Using a 240v switch on a 12v circuit

[Guest]

7 hours ago, Jen-in-Wellies said:

Mains AC switches move the contacts apart over a relatively short distance and rely on the 100 times a second drop to zero to quench the arc between the contacts. Switches designed for DC move the contacts a much larger distance apart as quickly as possible to quench the arc. This is more expensive and harder to manufacture than an AC switch. For higher current DC I have used a 12V 16A DC rated automotive switch in a mains pattress blanking plate, drilled to take the switch. Still looks nice and neat. Alternatively, an automotive relay can be used as described by others. I did this on the bilge pump, where a separate float switch was rated for 2A, but was much cheaper than the high current switches.

 

Jen

This is a good idea. If my mains style switches ever fail on the Gulper etc I will do exactly this. Blanh plates and automotive switches are buttons to buy.
The mains style switches are still going strong for DC use on our boat (almost 15 years old) but as others have said, the quality of mains switches has deteriorated greatly. 

[ditchcrawler]

1 hour ago, catweasel said:

This is a good idea. If my mains style switches ever fail on the Gulper etc I will do exactly this. Blanh plates and automotive switches are buttons to buy.
The mains style switches are still going strong for DC use on our boat (almost 15 years old) but as others have said, the quality of mains switches has deteriorated greatly. 

ours are 18 and no failures yet

[The Welsh Cruiser]

Would it be safe to use a 240v switch to isolate my solar panels from the controller? I can't find a neat alternative with the correct rating. 3 x 125w panels 30a controller. 

[BEngo]

You should be OK with something like an electric shower or cooker switch unit with a good excess of rated capacity over the max likely output of your panels.  Thee tend to be double pole switches and one suited to a 10 Kw shower will handle at least 40 A.   Something higher rated would be even better.

 

I assume you will only be using it to isolate the panels in emergency, when some switch damage will be acceptable or when they have been darkened so there is negligible output to switch in any case.

 

Or use a small switch that looks pretty and a bloody big relay suitably rated- not an automotive 1 inch cube type!

 

N

[The Welsh Cruiser]

10 minutes ago, BEngo said:

You should be OK with something like an electric shower or cooker switch unit with a good excess of rated capacity over the max likely output of your panels.  Thee tend to be double pole switches and one suited to a 10 Kw shower will handle at least 40 A.   Something higher rated would be even better.

 

I assume you will only be using it to isolate the panels in emergency, when some switch damage will be acceptable or when they have been darkened so there is negligible output to switch in any case.

 

Or use a small switch that looks pretty and a bloody big relay suitably rated- not an automotive 1 inch cube type!

 

N

Thanks it's for when I have to replace the fuse between the controller and battery, these wear out every 6 months or so for some reason. The manual says I should disconnect the panels before I do this but other than covering the panels or waiting until it's dark, I have no way of doing this at the moment.

[ditchcrawler]

1 hour ago, The Welsh Cruiser said:

Thanks it's for when I have to replace the fuse between the controller and battery, these wear out every 6 months or so for some reason. The manual says I should disconnect the panels before I do this but other than covering the panels or waiting until it's dark, I have no way of doing this at the moment.

The fuse should not be failing like that, how close is the rating to the current its carrying ? It sounds though it may be to small

[Chewbacka]

1 hour ago, BEngo said:

You should be OK with something like an electric shower or cooker switch unit with a good excess of rated capacity over the max likely output of your panels.  Thee tend to be double pole switches and one suited to a 10 Kw shower will handle at least 40 A.   Something higher rated would be even better.

 

I assume you will only be using it to isolate the panels in emergency, when some switch damage will be acceptable or when they have been darkened so there is negligible output to switch in any case.

 

Or use a small switch that looks pretty and a bloody big relay suitably rated- not an automotive 1 inch cube type!

 

N

If the panels are wired in series so you had an open circuit voltage over 100v dc I think the contact separation would be too small to quench the arc if the switch were opened under load.  So it would handle the current and would isolate if opened with the panels in the dark, but it may not end well if opened under load.

[Flyboy]

2 hours ago, The Welsh Cruiser said:

Would it be safe to use a 240v switch to isolate my solar panels from the controller? I can't find a neat alternative with the correct rating. 3 x 125w panels 30a controller. 

Why don't you use a 40 amp double pole switch and wire the 2 poles in parallel.  You then have an 80 amp single pole switch.

[WotEver]

10 hours ago, ditchcrawler said:

The fuse should not be failing like that, how close is the rating to the current its carrying ? It sounds though it may be to small

You echo my thoughts. 

[Jen-in-Wellies]

12 hours ago, The Welsh Cruiser said:

Would it be safe to use a 240v switch to isolate my solar panels from the controller? I can't find a neat alternative with the correct rating. 3 x 125w panels 30a controller. 

