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'[EE] Stabilising an el cheapo IC driven alternator'
2005\12\08@014400 by Russell McMahon

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I can and will try this for myself but, as I need the result in 48
hours time I'll also ask here. Someone should have invented this wheel
already.

I have an exceedingly cheap and cheerful petrol motor powered
alternator rated at about 700 watts max. (Cost about $US65 new).

Voltage stability at constant load is "OK" but if you step-change the
load it surges extremely badly. Variation is enough for incandescent
bulbs to dim badly and/or get VERY bright for a second or so. I
measured the surges a while ago but don't recall the results - very
nasty is enough to know. Some loads don't mind this while others would
die.

I need to run a PA system and bass guitar amplifier for a concert 48
hours from now. Required wattage is liable to be under 100 watts.

I could:

1 - Pray

2 - Add a large swamping load first and try to ensure nobody step
changes the load.

3 - Add a manually multi step switched load and use this to phase in
and out real loads. Actually quite easy to do.

4 - Make an electronic stabiliser - eg smoothly winds in a large
resistive load, then step adds true load and matches it by dropping
off resistance and then slowly winds off most of the DC load. Could do
this only when load is added or removed at known points or leave some
resistor load in to allow auto action to handle step changes along the
way.

5 - Add a "spinner" - an unloaded motor which acts as a rotary
capacitor.

6.    Use a DC/AC converter - with a lead acid battery charged by the
alternator (if needed)

7- Some combination (especially 1 :-) ).

______

1.    On an 'as required' basis.
2.    Should be effective with vigilance.
3.    Is easyish and effectiveish.
4.    is not hard and arguably the best long term solution BUT there's
too much else to do unless it's essential to do it this way,.
5    I'm not sure how well this works on 1 phase due to the quasi
rotating field compared with 3 phase.
6    Cheating. Probably easiest at the power level concerned.

Thoughts ?


       Russell McMahon



2005\12\08@022049 by Marcel Birthelmer

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Maybe you could use your drummer as a decoupling capacitor.

- Marcel



Russell McMahon wrote:
{Quote hidden}

...

2005\12\08@022355 by Vasile Surducan

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If you'll pray, He will answer you the same as me:
- I can help you if you'll help yourself.

There is a cheap alternative you didn't mention it:
- use a feroresonant stabiliser after your mains generator. Is able to
stabilise from 180 to 240V (european style) at up to 5KW. You should
found such stabiliser on any second hand rubish store.

Vasile


On 12/8/05, Russell McMahon <spam_OUTapptechTakeThisOuTspamparadise.net.nz> wrote:
{Quote hidden}

> -

2005\12\08@033532 by Brent Brown

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Hi Russell,

Use a cheap UPS? May have better regulation (repeat, may). Your
generator, if it's the same one I'm thinking of, I think also has a 12VDC
output, use it to charge the battery in the UPS. 425VA UPS is around
US$67, or 660VA around US$76. Have thought of the same idea for keeping
my UPS/PC running during longer power outages.

Brent

{Quote hidden}

> --

2005\12\08@035619 by Enrico Schuerrer

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----- Original Message -----
From: "Russell McMahon" <.....apptechKILLspamspam@spam@paradise.net.nz>
To: "PIC List" <PICLISTspamKILLspamMIT.EDU>
Sent: Thursday, December 08, 2005 7:44 AM
Subject: [EE] Stabilising an el cheapo IC driven alternator ~~n


| I have an exceedingly cheap and cheerful petrol motor powered
| alternator rated at about 700 watts max. (Cost about $US65 new).

[different assumptions]
|

One of the easiest tasks to solve your problem quick is to give the
alternator more load - if you need 100 W give him 400W preload. If you
change the load then the difference is only small so the load regulations
are only small.

regards

Enrico

2005\12\08@042726 by Russell McMahon

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> Use a cheap UPS? May have better regulation (repeat, may). Your
> generator, if it's the same one I'm thinking of, I think also has a
> 12VDC
> output, use it to charge the battery in the UPS. 425VA UPS is around
> US$67, or 660VA around US$76. Have thought of the same idea for
> keeping
> my UPS/PC running during longer power outages.

Quite possibly the same.
GMC. Chinese. "2 HP" petrol motor.
750 W large lable but 550 W fine print avg and 750W peak.
12V output (nominally 14V) is rated at "less" - maybe 6A? from memory

A battery charger into a battery and an inverter (all of which I have)
would work, but is more annoying than I'd like to have to use.



