Electric Help

I'm planning on building a son of fermentation chiller soon for my next brew and I'm wondering if there's some good resources for wiring help? I know the instructions say to just use a 1K ohm resistor and assume 10 mA for an LED but is all that correct? Doesn't the resistance of the fan come into play too? (For that matter the thermostat as well?) I thought the whole circuit had to be looked at.

I got a couple 80mm fans coming from newegg already and I'm getting my insulation this weekend.

If you are using a 12V supply and the LED and resistor are in series, you will drop .7V across the LED since it is basically a diode. That leaves 11.3V across the resistor. 11.3V / 1000 (1k) = 0.0113A, or 11.3mA. Usually, most LEDs will handle up to 30mA, but that depends on the LED specs.
Not having the schematic in front of me, I can't tell you much more than that.

bull8042 said:

If you are using a 12V supply and the LED and resistor are in series, you will drop .7V across the LED since it is basically a diode. That leaves 11.3V across the resistor. 11.3V / 1000 (1k) = 0.0113A, or 11.3mA. Usually, most LEDs will handle up to 30mA, but that depends on the LED specs.
Not having the schematic in front of me, I can't tell you much more than that.

Click to expand...

It's been far too many years, but I recall that an LED drops about 1.2 V, not the "typical" 0.7 V of a standard diode. Of course, please don't trust my rusty memory...

Edit: ...or is it 2.2V? Either way, I'm pretty sure an LED drops quite a bit more than the typical diode. Has something to do with bandgap, I think...

So basically if I use a 1K ohm resistor I'm safe and don't question it. After I get all my equipment in order I'll double check everything here before I fry it. I plan on building the box this weekend and doing electric work through the next week. Thanks for the help!

bull8042 said:

If you are using a 12V supply and the LED and resistor are in series, you will drop .7V across the LED since it is basically a diode. That leaves 11.3V across the resistor. 11.3V / 1000 (1k) = 0.0113A, or 11.3mA. Usually, most LEDs will handle up to 30mA, but that depends on the LED specs.
Not having the schematic in front of me, I can't tell you much more than that.

Click to expand...

bull; on most general led's they operated at 20ma needing a 470 ohm resistor I recall with a 12 volt power supply. One must add that the power supply or cube will read higher than the rated output hence pushing the led harder making for a brighter but shorter led life span. Unless you have a selection of resistors to add in line with a digital meter your only be at a close guessing game on the led's ma draw for the given led that is to be used. Those rotary muti-resistance units from Radio Shack sure come in handy when establishing the correctly needed resistance for those scratch built projects. They are cheap and handy as hell plus come with leads and alligator clips. Man can never have too many alligator clip jumpers, mine walk away offten. I would start high on the resistance scale while reading your meters ma scale, keep reducing the resistance until you establish the maximum continuous ma rating of the led your using, do not use the maximum surge ma numbers which are a lot higher plus a shorter life span.

Off topic but I must add;
I just got home from having two discs plasma cut away from pressing on the spinal column nervers. Let the games begin as the hospital meds are starting to wear off with me finding out what post surgery pain is while it's getting worse. I've the next 3 to 10 days to look forward to with this pain plus making meds adjustments as needed.
I'm a stubborn Germam I will make it. Cheers. Carl on the mend seems sleep is my best friend while I recover and heal. Dreaming of brewing ideas helps before I zonk out.

1K resistor is a good value for a 12 V supply and 10 mA LED current.
470 Ohm is good for 23 mA LED current assuming 1.2 V LED drop.


Cheers,
ClaudiusB

jpc said:

It's been far too many years, but I recall that an LED drops about 1.2 V, not the "typical" 0.7 V of a standard diode. Of course, please don't trust my rusty memory...

Edit: ...or is it 2.2V? Either way, I'm pretty sure an LED drops quite a bit more than the typical diode. Has something to do with bandgap, I think...

Click to expand...

