On January 21, 2019 at 09:45, highfigh said...
Re my comment that doubling a wire gives you about the same resistance as a wire three numbers smaller (wire diameter larger, numbers smaller).
Really? Did you look at the chart for the resistance of 24ga vs 18ga? I did and that's why I wrote that the resistance would be ~25%. Jesus!
No need to bring him into it. He does everything wirelessly.
Read, don't skim! I have to tell myself to do the same but if you doubt my statements, the least you could do is look at the source!
I was remembering a similar discussion from some time ago. No, I didn't look and haven't looked for more than a year. But here's what I found upon looking:
My chart says the resistances of these wires are this:
24 gauge, 25.67 ohms per thousand feet
21 gauge, 12.8
18 gauge, 6.385
I claimed that two 24s in parallel have a resistance almost exactly the same as a 21 gauge wire. From the numbers above, two 24s in parallel have a resistance of 25.67/2 = 12.835 ohms per thousand feet.
I said that two of these paralleled pairs of 24s would have a resistance nearly the same as an 18 gauge wire. Two wires of 12.835 ohms in parallel have a resistance of 12.835/2 = 6.4175 ohms per thousand feet.
Those numbers are very very very close, close. Aren't they?
I think you understood me to mean something else. What did you think I was saying?
Will two power amps produce the same output into low impedance loads? Why not?
Because red herrings swim sideways. What does this have to do with the discussion? I assume you mean connecting two power amps to one load; this will cause interaction between the output stages that would likely damage the amplifiers, so it's not worth thinking about.
Power supply. If one power supply is more robust, the output will be more similar to connecting to a higher impedance load and if not, we'll see them rated for output @1KHz into 8 Ohms. Also, did you NOT see my comment about a regulated supply?
Yes, I saw that comment, and I wrote this. Perhaps we should both read everything:
Oops, that last assertion doesn't pan out.
A power supply rated for more current will be able to output more current than one rated for a lower current. But you're talking about somehow getting more current out of a supply at 12 volts than out of another supply at 12 volts, with the same load each time. That won't happen. 12 volts divided by the same load in two different setups will be the same current.
I missed one point -- if one supply is underrated for the job, then yes, a power supply that can do the job will work better. That has nothing to do with robustness. A robust supply might be one that can survive a short circuit, after all, which is not an issue here.
Maybe you should have responded to the original- you wasted time with your first comment about not having time and here you are, not responding to it again.
You're right.
On January 21, 2019 at 09:47, buzz said...
With respect to using a capacitor to augment available current for operating the gate lock:
First, there is the assumption that the lock operates from a DC drive. I have no depth of installer experience here, but just listening to the action as I enter various spaces, many locks operate from AC. Of course, as the installer you would have control over this point.
Good points.
Second, capacitor charging and support times are a consideration. One should not assume that the door operator (the human) will instantly yank the door open after the lock is enabled.
Hence my statement that the door should spring open, or something along that line.
My guess is that several seconds of support would be appropriate. Now, what happens if the person failed to meet the timing window and must then wait until the capacitor recharges before the next attempt?
The timing is likely to be less than a second. It needs to pop open a solenoid, and in a second, enough charge is likely to accumulate to make a pulse of several amps possible.
However, Highfig's suggestion of putting a battery there is BY FAR the better idea:
*Trickle charging, even on one 24 GA wire, (I said one wire instead of one pair because all the circuit grounds would be tied together) would be 24 hours per day with no large currents
*the battery would easily always be able to supply several amperes for several minutes, way beyond what's required to pop a solenoid.
Years ago in car audio we experienced the benefits of adding huge capacitors, in that if large enough, they almost behave like batteries. Batteries would be even better here.
