Breaker / Fuses MPPT-Solar Panels?

[andreas.mehlin]

reading manual from morningstar about my MPPT.

They say I must have a breaker/fuse between both solar panels and mppt & mppt and batteries.

Are you all people doing this too? Or is it just the formal way to do it?

[GeoPowers]

Originally Posted by andreas.mehlin

reading manual from morningstar about my MPPT.

They say I must have a breaker/fuse between both solar panels and mppt & mppt and batteries.

Are you all people doing this too? Or is it just the formal way to do it?

Yes, that is how I set mine up. I used breakers for both, with the breakers as close as I could to the panels and the batteries, respectively.

Frank

[witzgall]

Yes, you need both. To protect the panels, and to protect against a short that could start a fire between he controller and the batteries.

Chris

[Albro359]

Agree...that's my setup too

[Paul L]

What good is the breaker on the solar side going to do? If you have for example a panel that will put out max 20amps, you have a cable that can take max50 amps and you use a breaker at 25amps. If the able gets a short, the panels will never go above 20amps, so the breaker will not trip.
The breaker on the battery side makes sense, as much larger currents are available.

[witzgall]

As I understand it, it protects the panels. A short could damage the cells, or the diodes.

Chris

[Paul L]

Originally Posted by witzgall

As I understand it, it protects the panels. A short could damage the cells, or the diodes.

Chris

Breakers don't trip because of a short, they trip because of current passing through them that exceeds their rating. Where is this current going to come from if only the panels are available to supply it?

[djmarchand]

I agree with Paul L and I don't believe that shorting a solar panel will harm it. Does anyone have any specific references to support this view.

If correct, the breaker would have to be sized just right: high enough to pass the I maximum power point but low enough to trip at I short circuit. On a Kyocera 135 watt panel, there is less than an amp difference between the two. What kind of breaker is going to deal with that?

David

[goboatingnow]

PV panels are a current source, they can't be affected by a short.

Dave

[s/vPainkiller]

Blue Sky's installation guides appear to have a fuse between the controllers and the batteries, but not between the solar panels and the controller. Not sure what other mfg's require, but since I have a Blue Sky unit in transit from SALT Service I plan on installing per their manual. YMMV....

Scott

[GeoPowers]

Originally Posted by Paul L

What good is the breaker on the solar side going to do?

It makes it pretty handy to isolate the MPPT controller for maintenance and/or isolate the panels as a power source in case you are generating power from other sources.

Frank

[Paul L]

Originally Posted by GeoPowers

It makes it pretty handy to isolate the MPPT controller for maintenance and/or isolate the panels as a power source in case you are generating power from other sources.

Frank

You still have the breaker between the MPPT and the batteries to shut off power source to your system. What we are talking about here is another breaker between the panel and the MPPT controller.

[ExRonin]

As commented on other threads I recommend installing a relay (30A auto style) between the PV and the MPPT. This not only allows isolation of the MPPT for maintenance, but also allows the solar regulator to be turned "off" to prevent conflicts with other regulators (shore charger, alternator, etc). As far as am breaker or fuse between the MPPT and the PV this makes no sense as commented by others. Fusing between the MPPT and batteries IS important.

[GeoPowers]

Apparently it makes sense to MPPT manufacturers such as Morningstar and Outback. The relay and breaker or fuse support the same notion, but I would check the max operating voltage of the auto relays carefully as they are sold for 12V systems. My system typically puts out 85-95V, with a Voc higher than that. When I looked into this I found a few around 27v, and the max operating or "switched" voltage I could find was 50V.

[ExRonin]

GeoPowers

Fair point on voltage rating for the relay. I typically deal in 12V systems with 17V or so output panels in parallel, where a 30A auto relay is absolutely appropriate. In higher voltage systems, a more appropriate relay, such as an Omron (available from Digikey.com) can be used. Further to my prior post, here is a sample system diagram: