The AM Forum

I have a blower to use with an amp, and it's 3 phase.

Baldor 3450 RPM
208V / 220V / 440V
4.5A / 4.4A / 2.2A

I know people run 3 phase motors on single phase, so why not? It seems like two phases would be connected across the 240V, and the third phase wire would go through a capacitor to one or the other line wires, so that the motor turns the right way.

My question is, what size of capacitor should be used? I am guessing at 240V/4.4A  it is about a 1HP motor. Is there any chart or rule of thumb on cap value for a particular HP rating on a given voltage?

I realize that it may be desirable in some case to switch in a larger capacitor to start up the motor quickly and then run it with the presumed correct cap under the fixed load represented by the blower impeller and tube airflow.

Secondly, mindful that I would have two phases 180 degrees apart between the 240V wires L1 and L2..
Would it make any sense to connect L1 to one of the motor's wires, and have L2 go through the capacitor to the second wire and also L2 go through a small low-DCR inductance to the third wire, so as to balance out the phases better?

I don't want to buy a VFD or make a rotary converter for this. I did find this circuit  attached, but others say 70-100uF for starting and 10-15uF per HP for running.. The relay is a potential relay but could be subbed with something else probably.

It's been a while...You will need 2 capacitors (if memory serves) to create the three phases. First winding gets straight power from the outlet, then one capacitor charges and releases power to create the second phase and the third capacitor takes a little longer to charge/discharge to create the third phase. The size of the capacitors are the trick. There are formulas. Google says you can do it with MOSFETs.

http://powerelectronics.com/power-management/three-phase-motor-driver (http://powerelectronics.com/power-management/three-phase-motor-driver)

Ken
N4zed

I don't have a complete answer to your question but standard 240V to your house is single phase.  L1 and L2 are not 180 degrees out of phase.  Think about the feed to your house - it's the secondary of a center tapped step down transformer.  The confusion may come from folks referring to the two hot wires in a 240V outlet as "phase to phase" and 120V as "phase to ground".  Hopefully someone else has your complete answer.

I know you don't want to use a VFD (I did a VFD on my 3 phase ROTRON), however, it looks like the version for your application is really cheap, if you change your mind.
http://factorymation.info/catalog/FM_Catalog_Spring_2014/files/assets/flash/pages/page0007.swf

L1 and L2 in the diagram are from a standard single phase pole pig with a center tapped secondary and so the L1 and L2 are having a phase difference of 180 degrees and 240V between them. It can be shown to be so because the addition is such that the line to neutral value is half the line to line value.

VFD cost $100.. not too bad but I would try not to spend that. The capacitor solution should be tried. I have not found a chart yet, only some suggestions.

An idea that comes along with VFDs is that a temperature could be taken of the tube anode and the blower speed adjusted to suit. The amp could be quieter in that way. Not sure about adding the complexity. In any case the manometer reading could be taken and the blower adjusted if needed.

What size is the motor? Most of the Baldor 3450 RPM 208V / 220V are in the one to three HP range! How big of an amplifier are you dealing with?  Half to one horse signal phase motors are fairly common and I would change the motor, if the rest of your amplifier is three phases driving the blower is going to be the least of your problems. Three phase power supplies are troublesome at best to convert and you will have issues with the filtering that was good at three phases being poor at signal phase.

This is a pic of the 3 phase converter for my South Bend 10L lathe 1HP 3phase motor.. A 3HP 3Phase motor is used to convert the 220vac to the 3 phase. No relays are used, just caps, which are out of a Siemans LRV. Oil filled, but I can't find the schematic. It is still a bread board circuit after a number of years!

YouTube video has the schematic;

https://www.youtube.com/watch?v=Vm7sgy1JR1s

73,
Ken

The motor is probably 1HP, being it is 208V/4.6A or 220V/4.4A. I could change it but am trying to avoid spending. A motor may turn up at some point but for now the capacitor idea is most attractive.

It all has to fit on one cabinet and I have the feeling it's going to be a monster so I do not really want to have to use space for an additional motor to make 3 phase.

The amp is going to be a heavy duty AM-rated amplifier. I have been scrounging parts for a few years for it. I believe I may have enough to start. I have some assistance from a local friend as well. The draft of the schematic still has a lot of wiring errors in it, not ready to post.

You cranked up a one horse thirty four hundred RPM blower yet? They tend to be a bit noisy. How big is that amplifier going to be?

For what he is planning, a bit of blower noise is the least of his worries. ;)

In his huge building it won't be a big deal.

He got the blower from me (I have more), it came out of a Harris 25kW FM TX.

Just a gentle breeze pushing thru a 4CX20K originally.

This guy has a simple fix:

http://www.gwm4-3phase.com/uands/static1.htm

73DG

The usual method is to increase the size of the cap (non-polar oil cap is nice, but a motor start cap with adequate voltage rating works) until you find that the motor starts and runs with adequate power... you can check the AC voltage with a scope or meter on the cap supplied winding, the scope will of course help to show the phase relationship too. It's an empirical method.

I use this method + a three phase "pony motor" to run my old trusty-rusty Index milling machine.
The three phase motor generates the third phase off the standard 240 volt two phase just fine.
You could use a small three phase pony motor too, if you wanted.

My old friend Russ ran his three phase powered milling machine by merely using the "third" winding as the "start" winding for the motor, he just touched the lead to the cap until the motor started! It ran fine, of course with slightly less torque, but more than enough to do 98% of all jobs.

Fyi, and all that...

             _-_-bear

Pat:
Slow on the draw sorry…..
Here is a very good article that explains how to determine the capacitor values.
http://www.waterfront-woods.com/Articles/phaseconverter.htm
I use a 7K 10W in series with a 120VAC relay for the voltage sensing relay.
I have been using this setup on my 2H.P. vertical mill for about ten years and it works FB.
This is probably overkill in your application but explains the procedure.
I would try the link provided by W7TFO in your application first, simple straight forward.
My mill has a newer high efficiency motor and they tend not to ‘like’ the single cap approach.
I tried it but had lots of growling and heat from the motor.
The single cap approach might work FB for your application though.
Tell us what you find
Best regards
Ted / KC9LKE

As always please use bleeders on the caps, especially if there is a reversing switch between the motor and caps. :o

Those article should be what I need to start. Some old AC type caps ought be on hand. I just got an RF amp off my bench so the blower would logically be something to work with first.

All the help and articles make a lot of sense. I will try the blower first with caps and see if it is satisfactory.

I think most of the gross errors are out of the preliminary schematic at this point. Its turned out to be more complex than I wished, but having a few solid state time delay relays on hand is OK to sequence the power-up (if I get tubularly fanatic, yes there are 2D21's and 2050's here..)

The liberal use of on-hand mercury relays/contactors should add a nine to the possible up time.

As yet no plate or grid overloads are in place but with a grid dissipation of >200W it should not be too big an issue. The energy in the power supply (for flash-overs etc) is nicely limited by a 10uF cap size, usable because of the choke input filter. The 30H choke is rated only 1.3A but at 55 Ohms and with the good wire size it seems to have, it should not be an issue to occasionally see 2A.

I have tried to keep the plate and grid current metering separate. I am always annoyed by deflection of one or the other meter by the wrong current. To avoid burnout of current sensing resistors, they are 20W units. I think all the parts are finally on hand, maybe not all the the 1000pF caps in the RF section.

No bias is in place at this time. Something to consider, what to do about it.

I left the RF section substantially the same as in the GPT-10K because it simplifies things and the pi coil is DC-rated, but it could be changed. Thing is, doorknobs are out of the question in this.

TR switch is the same design that has been in use. It looks complex but it serves to disconnect all in out and antenna ports from the gear when power is off. The plan is to use 600VAC 3 phase 20-30A contactors for the TR switch. If leads are short and relay coils bypassed it should be OK. This has worked here so far without SWR issues.

