TV with a DC PSU

[nirvana]

Stick your recs in here

Sony Bravia KDL-48R550C /48R530C / 48R510C / 40R550C / 40R530C / 40R510C / 32R500C it looks like

And a samsung un32j5003

why is this info useful? you need to prep for the DC future cos AC is poo 

I'm not advocating watching TV, in fact the opposite but it's an important medium for movie nights and watching loonies on you tube, etc

Edited December 23, 2021 by nirvana

[nirvana]

this one looks ok for your boat or your camper or sitting in the basement  Sony Bravia KDL32RE400

 

Edited December 23, 2021 by nirvana

[Libspero]

All TVs are fundamentally DC.

Probably better just to get a cheap one and hack out the transformer and supply DC direct.

If you can find one with an encapsulated power supply that’s fine,  but if you struggle,  it shouldn’t be a major effort to hack one instead..  quite a few YouTube vids on it. 

[nirvana]

9 hours ago, Libspero said:

All TVs are fundamentally DC

sure, is there actually any electrical device without an external psu that don't use a transformer?

interesting idea re just ripping out the transformer, off to look for a 27" monitor that sucks less than 30w lol

[nirvana]

@Libsperoor anyone else, how would you eliminate this power board? it's got like 6 wires coming from it 

 

[Libspero]

17 minutes ago, nirvana said:

@Libsperoor anyone else, how would you eliminate this power board? it's got like 6 wires coming from it 

 

Yep..  That's a bit of a mess. 

Often they have a 12v or 19v input pin you can link up to,  but there's nothing obvious in yours. Perhaps that white connector at the bottom,  but I wouldn't want to bet the farm on it. Otherwise you'd have to find the DC side of the transformer (or ideally downstream of the rectifier) and hack in there.  But that's starting to require some experience and not caring if you kill the TV. 

Perhaps plan "a" of finding a 12 volt TV will be more straight forward..  it does restrict your choices though. 

[nirvana]

2 hours ago, Libspero said:

Often they have a 12v or 19v input pin you can link up to,

that pic above is probs what I've got in an old 24" monitor so no big deal

did a bit of research and it looks like if you have a 12v 'PWR upgrade' connector like in this pic from a JVC you can just wire straight into that (2 pin block centre right).....it's a challenge now to see how cheap I can pick up a second hand tele 

 

Edited December 24, 2021 by nirvana

[The Bear of Doom]

4 hours ago, nirvana said:

@Libsperoor anyone else, how would you eliminate this power board? it's got like 6 wires coming from it 

 

That PSU will most likely have several DC outputs at different voltages, though in some cases more than one wire may be used for each voltage rail in order to increase the current carrying capacity.

With luck, one or both of the boards will have the output voltages written next to the corresponding connector pins, otherwise you would have to work it out by measuring them with a multimeter.

I would only attempt to measure the DC output voltages if you are confident of using a multimeter around live mains supplies! That type of PSU is a switched mode PSU which converts the AC input at mains voltage to DC at 300+V so is potentially dangerous. The high voltage DC is then converted into high frequency AC and fed through a transformer (the square item covered in yellow tape on rhe left of the board) - this allows for a more efficient and compact PSU because of physics and that 

The 0V wires are usually coloured black, but I wouldn't take that as a given. Sometimes the 0V lines are connected to copper traces which surround the board mounting holes so they are electrically connected to the equipment chassis/cabinet, but again that does not always happen.

I would also be very wary about powering up a bare board PSU outside of its equipment (as in the photo), as you run the risk of shorting something out underneath, and depending upon the design of the equipment, the cabinet may offer some protection against accidently touching mains live components.

[The Bear of Doom]

One other thing to add in general, is that if you are serious about adapting something to DC only operation, a service manual with schematics and PCB layouts may be available online and will be of great assistance.

Archive.org have many manuals on their site; manualslib and elektrotanya are also good. Usually a web search on the equipmenr model number will turn something up.

[nirvana]

26 minutes ago, The Bear of Doom said:

I would only attempt to measure the DC output voltages if you are confident of using a multimeter around live mains supplies!

I understand puters, less so electronics and circuit boards lol

so would it be possible to get rid of the main board and feed DC direct into those wires? or am I probs wasting my time?

cheers

[The Bear of Doom]

3 minutes ago, nirvana said:

I understand puters, less so electronics and circuit boards lol

so would it be possible to get rid of the main board and feed DC direct into those wires? or am I probs wasting my time?