The switch for my solar panels is currently (see what I did there!) a 240V one. It switches 3 x 80W of panels, wired in series to give 60V, so plenty of possibility of arcing when switching off. It has survived so far, mostly as it is very rarely turned off. The switch contacts can take the up to 4A of current no problem when closed, which is more of an issue 99% of the time to prevent the switch overheating. Are your panels in series, or parallel? What voltage and current is the switch going to take? If/when it gives up the ghost I'll replace it with an automotive switch in a blanking plate as per posts 75 and 76. I came up with that idea when working on solar on friends boats and camper vans a couple of years after installing the solar on my boat.

 

Jen

 

Alternatively, only turn the switch off when it is dark outside! ?

[WotEver]

42 minutes ago, Jen-in-Wellies said:

Alternatively, only turn the switch off when it is dark outside! ?

Or after covering them with a blanket/tarp/cardboard/duvet/dog blankets...

[Chewbacka]

7 hours ago, WotEver said:

Or after covering them with a blanket/tarp/cardboard/duvet/dog blankets...

It is a surprisingly small area of each panel that requires shading for the panel voltage to drop down.  Try it and see.

 

Added - if we get a sunny day anytime soon...........

Edited December 19, 2018 by Chewbacka

[WotEver]

1 hour ago, Chewbacka said:

It is a surprisingly small area of each panel that requires shading for the panel voltage to drop down. 

Ok then..,

 

8 hours ago, WotEver said:

Or after covering them with a blanket/tarp/cardboard/duvet/dog blankets, post-it notes...

 

[The Welsh Cruiser]

Regarding the fuse between the controller and battery: It's a 30a fuse. It doesn't blow as such but after a while, 6 months to a year fails to make proper contact and the connection fails. Taking the fuse out and putting it back in solves the problem for a while but a fresh one is better. These are standard blade fuses. When I examine the failed fuses there are ever so slightly grooved where they have sat in the contacts of the fuse holder. 

[bizzard]

7 minutes ago, The Welsh Cruiser said:

Regarding the fuse between the controller and battery: It's a 30a fuse. It doesn't blow as such but after a while, 6 months to a year fails to make proper contact and the connection fails. Taking the fuse out and putting it back in solves the problem for a while but a fresh one is better. These are standard blade fuses. When I examine the failed fuses there are ever so slightly grooved where they have sat in the contacts of the fuse holder. 

I'd clean all the fuse ho;der contacts. Aerosol of Industrial spirit would be best, Remove fuses and Squirt it on and then push and pull the fuses in and out a few times.

[ditchcrawler]

1 hour ago, bizzard said:

I'd clean all the fuse ho;der contacts. Aerosol of Industrial spirit would be best, Remove fuses and Squirt it on and then push and pull the fuses in and out a few times.

Or buy a better fuse carrier

[WotEver]

35 minutes ago, ditchcrawler said:

Or buy a better fuse carrier

Indeed. Use a megafuse which has bolted terminals. 

[Jen-in-Wellies]

1 hour ago, WotEver said:

Indeed. Use a megafuse which has bolted terminals. 

Or a midi fuse, which is probably a better fit for the currents the controller can deliver. Midi fuses use bolt on terminals, similar to mega fuses, but are smaller, surprise! Also a slightly higher capacity fuse, 40A or so would be a good idea. The controller and panels could be producing 30A on a very sunny day. The fuse is just there to blow under a fault condition.

 

Jen

Edited December 20, 2018 by Jen-in-Wellies

[ditchcrawler]

55 minutes ago, Jen-in-Wellies said:

Or a midi fuse, which is probably a better fit for the currents the controller can deliver. Midi fuses use bolt on terminals, similar to mega fuses, but are smaller, surprise! Also a slightly higher capacity fuse, 40A or so would be a good idea. The controller and panels could be producing 30A on a very sunny day. The fuse is just there to blow under a fault condition.

 

Jen

 

55 minutes ago, Jen-in-Wellies said:

Or a midi fuse, which is probably a better fit for the currents the controller can deliver. Midi fuses use bolt on terminals, similar to mega fuses, but are smaller, surprise! Also a slightly higher capacity fuse, 40A or so would be a good idea. The controller and panels could be producing 30A on a very sunny day. The fuse is just there to blow under a fault condition.

 

Jen

And that is a fault with the current from the battery causing the problem, not from the controller. I am sure your cables are rated above 40 amps to avoid volt drop

[Chewbacka]

5 hours ago, bizzard said:

I'd clean all the fuse ho;der contacts. Aerosol of Industrial spirit would be best, Remove fuses and Squirt it on and then push and pull the fuses in and out a few times.

After cleaning a bit of dielectric grease (switch lube) on the contacts before you push the fuse in will keep the oxygen away from the contact area.

[jonathanA]

Dielectric grease ?

 

if not then why not try some powdered unicorn horn or rocking horse droppings....  ?

 

coat....