On 28/03/2017 1:16 AM, dagmargoodboat@yahoo.com wrote:> On Sunday, March 26, 2017 at 2:33:13 AM UTC-4, Sylvia Else wrote: > >> Finally got the engine running today, using this ignition circuit, and >> LPG, after many hours spent cursing a PIC32MX that I was temporarily >> using to generate the trigger pulse - got caught out by yet another PIC >> errata - input capture doesn't work when the processor is in the idle state. >> >> Sylvia. > > Was that PIC quirk the problem? Otherwise, I'd ask > o Whether C4 might be bad, open, or the wrong value?No, and I even replaced it. Its value is far from critical anyway.> > Or, that not being the case, maybe the LT1243's upset about having its > FB pin pulled all the way to +5v (wind-up?)?It's within spec. Another possibility is that the LT1243 is interpreting the sudden drop in FB as an indicator of an output short, but if so, I'd expect it to object to every such occurrence, not just the first.> > Is the LT1243's Vref getting glitched from your reset circuit, upsetting > the LT? > > Just some wild ideas. From your description it really sounds like it's > RT/CT pin-related, and you've already put your finger on it (so to speak :).The IC is not really designed with this application in mind. Perhaps it just plain doesn't like being used this way. Sylvia.
Ignition circuit issue.
Started by ●March 26, 2017
Reply by ●March 27, 20172017-03-27
Reply by ●March 27, 20172017-03-27
On 28/03/2017 10:25 AM, Jim Thompson wrote:> On Sun, 26 Mar 2017 15:36:06 +1100, Sylvia Else > <sylvia@not.at.this.address> wrote: > >> I'm using this circuit to provide 250V pulses to an ignition coil. >> >> https://www.dropbox.com/s/1w33uss3eedem05/ignition2.pdf?dl=0 >> >> The IC is a Linear Technology LT1243. >> >> 12V is provided on G$1 to the left. G$2 accepts a trigger pulse, >> and G$3 is ground. >> >> LTSpice says that this works, and indeed the real implementation >> does. Mostly. >> >> The difference is that after the circuit has been triggered once, >> it won't charge the capacitor again (above about 25 volts) for a >> varying period that can be up to half a minute. It's as if the >> wrong level is being used internally to compare with the feedback >> pin. In that regard, I'll mention that Q3 is used to pull FB up so >> that the circuit stops driving the FET, since otherwise the SCR >> never turns off. I've checked, and the problem is not that Q3 >> remains on, nor is it that the SCR fails to turn off. In any case, >> the 1.5uF capacitor C1 does get charged somewhat, as I mentioned >> above. >> >> When the issue resolves, it does so rapidly, within a fraction of a >> second. >> >> Connecting an oscilloscope probe to the RT/CT pin of the IC >> restores function, but only if the scope is set to DC coupling - >> not AC coupling - and functioning continues only as long as the >> probe remains connected - until the aforesaid varying period has >> elapsed. Touching the pin with a finger has a similar effect. >> >> That is, connect probe; works. Disconnect; stops working. >> Reconnect; works, etc. until eventually it starts working >> continuously. >> >> This cannot be capacitive loading - there's already a significant >> capacitance between RT/CT and ground. >> >> The fact that the coupling has to be DC made me think that some >> small current was flowing to ground through the scope, so I bridged >> C4 with a 100K resistor. It didn't make any difference. >> >> I tried changing the IC (a pain, given that it's surface mounted), >> but again it made no difference. >> >> Any other ideas about what might be happening here. >> >> Sylvia. > > Using a PIC when you should have gone analog >:-}Nah! Used a boost converter chip when I should have used a PIC. A 28 pin PIC32MX seems a bit over the top for this, but what the hell? It's not even more expensive.> > <http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf> > > <http://www.analog-innovations.com/SED/CDI_Inductor.jpg> ...Jim > Thompson >Don't quite see how that works - does it rely on the reverse breakdown of D3? Sylvia.
Reply by ●March 28, 20172017-03-28
On 28/03/2017 10:31 AM, Lasse Langwadt Christensen wrote:> Den tirsdag den 28. marts 2017 kl. 01.25.23 UTC+2 skrev Jim > Thompson: >> On Sun, 26 Mar 2017 15:36:06 +1100, Sylvia Else >> <sylvia@not.at.this.address> wrote: >> >>> I'm using this circuit to provide 250V pulses to an ignition >>> coil. >>> >>> https://www.dropbox.com/s/1w33uss3eedem05/ignition2.pdf?dl=0 >>> >>> The IC is a Linear Technology LT1243. >>> >>> 12V is provided on G$1 to the left. G$2 accepts a trigger pulse, >>> and G$3 is ground. >>> >>> LTSpice says that this works, and indeed the real implementation >>> does. Mostly. >>> >>> The difference is that after the circuit has been triggered once, >>> it won't charge the capacitor again (above about 25 volts) for a >>> varying period that can be up to half a minute. It's as if the >>> wrong level is being used internally to compare with the feedback >>> pin. In that regard, I'll mention that Q3 is used to pull FB up >>> so that the circuit stops driving the FET, since otherwise the >>> SCR never turns off. I've checked, and the problem is not that Q3 >>> remains on, nor is it that the SCR fails to turn off. In any >>> case, the 1.5uF capacitor C1 does get charged somewhat, as I >>> mentioned above. >>> >>> When the issue resolves, it does so rapidly, within a fraction of >>> a second. >>> >>> Connecting an oscilloscope probe to the RT/CT pin of the IC >>> restores function, but only if the scope is set to DC coupling - >>> not AC coupling - and functioning continues only as long as the >>> probe remains connected - until the aforesaid varying period has >>> elapsed. Touching the pin with a finger has a similar effect. >>> >>> That is, connect probe; works. Disconnect; stops working. >>> Reconnect; works, etc. until eventually it starts working >>> continuously. >>> >>> This cannot be capacitive loading - there's already a >>> significant capacitance between RT/CT and ground. >>> >>> The fact that the coupling has to be DC made me think that some >>> small current was flowing to ground through the scope, so I >>> bridged C4 with a 100K resistor. It didn't make any difference. >>> >>> I tried changing the IC (a pain, given that it's surface >>> mounted), but again it made no difference. >>> >>> Any other ideas about what might be happening here. >>> >>> Sylvia. >> >> Using a PIC when you should have gone analog >:-} >> >> <http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf> >> >> <http://www.analog-innovations.com/SED/CDI_Inductor.jpg> > > why even bother with CDI? most car do fine with regular coils, many > coils even have the driver igbt buildin all you need is a 5V driver > for a few ms of dwell time >My application is a backup "portable" generator. One useful feature of CDI in this application is that it doesn't require a large input current, meaning that I can start the generator using cheap dry cells, and then let it power itself. No need for limited life failure prone rechargeable batteries that need to be kept topped up lest they die. Sylvia.
