Single Phase Alternator Design

[bcavender]

A manufacturer rep made the comment to me that “All permanent magnet alternators are three phase.” And looking at several “single phase” alternator head configurations, they are connected zig-zag or double delta WITH kw/kva capacity reduced 30-45% to meet the single phase requirement.

I have puzzled for a while as to why some nature of single phase winding design could not be created rather than paying for a machine that is larger in size/cost than the application requires?

I suspect I have missed some key fact in my searches … or it is simply a matter of economics that there isn’t enough benefit or demand to design/support such a product.

Can someone that’s been around this rodeo before help me understand what I am missing or a proper place to learn the real scoop about this?

Thank You!

Best regards,
Bruce

 

[waross]

A manufacturer rep made the comment to me

Ask someone in the design office the same question.
Change that to Many permanent magnet generators are three phase.
Many PM alternators are intended to have the output rectified to DC.
Three phase gives much less ripple and is a more efficient use of material.
That said, I have seen single phase PM alternators. Mostly in very small sizes. The first alternator that I ever took apart was my bicycle
generator. It had a six lobe magnet, but only a single phase winding. The six lobes gave three cycles per revolution rather than one and it was able to generate a usable voltage at one third the speed of a hypothetical generator with the same winding but only two magnet lobes.
In the case of excited alternators:
When the market for single phase alternators is compared with the market for three phase alternators, and economies of scale are considered, there are very few single phase alternators built in sizes above about 15 KVA to 20 KVA.
Above that size, the single phase market is served by three phase alternators connected in either zig-zag or double delta.
The four wire, 120/240 delta connection may also be used for single phase service.
All three connections develop 2/3 of the KVA of the three phase rating.
Many use the same prime mover, and the PF goes from 0.8 to unity.
On all three connections, the kW goes up 25% to reflect the improved PF rating. That said, it does no good for low power factor loads.
If the load power factor is 0.8, the alternator will be KVA limited despite the higher allowable kW.

Four wire delta when the wild leg is ignored and only single phase power is supplied.
O

A manufacturer rep made the comment to me that “All permanent magnet alternators are three phase.”

Some may consider that comment a little foolish.
There may be a 1/3 saving in copper with a dedicated single phase set compared to a reconnected three phase set, but that is over-ridden by relative market size and economies of scale.
A note for those of you who have seen single phase generators in sizes larger than 20 KVA.
With a special order in hand for a large number of sets, it may be economical to do a run of single phase only sets. If you see a single phase alternator much larger than 20 KVA there is a good chance that it is military surplus.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bcavender]

Waross,
Thanks for your reply!

In your opinion, who are the current leading suppliers for sub 10kva, split/single phase 240v alternators that are not cut off at the knees by international problems?

Likewise, do you see any permanent magnet alt mfgrs (single or three phase) moving real product off their shelves to the US market?

Seems to be a lot of specialty companies but few that make 5 & 10 kva heads for common use.

Appreciate your thoughts greatly!!!
Bruce

 

[waross]

What is your intended use?
Permanent Magnet Alternators tend to be special purpose machines.
The output of a generator with fixed excitation varies considerably with the load. The voltage range may be 2;1 or more.
That is 100% voltage at no load, 50% or less voltage at full load.
One application is a Permanent Magnet Generator, PMG. supplying power to an Automatic Voltage Regulator for a larger alternator.
The other application is very small loads such as motorcycle alternators (the smaller bikes) and bicycle generators.
On small engines using a permanent magnet alternator, the headlight is typically wired direct and is on at all times.
The voltage is controlled by burning off excess power in a Zener diode with a heat sink at higher RPMs.
It is not uncommon for the Zener diode to fail if the bike is rev'ed up to max RPM without a headlight to use some of the power generated at high RPM.
Brands: Much of my work was with F. G. Wilson sets, under a variety of marketing names. F. G. Wilson, Caradon, Olympian (Cat). Cat bought sets for their Olympian line until they bought the entire company.
F. G. Wilson is now owned by Cat.
I avoided Asian brands.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bcavender]

Application: Remote/Reliable Prime power (5-10k, 60 Hz, 240v split, 1800rpm max - would like 1200rpm/6 pole)

