LED DIY : Making of a "DJ SET "-style grow led light .

[guod]

Power cable dia for ~2 m ?
(cable from Main PSU to box ... )
2 x 0.75 will be ok ?

up to 5m 0.5mm² will be OK

 

[stardustsailor]

Ok..Doing some tests ...
Made 3x "loads" ( 3x strings of 10 CW leds in series ....)

Fans work great ...
Massive airflow ..
Rel .low noise ....

I'm having trouble with analog dimming ....

Pot works really great ,with high precision ..
But it does not get any lower than ~550 mA ...

Guod ,any help on that ?
Can't figure out ,what's going wrong....
(180 ohm resistor - 1 K pot )

.....

 

[guod]

wireing correct?

 

[stardustsailor]

Yes ,exactly like that ...
I'll change the wires ,because are taken from an old computer...( way thin & flat wiring ... )
Maybe wires too small in Dia ,thus increasing resistance ....
But still ,I do not think that is the reason behind the 550 mA lower limit ....
Can't figure out it ,really ....
Everything is correctly placed ,wired & connected ....
WTF ?

( 180/1180 ) *5 = 0.7627
5 - 0,7627= 4.2372 V ....
Max voltage(with pot ) should have been -as stated - approx .4,2 V ....
~ 112 mA ,had to be , the minimum current limit ....

 

[guod]

wires will be OK, thats only some mA.
voltage are also correct?

 

[stardustsailor]

Input voltage you mean ? 48 V ....

As for the rest ,of the voltages ,haven't measure them (yet ) ...
Later on ...
...
I'll post the results ...
I've to go for work ,now ...

 

[guod]

Input voltage you mean ? 48 V ....
nop, voltages on the pot as given in pic two (Voltage test-points)

next simple test is brigde(red) the contacts you see in this pic, led have to go off

 

[stardustsailor]

Input voltage you mean ? 48 V ....
nop, voltages on the pot as given in pic two (Voltage test-points)

next simple test is brigde(red) the contacts you see in this pic, led have to go off
View attachment 2542624

Yes ,I did that and indeed leds go off ..

 

[guod]

Yes ,I did that and indeed leds go off ..
bucks work as they should...
please check the smd-resistor with an ohmmeter, looks like this is not 180 ohm but 1800 ohm

 

[stardustsailor]

Nope ...
I still get the same readings ....


Black for GND
Yellow for Vref
Green for Analog Dimming .


Without Pot .
5.43 -5.5 Volt between GND and Vref


Pot :
GND at 1
Vref at 3
(if opposite ,pot operates opposite,as Guod stated .
Just a simple personal preferance issue )....
An.Dim . at 2


Pot fully clockwise : Min current = 550mA (still.... )


Pot at "0" : max current =~ 710 mA .


A. Dim & Ground : 1.14 Volt ,instead of 4.2 ...(with pot )
???


Vref - ground (with Pot ) ..Same ~ 1.14 V ,instead of 4.2 (pot fully turned clockwise ) .....

???

I don't understand ...
WTF is not right ?

 

[guod]

Vref has to be always 5.xx V. should not change if you turn the pot.

 

[stardustsailor]

Yes ,I did that and indeed leds go off ..
bucks work as they should...
please check the smd-resistor with an ohmmeter, looks like this is not 180 ohm but 1800 ohm

Yes ,it writes " 1800 " on it ,but it is 179,99-180,6 Ω ...

 

[stardustsailor]

Vref has to be always 5.xx V. should not change if you turn the pot.

V.ref ( voltage taken with pot on ,between gnd and Vref ...) is not 5.xx
Is ranging from 1.14 (pot at 0 ) to 1.2 (pot at max )

Without pot ,yes, then Vref is ~5.5 Volt .....

Any ideas ,so far ?

 

[guod]

looks like we have a to high load on Vref. check the resistance between 1 and 3 at the pot. 1000 ohm you should read here.

 

[stardustsailor]

Yes ,I've already did that .Correct .1 K .

 

[stardustsailor]

Replaced Vishay 1K pot with one Bourns 3296 high precision-multiturn- trimmer ....
At 10 K .

Went as low as 60mA ...
Really smooth -great! - analog dimming ..
(up to 710mA ... )




Still don't get it ...
1 k ,is the right one( based on "voltage divider " equations ) , not 10 K ....

 

[guod]

disconnect the wire from contact 2 of the pot, which goes to Van... check vref again.

 

[stardustsailor]

Ok ,will do ..
Wait a bit ...

 

[stardustsailor]

~4.8 volts ....

 

[stardustsailor]

We need a bigger pot ?

180 & 2200 ?

180/ 2380 =0,0756...*5 = 0,3781
5 -0,781= 4,621
Nope ...~53 mA minimum current ...
"No go " ...