# a Hella of a thing !!



## mentaliss (Oct 23, 2012)

Ok Ive done something very wrong or its just a coincident, I have extended the ' Mains' system in the MH mainly to create different locations for the socket outlets, not to have more devices..tested said work with polarity tester etc, etc everything just fine. 
I at the same time I extended the 12vlt system with the HELLA type single pole wall outlets and there's the problem...is there a special way the sockets and plugs must be wired as there is no indication which spade terminals are positive or negative ??..Voltmeter indicates all three new outlets 13.8 volts.
I also changed the 'Cigar lighter' type plug on the TV 12vlt power supply cable (used when no mains supply is available) wired that in the HELLA plug using the striped section of the cable to the centre pin...connected to the TV and nothing and now the TV doesn't work at all...I noticed that the HELLA plugs have 8AMP fuse's whereas the TV spec shows 12volt/3amp...good advice would be most wellcome


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## eurajohn (May 9, 2005)

If you use your multi meter to test the socket, so long as you have the relevant leads plugged into the unit i.e. red to red black to black; put the red lead into the supply socket to touch the connector in the centre bottom and the black lead against the side you should then read a figure which will relate to the voltage available if there is a - (minus) sign before the figure you have it wired reverse polarity, which will likely kill your TV or if you are lucky a fuse within it.
Better to test the wiring when connecting, using the same protocol if the red lead from tester is on live and the black is on ground then the display will not show the - (minus)


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## pippin (Nov 15, 2007)

I dunno about your MH but Hymers are really confusing on wiring colours.

The mains stuff is conventional blue, brown, yellow/green.

However the 12V DC wiring has the BLUE as 12V positive and BROWN as the -ve (chassis) connection.

Catches many of us out that does!


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## 113016 (Jun 5, 2008)

Not been a trained electrician, but is not the 13.8 volt showing the state of the battery and you are probably hooked up to mains.


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## eurajohn (May 9, 2005)

Graham, I'd say you are correct ref the voltage shown.
I read the problem to be that after plugging in the TV to a new socket the TV no longer works, which to me suggests the polarity of the socket was reversed.
My suggestion was a way that anyone with a volt meter could check for what colour wires were what (pos or neg)


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## mentaliss (Oct 23, 2012)

Grath said:


> Not been a trained electrician, but is not the 13.8 volt showing the state of the battery and you are probably hooked up to mains.


 thanks ,but definitely not wired up to the mains the sockets are all wired to the 12 volt system if anything I believe the polarity somewhere within the system is reversed!!


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## mentaliss (Oct 23, 2012)

eurajohn said:


> If you use your multi meter to test the socket, so long as you have the relevant leads plugged into the unit i.e. red to red black to black; put the red lead into the supply socket to touch the connector in the centre bottom and the black lead against the side you should then read a figure which will relate to the voltage available if there is a - (minus) sign before the figure you have it wired reverse polarity, which will likely kill your TV or if you are lucky a fuse within it.
> Better to test the wiring when connecting, using the same protocol if the red lead from tester is on live and the black is on ground then the display will not show the - (minus)


 I think your right, somewhere there is a reversed polarity and its dun' the TV in should have tried a basic device first!!


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## eurajohn (May 9, 2005)

He was not suggesting you had connected mains, simply that at the time of test your vehicle was on mains hook up, therefore the battery would have been being charged, hence the 13.8 volts reading.

Rather than trying some other item in the socket test the polarity by using the sequence in my original answer.


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## 113016 (Jun 5, 2008)

eurajohn said:


> He was not suggesting you had connected mains, simply that at the time of test your vehicle was on mains hook up, therefore the battery would have been being charged, hence the 13.8 volts reading.
> 
> Rather than trying some other item in the socket test the polarity by using the sequence in my original answer.


Thanks John for pointing that out to the OP. he didn't understand what I was getting at!
As you were aware, I never said the mains and 12 volt were mixed up, but the hook up lead was in and the battery was charging was my implication.
Hence 13.8 volt. Had it not have been charging, I would have expected 12.7 Volt or lower.


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## erneboy (Feb 8, 2007)

A more basic device might well have worked fine. You need to check the polarity as described earlier, Alan.


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## dalspa (Jul 1, 2008)

The 13.8v reading could have come about if there was a solar panel on the roof (in daylight), and not connected to electric hookup.

DavidL


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## 113016 (Jun 5, 2008)

dalspa said:



> The 13.8v reading could have come about if there was a solar panel on the roof (in daylight), and not connected to electric hookup.
> 
> DavidL


.

Yes it could, very true  
Basically, it is showing charge


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## pete4x4 (Dec 20, 2006)

Sorry to be blunt but it doesn't matter what the rest of the motorhome is doing/wired if you take a multimeter and check that the center pin is positive then the socket is wired fine.
If you can't do that then leave well alone and get someone who does understand.

