Builiding of a complete 6kW PV inverter with MPPT chargers


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wiseguy

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Joined: 21/06/2018
Location: Australia
Posts: 1088
Posted: 08:01am 30 Apr 2024      

Roger, the specs on the ST STPS61150CW diode are pretty good.  Maybe Dex should replace his diodes with those based on your experience and if there are still issues copy your (Poidas) chokes.  

I like the "non repetitive" rating given for parts. I am assuming that does not mean never do it again or it will fail, cause that would mean the first experience damaged/weakened the part.

I take it they mean allow sufficient time for any hot spots in the junction to dissipate before hitting it again.

The Absolute maximum of 80A RMS per diode is ~ 110A peak

For a 10mS sine (non repetitive) it is 500A per diode.

So for just the two diodes in one pack they can take a belt of ~1000A for a few milliseconds, which is nearly double the diodes that failed.

Given that Mab also recently had a similar MPPT failure - not uncommon for MPPT units (also not uncommon for Victrons with their expired warranty still in sight...) I decided to read up on what makes MPPTs fail to try to find out what part/s are getting stressed.

I killed a diode and FET in my unit bench testing a while ago, so I got the sense that maybe MPPT failures might not be rare events,
Edited 2024-04-30 18:01 by wiseguy