Is there such an animal as as switch off relay ?

Superaquarama

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5 Sep 2013
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I've fitted a small 12v solar panel to keep the battery topped up.

Instructions say not to have it connected when the engine's charging as well, but inevitably I'll forget to unplug it at some point.

Question is, therefore, is there some relay or device that can disconnect the solar panel automatically as soon as the ignition switch is turned on ?

Maybe it's a simple answer that I'm just overlooking, but any ideas would be appreciated.

Thanks.
 

JumbleDuck

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SW Scotland
I've fitted a small 12v solar panel to keep the battery topped up.

Instructions say not to have it connected when the engine's charging as well, but inevitably I'll forget to unplug it at some point.

Question is, therefore, is there some relay or device that can disconnect the solar panel automatically as soon as the ignition switch is turned on ?

Maybe it's a simple answer that I'm just overlooking, but any ideas would be appreciated.

Thanks.

A relay which opens when energised is called "Normally Closed" or NC (as opposed to "Normally Open" on NO). Any changeover (Single Pole Double Throw = SPDT) relay is both; car spares places are full of 'em.
 

Superaquarama

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5 Sep 2013
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Many thanks, Jumble. Yes, I can see now that a 5 contact changeover relay is the answer, with the ignition switching the relay to nothing. So it seems the connections would be:

30 - in from solar panel
87a - out to battery
85 - negative
86 - to ignition switch
87 -not connected

Am I right ?

Thanks again
 

William_H

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West Australia
a small solar panel will presumably not have a regulator or controller so I can see no reason to be concerned if the panel is connected when the engine starts charging. I know some people who do have panel connected to the engine start battery full time no reg. With a regulator it might be different if regulator tries to regualte the battery voltage by bypassing it (shunt type) it might get hot trying to reduce the battery voltage when alternator tries to get it up. This would depend on voltage settings of course. olewill
 

elton

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Durham, England
I've fitted a small 12v solar panel to keep the battery topped up.

Instructions say not to have it connected when the engine's charging as well, but inevitably I'll forget to unplug it at some point.

Question is, therefore, is there some relay or device that can disconnect the solar panel automatically as soon as the ignition switch is turned on ?

Maybe it's a simple answer that I'm just overlooking, but any ideas would be appreciated.

Thanks.
You want a Schottky diode in the feed from the solar panel. That'll stop current flowing back through the panel when the voltage at the battery is greater than that out of the solar panel.
 

Superaquarama

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5 Sep 2013
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Many thanks for the further replies, everyone. I tend to agree, William, with no regulator it may be unnecessary and perhaps just the mfrs covering all eventualities.

But yes, a Schottky diode would be simpler still ! Thanks, Elton and Beyond.
 
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