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Well, I didn't see the edit before I headed to the bench. I found a 26.9W bulb and tried it. With SUCCESS! The bulb limited the current to 1.8 amps, then shorting the bulb the current rose to 3.2 amps and the pump ran at full speed.
It did not work completely as I expected. I found there to be quite a large delay between the time pump was started with the bulb and when it could be run without the bulb. I expected since we were dealing with the short startup current, as soon as the pump started I would be able to short the bulb and go to full power on the pump. That was not the case, it was (felt like) several seconds before I could bypass the bulb. These were "gut" expectations, not based on anything factual.
Now I guess I really need to get a smaller value high wattage resistor to build a start circuit.
The cold resistance of a bulb is much less than the hot resistance so your bulb could be anything from 1 to 5Ω. I'd get a few different 20W resistors - 0.25, 0.5, 1Ω and just see what works. I think with the right resistor you shouldn't need any additional parts - relays etc. You could series parallel four 10W 0.5Ω resistors.
I would have thought a light bulb would have had (a limited) NTC. Unless the resistance change was quick, I didn't notice any appreciable difference in the (Harbor Freight) ammeter reading between first starting and when I shorted out the bulb.
Which one of those power supplies did you buy. The listing is for a "collection listing" and you may not have gotten what you think.
Second thought is that while pumping air doesn't really require much work for a diaphragm pump, pumping liquid is hard. Especially if pump is lowest point in a long run.
Third, if you can run it off a car battery pumping air can you use the car battery to power application and measure current? Will it load up and stop with car battery when used in your application?
Fourth, someone mentioned wire size and run. How far from the pump is the power supply?
Done with the numbers. What happens if you turn the power supply on and then power the pump through a switch or relay? Though not ideal it may work.
Per post 1 the 20A supply which runs at just over 3 amps from a car battery in post 9.
I did not notice the question on wire run length, but it is only the 12" leads from the pump plus whatever 18" jumpers are needed to make the test circuit.
All of the circuits from post 14, where the capacitors were introduced have been started by turning on the power supply and then the pump. (even a most of the tests before that, though there isn't a post to indicate that). What happens, as soon as the switch is closed, the power supply shuts down, then turns on, then shuts down.
Testing under load requires getting the pump to start, which I cannot. I do not know and have not tested the pump under load.
yes power supplies , especially mains fed ones, usually have output short cct protection, and if the vout doesnt get up into regulation within say 500ms, then the psu will just shut down...then sometimes it re-tries, 'hiccups', or otherwise latches off till you recycle the power.
Make your own with a ucc28c43 which doenst have this shutdown feature...then you can have a current limtier at startup, and then make it voltage regulated thereafter.
... No place for an ICL? Have to find out the current draw of the pump under its full use before the figures of an ICL can be matched up. An ICL at steady state max is the typical resistance of the device at that rated current draw under use after initial power start up. example an 4 Amp ICL rated at 25°C at 3Ohm heats up at current draw to lower resistance to .12Ohm at 4A, no further.
So if your pump runs more current under use, note that current then choose an ICL that matches the current with an agreeable start up cold resistance that is high ehough to allow the power supply to start properly. The stated bulb resistance range of 1-5 Ohms is applicable in range of an typical ICL within the current ranges of the pump. (There are models that would work)
I am hoping the faceplate is correct, that under full load it will be 15 amps. If you notice, I have been calculating the current limiting resistor based on the full load amps of the power supply, not the pump. This is prudent since the power supply is larger than the pump thereby supplying more current than the pump "should" ever require while staying under the power supply capacity. Analysis paralysis.
I finally found, ordered and received a pair of 1 ohm 10 watt resistors.
V+ -> ammeter -> resistor -> switch -> pump -> V-
One 1 ohm resistor is all it takes to keep the power supply from shutting down and the pump to start running. The ammeter is reading 2.8A and the power supply V+ to V- is reading 10.7V.
I also used the 1 ohm resistors to test the power supply.
With a 1 ohm load, the voltage is 8.8V and the amperage is showing as 7.5A.
With a 2 ohm load, the voltage is 9.9V and the reading is 4.33A.
For kicks (and the fact I have the stuff to do it), I hooked up a SOLA 24VDC 1.3A power supply with a 21 ohm load. At power on (no load), the voltage is reading 24.1V. When connected to the 21 ohm load, the ammeter was read 1.2A while the voltage dropped to 23.7V.
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Nevermind.
