Solar ON/OFF switch for 60volt system?

[tulsag]

I have 3-85watt, 20volt solar panels in series (60 volts) down the port side of the bimini and 3-85 watt panels in series (60 volts) down the starboard side. Both sides are then joined in parallel. I want to install an ON/OFF switch between the panels and the controller so that I can shut-off the solar panels if I need to during daylight hours.

The problem: Blue Sea makes 'battery ON/OFF's switches' but they are only rated to 48volts.

1) Is that important? (The amps rating for the switch is 300amps, so will I be fine running 60 volts @ 5amps?

2) Should I be worried that 60volts is too high for a marine system?

3) If my system is fine, who sells ON/OFF switches for 60volt ratings?

4) Does the black line (negative) need to be severed also, or is just running the red (positive) through the ON/OFF Ok?

Mark

[noelex 77]

Yes, this is a significant problem that is largely ignored by people installing solar systems. I have seen many potentially dangerous installations.

Switching (or providing over current protection) to very high voltage alternating current systems is not difficult. The voltage cycles through 0v and this naturally extinguishes the arc. Low voltage DC (12 or 24 v) switching is also easy. The voltage is too low to support a large arc. This lures people into thinking higher voltage DC circuits are also simple.

High voltage (200v +) is very difficult to switch. Solar panels operating at 60v DC are a bit between these two extremes. Don't assume a switch, fuse or circuit breaker rated for 250v AC is fine at 60v DC. Generally it is not.

Unfortunately, switching or providing overcurrent protection to high DC voltages is very good at starting fires. I think some marine solar installations are quite dangerous in this regard.

The best policy is check the DC rating of any switch or circuit breaker used. High voltage DC circuit breakers (which both act as switch and provide over current protection, although there is arguably little need for the latter) are available but they take a little finding.

Parallel connection of solar panels is generally better for shade tolerance so this may be a better option in your case, but many boats are using high voltage solar panels without an option. Unfortunately often the installation does not give any thought to the dangers and specific requirements associated with higher DC voltages.

[hellosailor]

Mark-
I would try DigiKey, Mouser, and Newark Electronics. All major electronic parts suppliers, all excellent tech support online or by phone. Let them knew the power ratings that you need, and that you probably should need water-proof switches or a waterproof enclosure for them.
The alternative would be high power DC connectors, similar to those used by tow trucks for commercial battery jumping or in theatrical lighting, something to physically unplug rather than a conventional switch. Somewhere in there, should be something rated for the job. If you can't find anything...use proper fuses and just pull them if need be.

[Frankly]

Mark considering that a solar panel string is current limited, exceeding the DC rating of a battery switch by a reasonable margin would not concern me. Breaking HV DC can be problematic in a lot of situations but just would not expect a problem in this case. I have the small two pole Blue Sea Battery Switch in my system (haven't installed the panels yet) and it only carries a 30V DC max rating. Contacts might pit a bit with a lot of use but just don't see a big explosion or continuous arc coming.

Obviously the "letter of the law" mentality crowd will not be happy, but I have been at this for a long time and just wouldn't worry me.

Be sure to fuse the feed between the controller and the battery bank though.

[noelex 77]

I hesistate to use YouTube to support my position, but I think it is important that people understand the difference between interrupting DC and AC voltages. These videos are at a higher voltage than boat solar installations. 220v DC for the first, but the current is not high. The second is at 380v Dc with a polarised DC circuit breaker installed the wrong way around.

https://m.youtube.com/watch?v=Zez2r1RPpWY

https://m.youtube.com/watch?v=Cup5fMGaE2g

60V DC is very different to 220v DC, but it is also very different to 12 or 24v DC or to 220v AC. These videos are not an accurate representation of the effects of 60v DC, but nevertheless I hope they convey the message that higher DC voltages are not easy to interrupt and arching DC is good at starting fires. Do not try to interupt (switch, fuse or circuit breaker) With devices that are not rated for these voltages, the current generated by solar panels is enough to produce these effects.

Boat solar installations are moving from relatively low voltages to higer DC voltages. People with experience dealing with 12 and 24V DC often treat these higher voltages in the same way, with the same equipment. Some caution is needed to make sure the equipment is suitable. The good news is that solar regulators transform the higher voltages of solar panels down to battery voltages so these concerns are only upstream of the converter.

[Bleemus]

Nice videos! I have four Kyocera 140w panels with each two in series to a bus bar. Open circuit voltage is 22.1v per panel if I remember correctly. If I put the following Blue Seas switch in the positive line from bus bar to battery would I be asking for trouble? It is rated 48v DC.

http://amzn.to/2yXcJcC

[noelex 77]

Originally Posted by Bleemus

Nice videos! I have four Kyocera 140w panels with each two in series to a bus bar. Open circuit voltage is 22.1v per panel if I remember correctly.

