Selecting electrolytics for automotive DIY? - Page 1
Forum section: electronics / projects

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: September 30, 2013, 09:05:58 pm
content: Does anybody have some hard info on what makes a family of electrolytic caps 'automotive grade' or the opposite: Marked 'Not for automotive'?In the very near future I will recap the ECU of my car, a Lexus LS-400. These caps are a known weak spot on these cars, and I suspect a replacement is warranted as part of my own 'extended service' maintenance program.However, finding suitable replacement caps is apparently not a trivial job, if you want to do it properly. Sufficiently small, automotive grade, low ESR electrolytic caps are as rare as hens teeth at the usual suppliers. This has me wondering just how critical the 'automotive' part is?The ECU is in a relatively benign environment, inside the cabin behind a panel. So temperature sensitivity may not be too much of a concern. On the other hand vibrations may still ruin the day, and due to the inaccessible location I'd rather not have to check the ECU regularly for problems. I intend to fixate the caps using electronics grade, non-corrosive Silicone rubber.

author: nctnico
author_rank: Super Contributor
timestamp: September 30, 2013, 09:13:25 pm
content: The ECU in my car has all 63V 105deg capacitors. When ordering check the number of service hours. Some last 1000hours at 105 degrees while others last 10000hours at 85 degrees. For each 10 deg increase in temperature the life span is halfed.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: September 30, 2013, 09:27:07 pm
content: Quote from: nctnico on September 30, 2013, 09:13:25 pmI believe the originals in my car are also 105oC caps. However the caps people recommend as replacements, the Panasonic FR series, are clearly marked 'not for automotive', which had me wondering why. All the ones which are automotive grade, seems to be at least 125oC. If there are no other concerns, then the FR caps should do nicely. Just wondering about vibration and potentially other nasty traps for new players.AFAIK the automotive grade electrolytics are designed to cope with the vibration issue, which is in part why they are physically larger than the 'normal' caps.

author: mariush
author_rank: Super Contributor
timestamp: September 30, 2013, 09:59:19 pm
content: FR series has a high lifetime rating, up to 10000h @ 105c depending on the can size.I don't remember exactly the exact explanation, but some time ago I also heard that the electrolyte used is also a bit different compared to some other very low esr capacitors... less water, more paste like, something like that, which is supposed to help with preventing formation of gasses inside I think.Rubycon has some series of capacitors that are rated for 130c, like the RX30 series - they're available at Farnell. I've used some of these and they're good, but to match the impedance and ripple values you have to choose larger can sizes (for example if you have 1000uF 16v capacitor, you would have to get 1000uF 35-50v version of RX30, which would get close to the specs of the 1000/16).

author: free_electron
author_rank: Super Contributor
timestamp: September 30, 2013, 09:59:29 pm
content: the electrolyte.. electrolyte can freeze ...

author: nctnico
author_rank: Super Contributor
timestamp: October 01, 2013, 09:53:31 am
content: If the ECU is inside the passenger compartment then 105deg. caps will be fine. Vibration shouldn't be an issue either. In some cars the ECU is mounted under the hood and some electronics may even be mounted on the engine itself. Then the story is completely different ofcourse.

author: pgross
author_rank: Contributor
timestamp: October 01, 2013, 10:40:28 am
content: You do not specify whether you're looking for thru-hole or SMD types.I have utilized Nichicon caps for several new projects and recapping (audio- and measure equipment). During my search foralternative and best fit types, I have come across the 125°C BT range from Nichicon, they're specified for industrial andautomotive use:http://www.nichicon.co.jp/english/products/alm_mini/pict_f.htmYou could also take a look at the BX series, they're 150°C andQuoteBest RegardsPeter

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: October 01, 2013, 01:54:29 pm
content: Thanks for the comments, everyone.Quote from: free_electron on September 30, 2013, 09:59:29 pmLowest temperature measured in Denmark, ever, is -31oC, and below -20 is fairly unusual. Hopefully this shouldn't be a problem then.Quote from: nctnico on October 01, 2013, 09:53:31 amYes, this is also the thinking I am coming around to. The ECU is inside the passenger compartment, behind a panel in the RH foot well, toward the firewall. As for vibration, then this isn't an off-road vehicle. It is in fact quite benign as cars go, as you cannot even hear or feel the engine idling when the doors are closed. The only noticeable vibration while driving is what is transmitted through the wheels and suspension from the road surface.I have decided to go with the Panasonic FR caps, at least until I know for certain that larger lead spacings can be used.Quote from: pgross on October 01, 2013, 10:40:28 amI need through hole caps.The problem isn't finding automotive spec caps, but to find some with appropriately narrow lead spacing, plus a sufficiently low ESR to go along with that. If I find the lead spacing is larger than expected, then the situation is a lot more manageable. Appreciate the pointers though, will keep those options in mind.

author: G7PSK
author_rank: Super Contributor
timestamp: October 02, 2013, 02:55:25 pm
content: Quote from: free_electron on September 30, 2013, 09:59:29 pmI found that out with CFL's in outside lamps last winter, the caps froze and burst on 3 lamps one after the other.