Digital Terrestrial TV Reciver

[JSB]

Hi Folks

Have a TV onboard and decided to go 'Free to View'. Purchased a Sagem ITD 60 and set it up at home. Worked fine from the mains via a 12 vollt AC/DC adaptor supplied. Tried it on the boat direct from the battery, result was a loud click and a smell of burning. I did cut the wires from the adaptor and remade them to the battery. Though I had temporarily lash up to see if things worked I am reasonable certain the polarity was right. Any idea's?

John

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[duncan]

I know it's obvious but you would have had more than 12v from the boat, and up to 14.6 'ish if the alternator etc charging so it may have been the fact that that unit didn't like the voltage. I say that unit 'cos I understand that some (most?) are tolerant of the above range from the posts on here.



<hr width=100% size=1>madesco madidum ..../forums/images/icons/smile.gif

 

[Bergman]

First thought is does your boat have a 24V system - that would probably have done it.

If not then a reversal must be best bet, although I would have hoped that the unit was protected internally against reversal.

Only other thought was the mains unit really 12V.

I suppose its knackered whatever the cause

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[andyball]

easily done- the common adaptor plugs are wired differently from one manufacturer to another.

Will admit that I've done something similar with a mains adaptor onboard - forgot that I'd previously reversed the contacts to power some other item & blew a tv/pc adaptor - oops.

On the other hand- despite click & burning smell you've possibly just blown a capacitor- strangely some gear has sort-of polarity protection ...but after a polarity sensitive electrolytic capacitor - replace that & all ok again ( well, mine was...).

worth a look inside if you can solder.....though if running straight of boat 12V capacitor fairly redundant anyway; so get the polarity right & try it.

Comments over 12V not being 14+V are valid, but wouldn't expect such instant blow-up.

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[rickp]

I'm wondering if I need to get a 12v regulator to power the LCD TV and Freeview box from the cigar socket. Both TV and Freeview box run off 12v and I've got an appropriate cable which gives the right polarity - but of course, it can be a tad more than 12v.

I guess I could try and find a brick that regulates 12v at the required 2amps, to be safe.

Rick

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[andyball]

don't rush & buy one....just 'cos the adaptor says 12V doesn't mean it isn't higher in use. Check it with a meter while the item is on.

If it's really 12V- a regulator is the only safe-as-houses way, alhough many posts here have reckoned no probs running "12V" tv's/digiboxes off 14+.

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[William_H]

The trap with those round plugs about 5mm in diameter with a centre conductor as used for external power for electronics, drill charging etc. is that the centre conductor is not always positive often negative. This may have led you to reverse polarity. it may need proffessional repair if you don't feel up to opening it up yourself. Most mains power pack transformer type have really bad regulation so that the device can cope with up to 15 volts easily however if it is a switch mode power pack light in weight and usually rated for 115 to 250 volts then these give a very accurately regulated 12 volts and the Tv etc may need a regulated 12 volts.
To RickP regarding a brick 12v to 12 v regulator design wise you can use a regulator chip like 7812 however these give accurate 12 v out but must have a min 15 volts in so would be no good on a low battery. The alternative which gets expensive and wastefull of power is to convert the 12v input to AC at high freq rectify it and regulate the output to 12 volts this means that the regulator could give 12 volts out with possibly down to 8 volts in but at low efficiency. If you are going to do that you might as well use a small inverter and the original power pack with similar efficiencies and the possibility of using the inverter for other things. Regards will


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[rickp]

Will - indeed, trying to make a power supply that can both buck and boost is probably beyond my somewhat basic electronics capability.

I reckon my freeview box would be fine, its the LCD TV that is the cause for concern. I may open it up and see if I can find any regulators at the input - and then chicken out and run it on an invertor anyway.

Rick

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[JSB]

Re: Digital Terrestrial TV Receiver

Thanks for the info folks and sorry about the spelling of 'Receiver'. I use a separate battery for TV/Digi box so without doubt it is a 12 volt supply. It looks from the advice that I may have just got the wires back to front. I will open the box as I have nothing more to lose. I will buy another though and will be more cautious.
Regards
John

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[robp]

You're obviously knowledgeable Will but just a word of warning to those who might use switch mode DC to DC convertors. I've buggered up two laptop DC/DC convertors and one battery. Probably by leaving it connected and on whilst engine starting! The service circuit on my boat is still connected to whichever battery is selected. Whatever the alternator put out, the switch mode didn't like it. So it seems best to disconnect TV's, Laptops etc whilst starting the engine. It's easy to forget.

