Power factor - getting full power from a generator and maximizing efficiency

[Doug]

This Forum needs a technical archive area so these discussions can be shortened up.

COnstantly the same things are brought back up because the information is hard to find.

[Ian]

Thanks for all the replies guys.

My take, then, is that my setup is not perfect but as long as things stay within the expected behaviour patterns and the kit stays reasonably cool, there is little to worry about.  Similarly, whilst something could be done to improve the setup, knowing exactly what to do is not simple so it is best left alone.

Regards and once again thanks for the help,
Ian

[mobile_bob]

i would highly recommend a book that covers the subject

written by this fellow down south, an electrical engineer that works for a utility company

not only does the book cover listeroid power production, but has a really good section on
powerfactor and another section on power factor correction for the average guy.

if you get his book and read it, you will have a working knowlege of all sorts of electrical concerns
including power factor, know how to measure it, and how to correct or improve it.

i would argue that simply ignoreing power factor is the wrong approach in a small system such as
is typical with a listeroid/st genset.

if one is going to all the trouble to set one up, why not optimize the system?
you might be lucky and find your powerfactor is already very good, on the other hand
you might find it to be very low and in need of improvment.

i drug my killawatt meter all over the place just for kicks, for instance my bench grinder has a pf of around .28
while running with no load and only about .35 when i am grinding,,, thats horrible! my drill press is only marginally better
and my refrigerator is around .78 or so and needing improvement, some of my compact floresent bulbs are terrible
as are some of my old computer power supplies (newer supplies are pf corrected by law)

go to utterpower.com and look for Bill Rogers book.

the best book on this subject i have ever found, mainly because it is written in such a manner
that one can understand the principles and understand how to apply them when it comes to correction.
most books on the subject are written by EE for EE or EE students using high dollar test equipment
and difficult to understand procedures generally outside the abilities of the average diy'er to understand and impliment
even if he were to buy the expensive equipment to test with and use one time.

Bill covers other neat stuff like induction generators, parallel operation and other topics commonly discussed here in his
book.

Reportedly he is working on a second book, one i am eagerly awaiting 

bob g

[Doug]

I should write book.

Good way to use some of my slack time!

" The Hitch Hikers guide to home Generation ".....
" Riding the little Bus, a guide to creating your own home electrical utiliy ".....
" Electrons for Dummies ".....

In no way am I making light of Bill Rogers or his books. Just making funny

Doug

[mobile_bob]

go for it Doug!

we need more current books being written on this and other topics that use
the currently available stuff

the 70's was an age when 100's of books were written, and alot has changed since then

we don't have to settle with car batteries, delco generators driven by B&S, and WW2 military surplus
rotary inverters today.

bob g

[compig]

This Forum needs a technical archive area so these discussions can be shortened up.

COnstantly the same things are brought back up because the information is hard to find.

http://listerengine.com/smf/index.php?topic=4745.0

[Doug]

But I love rotory inverters Bob.....

Dead simple and can be rebuilt again and again....

[mobile_bob]

i love the rotary inverters too, i have one i traded a 800 watt coleman pos for
the guy didn't want to listen to the whir, and i was only to happy to relieve him of that problem

it is one of the rediline 1500watt jobs, and i think it can surge 4kwatts!

not the most efficient inverter on the market today, but with autostart it draws zero power when asleep
and is all but bullet proof.  the ~60% efficiency is a big turnoff for most folks, but thats the tradeoff
high efficiency sometimes can be delicate, relatively speaking and lower efficiency sometimes can be beat on
and put away wet and just keep on working.

for short duration, hard to start loads, it is hard to beat

i wish i had a 24volt version that was rated at 3kwatts continous or above
now that would kick ass

i had considered at one time useing a dpdt relay/contactor so that the rotary inverter could start the difficult load
and once started the relay could then be tripped to switch over to a smaller high efficiency electronic inverter.

a 400 watt pure sine wave inverter will run a refrigerator but it cannot start one, the rotary would have no problem
yanking a fridge to life and then drop out and switch over to the 400 watt unit.

best of both worlds in my opinion.

taking it further, one rotary could do the starting duty for several smaller high efficiency inverters dedicated to specific loads.

that would be useful and pretty cool because then you could match the smaller inverters to the specific load and get them running
at their peak efficiency.

overall it would be a redundant system, robust, more efficient and cheaper than a single large pure sine wave inverter.

i haven't seen anyone assemble such a system, but would be interested to hear of someone that has.

bob g

[Doug]

They get significantly more efficient as they get larger Bob. And the higher input DC versions also are an improvement but your not going to find a large one kicking around.

Persoanly I would love to try and make one  If I could find a lage DC compound motor, but it wourl require some machining and serious rework to build.

I have thought about and maybe someday will even do it.....

