Navitron Renewable Energy and Sustainability Forum

Energy/Electricity Storage and Use/Grid Connection => Off-Grid, Batteries & Inverters => Topic started by: billi on November 24, 2011, 10:57:07 PM



Title: blocking diode
Post by: billi on November 24, 2011, 10:57:07 PM
Hi

I need to put one or more Blocking Diodes in between the Battery and my windturbine  so no power can  flow towards the turbine and its dump

So am i right that the diode is placed just in line with the positive wire ?   and the threaded connection faces towards battery

(http://www.reuk.co.uk/OtherImages/30A-schottky-diode.jpg)

Problem is my wire is 70 mm2  :-\   and that tiny diode  a bit small , but i could use 3 or 4 in parallel and connect to a bus bar  to achieve  a biger diameter at the connection  

Any ideas

Thanks Billi


Title: Re: blocking diode
Post by: johnrae on November 25, 2011, 12:17:03 AM
Ideally you should have provided the part number but I can just see the symbol which suggests the cathode is the screwed stud.  However I do not fully understand what you mean when you say battery power goes towards the turbine and its dump.

Could you perhaps provide a sketch of your intent so's a definitive (and hopefully correct) answer can be given.


Title: Re: blocking diode
Post by: billi on November 25, 2011, 12:27:10 AM
Thanks John

My turbines controller has a dumpelement connected that starts dumping at say 29 volt ,

Also there are 4 kw of PV  but much better controllers that charge with temperatur sensors   and reach  charge voltage upto 31 Volt

I do not want to allow that power from the PV is dumped  there at 29 volt as well at the turbines controller and burn out the 2 kw dumpelement

So thats why the diodes 

Thanks Billi


Title: Re: blocking diode
Post by: johnrae on November 25, 2011, 12:36:10 AM
Remember that you will lose about 0.7 volts across the diodes so you need to account for that when setting up your turbine charge controller  ie battery + 0.7 volts


Title: Re: blocking diode
Post by: Antman on November 25, 2011, 07:45:23 AM
Billi

In the diode shown, current will flow from the tag (top right) to the stud (nut) end and johnrae has said.

I am also slightly confused but I think it may result from a typo in the original post.

Did you mean "...so now power power can flow towards the turbine and its dump" or "...so no current can flow towards the turbine and its dump" ? I suspect that the "w" makes a difference which way round the diode is fitted.

I admit to not being involved in wind power but my observation/question would be that if you have two charge sources, one at 29V the other 31V, the 31V will always dominate. Thus the wind will not contibute anything if the PV is generating and holding the batteries at a higher voltage than the wind charge controller will allow.
Also how doe the wind charge  controller sense the battery voltage? It is possible that by blocking the battery with a diode you could also block the voltage sensing on the controller.

Ignore me if I have the wrong end of the stick!

Regards
Antman


Title: Re: blocking diode
Post by: billi on November 25, 2011, 09:43:16 AM
Hi Antman   you are right  " no Power can flow to the turbine "  is the idea  


Quote
I admit to not being involved in wind power but my observation/question would be that if you have two charge sources, one at 29V the other 31V, the 31V will always dominate. Thus the wind will not contibute anything if the PV is generating and holding the batteries at a higher voltage than the wind charge controller will allow.

I do not use the dump element at the wind turbine  , because of this reason  Antman
I have a AC heater that  i  use  and is switched on by my inverter at say 30 Volt and  Wind is then dumped in my house,  as well as some PV   and this holds the Windturbine  as well

But now  i would like to run a GTI (MPPT range 10.5-30 Volt )in parallel with my charge controller  to hopefully increase the performance of the turbine in low wind . And feed that AC 230 Volt into my house directly

But i need that Diode  that the GTI is not feed from the Battery , but the battery clamps the voltage range down to a secure range for the GTI

Something like this here  in the drawing ....

