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Load on a power supply?
MUFF WIGGLER Forum Index -> Fractional Rack Modules  
Author Load on a power supply?
whomper
Hi,

I have a Blacet 500ma power supply with several modules drawing power.
As I also have 3rd party modules, ones that I am not sure how much power they draw, I am having difficulties assessing my limits with respect to amperage load.

is there any clear way to assess the power supplies limit in real world, and not theoretical calculations?

Whomper
consumed
whomper wrote:
is there any clear way to assess the power supplies limit in real world, and not theoretical calculations?


yes. add modules until most of your modules malfunction on power up. you have just hit your real world limit. remove a module or two and buy a new supply. lol
Muff Wiggler
Good question! If you get really really good at circuits, you can look at the components on a board, know what draw each component adds, and realistically ballpark the draw.

Me, I can't do that lol I usually check with the designer of the circuit, who often knows how much current the unit will pull.

If not, you can build a little rig to test current draw. I haven't done this yet, but it's been on my to-do list for a while. So far I've always gotten an answer from the designer, so haven't really needed to.

Basically, you would need to take a power cable, and cut it up a bit. You'll need to cut the negative and the positive wires (leave the center ground wires intact), somewhere before the MTA connector that joins your module. Next, you need to come up with a way to connect/disconnect the cut you have made, in each wire. Perhaps alligator clips with rubber insulation.

You need to measure the positive and negative rail seperately, one at a time.

Start with your power supply OFF, the alligator clips on both power rails connected. Connect the power cable to the PSU, and to the module. Power the thing up to make sure both alligator clip joins are working, and the module is powered. Now turn the PSU off.

To test one of the power rails (doesn't matter which one you check first, positive or negative - most modules have a larger draw on the + side, but some have a larger draw on the -), you'll need to 'break' the wire (disconnect your alligator clips), and insert a multimeter IN THE POWER PATH of the wire. ie., connect the alligator clip coming from the PSU side of the wire to one side of your multimeter, and connect the other side of your multimeter to the alligator clip going to the module.

My meter can auto switch negative and positive, so I don't have to worry about hooking it up the wrong way - but check with yours.

Now set your meter to measure mA's, say in the 0-100ma range.

Turn on the PSU.

Plug as much shit into the module as you can, and set every knob that might increase voltage to max (clock rate, etc).

Your meter will tell you how much current is being drawn.

power off, repeat for the other power rail.

Write down the numbers.

Done 8)
consumed
seriously though--theoretical limits may not correspond to the real world. and with lower quality designs/parts/etc, you also start to run into efficiency questions as well. paul/motm always recommends to run only up to 75-80% of the theoretical limit of your supply. reason: the last 20% is where the psu really heats up. ive proven this. (i have a maxed out PSU at the moment.)
Kwote
consumed wrote:
(i have a maxed out PSU at the moment.)


DANGER WILL ROBINSON?? or are you simply just gonna grab another supply no harm no foul?
J.w.M.
So... what happens when you max out a PSU? While I've heard that a single Blacet power supply can usually power an average of two racks worth of modules, I've also heard the estimate as only one VCO/Filter/VCA/EG per PSU. When I go over that, will I run the risk of screwing things up permanently?
Muff Wiggler
i don't think you can damage anything by underpowering it

Best way to test (courtesy of Grant R)

Plug a VCO into the PSU, power it up, let it warm up.

tune it so you can play an interval and maintain proper tuning. Use a tuner to watch the stability of the VCO.

Now, power down the PSU, and add some modules. Power back up, let warm, check the tuning stability on the VCO. As long as it stays solid you are good. When the VCO starts to become unstable, you are asking for too much from the PSU.
Kwote
Muff Wiggler wrote:
i don't think you can damage anything by underpowering it

Best way to test (courtesy of Grant R)

Plug a VCO into the PSU, power it up, let it warm up.

tune it so you can play an interval and maintain proper tuning. Use a tuner to watch the stability of the VCO.

Now, power down the PSU, and add some modules. Power back up, let warm, check the tuning stability on the VCO. As long as it stays solid you are good. When the VCO starts to become unstable, you are asking for too much from the PSU.


werd. still don't have a tuner though. what about that software oscilloscope? any tests you can run on that. i'm guessing no.
Kwote
J.w.M. wrote:
So... what happens when you max out a PSU? While I've heard that a single Blacet power supply can usually power an average of two racks worth of modules, I've also heard the estimate as only one VCO/Filter/VCA/EG per PSU. When I go over that, will I run the risk of screwing things up permanently?


i'm trusting from my own experience and everything Muff's posted regarding this subject in the past, that you can go ahead and power up 6u worth of frac modules on the PS500. i'm getting close to my 550 limit and everything's running smooth as a newboarnzz beee hind.
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