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Posts posted by Callipygous

  1. 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.

  2. 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.
    Most are available for about $25.

    Why complicate things ?

    I have been trying to figure this out. It looks like there are some options that are basically what I'm using, which is variable input,  adjustable output in the ~3-30v range. Then there are some other ones that seem like they might be easier to use and more reliable, because they aren't adjustable, they just put out 12v. So far I haven't figured out how to consistently find and filter those. This is the closest I have found so far. The downside is they talk about current more like 50mA, not the 1-2 amps I think my latch probably needs.


    You have any hints for how to specify the non-adjustable types? Does the one I linked even seem like what you were referring to?

  3. I made a project involving voice recognition on a raspberry pi so you can speak a password to open a box. Long story short, my DC-DC step up converter to power the latch seems to be super unreliable. I am wondering if some of my trouble is related to how I have it wired up and if someone could suggest a better approach.

    I have 2 battery packs (https://www.adafruit.com/product/354) wired in parallel.

    Those are powered off a charger (https://www.adafruit.com/product/390) So output of this board, and the two batteries, are connected to the main positive and negative lines at the edge of my PCB.

    Attached to those lines I have a boost converter (https://www.adafruit.com/product/2030) which powers my raspberry pi.

    Also attached to the main lines, I have an adjustable boost converter (https://www.amazon.com/gp/product/B01MS3IAVL/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1) the positive on the positive line, the negative comes back to the collector of a TIP 120 (https://cdn-shop.adafruit.com/datasheets/TIP120.pdf) the emitter goes to the negative line on the PCB. The base is connected via a resistor to GPIO on my raspberry pi.

    I had it all sorted out and working about 2 weeks ago, and then it just stopped. I have had problems numerous times when I came back to the project and the output voltage of my converter had drifted from the desired 12V. So when it stopped working I opened the box up and checked on it, it was putting out 5 volts and wouldn't respond to adjustments on the potentiometer.  I have been troubleshooting all weekend, but just now I tried wiring it directly to the battery lines and it works as expected. Is something about my setup throwing it off? Do I just have a cheap, unreliable boost converter? Interestingly, on my original order it says the input range is 3-32v, but now the link I provided says 5-32v. Could my problem be related to low input voltage?


  4. I am going to attempt to put this in laymen's terms to the best of my understanding, and probably butcher it in the process. I look forward to your corrections.

    We have a few carefully arranged coils of wire known as the stator. We are going to apply a voltage to it, which is going to cause current to flow. Current flowing through a conductor generates a magnetic field. Because of the nature of three phase AC power, and how we've arranged our coils, our magnetic field is rotating in a circle at 3600 RPM (dependent on who's electrical standard you are using and how you've set up your coils)  around the rotor. 

    A magnetic field moving relative to a conductor generates current (or maybe voltage would be more correct?) , so now we have current flowing through our rotor coils. Rotor coils with current flowing means they are generating their own magnetic field, which is stationary because the rotor is stationary. The rotating magnetic field moving past the stationary one exerts force between the two, our stator is bolted down and our rotor isn't, so the rotor begins to spin. Now the rotor has a rotating magnetic field, which is moving relative to the stationary stator coils, so it begins to generate a current in them. This current is in the opposite direction of the one produced by the mains, and at some point the forces of magnetism and friction balance out at some RPM, I'm guessing for a motor with no load, somewhere slightly below 3600 rpm.

    How'd I do?

  5. 19 hours ago, studiot said:

    Yes I said 'complex'. and you said 'complicated'.

    Whilst both mean much the same in common parlance, complex has a particular meaning in Science in general and Mathematics in particular.
    In this context complex means 'made of more than one (maybe many) parts'.
    So when I say the quantities are complex I mean the maths uses special numbers, called complex numebrs, which are made of two parts.
    From you description I don't think you have met these?


    I have met them, but as I mentioned earlier, it has been a very long time since I have had to do anything with them.



    It is the series connection of these two windings with opposing currents/voltages that prevents the whole thing spinning out of control and maintains the desired speed.

    So now, in answer to your question ( but I'm not sure what other voltage there is. ) we are working with 3 voltages,  - the supply, the stator voltage and the opposing rotor voltage
    and 3 current - The rotor current, the stator current and the diference between the two.


    That part is throwing me off. My (limited) understanding of circuits includes a rule that in a circuit with no branches, voltage can vary from point to point, but current is the same throughout. If they are wired in series, how can they have different currents?