       RM

2005\12\08@055002 by Michael Rigby-Jones

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{Quote hidden}

This sounds suspiciously like the generator set I posted about some time back, wrt to the unusual alternator configuration.  Is it a two stroke engine?  The one I was fixing had awfull frequency  changes with transient loads as well, but to be honest what can you expect from a mechanical governor in a $65 generator set?

If it's the same, the voltage regulation is so poor simply because there is no "active" regulation to speak of.  The field coil is driven from the high voltage output via a current limiting capacitor, and I suspect something like magnetic saturation is used as a crude regulator.  I did think a proper electronic regulator could probably be cobbled together given sufficient motivation (which I didn't have at the time).

Regards

Mike

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2005\12\08@055914 by Ling SM

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> I have an exceedingly cheap and cheerful petrol motor powered alternator
> rated at about 700 watts max. (Cost about $US65 new).
>
> Voltage stability at constant load is "OK" but if you step-change the
> load it surges extremely badly. Variation is enough for incandescent
> bulbs to dim badly and/or get VERY bright for a second or so. I measured
> the surges a while ago but don't recall the results - very nasty is
> enough to know. Some loads don't mind this while others would die.

Maybe this:

http://www.apc.com/products

Ling SM

2005\12\08@061141 by Russell McMahon

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> This sounds suspiciously like the generator set I posted about some
> time back, wrt to the unusual alternator configuration.  Is it a two
> stroke engine?  The one I was fixing had awfull frequency  changes
> with transient loads as well, but to be honest what can you expect
> from a mechanical governor in a $65 generator set?
>
> If it's the same, the voltage regulation is so poor simply because
> there is no "active" regulation to speak of.  The field coil is
> driven from the high voltage output via a current limiting
> capacitor, and I suspect something like magnetic saturation is used
> as a crude regulator.  I did think a proper electronic regulator
> could probably be cobbled together given sufficient motivation
> (which I didn't have at the time).

At the time I passed your comments & description on to a friend who is
highly experienced in such areas and he said that the system you
described is very common in lower cost units.

This was son the "some day" list when I received  acall today asking
me if i could provide a concert power source in 48 hours time. So a
short term fix is requirded. Said knowledgeable friend suggested 200
watts of lighting - essentially my solution 2 - but one would still
want to avoid step load changes.

I'll be having a look at this tomorrow (now today as it's 12:11am
here).


       RM


2005\12\08@062751 by Michael Rigby-Jones

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{Quote hidden}

Some kind of damping mechanism on the governor may help to prevent the 'hunting' you get on load changes.  I think the fact that a capacitor is used to drive the field coil means changes in RPM (and hence frequency) have a big impact on voltage.  I actualy have a crude generator test set that includes a frequency meter, voltage meter and a switchable load.  The frequency (and voltage) did vary quite widely from unloaded to fully loaded in the order of ~5-7Hz IIRC.

I just find it truly amazing that these things can be built and sold with some profit at $65, that the performance is somewhat lacking is really not surprising!

Regards

Mike

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2005\12\08@071207 by Russell McMahon

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> I just find it truly amazing that these things can be built and sold
> with some profit at $65, that the performance is somewhat lacking is
> really not surprising!

So do I. And I suspect that they may not be able to be. Getting
product into the world and providing traction for the growing /
stretching / learning giant may be more important than making ends
meet in a realistic manner. I strongly suspect that there is more than
just the 'invisible hand" at work here. And we are all cheerily
revelling in their largesse - something which we are certain to regret
in the next few decades. I have *nothing whatsoever* against the
Chinese people, and I can understand much of the behaviour of the
Chinese leadership, even though I often enough personally dislike what
they do, but "we" in the west (and elsewhere) (I very much included)
are bringing doom on ourselves as we buy our $US65 engine alternator
sets and bounteously cheap bags, pens, tools, paper, batteries, ....
without any great thought of where it will lead. It's going to be
interesting :-).




       RM




2005\12\08@080307 by olin piclist

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Russell McMahon wrote:
{Quote hidden}

How about the obvious #8: get a genset intended for the job.  You'll
probably pay for it in frustration, broken equipment, hassle time, and/or
add on equipment before you're done either way.

