Finding equivalent capacitors...car electronic

thumper300zx

Member
2019-05-29 11:19 pm
I have a car electronic with some capacitors I need to replace. One is a Rubycon RX-20 63v 47uf 125*c 10mm diamter. I have found a suitable replacement for that on Digikey. The others are 40v 47uf and 25v 47uf, both also 10mm diameter and 125*c. I can't tell the brand, but it has a triangular looking logo with three points (almost looks like Mitsubishi logo). It seems maybe in the last 30 years the 25v 47uf are typically smaller diameter (5-6mm) and if not, I'm having trouble finding the higher temperature rating. Any help finding these or what would be a suitable replacement would be greatly appreciated. I already have something for the 40v.

board_top.jpg
 
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The Rubycon RX-30 series should do fine. They are rated 2000Hr@130deg.

For the smaller ones, it won't hurt to go to a higher voltage rating (generally, I don't know what your unit is) to maintain diameter if you really had to. Lead spacing is an important dimension to know.

Personally, I would bash 3 of these in and be merrily on my way:

https://au.element14.com/rubycon/63rx3047m10x12-5/cap-47-f-63v-20/dp/8127220
 

thumper300zx

Member
2019-05-29 11:19 pm
Mitsubishi produced a lot of electronics for vehicles. They also produced capacitors.
They don't look swollen or damaged. Why replace them?


This device is a fuel pump control module for my 300zx. They are notorious for going bad. With it bypassed, my car will run great. With it in, the fuel pump will occasionally pass through no power and stall the car. It's getting progressively worse. Usually there is something obviously bad with the board. In this case there is not. It is usually fried transistors. Next is capacitors or solder joints. I can't see anything visually obvious. It was suggested by enthusiasts to replace the caps and see how it goes.

The fuel pump itself and the relay to it have been replaced. The fuel pump was probably weak before, but not dead.
 

thumper300zx

Member
2019-05-29 11:19 pm
You might not need 125 deg rating at all. Measure the temperature where this control unit lives and then you will know. I suspect 105 deg rating would also be alright. Otherwise, there is other suppliers of passive parts. Try Farnell.


edit: Is the device faulty?

Yes. It acts as a variable ground for the fuel pump. The pump gets power directly, then heads to the fuel pump controller which, based on other ECU signals, lowers or lifts voltage (3 voltages/speeds). The car will stall intermittently connected to it. Bypassing and grounding the pump it does not cut out. When bypassing, it always runs full speed. It is suggested to only bypass until the controller is replaced. A new controller (discontinued anyway) runs $400+. A used one will likely have more miles than mine, so I thought I'd just try to repair.
 

thumper300zx

Member
2019-05-29 11:19 pm
The Rubycon RX-30 series should do fine. They are rated 2000Hr@130deg.

For the smaller ones, it won't hurt to go to a higher voltage rating (generally, I don't know what your unit is) to maintain diameter if you really had to. Lead spacing is an important dimension to know.

Personally, I would bash 3 of these in and be merrily on my way:

https://au.element14.com/rubycon/63rx3047m10x12-5/cap-47-f-63v-20/dp/8127220

So, it would be ok to replace capacitors of different voltages (25, 40, 63 x 2) as long as higher?

I already have the 40vs. So I guess I could just use one in place of the 25? But I couldn't use 3 25s to replace higher voltage, correct?

I also got Rubycon RX-30 25's, but I wasn't paying enough attention and they are small (6mm, so very short lead spacing). They also have short lead length. I also couldn't find them on Rubycon's RX-30 data sheet, so wondering if they might be knockoffs.

rx30.jpg
 
Last edited:
The Rubycon RX-30 series should do fine. They are rated 2000Hr@130deg.

For the smaller ones, it won't hurt to go to a higher voltage rating (generally, I don't know what your unit is) to maintain diameter if you really had to. Lead spacing is an important dimension to know.

Personally, I would bash 3 of these in and be merrily on my way:

https://au.element14.com/rubycon/63rx3047m10x12-5/cap-47-f-63v-20/dp/8127220

I misaligned v ratings reading your post. I get what you're saying now -- I can go with the higher V rating for all four capacitors and be fine. Thanks for the help. I'll just replace them and then see if I still have a problem. It's not tough to take back out or bypass again until I figure this out (though it looks like all my caps were good, unless they are failing at a higher temp, which I guess is possible since it's intermittent and they don't have visible issues).
 
(snip) It is usually fried transistors. Next is capacitors or solder joints. I can't see anything visually obvious. It was suggested by enthusiasts to replace the caps and see how it goes.

How are the new caps working?

Certainly by the size of the heat sinking, those two power transistors clamped to each side are expected to get hot. Have you ensured they have good thermally conductive pads? Can you monitor their temp when the car stalls? Iow, is the stalling random, or related to temperature or run time?

This is the place to get it figured out, so look forward to your updates.
 
How are the new caps working?

Certainly by the size of the heat sinking, those two power transistors clamped to each side are expected to get hot. Have you ensured they have good thermally conductive pads? Can you monitor their temp when the car stalls? Iow, is the stalling random, or related to temperature or run time?

This is the place to get it figured out, so look forward to your updates.

I was about to come back to post when I got notified of your reply. So far so good. I only replaced the four caps. I have done two full drives to and from work plus a few other trips.

I'll go another week and report again.

When I removed the original caps and tested them at ambient, they all fell within uf rating...but maybe when hot they cut out.