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Forum Index : Windmills : Best Config for a 6.5hp Petrol Backup

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JamieN

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Joined: 28/04/2009
Location: New Zealand
Posts: 5

Posted: 08:25am 28 Apr 2009

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Hi All

I have brought a petrol motor with a starter motor and i wish to use this for backup purposes

I have a 2 100s ,80s and a 60s

Which stator and config will be best for this.

Thanks

Jamie
Auckland NZ

greendreamin
Newbie

Joined: 02/02/2008
Location: Australia
Posts: 20

Posted: 01:50pm 29 Apr 2009

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hi there
dont know what others will suggest but for simplicity belt it up to a bosch
alternator, like the ones off the 90s v6 (the regulator had a EFI style plug on
it) commodore then connect the sense wire to the batt positive via a variable
resistor or a diode and you can dial up the voltage you want, presto made
for high speeds, and save your f&ps for the wind
Stu

JamieN

Newbie

Joined: 28/04/2009
Location: New Zealand
Posts: 5

Posted: 07:57am 18 May 2009

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This will work but cost is an issue.

I have 2x100s 2x80s and a 60s (well i am wiring 2 80s to 7p).

So I want to use these for my backup but Im not sure what configuration is needed.

My engine lowest revs is 3600rpm.

Thanks

sPuDd

Senior Member

Joined: 10/07/2007
Location: Australia
Posts: 251

Posted: 10:23am 18 May 2009

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JamieN,
why won't the unit go below 3600rpm?
Can you not tinker with the carbie?
Variable rpm would be nice. You could have a micro controller take care of the entire charging and engine system. Failing that you will have to gear it down with belts or whatever.

sPuDd..
Edited by sPuDd 2009-05-19

It should work ...in theory

Robb
Senior Member

Joined: 01/08/2007
Location: Australia
Posts: 221

Posted: 07:06am 19 May 2009

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The costs of the gearing equipment required will be greater than an automotive alternator from a car wreckers. Add to that losses and the need to regulate the output.

If you rev your F&P up to that speed it will self destruct.

Automotive alternators work from 1000 to 10,000+ RPM so a direct drive would be possible. If you get one with an in built regulator it should be included in the price.

I would say that engine probably has a top governed RPM close to 3600 RPM rather than that being the minimum speed.

windlight
Guru

Joined: 03/03/2007
Location: Australia
Posts: 331

Posted: 11:54am 19 May 2009

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Looks like the classic Chinese copy of a Honda, sold with many different paper stickers and manes.

Which ever way you go remember using a F&P with the engine will not have the cooling advantage of one up in the air.

Personally I use a Bosh alternator, there is doing it on the cheep and doing it.

allan

"I like this place and willingly could waste my time in it" - (Act II, Scene IV).

JamieN

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Joined: 28/04/2009
Location: New Zealand
Posts: 5

Posted: 10:55pm 21 May 2009

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Thanks Guys

Am I able to hook 2 12v alternators in series ?
or should I find a truck one ?

windlight
Guru

Joined: 03/03/2007
Location: Australia
Posts: 331

Posted: 12:13am 22 May 2009

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You could use 2 X 12V alternators but, there is always a but, as the frame of an auto alternator is negative the second alternator has to be insulated from it's mounting as in that case it is 12+ volts, not easy on a vibrating engine.

Just obtain a 24v unit, but, then you will need to adjust the regulator to adequately charge the batteries above 28V.

In my case I have a universal Bosh alternator with inbuilt regulator looks like a to3 package, I eased it out, interrupted (put insulation tape between the press fit connections) the voltage sensing, connected two wires to the outside and place a string of 3A diodes in series. Each diode raises the output voltage by 0.6V because the sensed voltage is dropped by that amount.

allan

"I like this place and willingly could waste my time in it" - (Act II, Scene IV).

oztules

Guru

Joined: 26/07/2007
Location: Australia
Posts: 1686

Posted: 08:32am 22 May 2009

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Alternators are wonderfully simple devices. The auto elec will tell you how complex they are and how smart you have to be to work on them.

It turns out the opposite is true.

The bits we are interested in is the rotor and the stator and the diode bridge... the rest can be tossed out for RE purposes.

There is nothing tricky with these parts.

Think of it like a windmill alternator. The faster you spin it, the more voltage you get (for a given rotor field). It's that simple, and the same physics applies, and the same electrical laws.

In fact, you will get a lot more power out of a 12v alternator running at 24v than a 24v alternator... why?

Well, just like windmill alternators, the resistance is the killer. If the stator basket of a 24v alternator has twice the turns of a 12v alternator in the same space, it will likely carry a whole lot less current for the same losses as a 12v coil basket. In fact even if there were space to wind twice the turns of the same thickness wire, we would end up with twice the resistance.....

So If it were me, I'd get the nearest available 12v alternator, rip out the regulator, gear it up to the motor, and get ready to test.

In this application, a normal regulator style 24v alternator would still not be ideal, as when the battery SOC is low, it would stall your little motor... ie it would supply the rotor with the max current to get the battery back up to 28v.... with a car/truck motor this is no problem, also in a truck it will be very short duration.... truck batteries are not that depleted after a start. Normally a minute or two is the most that max power will be transferred to the batteries, after that it tapers off. (even my D6 caterpillar only uses 20-30A for a minute or so, then winds back)

What is usually done in this application, is to use a rheostat (big wire wound volume control) or even a few tail lamps in series with the rotor, to control the current to the rotor field. This allows you to dial up the current that your motor can supply without lugging... it's that simple.

It should cost nothing to do but for the brackets you need to fashion to hold the alt, the rheostat or tail lamps, the pulleys.... and of course an old alternator... probably free.

Your motor looks like a copy of the Honda GX160.. around 5hp?? 3600 rpm will be near where your maximum efficiency will be... so adjust your lamps or rheostat for this rpm for the amps you want... You may need to fiddle with the pulley sizes to get the best transfer.

Now this is not a set and forget system, you will have to use a dump load controller or similar to shut down the motor at your desired cut off voltage. You can build your own controller (I posted one on fieldlines somewhere a few years ago), or you can give her a few hrs charge when you think it needs it.

For fully automatic, it will require a voltage controller (like above), and some form of current limiting to the rotor to stop it o/loading the motor at low battery voltage....(the regulator will try to go for broke at first, lugging your motor).

The other problem with a normal regulator, is that it will waste motor time and fuel as it approaches the end of bulk charging, and waste more and more as SOC increases to full.

You are using this to recharge a 24v RE battery bank aren't you?

..........oztules

Edited by oztules 2009-05-23

Village idiot...or... just another hack out of his depth

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