62 replies to this topic

[CCH Concepts]

i think i have not put my point across very well. the point i intended to make is that there was no need for me to go to the the extent of explaining why the voltage drop was there as you dint need to know this to light an led. that there are some things you just have to except or it gets very complicated to understand why that is the case.

[mike_au]

I'm not an EE or anything so I won't try to argue why things do and don't work, but from experience I can safely say that a standard blue LED with no current limiting resistor will quickly turn into a smoke emitting diode if you put 5V across it. The same diode will work perfectly from a 12V supply with a single resistor in series with it.

Maybe it is just luck or magic, but I have some in my car and they have been going strong for a couple of years now.

I'm fairly sure I know how to work out the optimal series resistance to produce the maximum brightness without exceeding the LED specs, but since low brightness would be better suited to this situation, why worry about it? just pick a big-ish resistor, put that in and see if you like it, if it is too dim, pick a smaller one and try again. If you want to do it quickly grab a variable resistor and spin it until you get the brightness you want, you can even go back and change it later. That seems like it would be the least stressful way, and you get exactly the brightness you want.

[cooperman435]

The point being made here is that voltage dividers, quantum Physics and flux capacitors are all redundant and in fact not needed in this application where an led must be lit from a 24v DC source without damage.

Im sure someone out there can simply give you the Maximum and Minimum ohm-age that a resistor needs to be in this instance if you can supply the Maximum and Minimum voltage you need across the LED.

[PyroCreationZ]

Thanks everyone, I'm sure I'll manage to light a few LED's with an resistor in series.
And CCH I hope you don't feel too offended as I'm sure it was no one's intention to do so.
Besides there are enough LED calculators out there. The link CCH gave is actually a good place to go as they have a program Electronics Assistant wich I downloaded and is very usefull.

[PyroCreationZ]

I will also install a voltage meter in my system but was wondering if I can also connect this to the 24V power supply?
For now I have a 4xAA battery holder. I'm using AA batteries with an output of 1.2VDC so that makes 4.8VDC total.
Even though the meter requires 5VDC it does work @ 4.8V or even a bit lower.
The meter has 4 pins: 2 for the matrixes to light up (+5VDC / GND) and 2 for voltage measuring (+V / -V).
So it needs +5VDC to work and has a power dissipation of 50 - 60mA.
My calculations:
R=V/I
R=24V/0.05A & R=24V/0.06A
R=480 Ohms & 400 Ohms
So I need to put in a resistor somewhere between 400 & 480 Ohms.

Or doesn't it work that way?
I won't try this untill I've heard from you guys as it's an expensive thingy in the panel.

Edited by PyroCreationZ, 11 December 2009 - 05:57 PM.

[Arthur Brown]

The meter is a device I would NOT run off a series resistor, though it might work it might also not work well.

A suitable 5v regulator would be a three terminal chip possibly a 7805 or a 7905 and which one depends on whether you need a common positive or a common negative supply.

[PyroCreationZ]

The meter is a device I would NOT run off a series resistor, though it might work it might also not work well.

A suitable 5v regulator would be a three terminal chip possibly a 7805 or a 7905 and which one depends on whether you need a common positive or a common negative supply.

I think I know what you mean but I don't have enough understanding of electronics to do so, so for now I'll stick with the batteries.
Maybe that's something for the future if I were to build a new system.
Thanks though.
btw: I think I would need a common negative but I'm not sure lol

Edited by PyroCreationZ, 11 December 2009 - 07:06 PM.

[Arthur Brown]

For a good meter search http://uk.rs-online.com for 315-9458 and get a local electronics shop to order one for you along with a press switch! It's moving coil so it works off the voltage it's reading!

[PyroCreationZ]

For a good meter search http://uk.rs-online.com for 315-9458 and get a local electronics shop to order one for you along with a press switch! It's moving coil so it works off the voltage it's reading!

That's the one I was going to buy at first but when my dealer said I could get this one for the same price I obviously took that one

[mike_au]

Did you tell the dealer that you wanted it for measuring the voltage on a 24v system?

He isn't doing you any favours by suggesting a device that needs a 5V supply to work, the analogue one would have worked fine without a voltage regulator.

If you told him what it was for and he recommended that one, I would be going back, complaining and asking them to swap if for the other model.

[PyroCreationZ]

Did you tell the dealer that you wanted it for measuring the voltage on a 24v system?

He isn't doing you any favours by suggesting a device that needs a 5V supply to work, the analogue one would have worked fine without a voltage regulator.

If you told him what it was for and he recommended that one, I would be going back, complaining and asking them to swap if for the other model.

Yep, I told him I needed a voltage meter that can measure up to (at least) 24V, though I didn't mention it was for a firing system.
They had two models: the analogue and digital one but I chose the digital one because I like the LED display.
It can measure up to 200VDC but it need a 5V supply.
Analogue would be easier but it's less fancy
Don't worry, I'll just use the battery pack as supply.
It will do fine though it adds a few extras to the system unless someone wants to explain me how I should connect it to 24V with that voltage regulator.
I don't exactly know what is meant with "common positive / negative" therefor I wouldn't know exactly what to get and how to connect it.
(I'm foreign so sometimes I don't understand everything in English terms)

Edited by PyroCreationZ, 14 December 2009 - 01:43 PM.

[CCH Concepts]

voltage regulators are easy to use. they should have a schematic in the data sheet.

LM7805 data sheet

look at page 21.

[PyroCreationZ]

I now know what is meant with common negative or positive.
I've seen a professional system wich uses a common positive and switched negative.
I think this is the safest method though I'm not sure.
Can anyone explain me why one is better than the other?

[Arthur Brown]

There is no "Best" they are equal alternatives.

In most UK market cars they use chassis as negative and lots of things that run off car lighter sockets need to be negative earth However if the device has a plastic box and no external (connected ) metalwork then either will be fine. ( I cannot consider that I wouldn't want an in car charger for a firing system as 12hrs by a mains socket in the 5th Nov season can be hard to find)

[PyroCreationZ]

There is no "Best" they are equal alternatives.

In most UK market cars they use chassis as negative and lots of things that run off car lighter sockets need to be negative earth However if the device has a plastic box and no external (connected ) metalwork then either will be fine. ( I cannot consider that I wouldn't want an in car charger for a firing system as 12hrs by a mains socket in the 5th Nov season can be hard to find)

Thanks.
I have been busy all morning figuring out my scheme for the firing system.
I'm now using common negative as I have metal parts "sticking out".
I used the chassis from my DIN plugs as negative. If I'd switched it and put the positive on it, it would not be safe.
I think (and hope!) I got everything right now...
Guess we're about to see in a few days lol.

btw: Happy New Year (to all)

Edited by PyroCreationZ, 28 December 2009 - 11:10 AM.