General > General Technical Chat
Looking for mechanism by which motor run capacitors would be slowly destroyed
<< < (3/4) > >>
jonpaul:
Motor caps are made to JUST meet the spec and lowest cost.

Both film and oil filled caps are available as motor/run/start and lighting ballast/PFC.

Most are rated ONLY for mains freq ripple current.

At 8 kHz or HF, the ESR/ESL will cause higher losses and stress the terminations to foil connections.

The SMPS/HF rated caps have multiple tab to foil and end caps to increase the HF current rating.

Consult the cap mfg specs if HF use above mains Freq is needed.

Jon

CJay:
If I understand your first message, you're using run capacitors designed for continuous duty at 50/60Hz in a non-motor application at 8KHz and asking them to supply 20-40 amps?

Have you considered they just might not be suitable for that use?

Have you measured their temperature under load?

bdunham7:

--- Quote from: johansen on November 01, 2023, 04:22:38 am ---Any other ideas?

--- End quote ---

Use a capacitor that you have complete specs for and is designed for the purpose?  Actually measure the current through the capacitor under regular and "overload" conditions and then contact a product rep and ask them to help you select the right unit?

KEMET C4AQIBW5400M3OJ is a 40µF DC-Link capacitor rated for 28.7A @ 10kHz and it costs $6 in bulk quantities.
johansen:

--- Quote from: CJay on November 02, 2023, 06:29:20 pm ---If I understand your first message, you're using run capacitors designed for continuous duty at 50/60Hz in a non-motor application at 8KHz and asking them to supply 20-40 amps?

--- End quote ---

Not my product, but its an established company that made some changes recently, one of which is they now use toroidal inductors instead of E cores with wide open air spaces. this is leading me to think the inductors saturate much more harder faster and this is why the capacitors are failing much quicker.

But yes the ripple current they have to pass is going to be rather small during the nominal load. product is designed to handle 5 or more times the nominal load for 2-5 seconds, and the only way to do that economically is to just let the inductor saturate.
johansen:

--- Quote from: bdunham7 on November 02, 2023, 07:36:39 pm ---KEMET C4AQIBW5400M3OJ is a 40µF DC-Link capacitor rated for 28.7A @ 10kHz and it costs $6 in bulk quantities.

--- End quote ---
interesting, that's cheaper than many motor run caps.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod