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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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Variable load for testing phase convertor
Hi all,
Soon I should have most of the components necessary to build my phase convertor. I'd like to do a few trial runs in which I wire the components together and test the convertor's performance before I go to the time and expense of building a metal chassis to mount it on. So today I was wondering how I could create a variable load in the range 0.5 to 2 hp. Has anyone done this before? The only three phase workshop machine I have is a power hacksaw with a 1 3/4 hp motor. This runs through a static phase convertor I built and I don't really want to disturb the wiring if I can avoid it. Ideas I had are as follows, with some disadvantages listed: Motor bolted to wooden board. Insert 2" x 4" under pulley and lever upwards to create load. Load control is a bit crude, as is the whole setup, but I've used it before and it works after a fashion. Sets fire to wood, too. Motor bolted to board with slightly more sophisticated homebrew braking system, possibly allowing weights to be loaded onto a lever. Still crude, but a bit more controllable. Motor driving variable pitch propeller in small tank of liquid. Neat, but I don't know where to get a variable pitch propeller for little money, or how to match it to the motor. Bolt car brake disc/drum to motor pulley. Use hydraulic calipers to apply load. Could be quite neat, but it would be a faff to build because of needing a reservoir, flaring pipes etc. I'm also not sure how to regulate the pressure. Plus car parts dealers in our area charge big $$$ for car parts. I rather like my final idea. A while back a friend offered my a hydraulic pump from a concrete crusher (i.e., a test rig for measuring compressive strength). I think it has a 2 hp three phase motor and is the kind where the motor is mounted vertically on top of the pump, with the pump hanging down into the reservoir. So I thought I could cut a 47 kg propane cylinder in half, make a plate to cover the opening and mount the motor/pump unit on top. Then I could have the oil circulating through a needle valve which regulates the load. Plus I'd need a pressure relief valve, contactor etc. It sounds like a neat idea but I'm unsure how much the hydraulic bits would cost. Any thoughts? Has anyone done this before? I don't want to spend too long on this, because I want to put my effort into the phase convertor, but it would be nice to have a controllable load. Best wishes, Chris |
#2
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I have been told that large gensets are tested with a tank of salt
water? and the electrodes connected to the phases are lowered to increase the surface area and therefore current passing through the fluid and so increasing the load. Maybe you could do something on these lines with a large car alternator. Christopher Tidy wrote: Hi all, Soon I should have most of the components necessary to build my phase convertor. I'd like to do a few trial runs in which I wire the components together and test the convertor's performance before I go to the time and expense of building a metal chassis to mount it on. So today I was wondering how I could create a variable load in the range 0.5 to 2 hp. Has anyone done this before? The only three phase workshop machine I have is a power hacksaw with a 1 3/4 hp motor. This runs through a static phase convertor I built and I don't really want to disturb the wiring if I can avoid it. Ideas I had are as follows, with some disadvantages listed: Motor bolted to wooden board. Insert 2" x 4" under pulley and lever upwards to create load. Load control is a bit crude, as is the whole setup, but I've used it before and it works after a fashion. Sets fire to wood, too. Motor bolted to board with slightly more sophisticated homebrew braking system, possibly allowing weights to be loaded onto a lever. Still crude, but a bit more controllable. Motor driving variable pitch propeller in small tank of liquid. Neat, but I don't know where to get a variable pitch propeller for little money, or how to match it to the motor. Bolt car brake disc/drum to motor pulley. Use hydraulic calipers to apply load. Could be quite neat, but it would be a faff to build because of needing a reservoir, flaring pipes etc. I'm also not sure how to regulate the pressure. Plus car parts dealers in our area charge big $$$ for car parts. I rather like my final idea. A while back a friend offered my a hydraulic pump from a concrete crusher (i.e., a test rig for measuring compressive strength). I think it has a 2 hp three phase motor and is the kind where the motor is mounted vertically on top of the pump, with the pump hanging down into the reservoir. So I thought I could cut a 47 kg propane cylinder in half, make a plate to cover the opening and mount the motor/pump unit on top. Then I could have the oil circulating through a needle valve which regulates the load. Plus I'd need a pressure relief valve, contactor etc. It sounds like a neat idea but I'm unsure how much the hydraulic bits would cost. Any thoughts? Has anyone done this before? I don't want to spend too long on this, because I want to put my effort into the phase convertor, but it would be nice to have a controllable load. Best wishes, Chris |
#3
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Consider this: Get 3, 220 V "variacs" (variable autotransformers) or a
single 3-phase, ganged, 220 V variac. Connect each of your 3 phases through each of the variacs to 3, 220 V, 200 Watt lamps, 3 in parallel, to each variac. At full brilliance, the 9 lamps would be "drawing" nearly 3 HP. Bob Swinney "David Billington" wrote in message ... I have been told that large gensets are tested with a tank of salt water? and the electrodes connected to the phases are lowered to increase the surface area and therefore current passing through the fluid and so increasing the load. Maybe you could do something on these lines with a large car alternator. Christopher Tidy wrote: Hi all, Soon I should have most of the components necessary to build my phase convertor. I'd like to do a few trial runs in which I wire the components together and test the convertor's performance before I go to the time and expense of building a metal chassis to mount it on. So today I was wondering how I could create a variable load in the range 0.5 to 2 hp. Has anyone done this before? The only three phase workshop machine I have is a power hacksaw with a 1 3/4 hp motor. This runs through a static phase convertor I built and I don't really want to disturb the wiring if I can avoid it. Ideas I had are as follows, with some disadvantages listed: Motor bolted to wooden board. Insert 2" x 4" under pulley and lever upwards to create load. Load control is a bit crude, as is the whole setup, but I've used it before and it works after a fashion. Sets fire to wood, too. Motor bolted to board with slightly more sophisticated homebrew braking system, possibly allowing weights to be loaded onto a lever. Still crude, but a bit more controllable. Motor driving variable pitch propeller in small tank of liquid. Neat, but I don't know where to get a variable pitch propeller for little money, or how to match it to the motor. Bolt car brake disc/drum to motor pulley. Use hydraulic calipers to apply load. Could be quite neat, but it would be a faff to build because of needing a reservoir, flaring pipes etc. I'm also not sure how to regulate the pressure. Plus car parts dealers in our area charge big $$$ for car parts. I rather like my final idea. A while back a friend offered my a hydraulic pump from a concrete crusher (i.e., a test rig for measuring compressive strength). I think it has a 2 hp three phase motor and is the kind where the motor is mounted vertically on top of the pump, with the pump hanging down into the reservoir. So I thought I could cut a 47 kg propane cylinder in half, make a plate to cover the opening and mount the motor/pump unit on top. Then I could have the oil circulating through a needle valve which regulates the load. Plus I'd need a pressure relief valve, contactor etc. It sounds like a neat idea but I'm unsure how much the hydraulic bits would cost. Any thoughts? Has anyone done this before? I don't want to spend too long on this, because I want to put my effort into the phase convertor, but it would be nice to have a controllable load. Best wishes, Chris |
#4
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Robert Swinney wrote:
Consider this: Get 3, 220 V "variacs" (variable autotransformers) or a single 3-phase, ganged, 220 V variac. Connect each of your 3 phases through each of the variacs to 3, 220 V, 200 Watt lamps, 3 in parallel, to each variac. At full brilliance, the 9 lamps would be "drawing" nearly 3 HP. Bob Swinney It's a nice idea, but a three phase variac will cost big money. At least round here it will. I've seen them sell on eBay for £100+. Chris |
#5
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Might be worth playing with an alternator by connecting it to an
electric motor and placing some electrodes in a salt solution to see how the load varies with surface exposure. I don't see the variacs are required. IIRC the test set-up I mentioned didn't produce gassing due to the AC nature and the O2 and H2 gases apparently recombined at the electrodes. If done outdoors then the alternator may be able to be used as standard DC output otherwise you would have to get at the internals and the internal 3(or more in some cases) phase in the alternator. Christopher Tidy wrote: Robert Swinney wrote: Consider this: Get 3, 220 V "variacs" (variable autotransformers) or a single 3-phase, ganged, 220 V variac. Connect each of your 3 phases through each of the variacs to 3, 220 V, 200 Watt lamps, 3 in parallel, to each variac. At full brilliance, the 9 lamps would be "drawing" nearly 3 HP. Bob Swinney It's a nice idea, but a three phase variac will cost big money. At least round here it will. I've seen them sell on eBay for £100+. Chris |
#6
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David sez:
"I don't see the variacs are required." You also must not have seen where Chris wanted a variable load. Bob Swinney |
#7
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Use a water pump, and a valve to adjust the flow. For a proper job, mount
the pump on bearings so it can rotate, restrained by a spring balance, which is the basis for a Heenan and Froude water brake engine dyno. Geoff |
#8
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Geoff M wrote:
Use a water pump, and a valve to adjust the flow. For a proper job, mount the pump on bearings so it can rotate, restrained by a spring balance, which is the basis for a Heenan and Froude water brake engine dyno. Geoff Thanks for the suggestion. I don't have a water pump, but I've been offered a 2 hp hydraulic pump/motor unit free. I don't see a problem with using this, do you? Best wishes, Chris |
#9
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On Fri, 23 Sep 2005 22:42:14 +0000 (UTC), Christopher Tidy
