Electric Advice Please

[Ray]

Not my strong point but I'm learning!

There is a 12v table lamp on my new boat that doesn't work (it is the type with a bar switch that you press as part of the bulb holder)

The bulb looks OK, the cable disappears into the bowels of the boat. If necessary I'll pull up flooring etc to find where it goes and/or try a new bulb anyway.

However as I have one of those screwdrivers with a light in the handle to detect current it seems I should try that first. So do I just remove the bulb and touch the screwdriver to terminals in turn with the switch in both positions? Or what?

Thanks for any advice that stops me doing something silly :)

[OldBerkshireBoy]

12 minutes ago, Ray said:

Not my strong point but I'm learning!

There is a 12v table lamp on my new boat that doesn't work (it is the type with a bar switch that you press as part of the bulb holder)

The bulb looks OK, the cable disappears into the bowels of the boat. If necessary I'll pull up flooring etc to find where it goes and/or try a new bulb anyway.

However as I have one of those screwdrivers with a light in the handle to detect current it seems I should try that first. So do I just remove the bulb and touch the screwdriver to terminals in turn with the switch in both positions? Or what?

Thanks for any advice that stops me doing something silly :)

Please put the screwdriver back in the toolbox.

One of these will find any signs of current in a cable, very useful this time of year for finding where the fault is in Christmas tree lights.

There are cheaper and more expensive versions around however Fluke is a recognised brand in electrical testing equipment.

https://www.google.co.uk/aclk?sa=L&ai=DChcSEwjN07fRnpvfAhXLCtMKHd3oDXQYABAHGgJ3Yg&sig=AOD64_3fZ8MxN4jnAn8sDdsBX7qmDq-1LA&ctype=5&q=&ved=0ahUKEwjzobDRnpvfAhUNNOwKHS1MBk8Q9aACCDc&adurl=

[Ray]

Perfect, thank you 

[OldBerkshireBoy]

2 minutes ago, Ray said:

Perfect, thank you 

No worries.

There is a saying which I can`t completely recall, The Amps xxxx, the watts xxxx and the volts make you jolt! 

[FairTmiddlin]

The Volts make you Jolt

But the mills that Kills

As little as 30Mah across your heart can be enough to kill you

Those little clear screwdrivers with a resistor and a Neon bulb should be outlawed. Don't put it back in the box throw it in the bin and buy a multimeter and watch You tube as to how to use one.

One of the best ways to learn about Electronics is to watch Bigclivedotcom on YT

[Chelsea14Ian]

Think the advise from others helpful,sorry I can't help,I always get a man in.Dont know one end of a screwdriver from another.If it's cooking or food I'm your man.

[Ray]

I still suffer from my childhood affliction of "taking things apart to see how they work" 

I must admit I do get a kick out of fixing something myself, but I'm very careful with my expensive toys!

[Smoggy]

Those screwdrivers work for 240v but not for 12v, throw it in the bin anyway.

Are you sure it's not a 240v shore power light? Patchy knowledge is scary with electrics.

[TheQ]

I did buy a secondhand caravan where the lighting didn't work, I traced the cabling back and found the 12V lighting had been connected to the 240 input....Not surprisingly none of the lighting ever worked again

Until the caravan was rewired and the lighting replaced... They were lucky not to burn the thing down..

[ranworthbreeze]

9 hours ago, FairTmiddlin said:

The Volts make you Jolt

But the mills that Kills

As little as 30Mah across your heart can be enough to kill you

Those little clear screwdrivers with a resistor and a Neon bulb should be outlawed. Don't put it back in the box throw it in the bin and buy a multimeter and watch You tube as to how to use one.

One of the best ways to learn about Electronics is to watch Bigclivedotcom on YT

Hi Nigel,

Some sound advice, 30 ma could kill someone with a weak heart but the industry standard on earth leakage or residual circuit breakers is set at 30 ma as a prevention from death by an electric shock.

Ideally Ray needs to sort out his electrics be they 240 ac or 12 volts dc, table lamps need to terminated into suitable plugs and sockets rather than cables going under the floor. For a 12 volt table lamp you need to use a cigar lighter plug and socket or a none standard plug & socket.

The testers and neon's suggested are not suitable for dc voltages, as already suggested a good multi meter  that can read ac & dc voltages is the best option.

Regards

Alan

 

[grendel]

it might also be worth just checking a fuse hasnt blown before digging everything out.

