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Old 29-08-2012, 13:17   #31
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Re: 110v Lights to 12v / Removing Transformer

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Originally Posted by Ex-Calif View Post
Sara - While the switch will likely work, why the complexity? If you go only 12v and you are at shore presumably your battery charger is plugged in and you have an endless supply of 12v?Forgetting to switch etc. etc.
I had a coupla reasons, but they may not be good ones. Mostly I figured that the lights might last longer. If the 12v charging fluctuations do shorten the life, then running it 'most of the time' on the 110 should use less energy and protect the bulb.

One of these lights will be left on 24/7 most of the time. Old habit left over from my Grandpa. He always left a bulb burning, both to make it difficult for an observer to tell when we were aboard, and to help keep the interior dry.

It occurs to me while I write that, that we are talking LEDs which don't give off the heat an incandecent does, which is how it helps keep the boat dry. So that may not be a useful reason at all.

So maybe leaving the 110 line is gilding the lily? I am prepared to be disuaded from going that route if there isn't really anything to gain by it.

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Originally Posted by Paperbird View Post
What's the model name of the Ikea goose neck lights? We've been looking for some Ikea LED reading lights for the aft bunk.
The light we are using is a wall mounted gooseneck like this table stand design;

JANSJÖ LED work lamp - IKEA

They also offer it in clip on, but I don't see the wall version on the website. They do ahve lots of other desighs for wall mounted reading lights.

Wall Mounted Spotlights - IKEA

I bet any of them would be pretty much the same.

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Originally Posted by Dsanduril View Post

I'm tempted to see if I can find time to hook one up at home this weekend and run it 24/7 at 15V to see what happens as a worst case test. If I can find the time... So many more worthy boat projects to do, but this sounds fun.
Well do tell us how it works when you try it! I am mounting the lights this weekend and installing the new batteries. The electrician is coming next week to do the wiring runs. And then we can try it ourselves.
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Old 29-08-2012, 18:10   #32
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Re: 110v Lights to 12v / Removing Transformer

Well - If I did go with dual voltage system I might try to figure out how to wire all the lights into one "supply" switch rather than each light having a "shore and sail" setting.

That way you only have to remember to throw one switch over.
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Old 29-08-2012, 18:43   #33
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Sara, I did an entire house with A/C LED lights and separate 12v wiring to bypass the transformers. The house ran off batteries but building codes required I wire for A/C. Stranded wire was used for the 12v wiring. I had to put the switch at each light to make the change there. But I didn't use it as much as I thought I would because the inverter didn't seem that inefficient.

On my boat I just eliminated the transformers because I figure if on shore power the battery charger would certainly keep up with the lights. Didn't see why to bother with A/C wiring. However I'm starting to put 7812 voltage regulators on the lights to keep them at a constant output. Don't know if it will save me any juice but at least the lights on the same line as the stereo won't pulse to the music.

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Old 29-08-2012, 18:53   #34
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Re: 110v Lights to 12v / Removing Transformer

What about the heat generated by halogens? Doesn't that represent wasted energy?
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Old 29-08-2012, 19:02   #35
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Re: 110v Lights to 12v / Removing Transformer

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While I haven't studied this thread in great detail, I am sure you will find that the 12 V source will be a DC source. The transformer would only "transform" this to 120 V if the 12 V was AC.
Being an electrician of 30 years, I can tell you that a transformer is two sets of windings that act upon each other, if you put 120 in one side and get 12v out the other side, without studying the circuit............. I am saying to be careful. Think about what you said, 120v ac in and 12v dc out, why would you automatically think it can't be reversed? Not saying it is a definite problem, but one I would check out before someone got hurt.
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Old 29-08-2012, 19:03   #36
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Re: 110v Lights to 12v / Removing Transformer

Halogens are great for providing a full spectrum of light but they are not nearly as efficient as LED's
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Old 29-08-2012, 19:08   #37
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Re: 110v Lights to 12v / Removing Transformer

A 10:1 stepdown transormer with 120 VAC going into it will produce 12 volts of AC, not DC. If you want 12 VDC you then have to rectify the AC.

