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| gilarion Member Since: 05 Dec 2013 Location: Wales Posts: 5117   
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Electrical experts Is it possible to power a 120w 10 amp light bar via an AC transformer?
The reason I ask is that I have a narrow boat that I wish to install a light bar to, the only problem is that I do not have suitable wiring at the front of the boat, just some thin cable that powers a single 12v spotlight and so I thought rather than try to wire 60ft of boat from the stern where the batteries are to the bow with heavier cable, if I could plug in a transformer into the AC supply at the front of the boat provided by the twin alternators via an inverter that might be a simpler option. I will only ever power the light bar with the engine running feeding the inverter. If its possible what transformer would I need. For those who like Welsh Mountains and narrow boats have a look at my videos and photos at.. http://www.youtube.com/user/conwy1 |
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18th Feb 2015 3:54pm |
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| couplands Member Since: 31 Aug 2011 Location: Peak District & Cornwall Posts: 1826  
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You could try and find a high wattage power supply from a laptop. Something like this (but a Google search shows many more) http://www.maplin.co.uk/p/maplin-120w-auto...ging-n63kb
cheers simon |
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18th Feb 2015 4:17pm |
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| gilarion Member Since: 05 Dec 2013 Location: Wales Posts: 5117
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I have been thinking there might be another way.
Just out of interest, and you can tell I am a complete novice when it comes to electrics, especially 12 DC electrics, but could I use a relay and power the light bar from the existing wiring I have that powers a 12v spotlight. The wiring is not that thin it looks to be about the same gauge that you find on car headlights. For those who like Welsh Mountains and narrow boats have a look at my videos and photos at.. http://www.youtube.com/user/conwy1 |
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18th Feb 2015 4:25pm |
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| leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582
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Errr if it is a LED light bar the simple answer is no.
An AC transformer will change the voltage up or down but it will still be AC voltage You need to change your 240v AC to 12 volt DC with a minimum current rating of 12-15 amps. 120 watts at 12v DC = current draw of 10 amps, allow a bit for current surge on switch on etc so need a DC power supply of minimum 12 amps Brendan |
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18th Feb 2015 4:34pm |
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| leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582
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What is current draw of the 12v spotlight? Or power/wattage off the spotlight.
Brendan |
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18th Feb 2015 4:36pm |
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| gilarion Member Since: 05 Dec 2013 Location: Wales Posts: 5117
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I do not know and my boat is at a Marina but I can say that the spotlight was fitted when I bought the boat and is as follows
6" Rectangle Lamp powered by a 12V H3 type bulb, it is used as a tunnel light and works fine illuminating a tunnel but I want something much brighter The other thing the maximum length light bar I can fit on the front of the boat is 23 inches. which will go over the double doors I cannot fit it to the roof of the boat as there is chimney fitted there from the wood burner and is in the way For those who like Welsh Mountains and narrow boats have a look at my videos and photos at.. http://www.youtube.com/user/conwy1 |
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18th Feb 2015 4:43pm |
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| leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582
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Rectangular work light with a H3 bulb is most likely a 55/60 watt bulb drawing about 5 amps.
Yes there are some high power H3 bulbs at 100 watt 8.5 amp but I would have my doubts of those being fitted to a work light. So fitting a 120 watt LED light bar to the wiring of a possible 60 watt light bulb would not be the most sensible option in my opinion. Overloading a wiring circuit is not good practise and the possible consequences could be potentially lethal in the worse case scenario. Have a few words with K9F he does a bit of sparking in slightly larger boats then a canal version. Brendan |
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18th Feb 2015 7:40pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17722 
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Yes, you could run it off the mains via a transformer but only if you rectify the low voltage ac output of the transformer using a full wave bridge rectifier (which will convert the ac to an approximation of a dc supply).
Without the rectifier you'll probably find the light bar glows rather dimly. |
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18th Feb 2015 8:25pm |
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