coils - Information (Duty Cycle)

Post by 350matt » Wed Mar 06, 2019 6:28 pm

Thanks for this Carl

do you have any dyno charts showing just the effect of the coils on their own
I'd still be be happy with mine if there was no performance advantage over stock to be honest as the quality of the part and lifetime guarantee makes them worth the purchase price alone

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Re: Coils - Information (Duty Cycle)

Post by Ryan Rotary Performance » Thu Mar 07, 2019 8:38 am

350matt wrote:
Wed Mar 06, 2019 6:28 pm
Thanks for this Carl

do you have any dyno charts showing just the effect of the coils on their own
I'd still be be happy with mine if there was no performance advantage over stock to be honest as the quality of the part and lifetime guarantee makes them worth the purchase price alone
Not yet, but I'm hoping to do this in the near future we have a few dyno days in the calendar so can bolt this onto one of them. :thumright:

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Re: Coils - Information (Duty Cycle)

Post by 350matt » Thu Mar 07, 2019 3:59 pm

Jolly good, I look forward to seeing the results

I'd say the increased spark energy 'should' be worth something especially with regard to fuel consumption as our combustion chamber shape is god-awful

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Re: Coils - Information (Duty Cycle)

Post by Ryan Rotary Performance » Thu Mar 07, 2019 5:07 pm

warpc0il wrote:
Wed Mar 06, 2019 1:09 pm
At last some evidence that supports my experience and assumptions regarding dwell changes for D585 coils.

1. While increasing the dwell should increase the spark energy, it's unlikely to make any noticeable difference to engine power. The combustion charge is either correctly ignited, or it isn't.
2. Increasing the dwell proportionality increases the workload of the coils and therefore the likelihood of load-related failures.
3. Not changing the dwell has little downside, a potential upside in reliability and allows you to replace any/all of the D585 coils for either OEM or RRP Mk2 without damage, whether this is a permanent change or just substitution for fault-finding.

Would that be a fair interpretation Carl?
Dave further to your questions, I found this from BHR (The coils you have) and here is their verdict on Dwell timings (for those interested in the new BHR kit, its worth noting the coils in their new system have the same internals)

"In having the issues arise with the coil kit and investigating the situation we discovered the following;

1) N/A applications that are NOT using some sort of re-flash/EMS device are completely fine with the BHR kit as is.
2) Those who have a re-flash/EMS device (even while N/A) will be able to see some small additional gains and we will address this with each of you.
3) The seriously boosted engines (such as 7 PSI, manifold, or more) need this fix and should either exercise restraint or re-install the OEM coils until we contact you.
4) Nitrous users are in both groups 1 and 2 above.
5) GReddy Turbo Kit users are in group 2."


Interesting to note he expresses to fit OEM coils instead of unmapped BHR coils.

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Re: Coils - Information (Duty Cycle)

Post by warpc0il » Thu Mar 07, 2019 5:31 pm

Indeed interesting as my D585 are the original BHR kit, circa 2010

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Re: Coils - Information (Duty Cycle)

Post by Goobie » Fri Mar 08, 2019 10:52 pm

Any test results for the D585-R version? Aka - D969

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Re: Coils - Information (Duty Cycle)

Post by Ryan Rotary Performance » Sat Mar 09, 2019 10:45 am

Goobie wrote:
Fri Mar 08, 2019 10:52 pm
Any test results for the D585-R version? Aka - D969
I'm pretty sure Revs have discontinued these.

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