How do those *digital* capacitor discharge ignition systems control spark energy and even spark duration? For instance how do you produce either 150mJ or 300nJ spark?
Re: CDI
Posted: Sat Jul 01, 2023 10:21 am
by kb1gtt
On small engines I think spark duration and energy are mostly fixed. Components are selected and the trigger signal is also fixed. However I understand that you can get a certain level of control. With CDI you basically charge a cap, then you quickly discharge the cap through a step up transformer. If you charge the cap up to something like 8V, you'll get less energy when you dispatch that energy through the transformer and gap. If you charge the cap up to 12v, you get more energy.
I think the coil on plug setups found in cars are typically CDI. CDI has less inertia in the system which allows for faster and probably hotter spark potential. Spark energy in a coil will likely be lower heat for a longer duration.
I would think parameters for CDI duration and energy would primarily involve gap, transformer step up ratio, cap uF value and capacitor charge voltage. With some searching I'd bet an equation could be found or made which correlates those parameters.
The cap and transformer are going to prevent some level of energy from converting into spark energy. Keep in mind the stored energy is a max available energy.
Hmmm. That pic circuit look very similar to the direct injection driver boost circuit.
Here I got spark! Problem: only one spark every 15 seconds. This (weak?) converted takes 15 seconds to reach 380v on the capacitor. I assume weak boost converter is the problem here?
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As arrived module output was 80v, things were peaceful. I've started cranking pot to increase voltage...
First it has burned one resistor, then it has burned two resistors in series! Note the heat shrink has failed to keep the magic smoke inside. I did not even have a chance to attempt sparking.
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Re: Digital CDI for large engines
Posted: Mon Aug 28, 2023 12:57 am
by kb1gtt
I recall a QUCS or ltsoice simulation somewhere. Perhaps this would be worth attempting to simulate it.
I know what's going on, I am burning/shorting IGBTs!
I've replaced unknown/old/fake BTS2140 with a legit ISL9V3040 and everything seems to start working at 220VDC. Once I've cranked voltage up I got a single unscheduled spark on the "spark plug" and then yet another resistor went in flames.
Power supply claims 390V so I should not be exceeding the 400V limit of ISL9V3040. There is also "SCIS Energy = 300 mJ at TJ = 25°C" am I exceeding that?
Re: Digital CDI for large engines
Posted: Tue Aug 29, 2023 9:16 am
by kb1gtt
Scope traces? It's hard to guess when we have little data. If you scope it out, then make sure you using 10X scale or make sure you have a probe capable of 400+V. Often a 10X probe can handle around 400V. So beware and keep an eye on the voltage capability if you try to use a scope.
I might guess you have some kind of kick back, which is exceeding the voltage. I sounds like you are hitting the Over Voltage Protection (OVP) decently hard, which probably heats up the driver chip. I suspect it then eventually causes a thermal shutdown, or breaks the OVP circuit. Once OVP is broken, then I expect you get additional damage, as the kickback voltage moves upstream breaks other components.
Re: Digital CDI for large engines
Posted: Sat Sep 09, 2023 1:06 am
by AndreyB
Trying to run 69694G coil using STGB10NC60HDT4 600V IGBT
Happy 200v
IGBT shorts out after few pulses at 260v When smoke was released it was 0.1ms pulses with 30ms gap.