125K Multi-Input Inverter: No Paralleled DC Strings Allowed!

If someone calls in with a 125K that used to be running, but now won't start up at all, even though voltages are good, ask them:

  1. How many strings are connected to the bottom of the inverter?
  2.  Have checked the inverter's DC fuses?

DC fuses can blow for a variety of reasons--most of them related to designer or installer error.   But if you have a blown fuse on each and every string and the inverter won't start up, then most likely the strings are being paralleled in the array and are coming in sets of 2x or more down each homerun.  

If they are doing this, then you'll have far fewer homeruns at the inverter than you'd expect for such a large inverter (i.e. 10 or less strings connected to the inverter that the field tech can see).

Important: No paralleling strings before the inverter can ever be allowed on the 125K: the internal DC wiring of the inverter is sized for single strings, and the 20A DC fuses are sized to protect this wiring. The fuses cannot be upsized or the inverter's DC wiring will be damaged.

It is VERY POSSIBLE that we are going to see more cases where people are calling in with this scenario, as the winter changes to spring and the sun's elevation angle increases.  Higher sun in the sky = more DC current = more opportunities to blow DC fuses when the inverter is operating.

If someone reports this scenario, they need to run additional DC homeruns for any/all strings that are being paralleled in the array.  Don't keep replacing the DC fuses--repeated exposure to higher-than-intended current could damage inverter components, and waste a lot of DC fuses.

For any potential RMA cases where a 125K multi-input was subjected to paralleled strings, all details of the case need to be evaluated by senior members of the Solis support team to determine if the inverter is eligible for RMA/covered under warranty.

Victor is the author of this solution article.

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