Best prospect so far-Have been talking w RFL Alternators 4 pole(Aussie).

https://rflalternators.com/products/4-pole-alternator-series/

They seem to have some nice PMG specs with ZERO on board electronics sold into public safety/Mil markets. No rectifiers buried in the rotor is good. Price is a bit higher, but reliability justifies it. (Though your comment on voltage regulation is on point as RFL lit doesn’t spec no/full load regulation). Found one reseller stateside and their people complain shipping takes six months. No cigar :^(

Looked at SOGA (Italy-A stateside guy priced me a 2kw pmg at $5.5k to make me go away). MeccAlte-can’t find a reseller for their PMGs … likely they only want to talk if you want to do 100s. Ditto PMG specialty companies I search up.

India machines turn up in searches, but look dicey (free energy) w no stateside dealers/stock. Chinese machines appear workable (Greef), but again no US stock/long shipping/questionable performance and service. Got to say they do have a broad array of standard products, but it’s likely that supply could dry up in a hurry over political issues.

I’m surprised someone would employ a zener rather than these tiny & very cheap DC-DC bricks to avoid pwr waste and fire liability. I put a bunch of those through rigorous testing for a fiber app and they are engineered like a brick house.

Wilson 6.8 looks real good, but it’s diesel only. Fuel for my app is natgas.
Olympians start at 100kw+. Couldn’t find Caradon.

In the 21st Century, I would have thought someone would address the better-thanHarbor-Freight 240 split/1ph alternator market in the USA.

 

[waross]

A Permanent Magnet Alternator is limited to small sizes.
A Permanent Magnet Generator, PMG, is an accessory to an alternator that is used to supply the field current.
The Zener regulator circuits have been around for over 50 years. Newer bikes may use a different system for regulating.
There is not much made anymore without rotating diodes.
Forget 1200 RPM. You don't need it and you probably won't find it in the size range of interest.
That was common for larger sets 60, 70, and 80 years or more ago.
Back then, automobile engines were considered worn out at 60,000 miles.
Engine technology has advanced a lot since then. Both for auto engines and genset engines.
I would avoid 3600 RPM, particularly for prime power.
In the under 10 KVA range you will find some good capacitor excited single phase alternators.
The voltage regulation is acceptable.
To raise the voltage, add more capacitors in parallel. The capacity versus voltage curve is fairly linear, so you can use simple scaling to determine how much capacity you want to add. (And they also use a rotating rectifier.
The development of brushless alternators was a huge step forward for reliability.
It allowed the removal of slip rings, commutators and brushes.
With that advantage came the very reliable rotating rectifiers.
Live with it. Don't try to go backwrds in technology.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[catserveng]

Take a look at MOOG, have a number of options at 1200 RPM,

https://www.moog.com/content/dam/moog/literature/MCG/AGMatrixSeriesAlternators.pdf

MikeL

 

[waross]

I tried to find out more about Moog and got this:

DISCONTINUATION OF GENERATORS

Generators were discontinued by Moog. AVL has purchased this product family. Please contact AVL for further information.

I couldn't find anything about regulation or voltage control.
Can you give us any information on voltage regulation on a Moog generator?
Thanks Mike.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[catserveng]

I ran into Moog alternators about 3 years ago, dealing with some oil field service equipment where they had been used as house power, all in the range of 15 to 30 kW. I didn't get too familiar with the generators since we found the problems were in the connections and distribution. Also have seen their products at several military sites, mostly Air Force, in ground support and other equipment.

I had heard Moog had sold off the GES line but retained the AG Matrix line.

These PM Alternators put out a fairly stable voltage output within their rated capability, but I think the motor starting and fault current capabilities are not as good as a unit with either an SE or PMG excitation system. The ones I have run across are VERY compact and quite simple, but typically there are used in applications for "house power" on different types of equipment. And their cost per kW seems pretty high for the better built units. This size range really isn't in my wheelhouse so I don't have a lot of good info about them. CAT used Moog and an ABB product PM alternator on some paving equipment lines, but since have gone to a switched reluctance generator (SRG) on that type equipment. Those ranged in size from 20-40kW.