(http://www.windynation.com/community/attachments/leamy-bat-12-jpg.346/?embedded=1)

(http://www.windynation.com/community/attachments/battery-gti-jpg.347/?embedded=1)

Hope this make sense  ::)





Title: Re: blocking diode
Post by: Antman on November 26, 2011, 04:41:18 PM
Hi Billi

In the second diagram, the 'triangle' is representing the diode (I assume). Normally the 'point' of the triangle would be the direction of current flow. But confusingly, the arrows point in the opposite direction.
This may be contributing to the confusion and hence the lack of knowledgeable replies - hence why I will bump it again.

In a diode - approximate symbol below but drawing with text characters is not easy so allow some imagination and assume the arrow is formed with the ">" being a steeper angle!....

          |\  |
-------|  >|-------
          |/  |
Anode          Cathode

Current flows this way >>>>>>>>>>
So any voltage applied to the cathode will not appear at the anode terminal.

Hence the confusion in the second drawing.


If I am correct in assuming that you want the wind turbine to charge the batteries but not to be affected by the PV charge controller, then the cathode (arrow tip) of the diode needs to connect to the battery and the anode to the wind turbine busbar.
The first drawing is correct in this respect.

But in doing this, I suspect that the wind turbine will no longer contribute to the battery charging when the solar PV is generating because the 30+ volts across the batteries will reverse bias the diode - meaning it cannot conduct with only 29V coming from the wind genny. So presumably the wind dump load would then have to absorb the entire wind turbine output.

As for connecting the diode, I would parallel 2-3 (depends on rating of what you have) so that the total diode continuous current rating is double your peak wind turbine current (for reliability). Mount copper busbars on insulators and connect the diodes to those so that you also have a stout connection for the cable lugs to bolt onto.

Antman


Title: Re: blocking diode
Post by: billi on November 26, 2011, 05:25:13 PM
Thank you Antman

Quote
But in doing this, I suspect that the wind turbine will no longer contribute to the battery charging when the solar PV is generating because the 30+ volts across the batteries will reverse bias the diode - meaning it cannot conduct with only 29V coming from the wind genny. So presumably the wind dump load would then have to absorb the entire wind turbine output.

As for connecting the diode, I would parallel 2-3 (depends on rating of what you have) so that the total diode continuous current rating is double your peak wind turbine current (for reliability). Mount copper busbars on insulators and connect the diodes to those so that you also have a stout connection for the cable lugs to bolt onto.

Antman

Yeah , i am aware that the dump of the turbine  has to take the power when  voltage higher than ca 29 V  ,  but have other ideas as well

Will built a busbar  for  the diodes

Thanks







Title: Re: blocking diode
Post by: johnrae on November 26, 2011, 07:20:40 PM
You might also want to consider a charge controller between the turbine and the battery to prevent the possibility of over-charging when it's blowing a 'howler'


Title: Re: blocking diode
Post by: JohnH on December 01, 2011, 11:19:31 AM
Hi Billi

The diode you have, did this come with the system? I ask because looking at the type letters it looks like a Schottky diode. They have a low forward voltage drop at about 0.2V and hence are used mainly for high speed switching. Their disadvantage is that they have a relatively low reverse voltage and high leakage current.
I don't know if it would be suitable for your application.

JohnH


Title: Re: blocking diode
Post by: billi on December 01, 2011, 11:26:03 AM
Hi John

No  i have not got the Diodes yet .
Do you have  a better model  ?


Title: Re: blocking diode
Post by: JohnH on December 01, 2011, 01:32:11 PM
Billi
I would have thought a standard high current metal stud diode would suffice mounted on a heat sink with mica insulators if needed. Depending on the max forward current, the 25F10, 40HF10 or 70HF10 series diodes which are available from Farnell.
JohnH


Title: Re: blocking diode
Post by: fred bloggs on December 01, 2011, 02:43:43 PM
Billi

I have dozens of Industrial Stud diodes upto 300Amps rating, all gathering dust, therefore if you want a couple of them, PM me and I'll shove them in the post (my good deed for the week-FOC). Tell me the maximum rating (current) you are looking for.

