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Need help powering a 12V vehicle video monitor from 5V

jasongitar

Sep 4, 2015
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So for a project I am doing, I'm taking a 5V USB power bank through a 12V booster step up regulator to power a 12 volt monitor. So far all I am getting is smoke coming off the booster. Been asking for help through electronics people I know, but I am not really getting anywhere, so I thought I would ask at this forum. I drew up a little diagram to show what I am doing. Please help :)
 

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Arouse1973

Adam
Dec 18, 2013
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Hello
How much power does the monitor use and what is the rating of the booster. A link to both would be useful.
Adam
 

Arouse1973

Adam
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The TV only draws 250 mA so I dont understand why it shouldnt work. The booster can supply 1.4 Amps. Whats not clear is at what voltage can it supply 1.4 Amps. Let me have another look.
Adam
 

Skidood

Aug 24, 2015
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Since you saw smoke, the step up device is surely toast. I am guessing the problem has to do with the grounds somehow...I assume you are testing this on your bench and not in the car? Try it without connecting the RCA cable.....
Actually FIRST, connect the monitor to a 12 V battery or other 12 V power supply to see if it's not internally shorted...try to confirm the current draw as well...250 mA sounds a bit low to me..
 

jasongitar

Sep 4, 2015
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Thanks Adam! Not sure where to go at this point with it, but I appreciate you looking into that.

Thanks Skidood! That's a good idea! I think you are right about the grounds situation, something is off. Seems like such a simple
thing to figure it out. Connecting the monitor straight to to a 12V source is probably the way to go, just got to figure out where to
get that.
 

Old Steve

Jul 23, 2015
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The TV only draws 250 mA so I dont understand why it shouldnt work. The booster can supply 1.4 Amps. Whats not clear is at what voltage can it supply 1.4 Amps. Let me have another look.
Adam

Adam, the DC-DC converter listing says 'up to 1.4A'. Allowing for that being the absolute maximum output current, you can bet that's at the absolute minimum output voltage. ie 2.5V
So, 2.5 x 1.4 = 3.5W
3.5W / 12V = 290mA

All of these sellers tend to exaggerate, so it probably can't really supply this much current continuously.
Then, if we take the monitor seller's claim of <3W, and allow for some exaggeration here as well, this power supply is probably insufficient, or at the very least borderline. (In the listing, they also say that it uses 120mA.)
To be on the safe side, I'd go with something that can produce at least 0.5A at 12VDC.

jasongitar, as suggested by Skidood, at this point I'd test the monitor on a good 12VDC supply, perhaps a 12V SLA or other lead-acid battery to make sure it works OK, measure the current if possible, then get a better-suited 5V to 12V DC-DC converter. (The second one that you linked to and purchased might still be a bit on the small side. You can bet that the maximum 3A is probably only available at the minimum 1.25V, making 3.75W total. 3.75 / 12=313mA - pretty close to the line still.)
As Skidood also said, if the original DC-DC converter has released it's magic smoke, it might well be dead now.
Test it for 12VDC out, then if it's OK put it aside for another project.
 
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Arouse1973

Adam
Dec 18, 2013
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Adam, the DC-DC converter listing says 'up to 1.4A'. Allowing for that being the absolute maximum output current, you can bet that's at the absolute minimum output voltage. ie 2.5V
So, 2.5 x 1.4 = 3.5W
3.5W / 12V = 290mA

All of these sellers tend to exaggerate, so it probably can't really supply this much current continuously.
Then, if we take the monitor seller's claim of <3W, and allow for some exaggeration here as well, this power supply is probably insufficient, or at the very least borderline. (In the listing, they also say that it uses 120mA.)
To be on the safe side, I'd go with something that can produce at least 0.5A at 12VDC.

jasongitar, as suggested by Skidood, at this point I'd test the monitor on a good 12VDC supply, perhaps a 12V SLA or other lead-acid battery to make sure it works OK, measure the current if possible, then get a better-suited 5V to 12V DC-DC converter. (The second one that you linked to and purchased might still be a bit on the small side. You can bet that the maximum 3A is probably only available at the minimum 1.25V, making 3.75W total. 3.75 / 12=313mA - pretty close to the line still.)
As Skidood also said, if the original DC-DC converter has released it's magic smoke, it might well be dead now.
Test it for 12VDC out, then if it's OK put it aside for another project.

