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Old 05-12-2012, 01:09 PM   #1
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Power transformer

All our lights stopped working on AC power last night. This morning I verified that the switch and breaker were functioning, then traced the wire and power to these two small metal boxes. On the outside they say "Dry Type Power Transformer 769G"

Under the cover it says Either HV can Be used with Either LV. Under that are two wiring diagrams. One shows 240V on top 24V on the bottom, the other shows 120V on top 12V on the bottom.

I know they convert AC to DC power, but can the be repaired? Can I verify they are working in some way? There is a mass of wires going in and out.

We are in the Bahamas on the boat, we will need AC lighting pretty soon.

Any ideas would be great.

Thanks,
Doug
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Old 05-12-2012, 02:08 PM   #2
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Originally Posted by Dougcole View Post
All our lights stopped working on AC power last night. This morning I verified that the switch and breaker were functioning, then traced the wire and power to these two small metal boxes. On the outside they say "Dry Type Power Transformer 769G"

Under the cover it says Either HV can Be used with Either LV. Under that are two wiring diagrams. One shows 240V on top 24V on the bottom, the other shows 120V on top 12V on the bottom.

I know they convert AC to DC power, but can the be repaired? Can I verify they are working in some way? There is a mass of wires going in and out.

We are in the Bahamas on the boat, we will need AC lighting pretty soon.

Any ideas would be great.

Thanks,
Doug
LV stands for low voltage and HV stands for high voltage.

Not knowing how your vessel is wired I would assume you have AC lighting so:

I would say your transformer is a step up which means it goes from Low Voltage ( LV ) to High Voltage ( HV ). Meaning your input voltage is from ( LV )24V to ( HV )240V or (LV)12V to ( HV side) 120V. Your transformer doesn't convert your voltage from DC to AC, that is the job of the belongs inverter. The Inverter takes the battery voltage and converts it to AC to transform. If there isn't any input voltage ( 12vac or 24vac ) on the LV side you will not get any Output voltage ( 120vac or 240vac ). I would check to see if the inverter doesn't have a fuse blown on that unit.

If you are using shore power your transformer is a Step-down which is opposite of what I just wrote.

Meaning your lights are all DC: I would check your converter that is after the transformer to make sure the fuse isn't blown. In any case I would say the transformer is okay unless you get a strong smell as burnt varnish from the transformer then it will mean the transformer is gone. Very seldom does a transformer open circuits but it does happen so check to make sure all connections are connected to the taps.

The transformer can be repaired if that is the issue but it will take someone to know how to troubleshoot it or replace the core and for the inverter or converter, if it is gone then I would say it is probably better to replace it.

I hope this isn't confusing and it is somewhat of a help. lol I got confused re-reading it myself and when I'm not in a hurry and got some time, I will proof read and make any corrections. I believe it is okay though.

Elwin
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Old 05-12-2012, 04:14 PM   #3
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All our lights stopped working on AC power last night. This morning I verified that the switch and breaker were functioning, then traced the wire and power to these two small metal boxes. On the outside they say "Dry Type Power Transformer 769G"

Under the cover it says Either HV can Be used with Either LV. Under that are two wiring diagrams. One shows 240V on top 24V on the bottom, the other shows 120V on top 12V on the bottom.

I know they convert AC to DC power, but can the be repaired? Can I verify they are working in some way? There is a mass of wires going in and out.

We are in the Bahamas on the boat, we will need AC lighting pretty soon.

Any ideas would be great.

Thanks,
Doug
If they convert AC to DC power, they are more than transformers. Transformers convert AC from one voltage to another or to the same voltage while isolating the output from the input. Transformers cannot convert AC to DC.

Your description doesn't really give enough information for a reliable response and by your description, I am thinking you don't know a lot about electricity. If I were at your boat, I could identify and test them. I am not.