[Ray]

Great advice as ever, thank you guys. I will test, investigate and possibly end up removing it. But only once I've found where and how it connects into the system.

I'll check for a blown fuse too! It's often the simple things I overlook!

[Smoggy]

It's the description of the switch that makes me think 240v, sounds like the classic table lamp type bulb holder.

If you check with a multimeter check for 240v first and remember it needs to be set to AC as it's the one you need to be more wary of, just because there isn't shore power plugged in doesn't mean there isn't an inverter tucked away somewhere if you don't know the boat very well.

If it is a 240v light it definately needs rewiring via plug and socket and should certainly be fused somewhere along the line whatever voltage.

Sorry if we're treating you like an electrical idiot but the question comes across as if you are not to knowledgable in this area, better to feel insulted than cooked.

[grendel]

It has been known that people take a standard 240V lamp and just replace the bulb with a 12v one

[ranworthbreeze]

7 minutes ago, grendel said:

It has been known that people take a standard 240V lamp and just replace the bulb with a 12v one

I did that with our 12 volt table lamp, I just bought a 12 volt bus-lamp (es 20 watt 12 volt) and fitted a fused cigar lighter plug We use this for subdued lighting when watching the TV.

Regards

Alan 

 

[Ray]

8 minutes ago, Smoggy said:

It's the description of the switch that makes me think 240v, sounds like the classic table lamp type bulb holder.

If you check with a multimeter check for 240v first and remember it needs to be set to AC as it's the one you need to be more wary of, just because there isn't shore power plugged in doesn't mean there isn't an inverter tucked away somewhere if you don't know the boat very well.

If it is a 240v light it definately needs rewiring via plug and socket and should certainly be fused somewhere along the line whatever voltage.

Sorry if we're treating you like an electrical idiot but the question comes across as if you are not to knowledgable in this area, better to feel insulted than cooked.

Not insulted in the least, a little knowledge is a dangerous thing and I have just a little knowledge! 

Maybe one day someone else will ask a similar question and I'll be able to help or at least advise how to be careful 

[annv]

Hi Ray There are two types of screw driver type testers.   to use/test with a 12 volt one you need a black/earthing wire that comes from top of tester, this clips on to a earth point or body of the bulb holder. The other type which is 240v mains has no wire just a metal end that you place your finger on,  the other end you place on the live term/wire if live the little neon bulb glows, this doesn't work on 12/24 dc voltage. you will only get 240 volts ac if you are plugged in to shore power or have a inverter switched on. Any and all switches/bulb holders can be either 12v dc or 240 ac so be careful a voltmeter first switched to 240 v ac FIRST then 12v dc next is safest way. Do you have shore power?. John

[Ray]

Hi John, yes we have shore power and an inverter, this lamp isn't working on any system at the moment but of course it's cable may just end with a plug that's not plugged into anything. To my admittedly untrained eye the wire looks much more suited to 12v than 240.

I do have a voltmeter! I forgot I bought it in connection with the project of fitting a new car radio in my last boat. So my next visit to my boat I'll take it and see what's what. Starting with it set for 240v AC - I didn't know about switches and bulb holders being suited to both 12v and 240v, that is counterintuitive to the uninitiated like me!

[grendel]

if its any consolation we have just been having a discussion in the office regarding the two phase voltages and phase rotation and currents in cables coming from a Schott T transformer, that takes 3 phases incoming at 120 degree phase rotation and outputs two phases with a 90 degree phase rotation- talk about brain bending.

[Ray]

That would indeed be some consolation... if, that is, I understood a word of it 

[grendel]

once they got into the maths of it all, they left me trailing in the dust.

[Ray]

Maths as well!! I'm definitely still at the "don't cut the red wire" stage 

[tjg1677]

simple thing to do. take the bulb out and read the volt / wattage on it. that will tell you if it is 12v or mains.

 

[Ray]

Yep, that's where I started, definitely a 12v bulb and it's not blown. Just no idea where it's power comes from or why it's not working... so far!

[annv]

Hi Ray It likely to be just a corrosion problem, boat builders use crimp connectors and don't grease them with  vaseline/petroleum jelly, first before crimping i have had to reconnect/remake  inumerable connections on boats for this reason, start at fuse board and work your way to bulb with a meter or tester, soldered joints are best but otherwise dip end in vaseline be for crimping with proper crimper,  pliers are no good not enough pressure. John