Car ECU capacitor replacement - Page 1
Forum section: electronics / projects

author: speedb
author_rank: Newbie
timestamp: June 29, 2023, 09:03:21 am
content: I'm doing some preventative maintenance on my car's 30 year old ECU to replace its three electrolytic capacitors and was wondering whether I would be able to / would it be a good idea to substitute them with polymer capacitors?How much longer would I expect the lifetime to be (as a very rough estimate), and would the minor differences in ESR values affect the rest of the ECU?Cheers

author: SeanB
author_rank: Super Contributor
timestamp: June 29, 2023, 09:42:02 am
content: Polymer will last equally as long, but as the originals are 30 years old, and still good, easiest to simply replace them with the exact same brand and series of capacitor, possibly a higher voltage rating, so as to get another 30 years out of them.

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 29, 2023, 10:51:47 am
content: I have donelotsof ECU capacitor replacements and PCB repair.I just use roughly equivalent families of caps from reputable brands (Usually Rubycon, Nichicon and United Chemicon/Nippon Chemicon)I don't bother with worrying about changing capacitor type, even if the car lasts another 30 years, it isn't hard to just replace the caps every 3 decades.I try to choose long lifetime rated 105degreeC caps and call it good.Usually there are no special requirements on the caps used in ECU's besides physical size, and 30 years on, almost any decent capacitor will be better than what was originally in there (capacitor plague anyone?).

author: Uky
author_rank: Regular Contributor
timestamp: June 29, 2023, 08:37:53 pm
content: (Slightly OT...)I was asked by a friend for advice regarding the stereo system in his vintage car. It did sound awful. Indeed, spare parts was available but very expenceive. I told him that "If you plan to purchase any replacement anyway, at least give the old system a chance by replacing all electrolythic capacitors that you can find. And use high quality components (like 105C rated components). He did a,d reported back that "For a fraction of the cost, it feels like I have a new system!".So not only ECU's can benefit from capacitor replacements...

author: james_s
author_rank: Super Contributor
timestamp: June 29, 2023, 09:10:26 pm
content: I've done this several times, I just use good quality long life rated 105C electrolytics.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: June 29, 2023, 09:59:10 pm
content: Funny, here those are the brands that are failing even the early Panasonic ones.I use Panasonic made after 1990 designed not to physically leak NHG type mainlydepending on whats required.Jeff

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 29, 2023, 11:26:19 pm
content: During the 90's - 00's a lot of these brands were counterfeited and the penny pinching bean counters saw these cheaper fakes used in all sorts of products. Even when genuine caps were used, they were run right up against their rated specs to save a cent or two, hence the well known capacitor plague.Plus these capacitors are now 3 decades old anyway and often the ones you see failed are usually in high stress locations like SMPS, computer mothernoards, the aforementioned ECU's etc.

author: David Hess
author_rank: Super Contributor
timestamp: June 30, 2023, 10:31:55 am
content: The much lower ESR of polymer electrolytic capacitors will cause problems in some circuits, so I would not do this substitution.I might replace them with properly voltage derated tantalum capacitors if I never wanted to change them again.

author: james_s
author_rank: Super Contributor
timestamp: June 30, 2023, 10:52:22 pm
content: Tantalum capacitors in the required values are likely going to be expensive, and in the past at least they were prone to failing shorted. The original electrolytic capacitors lasted 30 years, good quality modern electrolytics should last even longer.

author: David Hess
author_rank: Super Contributor
timestamp: July 01, 2023, 12:11:18 am
content: Quote from: james_s on June 30, 2023, 10:52:22 pmBulk decoupling capacitors chiefly rely on low impedance at the frequencies of interest. The solid tantalum capacitors can have 1/4 the capacitance to achieve the same impedance. They would still be more expensive though, but not by a huge amount.If anything modern aluminum electrolytics seem to last for shorter durations because they are more efficiently designed with smaller volumes.

author: james_s
author_rank: Super Contributor
timestamp: July 01, 2023, 01:20:02 am
content: Quote from: David Hess on July 01, 2023, 12:11:18 amI think they last shorter durations because they're used in much more demanding applications like high power SMPS that were not common several decades ago. You can still get high quality parts that are rated for 10,000 hours or more at 105C.

author: SeanB
author_rank: Super Contributor
timestamp: July 01, 2023, 10:53:30 am
content: The modern ones simplest to move to a slightly higher voltage, which then comes in the same size case as the old one, and, because you now are running it well below spec, will last a long time as well. Was common on telecom systems to see 50V electrolytics used on 5V rails, even if the same capacitor was available in a 16v version, but the 50V one was used, because, even after 30 years in service (typical for most phone systems, they are normally well designed and conservatively operated) they still will be well within all the original test parameters in all respects.

author: David Hess
author_rank: Super Contributor
timestamp: July 01, 2023, 01:20:09 pm
content: Quote from: james_s on July 01, 2023, 01:20:02 amThe reason I say that is that they seem to last for shorter duration in both low and high ripple current applications, including high power switching mode power supplies. In the past there were no point-of-load switching regulators, but there were still plenty of off-line switching power supplies.In low ripple current applications, capacitor size has an effect because of the square-cube law. Larger capacitors have larger volumes of electrolyte to the third power while leakage through the seal only increases to the first power. In high ripple current applications, they have more electrolyte to the third power and greater surface area for heat dissipation to the second power.Older capacitors are less likely to give ripple current specifications for switching power supply designs, but that does not mean they were not suitable, like the old Sprague 30d axial aluminum electrolytic capacitors. And while modern capacitors are more efficient, they are also better specified.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: July 01, 2023, 09:56:15 pm
content: David, yes physicial size is also a factor in failures.Jeff