correct voltage regulator

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Forum Name: General Discussion
Forum Discription: General Mobile Electronics Questions and Answers
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=121193
Printed Date: July 04, 2025 at 5:30 PM

Topic: correct voltage regulator

Posted By: Jasonb61
Subject: correct voltage regulator
Date Posted: April 06, 2010 at 7:45 PM

Ok, fairly simple but I need to make sure I'm on the right path.

I have the power supply for my monitor on a relay so it gets a ground connection when the head unit is powered on.

This works well, but the relay I used says "Nominal Coil Voltage: 9v" and I'm worried it will burn out over time and I want to save myself the hassle and use a VR to drop the 12v across the coil, down to 9v or so. Can I use the 78L09? It's rated at 100mA though.. not sure if that will work or not.

I'm not sure how many amperes my monitor pulls but it is a Lilliput 809GL-80NP/C/T VGA Touch Screen.

NOTE: The relay I am using is on a circuit board with other audio-related stuff and is NOT a standard auto relay.. that's why it's the 9v one. It's one of the small blue ones from radio shack.."OEG - SRUDH-SS-109L"

sorry if this is a little confusing lol

Thanks,
-Jason

Replies:

Posted By: anonymous1
Date Posted: April 06, 2010 at 8:38 PM

Off the cuff I would say that the 9v reference means you need at least 9v to pull the contacts in, and 12v would probably be just fine forever.

Secondly, if you were goung to spend the money for a regulator, why not just buy a cheap 12v relay from Radio Shack or an auto parts store and be done with it?

There probably really isnt going to be any difference that you'll ever see, but you'll sleep better at night knowing that you spent $10 doing something proactive.

Posted By: Ween
Date Posted: April 06, 2010 at 10:17 PM

hi,

do the specs for the relay show a coil resistance? or measure the resistance with an ohmmeter.

add a resistor one third of the vlue of the coil resistance in series with the coil.

you'll probably need a resistor rated at one watt (for safety).

you can use ohms law to check power consumed by the added resistor.