Simplest way to generate 3-phase for test bench? - Page 1
Forum section: electronics / repair

author: iXod
author_rank: Frequent Contributor
timestamp: August 01, 2016, 03:25:06 pm
content: Sometimes I need to diagnose/repair small 3-phase brushless blower motors with integrated SMPS motor driver PCB. Have only 120 and 240v single-phase power available.Thought about a VFD and fixing frequency param to 60 only (yes, I'm in USA) and vary only the voltage, but as good as this sounds it's not do-able, with the VFDs I tried.What's the simplest way to get 3-phase power? Need less than 10 amps.Thanks.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 01, 2016, 04:50:53 pm
content: Simplest way is to buy a phase converter. Various types and sizes are available. Something like the following.https://www.zoro.com/phase-a-matic-phase-converter-static-1-3-hp-pam-300hd/i/G1518142/

author: kolbep
author_rank: Frequent Contributor
timestamp: August 01, 2016, 05:04:02 pm
content: What about Coupling a Single Phase Motor (on Speed Control), to a 3 phase motor / alternator?Would that work

author: Excavatoree
author_rank: Frequent Contributor
timestamp: August 01, 2016, 05:21:02 pm
content: Quote from: kolbep on August 01, 2016, 05:04:02 pmThose do work (search for rotary phase converter) but they are typically used for higher power applications. Many are choosing to use electronic phase converters now that their costs are lower than they were when the rotary phase converter was popular.My dad uses a rotary converter he cobbled up from a single phase motor and a three phase motor to power his milling machine, but it's clunky, large, and a pain in the rear.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 01, 2016, 05:32:22 pm
content: A small rotary converter with VFD motor basically gives you a variable Frequency and Voltage unit.The short circuit capacity is also limited to the flux in the generator and limit on the exciter system. Much cleaner and safer than a VFD to test motors.However, you could also use a three phase variac. I've revised fan motors for trains as a summer job and used a three phase variac for this.Note that a three phase variac I used then is the size of a cabinet.

author: iXod
author_rank: Frequent Contributor
timestamp: August 01, 2016, 05:57:02 pm
content: 1ph motor speed control is usually "iffy". 1ph motor (at full speed) to drive 3ph motor or alternator would work. If motor speed specs (ie, both 1750) the 3ph should output its rated voltage.Or 1ph -> 3ph VFD driving 3ph motor driving another 3ph motor or alt. But that kinda misses the "simple" requirement...Thanks.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 01, 2016, 06:11:51 pm
content: Define simple. If you want cleaner 3 phase, or to have more power margin, nothing is much simpler than pulling out the credit card.https://www.zoro.com/phase-a-matic-phase-converter-rotary-1-hp-208-240v-r-1/i/G7969981/?gclid=CLCY28nmoM4CFQGRfgodGG4HEw&gclsrc=aw.dsI don't necessarily recommend the brands I have posted, they are just examples. The smaller electronic converter posted earlier is under $200, the one above is under $600. Shipping will add a fair amount. If you are going to be using this regularly those dollar amounts seem quite reasonable. Space would be something of an issue, particularly for the larger unit. Any of the commercially supplied units will be relatively trouble free, unlike the set ups which bodge together a couple of motors. Unless you are really good at mechanical work you will end up with the maintenance nightmares mentioned above.Depending on your usage a fair amount of wiring would be appropriate, setting up a receptacle on your bench and so on, departed further from simplicity.Another option would be to set up a toolkit with the instruments you need and then do the work at the customer site. They obviously already have the power available.

author: Anks
author_rank: Frequent Contributor
timestamp: August 01, 2016, 06:52:02 pm
content: Signal generator and some high power audio amplifiers may work. Crown macrotech have been used in labs and I've seen them drive a short but weather or not they can produce the voltage swing necessary to drive a motor or I've no idea.Just an idea

author: Kevman
author_rank: Regular Contributor
timestamp: August 01, 2016, 06:54:18 pm
content: Quote from: CatalinaWOW on August 01, 2016, 04:50:53 pmThese are just caps and a time-delay-relay in a box to get the pull a line out of phase for just long enough to get the motor spinning. They don't create any phases. The motor being powered will only have 2/3 its rated power as one winding will be completely ignored during running.They can be used with a second three phase motor, though- the other (unloaded) motor will generate the phase on its unpowered winding. Not sure that's what you want.You can always use a function generator and 3 audio amplifier channels!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 01, 2016, 07:29:29 pm
content: If it's a brushless with a SMPS, does it actually need to be supplied AC?

author: iXod
author_rank: Frequent Contributor
timestamp: August 01, 2016, 09:16:19 pm
content: Quote from: mikeselectricstuff on August 01, 2016, 07:29:29 pmYou're thinking 240vdc? (c;Thanks.

author: iXod
author_rank: Frequent Contributor
timestamp: August 01, 2016, 09:17:32 pm
content: I'm liking this:

