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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Power feed problem
I have a Central Machinery (HF) power feed on the X axis of my RF45 clone mill and it's acting weird . Works fine on the fast move button but the speed settings are messed up . It doesn't start turning until I get to "2" on the dial and by the time it's up to 3 it's going full speed . It just started yhis , today is the firt=st time I've seen this .. When it was working right it would start before I got up to one and would ramp up perfectly as i turned it up . Am I looking at a bad rheostat or maybe just dirty ? Should be clean , that unit is sealed up tight - but ya never know . -- Snag Illegitimi non carborundum |
#2
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Power feed problem
That sounds like a bad SCR.
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#3
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Power feed problem
On 7/13/2020 5:25 PM, Michael Terrell wrote:
That sounds like a bad SCR. OK , I don't know a lot about SCR's , but I have some experience with electronics . How do I test it ? I was planning on starting by checking the resistance of both sides of the control pot ... but I have no idea how to test an SCR . -- Snag Illegitimi non carborundum |
#4
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Power feed problem
The easiest is to just replace it. Use the same part number. The sensitivity varies all over the map, with different types. They are usually cheap, and a lot cheaper than a test fixture.
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#5
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Power feed problem
"Snag" wrote in message ...
On 7/13/2020 5:25 PM, Michael Terrell wrote: That sounds like a bad SCR. OK , I don't know a lot about SCR's , but I have some experience with electronics . How do I test it ? I was planning on starting by checking the resistance of both sides of the control pot ... but I have no idea how to test an SCR . -- Snag Illegitimi non carborundum =========================== A thorough test requires lab equipment to measure Off-state leakage current at full working voltage and the minimum gate triggering current, but a functional check is simple: https://www.circuitstoday.com/how-to-test-an-scr I'd suspect an intermittent pot wiper contact. |
#6
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Power feed problem
On Tuesday, July 14, 2020 at 5:57:09 AM UTC-4, Jim Wilkins wrote:
"Snag" wrote in message ... On 7/13/2020 5:25 PM, Michael Terrell wrote: That sounds like a bad SCR. OK , I don't know a lot about SCR's , but I have some experience with electronics . How do I test it ? I was planning on starting by checking the resistance of both sides of the control pot ... but I have no idea how to test an SCR . -- Snag Illegitimi non carborundum =========================== A thorough test requires lab equipment to measure Off-state leakage current at full working voltage and the minimum gate triggering current, but a functional check is simple: https://www.circuitstoday.com/how-to-test-an-scr I'd suspect an intermittent pot wiper contact. +1 If turns out to be the SCR, let me know. I have some SCR's I salvaged from the scrap yard. I forget the specs, but they are good for about 1000 amps. Dan |
#7
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Power feed problem
Jim Wilkins wrote:
OK , I don't know a lot about SCR's , but I have some experience with electronics . How do I test it ? I was planning on starting by checking the resistance of both sides of the control pot ... but I have no idea how to test an SCR . In principle, it's easy 8-). First, test it like a diode, however if it conducts either way it's faulty. Then test it forward biased and momentarily connect gate to anode. It should start conducting and stay that way. There are two traps in this: One is that an SCR generally needs at least two forward diode drops, 1.4 volts, to work at all. The other is that "latching" the SCR on requires some minimum current, maybe 1% or less of running current. Far more than a normal diode tester provides. A car battery and taillight bulb would probably work. HTH, bob prohaska |
#8
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Power feed problem
On Mon, 13 Jul 2020 17:18:17 -0500, Snag wrote:
I have a Central Machinery (HF) power feed on the X axis of my RF45 clone mill and it's acting weird . Works fine on the fast move button but the speed settings are messed up . It doesn't start turning until I get to "2" on the dial and by the time it's up to 3 it's going full speed . It just started yhis , today is the firt=st time I've seen this . When it was working right it would start before I got up to one and would ramp up perfectly as i turned it up . Am I looking at a bad rheostat or maybe just dirty ? Should be clean , that unit is sealed up tight - but ya never know . Got a bad pot ..rheostat. Open and spritz the pot with cleaner. However..it may be bad..so check with any online sorce for new potentiometer. Gunner __ "Journalists are extremely rare and shouldn’t be harmed, but propagandists are everywhere and should be hunted for sport" Yeah..with no bag limit. -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
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