(begin insane rambling) Something ambitious is still in the mind as well but not in a diagram. The RF chassis the parts are from is still intact. I have seen where others have made the Henry 5KW, 13.5MHz RF generators into 6M amps and all of that fits into the chassis. Wild idea -have that for 6M, and directly above the tube mount a low-capacitance 50KV 50A Jennings vacuum switch with 70dB isolation, and from thence and close by, the input to the HF pi tank. Possibly this could cover HF and 6M. It would all depend on very short wiring, have to see if it can be realized in physical form. A possibility is certainly having the PI coil be the top part of the RF choke for 6M. (end insane rambling)

Patrick-
When you try that blower, with just the simple capacitor trick, watch the temperature of the motor. The motor may run too hot to hold your hand on it.  The problem is that the blower is a continuous load (think like CCS) and it was designed to work with a 1 horse motor.  A drill press or milling machine is a variable, intermittent load  (think like ICAS) and can adjust its horsepower demand downward just by slowing the cutting feed.   When the simple capacitor trick spins the motor but with reduced horsepower, the blower/motor combination may have problems getting up to design speed, which causes increased current draw, which causes overheating and slowly burns up the motor windings. 

I suggest you use the idler motor method if the electronic drive is too much for the budget.

73
Chuck K7MCG

I will be watching the temperature and current.  I got together 46uF of oil caps and got it to spin up but it's not enough to get to full speed and that is not enough to 'start' it. I need to find more microfarads and get closer to the recommended values before proceeding.

It did spin up well when connected to a 1KVA 240V step up transformer. Starting current was about 25A and would have dropped once it was to speed and the big cap switched out. The quick setup was not up to the task but proved the idea to proceed.

The testing lasted only a few seconds each time. No going to burn anything out. Sure if this does not work right I'll have to use a VFD or idler but we'll see.

just ordered the caps 80uF 12uF and 5uF on the pay place.

Sometimes it’s easy to just use a signal phase motor, and maybe cheaper than buying lots of other stuff to try to get a three phase motor to work in a signal phase world.
Look at EBay:

http://www.ebay.com/itm/Baldor-1-HP-electric-motor-3450-RPM-/252170904360?hash=item3ab68ea328:g:dw8AAOSwo0JWPj3V

What do you have for a plate transformer for this huge amplifier? Is that three phase also? At some point maybe a surplus three phase 10 Kw generator may be the best alternative. Something to be said for having to go out and crank up the diesel generator prior to making a QSO

The caps showed up today Polypropelyne film ones. 80, 12, and 5 uF.
(edit: $33 shipped for the above new caps from the pay place. Keep in mind next time the HVAC guy wants $45 for a single cap..)

I don't know so much about swapping motors. Is it a guaranteed fit to the base and bolt patterns if the NEMA frame size is the same?  (what about shaft diameter, certainly length, RPM, and direction)

I can sure appreciate the brag points associated with having to use a 3 phase generator to run the amp.. but I have to be somewhat practical and run this off 240VAC single phase. The problem with using a generator is how to key it.

The most recent schematic is attached. It changes from time to time. It has details of the plate transformer and the motor phasing circuit. You know how it is the final schematic is never done til the equipment is done. Got lots of advice right here!

One last thing electrically is wanting to use an MB-xx style cathode tank. one knob tuning to cover HF. I don't know that anyone has done that with a grounded grid circuit, quite a departure from the usual use of such circuits.

I got lucky and was able to get a single phase blower for my 4cx-----   rig...........It works well and gives none of the problems that I had trying to keep the 3 phase blower working with a cap start-run setup....The blower had a sail switch that I kept in the circuit but I eliminated the 2 other safety switches that wouldn't let the filaments come on unless the blower is running...Military redundancy......I also put the blower outside on the shack wall and ducted the air to the tube...Much quieter  Good Luck...