Sorry, I need to improve my proof-reading skills a little.... I left off the "1". Here is some more info:

[FONT=Arial, Helvetica, sans-serif]It is safe enough to assume 1.7 volts for non-high-brightness red, 1.9 volts for high-brightness, high-efficiency and low-current red, and 2 volts for orange and yellow, and 2.1 volts for green. Assume 3.4 volts for bright white, bright non-yellowish green, and most blue types. Assume 4.6 volts for 430 nM bright blue types such as Everbright and Radio Shack. Design for 12 milliamps for the 3.4 volt types and 10 milliamps for the 430 NM blue.

....Compliments of the interwebz....
[/FONT]

I have a power adapter that says 12V DC 1A. My question is after I cut the plug off do I how do I tell which is positive and negative? Does it matter? I'm thinking yes. I don't have a multimeter but I'll soon have a spare computer fan. I bought two in case I broke something.

One wire does have white dashes running along it. That's probably a clue huh?

hlumbard said:

I have a power adapter that says 12V DC 1A. My question is after I cut the plug off do I how do I tell which is positive and negative? Does it matter? I'm thinking yes. I don't have a multimeter but I'll soon have a spare computer fan. I bought two in case I broke something.

One wire does have white dashes running along it. That's probably a clue huh?

Click to expand...

Yea, as a kind of general rule of thumb, the dashed or striped wire goes to the outside. If you look at the adapter, you'll need to determine if it's center positive or center negative. The center positive markings look something like

(-)----(----(+)

..so in this case the dashed wire is generally the negative side. Again, this may not be the case with your power supply. For any type of electrical work, I'd pick up a multimeter. They are cheap, and will help to make sure you are wiring things correctly.

Having the right tool for the job isn't really my thing. Ha! Every time I do a project I'm always working WAY harder than I need to because of lack of proper equipment. My converter is like you said, negative on the outside so I'm pretty sure the dashed wire is negative. Thanks! I'll be sure to post pictures when it's all done.

Excuse the rant here first:

The people at RadioShack should be required to know something about electrics, or at least one person at all times. The MANGER finally came to assist me and I told him about my simple thermostat, fan, LED circuit and he had know idea how to hook that up. I said it didn't matter, "Do you know anything about resistors?" I asked. "I know when you bring in a broken one to replace it with the same thing." I **** you not, that's what he said. I told him thanks for nothing and bought the following:

1 red LED 12VDC 20mA 1.5mcd (I think that's brightness) it also says with integrated resistor but it just looks like and LED to me.

2 White LEDs FW current 25mA, FW supply 3.3v (typical), 3.6V (max)

and a 5 pack of 1K-Ohm Resistors, 1/2 watt, 5% tolerance.

How do I look to hook this up to my power supply now? I still don't have my fan yet, so I'm not sure of it's specs. I think I need a good overview of electric circuits because I don't have the foggiest idea of what matters most, volts, amps, watts? All I know is "Volts hurt, Amps Kill".

hlumbard said:

Excuse the rant here first:

The people at RadioShack should be required to know something about electrics, or at least one person at all times. The MANGER finally came to assist me and I told him about my simple thermostat, fan, LED circuit and he had know idea how to hook that up. I said it didn't matter, "Do you know anything about resistors?" I asked. "I know when you bring in a broken one to replace it with the same thing." I **** you not, that's what he said. I told him thanks for nothing and bought the following:

1 red LED 12VDC 20mA 1.5mcd (I think that's brightness) it also says with integrated resistor but it just looks like and LED to me.

2 White LEDs FW current 25mA, FW supply 3.3v (typical), 3.6V (max)

and a 5 pack of 1K-Ohm Resistors, 1/2 watt, 5% tolerance.

How do I look to hook this up to my power supply now? I still don't have my fan yet, so I'm not sure of it's specs. I think I need a good overview of electric circuits because I don't have the foggiest idea of what matters most, volts, amps, watts? All I know is "Volts hurt, Amps Kill".

Click to expand...