Yes Steve, that was my thinking also. I couldnt find any info in the link he supplied.
Thanks Adam
 

cjdelphi

Oct 26, 2011
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Maybe you connected the power backwards shorting out the step up reg?

If so confirm the tv still works
 

jasongitar

Sep 4, 2015
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Old Steve, thank you for your insightful information about all this. I wish I knew more intricate details about electronics like you and the others on this post do. I guess you can only learn by doing it and making mistakes. I guess starting with the 12V power source directly into the monitor is the first place to start.

Thanks cjdephi, you just may be right about shorting it, we'll have to see.

I'll keep you all updated with what happens.
 

Osmium

Jan 28, 2013
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ummm... maybe I'm missing something - sorry if that's the case, but the monitor spec says it runs with a 5v-24v supply. Have you tried the monitor directly to the usb supply?
 

Old Steve

Jul 23, 2015
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I don't think you're missing anything, but I sure missed that. :oops:
Well spotted Osmium. :)

I was blindly responding to @jasongitar 's original "I'm taking a 5V USB power bank through a 12V booster step up regulator to power a 12 volt monitor" and "Hi Adam, thanks for your reply. the monitor uses 12V"

At least I'm not the only one. :D
Of course, that's assuming that listing is correct. Further down it says "The power supply: DC12V".
It's definitely worth connecting it to a 5VDC supply to see if it works.....

monitor listing said:
Monitor Featrues:
Display size: 4.3 inch
Display Format: 16:9
Power < 3W
Power: DC 5-24V
Video: Rear view camera input all the way, all the way DVD video input
Format: PAL / NTSC dual-mode automatic switching
Contrast Ratio: 350:1
Brightness: 300cd/m2
Number of pixels: 480 * 272 Response time: < 12ms dynamic picture display smoothly
 
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jasongitar

Sep 4, 2015
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Just tried the 5VDC supply directly to the monitor and nothing.

Purchased the other step up booster and can only get the power from the 5VDC supply to go to 10V according to the multimeter. I tried
connecting that 10V booster to the monitor and I just get one little light blink from the monitor like it wants to work.

Not sure what to do at this point.
 

Old Steve

Jul 23, 2015
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Just tried the 5VDC supply directly to the monitor and nothing.

Purchased the other step up booster and can only get the power from the 5VDC supply to go to 10V according to the multimeter. I tried
connecting that 10V booster to the monitor and I just get one little light blink from the monitor like it wants to work.

Not sure what to do at this point.
So, did you end up testing the monitor separately, on a 12VDC supply?
 

jasongitar

Sep 4, 2015
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Yes, I purchased 2 of these monitors and tested one on 12V supply and it worked perfect, but same situation when trying to power them individually with the 5V battery power pack and booster. I even bought another 5V battery and booster and same results.
 
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Old Steve

Jul 23, 2015
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Yes, I purchased 2 of these monitors and tested one on 12V supply and it worked perfect, but same situation when trying to power them individually with the 5V battery power pack and booster. I even bought another 5V battery and booster and same results.
Did you only buy the low power units you mentioned the other day, or a different higher powered one?
They were both unsuitable. You want one that can provide at least 0.5A at 12V, and even better would be one that can provide 1A. Don't be skimpy in this regard.

What I would do is connect the monitor to 12VDC, get it working, then measure the current that it uses and go from there, buying a power supply to suit. Whatever current it uses, buy a DC-DC converter that can handle at least 1.5 times what you measure.

You can measure the current by putting a very small 1W resistor in series, between the battery + terminal and the monitor + terminal, then measure the voltage across that resistor when the monitor is powered up.
The current will be the measured voltage divided by the resistance. A 1 ohm or even better, 0.47 ohm resistor would be fine for this.
(The lower value resistor will keep the voltage to the monitor higher, and dissipate even less power. An 0.25W resistor would do if it's 0.47 ohms. For a 1 ohm, use an 0.6W or 1W. Always err on the safe side.)
 
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jasongitar

Sep 4, 2015
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Hi Steve,

I have had the lower powered units for a little while now. A friend of mine had a 12V power source he used to power one of the monitors and that is how I was able to check that it works.

Can you recommend a specific DC-DC converter and power supply I can purchase off of Amazon or another site? I am so new to this, and still a little confused, I just want to make sure I purchase the right thing.

Thanks for for breaking it down and explaining it all to me Steve. Hopefully this will all get it to work :)
 
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