Fish Tank LED Power Supply Gets Hot then shuts down

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

so lets see the display assembly

It's EXACTLY one of these

It has many options like controlling the intensity of different colors, manually controlling the fan, and where matters of time are concerned, you can set the date and time, but also some stuff about the moon phases, the time of day for sun up and sun down ... even the ability to set the offset for the RTC if it drifts ...

[stj]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

so lets see the display assembly

[eccerr0r]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

A 4W incandescent night light bulb gets to incandescent hot...
but that's a very small area...

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

It shouldn't get that hot with the heat sink. At 200mA of 12V to 5V it should get less than 1.5 watts and this is in the threshold of not needing a heatsink at all. Did you measure current and see what happens as you disconnect possible consumers of the 5V from the 7805?

Well so the bench power supply tells me how much current is being consumed and yes ... when I run one fan it consumes about 140ma - but again, that's not going through the 7805 ...

When I have two fans only connected, the 7805 gets BARELY warm after about three minutes ... but as soon as I plug in the LCD display, it heats up RIGHT NOW too hot to touch ... the laser temp gizmo says its 67C and the LCD screen adds about 160ma to the pull from the PSU.


I should also note that when ONLY the LCD display is running, (no fans connected), it draws 260ma and it heats up that 7805 to 67C.

The PSU says that the circuit is consuming about 3.7 to 4 watts ... I didn't think you could heat stuff to 67C with just 4 watts can you?

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

i use those buck modules all the time, they are really good - but dont trust the pot on them.
cut the track for the pot and link one of the fixed resistors

I've never used the POT on them ... always the trace cut!

[eccerr0r]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

It shouldn't get that hot with the heat sink. At 200mA of 12V to 5V it should get less than 1.5 watts and this is in the threshold of not needing a heatsink at all. Did you measure current and see what happens as you disconnect possible consumers of the 5V from the 7805?

[stj]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

i use those buck modules all the time, they are really good - but dont trust the pot on them.
cut the track for the pot and link one of the fixed resistors

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

OK, replacing the 7805 didn't help the heat situation. I know that the higher the input voltage on those regulators, the hotter they run, so here's what I think I might do next ... well ... one of two options:

1) I could run 12 volts into a buck converter and drive the board at around 6.5 volts. But I would need to cut the trace on the PCB so that I can still feed 12 volts to the fans.

2) Same as above, only instead of powering the board with a 7805, I use a miniature buck converter that would be a replacement for the 7805, driving the board at 5 volts and heat wouldn't be an issue since they can tolerate several amps. I've already got a grip of these and they should work fine for powering that MC and its related hardware.

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

OK, some interesting new knowledge ...

When the other two fan ports wouldn't lite up the fans, I suspected that maybe it had something to do with the thermistor mounted above the MC and I tried warming it up but no luck... so I decided to see what this board does with the LCD screen attached to it so I pulled it out of the chassis and connected it.

When it boots, it says that it is Jan 1, 1980, and that it was 80 degrees ... so I then connected the other fan to the nonworking port and when I heated the thermistor this time, it kicked on the other ports.

There are two fans on each end of the unit, and they are mounted so that one side blows air into the unit and the other side blows air out so I'm sure that they connect it so that only two fans are moving air until it gets too hot then it kicks on the other set ... and it also kicks up the fans that were running so that they run faster.

When I was done testing, I cut power and felt the heat sink on the 7805 and it was TOO HOT TO TOUCH

Any thoughts on that? It's just a 7805, and I have a bunch of those with new heat sinks should I replace it?

Current draw was only half an amp on the 12 volt bench supply. So the 7805 is powering the MC, and the LCD screen but the fans are sourced from +12 outside of the 7805 and they take about 140ma each and I had three of them running so the 7805 was technically only taxing the power supply with less than 200ma and it got that hot.

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

i think you probably dont need more than 500w - real 500w that is, not the inflated BS on a lot of psu labels
did you check all the fans for current draw?