Like wise when you cut the cigar lighter connector off the cable you would have also have checked which cable is positive and wired it up accordingly. You cannot assume.

Did you by anychance open up the connector to check for any vehicle protection,I don't know what tv you have but some put protection for over voltage and reverse polarity in the cigar plug.

Lessons I feel have been learnt possibly expensively but if you don't have a meter go and buy and check it out as others have already suggested.


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## mentaliss (Oct 23, 2012)

pete4x4 said:


> Sorry to be blunt but it doesn't matter what the rest of the motorhome is doing/wired if you take a multimeter and check that the center pin is positive then the socket is wired fine.
> If you can't do that then leave well alone and get someone who does understand.
> 
> Like wise when you cut the cigar lighter connector off the cable you would have also have checked which cable is positive and wired it up accordingly. You cannot assume.
> ...


 __________________________________________
Thanks for your sympathetic approach to my frustration, the cable indicates the positive conductor via a stripe this was wired to the center pin, since my post I have checked all the installed sockets and plugs and they are as should be which now brings me back to the TV...Don't want to open up the TV or say here what make it is as its going back to the Man' next week (still under warranty) however what concerns me now is, why did the TV blow if the wiring connections were correct .. I'm beginning to question my confidence and ability..I'm going to buy a 'ginnie pig' cheap wired HELLA device to try out the connections before I connect up the expensive TV again :roll:


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## pete4x4 (Dec 20, 2006)

I have loads of sympathy for you, from your last post it would seem that you do know what your doing. Up to that point we were all wondering a bit.
The tv doesn't work on mains either I take it?
Are you still getting 12v out of your modified 12v lead?


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## safariboy (May 1, 2005)

mentaliss said:


> pete4x4 said:
> 
> 
> > Sorry to be blunt but it doesn't matter what the rest of the motorhome is doing/wired if you take a multimeter and check that the center pin is positive then the socket is wired fine.
> ...


There us a good chance that the TV will be OK. It is quite normal (though not universal) to connect a diode across the 12V supply so it shorts the supply and blows a fuse if the polarity is wrong. I have made the same mistake as you but never (so far!) actually damaged anything. There is likely to be a fuse in the 12V TV power plug so try that first.


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## mentaliss (Oct 23, 2012)

still mystified !! rechecked and confirmed center pin in the sockets and plugs are wired as positive, reads 12.15 volts, 12.43 volts on meter, the standard fit cabin 12 volt cigar lighter outputs 14.2v (with the engine running) and the portable 12 volt fan when connected to this cigar lighter works fine, 

Plug the same fan into anyone of the 3 'house' sockets doesn't work at all? :? even though I have already established that the sockets are wired correctly.. ie Volt meter negative black probe to the earth socket band and the positive red probe to the center pin therefore does the fan require more than 12 volts? would the fan's load reduce the voltage supply at the socket/


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## safariboy (May 1, 2005)

My next test would be to check that the plug is connecting properly. I find that these coax plug/sockets often do not. I have one (a small battery charger) that only connects up in one position. If you can get access to the fan wiring after the plug see if there is a voltage there.
The fan is unlikely to be drawing too much current. It would make some effort to rotate.
If it is possible to change the plug/sockets I would get one of the flat pin type from a caravan shop CAK tanks ref EAD403. They are much more reliable.


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## mentaliss (Oct 23, 2012)

*THANKS too you all for your support,* 
Problem resolved  Im not sure if this happens but my theory is that when I tested the current to the sockets/ plugs I kept getting a different voltage reading's sometimes as said in previous post there would be 12 volts and sometimes the voltage would be below 12 volts...odd.. and then by accident I noticed that the 12 volt fuse board was partially lit up by a blown 20 amp fuse......changed it straight away and suddenly all the new sockets became usable..fan works!! so why did I get voltage reading's with the main 12 volt 'house' supply fuse blown.... is it, that electrical current is still within the supply chain even if the main fuse had blown  :?


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## pete4x4 (Dec 20, 2006)

The voltage can come from anywhere typically something that is sensing that 12volts is present, this is normally done via a resistor which will not supply any current but give you a votage.
I think there was another post which highlighted exactly your problem when using digital multimeters, they take no current so can give false readings. If you use an analogue meter which needs some current to drive the meter then it would have shown 0 volts.
I have in the past used a 1k resistor across the terminals of the multimeter to make sure that I'm not being fooled.


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## safariboy (May 1, 2005)

Congratulations. It only goes to show that trying to diagnose faults from a distance is a mugs game.
As for your voltage. My guess is that you were using a small digital meter. You can get odd voltages because they have a very high resistance and so a very slight leak (for instance damp or dirt on the fuse board) onto an isolated wire could give a reading. The damp could be so slight that you did not notice it. When the fuse was in place a minute current will flow but far too small to notice.
The question then is why did the fuse blow. This might have been because of the TV being connected pos to neg.
Anyway enjoy it now.

best wishes

Safariboy


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