Capacitor Question

[Zarniwoop]

Hey all,

I need to perform a modification to the EFI system in my car to correct an overfuelling issue. The modification involves installing an electrolytic capacitor across two terminals of the multiplug harness to act as a filter, which in turn will correct the overfuelling issue.

I understand how the filter arrangement works with the electrolytic, but I am also aware that the max temperature the electrolytic will work at is 105*C, otherwise it may dry out. Now since this mod is in the engine compartment, I can almost guarantee that it will be hotter than 105*C in there.

So my question is: 'Is there another type of capacitor which I can replace the electrolytic with to ensure longevity?'

The Electrolytic is 100uF 25V type.

Cheers!
Grant

 

[john1]

maybe you could mount the cap somewhere else,
and run a wire over to the connection ?

 

[Zarniwoop]

So basically John1, what you're saying is "no"?

 

[Roff]

I know it gets damned hot in the engine compartment, but is the location you have in mind really hot enough to boil water?

 

[Zarniwoop]

Well it is about 30cm from the head, and the cam covers on the head certainly do get hot enough to boil water. I wouldnt imagine the capacitor itself getting to 100*C+ (maybe closer to 80*C) but wouldnt operating under such hot conditions shorten the lifespan anyhow?

 

[Roff]

Most solid tantalum caps are rated to 125C, and they don't have a liquid dielectric.

 

[TKS]

you could also place a fan on it whit a heatsink..

 

[kentken]

Also, get the highest quality one you can find.
Not at radioshack :wink:

kent

 

[Johnson777717]

but wouldnt operating under such hot conditions shorten the lifespan anyhow?

yes, theoretically it would, especially with vibrations caused by the engine etc.

You can buy high temp electrolytics (I've seen up to 125*C at Digikey). Maybe you can get a hold of a military grade electrolytic which will probably have a higher rating??? I'm not sure there.

Also, you can consider sheilding your capacitor from external heat sources with some sort of high temp plastic, or aluminum enclosure.

Also, you can compare the temperature ratings of nearby hoses, electrical wiring etc. Maybe you can guage the approximate temp off of that?

Also, with the credibility of the electrolytic longevity (or lack thereof) in mind, can you use a different type of capacitor? As suggested, a tantalum, or polyester, silver mica etc? Those might have a higher temperature rating.

 

[Oznog]

Does this signal come out of the EFI computer? If so, can you place the capacitor at the computer, which is located in a place with lower temps by design?