12 Volt dilema revisited...

[48Rob]

Okay, I'm back working on the 12 Volt television problem (challenge).

The LCD television came with a 120V to 12V adaptor.


I wired the TV to my 12Volt battery system (and put the adaptor in the drawer).

NOWHERE in the manual, or on the TV does it give an acceptable voltage range.
The adaptor, measured, puts out 12.5Volts

In battery mode only (fully charged battery, charger disconnected) the range is 12.9Volts- 12.1Volts, or thereabouts.
I feel completely safe operating the TV in battery mode, anywhere on that scale.

When the Deltran charger is hooked up to shore power, charging the batteries and providing power to the 12Volt appliances in the trailer, the voltage goes as high as 14.5Volts.

I am unwilling to take a chance on zapping the (not cheap) television.
As yet, mail to the company (in China) has not netted me an answer as to the acceptable voltage range.

So, I have two ideas, but seek input.

Idea #1 is to install a power supply, so that the trailer can be run on battery power, or converter power, controlled by a switch, allowing me to avoid the high charger voltage.
The power supply puts out 13.5Volts, a little high, but closer to acceptable, and more so once a load is placed on it...somewhere around 13V.

Idea #2 is to place 1 or 2 (1Amp) diodes in the line to the TV.
Starting with 14.5V, one Diode would limit the voltage to 13.8V, and two would bring it down to a very safe 13.1V.

Problem with this "fix" is that while it cures the high voltage from the charger, the diodes still act when the charger isn' part of the equasion, such as running on battery power only.
In that scenario, starting with 12.9V, the first diode brings voltage to 12.2, and the second brings it to 11.5.

That seems a little low, but then where are we when the battery bank is nearing 50% discharge...starting at say, 12.3V the two diodes drop the voltage to the TV to 10.9V

Seems like low voltage could cause just as much damage to the TV as high voltage?

Idea #3 is to use the supplied power source for the TV, but, that means switching the TV back and forth from battery power, to adaptor power.
Not an unreasonable thought, but if I have to switch back and forth, I'd rather throw the switch and have reduced voltage throughout.
My DVD player, LED's and future items will no doubt benefit from a more reasonable voltage.

Help?

Rob

[Guy]

Rob,

What about using an inverter?

[Sonetpro]

Rob, I still think you should use a small inverter. $40 and you don't have to worry about it. Constant voltage. Low voltage can do damage to electronics. Just my opinion. That's what I'm doing for my LCD.

[BrwBier]

Since most of the electronics are made by very few company's, why not find another lcd tv with a not in china address and ask them about voltage range. I would think their answer would be suitable for your tv.
Brwbier

[Q]

Rob,

I think it's unlikely that the TV would be damaged by anything up to 15V but who knows? Have you looked at the owners manual, as some manuals give the max voltage in the specs section. If you're unable to get the max voltage specs I would suggest using the silicon diodes. Low voltage surely won't damage the TV.

BTW, what brand and model is it? I have a Casio 4" that works fine up to 15 volts.

Q

[GeorgeTelford]

Hi


Use a mains relay, when the trailer is not hooked up (to mains supply) relay defaults to allowing direct connection to leisure battery.

When mains is present relay switches and routes battery power via the diode set up.

Reasoning, If mains is present I always have my charger/power supply on which means that reduction would be required.

Cheap solution and radio shack or similar outlet will have all the parts fairly cheap. (under $10)

Other solution is small cheap invertor, this does lead to uncalled for losses when not connected to mains supply (it would then be better to power direct and avoid the invertors losses) the plus side is that a small invertor as many other uses, plug in your phone charger, laptop etc.

I would use the relay for the TV on the basis that its cheap and automatic, also is the most efficient system.

[48Rob]

Hello all,

Thank you for your replies.

The monitor is a Chinese model, here is a link to the info.
http://shinmong.en.ec21.com/GC00741343/CA00741372/15.2_LCD_monitor_TV_(SMT-152TW).html
There is nothing in the manual, or on the monitor regarding acceptable voltage range.
A look at other Websites hasn't turned up any useful info.

A classic case of "should have bought a made in USA product...
This monitor was in the $250 range, the monitors with names I could pronounce were in the $700-800 range...

I've considered an inverter, but the excess power consumption makes it a difficult pill to swallow.
I have several inverters, we use them almost daily on the job, and they are handy devices.
While hooked to our vehicles, they provide power in remote locations, and are much appreciated, but there is a big difference between powering them from a vehicle alternator, and a finite capacity battery bank...

George, your idea sound interesting, can you explain further?

I like the idea of a relay doing automatic switching, but do not understand how that works?

I have a friend who is an electronics person who can help, but I'm always up for learning something new!

