Need help sourcing a power supply: +5VDC >=120A

[John Craver]

Hi, all.

I have a bit of a strange request. At work, I have a device that I have to repair that uses 400 multiplexed itty bitty incandescent lamps (10 rows of lights, each with 40 lights). They each use 5V at 300mA when they're on (they're actually 1.5V lamps, but they have a 4R2 resistor and 1N4002 diode in series with each one to make it compatible with 5V. I know, it's inefficient to do it that way, but that's the way they did it, and my timeframe is a bit tight to be modifying it now).

Anyone know where in town I can get a power supply that could supply 120A at 5V? Alternatively, I can power each of the 10 banks of lights individually, and use multiple smaller power supplies.

Any advice with this is appreciated. Frankly, I'm stumped.

Thanks
-John C.

--
VanHackspace (VHS) general list: vhs-g...@lists.hackspace.ca
http://vancouver.hackspace.ca/wp/mailing-lists/

[Stephen Young]

To make it clear,

the ROWs are multiplexed?

Each LAMP requires 300mA?  I.e., each lamp sits in parallel on the row bus?  If yes, can you modify to put them in series (60Vat 300mA, easier to deal with...)?

One Q&D solution would be to modify a few old microwave transformers by replacing the secondary, as if making a spot welder, low volts, lotsa amps...

SDY

---

From: John Craver <jcr...@shaw.ca>
To: vhs-g...@lists.hackspace.ca
Sent: Friday, November 9, 2012 12:47:52 PM
Subject: Need help sourcing a power supply: +5VDC >=120A

[Stephen Young]

Another question, what was used to power them "before"?  Can't it be fixed?  Did it ever work?

SDY

---

From: John Craver <jcr...@shaw.ca>
To: vhs-g...@lists.hackspace.ca
Sent: Friday, November 9, 2012 12:47:52 PM
Subject: Need help sourcing a power supply: +5VDC >=120A

[David Carne]

If they're multiplexed, then they're not all on at the same time, are they? How is the multiplexing done?
 Whats the maximum that can be on at any one time [during the multiplexing?]

 I strongly doubt the old power supply was 5V/120A, unless it had welding-cable size wires coming out of it!

--David Carne

[John Craver]

It's a 2 foot diameter replica of the Science World dome made from 1/8" steel plates and chrome plated. There are 400 holes drilled in it, each with one of these lamps. Apparently it was built int the early 90's (which makes it almost as old as me), and there was no controller, no driver, and no power supply. Just the dome with the lamps and wires.

As I mentioned before, there is a 4.2 ohm resistor and a 1N4002 soldered in series with each lamp, then covered in heat shrink.

Yes, you are correct, there are 40 lamps connected to each bus, and there are 10 buses.

Unfortunately, this project had absolutely no documentation

And to boot, it has to be mounted onto the CEO's car in 10 days, in preparation for the Santa Claus parade, so it has to be powered off of a car battery.

----- Original Message -----
From: "Stephen Young" <frenchcanadi...@yahoo.ca>
To: vhs-g...@lists.hackspace.ca
Sent: Friday, November 9, 2012 1:08:55 PM
Subject: Re: Need help sourcing a power supply: +5VDC >=120A



Another question, what was used to power them "before"? Can't it be fixed? Did it ever work?


SDY

[Stephen Young]

Plug in the soldering iron, get the LEDs out and start 'bussing'!

SDY

---

From: John Craver <jcr...@shaw.ca>
To: vhs-g...@lists.hackspace.ca

Sent: Friday, November 9, 2012 1:19:28 PM

[Stephen Young]

Why is it dawning on me that it was never functional, Edsel style (design the car first and then try to fit a power source into it ;), the company lost a lot of money on that one...).

So what you originally wanted is a DC-DC converter, high amps...  Or a few medium amps...  Newark or Digikey, delivered by Tuesday, have you checked them out?

I still think that re-LEDing the whole ball of wax (...) is the way to go, is it feasible?

SDY

---

From: John Craver <jcr...@shaw.ca>
To: vhs-g...@lists.hackspace.ca

Sent: Friday, November 9, 2012 1:19:28 PM

[John Craver]

One more important detail that I missed out:

There are 40 bulbs on each bus. Each bulb in the bus is connected to the 9 other bulbs in the other buses. This gives a 10x40 matrix, so that each bulb is individually addressable. The project requires that they still remain individually addressable.

----- Original Message -----
From: "Stephen Young" <frenchcanadi...@yahoo.ca>
To: vhs-g...@lists.hackspace.ca
Sent: Friday, November 9, 2012 1:22:12 PM
Subject: Re: Need help sourcing a power supply: +5VDC >=120A

Plug in the soldering iron, get the LEDs out and start 'bussing'!