Let me take a wack at this while i'm under pain meds, worth a laugh later on me.
First off with the 20mA LED having the intergrated resistor your good to go directly off your 12 volt power supply but only if its output is 12 volts as many are higher especially on a light load the LED will pull on the cube or power supply. This may push the mA draw over the maximum continuous mA of that LED. A low ohm resistor may be needed to drop the mA and correct for this.
On your 1.5mcd I find this rather low as big bright LED's at Radio Shack go up to 5,000 mcd and this without being a super bright blinding LED flashlight, yours seems rather low in mcd. On your fan when you get it 95% plus of them will run with the polarity hooked up correctly or not at all if reversed so the fan is a simple hookup. Do not use the two white leads some fans have as these are for a temp probe for the fans inlet air temp. Hook up your ON LED after the switch so it is always reading 12 volts not the variable voltage for the fan speed unless you want the LED's brightness to vary with your fan speed. I bet not.
No worries about doing yourself in as it takes over 70 to 100mA at 100 volts do yourself in under the right conditions like standing in salt water licking the chrome fixture unless you have bad health or heart to begin with.
Remember LED's are current sensitive talking mA here vs voltage that will destroy one instantly, they also do not like reversed polarity.
There is a reason why good digital meters have fuses inside and yes I have tested them and they can save a meter. Smoked Flukes are cheap, Non-Smoked working ones are not, trust me on this one.
I now turn this over to bull this is his domain.

How could an LED have a built in resistor when it doesn't know what else is going to be hooked up in the circuit? I just burned out one of my whites because I had hooked it up with the 1k ohm resistor and nothing showed up. I think because I only need a 320 ohm (does this seem right? I used an online calculator). So I hooked it up directly to the supply and it fizzled out. I had an extra of this one so it's ok.

hlumbard said:

How could an LED have a built in resistor when it doesn't know what else is going to be hooked up in the circuit? I just burned out one of my whites because I had hooked it up with the 1k ohm resistor and nothing showed up. I think because I only need a 320 ohm (does this seem right? I used an online calculator). So I hooked it up directly to the supply and it fizzled out. I had an extra of this one so it's ok.

Click to expand...

NO! Using no resistor when a 1K ohm resistor was needed could burn it out.
Using 1K ohm instead of 320 ohm just made the LED's output lower or dimmer.
There is a maximum continuous LED mA current and a maximum surge mA and this is a wide range of mA difference between the two currents. A short flash should not cause a LED failure unless you pushed mA numbers way beyond the LED's specs. They can be hammered to a certain limit but not way beyond the mA rating. Extras come in handy besides that rotary multi resistance scale unit. This alone will pay for itself in saved parts that you otherwise let the smoke out. It's rather hard to burn one up unless you applied current way over the surge amount besides reversed polarity on them. This is why you start out with a higher ohm resistance while measuring the mA the LED draws then correct to the proper resistance that matches the specs to the given LED used. Those wort packs will mess up your mA ratings of the LED's because their output is much higher than the rated voltage on the cube or wort power supply.
Note what bull stated above, different color LED's also have different mA currents besides voltages. Check twice and not smoke once.

Post the part numbers please.

QUOTE]How could an LED have a built in resistor when it doesn't know what else is going to be hooked up in the circuit? [/quote]

The 12 V LED can be used as as a 12 V pilot light, as is.
To use the LED in any other application use one without the internal resistor.

I just burned out one of my whites because I had hooked it up with the 1k ohm resistor and nothing showed up. I think because I only need a 320 ohm (does this seem right?

Click to expand...

Using a larger value resistor than required will not damage the LED.

Edit: I type too slow


Cheers,
ClaudiusB

Yeah, I blew it when I hooked it up without the resistor at all. The red LED is part # 276-209

Here's what I'm hooking up in the next couple days:

12VDC 1Amp supply
Ritetemp thermostat
This fan
And I want an LED indicator light. It looks like a 320 ohm resistor before the LED will do it then.

Thanks for all the help guys!