Doug

[jzeeff]

I built a mini automatic transfer switch with a relay and some 120VAC plugs.    It allows me auto switch between two sources and should work for starting a motor and then switching to something else (just unplug the primary and it switches to backup).  It does allow a PC to move from generator to mains power without a glitch.

If I built another one, I might use solidstate relays.

I haven't been able to find any sources for a high current .2H inductor to build a passive harmonic power factor corrector.  I'll probably use nothing or my Sola Ferroresonant power conditioner and live with the 140 watt (out of 1000 max) fixed overhead it has.

[mobile_bob]

Doug:

one of those old lincoln torpedo welders are a motor/generator
certainly large enough to use as a platform for a large  rotary inverter.

would be interesting to see someone build one.

bob g

[Doug]

Hmm I never thought of that but your right Bob I think that would work.

[Chris R]

Let's see if we can put some new life into this post. It's an old post but a good one.
I had some questions about power factor and did a search and came up with these postings. After reading them I have even more questions.

My only question right now and to keep it as simple as possible is this:
My Lister VA has a Lima Mac internally regulated genhead that I think is 5KW with a power factor of 1.
I am just putting into service an ST1 (about 8 hp)  with a Lima/Marathon AVR unit I don't know the KW rating on the gen but I think it is 6kw. It has a power factor of 0.8
I am in the process of rebuilding my Lister LPW3 with a Stamford genhead of about 13 KW with a power factor of 0.8

House loads are outback inverter with the gen in load set at 20amps (I think)
Compact floresent light bulbs. Washer, gas dryer, sunfrost refridgerator, 1/4 pressure pump. 12,000 BTU mini split A/C. The lister VA will handle the loads without too much problems. Just don't go hodwild.
So I do not have many resistive loads. I don't know if the inverter is resistive or an inductive load.

So my question is, If I had a choice, am I better of with a genhead with a PF of 1.0 or 0.8?
My gut say with a PF of 0.8???
Any takers

[Thob]

The answer to your question can found in the book the mobile_bob mentions above.

"The Home Power Producer's Guide To Electrical Reality"
By Bill Rogers

Available from George at Utterpower:

www.utterpower.com

The book contains a lot more useful information as well, and it is available again.  I just bought myself a copy, along with the utterpower CD.

[mobile_bob]

if everything else is equal, a generator with a pf of 0.8 will be a better unit for mixed loads
than one with a pf of 1.0

there are a few notes that need to be made

when a generator is rated at a certain pf, it is rated to provide a certain amount of power without undue heating, or undue voltage drop, and maybe a couple of other factors like distortion or exceeding field current etc.

there will be examples where another genhead might do better even though technically by spec it shouldn't, however if you measure everything you will generally find it is running hotter than spec, or the voltage is drooping under spec, field current it running higher or the distortion is getting over spec's, or something else.

so what does this come down to ?

for example  

given two genheads, genhead A rated at 6kwatts at pf 1.0 vs. genhead B rated at 6kwatts at pf 0.8   my money would be on genhead B.

the reason being genhead B can deliver all of its rated 6 kwatts into a mixed load with a pf of at least 0.8, while genhead A cannot deliver its full rated 6kwatts into the same load

usually we find that generators that are rated at pf of unity or 1.0 are meant to power resistive loads and are referred to as light plants...   if they are not referred to as light plants it is left to the user to understand that the unit will not deliver full output into a mixed load.

even if the unit appears to be able to drive a mixed load up to the nameplate rating, the unit will likely overheat and die a premature death.

probably ran around the block on this one, power factor and its correction has been a topic that i have long had a real interest in.  this topic is very hard to get good answers on, and often you can get all sorts of answers even from EE on this topic.

my favorite answer is "why do you care, you aren't charged for poor power factor by the power company?"   usually i get a big blank stare or silence when my response is "but i am the power company dammit"

for a better explanation on the topic of power factor and power factor correction, written by an EE with years of experience working for a utility company and also an avid DIY'er, that is presented in such a manner that most normal people can understand it, i would suggest Bill Rogers book.. it can be found at Utterpower.com   the book was out of stock for some time, but my understanding is it is back in stock.

i cannot over promote this book!

it is my opinion that any serious diy'er should avail himself of information on power factor, he ought to get a firm grip on the concept and understand what exactly it is and how to correct it as needed.

because we as diy'ers don't generally overbuild their gensets to the point that they have tons of excess capacity, for a plethora of reasons that most know all too well. Because we build gensets that are generally a bit smaller than we would like, means we need to manage our loads. a significant part of management is power factor!

why build a genset that is for instance 10 kwatts with a pf of 1.0 and find we cannot power much more than 8kwatts of load without overheating the generator or having too large a voltage drop?  why do this when we could educate ourselves on power factor and its correction and get better utilization of the 10 kwatt rating?  getting to a pf of .95 will allow the same genset to deliver 9500watts without overheating or badly drooping voltage.

i could go on, this is afterall a favorite topic with me  

hopefully this will help

bob g