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how far can you push the blacet psu?
MUFF WIGGLER Forum Index -> Fractional Rack Modules  
Author how far can you push the blacet psu?
johnnymad
i just sold a bunch of my frac rig and would like to sell one of my power supplies. i'm hoping to sell one and power my whole rig off of one psu. i did the math, and it would be close to a 600 ma load on my power supply. i know blacet states it's conservatively related, but would that be pushing it too far? i think i read somewhere on the forum that 550 ma wouldn't be a stretch.
Babaluma
i have no hard evidence to go on other than recommendations, but if it were me i wouldn't want to push it that far. it could be a fire hazard and safety first!!!

does anyone know how to ACTUALLY MEASURE the current draw from a PSU? i.e. where do i stick my probes, and how to i set/read my DMM?
DGTom
I ran 3 rows, prob close to, or just over, 600ma off 1 PS-500... it worked, I didn't feel good about it tho & wouldn't want to do it for long.

Get an 800ma/Rail PSU, it'll be much happier, your modules will be much happier & you can sell both your Blacets.
Cat-A-Tonic
I ran 2.5 racks of Frac from one Blacet PSU when I was first getting started.
I added an STG YU Gate Delay and it wouldn't function in its full range when starved of power.
Try it out, and if you notice starvation malfunctions you know you are over the limit.
Exuviae
http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200 321255_200321255

I picked up one of these bad boys on Sunday at Menards and my two racks of frac that are supposed to be pushing 500ma based on Blacet's max current draw, don't go over the 300ma mark even at high patching on all available modules.

This thing, in Amp mode, only gives you a reading the first number of your ma (3=3xx) - but that being said, I am waaaaaay lower than I thought I was.

$27 well spent.

do it.
Babaluma
repeat: where do you stick your probes?
BugBrand
You shouldn't be looking at the wall power draw! Its the power coming out of the PSU that you're concerned with. (I'm shakey at the calculations)

You want to stick your multimeter in series with the PSU output powerline.
Def. attach it with the power OFF!

Do the positive rail first -
- disconnect the +ve cable from PSU to rack/distro.
- attach one probe to PSU +v and then the other probe to the rack.
- switch ON and observe current draw.
(it doesn't matter too much which way round you get the probes - you may get a negative reading but that doesn't matter in this case)

Turn OFF.
Remove multimeter.
Re-attach +VE cable

Do the same again for the -ve side.

Job Done!
Exuviae
EDITED for clarity:

If you put this between the PSU and the wall - this tells you how much power the PSU is drawing from the wall. if the PSU is only drawing 300 ma from the wall, which is what the modules are "requesting", how could the PSU be delivering more than that to the modules?

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200 321255_200321255

am I missing something here?
consumed
consumed
this diagram will give you a per-module measurement on each rail
however, i imagine you could set the same up between the psu and distro to measure total draw

also, i believe the draw will increase or decrease based on what you've got patched up.
BugBrand
I think....
(please someone clarify)

P=IV
Power = Current x Voltage

Ideally, the Power for primary (power inlet) and secondary (to local regulators) will be identical but in practice a transformer will lose some due to not running at 100% efficiency.

Lets take 75% efficiency as an example.

12 watt supply at 120v
gives I_input = 0.1A

75% of 12watt gives 9watts the other side.

But the secondary is at, say, 30V (two x 15v)

9 watts supply at 30v
gives I_output = 0.3A

***
In essence:
The difference of Input current vs Output current is due to the different voltages at primary and secondary.

(if you're measuring 300mA going IN to the PSU then the output current will be larger than that!)

consumed wrote:
this diagram will give you a per-module measurement on each rail
however, i imagine you could set the same up between the psu and distro to measure total draw

also, i believe the draw will increase or decrease based on what you've got patched up.


All true!
johnnymad
DGTom wrote:
Get an 800ma/Rail PSU, it'll be much happier, your modules will be much happier & you can sell both your Blacets.


i think i might do that. the hex zone is the main problem. without it, i'd be well under 500 ma. d'oh!
Exuviae
Well - this thread has gotten me thoroughly concerned enough to email JB himself and ask about my specific power drawing.

I have one Blacet PSU (500ma) and according to the Blacet website, I am running 497ma worth of modules...Blacet only - no DIY or otherwise...so I guess I need to know for sure since the amperage reader I bought apparently doesn't give the appropriate info confused
Muff Wiggler
John has told me that the Blacet PS500 will work just fine supplying up to 550ma.
Adam-V
BugBrand wrote:
I think....
(please someone clarify)


Sounds about right to me.

Cheers,
Adam-V
Exuviae
Muff Wiggler wrote:
John has told me that the Blacet PS500 will work just fine supplying up to 550ma.


Thanks for sharing, Muff!
Muff Wiggler
no problem! I should have also mentioned that I run all of my (many) PS500 units very close to 550ma, and have for years, without any trouble at all 8_)
Exuviae
Again, Muff, thanks.

This is exactly why I love this place!
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