Reply by ●March 28, 20172017-03-28
On 28/03/2017 02:03, Sylvia Else wrote:> On 28/03/2017 10:25 AM, Jim Thompson wrote: >> >> <http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf> >> >> <http://www.analog-innovations.com/SED/CDI_Inductor.jpg> ...Jim >> Thompson >> > > Don't quite see how that works - does it rely on the reverse breakdown > of D3? > > Sylvia. >D3 acts normally, the output is a large negative spike. piglet
Reply by ●March 28, 20172017-03-28
On 28/03/2017 6:39 PM, piglet wrote:> On 28/03/2017 02:03, Sylvia Else wrote: >> On 28/03/2017 10:25 AM, Jim Thompson wrote: >>> >>> <http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf> >>> >>> <http://www.analog-innovations.com/SED/CDI_Inductor.jpg> ...Jim >>> Thompson >>> >> >> Don't quite see how that works - does it rely on the reverse breakdown >> of D3? >> >> Sylvia. >> > > D3 acts normally, the output is a large negative spike. > > pigletYes, I see it now. Sylvia.
Reply by ●March 31, 20172017-03-31
On Tue, 28 Mar 2017 15:19:59 +1100, Sylvia Else <sylvia@not.at.this.address> wrote:>My application is a backup "portable" generator. One useful feature of >CDI in this application is that it doesn't require a large input >current, meaning that I can start the generator using cheap dry cells, >and then let it power itself. No need for limited life failure prone >rechargeable batteries that need to be kept topped up lest they die.And the problem with CDI, which several motorcycle manufacturers and Mercury Marine discovered the hard way, is that the brief spark is lousy at igniting less than optimum mixtures. Sure, it'll fire a plug dipped in oil but it won't fire a non-optimum mixture. Something common when trying to crank an engine under adverse conditions. The MSD (Multiple Spark Discharge) company solved this problem by firing up to 8 sparks per ignition event. That company has been around for 30 or 40 years now. I suggest that you scrap that circuit and go back to the pulse triggered Kettering-type ignition. A GM HEI module from the 70s up through when they gained a 5th terminal makes an EXCELLENT controller. IT will work with points, variable reluctance or pulse input. Adding external inductance in parallel with the coil will lengthen the spark and make it more likely to ignite a crappy mixture. A brand name AGM battery (Enersys Odessey for example) will maintain most of its charge for a year or more and a Battery Tender costs almost nothing. John John DeArmond http://www.neon-john.com http://www.tnduction.com Tellico Plains, Occupied TN See website for email address
Reply by ●March 31, 20172017-03-31
On Fri, 31 Mar 2017 14:41:00 -0400, Neon John <no@never.com> wrote:>On Tue, 28 Mar 2017 15:19:59 +1100, Sylvia Else ><sylvia@not.at.this.address> wrote: > > >>My application is a backup "portable" generator. One useful feature of >>CDI in this application is that it doesn't require a large input >>current, meaning that I can start the generator using cheap dry cells, >>and then let it power itself. No need for limited life failure prone >>rechargeable batteries that need to be kept topped up lest they die. > >And the problem with CDI, which several motorcycle manufacturers and >Mercury Marine discovered the hard way, is that the brief spark is >lousy at igniting less than optimum mixtures. Sure, it'll fire a plug >dipped in oil but it won't fire a non-optimum mixture. Something >common when trying to crank an engine under adverse conditions. > >The MSD (Multiple Spark Discharge) company solved this problem by >firing up to 8 sparks per ignition event. That company has been >around for 30 or 40 years now.Yep. I devised schemes to do just that when I was at Philco-Ford in 1968 and Dickson Electronics 1970-72... works quite well with this "self-inverting" method.... <http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf>> >I suggest that you scrap that circuit and go back to the pulse >triggered Kettering-type ignition. A GM HEI module from the 70s up >through when they gained a 5th terminal makes an EXCELLENT controller. >IT will work with points, variable reluctance or pulse input. Adding >external inductance in parallel with the coil will lengthen the spark >and make it more likely to ignite a crappy mixture. > >A brand name AGM battery (Enersys Odessey for example) will maintain >most of its charge for a year or more and a Battery Tender costs >almost nothing. > >John >John DeArmond >http://www.neon-john.com >http://www.tnduction.com >Tellico Plains, Occupied TN >See website for email address...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Thinking outside the box... producing elegant solutions.