    My understanding of slip is when there is enough load on the rotor that the force exerted by the magnetic field is not strong enough to spin the rotor at the same rotational speed as the magnetic field. So while our two fields would ideally keep up with each other, with the N's and S'es always pulling in the right direction, the rotor will fall behind some percentage of the time and either not get pushed by part of the cycle or get pulled the wrong direction. I assume learning about the different currents you referred to will illuminate how that relates to a change in current draw on the mains.

  6. Thanks for the replies.
    I would be interested to hear more about the relationship between impedance and and slip. It seems like this is basically the same thing as in rush current, which I understand as far as what it does, but not so much the nuts and bolts of why and how.


    John, your comments on back emf were helpful, just knowing some better keywords to search yields better results than I was getting before. But I was wondering, if the lower RPM is the result of lower line voltage, then it seems like the lower emf produced wouldn't be that much of a difference. Both line voltage and back emf went down, so wouldn't that leave them mostly in line with each other? I guess that assumes that a drop in line voltage produces an equal drop in back emf.


    1 hour ago, studiot said:

    By this I assume you mean the supply or line voltage. Is that correct?

    Now how is you mathematics ?

    I think that's what I mean? I would say yes, I mean the line voltage, but I'm not sure what other voltage there is.

    As for my math, I got good grades with minimal effort up through intermediate calculus. Since then I have spent about 10-12 years in jobs where the hardest math I had to do were angle and side length calculations with sine, cosine and tangent. I think I can wrap my mind around some complicated stuff, but it might take me a while and my definition of complicated is probably different from yours.

  7. I have come to accept that when an induction motor receives lower voltage than it was designed for it will pull higher current. This doesn't make any sense to me, but I have seen it stated enough times that I'm willing to believe it. Everywhere I look provides total nonsense explanations. They say things like "the motor will draw more current in an attempt to maintain its torque" as though the motor has agency and chooses how much current it draws, or "in order to provide the same power" as though the motor cares how much power it provides.

    The version that would make sense to me is you have a resistance, both in the actual windings, and in magnetic impedance(?), and if you apply a lower voltage Ohm's law means that it draws a lower current. If that results in a lower power output... what does the physics of the situation care about that? It seems like it should just spin slower, or not be able to move as heavy of a load. I always thought of wattage as a rated upper limit for a motor, not a target it actively tries to hit. Can someone help me out with a proper explanation of what force is at play here that causes the amperage to increase?

  8. 1. Expose them to the fact that someone disagrees with them. People with those kinds of beliefs have often spent most of their lives surrounded by people who unquestioningly think the same. 

    2. Abandon all hope that you can actually alter their belief, because that's what it is: a belief, not a hypothesis.

    3. Focus on exposing people who are not yet entrenched to a variety of perspectives. This guy probably wont be convinced, he may gradually find himself in a less aggressive stance, or may not. Hope for his children remains.

  9. Yeah, I can see the benefits of that approach. Maybe im wrong, but I feel like my circumstances have some additional hurdles. The organized group effort sounds good for a city park, but im dealing with more of a wooded area out in the hills. I feel like one (particularly me) would have a hard time coordinating a group to go out there, trek through poison oak, and gather trash in hard to reach, off-trail locations. Especially without trampling a lot of flora.

    The supervisor I report to knows that I've been hauling tires out with a backpack for the better part of 2 years and has yet to say "hey man, why dont you just get em to the trail and we'll come get em with the 4 wheeler?" Or any similar offer. He said cars are just a no go, and I shouldn't touch buried items. He also said hes had permits in to deal with similar items for about 5 years... My confidence is low.


    I am also interested in learning about it anyway, even if most of it should be left to the pros.

  10. My favorite local park is unfortunately place below a road, which has turned it into a dumping ground. I have spent a considerable amount of time, money, and effort removing as much of the trash as I can, but the process raises some questions about which items are worth the effort.

    Some items seem like they have a pretty low impact other than being an eyesore, like glass. other items require a disproportionate effort due to size, weight, and location. The park service has told me that some of them are not worth removing because the impact of digging them out, and erosion in hauling them out of the park outweighs the environmental impact of leaving it there, like car chassis.

    I have tried for a while to find a resource to help me understand the impacts of various materials so I can better gauge the pros and cons, but I haven't found anything.

    Examples of the kinds of questions im trying to answer:

    Does glass actually have any impact? What about aluminum cans?

    I know tires are toxic. Is there a point where the process of removal (disturbing the creekbed) out weighs their impact?

    If a car battery has long since rusted out, and has been sitting in a creek for years, is it still a hazard, or have the dangerous chemicals probably all washed out?


    Information, or tips on where I could read up would be very appreciated.