Most of the blower noise in my shack now is from the Tucker transmitter and is present because of the open front at the bottom where the modulator blower is (wide size rack, no panel to fit there) and also some noise from the perforated grille on the front of the RF deck. A piece of glass or clear plastic could be put behind that and the hot air let go up out the top opening and to the rear. it would leave only the 'hum' of the blowers, and get rid of the air noise. I hope anyway.

That said, the HVAC unit makes more noise than the transmitter. The Behringer mike compressor in use has a gate. It works well to silence the noise when I am not speaking. The effect is funny. After the last syllable, the noise starts to creep up but is suddenly cut off. Why it's called "Amateur" radio  ;D Not so many folks have a studio, most sit with the mike next to the transmitter..

I am paying attention to the blower mentioned here, and have some ideas to reduce the 'air noise' from the blower intake and the cabinet exhaust. I have been thinking about the kind of ductboard used for HVAC work, it is designed to stop noise. If there are a couple of 90 degree turns for the air entering and leaving the cabinet I believe the noise could really be abated. An experiment, but that's my favorite part. And maybe why it takes me forever to finish stuff, but it is the enjoyment, after all.




The noise issue is more important and should be a meaningful discussion. More comments are welcome! (I can't really put the blower outside here.)

Most of the noise from a blower, putting aside the air noise, seems to be mechanically conducted vibrations from the motor amplified by the metal enclosures. I can't count the ham-fest 3450RPM blowers that have turned out to be very vibratory. Hopeless to try and balance them.  Or I don't know how..

Old blowers make more noise because of several factors. I think all would agree there are several kinds/causes of noise. Anyone add to this or suggest corrections?

1.) The wheels or whatever have become unbalanced and cause vibrations. All it seems to take in cases where wheels are of thin material is jarring the blower a few times to incrementally make this kind of problem increase.

2.) Ball bearings are wonderful but any ball bearings present tend to make a wide spectrum of noise. Oiling them helps but the noise is conducted vibration too. The older they are the worse it is. The thinner the end caps that hold the bearings, the wrse it gets.

3.) The higher the speed, such as with the desirable 3450+ RPM blowers needed for high pressures, the louder all of this noise is.

4. A blower that, when spun by hand, does not keep spinning for a few seconds has a lot of friction. Some people told me that its normal, but I have seen for myself quite large motors, large in relation to household stuff, say 3HP, that spin freely and don't make much noise. So?

The 3 phase motor I have here, it makes a slight 'running' noise when spun. I feel like it is going to be quite noisy mechanically. Consider it is a pull from an Ampliphase transmitter, so it is got a lot of hours on it. It should be looked up to see if it needs lubricated or what. I don't know if I will have time to play with it this weekend.

You can purchase clip on weights for the blower wheels.   I do not know where,  but I had a bag at one point.

I also have a single phase blower (squirrel cage) from a TV transmitter.   Not quiet,  and you can see the thing vibrate.

I've found,  for quite,  a rotary blower is the hot ticket.   I've got one for the transmitter / amp I got that filament choke for.

Mine has a 10 inch opening and exhaust,  and moves more air than any centrifugal I've owned,  sans  one in my swamp cooler.   It is balanced,  and quiet.   Quieter than an EBM / Pabst.  They are used in 'indoor hydroponic cultivation'  I believe,  as that's where I got this one, a local grow store.

https://www.hydroponics.net/i/131324

They don't list back pressure,  but I have NO doubt it blows more air,  at twice or more force,  than the TV blower,  which had a 4x15 IIRC.

Not cheap,  but not expensive if you shop around.   I paid about 140 for mine.

Harbor Freight also has a huge blower for about a hundred bucks,  squirrel cage style,  designed as a dust collection unit.   I had planned on using it, n found my current one.

Also,  any 90s will cause turbulence and increase sound for a given output.   You have to increase airflow to compensate.