My suggestion - Call in an electrician. You don't want to damage anything and to don't want to electrocute yourself.
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Old 05-12-2012, 05:23 PM   #4
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Thanks Guys,

RW, I'd say my electrical skills are near or just below average for someone who works on an old boat way too damn much. I'm not going to electrocute myself. Plus, calling in an electrician is not so easy in the Bahamas. I tried to give the most detailed description I could, my apologies if I sounded like a simpleton.

My lights are DC lights, which is why I assumed they converted AC to DC power. The problem is the same as it always is with my boat, the wiring is 32 years old, access is very difficult, wire tracing is a total pain.

If there is AC power coming into the boat then the lights will not work on DC, even if the AC switch on the panel is turned off. I'd be happy to live without AC lighting for this trip, is there a simple way to disconnect it so the DC would function when I have AC power?
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Old 05-12-2012, 06:52 PM   #5
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I would like to help you, I really would. And I'm not trying to insult you.

There's no way I can begin to suggest anything that you might connect or disconnect to get your lights to work. Someone has to be there to observe what you have and what has failed.

If you don'y have a volt/ohm meter and know how to use it and what to measure, you're at the mercy of someone who does.
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Old 05-12-2012, 07:31 PM   #6
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I was only slightly insulted.

I have a fluke multi meter, I understand both the ohm function and how to measure both ac and dc voltage.

The problem is that I'm facing a needle in a haystack issue. I'm asking for some direction here as to where to start to:

1. Verify that the transformer is working.

2. If not, find a simple way to disconnect the ac function of my house lights, so that they will work on dc power even when there is ac coming into the boat. Maybe pulling a relay somewhere?

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Old 05-12-2012, 07:58 PM   #7
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I would like to help you, I really would.
I agree, it is so hard to troubleshoot without seeing the schematics etc. You can verify the Tx by checking the output voltage i.e. before the converter. If none, then it isn't putting out and it is whooped, if so, then you will have a voltage reading.

There maybe two circuits for your lighting, a AC for some and a DC for the rest. Again, hard to troubleshoot from way up here in the far North. Hmmm, if you turn off your AC through that switch then the other side of the switch should bring DC from your batteries to your DC light circuits... I think????

I tell you what, if you pay my way down, I'll bring my meter lol.... Just kidding.

I feel I am not a very good help here... hopefully one of the other boats in the area may have a Captain that understands a little about electricity and electric circuits. It just maybe a very simple answer that looks complicated when you don't understand how it all works.

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Old 05-12-2012, 08:29 PM   #8
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Originally Posted by Dougcole View Post
I was only slightly insulted.

I have a fluke multi meter, I understand both the ohm function and how to measure both ac and dc voltage.

The problem is that I'm facing a needle in a haystack issue. I'm asking for some direction here as to where to start to:

1. Verify that the transformer is working.

2. If not, find a simple way to disconnect the ac function of my house lights, so that they will work on dc power even when there is ac coming into the boat. Maybe pulling a relay somewhere?

Thanks
Well then, check the voltage at the input terminals. It should be 120 or 240 volts AC. Check the voltage at the output terminals. It should be 20 or 24 volts AC. If you have power at the input and not at the output, the transformer has failed. Failed transformers usually have a distinctive odor. You're more likely to find an electrician where you are than a specialized replacement transformer.

I seriously doubt removing a relay will make something work.

I don't know why your lights would be "AC". Lightbulbs don't care if they are powered by AC or DC current unless they are LEDs and these would usually run on DC current.

A marine electrician will spend fifteen minutes or less and know what the problem is and how best to fix it. He will also have a source of repair parts.
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Old 05-12-2012, 09:53 PM   #9
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What will the converter look like if there is one?

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Old 05-12-2012, 11:26 PM   #10
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Does the transformer look like this:
GE POWER TRANSFORMER 769 G | eBay

This one shows 120/240V input with 16/32V output but does the case look the same/similar?