Rob

[Greg M]

Rob,

Do you know the current draw? If it's fairly low (sub 1 amp), I'd look at a making a simple 12 volt voltage regulator using something like a 7812 regulator chip and a couple of capacitors. Just search the web for 12 volt regulator schematics and you'll find plenty of easy designs. Alternatively, I'm sure there are higher current, premade regulators out there for very reasonable money.

-Greg

[GeorgeTelford]

Hi Greg

The 7812 regulator as a major flaw for our application, the minimum input voltage is 14.5 Volts Datasheets etc here
http://www.national.com/pf/LM/LM78M12.html

The problem with regulators (in General) is that they drop the voltage continuously, ie say you have one that drops from 15 to 12v thats great, problem comes when you are not on hook up they all drop the voltage to a certain extent ie if the charger is off and the battery is at 12.9 it will be regulated down to 12.15 say as the battery voltage drops due to usage at 12.5v terminal the TV would only be getting 11.85 Volts

There was (its out of production now....) a regulator that was close to being servicable, not perfect but the parametors were near enough.

There are some regulators out there, the best priced one I found was £300 about $450 US


Rob

Relay works as follows



This diagram shows a relay at rest ie no power across the coil, this means the TV (number 30 in the diagram) is being powered directly from the leisure battery (number 87a)

Route 87 would have a diode in line, but 87 would not be connected to TV unless there is power across the coil, that power would be mains.

So if mains power energises the coil then the power to TV would be via 87 and the dropping diode.

The above is only an explaination of how relays work, a real mains relay will come with a diagram (usually printed on side of relay) So please those amongst us who recognise the above as a 12v Auto relay bear in mind I used it as a simple example.

Sized correctly an invertor will not waste that much power, (actually a regulator would probably waste as much if not more!!!!) I took a TV, Playstation 2 and DVD player away and ran both for days (5) from one 110 AH battery.

The relay idea would be most economical on battery power as the only loses would occur when connected to mains/shore power......

George

[Guy]

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[48Rob]

Greg, George, and Guy,

Thank you for the advice, diagram, and info!

Hope to have something put together this weekend.

Will report back.

Rob

[48Rob]

Okay, I think I have it figured out




Here is how it goes;

85 Is 12V power supply+
86 Is 12 V power supply negative.

30 is out to television

87 is power lead from the battery bank.
87A is power lead from 12V power supply.

When operating on battery bank, power feed is constant from 87 to 30.
When connected to shore power, the power supply will energize the magnet, disconnecting the battery and connecting the power supply lead.

The diode is to absorb static electricity that builds up from deactivating the coil.

So, all looks good, except...the ground wire from the power supply should also be connected to the television to complete the circuit?

When the relay switches between the positive leads, the ground is still connected to the batteries, but is no longer a complete circuit.

Should it also be switched like the positive wire, or does it not matter?

No negative wires, 120V or 12V are "grounded" to the trailer frame.
The battery terminal is the ground for that system, and the 120V system relies on the ground provided by the campground hookup.

Also, where before I considered using this relay to switch the entire trailer power supply from the battery/Deltran charger, to a separate power supply, I now plan to switch ONLY the leads to the television.

The power supply I refer to above is the one supplied with the TV.
It generates 12.5 Volts.
All other 12V items in the trailer can tolerate the higher voltage generated by the Deltran charger.

So, when remote camping, the battery bank runs everything.
When hooked to shore power, the battery bank/charger runs everything except the TV.

Rob

[GeorgeTelford]

Hi Rob

I take it you are going to use the power from the charger to switch the relay then, you will need one extra diode for that, this is to make sure that the battery doesnt keep the relay permenantly energised,
you can get a 120v relay, which will switch when mains comes in, all based on exactly the same principles,


Negative feed does not need switching, the dropping of voltage is done by the 12v positive side.

[Greg M]

Hi Rob

I take it you are going to use the power from the charger to switch the relay then, you will need one extra diode for that, this is to make sure that the battery doesnt keep the relay permenantly energised,
you can get a 120v relay, which will switch when mains comes in, all based on exactly the same principles,


Negative feed does not need switching, the dropping of voltage is done by the 12v positive side.

It sounds like Rob's using the power adaptor from the TV to power the relay (and the TV when on shore power) so the extra diode won't be needed to isolate the relay from the battery. My only concern (and it's pretty small) is that the voltage from the fully charged battery bank be low enough to not overvolt the TV. That seems pretty unlikely though.

-Greg

ps George. Thanks for setting me right on the 7812. I'm always forgetting to think about the overhead.

[bdosborn]

Rob,

What George is saying is to use a contactor with a 120V coil. That way the relay will switch to the diode circuit when you plug the trailer in to shore power. Pull the plug and the relay will switch back to straight battery power. Get a contactor with contacts that are isolated from the 120V coil so you can run 12V through them. You shouldn't have to isolate the coil ground with a diode. The only thing to watch out for is that electricaly held contactors can be noisy ie. they buzz.
Bruce