bgkh.sail ,
How strict are you on the physical dimensions? A rule of thumb is to not go larger since components in closer proximity on a board will generate more heat, however in some cases can be beneficial to go larger to gain better specs from a part. Polymer is generally better, however the ol’ electrolytics have been around for much longer and typically have more options available which may provide better specifications.
As Michael_Rudi suggests, if you are staying within the specifications rating whether that be temperature, voltage, current etc… choosing the part with better specifications would typically be best. However be sure to analyze the datasheet testing parameters as this will give specific details of their tests, and sometimes the tests can be done at lower ratings which may be stemmed from a marketing point of view to prop up the part. It is a good idea to leave head-room as well on these specifications, since sometimes a board may have unknown issues such as noise/voltage spikes or other design or age related problems that cause stress on other components.
Here are some DigiKey part offerings:
Polymer - 227ALG050MGBJ-ND
Electrolytic - Click Here
Notes to consider:
- Stay with automotive rated / AEC-Q200, these are designed/tested for temperature fluctuations and approved for automotive use where regular parts are not.
- Don’t allow things that are designed to move, “sit”. There is a great article regarding capacitors and their shelf life in This post - Why do electronic components have a shelf life?. Clicking on the Capacitors section, teaches the importance of not letting a capacitor be unused for long periods of time which would include receiving “new” product of which may have an expired date code from an untrustworthy distributor.
- If the capacitors are puffed, you most likely need higher voltage rating. If the capacitor is dried out, this is most likely a temperature issue but of course can be an amalgamation of various issues.
- “Lithium Capacitors”, or LICs are not recommended unless your capacitor replacement calls for this type specifically since it contains a lithium-like battery structure. More on that type of capacitor/battery is found here.