2005\12\08@084815 by Russell McMahon

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> How about the obvious #8: get a genset intended for the job.  You'll
> probably pay for it in frustration, broken equipment, hassle time,
> and/or
> add on equipment before you're done either way.

You seem to have overlooked the original "spec" :-).
It wasn't 'throw money at the requirement'.
It was 'are you able to meet this need within 48 hours from available
resources from a standing start while horrendously busy on all and
yon'.
Any fool can go out and spend enough money to buy a solution that
'just works'. It takes an engineer to dig in the shed and produce a
solution within available constraints. Or, I hope it does ;-). The
swamping load plus due care re load switching (2nd on my list after
"pray") seemed the most likely easy solution to work (and several
people have resuggested it, so maybe my #2 wasn't as clear as i
intended).

I actually bought the genset some months ago because 'I'd always
wanted one" and the price was such that it was worth seeing how good
it was. The answer was "Hmmm. OK, but needs work, I'll play with it
before we go on holiday in early January". Alas, someone else had
other ideas and it may be going to have to work 40 hours from now. I
imagine that 30 minutes or so playing sometime later today (2:37am
now) will produce a system that's good enough to *probably* not blow
up the amplifiers :-). We'll see.

Failing a straight resistive load, a resistive load with a sharply non
linear characteristic would be good. It would be easy enough to make a
controller with a few FETs (or even some )(gasp) Triacs (I've been
wondering what to do with the boxful I've got here for years :-) )
plus either incandescent lamps or heater elements (which I also have a
handful of). I can see the possibility of a Heath Robinson very quick
and exceedingly dirty dynamic load happening if the lamp lad alone
isn't good enough. There would also be a market for such if it was
cheap enough, as well it may be.

   Plug ($10 Chinese)(switchless) toaster oven into controller.
   Plug controller into alternator.
   Plug ...
   :-)

That plus #1 :-)

Nobody has commented on the suitability of a 1 phase motor to act as a
rotary electromechanical AC capacitor (such as works well on 3 phase
systems). I'll try that first as, if it worked, it would be an
exceedingly simple solution.



       RM





2005\12\08@090119 by Michael Rigby-Jones

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>-----Original Message-----
>From: KILLspampiclist-bouncesKILLspamspammit.edu [RemoveMEpiclist-bouncesTakeThisOuTspammit.edu]
>Sent: 08 December 2005 13:48
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Stabilising an el cheapo IC driven alternator ~~n
>
>
>Nobody has commented on the suitability of a 1 phase motor to act as a
>rotary electromechanical AC capacitor (such as works well on 3 phase
>systems). I'll try that first as, if it worked, it would be an
>exceedingly simple solution.

When the engine governor does it's underdamped response thing, I guess you could have some very heavy currents flowing, as the motor and generator move out of sync?

By the way, my cousin broke his by running a ~1kW toaster on it, which it managed for several weeks before the rectifiers (2x 1N5404 in parallel) in the end of the rotor went short circuit.

Regards

Mike

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2005\12\08@090247 by Vasile Surducan

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On 12/8/05, Brent Brown <spamBeGonebrent.brownspamBeGonespamclear.net.nz> wrote:
> Hi Russell,
>
> Use a cheap UPS?

Which has not a sinusoidal output but a DC one in the worst
circumstance and a square one in the best one.
I hope your power amplifier does not have transformers inside but
DC/DC converter...

cheers,
Vasile

May have better regulation (repeat, may). Your
{Quote hidden}

2005\12\08@090718 by Michael Rigby-Jones

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>-----Original Message-----
>From: TakeThisOuTpiclist-bouncesEraseMEspamspam_OUTmit.edu [RemoveMEpiclist-bouncesspamTakeThisOuTmit.edu]
>Sent: 08 December 2005 14:03
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Stabilising an el cheapo IC driven alternator ~~n
>
>
>On 12/8/05, Brent Brown <brent.brownEraseMEspam.....clear.net.nz> wrote:
>> Hi Russell,
>>
>> Use a cheap UPS?
>
>Which has not a sinusoidal output but a DC one in the worst
>circumstance and a square one in the best one. I hope your
>power amplifier does not have transformers inside but DC/DC
>converter...
>
>cheers,
>Vasile

Even the very cheapest one use the so called "modified sine" which is just a 3 level square wave.  However, they definately don't have any sigfificant DC component in the output.