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[rickp]

Well, I can confirm that the Sharp Aqueos LCD TV (albeit with a 'smart' 100v-240v mains adaptor) runs happily from the 12v supply on the boat (even at 14v), as does the Hauppage freeview box.

Rick

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[Guest]

Maybe because ...

its 12V in .....or as in most cases with car socket powered items anywhere between 12.5 and 14V ..... bjut the actual gubbins inside is at 3 or 5v having had the voltage stepped down internally for the electronics. Therefore the difference in 12 or 14V equates to a small amount when stepped down ....

12v to 3v = 1/4

1/4 of 14 = 3.5v

???


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
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[rickp]

Re: Maybe because ...

Sure, that was my thinking too. Its not specifically designed to run from a car socket (unlike the DVD player we have, which is) - the TV specifically says 12v. The PSU brick also kicks out a well regulated 12v - hence the concern.

I guess most regulators that can cope with dropping 12v to 5v, can cope with dropping from 14v too (with a little more heat generated). It all seems to work anyway, so the little horrors can watch TV/DVDs when we don't have shore power (such as the 5 days we were on the Dartmouth visitors pontoon recently, due to the lovely august weather .

Rick

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[Guest]

Re: Maybe because ...

Ive never had trouble with any item that is nominally 12V powered .... and I cannot think of anything more sensitive than PC or radio gear .... (I am most likely completely wrong there !!)

I use inverters, DC to DC convertors etc. and all worked whatever.

BUT it is very true that not all centre pins on plugs are +ve etc. Extreme care has to be taken to ascertain which is which .... often on the adaptor itslef is a little picture looking like a C with an line pointing into its centre .... this tells the polarity of the plug out.


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/

 

[philip_stevens]

Re: Maybe because ...

Nigel,
I have just bought three converters from Maplin. Have a look at UG32K - Universal DC Adaptor selling at £9.99, with a variety of plugs. Input voltage is 12 to 24 volts, with 1.5, 3, 4.5, 6, 7.5, 9 & 12Vdc ±10% fully regulated outputs.

The reason for 3 is for one to feed the Freeview, one for the extra powered speakers, and one for the DVD player.

The LCD TV is on next years wish list - to replace the little 5" CTV.

<hr width=100% size=1>regards,
Philip

 

[Guest]

Re: Maybe because ...

I remember buying one years ago from Radio Shack in States ..... they weren't available over here then ... cost me about 40 bucks .... lasted till quite recently ... in fact I think it still might work ..... but power output was weak ...

I am amazed at what is coming of the shelves now ... you can literally power anything in reason now from the car battery ..... inverters are becoming old hat and nearly defunct ..... at least the batterys are starting to have a rest from that bashing pushing an inverter ....


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/

 

[philip_stevens]

Re: Maybe because ...

Like you, I also bought one from Radio Shack, but the Aussie branch - Tandy - also years ago, and that one is on the boat and still working - well, I blew the fuse in it a week ago, but it's back in business again.



<hr width=100% size=1>regards,
Philip

 

[boatone]

Re: Maybe because ...

Doesnt matter whether you use a convertor or an invertor the device itself will consume some power in addition to the specific application load.
Ivertors dont need to bash the batteries....there are invertors and invertors as with everything else in life. I have a very efficient high quality Mastervolt 300watt invertor that only draws milliamps at rest.

Also, my experience is that low voltage devices actually operate better from their 240v mains supply unit than from a converted DC voltage. Certainly batteries in laptops, cameras, mobiles etc charge much quicker thru the 240volt line than from 12vDC

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[Guest]

Re: Maybe because ...

My Maplins ..... Ever Knight adaptor for Notebook PC charges fine .... not seen necessary to go back to inverter.


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/

 

[nictbrown]

The Sagem freeview box has a mains adapter that delivers about 17v open circuit dropping a couple of volts on load, so the boat voltage should not be a problem. Centre pin is the positive.

<hr width=100% size=1>Regards Nic