Determining polarity on a small wind generator

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Tulumtam
Tulumtam Solar Expert Posts: 37 ✭✭
in Wind Power Generation #1
Here is the situation:
There is a small wind turbine (brand unknown, Airbreeze-size) mounted on a pole on a roof. There are 3 cables coming out the bottom of the pole. Obviously, one is positive, one is negative and one is ground. How can I figure out which is which? They are all black, no other markings or codes to distinguish them from one another. The allen bolts attaching the turbine to the top of the post are stuck and won't budge. We have broken two allen wrenches and gone through a lot of WD40 trying to get those bolts loose. I have shorted each cable to each other and every combination has the same effect, which is to brake the turbine. Any ideas? The goal is to hook this turbine up to a new battery bank that also has a small solar array.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Determining polarity on a small wind generator

    You're making the assumption that the output is DC. It could well be that the three wires are the legs of 3-phase AC output.

    You need a digital multimeter and some wind. Measure the Voltage on both AC and DC scales across each combination of wires and see what results you get, including polarity. You will at least have to label the wires 'A', 'B', and 'C' in order to list the outcome.
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  • Tulumtam
    Tulumtam Solar Expert Posts: 37 ✭✭
    #3
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    Re: Determining polarity on a small wind generator

    I know the output is DC. A few weeks ago it was the only charging source on the old battery bank. They moved the turbine to accommodate a new water tank and in disconnecting the turbine, did not label the cables. With the turbine spinning in low wind, I have measured voltage across pairs of the cables. What I get is not very helpful - 0.1-0.7v DC with fluctuating polarity.
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  • Aguarancher
    Aguarancher Solar Expert Posts: 315 ✭✭✭
    #4
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    Re: Determining polarity on a small wind generator

    Was the turbine going through any device before it went to the battery? With fluctuating polarity reading on the DC setting it sounds like it might be AC..
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  • Tulumtam
    Tulumtam Solar Expert Posts: 37 ✭✭
    #5
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    Re: Determining polarity on a small wind generator

    Previously the turbine was connected to a 24v battery bank via a SPDT switch. I witnessed it charging those batteries, albeit never above 23.8v (tower and wind speeds both too low to expect much from it, but the owner is keen on having it back in the system to keep the batteries up a bit at night). The brake switch had a wiggly post on it, so I bought another one replace the old one when wiring the turbine back up to the battery bank.
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  • Tulumtam
    Tulumtam Solar Expert Posts: 37 ✭✭
    #6
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    Re: Determining polarity on a small wind generator

    I guess it would be helpful to provide the whole story… There were two wind turbines connected to a battery bank to power a small vacation house on the coast. Both turbines were on 2 meter high poles mounted on the 2nd story roof of a concrete house. I know that that poles are not high enough. I know that it is not a good idea to mount wind turbines on a house.

    One turbine appears to be a 24v AirBreeze or similar. No LED on the body, though. This turbine has had the ground cut off at the base of the turbine, so can't splice another cable on. So turbine 1 has only 2 cables, the positive and the negative.

    Turbine two is the one described below. 3 cables coming out the bottom of the pole, but not marked and we can't get the turbine off the pole to check the outputs directly from the turbine.

    Due to reconfiguration of the roof (moving the water tank to make space for a small solar array), the owner of the house would like to have at least one of the turbines wired back into the system. I chose the one with the ground, but we cannot determine which cable is which. He would be fine with me wiring in the other one, but since it has no ground, I am not too keen on that and cannot wire in the brake switch of there is no ground.

    The goal is to get one of these turbines up and running, preferably safely….
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: Determining polarity on a small wind generator

    The symptoms you report do not add up to a DC turbine.

    If one of the wires is a ground then shorting that wire to either of the other two (positive or negative) would not result in the turbine braking as ground is not electrically connected to the active wiring; it would not form a short circuit. However with 3-phase any two wires connected together will short 1/3 of the wiring and effectively brake the turbine. The fluctuating polarity is another indicator of AC; DC output would simply ramp up/down in Voltage in relation to the speed of the turbine (unless direction is actually reversed).

    I think it may be wrong to assume the turbines were installed properly to begin with. The mounting description, for example, sounds like someone didn't know what they were doing.

    Without actual manufacturer's data or taking the turbines down for bench testing it will be extremely difficult to get these working again. However, I have a suggestion: get six diodes and put two on each wire, one arranged as (+) output the other arranged as (-) output. Then connect all the (+) outputs and all the (-) outputs. Measure the Voltage and see what you get then. If it is an AC turbine you will see a higher Voltage output with fixed polarity. If it is a DC turbine you will see about the same output as without the diodes. If it has an internal short the turbine could lock up.

    Keep in mind that at their heart all generators are AC, so if this is a DC output turbine there would be some form of rectification within the turbine head. If that has failed (shorted or open diode) then the output will be low or even nil. A ground wire on a DC turbine is not normally connected to anything except the casing. Sometimes this is tied to negative, but in such an instance there usually are only two wires.
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  • Tulumtam
    Tulumtam Solar Expert Posts: 37 ✭✭
    #8
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    Re: Determining polarity on a small wind generator

    Yes, I fully agree that it is wrong to assume that anything was installed properly to begin with! Thanks for your insights on AC vs DC output. Very helpful. I will try the diode test that you propose, as I happen to have a handful of diodes sitting around!
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