diy auto top off

[BeanAnimal]

Melev,

I have not read the thread... but you could put an LED in series with the coil (not the best solution).

The best way to connect the LED would be to attach the ANODE to the input side of the relay coil and the CATHODE to ground (through a suitable resistor). This way the current draw of the coil is not being passed through the LED.

If you feel frisky and want to add a 2n3906 or similar PNP transistor, you can have RED and GREEN (or a bi-color) LED show the status of the relay coil. The circuit addition is rather simple and I can post if I have time later.

Bean

 

[melev]

If you can draw it where a reefer can understand it rather than a electronics major, I probably could build it.

 

[captbunzo]

I think that you should be able to wire the LED inline as long as it is rated for the same voltage as the relay.

tekknoschtev - Amusingly enough, I did NOT get the one I was talking about. They didn't freaking have it! But that's Radio Shack for you. I had a EE major friend in college you used to twist the Radio Shack moto into: "Radio Shack: You've got questions, so do we!" (Instead of the we've got answers part...

The one I got is basically this 7-9VDC/12A SPDT Mini Relay - except mine is only listed for 9V.

Anyhow, I got all of the parts - ended up spending more then I should have as I sprung for a $30 digital multimeter....

I came up with a really cool way to attach some of the parts together. I will try to take good assembly pics and post it in a thread or something later, along with plans & part numbers or something.

But that will AT BEST be in 3-4-5 days. Darn stinking busy weekend. On the bright side, I got 33 lbs of rock tonight to stick in my caribbean reef biotype tank at the office and actually get it started tomorrow. Woohoo!

 

[tekknoschtev]

Haha, yeah, radioshack, unless you are purchasing a mobile phone, they really are clueless. I dont go there unless I know 100% what I want. In. Out. Done.

Good call on the multimeter. We get ours from Harbor Freight for like $6 But I still have my good $50 one sitting in the case.

I'm hoping to get my parts in the next few weeks here, because I'm terrified about someone forgetting to top the tank off. If it goes for any more than 34 hours, we're sucking air.... Fortunately my family likes the tank too, and they'd hate to see it go downhill.

 

[BeanAnimal]

captbunzo...

LEDs need current limiting resistors. Putting the LED in series with the relay coil is not a good idea. The LED needs to be hooked to the postive side of the relay and ground. A currnet limiting resisistor needs to be on one side or the other of the LED.

 

[captbunzo]

LEDs need current limiting resistors. Putting the LED in series with the relay coil is not a good idea. The LED needs to be hooked to the postive side of the relay and ground. A currnet limiting resisistor needs to be on one side or the other of the LED.

I'll definately take your work and that and differ to your expertise. Any chance you can explain a few things to me?

1. What is a current limiting resisitor? Is it different then a regular resister?

2. Why is it required?

Although, I THINK I might understand now that I actually use my brain for a moment. For instance, let me just make up some numbers. Say I have a 9V LED that is rated for max current of 100 mAh. So if the relay draw 200 mAh, I burn out the LED.

So effectively you would want to wire it in in parallel to the coil.

And, I guess, the same MIGHT (?) be required for LEDs wired into the switch part of the relay. Of course, you'll want to make sure that you've connected the LED power in that case to the SWITCHED line attached to the relay switch, and not the power line.

Anyhow, sorry for the muddle and probably me using all of the wrong terms...

 

[chrisguy]

captbunzo - most LED's run at less than 3V. A resistor will reduce the voltage going into the LED.

Radio Shack sells 12VDC LEDs. They are in the section Parts, Tools & Wire ~ LEDs ~ LED Holders & Assemblies. 12VDC LEDs

Red 12VDC LED that easily mounts to a project box

These LEDs have a resistor built in and are very user friendly for people like me with limited electrical knowledge. They easily mount to a project box. This is a benefit to using a 12VDC relay. You can use these LED's and done have to be an electrician. If you use a lower voltage Relay, then you will likely need to add resistors to use standard LEDs

 

[BeanAnimal]

You kinda got the idea. Most LEDs are rated between 20-30 mA maximum. LEDs are current devices, not voltage devices. In other words they will use all of the current available to them. A lightbulb is a voltage device, it will use all of the voltage available. If put an LED accross a supply capable of 100mA, then it will burn out. The "current limiting" resistor is simply a resistor that is placed in series with the LED. The resistor uses up the excess current, preventing the LED from burning out. You can find dozens of LED resistor calculators on the net. It is simple ohms law... you may want to read a bit about ohms law if you are going to tinker with electronics.

For your use, anywhere you want an LED, simply connect it's positive side to your voltage source and the negative side to a suitable resistor that is tied to ground. The voltage source can be your power supply, the switched side of the relay, anywhere you want to "indicate" the presence of voltage. Just remember to calculate the proper size resistor for the voltage being used.

Do not attempt to connect an LED to AC line voltages... we are only talking about low current DC circuits here.

Bean

 

[captbunzo]

All this fun talk about LEDs and I don't actually plan on using any...

 

[budhorse775]

.