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 01, 2016, 10:45:10 pm
content: Quote from: iXod on August 01, 2016, 09:16:19 pmOr whatever its nominal internal DC bus voltage is

author: Seekonk
author_rank: Super Contributor
timestamp: August 01, 2016, 10:58:46 pm
content: I have a 100W 120V three phase VFD. With no load I can easily drive 1 HP motors. Not sure why you need something better. But you can buy 3 phase boards with FET drivers pretty cheap <$20 and just add 6 FET and power supply. Vary voltage with just a resistor. Look up EG8010 boards (single phase) for a possible link to the 3 phase version

author: iXod
author_rank: Frequent Contributor
timestamp: August 01, 2016, 11:19:37 pm
content: Quote from: Seekonk on August 01, 2016, 10:58:46 pmUsually not driving an AC induction motor, which VFD is great for. Sometimes need to power a PC board that uses 3-phase power (ie, machinery motor driver circuit) so other than 60 hz is a "no". So as much as I like VFDs and wish I could find a fixed-hz, variable-volts solution in a VFD I haven't seen this.Thanks.

author: Seekonk
author_rank: Super Contributor
timestamp: August 02, 2016, 11:38:57 am
content: I still don't understand your need. You say "Need less than 10 amps." as if it is something trivial.

author: Ian.M
author_rank: Super Contributor
timestamp: August 02, 2016, 12:11:22 pm
content: Definitely non-trivial. That's up to6.25KVA@208V, 3 phase, and it would need a carefully tuned and balanced20HProtary phase converter, possibly with a resistive ballast load on the wild leg to reduce the swing between no and full load. Even on a NEMA 14-50 circuit, you'd probably need a soft-starter or a pony motor to spin it up to avoid it tripping the breaker.

author: iXod
author_rank: Frequent Contributor
timestamp: August 02, 2016, 02:31:59 pm
content: Quote from: Seekonk on August 02, 2016, 11:38:57 amNot trivial. Just quantitive.

author: iXod
author_rank: Frequent Contributor
timestamp: August 02, 2016, 02:40:05 pm
content: Quote from: Ian.M on August 02, 2016, 12:11:22 pmIsn't it half that?VA = sqrt(3) x 10 x 208 = 3602 ?

author: Ian.M
author_rank: Super Contributor
timestamp: August 02, 2016, 03:59:36 pm
content: My mistake. You'll be generating the missing phase for a 240V phase to phase wild leg delta supply, so that's 240V * 10A * SQRT(3) = 4157VA. Rough rule of thumb for RPCs is you need twice as much idler as the max load, so you'd need a bit over 11HP. Next standard NEMA motor size is 15HP. If you actually need 208V delta (120V wye), you'll need buck transformers

author: Kilrah
author_rank: Unknown
timestamp: August 02, 2016, 04:07:31 pm
content: Can't you find 3-phase alternators with an exciter coil? Run it at fixed speed to get the freq right, then adjsut the voltage by changing the exciter coil current.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 02, 2016, 06:06:34 pm
content: That's a rotary converter. At work we have several installed upstairs with panels on a desk for testing purposes.

author: iXod
author_rank: Frequent Contributor
timestamp: August 02, 2016, 06:40:25 pm
content: Quote from: Jeroen3 on August 02, 2016, 06:06:34 pmCan you please describe design? Are these "built from scratch" or bought off the shelf? If so, what make & model?Thanks.

author: grifftech
author_rank: Frequent Contributor
timestamp: August 02, 2016, 09:06:35 pm
content: just call your power company and ask them for 3 phase

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 03, 2016, 01:44:26 am
content: Quote from: iXod on August 02, 2016, 06:40:25 pmThe second link I sent above is a rotary converter, available off the shelf. Instead of a belt linking the motor and generator they are on the same shaft. (Simple?) They are available in various sizes, though the price increases rapidly. Also a variety of vendors. I don't have much contact with the technology, but no one I know who uses them has any fundamental complaints. They take up room. That's about it.

author: iXod
author_rank: Frequent Contributor
timestamp: August 03, 2016, 01:55:35 am
content: Quote from: CatalinaWOW on August 03, 2016, 01:44:26 amThanks CWOW, but the request was to Jeroen3. I'd like to know what he is using.Cheers.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 03, 2016, 05:41:53 am
content: Well, my company deals in overhauling synchronous generators. You'll have some laying around that never got picked up, and you'll have contacts after 80+ years in business.You then "simply" buy an motor, a vfd, and ask someone to weld a frame to put them on. Shaft-to-shaft.Meanwhile you ask the electronics guys to build cabinet panel with banana plugs and some meters and buttons. You might also want anAVRin that panel.Easy really, trivial for us.

author: Someone
author_rank: Super Contributor
timestamp: August 03, 2016, 09:59:23 am
content: Quote from: grifftech on August 02, 2016, 09:06:35 pmRent a generator for the few days a year you really need it?

author: Ian.M
author_rank: Super Contributor
timestamp: August 03, 2016, 10:17:48 am
content: There is one issue with RPCs you need to be aware of - it is very difficult to keep them well balanced as the load changes, which means it is generally a *BAD* idea to run any electronics from the generated phase. As the OP wants to test/repair brushless motors with an integrated electronic switched mode controller, with three phase input, he'll need decent power quality and voltage stability on the generated phase, to avoid the risk of tripping any phase-fault protection, which is going to require a very carefully tuned RPC, of a much heavier rating than would be needed for an induction motor load. Its likely to also need ferroresonant transformer(s) to stabilise the output voltage.Even with excellent scrounging skills to get the parts for the RPC and voltage stabiliser, and assembling it all oneself to keep the cost down, if you cost in all the time spent chasing parts and trouble-shooting it, an off the shelf budget three phase generator set is likely to be a better deal for occasional use.