Or like this one:
Electrical :: Transformers :: General Electric 9T51B0107 Auto transformer - Mara Industrial Supply: Parts Done Fast



It is possible that someone used the transformer to drop 120ac dock power to 12volts to run the lights. A 12VDC bulb, incandescent type, will run on 12 vac. so maybe that is what was done to avoid running off the batteries/charger when plugged into dockside power. And yes, I just tried it, I have 12Vdc bulbs, an adjustable powerstat autotransformer and a DC power supply and it works. I figured it would but I'd never tried it before, no reason to.

As suggested , if there is no very strong acrid odour from the transformer[s] then maybe it is a blown fuse somewhere. Check the transformer input power AND the output. Just be darned carefull. If the transformer shows 12VAC on the output then you will have to look downstream for a blown fuse, a switch maybe to run the same lights from the DC system when needed or loose, faulty wiring.
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Old 05-12-2012, 11:35 PM   #11
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It looks exactly like the one the first ebay link. There are two of them actually, mounted so close together that I think the wiring runs from one to the other, but I could be wrong about that it is hard to see.

I removed the panels at the bottom, but couldn't find any terminals to poke with my multmeter to test input or output, just crimped connectors and about 6 wires running in. With where they are mounted under my dash, I have limited access.

If I could figure out which wire is running downstream, I could look for a blown fuse. It has the feel of a blown fuse, no burning electrical smell, I'm familiar with that smell.
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Old 05-13-2012, 12:32 AM   #12
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It is possible that someone used the transformer to drop 120ac dock power to 12volts to run the lights. A 12VDC bulb, incandescent type, will run on 12 vac. so maybe that is what was done to avoid running off the batteries/charger when plugged into dockside power.
Ya I bet you are right, the wire size maybe a bit bigger to accommodate that if that is the way it is and there may not be any inline fuse other than the Circuit breaker panel.

I bet there is an open somewhere and that the TX is okay. The best way to verify that the Tx is okay would be to expose the Prim and Sec leads then using your meter check the resistance readings instead of using power. You do not need power applied to check the TX. This will tell you if it is open or shorted.

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Old 05-13-2012, 01:16 AM   #13
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It's possible the two transformers are paralleled to increase capacity however this must be done carefully or some odd and , dangerous results can occur.

Without getting into that can you hear a hum when the circuit breaker is turned on. Even little ones like that will often hum although they may be quite quiet. Can you hear anything? If not then I would question whether or not they do indeed have input power.

There may be another way to do a bit of checking w/o diassembling the wiring. A volt pen will detect AC power by simply bringing it near the wiring. They sense the changing magnetic field around the wire caused by the AC. If it reacts then you at least know the power is at the transformers. I realize you are not at home but it might be worth looking for or asking around to borrow one. If no reaction then there is no power. They are not foolproof but can be handy particularily if you can borrow one.

You may be able to carefully jam the meter probes into the crimps enough to get a reading. I've often done that but BE CAREFULL.

Can you SEE any markings on the wires. Either labels or there should be writing on the Xfrmr leads. They may be hard to read.