I did, and what is interesting is that I can't get them all to run off of the main controller board - it seems like two of the four fan ports wont power the fans so imma check for voltage but I know the microcontroller is working because at least two of the ports work and if the other ones don't have voltage then its probably the transistor or something ... gonna dig into that now.

When I connect the fans directly to the bench power supply only three of them work ... they are old and have taken obvious moisture wear as there are some kind of crud deposits built up around them ...

I'm ordering two of these to replace all four.

Other than that, I can't find anything wrong with this thing ... so I've ordered replacement heat transfer pads for the transistors, plus a tube of thermal grease for the LEDs where they attach to the main heat sink ... the grease that's on there now is 20 years old so cleaning it all up and replacing that seems like the right choice ... and I'm just gonna tap the solder connections and maybe add a touch of leaded solder to them just to make sure there are no cracked solder points then ill put everything back together and make sure everything is completely away from any potential ground points and see what happens.

[stj]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

i think you probably dont need more than 500w - real 500w that is, not the inflated BS on a lot of psu labels
did you check all the fans for current draw?

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

Seems to me this would have been a better design for this unit vs what it is now.

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

So, given how this thing is actually wired up, does anyone see a problem with me wiring it for a single 1,000W PS vs two 500W PSUs as it is now?

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

i think the fault was one of those big power tracks shorting to the frame or a screw

See, I would agree with that if not for the long melted wire and all the burn marks on the master control board... clearly, an indication that something on that board was drawing too much current.

Also, given the way these LEDs are wired, I'm wondering if seeing 5 amps on the 5-volt line is really all that abnormal in this circuit.

Also, the burnt wire and fried board was all sourced from the +12 but then regulated down to +5 where the burn marks were around the regulator then on the opposite end of the board along the ground strip next to an op amp chip and two digital pot chips. The op amp chip drives the gates of the LED driver boards.

On the flip side of that burnt ground strip, +12 runs along that same edge and feeds the housing fans directly which are controlled via the microcontroller with a simple transistor switch, emitter to ground, base to MC through resistor and collector directly wired to the fans negative side and the positive side of the fans go directly to +12.

Also they only use one transistor for two fans and they're only S8050s.

Something else I learned is at the controller board, the pins that drive the gates ... are all connected in parallel ... this board has 6 separate connectors for the LED driver boards and on all of them, all pin 1s are connected, all pin 2s etc. etc. so each gate gets the same applied voltage on all driver boards, which Im sure just gives uniform brightness etc.

I replaced the caps on the main controller board and now that I know it's powered by +12, I'm going to connect 12 volts to it and see what kind of current its drawing. Though the housing fans are not connected and neither are the LEDs but maybe it will show me something useful. If the magic smoke doesn't start leaking ill take some readings around the board and see whats going on.

[stj]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

i think the fault was one of those big power tracks shorting to the frame or a screw

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

load balanced between the 5v and 12v - not bad.

I'm not sure what you consider balanced, but based on the current draw that I used to light up a row of LEDs, here is the load that would be placed on each transistor



In fact, I threw the circuit into a simulator and though I know the values aren't accurate, the LEDs are all set the same and clearly you can see that Q4 is the redheaded step child in this family...

[eccerr0r]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

Disconnect boards one at a time until the 5A stops being 5A ... ?

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

load balanced between the 5v and 12v - not bad.

But does this get us any closer to a solution?

[stj]

Re: Fish Tank LED Power Supply Gets Hot then shuts down

load balanced between the 5v and 12v - not bad.

[EasyGoing1]

Re: Fish Tank LED Power Supply Gets Hot then shuts down


And for anyone interested ...

Here is the front side of the PCB with its traces connected with orange lines





And here is the back of the PCB in mirror image with its traces connected with yellow lines




Here is the front PCB image again with both front and back traces





And here is the PCB with all traces, resistors and labels





And here is the schematic with the LEDs properly labeled in their respective colors