3

I'm looking into replacing the capacitors in the vehicles ECU. I know the ratings and voltages for the three. My question though is which would be better to go with, electrolytic or ceramic. I'm not worried about price of the caps just would like to know which would be the most reliable and will last.

The capacitors are:

  • 22µF 50V
  • 47µF 50V
  • 100µF 25V

Also if it helps it's for a 1996 Mitsubishi Galant VR-4 RHD.

I've read through Can I replace all electrolytic capacitors with ceramic ones? but didn't really answer my question unfortunately.

Thanks for any help.

Community
  • 1
OMEGA_RAZER
  • 33
  • 3
  • 1
    As Olin Lathrop pointed out in the other discussion, 100µF ceramic caps are rather exotic beasts. If the original design used electrolytic caps, why would you want to switch? – microtherion Apr 15 '13 at 23:18
  • 1
    Also: if you think the electrolytics are aged, you can just switch to new electrolytics. Suppose they last 25 years. What will be the overall condition of the *car* in 25 years? Will anyone care about the electrolytic capacitor's in that car's ECU 25 years from now? – Kaz Apr 15 '13 at 23:20
  • Have you actually measured these capacitors? I know it seems like these days everything can be fixed by changing caps, but that is due to manufacturing flaws, not inherent unreliability of electrolytics. – markrages Apr 15 '13 at 23:39
  • @markrages - I would beg to differ with your assessment that most capacitor changes are needed "due to manufacturing flaws". In all the LCD monitors and LCD TVs that I've brought back to life by simply changing out all the electrolytic capacitors there is strong evidence at really crappy capacitors being used!! I've fixed models from many manufacturers. – Michael Karas Apr 16 '13 at 00:15
  • 1
    @MichaelKaras it was as one-time event, see http://en.wikipedia.org/wiki/Capacitor_plague – markrages Apr 16 '13 at 00:32

1 Answers1

6

Capacitor selection involves a lot more engineering than just voltage and capacitance. Your plan could make the circuit worse instead of better.

High value ceramic caps are fragile, and have a dangerous failure mode in automotive applications: When they crack, they tend to become a low-value resistor. An automotive power system can supply high currents into this low resistance, dissipating enough power to start a fire. You can get special "automotive" capacitors, but inside they are just two capacitors (of twice the capacitance) in series, so that both have to fail before the fire starts. I expect you will find better cost and availability to just put two in series in your circuit.

High value ceramic caps are fragile. Some manufacturers only recommend placement with reflow, not with a iron that heats each end individually. Don't expect great reliability if you hand-solder the caps in there.

I would think high-temperature electrolytic capacitors should last the life of the vehicle. Replace, if you have to, with good-quality ones. But the designers of the ECU were designing it to last and you can assume they chose the capacitors wisely.

markrages
  • 19,905
  • 7
  • 59
  • 96