Regards

Mike

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2005\12\08@090738 by Howard Winter

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Russell,

On Fri, 09 Dec 2005 02:48:18 +1300, Russell McMahon wrote:

> Nobody has commented on the suitability of a 1 phase motor to act as a
> rotary electromechanical AC capacitor (such as works well on 3 phase
> systems). I'll try that first as, if it worked, it would be an
> exceedingly simple solution.

I'd hate to think what would happen when the speed of the motor and the generator get out of step - I think
you need to try this with a 'scope on the resulting output and see what it looks like - it may be horrible,
and if you're powering amplifiers that may end up as noise on the output.

My favourite would be a decent UPS (APC Smart-UPS for example) which would smooth the voltage wanderings by
changing transformer taps, and step in and take over if they pass way outside the tolerances.  I don't know
about there, but over here you can pick up second-hand UPSs pretty cheap, especially if the battery is on the
way out (irrelevant in this case because you won't be calling on it for more than a few seconds at a time).

I have a Smart-UPS 700 that could be pressed into service, but for the 24h shipping cost from here to there
you could probably buy a decent 10kW generator that wouldn't notice the load you're giving it!  :-)

I don't suppose you know anyone with a Landrover (the old ones, not the car-style they make now) with a power
take-off to which you could connect the alternator you have?  A Landrover engine wouldn't notice the load and
you could set the throttle by hand... just a lateral thought!

Cheers,


Howard Winter
St.Albans, England


2005\12\08@090755 by Alan B. Pearce

face picon face
>Nobody has commented on the suitability of a 1 phase
>motor to act as a rotary electromechanical AC capacitor
>(such as works well on 3 phase systems). I'll try that
>first as, if it worked, it would be an exceedingly
>simple solution.

That would probably need a reasonable rotating mass to soak up/deliver power
as the load varied.

another possibility you may wish to look at is to use a large isolating
transformer such as used with power tools when they are outside. I do
remember using 5KVA ones as filter transformers on the original Memorex
25/75MB winchester disk drives in various industrial areas of Auckland.
Worked very well for removing spikes and other nasties that upset the
electronics.

2005\12\08@091846 by Howard Winter

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Russell,

Another thought:  You may want to try a "surge strip" in
the mix, to provide some protection against overvoltage.  
The only problem is that it may blow its protection
device the first time a serious excursion happens - but
better that than the amplifiers!

Cheers,


Howard Winter
St.Albans, England


2005\12\08@113732 by Dwayne Reid

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At 12:23 AM 12/8/2005, Vasile Surducan wrote:
>If you'll pray, He will answer you the same as me:
>- I can help you if you'll help yourself.
>
>There is a cheap alternative you didn't mention it:
>- use a feroresonant stabiliser after your mains generator. Is able to
>stabilise from 180 to 240V (european style) at up to 5KW. You should
>found such stabiliser on any second hand rubish store.

I was going to suggest exactly the same thing until I read the
message about the poor frequency stability.  Those ferroresonant
stabilizers do not work properly away from the resonant frequency.

I think the cheap UPS is by far the best solution, especially if it
can be operated from the nominal 12Vdc output of the alternator.

Or: dig into a discarded UPS or battery-to-AC-mains invertor and rip
out the dc-dc convertor portion.  Then take the raw high voltage from
the alternator (I was going to say: 120Vac 'til I remembered that
Russell probably lives in 230 Vac country), rectify and filter it,
then use that to power the output bridge of the UPS.

We can purchase cheapie 300VA inverters here (Canada) for about $30
on sale at the local Canadian Tire store.  Regular (not sale price)
is about double that.  The inverter section is somewhat marginal if
operated at full output for an extended period of time but the output
bridge section seems to be robust.

dwayne

--
Dwayne Reid   <EraseMEdwaynerspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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2005\12\08@121330 by Rolf

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I thought the obvious #9 would be....

Rent a quality / capable power source for the occasion. This type of
once-off situation is the perfect "rent it" one.

Rolf

Olin Lathrop wrote:
{Quote hidden}

2005\12\08@122140 by Bob J

picon face
Let me ask you a silly question:  do you have a battery connected to the
output of the alternator?  The battery will act as a large capacitor, as it
does in an automobile.