Yes, but you would have to work out the required DC supply voltages and provide them all, and with the required current capability.

The tricky bit is if you only have one source of DC supply, say 12V or 24V, and you need multiple supplies such as +5V, +/-12V, 3.3V etc. The easiest way would be to use DC-to-DC converter modules to convert the 12V or 24V input supply to the required outputs. Electronics distributors such as Farnell, RS, etc sell these devices.

[The Bear of Doom]

The difficult thing would be working out the current requirements for each of the DC supplies.

For something like a LCD monitor or TV, the biggest current draw would probably be the backlight. Nowadays LED backlights are used, but previously miniature flourescent lamps (CCFL) were used which, if I remember correctly, use high voltages, either supplied from an inverter running from low voltage DC, or via a dedicated part of the mains PSU. If the latter you would unlikely be able to easily replicate this supply for the CCFL, though you may be able to replace them with LEDs (CCFL to LED replacement kits are available on eBay).

[Libspero]

1 hour ago, The Bear of Doom said:

The difficult thing would be working out the current requirements for each of the DC supplies.

Interesting explanation of switch mode power supplies..  I didn’t know they switched AC to DC then back to AC again before finally converting to DC..  that sounds unnecessarily complicated,  but I’m sure there must be a good reason for it.   
 

I assumed there would be a single transformer then a bridge rectifier to create DC,  then DC=>DC converters for the different voltages.  I had assumed if you injected DC before it got split up you could mimic the output of the PSU..   but from what you say,  I presume this is all happening on a chip now..  so high frequency AC from the yellow transformer no longer goes to a discrete rectifier,  but straight into a chip that outputs the different voltages on individual pins..  something like that?

[nirvana]

1 hour ago, The Bear of Doom said:

The easiest way would be to use DC-to-DC converter modules to convert the 12V or 24V input supply to the required outputs

yeah I'm ok with buck converters....in fact I've just ordered a big bugger from chi-na to make an MPPT with an ESP32...

I was thinking about making the ground floor a 'DC zone'.....I don't live down there so it's an experiment lol

Then extend it to puters, monitors, router etc....but the wiring might look a mess....

[dgul]

When we all need DC TVs to watch DVDs because everything has collapsed and the power grid is down, just go to a few of the majority of houses that are now empty and find a TV that fits the bill.  

[onlyme]

Pretty much all internal power supply boards will produce multiple end use voltages I would have thought, all you really need is to find the rectified voltage on the secondary of the transformer if you really want to convert a board, remove the transformer and replace with a DC power supply in the right range, introducing it where the secondary output was, the transformer will reduce incoming AC down to something accommodating for the DC supplies of off the rectified output. Might as well remove the rectifier diodes too at the same time.

[The XMAS Man]

On 24/12/2021 at 16:45, Libspero said:

Interesting explanation of switch mode power supplies..  I didn’t know they switched AC to DC then back to AC again before finally converting to DC..  that sounds unnecessarily complicated,  but I’m sure there must be a good reason for it.   

Transformer size and overall PSU efficiency.

The frequency of the secondary AC supply created in this complicated arrangement can be varied "on the fly", and is not restricted to the fixed 50/60Hz mains supplies that your electronics is plugged into. 

Being able to vary the frequency of a reconstructed secondary AC supply derived from a rectified and smoothed mains-level DC power bus allows lots of power-saving tricks that aren't otherwise possible.

The most important one being that no matter what the fluctuating current demands of your final DC output(s) are, you'll draw pretty much the same power load (Watts) from the mains regardless of the instantaneous load on the DC output side.

Linear supplies can't do that - as their name clearly implies...

 

 XMAS

Edited December 30, 2021 by The XMAS Man

[Option5]

7 minutes ago, The XMAS Man said:

Transformer size and overall PSU efficiency.

The frequency of the secondary AC supply created in this complicated arrangement can be varied "on the fly", and is not restricted to the fixed 50/60Hz mains supplies that your electronics is plugged into. 

Being able to vary the frequency of a reconstructed secondary AC supply derived from a rectified and smoothed mains-level DC power bus allows lots of power-saving tricks that aren't otherwise possible.

