LCD questions/ voltage

dreadshawn · 03-27-2006, 01:59 AM

So far it looks to me that there are only the three types of LCD's in the stickies are around on this forum, but I'll try anyway...
My LCD's that are set to arrive soon are the Power Acoustic PT-700MHR, and can be found anywhere with a search. It seems to be a nice little TFT LCD, and I am looking forward to installing it. When I come across sites like this that make extensive diagrams of how to regulate the voltage that the screens recieve, I am therefore curious as to which screens in the market does this apply to. Are most screens built without an internal regulator that governs the input voltage? Is this a problem that every installer must face?

If there is a website that I can be directed to to find all of my info, I will gladly go there and stop it with my dumb questions, but I have yet to find them.

Are there complete modules that can be used for this purpose? Is it specific to only the listed LCD's? Is mine exempt from these actions? I am not nervous about doing this, I just want to avoid unnecessary actions here. If my LCD already governs input voltage, why add these componenta from Radioshack?

Thanks for reading, and I hope to get to the bottom of this soon...

P.S.; my HU is going to be the JVC KD-AVX1, which came highly recommended.

Motorcity · 03-27-2006, 02:19 AM

The reason for using a power adapter for an lcd monitor is simple: Regulation.
Not as in a requirement, but as in protection by supplying a constant voltage.
Most lcd monitors sold for automotive use can handle automotive voltage safely and there is some sort of regulating going on internally. There has to be. LCD panels in general need 3.3 or 5 volts to operate, and only need this to be a few milliamps.
But, as I am sure you have seen plastered all over here and possibly other forums the failure rate among lcd monitors in the automotive world is quite high. Why? because they are being fed Unregulated power. A car typically outputs 11.5 to 14+ volts DC at any given moment. This constant fluxuation of voltage is death for electronics. Most can handle .6-1.2 volts in either direction over a short time, but the constant up/down of the voltage roller coaster that some of these monitors sees is simply more than they can handle.
By using a Regulated power supply, you are providing a smooth, constant, true 12 volts to your equipment, and thus ensuring that you won't be sentencing your LCD monitor to an early grave.
Now you may be wondering, why don't other automotive electronics suffer a similiar fate? They don't require a regulator or power adapter right?
Well, yes...and no. Car audio, and electronic components in your car have regulation built in. This regulation is much better circuitry, and, with the exception of the audio equipment, most of the componets don't draw enough amps to be a problem, so onboard regulation does not require much in the way of circuitry, electronics, etc.
So, IMO, to be safe and to protect your investment, use a dc-dc power adapter, a voltage regulator, or a dc-dc power supply.
Depending on what all you plan to run in your car, a single source will provide enough available amps to run several components.

alti · 03-27-2006, 02:28 AM

I depends on the individual electronic component that you are using, input voltages vary, one screen or electronic device might accept between 8v and 12v input, a car will usually produce 13.somthing v while running, and can sometimes spike depending on conditions.

If the specs for your screen say it can work with a wide range of voltage that you might encounter in a car then you can probibly get away without extra regulation. Personally i would always use regulated voltage.

dreadshawn · 03-27-2006, 10:20 AM

My LCD's input is listed at 12VDC, which I take to mean 12 Volts of Dedicated Current. Whether it can function properly under more or less, that is what I do not know. Hopefully my LCD's will come in with a manual that will better explain their capabilities. If anyone has experience with PA LCD's, their input would be greatly appreciated. I think that I am going to call up some audio/video companies and ask them about this. Thanks a bunch for the help, I appreciate it.

I just realized something... Since most LCD's are designed to run off 12VDC, and most DVD/CD players try to force you to ground off on the E-brake for the DVD's to play; perhaps all these are interconnected as a bastardized attempt by the companies to prevent any video from being played while driving (reducing liabilities, of course). Most cars jump to 13V-14V when on, and a hard-wire to a battery will sometimes cause problems with the LCD's recieving too much voltage, since most seem to have no internal voltage regulator.

Does any of this make sense? The whole thing is to prevent us from letting our friends and family watch movies/play games while driving... This will not solve my problem, as my car runs at 13V+ even when not running (chalk it up to a kick-butt alternator, lol!), so a hard-wire with these types of LCD's is forever out of the question for me. So there are no modules specifically for this problem. Well, time to enlist some nerdy friends of mine to help out with the upcoming "solder-fest.."

What would be a good power supply for powering 3 LCD's? I don't mind hardwiring a PSU to the battery, but what should be the output voltage/amps? Some of the ceaper ones are a 12V/15A; and I am not sure if that is overkill or not... Are there car-specific PSU's? On to more searching...

dreadshawn · 03-27-2006, 11:36 AM

Cool, I found a neat little power supply from Opus Solutions, and they have a DC/DC supply that is rated at 12V/5A output; and a quick call to Opus showed to me that The 80W model would be the best option for powering three LCD monitors, and the overall cost on their site is $72.00 without a case (circuit board only). They even provide the wires and the wiring diagrams to help clarify things a bit, and the rep. on the phone was really nice in answering all of my inane questions involving switches, splicing, grounding, etc. I will certainly shop around for a better price, but this guy seems like a good option. What do you think?

alti · 03-27-2006, 11:53 AM

that is a good option, and should handle the needs you have. It also has many other other features (delayed / triggered shutdown ect) and that is why the price is higher. Nice features to have though.

