anybody running a pm head?

[bschwartz]

I'll try to put some numbers to it in the next day or two.  I didn't think to get some exact readings off the ST-5 before pulling it out of the loop.  What I can say is that I was NEVER happy with the voltage fluctuations between loads particularly when unbalanced.  One reason I went with this oversized PM head is that I often have unbalanced loads as different units switch on in the house (refridgerator, freezer, microwave, hot tub, dish washer, clothes washer etc.), and sometimes the heavy loads are sharing one leg.  I wanted to know that the generator could supply all the power the 6/1 could put out on one side or the other.  So far, the voltage droop seems very reasonable.  Just from quick checks of the kill-o-watt plugged into an outlet in the house, I didn't know if there was a heavy load on the generator or not.  Let me explain a little.  On the old head, I could tell when there was a load by watching the voltage drop.  Now, I had to check the frequency to know.  Give me a little time, and I'll get some real readings, and pictures.

[BruceM]

Bob, In brushless heads, there is good transfer of the diode noise from the exciter back through the field coil to the connected AC, even though the exciter to field coil is radiated, not conducted.  The EMI is radiated (both H (magnetic) and E (electric) fields) at the exciter.

While noise suppression caps are easy to add to the diode bridge on a brushed head, it's going to be a bear with a brushless head.

Most AVRs on the market are also guilty of introducing significant EMI on the AC.  They bang high voltage with extremely fast rise/fall pulses, and don't have optimum circuit design for controlling EMI. For my AVR (not the simple model) I used two darlington bipolar transistors (TO-3 "cans") for controlling excitation pulses, and slow the rise fall time to 200 usecs.  I didn't do this on the simple circuit board as most people don't care about EMI.  To convert the simple PCB design, just use external power transistors, change the drive resistor and add a small cap to slow the rise/fall times at the darlington base.

[rcavictim]

anybody running a pm head?

I'm usually running to the head in the am.   

[bschwartz]

First numbers are in

frequency  leg 1 load   leg 1 voltage   leg 2 load   leg 2 voltage  total load
    61           0 W            121.2 V           0 W         121.3 V           0 W
    60.3       890 W          118.1 V           0 W         120.2 V         890 W
    59.9      1525 W          116.3 V           0 W         118.9 V       1525 W
    58.8      1415 W          113.7 V        1650 W       114.9 V       3065 W
    58.6      1765 W          116.8 V        1610 W       113.3 V       3375 W

Metro 6/1 on WVO (soybean)  4200 ft elevation, Georgia Generator 6.5k PMG
all readings from two kill-a-watts  (the last readings had the Kill a watt on leg 1 flashing)

I don't think the engine will do much more without heavy smoking, but not bad for free fuel.

[rcavictim]

Considering your elevation I think those loaded numbers look quite good for a 6/1.  Quite good indeed.

[BruceM]

I agree, those are good figures for a 6/1 at 4000ft even on dino.

[Apogee]

When looking at the rear of the PM head from Georgia Generator, is the back also sealed?  Basically, is the whole unit sealed tight similar to the unit from Utterpower?

I'm curious because they mention that it has a metal fan on the Georgia Generator site.  I am wondering if it's sealed because I wouldn't want those magnets attracting metal filings...

Anyone seen one in person to know?

Thanks,

Steve

[bschwartz]

No, they are not sealed like the utterpower units.  They are open on the bottom with cooling vents.  They would attract metal filings if present I'd think.  In order to get stuff in them, they would need to suck from the bottom, as they are closed off top and all sides.  That aside, I would think that any generator head will have magnets when spinning.  These seem less likely to easily get contamination inside compared to the ST head (I have both).  Anything else you'd like to know?

[Apogee]

Hi bschwartz,

Nope.

Thanks!

The genesis of my question lies in the fact that I do lots of welding and grinding in my shop.  I asked because there are always LOTS of metal filings around and am concerned about them being attracted to the head and ultimately ending up inside if I were to go that direction...

Looks like an outbuilding may be in my future just to be safe.

Thanks again,

Steve

[dubbleUJay]

Steve, you can put a few (or one) magnet/s close to the openings to act like a magnetic air filter should any fillings pass by!
Just an idea.

[mobile_bob]

Steve:

from what i have seen the pm heads are sealed up from fan airflow
the fan draws air into the shroud end grill and is directed over the finned exterior
of the case,

the idea being the stator heat is transmitted through the outer case and dissipated in the fins

this leaves one distinction between utterpowers head and the other pm heads, that being
how do you effectively removed the heat from the rotor?

the rotor should have less heat being a pm field as opposed to a wound field, but there
will still be some heat generated in the rotor due to induction back from the stator into the
rotor magnet pole pieces, how much heat? i have no idea.

apparently there is a significant concern with the rotor heating because the utterpower manufactures
decided to use a hollow shaft to allow for airflow through the shaft.

