Author Topic: Solar and Wind shunt controllers - dump load position?  (Read 7216 times)

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(unknown)

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Solar and Wind shunt controllers - dump load position?
« on: February 03, 2009, 02:13:46 PM »
Hi there.


I have a question regarding a dump load controller which can be used for both wind and solar systems. The controller measures the voltage of the battery and then uses MOSFETS to switch the negative side of the dump load. Because it is designed for use for either wind or solar systems, a Schottky blocking diode is included to prevent solar panels from draining the battery.


See diagram below:


http://i102.photobucket.com/albums/m103/beninstp/Connectiondiagramalternatives.jpg


My questions are:



  1. What is the best position for the positive dump load when using a solar panel, before the blocking diode (position 1) or after the blocking diode (position 2) and why?
  2. What is the best position when using a wind turbine and why?


Many thanks in advance.


Ben

« Last Edit: February 03, 2009, 02:13:46 PM by (unknown) »

ghurd

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Re: Solar and Wind shunt - dump load position?
« Reply #1 on: February 03, 2009, 07:54:01 AM »
Where did you find that circuit?


No need for a "load" on solar.  The fets simply need to be able to handle the PVs Isc.  Replace the load with a wire and connect in pos #1.


It needs to be a load larger than the windmill can supply for wind.  Connected in pos #2.


Parallel fets is asking for problems.  Easier to parallel individual fets and loads.


The wires for the voltage sensor must go all the way to the battery terminals, all by themselves.


G-

« Last Edit: February 03, 2009, 07:54:01 AM by (unknown) »
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(unknown)

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Re: Solar and Wind shunt - dump load position?
« Reply #2 on: February 03, 2009, 09:31:46 AM »
Many thanks, Ghurd. The circuit is a simplified representation of the Oatley K220A shunt regulator which I have bought. Info on the controller can be found at:


http://secure.oatleyelectronics.com//product_info.php?products_id=718&osCsid=c093e1e7cc951790048
425c9219b5fec


Scanned copy of schematic in the instructions:


http://i102.photobucket.com/albums/m103/beninstp/Circuitdiagram-1.jpg



  1. I can understand why you recommend attaching a solar panel at position 1 and just having a wire. This way, the solar panel would simply stop delivering power to the battery, and would only resume once the voltage had dropped a bit. However, some solar shunt controller circuits available on the net seem to place a dump load (usually high-power resistors) after the blocking diode (position 2) which causes the battery to discharge slightly until the voltage drops. Is there any advantage to this?
  2. I'm still not sure why you would attach a wind generator after the blocking diode (position 2). What is the difference between before and after? Does it have any bearing on the amount of turbine braking which can be obtained once the battery is full?


Many thanks again.


Ben

« Last Edit: February 03, 2009, 09:31:46 AM by (unknown) »

ghurd

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Re: Solar and Wind shunt - dump load position?
« Reply #3 on: February 03, 2009, 11:20:36 AM »
Those damn Oatley kits cause more confusion and problems than about anything else I can think of.  Can I say damn?


The wind generator is connected Before the diode.

The load is connected After the diode.


For #1, 'any advantage'.  Many advantages.  Too many to list and explain.


For #2...


Do not brake the turbine as the standard form of control.


Loading with a resistor or shorting the windmill has 100 problems.

Google search the board (in the top right menu) for "Oatley" should get many of the best problems.


Shorting is violent to the windmill.  

Balancing the resistor value to the windmill on the AC side (or before the diode) is impossible (it either runs away, or acts like a short).


A couple things to read,

http://www.fieldlines.com/story/2008/11/8/63523/3798 ("do not brake the turbine")

http://www.fieldlines.com/story/2008/5/31/54134/8788

http://www.fieldlines.com/story/2008/1/26/23318/5389


If you do a search for my 'ghurd controller', might find more related info.

G-

« Last Edit: February 03, 2009, 11:20:36 AM by (unknown) »
www.ghurd.info<<<-----Information on my Controller

Ungrounded Lightning Rod

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Re: Solar and Wind shunt - dump load position?
« Reply #4 on: February 03, 2009, 08:46:12 PM »
With a windmill you connect the load to the battery because you're not trying to eat the power as it is generated - maybe occasionally it's coming in too fast for a few seconds and you can't dump enough, sometimes it's coming too slowly and you can use that opportunity to catch up on what you missed (or just turn the dump load off when you've dumped enough) - you're just trying to keep ahead of the mill on the average.  Also, if your dump load is doing something useful you give it clean power.


Windmill dump loading is like a reservoir:

 - Windmill is the incoming river and rain, with wildly varying flow.

 - Battery is the dam and reservoir.  Let it get too full and the dam is damaged.

 - Dump load is like draining off excess water before the reservoir gets too full and the dam breaks.  Unfortunately it's not like a spillway, which gives higher flow with more water.  It's like a fixed-size drain.  So you turn it on when the reservoir is getting just to the desired level and try to keep it from being too overfilled too long.


You could use the same system for solar.  But solar has advantages:  You can safely short the panels upstream of the blocking diode and let the panels themselves be the dump load, getting slightly hotter than they would if they were delivering power (but no hotter than if they were just sitting in the sun unconnected).  The max current is limited by the sun's illumination.  So if your switching transistor can handle that current you don't need the dump load resistor-or-whatever, don't have to dissipate the heat somewhere, and don't have damage to the battery if the (nonexistent) dump load resistance fails.

« Last Edit: February 03, 2009, 08:46:12 PM by (unknown) »

(unknown)

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Re: Solar and Wind shunt - dump load position?
« Reply #5 on: February 04, 2009, 02:18:24 AM »
Many thanks to you both for your replies and explanations - I think I understand it now! The water analogy really helps to make it clear.


Just one more question regarding the difference between DIY series and shunt regulators for solar. Why short the panel (shunt regulator) when you can just disconnect it (series regulator)? My understanding is that if you are using MOSFETs, with series regulators there is usually a voltage drop as the mosfet is wired into the circuit all the time, whereas when it is just used to short the panel (shunt) it is only connected when needed and then the voltage drop doesn't matter. Is this correct?


Many thanks again


Ben

« Last Edit: February 04, 2009, 02:18:24 AM by (unknown) »

ghurd

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Re: Solar and Wind shunt - dump load position?
« Reply #6 on: February 04, 2009, 06:53:37 AM »
"Why Shorting?"  Name of the story.

http://www.fieldlines.com/story/2008/12/24/162442/74


Comes down to cheaper and easier.

G-

« Last Edit: February 04, 2009, 06:53:37 AM by (unknown) »
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Ungrounded Lightning Rod

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Re: Solar and Wind shunt - dump load position?
« Reply #7 on: February 04, 2009, 01:26:05 PM »
My answer:


Shorting wastes power as heat in the transistor when you don't need it.

Opening wastes power as heat in the transistor when you do need it.

« Last Edit: February 04, 2009, 01:26:05 PM by (unknown) »

(unknown)

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Re: Solar and Wind shunt - dump load position?
« Reply #8 on: February 05, 2009, 01:36:56 PM »
Great - thanks people!
« Last Edit: February 05, 2009, 01:36:56 PM by (unknown) »