SVeilleux9 wrote: ↑Sun Jan 12, 2020 1:46 am
I would recommend using a ceramic capacitor.
That would be great, except that 50v 220uF ceramic capacitors don't exist. Essentially all OEM ECUs use electrolytic bulk caps for both the main supply and main relay "power device" supply (ETB, stepper idle, GDI boost supply, solenoids, etc).
SVeilleux9 wrote: ↑Sun Jan 12, 2020 1:46 am
I typically have not heard or seen electrolytic's used as bypass caps for ICs since they have higher inductance (ESL) which is what you are trying to get rid of with a bypass cap.
That's correct, there's no reason to use an electrolytic as a bypass cap, since they're never more than a few uF at a few volts, and ceramics have lower series inductance and resistance (ESL/ESR). However, 100uF is not a bypass capacitor, it's a bulk capacitor. That said there's really no quantitative difference.
Here's one way to think of it: The job of bulk/bypass capacitors is to provide a local supply with lower resistance and/or inductance than the next supply up the stream. The wires from the fusebox/main relay to the ECU have a loop resistance of perhaps 25 milliohms, but a huge inductance of up to a few microhenries (model above is 10mOhm and 1uH). A typical 100uF aluminum electrolytic will have a typical resistance of perhaps 100 milliohms, but a relatively tiny inductance of only tens of nanohenries (2 orders of magnitude smaller than the wire).
If we really really cared about extremely stable voltage, maybe it would be warranted to stack tens of ceramic caps, but we sort of don't. The 100-150mOhm ESR of the electrolytic is absolutely acceptable for the cost and size savings it offers.