Best Regards

Fred


Title: Re: blocking diode
Post by: billi on December 01, 2011, 04:37:15 PM
Oh    :reindeer  santa is coming  will PM you 


Title: Re: blocking diode
Post by: fred bloggs on December 02, 2011, 11:55:41 AM
Hi Billi

 :reindeer is on its way as per your PM.

Best Regards

Fred


Title: Re: blocking diode
Post by: billi on December 02, 2011, 12:09:20 PM
Thanks Fred

very much appreciated   and strengthen   my believe in Mankind    :D


Billi


Title: Re: blocking diode
Post by: billi on December 07, 2011, 08:49:31 PM
thanks a lot  Fred  arrived today   and they look sechsy   ;D



Title: Re: blocking diode
Post by: Outtasight on January 08, 2012, 11:47:27 AM
Hi Billi,

Couple of things from your plans...

You need to bolt the diodes to a bus bar heat sink so that when running at high current they can get rid of the heat they generate.  20 Amps flowing through a diode drops 0.7 to 1.0V and would generate up to 20W of heat.  This needs to escape from the diode to whatever it is bolted to.

Next is the use of Grid Tied Inverters (GTIs) in your plan.  Doesn`t seem like it would work.  Where are you getting the 120V AC to power them from (they won`t start up on DC alone as they`ll have anti-islanding protection - even the cheap 600W Chinese one someone gave me does).

Then, even if you have a 120V AC supply to start them up, that AC supply will try to run the 500W dump load when there isn`t enough wind power to do it.  So you`d be heating your dump load from the "grid" source!

Next are the solar panels.  You show 20Voc panels connected in parallel.  This is too low to charge a 24V battery (fine for a 12V one).  You need pairs of 20Voc panels in series to make at least 30V at maximum power point of the panels - Vmpp (at Voc they make NO power - it`s the open circuit voltage with no load).

Finally, you`ve got a diagram that suggests connecting two 120VAC GTIs to two spurs on your consumer unit and implying that you`d get 240V AC from them.  This won`t work either.  They are designed to run in parallel but syncronously, so they`d pump 120VAC into your house via the two spurs.  But only if your house was running on 120VAC.  If you feed them 240VAC they`ll probably blow up.


Title: Re: blocking diode
Post by: billi on January 08, 2012, 12:28:35 PM
Thanks outa  

Actually  the drawings are from a guy in the USA   and not showing my system .... so  what i got now is a 300 watt 230 AC GTI

And  i have now connected it up   in parallel to my charge controller   and the blocking diode  as well  fixed to a  copper heatsink (actually just a pipe  :P )

The GTI  works and  feeds the house , as well if turbines output exceeds my actually consumer needs in the house , the internal charger of my inverter starts charging the battery.....

But  there are a few things i did not know up front  whistle,  
- The GTI  holds down my 24 Volt  Turbine to the GTI s Voltage range (11-30 V )   so the turbine is producing  ,power that i have never been able before in low wind (cause turbine was not generating enough volt to reach battery voltage) , but it does not speed up anymore  cause the GTI  holds down the Volt somehow  ::)

- I have a 1000 watt turbine and i thought the charge controller , cause wired in parallel , will take care of the watts exceeding the GTI  nominal watts , but that is not the case , or i have not seen this happening  yet


So actually i think now , i should have got the bigger China  GTI  say 1000 watt and with a  voltage range 22-50 Volt

And  have the two in parallel , but to optimize this idea , i would need a voltage sensing relay , that switches from the low voltage GTI  to the 22-50 Volt 1000 Watt GTI  ,when wind catches up and exceeds 22 Volt at the generator  :P


So a lot learnt from this 100 Euro project  so far

Hope that makes sense





Title: Re: blocking diode
Post by: billi on April 18, 2012, 12:50:57 PM
Quote
- I have a 1000 watt turbine and i thought the charge controller , cause wired in parallel , will take care of the watts exceeding the GTI  nominal watts , but that is not the case , or i have not seen this happening  yet


So actually i think now , i should have got the bigger China  GTI  say 1000 watt and with a  voltage range 22-50 Volt

And  have the two in parallel , but to optimize this idea , i would need a voltage sensing relay , that switches from the low voltage GTI  to the 22-50 Volt 1000 Watt GTI  ,when wind catches up and exceeds 22 Volt at the generator  Tongue


So a lot learnt from this 100 Euro project  so far

O dear    i must be lonely....   (start quoting my self) .....

