Author Topic: Put rectifier on tower or at batteries - impact on braking?  (Read 776 times)

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Grant MacLeod

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Hello everyone


This is my first posting on this forum.  I just bought 2 of Hugh Piggott's books including the Axial Flux windmill plans.  I took a day long workshop on solar and wind power recently.  It's just a hobby for me although my ultimate goal is to build a wind turbine capable of powering my well pump (via batteries and 220 VAC inverter) and a sump pump.  After Hurricane Juan a few years ago we lost power for 6 days.  Not having the well was the worst part.  Maybe I might play wioth something smaller first.


I've read the discussion in HP's book and elsewhere about the design decision on whether or not to put your rectifier on the tower or at your batteries.  The only compelling reason to put it near the batteries seems to be to allow the windmill to be braked by shorting the coil outputs.  Plus some maintenance advantages.  Any comments?


My question.  Is it possible to brake a windmill even if you bring DC down the tower.  I've seen some reference to it in HP's book but it was a little unclear to me.  I think I read you can short the DC output as long as you disconnect the batteries first and this will slow the windmill but I'm hoping for some clarification on this.  


Thanks

Grant MacLeod

Nova Scotia, Canada

« Last Edit: June 08, 2006, 08:11:00 PM by (unknown) »

Slingshot

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Put rectifier on tower or at batteries?
« Reply #1 on: June 08, 2006, 02:26:46 PM »
When you short beyond the diodes, the braking effect would be slightly diminished because instead of a short you now have a short in series with the rectifiers.  This effect would be insignificant for a high-voltage windmill, possibly so for a 12-volt as well.


An additional consideration would be whether the diodes might be damaged by the short-circuit surge current that will flow instantaneously before the windmill stops.

« Last Edit: June 08, 2006, 02:26:46 PM by Slingshot »

Flux

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Re: Put rectifier on tower or at batteries?
« Reply #2 on: June 08, 2006, 02:59:46 PM »
If you brake after the rectifier you must make sure you don't put a short across the battery.


Some machines use a change over switch but this leaves the mill open circuit during the change over. It should not be a problem but it does make life more difficult for the switch and dc switches are expensive .


Hugh suggests that you use a blocking diode in the battery line to prevent the battery feeding back into the switch. by using a double pole switch you can short the diode out in normal use to avoid the volt drop and it is only inserted as the switch changes over. This seems a better idea and is probably what you refer to.


You should be able to follow the diagram if you bear this in mind, the diode is in series with the line and you can short the mill side of the diode without shorting the battery as the diode blocks the current. One pole of the switch does the short for braking and the other pole shorts the diode in normal use.


If you brake on the ac side before your rectifier you need a 2 pole switch to short all 3 ac leads.

flux

« Last Edit: June 08, 2006, 02:59:46 PM by Flux »

Grant MacLeod

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Re: Put rectifier on tower or at batteries?
« Reply #3 on: June 09, 2006, 01:39:04 PM »
These responses definately connect the dots for me.


Thanks very much!

Grant MacLeod

« Last Edit: June 09, 2006, 01:39:04 PM by Grant MacLeod »