wrote: Geoff M wrote: Use a water pump, and a valve to adjust the flow. For a proper job, mount the pump on bearings so it can rotate, restrained by a spring balance, which is the basis for a Heenan and Froude water brake engine dyno. Geoff Thanks for the suggestion. I don't have a water pump, but I've been offered a 2 hp hydraulic pump/motor unit free. I don't see a problem with using this, do you? Hydraulic pump should work well. Most hydraulic pumps have some "drag" even with no hydraulic load -- which is OK because most loads you'll have on your converter will also have some minimum drag. You probably know that the fluid will get hot with extended testing. Your "brake" power is being converted to heat. No problem for short tests or with plenty of fluid. The hydraulic approach is considerably easier than a prony brake if you want any torque measurement. The primary downside is that hydraulics can be messy. Car brakes, disc or drum, tend to chatter. You don't notice a little chatter when decelerating the mass of a car, but you sure do in something like this! Torque data has a lot of noise in it. (Been there, done that.) If you have a pressure gage, you can record output power as pressure * flowrate. Flowrate will be pretty constant (displacement of pump * speed) because induction motors only vary a few percent in speed from noload to full load. --- Jerry Martes once built an eddycurrent dyno for studying RPC's. It worked extremely well, with torque easily adjustable from near zero to about 5 HP worth at 1725 RPM. It used a thick aluminum disc and four electromagnets made from alternator field coils. Torque was measured by means of a torque arm and straingage loadcell, speed with an inductive pickup. Both were recorded on a P.C. datalogger. I designed some elex for it: a high resolution (about 200 parts per million) speed sensor and a phasemeter that converted phase difference between two voltages (or a voltage and a current) to an analog voltage. I don't recall if we ever actually built either. The speed sensor (really time per rev) was only good for average speed; it measured counts during 1 rev from a 1 MHz clock. |
#10
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Don Foreman wrote:
On Fri, 23 Sep 2005 22:42:14 +0000 (UTC), Christopher Tidy wrote: Geoff M wrote: Use a water pump, and a valve to adjust the flow. For a proper job, mount the pump on bearings so it can rotate, restrained by a spring balance, which is the basis for a Heenan and Froude water brake engine dyno. Geoff Thanks for the suggestion. I don't have a water pump, but I've been offered a 2 hp hydraulic pump/motor unit free. I don't see a problem with using this, do you? Hydraulic pump should work well. Most hydraulic pumps have some "drag" even with no hydraulic load -- which is OK because most loads you'll have on your converter will also have some minimum drag. You probably know that the fluid will get hot with extended testing. Your "brake" power is being converted to heat. No problem for short tests or with plenty of fluid. I was thinking of 5 to 10 gallons of oil, which I reckon should be okay for short tests. snip Jerry Martes once built an eddycurrent dyno for studying RPC's. It worked extremely well, with torque easily adjustable from near zero to about 5 HP worth at 1725 RPM. It used a thick aluminum disc and four electromagnets made from alternator field coils. Torque was measured by means of a torque arm and straingage loadcell, speed with an inductive pickup. Both were recorded on a P.C. datalogger. This is another interesting idea. It sounds very like the electromagnetic retarders used on buses and trucks. I'd wondered about something like this, but I reckon the parts will be harder for me to acquire than the hydraulic parts. I might do a few simple tests before building a nice convertor, then do more thorough tests afterwards, or I might do it the other way round. I haven't decided yet. Best wishes, Chris |
#11
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One point of caution with the hydraulic would be the presence of high
pressure fluid. Bath University in the UK has/had a hydraulic dyno rig which used a valve to throttle the system and provide the load and because of the potential danger if pressurised parts of the system failed it was well shielded with no one being allowed within that area during a test run. Christopher Tidy wrote: Don Foreman wrote: On Fri, 23 Sep 2005 22:42:14 +0000 (UTC), Christopher Tidy wrote: Geoff M wrote: Use a water pump, and a valve to adjust the flow. For a proper job, mount the pump on bearings so it can rotate, restrained by a spring balance, which is the basis for a Heenan and Froude water brake engine dyno. Geoff Thanks for the suggestion. I don't have a water pump, but I've been offered a 2 hp hydraulic pump/motor unit free. I don't see a problem with using this, do you? Hydraulic pump should work well. Most hydraulic pumps have some "drag" even with no hydraulic load -- which is OK because most loads you'll have on your converter will also have some minimum drag. You probably know that the fluid will get hot with extended testing. Your "brake" power is being converted to heat. No problem for short tests or with plenty of fluid. I was thinking of 5 to 10 gallons of oil, which I reckon should be okay for short tests. snip Jerry Martes once built an eddycurrent dyno for studying RPC's. It worked extremely well, with torque easily adjustable from near zero to about 5 HP worth at 1725 RPM. It used a thick aluminum disc and four electromagnets made from alternator field coils. Torque was measured by means of a torque arm and straingage loadcell, speed with an inductive pickup. Both were recorded on a P.C. datalogger. This is another interesting idea. It sounds very like the electromagnetic retarders used on buses and trucks. I'd wondered about something like this, but I reckon the parts will be harder for me to acquire than the hydraulic parts. I might do a few simple tests before building a nice convertor, then do more thorough tests afterwards, or I might do it the other way round. I haven't decided yet. Best wishes, Chris |
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