What voltage...

Tem · October 28, 2003, 16:46

I have a biggish led display and I don't know what voltage it runs on...and I don't feel like frying it with a wrong guess.

The original plug has had three connectors, two of them being connected on the board. Kinda sounds like AC with extra ground, right?

Now that connector is long gone and there are just two wires soldered on those positions. One on the connected two and one on the lonely 3rd one.

These run on the board to "8750 GI KBL04 AC" middle legs (it's a 4 legged one). The outer legs are marked as + and -.

I believe this is it:
m http://www.fairchildsemi.com/pf/KB/KBL04.html m

There's a datasheet on that page. It shows + and - on the outer legs and ~~ on the middle legs. I'm convinced it wants AC in, right?

But what does that KBL04 actually do...? Convert every voltage to the right one, or just turn AC to DC...?

SteveJ · October 28, 2003, 16:50

It's just a 4A bridge rectifier ie. AC -> DC converter.

Can you get me a piccie of the surrounding board - there will probably be a voltage regulator fairly close by which should give a clue as to what the unit is expecting.

Anonymous · October 28, 2003, 16:51

I thought bridge rectifier's converted AC to DC. So that'd be AC in, DC out. Don't think they do voltage conversion.

Tem · October 28, 2003, 17:11

Ok, my cam doesn't really do closeups, but here's two:
m http://koti.mbnet.fi/temmeke/led/ m

Pic1 shows where the voltage comes in...and it seems to go straight to "everything"...

Pic2 shows 3 condensators that are directly on the output of KBL04. They are 16V 2200uF...so I suppose the output should be less than 16V.

12V AC? s:shock: :shock: s:shock:

Anonymous · October 28, 2003, 17:20

12V would be a good guess. Either that or 9, 6 ....

Tem · October 28, 2003, 17:27

Oh my...in my world AC starts from 220V...

Guess I'm off to buy some AC-AC converter then...thanks s:)

s:)

Anonymous · October 28, 2003, 17:45

Quote from: "Tem"Pic2 shows 3 condensators that are directly on the output of KBL04. They are 16V 2200uF...so I suppose the output should be less than 16V.

Yes, certainly no more than 16V, possibly less; it's usual to specify the capacitors at about double the expected voltage, since you really don't want to explode them s:shock: :shock: s:shock:

12V AC? s:shock: :shock: s:shock: [/quote]

Quite likely; you should be able to get a simple plug-top/walwart type step-down transformer (I don't know what you call them over there) that'll do 220V~ -> 12V~

SteveJ · October 28, 2003, 18:51

Tem,

I'd concur with Phil - almost certainly no more than 12 volts is required, and if finding an AC output adaptor proves problematic, it won't hurt to feed it DC, but I suspect it's going to be a hungry beast - expect it to want at least 2 or 3 amps when all the LEDs are lit.

If you get any response from it at 12 volts but it appears unstable (shuts down when a few LED's are lit) then try powering it from the car, but make sure you put a suitable fuse in line with it (~5 Amp should be OK) just in case anything goes wrong s:(

s:(

HTH

Tem · October 28, 2003, 20:31

Ok...I tried it with the DC input...and that bridge got really hot even if I didn't have all the leds on (there's about 1500 of them, so I guess they do take some amps).

Then I took that bridge off and soldered the wires directly to "DC outputs" of it and inserted DC power there. Seems to work like a charm now, thanks guys! s:)

s:)

Oh and it seems to run ok at 7.5-12V. No difference in led brightness or anything...

Didn't turn on at 6V at all.

Anonymous · October 29, 2003, 11:49

Tem ! please mate before you go off and think that it will work hunky dorey be warned that capsistors over a long period of wrong voltage going throught them are like littel bombs and when they explode will probobly take half teh PCb board with it ! i know from experience and blowing up a screen via wrong voltage s:cry: :cry: s:cry:

But i thought everyhting was ok the cap's got slithyly warm and i had run it for around an hour! then i closed it all back up put it int eh Nav pod and an hour on it went bang and cracked the LCD display.

My advise is depending on how long you have it on for it maybe install a small CPU fan over the caps drivine of the ACC and +Ve from the board

just an idea s:lol: :lol: s:lol:

Tem · October 29, 2003, 12:35

Buster, I had it on for some 2 hours yesterday. Nothing was hot to touch when I felt the board around every now and then.

Anyway, since it didn't power up with 6V, shouldn't 7.5V be just fine? Especially when the capacitors are rated up to 16V.

...I'm not too smart with this stuff, so please let me know, if I'm doing something weird s:)

s:)

Anonymous · October 29, 2003, 13:54

Well yes and no,

As the caps are rateda t 16V means that obviusly they would get hot and blow at over 16V +12% normally, But it somthings acts on teh toehr side of things like nominal power i.e. the smallest amount of power it can take to start the charge but if this power is not meet within IIRC 30% of teh nominal power than it could cause harm to the caps and therefore well go Boom Boom ! s:lol: :lol: s:lol:

Just food for thought! But you are more than likely to be ok s:wink: :wink: s:wink:

Tem · October 29, 2003, 14:13

Quote from: "Buster"But it somthings acts on teh toehr side

Is Cambridge doing another survey? s;)

s;)

Hmmmm...I'm a bit worried about boom booms these days...but if you say I'm ok, I'll take your word for it.

(+ goes to microwave oven and - to fridge, right?)

Anonymous · October 29, 2003, 14:48

thats it put it on defrost for 5 mins and it will be lip smacking s:wink: :wink: s:wink: