Callipygous

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Posts posted by Callipygous

Raspberry Pi controlling an electronic latch - Electronics help

10 hours ago, Sensei said:

You know that Pinput = Poutput , right? So Uin * Iin = Uout * Iout .. (unrealistic idealistic assumption that we have no loses.. so actually it is Pinput > Poutput )

On the page that you gave about batteries we can read: "Each cell can provide 1A of current for about 4 hours so all together the peak current you can draw is a little over 1.5 Amps. Note that these batteries are not designed to sustain such high loads, we suggest keeping any constant current draw under 1A."

Uin = 3.7 V Iin = 1 A so Pin = 3.7 W (with peak 1.5A * 3.7V = 5.55 W)

Then you say:

Which means:

3.7 W / 12 V = 0.3 A = 300 mA ...

Realistically, including loses on conversions, it will be less.

Do you think so your entire electronics is able to work with so low current?

I mostly agree with your math. The part I wonder about is whether the batteries have a fixed output, or a recommended maximum output. What I do know is that the project has worked successfully for reasonable periods of time. The latch is activated for 2 seconds at a time. I don't know if that qualifies as a sustained load, or if they really mean "don't draw that much for 2 hours" The link from my original order no longer works, but the latch is basically identical to this. That claims a draw of .43 amps, which is more than your calculation says my batteries should be okay with. So again, I don't know if it's really a fixed output or a maximum recommended, but I do know that it worked, repeatedly, and for a period of at least a few weeks. The latch at least appears to be ok with the available current. The issue seems to be with consistently providing that current. maybe some part of this set up damaged the converter?

Actually, I have two of those battery packs wired up in parallel, so really the peak output is doubled. So the latch is probably fine, though I'm not sure how much the Pi is adding onto that. Still not sure if a 2 second use should be counted against peak or sustained.

3 hours ago, MigL said:

A regular PC power supply is approx. 6 x 6 x 4 inches and will put out 300-400 watts.
At least  5v@12a and 12v@12a with trivial amounts on the -5v and -12v rails.
You can easily find smaller power supplies made for small form factor PCs that are about3 x 3 x 6 in., and will do about 180 watts; that should be able to supply you with plenty of well regulated 5v and 12v for your needs, without trying to step-up a 5v supply to 12v.

Ah, now I see the miscommunication. Those are both too large to meet my requirements. This entire project lives in a space that is about 4 wide x 3 deep x 4 high. And the front is slanted, so at the top its only about 2 inches deep. after the batteries, pi, and other components I really need the dc converter for the latch to fit into about 1x2x2. It also runs off batteries, so a PC power supply designed to plug into the wall doesn't fit the bill. I need something to step 3 volts up to 12 volts.

Raspberry Pi controlling an electronic latch - Electronics help

On 12/20/2020 at 2:55 PM, MigL said:

There are many small form factor, computer switching ( digital ) power supplies available on eBay, powered from your mains, which will supply both the 5V, as well as 12V, in several Amps.

building small transmitter and reciever

Well sweet hot damn son. So the gun in question is pneumatic, with a piston valve. Our favored projectile is a concrete plug made by using cuts of pipe the same size as the barrel as a form. I just said potato core because didn't put much thought into the sentence, not thinking that was the pertinent info. As I said, I don't have an accurate measurement, I was going by the fact that the rancher told us the fence we were firing toward was 700 yards away and we were getting a good deal past it.

building small transmitter and reciever

1. What I described is the full project I have in mind. I do really want to build it myself, that's at least half the fun for me.

2. I admit I don't have any sort of accurate measurement system, it's purely estimate. But why do you say that?

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