SDY

[John Craver]

Long-term, yes. But I have to have this done by the 19th, so I'm in a bit of a rush.

----- Original Message -----
From: "Stephen Young" <frenchcanadi...@yahoo.ca>
To: vhs-g...@lists.hackspace.ca
Sent: Friday, November 9, 2012 1:27:59 PM
Subject: Re: Need help sourcing a power supply: +5VDC >=120A

Why is it dawning on me that it was never functional, Edsel style (design the car first and then try to fit a power source into it ;), the company lost a lot of money on that one...).


So what you originally wanted is a DC-DC converter, high amps... Or a few medium amps... Newark or Digikey, delivered by Tuesday, have you checked them out?


I still think that re-LEDing the whole ball of wax (...) is the way to go, is it feasible?


SDY

[Stephen Young]

ORrrrrrrrr.....  Remove all the lamps (screwdriver on the outside, whack with a hammer, go to next one, repeat.  Shake the mess out.), mount a super-duper bright, 13.8Vdc powered LED on heatsink at the base, and let the light shine through the holes...

SDY

---

From: Stephen Young <frenchcanadi...@yahoo.ca>
To: "vhs-g...@lists.hackspace.ca" <vhs-g...@lists.hackspace.ca>
Sent: Friday, November 9, 2012 1:27:59 PM

[John Craver]

Tell ya what, that'll be my backup plan. I still have that 100W LED kicking around.

----- Original Message -----
From: "Stephen Young" <frenchcanadi...@yahoo.ca>
To: vhs-g...@lists.hackspace.ca, "Stephen Young" <frenchcanadi...@yahoo.ca>
Sent: Friday, November 9, 2012 1:31:40 PM
Subject: Re: Need help sourcing a power supply: +5VDC >=120A

ORrrrrrrrr..... Remove all the lamps (screwdriver on the outside, whack with a hammer, go to next one, repeat. Shake the mess out.), mount a super-duper bright, 13.8Vdc powered LED on heatsink at the base, and let the light shine through the holes...


SDY

From: Stephen Young <frenchcanadi...@yahoo.ca>
To: "vhs-g...@lists.hackspace.ca" <vhs-g...@lists.hackspace.ca>
Sent: Friday, November 9, 2012 1:27:59 PM
Subject: Re: Need help sourcing a power supply: +5VDC >=120A





Why is it dawning on me that it was never functional, Edsel style (design the car first and then try to fit a power source into it ;), the company lost a lot of money on that one...).


So what you originally wanted is a DC-DC converter, high amps... Or a few medium amps... Newark or Digikey, delivered by Tuesday, have you checked them out?


I still think that re-LEDing the whole ball of wax (...) is the way to go, is it feasible?


SDY

[David Carne]

John,

If they're going to be multiplexed in the standard way [Connect one row to gnd, drive column as necessary or vice versa, then repeat with next row], then you only need 40 * 300ma, which is 12A, which is much more realistic and doesn't require welding-cable thickness power supplies.

--David Carne

[Tom Keddie]

Since they're a matrix you can code the controller to limit the maximum current consumption (by limiting the number of lights on at one time).

I would use 10 x 1A supplies with mosfet control to feed the 10 side and use 40 mosfets to pull down the other side.  Write the controller so that only 3 of the lights on each supply are on at one time (to give 900ma with some margin for the p/s).  You only need to flicker at 50Hz to give the illusion they're always on.

Cheers,
Tom

[Stephen Young]

Now you see the importance of including ALL of the details in the original request (so as NOT to have blabber-finger SDY fill up the board with replies that suddenly cannot solve anything).

You main problem is the 12VDC battery, which will supply a spiky voltage between 11.5 to 15+ volts (remember that if you use a microprocessor to address the LEDs...), and having to supply a load that requires more voltage than that.

Can you add extra batteries?  They don't have to be on the alternator, the parade does not last that long.

If you can activate the light sources somewhat individually, your load will never have to be as significant as you fear.  Re-calculate.

Is this a Union place, i.e., can you use outside help without creating an internal storm?

SDY

---

From: John Craver <jcr...@shaw.ca>
To: vhs-g...@lists.hackspace.ca; Stephen Young <frenchcanadi...@yahoo.ca>
Sent: Friday, November 9, 2012 1:29:43 PM

[James Gregson]

Can you flash incandescents at 50Hz and still get meaningful output? Don't the filaments cool in the off parts of the duty cycle and lead to high lag on the on parts?

[Stephen Young]

True matrix, one bulb on at any one time, 5V at 300mA.  No more problem, but for multiplexing speed.  And number of lines.

right?

