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no image Friday, November 17, 2017 by john mantheakis

Using step up/step down transformers on micro hydro generator

I have a problem with voltage loss (100 metres run) and am thinking of solving it by using step up and step down transformers. I have designed a floating poncelet wheel hydro power generator and will use the  Windtura 750 / 3 phase alternator.

my problem is that theoretically I should be getting around 266 W at 28 A from the 3 phases. I have no way of knowing the exact voltage output when it is operating on the river.

My question is: if I use 3 single phase 1kva transformers wired for 3 phase step up at the source and the same type to be used at the load (rectifier/battery bank charge controller) .will the voltage input be crucial to the transformers? 

The system will be installed in a remote river in rural Tanzania.

Comments

  • by  Elizabeth Simon
    The exact voltage should not matter to a transformer as long as you do not exceed it's specifications. Whatever voltage you have will be stepped up/down and as long as your load is reasonably tolerant it should work.
  • by  john mantheakis
    Thank you. 
  • by  David Ashton (edited)

    Hi John.  I looked up the generator and thought it does not specify, it looks like a 750 W unit (fits in with your 266W x 3 phases).  My only comment would be to use transformers rated nearer the wattage of each phase.  

    A  1 KVA transformer will draw appreciably more magnetising current (wasted power) than say a 300 W one.  It sounds like you want it back to 24V at the other end,  so you have a second three transformers dragging your efficiency down.

    If you use standard mains transformers and run your power cable at 250V instead of 24V your currents will reduce from 28A to 2.8A and if you dimension your cable right you shouldn't get too many losses.  That's only 1A per phase at 250V so you'd get away with 1.5 mm2 or 2.5 mm2 cable, which are standard sizes for mains cables.

    Sounds like a nice project.  I'm originally from Zimbabwe (a bit to the south of you) but this is the kind of project that is so good in  Africa.  Good luck with it.

    PS just saw the graph of A / W vs RPM on the website, I see where you got the 266 W from.  But it does not change my thoughts - just dimension your transformers for the maximum POSSIBLE output from the generator - EG if you would see that 266W being a maximum, use 3 x 100VA transformers.

    • by  john mantheakis
      Hi David,

      Yes I plan to step up to 230v. At the other end I need to charge a 12v battery bank. Si ce I am using an MPPT charge controller; an input voltage of 30 plus volts will not be a problem. This alternator will give up to 40A under load. Voltage can go more than 60v per phase. Perhaps a 500w step up/step down transformers will suffice.

      Our camp is 2 days drive from our base in Dar es salaam so I will need to be sure that I have the right setup before going to install.

      Looks like Mugabe's reign is coming to an end! 

  • by  john mantheakis
    Hi David,

    Yes I plan to step up to 230v. At the other end I need to charge a 12v battery bank. Si ce I am using an MPPT charge controller; an input voltage of 30 plus volts will not be a problem. This alternator will give up to 40A under load. Voltage can go more than 60v per phase. Perhaps a 500w step up/step down transformers will suffice.

    Our camp is 2 days drive from our base in Dar es salaam so I will need to be sure that I have the right setup before going to install.

    Looks like Mugabe's reign is coming to an end! 

  • by  David Ashton
    John....your transformers should be rated for the maximum power they will have to handle, but this may not be at the voltage they are designed for - conflicting requirements and you will have to be quite careful in your specifications and selection.  Put 60V on a 12-250 V transformer and you will get 1250V out of it, you'd then risk insulation breakdown.  As you say 500VA transformers would give you a bit more headroom, but be careful about the voltages..

    I'd have a think about the tools and testgear you will take before you go as well.  Sure this is only electricity, not electronics (apart from the charge controller) but I'd take as a minimum a DMM and a clamp meter to measure currents.  A scope might be overkill but then again might show you the solution to a problem - something like the one I bought recently would be just the job.  Take some voltage dividers or voltage transformers to look at the high voltages.

    Mugabe - yes - after all these years it's almost anticlimactic.  No bodies in the streets, no curfews.  But that's Zim for you, great people generally :-)

    Oh, and write up your experiences on this - it would make a nice article - let us know when you get back!

  • by  john mantheakis
    David,

    My calculations show that I will be getting around 300W from the alternator. More than enough considering it will run 24-7-365. At the rpms I expect to achieve; the voltage will be approx 30v.  I could always change pulley ratios to better achieve this. The only problem is I will need to take extra pulleys with me. 

    I expect to have the unit ready by March. I will post photos and videos. 

    It is a remote place but stunningly beautiful. Plenty of wildlife too and every night we get leopards coming into camp.

    I plan on using 3 x 300W 24v to 230v transformers wired in a star configuration.


    • by  David Ashton
      John..you seem to have it all figured out, and I agree with your specifications for the transformers.  So can only wish you good luck with it.

      You don't say if you're already in Tanzania?  Never been there but anywhere in Africa is good, and as you say some parts are stunning.  Leopards...when I was 14 a friend and I took train / bicycles to a remote part of Zimbabwe and camped for a week.  The first morning we woke up to leopard prints round the tent.  I later lived in the area and saw leopard a couple of times.  So beautiful.

      Please do let us know how you go - contact Max or myself in these columns.

  • by  David Ashton
    John..you seem to have it all figured out, and I agree with your specifications for the transformers.  So can only wish you good luck with it.

    You don't say if you're already in Tanzania?  Never been there but anywhere in Africa is good, and as you say some parts are stunning.  Leopards...when I was 14 a friend and I took train / bicycles to a remote part of Zimbabwe and camped for a week.  The first morning we woke up to leopard prints round the tent.  I later lived in the area and saw leopard a couple of times.  So beautiful.

    Please do let us know how you go - contact Max or myself in these columns.

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