22v is not a concern. The potential is not enough to support a significant arc.

All, or nearly all marine switches, fuses, and circuit breakers are fine with 22v. However, wiring them in series you have 44v. This is getting closer to when you need to be careful. Fortunatly, it is not difficult to find marine switches rated for this voltage. Above 50-60v is when it becomes more difficult.

Some boats are now installing solar systems with voltages above this threshold. Often they note the device is rated up to perhaps 250AC and assume, incorrectly, that perhaps 60V DC should not be a problem.

[Bleemus]

Thank you noelex. I thought i had done my homework but your video links were quite illuminating.

[sailormed]

You can get the xorrectly rated DC interrupt breakers at most of the home solar installation shops. The difference between an AC and DC switch is the installation of a magnet that diverts the arc away from the opposing contact surface.

[noelex 77]

Originally Posted by sailormed

You can get the xorrectly rated DC interrupt breakers at most of the home solar installation shops. The difference between an AC and DC switch is the installation of a magnet that diverts the arc away from the opposing contact surface.

The magnetic field is one way DC circuit breakers deal with quenching the arc.

These are polarised DC circuit breakers and are an excellent solution. They need to be wired the correct way. In a solar installation the wiring direction is not obvious, and it easy to wire them the wrong way around, so follow the directions carefully.

There are non polarised DC circuit breakers that can still deal with reasonably high DC voltages. All these higher voltage DC breakers or switches are somewhat specilised items not usually sold in a marine, or electronic store, but not hard to obtain if you know what to look for.

Once again, this is not a concern for 12 or 24v DC, but above 50-60v DC it is something that you need to consider.

[Boatwright]

Circuit configuration matters:

No matter what the rating is on the switch, the correct procedure when disconnecting solar panels is to disconnect the load first.

No Load = Open Circuit = No Current (amps) = No Arcing at the panel switch and panel wiring connectors. Unless the panels are connected to a load or short circuited there will be no current flowing

The reason to have a panel disconnect switch is for convenience and safety when working on the system, or to simply disconnect the panels when away. It saves having to wrestle with the cable connectors.

Always disconnect the load between the controller and the battery first, and then any quality marine rated master switch will do the job fine. You do want the heavy conductors in a hd switch to carry the full panel output current, but switching arc is really not a real world problem if you are following correct procedure.

That said, DC arcing can be dangerous. A panel array of 60 volts @ 20 amps will produce an arc one could weld with. Be careful and follow procedure.

[ccannan]

Use an appropriately rated CB instead of a switch.

[Dsanduril]

As Noelex has noted, the whole problem with switching DC is quenching the potential arc. AC is easy, voltage goes to zero 50 or 60 times a second and the arc quenches itself.

For large DC installations most manufacturers go to a multi-pole switch, this allows each pole to be rated for a lower voltage but the overall assembly to be rated for the sum of the pole voltages. The poles get wired in series, and, critically, the operating mechanism must open all poles simultaneously. So, if you can get a two-pole switch rated at 48V you could rate that at 96V by going through the poles in series - as long as the poles operate simultaneously.

Quenching DC arcs is big business in utility solar, once you get above 48V you really have to be careful.

And yes, if you can drop the load first that is best, but some controllers won't like you just opening a switch, and, if you have a switch located on the supply side it should be rated for load-break in case someone forgets to disconnect the load side first. In industry we do use a lot of non-load-break switching (for safety disconnects, etc.), but they are interlocked so that they can't be opened when loaded. Unless you can arrange interlocks your supply switch should be rated for load-break.

[a64pilot]

I went simple, one 20 amp fuse for each 250W panel. 35V panels I believe or that is what I see on the controller anyway.
I have them in parallel and connected in a combiner box, that is where the fuses are, I can disconnect panels individually if I want to.
Incidentally the combiner box also has a lightning arrestor, although I do not put much faith in one myself, but don’t see how it could hurt.

[Boatwright]

"And yes, if you can drop the load first that is best, but some controllers won't like you just opening a switch,"

After talking to several techs with solar equipment suppliers, I believe this is based on poorly written manuals and simple confusion. There is no functional difference between turning off a switch at an appliance or fixture or disconnecting the circuit feeding same.

When questioned all the techs agree the problem is with disconnecting the PANELS under load.

I am also wondering why the original poster to this thread sees a need to turn off his panels during the day other than for servicing. The controller will automatically control charging current and when your batteries approach full charge your controller will taper off the panel's input without the need for any manual switching.