Motorcity · 03-27-2006, 01:08 PM

Quote: Originally Posted by dreadshawn

Hopefully my LCD's will come in with a manual that will better explain their capabilities....

HA! good luck. Any useful technical information will be lost in translation.
Your best bet is to just be safe and use the dc power supply you found through opus.

dreadshawn · 03-28-2006, 12:46 PM

Are there any HU's out there that have a good voltage regulator in them, or is this more of a "signal-only" affair with them? My HU is going to be the JVC KD-AVX1 CD/DVD player, and there seems to be so many "gee-whiz" functions on there that I am having trouble sorting them out! Is anyone familiar with this particular model? I am likely to go with the PSU for safety's sake, but curiostiy is what's got me posting the question now.

Thank's for reading, y'all.

shotgunefx · 03-28-2006, 12:54 PM

Here's my 12v 5amp regulator (well, could with a heatsink). The tiny little thing on the perf board. All told, about $4 in parts.

LD1084V12 regulator

Seeing I have no HU anymore, figured I'd use the radio power to supply the lilliput.

Motorcity · 03-28-2006, 01:58 PM

Nice simple setup. But, at full load, how hot?

shotgunefx · 03-28-2006, 02:28 PM

Quote: Originally Posted by Motorcity

Nice simple setup. But, at full load, how hot?

Good question. If I'm intepreting this great explaination and the datasheet correctly hot as hell without a heat sink at full load.

If that car is on it's dropping 12volts so 2v * 5amps = 10 Watts.

Without a heatsink, and a "junction to ambient" 50C that's about 500C (932F) above ambient.

With a sufficient heatsink the "junction to case" drops to 3C. So that's a much more managable 30C above ambient.

Then again, I'd take my knowledge of electronics with a grain of salt. I do.

Motorcity · 03-28-2006, 02:50 PM

Quote: Originally Posted by shotgunefx

Good question. If I'm intepreting this great explaination and the datasheet correctly hot as hell without a heat sink at full load.

If that car is on it's dropping 12volts so 2v * 5amps = 10 Watts.

Without a heatsink, and a "junction to ambient" 50C that's about 500C (932F) above ambient.

With a sufficient heatsink the "junction to case" drops to 3C. So that's a much more managable 30C above ambient.

Then again, I'd take my knowledge of electronics with a grain of salt. I do.

I think you may have mis calculated there. If that LDO reached 500c above ambient, it would have melted. Figure solder only needs 4-500f to melt, so if you had that LDO soldered, you would have cooked the board long before it hit the temp.
I think the unit is more likely to hit 130c or so at full load on a car, without a sink. This is still steaming hot. But, a decent sink shoud be all the cooling needed. I have some small aluminum sinks pulled from I-openers that I used to mod a few years back.
If you want a couple of them to play around with, drop a small donation in my tip jar and I will mail them out.

shotgunefx · 03-28-2006, 03:04 PM

Quote: Originally Posted by Motorcity

I think you may have mis calculated there. If that LDO reached 500c above ambient, it would have melted. Figure solder only needs 4-500f to melt, so if you had that LDO soldered, you would have cooked the board long before it hit the temp.
I think the unit is more likely to hit 130c or so at full load on a car, without a sink. This is still steaming hot. But, a decent sink shoud be all the cooling needed. I have some small aluminum sinks pulled from I-openers that I used to mod a few years back.
If you want a couple of them to play around with, drop a small donation in my tip jar and I will mail them out.

I don't think it's wrong. The datasheet says for every watt dropped without a heatsink adds 50c over ambient.

I'm not suggesting it would actually reach anywhere near that temperature as it has thermal protection built-in.

Though for ****s and giggles, I'll measure the temp with the lcd (when I'm done painting the housing) with and without heatsink. I'm pulling relatively little current through it though. I didn't get it because it was a 5amp, but because it was low-dropout.

I appreciate the offer on the heatsinks, but I've got quite a few TO2 sinks and a bunch from old hardware. Just didn't bother to put one on (yet)

Motorcity · 03-28-2006, 04:21 PM

I was looking at the wrong spec on that data sheet.
What puzzles me though, is that seems like a very high temp for that ldo to operate at. Given, most who would integrate that part would use a sink, but I can't get past the high temp relative to the drop. Oh well, I am no electronics engineer, so what the hell do I know?
Think I'll order up 1 of those next time I place an order w/Mouser and putz with it.

shotgunefx · 03-29-2006, 02:45 AM

Quote: Originally Posted by Motorcity

I was looking at the wrong spec on that data sheet.
What puzzles me though, is that seems like a very high temp for that ldo to operate at. Given, most who would integrate that part would use a sink, but I can't get past the high temp relative to the drop. Oh well, I am no electronics engineer, so what the hell do I know?
Think I'll order up 1 of those next time I place an order w/Mouser and putz with it.

I'm just glad you brought it up. I was meaning to do the math, but in my rush to get some stuff done, put it off for later (the lcd is still out more than in). I wasn't drawing much, so figured it wouldn't be a big deal for now.

I've got a couple other things to run off that and I probably would have been fairly upset if I did and melted it because I forgot to add a sink.

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