author: SeanB
author_rank: Super Contributor
timestamp: August 03, 2016, 11:08:06 am
content: Quote from: Jeroen3 on August 02, 2016, 06:06:34 pmI used to work where the 115VAC 400Hz 3 phase supply was provided by one. It, along with the big 28VDC 20kA supply, were in a separate 100 square meter room all on their own. It just had 2 buttons on the front panel, on and off, with all the other controls and the metering locked behind a perspex panel, so all you could do was see if it was working well by looking at the 3 meters. You could select ( if the panel was open) to see incoming phase voltages and currents on the left meter, and with the right one the outgoing using a similar switch. The middle one was just a vibratory frequency meter.The 28VDC supply was even simpler, just a power light, power key switch, and a voltmeter and DC ammeter behind the perspex.You might ask why a 28VDC supply capable of supplying such a ridiculously high current. It was used to test run aircraft engines in the service bay next door, which used the built in engine starter generator to turn the engine over, and using aircraft standby hydraulic pumps, which also run off the 28VDC battery supply, to provide lubrication and cooling oil for the first tests on first test run. We could also use it to start aircraft in for service, or to provide ground power during servicing. As we had typically 6 aircraft in at any time this all added up.

author: iXod
author_rank: Frequent Contributor
timestamp: August 03, 2016, 02:55:32 pm
content: Quote from: Jeroen3 on August 03, 2016, 05:41:53 amAn engineer's definition of trivial!Thanks!

author: iXod
author_rank: Frequent Contributor
timestamp: August 03, 2016, 03:14:55 pm
content: Quote from: Ian.M on August 03, 2016, 10:17:48 amThanks for that perspective Ian. It's something I would gain from (bad) experience, so you save me the pain.By "genset" I presume you mean single-phase motor driving 3-phase gen. How does this differ from driving a 3-phase motor?Cheers.

author: Ian.M
author_rank: Super Contributor
timestamp: August 03, 2016, 06:33:39 pm
content: No, I mean a gasoline or diesel engine coupled to a three phase generator head. Small ones are usually highly integrated with the generator bolted directly to the engine bellhousing, often without a separate bearing for that end of the generator rotor, and a control system for the throttle for frequency control, and power, and for the field current to maintain output voltage.A motor-generator set is a different creature - single phase motor driving a generator as Jeroen describes.

author: iXod
author_rank: Frequent Contributor
timestamp: August 03, 2016, 06:47:41 pm
content: Quote from: Ian.M on August 03, 2016, 06:33:39 pmRight. Thanks!

author: Electro Detective
author_rank: Super Contributor
timestamp: April 26, 2017, 10:39:37 am
content: Anks and Kevman suggested using a function generator and 3 audio amplifier channels.How does that get you 3 sine waves 120 degrees phase apart?I am guessing even if it was feasible you would need the signal generator putting out 50hz or 60hz going into a delay unit with 3 outputs with appropriate delay times, going into each amp channel.Anyone here want to offer the delay time math for 3 sine waves 120 degrees apart?Then you'd need amplifiers capable of putting out 120 volts without cashing in on some magic smoke...Forgive my skepticism

author: Jeroen3
author_rank: Super Contributor
timestamp: April 26, 2017, 10:49:25 am
content: You use a sound card.And you use sensing transformers in reverse.

author: capt bullshot
author_rank: Super Contributor
timestamp: April 26, 2017, 10:55:28 am
content: Quote from: Electro Detective on April 26, 2017, 10:39:37 amThat's trivial:http://wunderkis.de/pwramp3/(scroll down until the phase shifter)

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 26, 2017, 01:53:04 pm
content: Quote from: Electro Detective on April 26, 2017, 10:39:37 amMains transformers, connected backwards.

author: Anks
author_rank: Frequent Contributor
timestamp: April 26, 2017, 05:19:26 pm
content: Quote from: mikeselectricstuff on April 26, 2017, 01:53:04 pmcheers

author: David Hess
author_rank: Super Contributor
timestamp: April 26, 2017, 07:46:32 pm
content: Quote from: Electro Detective on April 26, 2017, 10:39:37 amEither build a three stage phase shift oscillator which is an almost trivial exercise or perhaps better, filter the output from a3 stage Johnson counter. The digital method lends itself well to a microcontroller implementation.3 linear power amplifiers capable of producing about a kilowatt of 3 phase power would not be fun though. 3 class-D audio amplifiers of the required power would be feasible though.

author: Electro Detective
author_rank: Super Contributor
timestamp: April 27, 2017, 09:35:57 am
content: Thank you for the replies,"using a function generator and 3 audio amplifier channels" for a usable low to moderate current 3 phase system isn't going to happen easily, with just those items at hand.