  11. Making a cryptogram as part of an extended puzzle/treasure hunt. I know what it says, and the only other friend I have that I think likes cryptograms is who I'm making it for. Anyone care to see if there is enough info to reasonably solve it?



    and if that proves insufficient, add on:





    3,5A would be the amperage at max output. You could easily run it at a lower mode at say 1,5A and it will still do it's job.

    Check your PM, I sent specs.

    I make a bit of a habit of posting silly-ass ideas like this on various forums. Fairly often people who seem more informed than me tell me that its not going to work the way I want it to and "heres what you would really need to make that happen". I usually do my best to respect the fact that they seem to know what they are talking about, and adjust my plans closer to what they say. But if im being honest, the fact that you are both the dude selling the flashlights, and the dude saying the flashlights are the solution, has damaged my trust a bit, and my reading elsewhere is leading me to believe it shouldnt take that much tech or that many lumens.

    So I'm going to try to direct this back towards the physics of the question. If I build a box, sphere, whatever shape enclosure from whatever seems appropriate down at the ol' hardware store (read:dirt cheap) and pick up a pile of whatever solar powered landscape lights I can find (read:dirt cheap) and plug them all into said enclosure somehow...

    I figure I now have a somewhat respectable light source. However, its all bouncing around at weird angles, and most of it is going to end up absorbed by the enclosure rather than directed down my aperture toward the target. I realize with passive optics its not really going to be possible to direct all those weird angles where I want them, but are there means to significantly improve the amount that ends up going the right direction? Via a properly shaped reflector and/or lens setup, could I increase the output through the aperture 3, 4, 10 fold?

  13. I dont know what many of those words mean, but it sounds good.

    To give me a feel for scale... 3.5 amps, if I want the light to stay on all night, lets say 10-12 hours to account for winter, that means I need 35-42 amp hours. Seems like a fairly substantial battery pack, isnt it? What sort of voltage?


    Looks like minimum daylight in my area is actually about 9.5 hours. Suppose we could set the sights lower and assume they wont be out looking for it past 2am.

  14. Honestly, on the scale of this project, if the radius went up to like 200 feet it wouldnt be tragic. Were talking about caches that are several miles apart, and you wont know to look for the light until you read the clue at the previous cache anyway.


    I dont want you to be able to follow the light all the way to it, and I want to minimize how much it disturbs other park users and wildlife, so I would like it as restricted as is reasonable.

  15. Does it have to be visible from the whole radius of those 5,6 miles or will a directional beam be sufficient?

    No, I specifically want it to only be visible from one spot. think geocaching, ideally I want you to have to stand in a particular 5-10ft circle (at the previous cache) and the light is your only method of finding the next cache. I think my challenge here is going to be restricting it enough over that distance while still having it bright enough. Like, if I could just put a landscape light in the dirt at the right location, I think that might be visible across the valley, but if you're seeing through a half inch tube, most of that light is blocked. Im assuming I need to direct more of the light down the tube than a half inch circle would normally get without my help.


    And long time is right, Phi. I dropped in a while ago for one post, but I think even that was years ago.

  16. Defining visibility:

    The idea is for it to be visible at night. The location is in the hills about 5 or 6 miles from the nearest town. That being said, its about 5 or 6 miles from several towns, sort of nestled in the dead space between them. The goal is certainly not to illuminate any surface from 2 miles away, more like make it look like there's an unusually low star in the middle of one of the hills across the valley. I was reading that the human eye can detect candle light from something like a couple of miles, but I think that was more of a theoretical limitation than a practical one. If it could appear a little brighter than any actual star that would be cool, but I wouldn't want anything more than that.

  17. I want to make something like a solar powered landscape light visible from several (2 to 5?) miles away, but only from one location. The one location part seems relatively easy, I can just put it in a box and make the opening a long tube, pointed at the location. I am less sure about it being visible from that far away. To make it easier to spot, I was wondering if it is possible/practical to direct more of the light down the tube to increase the intensity. My first thought was to coat the inside of the box (sphere?) with something reflective, so light from the source bounces around until it eventually goes out the right way, rather than just being absorbed. next I was wondering about properly shaped lenses and reflectors. Like if i were to put a parabolic reflector on the side opposite the opening, am I gaining anything significant? Would a dome shaped lens at the opening refract enough down the tube to make a difference? If you can't tell, I don't have much experience with optics. Not sure what the best reward/effort option might be. Generally restricted to the low tech/DIY options, though not against spending $50 bucks or so on a lens if it would make a difference.

  18. 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.

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