Why though on a boat convert 12 VDC to 120 VAC and then back to 12 VDC?. THAT is very inefficient because of the energy loss when converting the power.
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Old 30-08-2012, 08:53   #38
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Re: 110v Lights to 12v / Removing Transformer

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Being an electrician of 30 years, I can tell you that a transformer is two sets of windings that act upon each other, if you put 120 in one side and get 12v out the other side, without studying the circuit............. I am saying to be careful......
Welcome aboard Erie bound, good to have you posting on CF and I look forward to more electrical input from an experienced electrician like yourself .

Not sure if you realized but the OP was originally thinking about removing the 110 V AC transformer and using the boat's 12 V DC system to supply the power to the 12 V LED. The OP then considered concocting a switch arrangement so that the LEDs could be supplied either by the boat's 12 V DC system or the original 110 V AC. At no point was a 12 V AC source considered. In fact, I am not aware of any boat anywhere that has a 12 V AC system - but of course there might be one somewhere in the world

Thus it remains impossible for the 12 V DC to be stepped up to 110 V AC by the simple injection of the DC directly into a transformer winding - unless transformers in the good old USA follow a completely different set of rules than that promulgated by the likes of Faraday, Kirchhoff, Maxwell, Ohm, Tesla and so on

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.....Think about what you said, 120v ac in and 12v dc out, why would you automatically think it can't be reversed? Not saying it is a definite problem, but one I would check out before someone got hurt.
Fair call, let's think about it for a moment - 120v ac in and 12v dc out - usual practice would be a step down transformer followed by a diode bridge rectifier. To go from 12v dc up to 120v ac will require a dc to ac convertor followed by a step up transformer. I grant the transformer could be the same one in both cases but I yet to see a diode bridge rectifier that can double as a dc to ac convertor.

Mind you, I did try once reversing the polarity of the batteries in my AM transistor radio receiver and then talking into the speaker to see if it would become a transmitter - it didn't. Disclaimer, I was very very young (single digits), willing to take long shots and still had much to learn
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Old 30-08-2012, 09:13   #39
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Re: 110v Lights to 12v / Removing Transformer

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Originally Posted by Mahaila View Post
I'm starting to put 7812 voltage regulators on the lights to keep them at a constant output. Don't know if it will save me any juice but at least the lights on the same line as the stereo won't pulse to the music.

Ron
Putting the 7812 regulators in line will certainly protect 12 V lights from voltages higher than 12 V, but you also have to consider they will introduce a 2 Volt drop, so you won't even get 12 V to your lights unless the 7812 is supplied with close to 14 Volts or higher. So your lights will last a very long time, but may not be as bright as you would like.

Chip
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Old 30-08-2012, 09:20   #40
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What Ex-calif said is the best way to have both 110 and 12 volt on a single lamp. It eliminates the potential to accidentally run both or any possibility of back feeding either direction.

Edit: just re-read his post. He intended to wire all the lamps on a single source switch. This would be easier to manage but more difficult to initially install.

It would be easier to do it at each lamp by installing a on-off-on switch in the DC side of the lamp. Think of it working like a Y valve or shorepower type of switch. It only allows power from one source or the other and automatically disconnects the unused source.

Source A would be 12 vdc from the built in 110 vac transformer, and source B would be 12 vdc from batteries.

It would be an easy upgrade to add an inline voltage regulator to the 12 vdc battery side so the LEDs are not stressed when batteries are charging at greater than 12 vdc. I think I would wire the regulator into the circuit for all the lamps (maybe back, just after the breaker), that way you only need one regulator.


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Old 30-08-2012, 17:17   #41
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Re: 110v Lights to 12v / Removing Transformer

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Originally Posted by Gene :^) View Post
What Ex-calif said is the best way to have both 110 and 12 volt on a single lamp. It eliminates the potential to accidentally run both or any possibility of back feeding either direction.

Edit: just re-read his post. He intended to wire all the lamps on a single source switch. This would be easier to manage but more difficult to initially install.

It would be easier to do it at each lamp by installing a on-off-on switch in the DC side of the lamp. Think of it working like a Y valve or shorepower type of switch. It only allows power from one source or the other and automatically disconnects the unused source.

Source A would be 12 vdc from the built in 110 vac transformer, and source B would be 12 vdc from batteries.