To the OP, Winco and Stanmford offer a number of smaller 240/120 single phase units used in construction, rentals, standby and prime applications in some pretty crappy environments. While they do have rotating rectifiers and AVR's, their technology is well known and lots of folks all over the world can keep them going. I think most of these are 1800 rpm machines,

https://www.wincogen.com/wp-content/uploads/PD/Spec_Sheets/GenEnds/SP-218_STAMFORD-2-BEARING.pdf

They also have some smaller more compact units, mainly see these on PTO generators,

https://www.wincogen.com/product-category/current/pto_2_bearing/?v_output=120_240v1p

MikeL.

 

[bcavender]

I’ve seen a couple companies selling alternators like this. It pretty out of the box to say the least in terms of getting them mounted.

It would be interesting to see a set of these actually integrated to a prime mover.

AVL looks to be a systems integrator vs pushing out lots of alts that can be installs broadly with typical electrical/civil works folks.

It’s interesting, but I don’t have a clue about where to start thinking about mounting this style rotor/stator.

Love the size/tech though.

 

[bcavender]

Mike,

I expect the Moogs were embedded into specialized equip that only would fly if significant volume was there to amortize the engineering and special machining.

I read a research paper some time back about switched reluctance generators which are supposed to be attractive for their completely passive rotors from a reliability perspective. These grew out of the ballistic missile arena for ‘short lived’, very high rpm, exhaust driven passive rotor generation to operate flight controls.

I didn’t know they had moved into industrial production. A flux switching rotor without PMs or windings should have some degree of reliability improvement.

Very interesting.

Will have to search that rabbit hole for vendors.

Thank you!!!

 

[catserveng]

What are you using as the prime mover? Most engines, gas and diesel, have flywheels and flywheel housing that conform to SAE patterns, the Stamford generators can all be had with close coupled adaptors and flex plates for flywheel mounting. Your primary design criteria would be building a proper base. You could also go to a single bearing generator close coupled and get by with a lighter, less rigid base, but you need to follow proper design criteria.

Or you may want to look to a packager of smaller units, someone like Arrow,

https://arrowengine.com/products/arrow-original-equipment/engines/generator-set

whole builds sets for mostly for oil and gas applications, but their stuff is well built and rugged.

MikeL.

 

[catserveng]

On the SRG's, the first ones I saw were on fish processing ships and shaft generators, supplied by ABB marine group, the generators made by someone else. When they worked they seemed awesome, when they didn't finding someone to work on them was a pain. Although it was usually a case of its good or its not, and field repair was limited. And CAT did some work with that technology for high power support for some missile tracking systems power units in conjunction with one of the large players in military contracting.

Yes, they are in use in some earthmoving/construction applications, not where I normally work but sometimes am asked to help, especially now in our area electrical safety regulations prevent the machinery techs from diving into anything above 50V.

MikeL.

 

[waross]

I am a little concerned about voltage regulation.
It seems unusual that the specs make no mention of voltage regulation.
There are times when you need to adjust the output voltage of a generator to meet site specific conditions.
I would much rather adjust the voltage by turning a small potentiometer adjustment than have to buy and install buck or boost transformers.

Are you designing sets for resale or looking for a set for personal use?

If you can live with diodes, you can get quite good regulation without any other electronics.

Start with a set with a brushless exciter.
Add a constant voltage transformer, a series resistor to adjust the open circuit voltage and a bridge rectifier.
Then add a window type CT with the load conductors passed through the window in opposite directions.
Drop the current through an adjustable resistor to develop a voltage and, rectify that voltage and connect it in parallel with the constant voltage rectifier.
This scheme is capable of 5% voltage regulation or better.
An AVR may be added to bring the voltage regulation to about 2%.
In the event of failure of the AVR, you can operate with 5% regulation while waiting for parts.
Rectifiers and diodes: If you are designing, you can go over spec on these and add freewheeling diodes and surge suppressors. This will make failure very unlikely.
It's and old system, that has been overcome by advances in electronic AVRs.
An electronic AVR is so much cheaper than a constant voltage transformer and a CT.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bcavender]

SRGs are interesting from an efficiency (and other points). It’s a bit of a mind bender for me just getting on board. Pretty clever design. I found a vendor in Estonia with 5&10k units. Not bad looking.

http://kaskod.ee/products-services/switched-reluctance-generators/switched-reluctance-generators/

Still, the electronic complexity level leads me to think a design with minimal electronics is still the more long lived approach given vibration/heat/etc, but in an application where input energy/noise were drivers, I could see applying a Kaskod or equivalent.

