A few questions.

[MikePL]

1. I bought some things from Kaidomain (first time). Is it normal that I didn't get any confirmation e-mail? My PayPal account was billed and the title was 'order #..... from Kaidomain' or something like that. I typed my order number together with ZIP code in their tracking form but got 'input error'. I tried contacting KD by e-mail two times (10 days ago and 3 days ago) explaining my situation and inquiring about the status of my order but got no reply. My order was placed Nov 17. Is it normal? Should I worry? I ordered on the same day from DealExtreme and got lots of e-mails and my package arrived days ago.

2. I am looking at this driver.
http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=2982
I understand the specs but I don't understand the explanation as it explains it all in flashlight terms.

It says that I can power up to 4 or 5 LEDs in series. But what LED's. There is a different power consumption if we use five 1W LEDs and five 5W LEDs. So how many watts can it withstand?

I assume that powering the LEDs in series (for example 5) divides the current by 5. So there's no sense in connecting 5 LEDs in series as each one would receive 151mA (755/5). Or maybe I am wrong?

What about connecting the LEDs in parallel? This way each LED would get 755mA. Am I right? But again, can it withstand 4 or 5 LEDs?

If anyone could help me with this, as KD gave some overall examples but the basic data are missing.

3. And the last question. Where can I get good RED LEDs? I am interested in 3W ones and of course not expensive. Everywhere I look, I get either nothing or some pricey $6 red LEDs. Aren't LEDs supposed to get gradually cheaper? Are there LEDs that cost $2, $3 or $4?

 

[TorchBoy]

I had a couple of those boards arrive today. You can't run 1W LEDs on it (unless you put them in parallel) because the board outputs a fixed 750mA. With a 3.6V LED that's 2.7W (P=IV), so you'll be able to run 3W LEDs in series quite nicely.

If you use three 1W LEDs in parallel they will each get about 250mA, depending on their individual operating voltages.

The way it can handle 5 LEDs (in series) is by using a suitably high input voltage. 3.6V x 5 = 18V.

 

[TorchBoy]

My order was placed Nov 17. Is it normal?

No way! That's almost a year! I know they're slow but even they aren't that bad normally.

Just checked and the Paypal receipt email was the only one I got. It took that order (just a smallish one) only 8.5 days to get here. I presume everything was in stock.

 

[TorchBoy]

3. And the last question. Where can I get good RED LEDs? I am interested in 3W ones and of course not expensive. Everywhere I look, I get either nothing or some pricey $6 red LEDs. Aren't LEDs supposed to get gradually cheaper? Are there LEDs that cost $2, $3 or $4?

If you're prepared to wait for a custom order:

Emitter: http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=3312 = $4.84.
Star: http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=3313 = $4.84.
Star: http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=3314 = $4.84.

Don't know what the difference between the last two is. I suspect a typo in the size of one of them.

:welcome: BTW.

 

[MikePL]

Thanks a lot for the replies. Oh yeah, welcome to CPF, hello everybody. I usually post in the LED section but this topic got somehow moved to flashlights. Not my idea, though.

Question number 1 has solved itself. My items arrived safely. Simply something must have gotten fu#&ed up by the post office (as usual) and that's the reason for the delay.

But I still don't understand what you write about connecting the LEDs. Isn't current supposed to be divided when we connect LEDs in series. For example if we have 300mA (source) and we connect 3 LEDs, each one of them will get 100mA. In parallel the current is not divided. What you wrote above is exactly the contrary, so who is right? And so the question is still the same. How do I connect LEDs to this driver? In series or parallel? I would prefer in parallel so that every LED gets the 755mA and not a fraction of it.

On the back of the driver there are two 'rings'. Which one is positive and which one negative? My intuition tells me the inner part is (+) but I prefer to ask.

 

[Power Me Up]

But I still don't understand what you write about connecting the LEDs. Isn't current supposed to be divided when we connect LEDs in series. For example if we have 300mA (source) and we connect 3 LEDs, each one of them will get 100mA. In parallel the current is not divided. What you wrote above is exactly the contrary, so who is right? And so the question is still the same. How do I connect LEDs to this driver? In series or parallel? I would prefer in parallel so that every LED gets the 755mA and not a fraction of it.

If you have the LEDs connected in series, the current will be exactly the same through all of them. If they're connected in parallel, the current will be split between them, but not necessarily evenly.

Think of the difference between traffic forced to go down a single lane (series connection) versus being split up between multiple lanes (parallel connection)

 

[Fallingwater]

The one thing I ordered from Kai (a supercheap mp3 player) arrived without any confirmation, and I got no reply to my inquiring emails. I was starting to worry, when I finally found it in the mail.

DX, on the other hand, confirm everything, send out emails for new developments and are quick to answer to questions.
Considering most of the stuff that's on Kai is on DX too (with a few exceptions, such as the LiIon D cells) I can see no very good reason to shop from Kai, unless you want one of the exceptions.

 

[MikePL]

Power Me Up,
yup, now I remembered that I got it all wrong. Thanks for straightening things out.

 

[TorchBoy]

So you're all clear now Mike?

 

[MikePL]

Torchboy.

Yes, thanks a lot. All the things are clear now...

Connected in series = all LEDs get full current
Connected parallel = LED gets current divided by LED quantity

I think I got it wrong because normal bulbs get dimmer when connected in series but they are voltage driven, not current driven.

Although, no.... wait a moment. I forgot to ask if this LED driver needs any type of cooling when I connect it to, let's say 12V and hook up three 3W LEDs. There's a lot of power to deliver and I see no heatsink.

 

[TorchBoy]

It's a buck supply so it shouldn't get very hot. I should be testing just that arrangement later today before posting the bits (sans battery) to my cousin for his boat lighting.