# Power supplies (2)

A project log for SPDT16: 16-bits arithmetic unit with relays

Let's imagine I could get about 200 SPDT relays. Of course I would know what to do with them :-D But will 200 be enough ?

Yann Guidon / YGDES 04/18/2016 at 02:272 Comments

Since the voltage is settled to 3V, the next step is to provide it with a suitable current. I expect the consumption to be significant: if one relay coild draws 1/2W, a whole system with 200 relays will draw 100W !

So let's start with finding a beefy power supply in this range. I have this one:

Is 150W enough ? If not, I can find another.

(Edit: yup, while looking at another old project, I found a brand new 12V 30A "brick". With a fan. Now I hope it's sufficient.)

Now this outputs 12V but SPDT16 needs "around 3V". I must use "point of load" DC/DC step-downs. The advantage is that the current out of the main PSU is lower and the power rails are split, which increases reliability a bit and reduces the propagation of power spikes.

I have a few 14A regulator modules from PT/TI (the old "Big Hammer") with adjustable voltage output but these accept 24V and not 12V. Too bad, they look rad. Next time, maybe...

But then I remember I bought some incredible and cheap DC/DC modules on eBay (look them up, they're amazing).

Now we're speaking:

• 12Vin : check
• 16A out : check

and smaller as well !

So I can plop one of these to power a section of the circuit, which will be somewhat isolated from the rest, while slurping amperes from the main PSU. I can locally adjust the working point to draw less power.

I knew it was a good idea to buy them !

(I added the datasheet to the files section)

Now I have to find/add "suitable" capacitors...

(update 20160401)

OK, I may have overestimated the power consumption.

At 150mW (max?) per relay, 200 relays will draw 30W.

At .08A (max?) per relay, 200 relays will draw 16A.

So one SIP module will be enough :-)

Another module might be necessary though for the TIL311...

## Discussions

esot.eric wrote 04/21/2016 at 09:57 point

Wow, those tiny things allegedly handle 16A?! Can that even be fed through all those pins?

Are you sure? yes | no

Yann Guidon / YGDES wrote 04/21/2016 at 09:59 point

That's what the datasheet says :-D

Are you sure? yes | no