Regards,
Bob

On 12/8/05, Russell McMahon <RemoveMEapptechEraseMEspamEraseMEparadise.net.nz> wrote:

>
> Voltage stability at constant load is "OK" but if you step-change the
> load it surges extremely badly. Variation is enough for incandescent
> bulbs to dim badly and/or get VERY bright for a second or so. I
> measured the surges a while ago but don't recall the results - very
> nasty is enough to know. Some loads don't mind this while others would
> die.
>

2005\12\08@125113 by James Newtons Massmind

face picon face
> I have an exceedingly cheap and cheerful petrol motor powered
> alternator rated at about 700 watts max. (Cost about $US65 new).
>
> Voltage stability at constant load is "OK" but if you
> step-change the load it surges extremely badly.

The old school solution is a Big flywheel.

---
James.




2005\12\08@134603 by olin piclist

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James Newtons Massmind wrote:
> The old school solution is a Big flywheel.

If I understand Russell correctly, this will only solve part of the problem.
Apparently there is a control loop adjusting the generator field current,
and this has large overshoots to step inputs.  If so, this would still be a
problem even with a perfectly fixed shaft speed.

2005\12\08@143153 by Russell McMahon

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>> I have an exceedingly cheap and cheerful petrol motor powered
>> alternator rated at about 700 watts max. (Cost about $US65 new).

> The old school solution is a Big flywheel.

Mechanically that's not an option due to the tightly integrated nature
of the design, Electrically, that's what the unloaded motor used as a
"spinner" does in the 3 phase version of this - it provides an
electromechanical capacitor which transfers power to / /from the
rotating motor inertia. Single phase version is liable to be less
suitable.

The "rent / borrow / steal one" option was not mentioned as I was
looking at how to use the one I had BUT we have a larger unit reserved
at the local hire outlet. Cost for half day rental would be not vast -
about the same as the cost of my unit :-) - but much less work for me
of course. But there's also no certainty that it would perform well
enough - although it's far more likely to.


       RM

2005\12\08@143626 by Russell McMahon

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Appended is a different solution to most being offered. Similar to the
UPS / inverter / charger suggestions but potentially more
sophisticated. And I 'just happen' to own one (two actually). Doh!

The newer one is capable of vector drive (unneeded here) and rated at
about 1 kW. I'm not sure how easily it can be setup to  start
instantaneously into load etc as I usually use it to ramp up a motor
in a dynamometer I use for exercise machine alternator testing. But a
quick skim of the manual should tell me).

Mine is actually 1 phase in, 3 phase out, and it may not like the
absolute phase imbalance. May be more hassle than it's worth to
investigate. We'll see. Rental still looking good ;-). (Optimum
engineering solution - more or less in line with Olin's suggestion
:-) ).




       RM

________________________________

Ken said:


Russell,

...

Another alternative would be a lowish-power single-phase in/out
variable
speed motor drive.  This is essentially what the newer "inverter mode"
portable generators use to achieve voltage stabilisation and true
sinewave
output.  You'd need to be happy that the alternator couldn't produce
enough
volts to pop the DC input stage.

2005\12\08@171945 by Peter

picon face

On Fri, 9 Dec 2005, Russell McMahon wrote:

> Nobody has commented on the suitability of a 1 phase motor to act as a rotary
> electromechanical AC capacitor (such as works well on 3 phase systems). I'll
> try that first as, if it worked, it would be an exceedingly simple solution.

Would it have to be a capacitor shunt motor ? Is there a 'dead zone' in
the rpm range of a squirrel cage motor between motor and generator
regimes ?

Peter

2005\12\08@172447 by Peter

picon face

On Thu, 8 Dec 2005, Vasile Surducan wrote:

> On 12/8/05, Brent Brown <RemoveMEbrent.brownspam_OUTspamKILLspamclear.net.nz> wrote:
>> Hi Russell,
>>
>> Use a cheap UPS?
>
> Which has not a sinusoidal output but a DC one in the worst
> circumstance and a square one in the best one.

Any cheap UPS will make something that resembles a sine wave to within
20% or better.

Peter

2005\12\09@055337 by Russell McMahon

face
flavicon
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Alternator output is 230 VAC.
There is a 14VDC output too but of limited capacity.

/ Let me ask you a silly question:  do you have a battery connected to
the
output of the alternator?  The battery will act as a large capacitor,
as it
does in an automobile.

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