SDY

---

From: John Craver <jcr...@shaw.ca>
To: vhs-g...@lists.hackspace.ca; Stephen Young <frenchcanadi...@yahoo.ca>
Sent: Friday, November 9, 2012 1:28:58 PM

[John Craver]

Geez. Massive brain fart.

Yes, by multiplexing these as they're wired up, the maximum current draw will only ever be 12A.

I've already received the mosfets from digikey, and I've confirmed that the lamps will not flicker at 60Hz.

----- Original Message -----
From: "Stephen Young" <frenchcanadi...@yahoo.ca>
To: vhs-g...@lists.hackspace.ca
Sent: Friday, November 9, 2012 1:42:44 PM
Subject: Re: Need help sourcing a power supply: +5VDC >=120A

True matrix, one bulb on at any one time, 5V at 300mA. No more problem, but for multiplexing speed. And number of lines.


right?


SDY

[Tom Keddie]

John,

Are you trying to make them into patterns or just illuminate them all?

Thanks,
Tom

[John Craver]

Ideally patterns, but illuminating them at all if it doesn't work.

[John Craver]

Well, Shee-it! I just wired up the lamp to an arduino and fed it a 0 to 10% duty cycle fade in/out pattern, and found that 12V is ideal for this arrangement. Problem solved, computer power supply it is.

Thanks for the help, all!

And Steven, thanks for your help and your witty (yet effective) backup plan.

-John

[Loial Otter]

Oh boy is this ever my kind of thing (anybody see my led displays?)

Okay, what you have is a matrix display. Very simple to drive but does take refreshing. At any given point only 1/10 of the lights are on. The normal way to drive this is to have a set of shift registers with high current latches or the like and some very beafy high-side switches on the commons. You clock in your data from a microcontroller and once ready you latch into the drivers. You then shift in the next line while its driving the common and latch while switching commons.

These things are brilliant. Your going to need a 12A minimum supply and possibly more like 20A.

I have some code from a while ago that drove some 160x24 dual colour led displays that was awesome... kinda got upset at that project when one of my prized displays went missing at a convention.

As for power requirements, my LED displays use three 10A 5V supplies in tandem if I remember correctly. The high current switching of the commons made them whine horribly though.

I'm pretty sure if we don't have shift registers at the space I have some myself. You need to make sure the commons are on the 5v side as hig-side control is much easier. You then will need the shift registers, transparent latches and 300mA drivers set up (mosfets work great for this... I might have enough but I remember there being some nice ones at the space too). The processor you'll need is probably a low end arm. A RPi may also work if you can get the SPI drivers set up (SPI can drive shift registers very well) but honestly I suggest using a seperate microcontroller so you can get the better timing. If you can refresh fast enough you can also get some level of dimming through pulse code modulation during refreshes.

Err... sorry about the long post... alternatively you can hire me for this one ;)

Regards,
    Loial

[Loial Otter]

Oh, if you can get 60 pins of GPIO or a FPGA/CPLD you can drive these with just the 300mA drivers and high side switches. (Though very tempting, the IGBTs on the shelf probably have too much leakage for this).

[John Craver]

I have an Arduino Mega 2650 that I could use. I also have another RPi. I'll probably go with the Arduino Mega for now, since I still need to get far more familiar with the RPi. I have some P-Channel mosfets for driving the high side, and some ULN2803s for the low side. Since I'm running these lamps at 12-15V-ish, at a 10% duty cycle (maximum), the ULN2803s should be able to handle the current. It seems to be working great according to the test circuit I wired up.

I may enlist your help if I get a request to replace the incandescent lamps with RGB LEDs. I'll have to drill out the holes to fit a 5mm led though; i haven't seen 3mm rgbs available anywhere.

----- Original Message -----
From: "Loial Otter" <loial...@gmail.com>
To: vhs-g...@lists.hackspace.ca
Sent: Friday, November 9, 2012 2:55:32 PM
Subject: Re: Need help sourcing a power supply: +5VDC >=120A

[Loial Otter]

yup, that'll do nicely. If you're going to use a series of shift registers i Highly suggest using the atmega's SPI channels. That'll allow the CPU to do other things while the data is being shifted out. The mega has enough pins though you might be able to just do 40 bits wide latching or, hmm, if you did 8-bit bus you could latch to each set of 8 in series then drive. Lotsa options.

[chris d]

Without reading most of the emails in this thread I'd like to answer the original question of where can one find a 120 amp power supply. i have such a beast, picked it up at an auction a while back. It has a knob to adjust voltage, 0 to 12 volts, and a digital voltage readout. It is rated to something like 200 amps and it weighs about as many pounds.

And it is for sale! $60 and I'll even help get it into your cat. Err car i mean.