power consumption of modular systems during power up

Hi,

I've stumbled upon a problem that has been less discussed (or maybe I haven't just found the right topics?).
I took time and effort to build a modular system and quadruple-check all the specs.
The specs of my system are +12V 932mA / -12V 474mA / +5V 0mA.
I'm using a uZeus with the 1A power adapter.
I looked at the specs and thought I'm still good but when I powered up lights started flashing and I powered off immediately.
Luckily all modules are fine. After recovering from the shock I found info somewhere that some modules need temporarily more juice at power up (especially digital modules?).
Why are the power consumption specs of modules not taking this into consideration?
Is there a way to calculate or otherwise find out the maximum power consumption of a specific module?
If not, how big of a buffer should I percentage wise leave so I'll not encounter these kind of problems again?

If I now go and buy the 3A boost power adapter for the uZeus will I be fine and able to power up above mentioned system safely without skipping heart beats or losing more hair?

Definitely go with that higher amperage "brick". That'll push the uZeus up to 2000mA on the +12 rail.

The problem you're running into is "inrush loading". When you switch on any electronic device, there's always some sort of higher load for the first few milliseconds, and that can pop the supply if you've gotten the current spec too close to the quoted operating tolerances. To avoid this, don't let each summed current value on the build's DC rails exceed 3/4ths of the stated P/S's maximum current per rail. This is actually a pretty common rule of thumb with modulars, tbh.

As for consumption specs, the reason you don't see this inrush figure is that sometimes it's an important factor, and sometimes not. As you've noticed, yep, digital modules are notorious for inrush issues. With simple analog modules, not so much. So everyone pretty much agrees that the "normal load" current figure is the correct thing to cite, and you just keep that "3/4ths rule" and the total current per rail in mind during the build process as that ceiling can vary from module to module and P/S to P/S.

Thanks for the reply and the very useful info.
The rule of thumb could at least be stated on the manuals of power supply modules. I'm pretty sure I'm not the only one who has not heard of the 3/4ths rule before.
I've now ordered the boost adapter!

the 3/4 rule is quite widely known - and mentioned in a lot of newbie threads - 90% of the one's I've seen anyway!

probably not documented in manuals as they expect you to have done your research!!

the rule also applies to all rails - I think you may still have issues with the -ve rail - so don't be overly surprised if the uZeus craps out even with the more powerful brick - make sure you've set the jumper to the higher power on the -ve rail - but iirc the max draw on that is 500mA which you are really very close to already!

EDITED Oct 16th 2021, 11:33

Yes, I had already thought about the possible issue with the -ve rail.
You certainly have an interesting way of trying to help somebody out in a condescending sort of way..

You certainly have an interesting way of trying to help somebody out in a condescending sort of way..
-- happygolucky

well - not meant to be condescending - forthright perhaps, but not condescending... at least you find it interesting!

possibly to do with the fact that I'm in my 50s from the North West of England, have lived nearly a 3rd of my life in Europe and don't take shit from people, even if they are paying me.. and you aren't!

well - not meant to be condescending - forthright perhaps, but not condescending... at least you find it interesting!

possibly to do with the fact that I'm in my 50s from the North West of England, have lived nearly a 3rd of my life in Europe and don't take shit from people, even if they are paying me.. and you aren't!

-- JimHowell1970

Such a welcoming place...

EDITED Oct 17th 2021, 19:48

it is man, it is!!

I find it extremely welcoming and friendly - especially after 16 years in the lowlands...

you just have to realise that our default settings are sarcasm and taking the piss - often out of ourselves and our friends - and that no harm is meant ... you ought to start worrying if we don't, though!

EDITED Oct 17th 2021, 20:12

The rougher the seas, the smoother we sail. Ahoy!

Everything seems to be working fine with the boost adapter even though I'm still almost maxing out the -12V rail.
I guess the modules need the extra from the +12V rail during power up...
Thanks again and I'm keeping my fingers crossed that all continues to keep working!
Now I'd like some fuss free time to really dig in and hear what I can do with my first modular set-up.

I like Doepfer cases they do a good job on power needs.

Erica, also. They've long had a thing for overspecced power supplies...a habit I definitely endorse! And Trogotronic has a 10 AMP supply, especially given that they also make vacuum tube modules. Case From Lake is 100% up there as well...big Doepfer or Meanwells, sort of like how the Monorocket stuff was overspecced.

The ultimate, though...that's got to be ADDAC System's 197 hp monsters. You can get these with up to 20 AMPS on the +12 rail!