I've seen people build mufflers for big blowers.   Equated to egg crate in a box,  with intake and exhaust ports.   Again,  they basically increase turbulence,  slowing the airflow.   Lower airflow = lowered noise.

Fwiw,  my box fan,  on high,  produces more noise than my rotary blower.

--Shane
KD6VXI

The pressure volume chart is there on the page so maybe they added it. The tube admits about 56CFM per inch of pressure. At sea level 1.2" is stated as the 4KW dissipation figure and 1.45" @5000 FT.  That blower would make about 150CFM through the tube assuming otherwise low impedance which is about twice the required flow in the forward direction and 1.5x if anode to filament cooling is used. It says it's speed controllable but also shows it as a capacitor run motor.

I have five squirrel-cage blowers in use here in various homebrew rigs. All were bought at ham flea markets for cheap, $10 -$20... Most of them had bearing noise that produced an irritating whine. They had lots of hours on them but were good quality blowers.  The air flow should be the only thing we hear if the unit is good.

The solution was to locate a motor rebuilding shop in Hartford and bring them in. For a reasonable price they replaced the bearings.   Big difference. Quiet and run like new.

Every city has a few of these rebuilders. Worth it to get a quiet background sound. Add a Variac on each blower and we can dial down the air to get reasonable cooling with minimum air noise.  The only variable then becomes obstructions in the air path like sharp objects that can cause whistles.  

Bearings replacement, a clear air path and minimum speed equals quiet operation. For both ssb and AM, there is nothing worse than a signal with noise background that is down less than -25 dB.  (noise gates don't cut it for AM)  If we strive for a natural signal to background noise level of -40 db or better, we are doing well.  


T

Yes,  the graph is new.   

They do move some air.

Mine can be controlled with a light dimmer,  to slightly less than half speed.   But,  it takes about 2/3 speed voltage to start.

My percentages are designed to err on the high side.   It probably spins slower,  and starts closer to half speed.

--Shane
KD6VXI

Bearings, balancing and the entire like are good but a one horse 3400 RPM blower is going to drive you out of the room! Don’t know what your requirements are going to be for that PA tube but I recall in a couple of the low power TV transmitters that I use to take care of in the analog day (5kW) that’s the blower that they used and it was good for fifteen inches of water thru a six inch duct. But you’re a big guy and should be able to take it, the noise at least. When they are set up right vibration was not a big deal and in continuous service they ran for four or five years before having to be replaced. Near the end of analog was replacing all the blower motors with Baldor units that I think were built in China that cost less than repairing the American motors and were just as reliable. If noise becomes an issue you can always put the blower outside or another room and use six or eight inch duct to connect, I never did that being every transmitter I work with was always in an unmanned aria but there would be something to be said for having air ducts and motors that start in another location when you turn on the transmitter.
Looking at the schematic I just wanted to warn you about what will happen if somehow your HV gets shorted to ground R6 and R15 will open dramatically! The same TV transmitters that I was talking about above had a 10 Ohm 225 watt resistor in series between the HV- and ground and when the PA tube would short out with 5Kv on the plate that resistor would explode. The stupid French tetrodes that they used would occasionally dead short every now and then and that ten ohm resistor was a sacrificial component to prevent real damage to the power supply, so of course it was installed down between the HV filter capacitor and input choke so there you were in the middle of the night fishing around to replace a huge resistor that you could not easily reach and was imposable to get a soldering gun down to. So I repositioned that so it was out in the open and easy to access so keep that in mind when laying out parts. D2, D3, D4 and D5 are going to save your meters but I am wondering what C9 and C18 are for? Remember if R6 or R15 open they will have 5Kv across them and not be real happy about it. R16 and R11 may be toast when R6 or R15 open too. Don’t get me wrong, I am not saying don’t do it this way because what your doing is standard in almost every vacuum tube broadcast transmitter just trying to point out that you want to have easy access to all that stuff so if in the event something in the tank fails or if you have a HV interlock and decide to test it or somehow forget that the HV is on and it does its job that’s the type of damage you can expect to see. Also why tubes instead of diode stacks?   

