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clats Newbie Joined: 01/10/2013 Location: United KingdomPosts: 6
Posted: 10:00pm 30 Sep 2013
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Hi all
This is my first time using a forum i usually try to find the answers through searching on search engines but i have hit a brick wall!. i am a newbie to power generation but i love tinkering!!
ok one of my problems is i have built a VAWT and when testing i was getting around 1 amp through a clip on ameter with the 2 ends of the wire connected, however when i add the bridge rectifier i only get 32 milliamp, i have tried multiple configurations with no success. i have used a ceiling fan as my generator and it has 2 coils.
i hope someone has the time and knowlege to help
many thanks
VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539
Posted: 11:14pm 30 Sep 2013
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Hi Clats
It sounds like from your description that you have initially measured the shorted amps as it is at virtually zero volts the amps will be higher when you put the bridge rectifier in circuit the junction resistance of the rectifier absorbed the small amount of power generated. A ceiling fan is a very low efficiency generator, so do not expect much power, you havent said what your load is, battery light globe etc.
All the best
BobFoolin Around
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 11:22pm 30 Sep 2013
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Your first problem is building a vawt, as its a low rpm mill and your alternator more than likely needs higher rpm to work better.
2 coils would imply to me you need 2 bridge rectifiers, one for each coil set (2 phase), then couple together the DC outputs of each bridge rectifier.
Pete.
Sometimes it just works
clats Newbie Joined: 01/10/2013 Location: United KingdomPosts: 6
Posted: 01:28am 01 Oct 2013
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thanks pete and bob for your reply i appreciate it.
i am trying to charge batteries up with the vawt 12v 660ah over 4 leisure batteries
im getting good enough voltage at low speeds its just the current has become a problem
yes the readings i mentioned were short bursts of spins by hand on the generator only (no wind capture device attached at this point)and i was getting roughly 1 amp which is good enough for me, with the wires shorted together and no rectifier connected. when i connect the rectifier ( 1 for each coil ) and wired in parallel when leaving the rectifiers and i short the wires together and perform the same test with short hand spins i only get around 30 milliamp. its burning my head out!!!
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 04:05am 01 Oct 2013
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From your descriptions its a bit difficult to figure out exactly what you are doing.
My suggestion is to connect your generator to your battery the way you intend to use it finally. You do have to use the rectifier.
Then, spin it by hand - if you must do it that way, and measure how much charging current flows into the battery. If you then measure 1 Amp, or whatever, with your clamp on meter (around *one* of the wires to the battery) then all is well.
I suspect your preliminary measurements above are quite meaningless but I can understand your enthusiasm in trying to measure something
Measuring short circuit current is fine with a solar panel but its not a good idea with a generator IMO.
BTW, to maintain the charge in your 660Ah battery bank you need more than 1A charging for several hours daily. That is, if you do not draw any current from your battery bank. If you want to use your battery bank to power something you have to replace that extra current too daily by your generator - I very much doubt your VAWT is up to that task.Klaus
clats Newbie Joined: 01/10/2013 Location: United KingdomPosts: 6
Posted: 04:10am 01 Oct 2013
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thank you klaus i will give that a try. its taken me two years to get where i am with this turbine and for it to not work is a real kick in the nuts, i may have to look at the possibillity of scrapping it and starting again
many thanks
clats Newbie Joined: 01/10/2013 Location: United KingdomPosts: 6
Posted: 05:30am 01 Oct 2013
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ha just figured out what the problem was, i was holding my ameter to close to the alternator. ha fool. at least it answers my other question, is it working well, answer no! it was picking something up it even reached 10 amps at one point
Thanks for all your advice.
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 06:18am 01 Oct 2013
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Are you sure you have both ends of each coil going to its own bridge and have not mixed up the windings in your wiring.
You do know most tong meters only work on AC, and you only clamp 1 of the phase wires from 1 coil, so im not sure where you get 1 amp from.
Is that 0.5 amp per coil x 2 = 1 amp or 1 amp per coil (2 amp total)
Have you tried spinning the shaft and measuring the open DC voltage to see at what shaft speed you reach around 14 volts.
That will tell you what rpm is required for cutin to start charging a 12v battery.
Pete.Sometimes it just works
sPuDd Senior Member Joined: 10/07/2007 Location: AustraliaPosts: 251
Posted: 11:38am 02 Oct 2013
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Remember to switch the meter from AC (on coil side of diodes) to DC (on battery side of diodes). It should work ...in theory
clats Newbie Joined: 01/10/2013 Location: United KingdomPosts: 6
Posted: 12:05pm 02 Oct 2013
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Unfortunately my ammeter doesn't have the dc function which is probably why was getting such a low reading, should i expect to loose much current through the diodes?
im thinking of scrapping it now as a lot of people have said using a ceiling fan on a vawt is pretty much useless, im taking apart a 2 phase fan motor as we speak to see what i can do with that, i would like to get my hands on the f+p motors that seem to be so abundant in your neck of the woods, but here in the uk they are not available.
ill get there some how, i never thought turbines would be so in depth on a diy level there seems to be so much i have yet to learn.
many thanks for everyone's input and time.
Craig
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 04:55pm 02 Oct 2013
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You should loose no current through the diodes, but you will loose some voltage through the diodes, as each diode will loose about 0.6 volts, and as there will always be 2 diodes in use per phase you will drop about 1.2 volts per phase through diode loss in the rectifiers.
A quick and dirty way to calculate AC voltage to DC is ....
AC volts x 1.4 - 1.2 = DC volts
Say 12 VAC.
12 x 1.4 = 16.8
16.6 - 1.2 = 15.6 VDC
Pete.Sometimes it just works
clats Newbie Joined: 01/10/2013 Location: United KingdomPosts: 6
Posted: 07:20am 03 Oct 2013
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thanks pete, in that case i should be ok current and voltage wise , im getting around 1 amp and 17 v with hand spins, its not great but its a start.
i am starting one tonight with a 2 phase fan motor i hope i get better results than with the ceiling fan.
thanks all
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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