Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

New guy with a 12v Poject Question

Status
Not open for further replies.

Scott P.

New Member
Hi all, first great site! I have a question that I need to seek the experts out there to find out how to make something. I need a device that can measure the voltage of a 12v electrical system and supply a ground or positive signal when voltage drops to a certain value. I need to be able to have a low wattage halogen lightbulb turn on when the voltage supplied to it has dropped to 10.5 volts. but have it NOT be lit when the voltage is above 10.5 volts. Is there such a part that I can purchase to make this work... or would it be easy enough to create from low cost parts on line or at my local Radio Shack?

Again, great site... and any help would be greatly appreciated!
 
An opamp or a comparator can detect when the supply voltage has dropped below 10.5V. Then the opamp or comparator can drive a transistor that turns on your light and the light's current will kill your 12V battery.

RadioShack is gone from Canada so I don't know what they still sell in your area.
 
this will work
still if you want to have a an indicator i would use a LED

if it's not nesecary to work with a relais than leave it out

Robert-Jan
 

Attachments

  • battery discharge protector.pdf
    262.3 KB · Views: 201
You might also want to consider a voltage reference as well. There are parts that are designed for under/overvoltage detection with Vref built in. Cheap and easy to get.
 
I'd go with what audioguru is implying: you should find another way to indicate the low voltage status. The halogen will drain the battery and if it burns long enough, it could damage the battery beyond recharging or repair.

Robert-Jan's idea of using an LED is better than a halogen bulb. Even better would be to use a CMOS 555 or other low-current method to periodically blink the LED briefly (say, blink it on for a few milliseconds every few seconds), which would let the battery last much longer but would still be noticeable.

Even better would be some kind of indicator which doesn't require power at all once it's set; say, a solenoid or servo could be triggered to flip a little flag. It would be green-side-up when the battery is OK and flip over to show the red side when the voltage drops past your trigger point. That way you just need one final burst of current to set the indicator, then shut the circuit down, leaving the red indicator visible.


Just some random thoughts,

Torben
 
Update. Okay since chatting and hearing what you had to say, I made a brief design change. Instead of having it alert me when voltage is low, I think I can just have it turn the thing I'm using to run off a low power mode, which I just realized it has. It say a momentary latch to a neg signal will dim the array to 50% power. This would be perfect. Now... can I get a momentary latch to a neg signal using a voltage monitoring devise? I just dont want to keep the batteries plugged in all the time, and also I need the outlet to run something else.
 
Hi Scott!

Perhaps we'd have a better idea of where to start if you told us what "it" actually is.


Torben
 
I have a store front with a marketing light array that I am using that needs 12V power. I am running it from a battery. I was hoping a could mount a light behind the counter that would indicate the battery is low, then I would connect the charger. When the charger is connected my door alarm would be off. Now, I see that I can latch gound to it and run it in low power mode. I just tried it, and I can tell from behind the counted when it is dim. Which would tell me to disconnect door alarm and charge battery for the light array. I hope this makes sense.
 
I have a store front with a marketing light array that I am using that needs 12V power. I am running it from a battery. I was hoping a could mount a light behind the counter that would indicate the battery is low, then I would connect the charger. When the charger is connected my door alarm would be off. Now, I see that I can latch gound to it and run it in low power mode. I just tried it, and I can tell from behind the counted when it is dim. Which would tell me to disconnect door alarm and charge battery for the light array. I hope this makes sense.

OK, I know that chances are excellent that you've already considered this idea and discarded it, but here goes anyway: why can't you use a power bar and plug both in at once?

I'm sure there's a reason; I just don't yet know what it is.


Torben
 
Because when the light array is powered the cord has to run right across the floor. I need to limit the time it is being charged, one so there is limited time the cord is in the way and two to keep my door chime alarm powered. Maybe pictures would help. I just thought I could create something simple so others that are at work can run it. Maybe I should just toss the light array. I do like it though it is very catchy!!
 
Gotcha. Don't scrap it yet. :) Of course my first thought is to buy some bulk cable and stick a plug on one end and a socket on the other, making a nice long extension cord, which you could run along the baseboard/ceiling corner so it wouldn't have to cross the floor. I assume that's also not going to work for some reason. However, I don't know why you couldn't use a power bar or splitter to power both the charger and the door dinger while charging (but that's a different topic).

Otherwise, if the low-power mode allows you to see when you need to run the charging cord across to the battery, and simpler options are out, your solution sounds like it should work.

Can you scan the relevant part of the manual or draw it out? I assume that it has some details on how to force the low-power mode. Or perhaps if you post the make and model number we could look it up online somewhere.


Torben
 
So is there a simple way to get a quick neg pulse when power drops? At this point it is more fun to me to create something like this. I am somewhat new at all this curcuitry stuff and I think it would be a fun thing to create, I just have no idea what curciut parts to use.
 
So is there a simple way to get a quick neg pulse when power drops? At this point it is more fun to me to create something like this. I am somewhat new at all this curcuitry stuff and I think it would be a fun thing to create, I just have no idea what curciut parts to use.

That's why I want you to post the relevant part of the manual--if it includes any diagrams that would be ideal. I want to clarify exactly what is meant by a "short neg pulse". It sounds like it wants a quick pulse below 0V but I am not sure from the terminology.


Torben
 
Well I tapped the wire that puts it on low power, to the ground side of the battery and that did it. It stayed in low power mode until I turned it off and the turned it back on. Worked like a charm.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top