'Cause guys like us are sick of solid state crap.

"We have MV rectifiers and are not afraid to abuse them!" Quote PJK.

73DG

A few tips about using remote-located blowers. Getting a quiet shack can certainly be a challenge sometimes:

For remote blowers, I have found that the ducting material needs to have a smooth inside, otherwise ribbing will cause air turbulence producing more back pressure, more air noise and less air flow. Thus, the blower needs to run faster = more noise, etc.

I once tried using 4" diameter PVC pipe as the ducting. The concept sounded good on paper, smooth inside, etc. The run was about seven feet from the blower mounted outside the wall to the tube chassis. But alas, the blower sounds were amplified like a trumpet!  It was like the blower was in the room, but even louder.  The PVC pipe had no sound absorbing qualities. The solution was to get some flexible fiberglass ducting on the internet that had a smooth interior. This solved all noise problems. IE, we need a ducting made of material that does not conduct noise well.

I also tried an outside-the-house blower that pushed air in. The downside was the weather moisture caused rusting of the tube and chassis components. In the winter it was murder when pushing in the cold air.  So, mounting a blower on the outside wall in a warm room is better.

Last, be sure to mount the blower on rubber or styro insulation, etc., without screws making a direct connection to anything that can transfer vibration.

Another experiment was to use acoustical panels on the walls and ceilings to reduce reflections.  A friend tried this and it was a bust. Small return for big effort.

I spent a lot of time making acoustical measurements with a meter and then adjusting all of these parameters. When using a big blower, eventually we can find a way to get it to run quiet.  For BIG rigs, sometimes the only way is to run the entire rig in another room remote.

The pleasure of operating in a quiet or almost quiet room cannot be emphasized enough.

T

I've got to get this blower spun up and see just how much noise it makes. I don't 'have' to use it, but if I do, then it leaves open the possibility of using a larger amplifier tube in the future.

The MV tubes are nice, about the largest commonly available size, and good to look at. Since the 3CX3000A7 does not glow, the MV rectifiers will serve that function.

That is one reason I want the amplifier to be in the room, so it can be seen. I don't always get what I want but it's worth trying for.

flex connection between the fan and the ducting can help eliminate noise transfer .

Its really nice having a silent transmitter in a quiet room.

One idea to remember is that they make in duct fans as booster fans for heating systems.
You can get a cheap plastic blade four inch one at home despot and better metal blade ones on line.
They are quiet and move a good amount of air.

As it turns out this is the only 3600RPM blower here. The others are 1720, etc. Almost every blower that is not a 3000+ RPM unit has not made the pressure needed to do this job, but I have only 5-6 blowers on hand.

I got this monster fired up. The schematic posted using an 80uF cap to start it worked well. It took about 15 seconds to get up to speed. It was run off a 120->240V 1KVA transformer for this experiment, and that may have limited the juice to some degree. When running the amp draw on the 120V side was 9A. This would be 4.5A on the 240V side, which is close to 4.4A the motor's rating. I need to measure the amps on each of the three wires on the motor as they should be balanced as well as possible consistent with the fan actually running.

It is quite noisy but I have hopes of noise abatement. I will work with this some more and make sure it is usable, does not overheat, etc.

Another thought about the design, what’s the insulation value of your filament transformer L2? I am use to broadcast service where the transmitter is on all the time but in Ham service the transmitter is almost never on compared to the amount of time spent in standby. On the broadcast transmitter that I have running on 160 what I do is use the key line to control the plate contactor so the HV is off until you switch the transmitter into ON, but looking at your design it appears that you have your HV set so its ON and are using X64 and R18 to cut off the tube when not transmitting or in standby. This is going to crank the cathode filament voltage way up and if L2 is not built with the right amount of insulation bad things may happen, also C5 will need to be able to withstand the high voltages that will appear on it at that time.