having said all that it is commonly written about in design text that a very large portion of the heat
generated by a wound field and back induction heating from pole faces (hysterysis and eddy currents)
is transferred back down to the shaft and through the brgs as hard as that is to believe.
(to me that seems like a long ways to go to get heat dissipated, but apparently it is so)
there is significant text in relation to specific lubrications being developed to handle and aid in transmission
of the heat from the rotor, through the shaft, through the inner race and to the outer race and into the case
ends.

i guess it stands to reason that getting airflow through tight airgaps in a rapidly spinning rotor might be sorta difficult
under any but very forceful application. forced blowers consume large amounts of power so i guess it stands to reason
a designer might want to avail himself to using time tested means of heat transfer.

as far as the utterpower pm heads they appear to be very well built, sealed to exclude damn near all entrance of
particulate matter, and have the hollow shaft.  i also believe that if another seller of those heads might also rate
them closer to 4 or 5kwatts, so it is probably something that speaks well of George to rate them conservatively
at 3kwatt and have a head that will run continuously under just about any possible conditions without issues of failure
giving the units a bad name.

you know how it goes, something that is new better be at least adequate, because if it fails in significant numbers there
is no way to reclaim the reputation later, or rather darned expensive to do so.

i don't know anyone running pm heads of other manufactures or from other sellers, perhaps they too are good for their
ratings and will prove to be dependable,, i guess we won't know till we see a few out in the field with reports coming back
about how they are doing.

anyway thats all i think i know  

bob g

[dubbleUJay]

Grinding dust gets into places you didn't know eve existed. It has an uncanny ability to teleport into the tiniest of enclosed and hermetically sealed spaces even if that space is under 50 feet of water. It's bloody amazing! If someone could harness the teleportation feature of grinding dust and direct it to a predetermined area, we could just cover ourselves in grinding dust and teleport everywhere and we wouldn't have global warming issues.

Jens

Could you write a paper about this pretty please

[BruceM]

Since I'm the resident EMI harpy, I'd like to add that a PM head has the best quality AC available today- while you may have some low frequency harmonics, there is NO high frequency EMI, the stuff that appears to accelerate cancers of all kinds and cause autoimmune diseases as well.

Brushless and Brushed generator head both put a lot of EMI on the line  because of excitation diode noise and because of PWM AVRs, if present.  The cost of high end filtering of a typical brushless head exceeds the cost difference.

On the brushed heads, diode noise suppression via 4- 0.1uF metal film caps, one around each diode of the bridge, is fairly effective, but you can still hear it on on AM radio, so if you wanted clean 60Hz, you still have to add an external filter (multistage LC), preferably surplus military grade. I have a design for low EMI AVR which is available on request, but there is no PCB for it.

[bschwartz]

Bob,  as I don't see anyone else chiming in about PMGs I'll say that I've been REALLY happy with my 6.5K from Tom Osborne.  I chose it over the utterpower unit due to loads available.  The Utterpower unit is a 3K unit which I think would only provide a continuous 1.5K per 120V leg.  Although I only have a 6/1, it reliably puts out a little more than 3KW, and my loads are almost always unbalanced.  I might have 500w on one leg and 2300W (or more) and 5 minutes later after the hot tub switches off, and we are cooking in the microwave, the loads may swing the other way.  All the time, voltages are rock steady!!  Yes there is voltage drop as the oid slows down from the load, but the voltages are nearly the same on both the loaded and unloaded leg.  I also liked the idea of a sealed unit, but I thought size would be more important to my situation.

-Brett

[Bill]

No, they are not sealed like the utterpower units.  They are open on the bottom with cooling vents.  They would attract metal filings if present I'd think.  In order to get stuff in them, they would need to suck from the bottom, as they are closed off top and all sides.  That aside, I would think that any generator head will have magnets when spinning.  These seem less likely to easily get contamination inside compared to the ST head (I have both).  Anything else you'd like to know?

As a new kid on the block, here on this forum, I'd like to describe an instance that happened to me that deals with magnets attracting contamination.

I'd found an old 1903 Stanley handplane that had been stored on its side.  From moisture of a wooden storage shelf, rust had pitted that side, so in my workshop, I was using a 6"x 36" upright sanding belt to smooth the rusty and pitted sides.  The belt/disc sander is 30 ft. from the end of the shop where a return air filter is for a corner heat furnace closet. About 6 ft. from the return air, between it and the distant belt sander, I have a metal storage cabinet with doors.  One the inside of the metal doors, I store odds and in's of different size magnets I find from time to time.

After, I'd finished flattening the sides of the handplane, I walked past the metal storage cabinet only to see patterns of blackish dust collected in the shape of the strongest magnets.  Air currents from the furnace blower had pulled Metal filings that traveled over 20 feet!!

Like the after-market magnetic drain plugs for your auto's oil pan,  I like the idea of putting some magnets in front of the PMgenerator's cooling ports.

By the way, I'm having trouble typing in this box as the last few lines keep jumping down under the bottom border even though I have extra blank spaces below this.  Any ideas how to correct this distraction?

It''s good to be here,
Bill