question

stevie-b666 avatar image
stevie-b666 asked

MPPT 250/100-MC4 VE.Can - Blocking diodes?

Hi...

...as the controller has only a single tracker, I understand the three MC4 pairs are connected as one pair internally.

Are there any built-in blocking diodes within the controller for the parallel connection, or is the expectation that each remote PV array feed is fitted with a bocking diode to prevent backflow?

Just want to avoid doubling up on blocking diodes...

KR

Steve B

MPPT Controllers
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2 Answers
JohnC avatar image
JohnC answered ·

Hi @Stevie_B666

The 3 MC4 pairs only exist because they're rated 30A. No internal string diodes, they just join to a bus. Add your own.

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stevie-b666 avatar image stevie-b666 commented ·
Hi @JohnC


... thought as much.


I'll do victron's design work for them and extend the Charge Controllers mc4 with a set of inline MC4 blocking diodes and thus improve the system's fault tolerance.


KR

Steve B

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Kevin Windrem avatar image Kevin Windrem stevie-b666 commented ·
Many panels, especially those that have paralleled strings, have blocking diodes built in. If they do, the additional diodes will introduce a slight loss you could avoid. It also increases the startup voltage slightly.
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dylan-hyslop avatar image dylan-hyslop Kevin Windrem commented ·
I dont know of any panels with build in blocking diodes?


Most panels have bypass diodes in them, very different thing..

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jetlag avatar image
jetlag answered ·

The module itself is a diode btw. ;-)

Why do you want to put diodes in at all? Because of the reverse current? There should be a reverse current rating given for the modules somewhere in the datasheet or maybe printed on the label.

It might be not neccessary at all to put diodes in the parallel strings as the modules might be able to handle this. And btw, the voltage difference between such pv modules can't be that high to cause such high reverse current in normal situation. I tested this out with my panels.

But if you still want to, then it is always better to use DC circuit breaker instead of diodes.

These inline MC4 diodes are very dangerous. I've seen already some tests on youtube where these diodes went up in smoke and fire. Just imagine, there is 10A continously with ~1V drop across the diode. This is 10W... this will melt you down the plastic housing and can even catch fire.

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