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Author Topic: Paralleling two generators?  (Read 9662 times)
northern installer
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« Reply #15 on: December 23, 2008, 06:44:24 PM »

Guy ,justme's suggestion of diodes would surely sort the problem on a dc setup? was this with dynamos,or rectified alternators? what type of winding?
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billi
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« Reply #16 on: December 23, 2008, 07:07:57 PM »

One day i will understand  Tongue  ...... why not just charge a battery  and invert  and export rest

Or export all and use whats needed


 bike


In my next live i am DC 

billi

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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
guydewdney
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« Reply #17 on: December 23, 2008, 07:47:44 PM »

Justme

when one is making more power than the other - how would that go 'back' through a bridge rectifier? In my first setup, it was:-

gen---Bridge rec---I
                           -------------inverter.
gen---Bridge rec---I

but this caused one to overheat.

so its now
gen---BR---inverter
gen---BR---inverter

The idea being, that the inverter has, internally, two separate DC to AC converters. The software refuses, in 'wind' mode to allow different voltages, within a small allowance, of the input to input 1 and 2. This works better.

I need to add MORE generators to absorb the power of the wheel. I could use another inverter (1,500), and two more BR's (600)..... or I could try a method of paralleling them up, and thus ending up with all the power I need, and minimal expense.

As for toothed belts - the list price of the big pulley nearest the camera is over 1000... (I didnt pay that  Lips Sealed ) - the equivalent 55mm wide, (enough for ONE or maybe two generator heads), similar size toothed belt pulley is 600 quid. Plus they need to be very accurately aligned- V belts need to be within 5mm axially, and 0.5 degrees (iirc)  - which is easy to do with a welder and a hammer.

Billi - Im not doing batteries - I dont want the expense or hassle, or piles of acid in boxes venting hydrogen gas, thank you Wink

NI - they are three phase alternators, currently wired in Star or Wye, but I am capable of wiring them in Delta. I chose Star, as its higher voltage, therefore lower current, therefore possibly lower heat losses.


* two gennys.jpg (60.1 KB, 640x480 - viewed 496 times.)
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northern installer
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« Reply #18 on: December 23, 2008, 09:53:44 PM »

Guy,have you checked the terminal voltage of each generator? and the end resistences of the bridge rectifiers?you should be able to parallel them into a battery,but I am not sure about how the dual inputs to the inverter will vary with load,but if one gen is producing more volts than its brother it will pass more amps,and run hotter;I would suggest putting the load of each ,separately into a known resistence,then checking the amps and volts at both ends of the bridge rectifier.It is unlikely that generators of the same design will put out exactly the same power,if this is so,it will come back to haunt you however you connect them.Never mind,its christmas=lots of tinkering time(sorry,cant go to Auntie Flos,got to get this generator working!) Nil desperandum mate!
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guydewdney
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« Reply #19 on: December 23, 2008, 11:17:19 PM »

Batteries are a non starter - these things generate hundreds of volts - they are currently making 350ish volts AC (wild). I dont fancy pluggin in a 500w resistor and measuring it with a 2.99 multimeter from maplin... Wink


The bridge rectifiers are - as I said - not just rectifiers - they are also load controllers etc - they are both 'identical' and should be the same.

I spoke, at length, to the manufacturer of the inverter (in the states). His suggestion was to add in a 1 ohm resistor on the 'hot' generator. This is a bit pointless - as the hot genny is just the one with the slightly tighter belt (which then heats up, slackens, and becomes the 'cool' genny). He then said - just connect the together (on the DC side)

small confession - When I first did this - I used pure, unadulterated, bridge rectifiers. No dump load controller (no dump load at all  Shocked ) - and this is when I noted the hot / not hot problem. The new 'wind interfaces' are much much more complex - and also have some dirty great big capacitors in them - plus some random electronics (that they cant / wont tell em what it does Roll Eyes ) I have NOT tried connecting the wind interfaces together at the DC side.


Ideally - I need a small pile of 1kw+ inverters, with their own wind interfaces, all with programmable power curves (it turns out that water wheel need an almost vertical curve - or you get oscillations). But I suspect the payback period would be a little excessive...
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johnrae
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« Reply #20 on: December 24, 2008, 02:41:09 PM »

Guy,
Considering the extra money you're looking at for another pair of "small" generators and bridge controllers it may be more economical to cut your losses, replace the two small generators and bridges you already have, and buy one generator capable of doing the full power capability of your system.

I'm sure you could get a single generator and suitable rectifier for less than the price of what you'll be incurring.  Bear in mind that a generator will absorb mechanical power from your prime mover the amount of power absorbed by your electrical load (plus efficiency/conversion losses)

Add to that the elimination of the technical problems of trying to do the "impossible".

If you wish to remain with belt drives then you should give serious consideration to sorting out the problems of slip and stretching that you report.  A decent generator running at 1500 or 3000RPM should be fairly easy to pick up. 

Your photo doesn't show the water wheel.  What exactly is your set-uo. The large wheel shaft runs at ?? RPM and the generators appear to run at about 5 times that speed.  Note also that one unit runs in reverse to the other- hence my previous cautions about phase directions.

I'm all for having a go at trying things but there does come a point when there's a need to stand back and re-evaluate the situation.

Happy Christmas
Jack
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guydewdney
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« Reply #21 on: December 26, 2008, 08:07:46 PM »

Hi Jack,

back from a long discussion with my brother at xmas, where he pretty much said the same.

Now - as I dont care what frequency the leccy is generated at (30 to 3000hz...) I am currently looking at a BIG ST style brushed genny, running at the 300ish rpm. Now - if I remove the AVR, and manually introduce a field voltage (fixed) so that I generate significant voltage at 300ish rpm, I should just de-rate the genny from (say) 15kw@1500rpm to 3kw@300rpm.... i assume....
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Justme
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« Reply #22 on: December 26, 2008, 09:23:15 PM »

If 1500 rpm is 50 htz then 300rpm could be about 10htz



Justme
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knighty
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« Reply #23 on: February 23, 2009, 09:31:40 PM »

would it not be easier to try and up the RPM to the right speed for the motor/generator ?

300 to 1500rpm sounds like a lot.. but it's not really that much... and if your belts/chains are lined up correctly they'll be very efficient...

if you know the max output of the waterwheel is 10kw, buy a 15/20kw gnenerator.... that way you only need 1 generator no matter the flow... the generator will be powerful enough to break the wheel and stop it over reving in times of high flow ?

(of your belt/chain drive was setup so the waterwheel would always be braked then you would always have the max output... say if the waterwheel has a min speed of 30rpm use the belts and chains to go from 28 to 1500rpm?

I've got an (old) machine at work that drops motor revs from 1400rpm to ~200rpm... using old belts and chains... not sure of the drop down at each stage but it goes from 4 belts to 3 belts to 1 chain to a twin chain.... works great, and would last forever if you over sized it a bit ?
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guydewdney
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« Reply #24 on: February 23, 2009, 10:35:43 PM »

Im now about to use this:-
Chain from wheel 3 -> 30 rpm
6 x V belts 30 rpm ->  100 rpm
Gearbox from 100 to 900rpm

Huge gert big 50Hp (37Kw) DC electric motor used as a genny.
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knighty
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« Reply #25 on: February 23, 2009, 11:05:11 PM »

sounds like a plan to me....

do you have the motor yet ? that thing will be a pita to move !  we have a 50hp motor at work (3 phase) and it's bloody massive - it used to pop 60amp fuese (all 3 of them) like they were fire crackers !
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guydewdney
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« Reply #26 on: February 23, 2009, 11:08:03 PM »

yup - about half a ton. Ratchets are useful.
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