I  was ignoring the GTI setup for a while and just disconnected the GTI  cause it is breaking  the windturbine too much ( trying to hold her to lower Volts) , and let it run on direct charging the batteries  for months now  ,  but due to the sunny weather in April   Battery was full  early , or in other words , windturbine chargecontroller started to dump into   its air heater in the shed

I found a bad connection to the air heater , a typical Chinese problem   called corrosion of material in harsh climate of Ireland  whistle

So the say 10mm2  DC cable to the Dump heater  was melting

So  i switched the GTI back on to direct feed  my Island System   to use windpower direct in the house   and  Dump on the AC side in the house instead

We had some windy days recently  and the 300 Watt GTI  was running flat out at 300 Watt  and 29 Volt ( 30 Volt is its limit)

The nice  thing i found out  , when there is more than 300 watts , that the GTI can feed into the house , the parallel installed charge controller kicks in and takes care about the exceeding watts ...

So   as a resume  for now of this experiment, 

I gained  some watts in low wind , cause the 24 volt windturbine   starts feeding my off grid house at 10 volt (generator output) , but breaks down the turbine too much  to get  up for the "right" speed   , so loose in midrange windspeed conditions , in high winds all is fine again

But overall  my impression is , that it supplements our PV much better with the GTI  than  as direct battery charging , cause for the reason  that  the battery Voltage is high  during the day (cause PV is charging)  and the turbine hardly gets over that voltage point to feed the battery 

So for us  it seems  to be the better idea   cause we gain  on days  now  some power , that would be lost  with direct charging ......
 Even  its only 30-60 Watt   per hour steadily over the day /night in low wind  , but its a  difference in the morning  , when i look at our battery monitor  and see  that PV has lesser work to do during the day

I  would really like to find/built a turbine  for low windspeed   ..................... but safe in high winds



Billi





Title: Re: blocking diode
Post by: biff on April 18, 2012, 01:55:33 PM
Hi Billi,
   "  I would really like to find/build a wind turbine for  low wind speed but is safe in high wind."
     Thats is truly a tricky one billi.That is exactly what all my experimenting with the different blades and hubs was about.The origional 2kw had very big low wind speed blades and performed even in a light thermal breeze.This was brilliant in nice weather but a nightmare in a force 8,It could not be left to its own devices and needed constant attention to draw off the power in ac lecky fires.
 So eventually after much faffing about i finally fitted 3 smaller 1kw blades on the origional hub and lo and behold it worked.Not only that..It works beautifully.I also added an extra controller because we now had a 120vdc x 650watt array.So one controller directing the solar and the other looking after the turbine both these controllers carry 2kw of resistors so there is an exellent safety margin.
   Its early days yet and we still need a good blow to test it properly but the signs are exellent.We are still waiting for on water heaters (2kw x 120voltdc immersions) and when i get it set up i will post some pics.
                                        Biff


Title: Re: blocking diode
Post by: billi on April 18, 2012, 02:39:27 PM
 ;D 

Hey Biff , for my situation   i think a wind driven Waterpump   would be ideal ,  cause i have a ca 100 kwh  storage lake 

they seem to work in low wind and my neighbour has one ...........  and still alive since i know this part of the world ( ca 30 years)

When i started  off grid , i figured out , wind energy needs  a lot of battery , or a big turbine  to supply  a daily need to the house .......



Hybrid  is the key  :)

Billi