Author Topic: Seeking advice on power distribution in large sculpture  (Read 672 times)

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Offline Involute

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Re: Seeking advice on power distribution in large sculpture
« Reply #25 on: May 21, 2018, 03:55:07 am »
Thanks for thinking this through, Brian.  They're 12V relays, but I get the idea.  I could probably overdrive them briefly with 24V, but 48V might significantly reduce their life expectancy, even if applied in brief pulses.  Regardless, I'd still need a supply capable of supplying full power, if only briefly.  So it seems to me that this approach, as well as PWM, would both be solutions for reducing heat (due to lower average power), but not the size of the supplies.  The relays won't be energized for more than 5 seconds at any time (and, generally, more like half a second), so I'm not sure heat is going to be an issue.  I don't think fans will be a big deal, since this thing is going to be making quite a racket on its own.
 

Offline BrianHG

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Re: Seeking advice on power distribution in large sculpture
« Reply #26 on: May 21, 2018, 04:30:00 am »
Are you saying you already have the 12v relays?
48vdv, 120vdc, 120vac versions exist.
If you are stuck with 12v versions because you already purchased them, the approach will be different.

If they are only going to be energized for a second or two at a time, with multiple seconds off, please provide us with the average duty cycle.

Maybe all you need is a good capacitor in the high 47000uf for around every 10 relays on each controller board which will have enough kick to switch on the relays, using a 1kw linear 12v unregulated supply.  1 beefy toroid should do the trick with a few stud diodes and 100000uf cap driving a whole bank of relays.  Don't bother with the PWM as this stage.  This type of supply and all the DC filter caps properly wired and laid out will send 2-3kw power surges without even noticing a thing.  No voltage regulation required for the relays, just use a 10v to 11v transformer.  For the MCU driving the transistors or logic level mosfets, just add a series 1N4002 and a big cap + 7805 which should handle any deep power sags.
« Last Edit: May 21, 2018, 04:40:28 am by BrianHG »
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Offline nctnico

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Re: Seeking advice on power distribution in large sculpture
« Reply #27 on: May 21, 2018, 04:38:09 am »
Thanks for thinking this through, Brian.  They're 12V relays, but I get the idea.  I could probably overdrive them briefly with 24V, but 48V might significantly reduce their life expectancy, even if applied in brief pulses.
Definitely not. The coil of a relay is an inductor so when power is applied the current will ramp up linear. So if you cut the power at the right time (=PWM) it is as if the relay is powered from a lower voltage. In one of my designs I used a 12V relay from a power input which can range from 20V to 80V. Using PWM and constant power control the relay is perfectly happy.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline BrianHG

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Re: Seeking advice on power distribution in large sculpture
« Reply #28 on: May 21, 2018, 04:42:05 am »
Thanks for thinking this through, Brian.  They're 12V relays, but I get the idea.  I could probably overdrive them briefly with 24V, but 48V might significantly reduce their life expectancy, even if applied in brief pulses.
Definitely not. The coil of a relay is an inductor so when power is applied the current will ramp up linear. So if you cut the power at the right time (=PWM) it is as if the relay is powered from a lower voltage. In one of my designs I used a 12V relay from a power input which can range from 20V to 80V. Using PWM and constant power control the relay is perfectly happy.
This is clearly a misunderstanding.  I was telling the OP to buy the same style relays with 48vdc coils.  The 48v version has 1.2kohm coil which makes for a much lower current allowing for much thinner conductors and a much larger acceptable turn on voltage.

This shrinks drive transistors, their heat, allows for my zener diode and cap trick.
« Last Edit: May 21, 2018, 04:45:53 am by BrianHG »
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Offline Involute

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Re: Seeking advice on power distribution in large sculpture
« Reply #29 on: May 21, 2018, 07:46:46 am »
> Are you saying you already have the 12v relays?

No, they're just the ones I initially zeroed in on due to cost, appearance, size, and preferring 12V to other choices.  The 12V preference was due to the realization that I'd be generating my small 5V logic supply on each PCB from the relay supply.  The current would be small, so a linear regulator dropping 12 - 5 = 7V wouldn't get too hot, and would be cheap and easy.  Increasing the relay supply invalidates that and pushes me into a small SMPS.  Not the end of the world, so if going to a higher voltage relay supply is warranted, so be it.  As I've said previously, I don't think heat will be a major concern, due to the low duty cycle of these relays, so I'm still not convinced I need to go to 24V or 48V, unless I'm missing some other benefits.
 

Offline KrudyZ

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Re: Seeking advice on power distribution in large sculpture
« Reply #30 on: May 21, 2018, 08:03:01 am »
Where will this sculpture be living?
You might have some serious issues with EMI, jamming radios, etc. all over the neighborhood...
 

Offline Involute

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Re: Seeking advice on power distribution in large sculpture
« Reply #31 on: May 21, 2018, 08:37:11 am »
> Where will this sculpture be living?

Unclear at this point.  I'll be building it on spec through crowdfunding.  Before the campaign, I plan to contact music festivals (Coachella, Lollapalooza, Electric Daisy Carnival, etc.) to see if they'd let me display it.  Ultimately, there's a new, interactive space opening here in Los Angeles later this year that expressed interest in a smaller version, though even that was beyond their budget.  I'm pretty sure they'd be willing to take this one for a deep discount (or even for free), which i'd be able to offer, since it will have already been paid for.  I realize crowdfunding's a long shot for something like this, but I need to go through this exercise just to figure out how much it will cost, and if it will work.  I plan on building one module for testing.
 


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