It would be an easy upgrade to add an inline voltage regulator to the 12 vdc battery side so the LEDs are not stressed when batteries are charging at greater than 12 vdc. I think I would wire the regulator into the circuit for all the lamps (maybe back, just after the breaker), that way you only need one regulator.


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The geekiest way would be to set up a circuit to sense presence of 110vac and autoswitch the entire lighting circuit.

Used to be able to go to Radio shack and buy all the bits to make stuff like that...
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Old 30-08-2012, 19:22   #42
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Lightbulb Re: 110v Lights to 12v / Removing Transformer

I've been buying and hacking the IKEA LED light fixtures for our boat, and I have about 25+ years of electronics career. And, I'm really cheap. So...

The #1 thing to keep in mind about powering LEDs is to regulate the CURRENT and don't sweat the voltage. LEDs are diodes, which will happily pass whatever current you can throw at them. So, the current must be externally limited to a known safe value.

Just about all the "white" LEDs now used for illumination have a forward voltage drop around 2.7 to 3 volts. As someone pointed out, one of the easiest ways to power them from a boat's 12v is to connect 3 in series. Here's a worked example, but please measure and use the appropriate values for your own LEDs.

[math edited out ]

Heck too much typing. Just use this calculator. As a worked example, plug in the following values:

LED diode forward voltage of 2.7v
LED recommended max current of 50 mA
Voltage of 15v
and 3 LEDs will be in series.

The calculator will do this nice little circuit:

+15V R = 150 ohms

... and specify what resistor you use, including power rating.

This will be safe to use, even when the engine is charging. Yes, when the voltage drops down to 12.5v, the current will drop by as much as half, but it's still alot of useable light. Or you can add a switch to change resistor values to give different brightnesses. We've actually found that as reading lamps we can run our IKEA fixtures at less than half of the original current but they're more than bright enough.

As already pointed out, better LED light fixtures will use a proper constant-current regulator so that the current doesn't vary if the supply voltage changes.

If you run a LED at 80% or less of it's rated current value (which is still plenty bright), it'll probably outlive you.

Bonus LED factoid - they're very sensitive to high voltage, especially a high reverse voltage. You can zap them by handling if there's static. I've had a couple of homemade LED nav-light assemblies fail, and my belief is that this was from static entering open connectors when the mast is off, or induced voltages from nearby lightning. When I rebuilt these assemblies this winter, I added one common diode (1N4004) "backwards" across the group of 3 LEDs, so that it will conduct whenever a reverse voltage is present. I also added a small capacitors in parallel with the new diode; this should eat up voltage spikes from static or nearby transient voltages.So far, so good.

[edit #2 - there's nothing to be gained from autoswitching between 110vac and 12v dc powering for LED lights. It's overly complex, potentially hazardous, will not save you energy, and it will be a likely point of failure... a weak spot. Put a bit more money into a slightly better charger instead. ]
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Old 31-08-2012, 15:55   #43
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Hmm I looked at the jansbo light, but the transformer showed a 4v output. So I wasn't sure how to use them in a 12v circuit. I really liked the light and was disappointed when I read the output voltage.
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Old 31-08-2012, 16:04   #44
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Re: 110v Lights to 12v / Removing Transformer

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Hmm I looked at the jansbo light, but the transformer showed a 4v output. So I wasn't sure how to use them in a 12v circuit. I really liked the light and was disappointed when I read the output voltage.
wire three of the 4v fittings in series,maeans you will havto have 3 lights on at a time but gets them to work of 12v
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Old 31-08-2012, 16:41   #45
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Re: 110v Lights to 12v / Removing Transformer

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Hmm I looked at the jansbo light, but the transformer showed a 4v output. So I wasn't sure how to use them in a 12v circuit. I really liked the light and was disappointed when I read the output voltage.
Well, that's the most important part of my oversized post above - the voltage doesn't really matter, just the current. If you don't have a current spec, then you can cut into the line feeding the LED, insert a current-reading meter, read the current when the LED is on, and that's your spec. Also measure the voltage across the LED itself, so you have accurate numbers to calculate with.

You plug these numbers into the calculator I linked to, to find the resistance needed for one or two of these LEDs in series and powered by the boat's 12v.

if any of the above was Greek to you, you will likely need help to complete this.
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