This post is about a one off system design for a unique set of stiff/unusual requirements.

Though I have to say that having a 5kw Kaskod for my home standby could be attractive depending on price/shipping. I’m not a big fan of small one lung engines. I’d really prefer a slower 2 or 3 cylinder mover that was really lightly loaded for torque. Running on natgas really makes for a long lived unit.

As a funny aside, about an hour before Thanksgiving Dinner yesterday, commercial power choked three times and died right as everything was 3/4 cooked. My wife looked at me, the kids, grandkids & in-laws and said … “I hope you have a rabbit to pull out of your hat!”

LOL … I have a couple gensets, one special unit that I inherited from my Father that he bought for his house when I was just leaving high school. (45+ yr ago).

It’s a Honda single cyl that I converted to trifuel about 12 yr ago with a MeccAlte 2 pole, 7k head. Plugged her in an it hit on the second rollover on NG. Made me smile.

Dinner went off without a hitch and Momma smiled. My Dad did good!

 

[waross]

If you want a standby unit, consider one of these.
They often go for under $1000 at equipment auctions.
Try it out ahead of the auction and don't bid on one that won't start or has obvious problems.
The standard is 6 kW or 8kW with four, 1000 Watt lamps.
There are some 20 kW sets as well. The 20 kW set has the same four 1000 Watt lights but has extra capacity to power a small construction site.
For standby use, the saving in initial cost will pay for decades of diesel fuel. Residential standby doesn't run many hours per year.
I have a 6 kW set and a 20 kW set.
The plan for the 20 kW set is to mount the mast and lights permanently to provide light for night time horse riding.
The trailer will become a handy utility trailer.
The engine may be used to power an old fork-lift The fork-lift has value but the original engine is beyond salvage.
The 6 kW set is adequate for standby power and may provide added lighting.
The excitation is by capacitors. No AVR or electronics.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

The 6-8 kW sets typically use a three cylinder Kubota, the 20 kW sets use four cylinders.
Mine may sit for 6 months or a year and then start up well.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bcavender]

Great idea. The three cyl Kubota diesels are solid. Have one in a sub compact tractor. Had not thought about that avenue for picking up a standby machine.

Be interesting to see what price/quality could be found.

 

[waross]

Take a look here:
Ritchie Bros. Auctioneers
If you sign in, you can check selling prices at previous auctions.
Both my sets have over 15,000 hours and both start whenever I want.
With a 6 kW set you will have to curtail the use of heavy loads. (Don't try to run the electric clothes drier while cooking Christmas dinner. No A/C)
With a 20 kW set you should be able to run the whole house and a moderate amount of A/C.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bcavender]

Will check out Richie.

I’ve been testing an interesting power monitoring system made by Emporia and it’s been helpful. The system comes with two large current transformers for house mains and the ability to add 8 or 16 tiny CTs on individual breaker circuits. I got 8.

The system captures data at the one sec level and stores it for up to a week before it starts overwriting it.

It uploads the data to cloud storage via its WiFi and their phone app lets you see what’s happening when you are anywhere (and presumably anyone they can potentially sell the data to). Not a fan of that, but I’m just planning on capturing data for a generator study and then taking it out.

Found some interesting things. Our LG natgas stove has electric resistance heat in both ovens at 700w each. Wife’s Oreck vac went 2.2kw. Didn’t see those coming. Mains power max for us after AC season topped out at 4kw. Lower than I expected.

The unit is real new and there are some tweaks coming, but the in-app chat gets questions answered quickly and the data acquisition/web backend performed flawlessly.

I easily exported 7 days of one sec data and pulled the emailed CSV into Excel where I could crunch it to suit.

A 6kw system would run everything I need in winter (have a NG dryer). Summertime though needs a bigger genset as the compressor chugs along at 3kva with a 54a, 240v start surge.

It will be interesting to see if my bride feels the big kw upgrade will be seen as a necessity.