T1, T2,T3,T4 are the input or HV side.
X1,X2,X3,X4 are the output or LV side
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Old 05-13-2012, 12:46 PM   #14
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A wiring schematic would be helpful but in lew of that a good photo or two would go a long way, if you have capability to do that where you are. With nothing, everyone is guessing, so here is mine. I'm guessing that your lighting is low voltage, either 12v or 24v. The transformer in question drops the voltage from 120v/240v to 12v or 24v. If your lights are not LED they would run fine on the low voltage AC. If they are LED they would require DC voltage. To get that from shorepower, your low voltage transformer output would then run thru a diode bridge to convert it from AC to pulsing DC. This would run an LED although it would pulse at 120 hz. This would probably not be noticeable, but I have never tried it. If anything else runs off this power, it would likely need a filter )a large capacitor) to convert the pulsing DC to steady DC. You would likely have a power transfer relay to disconnect from the battery source to the shore source if it is available. Do you or did you hear a clicking sound when you connect to shore power?
I suggest you start at the transformer. Do you have 120v (or 240v) AC accross the high voltage leads? If so do you have 12v or 24v AC accross the low voltage leads? If you have high voltage but not low voltage the problem may be the transformer. To confirm this, with all voltage 'off' check the continuity of the high voltage leads with your ohm meter. You shouldn't have more than a few ohms resistance. Do the same with the low voltage leads expecting the same result. If you dont have high voltage, the problem is upstream on the supply side. work your way back checking checking voltage. When you find it, the problem will be between there and next place downstream that doesn't have voltage. The transfer relay, if you have one, would disconnect the battery voltage source and connect the shore power source. I doubt that this is the problem as the battery source would be the normally closed contacts. Shore power would energize a coil which pulls the contacts from the normally closed. battery source to the normally open shore shore source.
This whole scenario seems unlikely though as I would think that low voltage lights would be hooked to the battery only. When hooked to shore power, your automatic charger would carry the lighting load.
There is my two cents worth, now it is time to head to the boat to put on a second coat of bottom paint.
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Old 05-13-2012, 08:08 PM   #15
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OK, A new development. This morning (sorry for the delayed reply inet here is sketchy at best) I followed the input wire all the way into to the transformer, checking for voltage as I went. I had it all the way down.

Next I turned off the ac lighting switch listened closely while my son turned on the switch again. I heard a faint click, no hum. At that point my wife who was in the aft cabin called out "hey this light just started working." I confirmed that all lights are now working on Ac and DC power. I didn't do anything at all, except jam my lead needle into a connector.

I'm not one to look an electrical gift horse in the mouth, but I know this is going to crop up again, I'm just hoping we make it home first, where I can line up an electrician. Of course, now it is working, which makes it harder to trace.

Bad connection maybe? I'm going to change out the one inside the transfomer that I messed with.

My lights are 12V BTW. And now, thanks to you guys, I understand how the transformers work, I think you are all right, they reduce the voltage. I think they are paralelled together, but I don't know why.

My heartfelt thanks to everyone who replied.

Doug
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Old 05-13-2012, 11:41 PM   #16
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Awesome Doug so glad we were of some assistance and that the lights came on, of course that is one of the gifts of being an Electrician, we brighten up everyone's world.

Safe travels

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Old 05-14-2012, 01:14 AM   #17
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The paralleling will increase the total capacity. Each individual transformer may be too small to run all the lights but paralleled, they can.

I won't say it's common practice particularily in small stuff like this, at least not in the stuff I worked on, but I was aware of it.

I'll venture to say some previous owner did this, Probably someone who had these lying about, so used them, rather than buy one larger unit.

Your poking and probing makes it sound like you do have a, one at least, poor connection.

Good that you got them working, at least 'till you get home.
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Old 05-14-2012, 05:53 AM   #18
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Switches lead a hard life , esp one that turns off DC.

Perhaps a small bag of replacement switches would be a start at modernizing ?

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Old 05-16-2012, 09:07 AM   #19
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Installing one or more transformers to run 12 volt lights from shorepower would be a strange way to accomplish this function.

On my boat, and I would assume most others, the 12 volt lights are powered by the batteries on shore power, just as they are when not on shore power.

The battery charger replenishes the power that is used by 12 volt lights and appliances.

Simple and effective.
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Old 05-16-2012, 09:12 AM   #20
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..................... Next I turned off the ac lighting switch listened closely while my son turned on the switch again. I heard a faint click, no hum. At that point my wife who was in the aft cabin called out "hey this light just started working." I confirmed that all lights are now working on Ac and DC power. I didn't do anything at all, except jam my lead needle into a connector.

...........Bad connection maybe? I'm going to change out the one inside the transfomer that I messed with.
Whoever juryrigged this setup probably used a relay to switch from battery power to the output of the transformers. The click you heard was the relay. The previous "non working" of the lights was probably caused by the relay not closing. This could be because of low voltage or mechanical wear of the relay.

Se my post above, this is the easiest way to set up boat lighting. You don't need transformers and relays.
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