The most important one being that no matter what the fluctuating current demands of your final DC output(s) are, you'll draw pretty much the same power load (Watts) from the mains regardless of the instantaneous load on the DC output side.

Linear supplies can't do that - as their name clearly implies...

 

 XMAS

Same thing with variable speed drives.

[The XMAS Man]

45 minutes ago, Option5 said:

Same thing with variable speed drives.

Yes, I was going to mention those too, but didn't want to frighten the non-electronics people off.

Being able to modify the frequency in any AC power application has always been a "game-changer" in many industries.

 

 XMAS

[Libspero]

3 minutes ago, The XMAS Man said:

Yes, I was going to mention those too, but didn't want to frighten the non-electronics people off.

Dosbods - always educational. 

And welcome back to the fold..  you were missed 

[Option5]

3 minutes ago, The XMAS Man said:

Yes, I was going to mention those too, but didn't want to frighten the non-electronics people off.

Being able to modify the frequency in any AC power application has always been a "game-changer" in many industries.

 

 XMAS

It's also how most EVs operate.

I wonder how many people who buy Teslas have any idea how they work.

[Libspero]

Just now, Option5 said:

I wonder how many people who buy Teslas have any idea how they work.

I don't think I fancy pulling an EV apart..  but I am still interested in the Ops question about circumventing the AC side of modern electronics and feeding directly with straight DC. 

Assuming you could get a multimeter on the DC side to find out the voltage being supplied,  how realistic is it to just bypass the switch mode supply and power up with a dc-dc converter? 

[The XMAS Man]

3 minutes ago, Option5 said:

It's also how most EVs operate.

I wonder how many people who buy Teslas have any idea how they work.

I know this, but must admit that I still don't fully understand "regen" under certain circumstances.

I get it when you're talking about electric cars going downhill and feeding the battery with charge - but when it comes to AC motor drives and solar panels feeding power back into the mains my head explodes.

If only I'd gone to university...

 

XMAS

 

 

[The XMAS Man]

5 minutes ago, Libspero said:

I don't think I fancy pulling an EV apart..  but I am still interested in the Ops question about circumventing the AC side of modern electronics and feeding directly with straight DC. 

Assuming you could get a multimeter on the DC side to find out the voltage being supplied,  how realistic is it to just bypass the switch mode supply and power up with a dc-dc converter? 

From my experience, this shouldn't be difficult at all. And at the risk of getting slated, I think in most cases with modern equipment it would be an absolute piece of piss.

Just don't be a cunt and ask me to get your telly working on 9 Volts right now...

 

XMAS

 

 

[Libspero]

4 minutes ago, The XMAS Man said:

Just don't be a cunt and ask me to get your telly working on 9 Volts right now...

 

Don’t worry,  I’m confident enough to have a bash at it myself if the occasion arises to do so.   Fortunately I know just enough to be dangerous..   

[The XMAS Man]

14 minutes ago, Libspero said:

Assuming you could get a multimeter on the DC side to find out the voltage being supplied,  how realistic is it to just bypass the switch mode supply and power up with a dc-dc converter? 

To add some meat to my previously flippant-sounding post, what you are suggesting there is very realistic in the case of many pieces of modern - and also plenty of vintage - electronics.

We have previously spoke of the AC-DC-AC-DC switched-mode converter, but some posters have already mentioned DC-DC converters, or "Charge-Pump" circuits. These are pretty much the same idea, but without the initial AC mains component. A DC to DC converter actually does DC-AC-DC. None of this is anything new - you would find similar ideas on 1960s battery-operated radios and tellies.

It ultimately depends on what the main DC voltage inside your piece of electronics is. Some will be 5 Volts, some will be 12 Volts. A few might be more weird and wonderful (9V, 15V, 24V) The problem is there is as yet no common DC voltage you can feed into everything - and therein lies your problem. Until a COMMON low-voltage DC Voltage supply is adopted universally, you'll sometimes need to frig around with a multimeter and a soldering-iron.

Unless of course you buy stuff designed to work in caravans. There are TVs from the 1970s that will quite happily work on 12 Volts DC.

Nothing you are proposing would be difficult for me to achieve, but until you can buy equipment that runs from a standard DC supply that all manufacturers buy into, then you are always going to be at the mercy of your local electronics geek if you want to get certain things working...

 

XMAS