double pole single throw switch


Postby mistyscamp » Sat Dec 05, 2009 6:15 pm

Hi, I want to put a switch in line on the solar panel that puts a trickle charge into my leisure batteries on my narrowboat. I am told I need a double pole single throw switch but how do I wire it. Any help would be greatly appreciated. thanks
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Postby ericmark » Sun Dec 06, 2009 1:09 pm

Are you sure? Normally solar panels are NEVER disconnected from the battery as it relies on the battery to stop the voltage going sky high.
There are two types of regulator both like wind chargers put any extra charge to what is required into a heat sink. But one has a single voltage and the other has three stages. Because the batteries can also be charged from shore or engine you will normally have blocking diodes between the regulator and battery although these may be built into the regulator.

See this Google "marlec.co.uk/products/windchargers/windcharger-controllers/hrsi-charge-regulator/" web site which details some of the advantages of a stage regulator and warns about need for diodes both to stop power from batteries returning to panel and the regulator trying to sink the main alternator output.

Common to use one regulator for both wind charger and solar panels.

Using a plug and socket to disconnect the solar panel would likely be OK as you are unlikely to unplug by mistake and you would insure it is covered so no light is getting onto it before un-plugging. But with a switch it could be flicked across in error. Two gang and two way with a sink resistor across one way could be an option either a toggle switch DPDT see Google "maplin.co.uk/Module.aspx?ModuleNo=2360" or a grid switch.

But re-check on switching as it can be dangerous to disconnect solar panels from the battery while light is still on panel.
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Postby sparx » Sun Dec 06, 2009 5:14 pm

Hi, the double pole switch has L&N in and L&N out.
simply cut both + & - wires putting them in the top 2 connections & out of the bottom 2 ensuring colours line up top to bottom (assuming you are using a domestic type switch).
regards Sparx
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Postby ericmark » Sun Dec 06, 2009 9:33 pm

With a Son and Daughter-in-law living on a narrow boat in Church Minshull on the Middlewich branch of the Shropshire Union I am interested in what you are doing.

I have a 3Kw inverter ready as Christmas present and it seems this will draw around 2.5A with no load.

So the next step is solar or wind power to keep battery charged while inverter is ticking over in order to work fridge and freezer.

With more than 300AH of battery a small solar panel is unlikely to ever over charge the battery so my son and I have considered just using a diode to stop any reverse current and no regulation. Basically it will just reduce the discharge rather than re-charge the batteries.

Any further panels would then have regulation. However his boat is negative earth and not earth return so only single pole switching will be required. Good job when one looks at size of isolator for the 250A feed to inverter.

As a result I would appreciate being updated as to how your project goes and will watch with interest.

I have also been considering cable sizes and after some thought I think 50mm will be ample for the short run. But can't ask on canal forum as son also uses it and he would work out what he is getting for Christmas.

Both my son and I are electricians and I have done a lot of auto electrics but with narrow boats we are learning a whole new system.

The idea of putting diodes in the earth cables seems totally alien to all we have been taught yet it is normal with narrow boats. But also some people on board the boats seem to have some funny ideas and old wives tales seem to rule with many following the few's lead even when wrong.

Battery charging seems to be one of those subjects with loads of half truths being told. The digital volt meter is a great tool but only when one knows what the readings mean.

So I look forward to following what you are doing. And why you need double pole switch. Do remember this forum checks all posts before release so Sparx likely never saw my reply before he answered.
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Postby mistyscamp » Sun Dec 06, 2009 11:08 pm

Hi, Thanks for the information, Perhaps I should have told you all that the solar panel is only very small and is only used when the boat is moored up for any time not being used. When I cruise I unclip the crocodile clips from the batteries. I recently had the BSS certificate done on the boat and the examiner does not like crocodile clips being used as he says they may flick off, so suggested that I wire the solar panel onto the batteries and put a switch in line so that I can switch the solar panel off when cruising. The instructions on the solar panel say not to cruise with the solar panel attached. I thought this would be a very easy job but am now worried that I have bitten off more than I can chew.
Now armed with the full story can anyone give me any more advice on the best way to do this job. regards
mistyscamp
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Postby ericmark » Mon Dec 07, 2009 11:26 am

Plug and socket is way to go I would think. Crocodile clips as he says can get knocked off and then you can get damage to panel, and high voltages from panel, plus they could short out battery.
The plug and socket should be of a type not used by you for mains supply. There are the cigarette type as used in cars which would then be handy for other items, but I don't like the security of connection on those. There is a variation on them used in wagons still coaxial but more positive but would require a hole to mount. And there is standard caravan type small and flat.
But any plug and socket arrangement would do. Better if pins are shielded so you can't touch by accident.
Some types are here.
Google "maplin.co.uk/Module.aspx?ModuleNo=99505"
Google "maplin.co.uk/Module.aspx?ModuleNo=1055"
Google "maplin.co.uk/Module.aspx?ModuleNo=219727"
Google"maplin.co.uk/Module.aspx?ModuleNo=1027"
There are many more. But don't use any type you also use with mains. Whole idea it can't by accident become disconnected. I would also include a in-line fuse holder i.e.
Google "maplin.co.uk/Module.aspx?ModuleNo=418"
And a fuse of lower rating than cable i.e. around 10A well under the output of solar panel just in case wire is ever damaged so it would not burn out all the way back.
There are many more places than Maplin to get plugs and sockets but they had short web addresses. Only giving an idea. Caravan shop or if you have loads of money a boat shop may also have some suitable plugs and sockets as will B&Q.
If you already have 12v outlets around the boat then go for same type. My son uses Google "maplin.co.uk/Module.aspx?ModuleNo=1054" as fused in plug and will also fit in cig lighter in car. Plus socket has cover on and looks neat.
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Postby mistyscamp » Mon Dec 07, 2009 4:28 pm

Hi All, Many thanks for your comments. I have fitted a double pole switch in line and all seems to be working well, although no sun at the moment on solar panel, lord knows when we'll see the sun again. I'll update if anything changes. regards.
mistyscamp
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Joined: Sat Dec 05, 2009 6:11 pm


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