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  1. #1
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    Default Measuring impedance in anode connections

    If i want to test effectiveness of anode connections, using a multi-meter, what two points do i connect - also is the connection polarity sensitive?

  2. #2
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    Default Re: Measuring impedance in anode connections

    Quote Originally Posted by eddystone View Post
    If i want to test effectiveness of anode connections, using a multi-meter, what two points do i connect - also is the connection polarity sensitive?
    Set your multimeter to read ohms (not milliohms) put one probe on, for example, a propeller blade and the other on the hull-mounted anode that is protecting it (it should be fairly close) on the anode (not the stud). Either way round. You should aim for anything between 0 and 0.4 ohms. (That's assuming when you touch your two probes together your multimeter reads zero)

    www.solocoastalsailing.co.uk
    Last edited by Plum; 18-05-19 at 21:27.

  3. #3
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    Default Re: Measuring impedance in anode connections

    Quote Originally Posted by eddystone View Post
    If i want to test effectiveness of anode connections, using a multi-meter, what two points do i connect - also is the connection polarity sensitive?
    Set you multi-meter on its lowest ohms range , (probably 200 ohms)
    Measure the resistance between the anode and the item(s) it is fitted to protect ( clean patches on each to ensure a good contact with the probes)
    It is not polarity sensitive

  4. #4
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    Default Re: Measuring impedance in anode connections

    You can also select continuity test if the meter has it as an option, connect one probe to the anode and the other to say the prop and it should bleep if a good circuit.

  5. #5
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    Default Re: Measuring impedance in anode connections

    Quote Originally Posted by Scubadoo View Post
    You can also select continuity test if the meter has it as an option, connect one probe to the anode and the other to say the prop and it should bleep if a good circuit.
    But it may beep when the circuit is not good enough. Mine beeps when the resistance is below 60 ohms.

  6. #6
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    Default Re: Measuring impedance in anode connections

    In fact the resistance does not matter so much, high resistance in thousands of ohms will still do the job. However for long life and robustness of the connections you should get as low as possible with stout wiring. ol'will

  7. #7
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    Default Re: Measuring impedance in anode connections

    Quote Originally Posted by eddystone View Post
    If i want to test effectiveness of anode connections, using a multi-meter, what two points do i connect - also is the connection polarity sensitive?
    I'm assuming people know that impedance and resistance are not the same thing.

  8. #8
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    Default Re: Measuring impedance in anode connections

    Quote Originally Posted by thinwater View Post
    I'm assuming people know that impedance and resistance are not the same thing.
    Some may be aware that there is a difference but most probably do not know the difference................. You had better explain .

  9. #9
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    Default Re: Measuring impedance in anode connections

    Quote Originally Posted by VicS View Post
    Some may be aware that there is a difference but most probably do not know the difference................. You had better explain .
    The short answer is that resistance is for DC and impedance is for AC. The long answer won't fit in a blog post. In this case, the OP meant resistance, since anodes are DC elements, although in this case there would be very little difference, since there is minimal reactance.

    https://www.physlink.com/education/askexperts/ae517.cfm

  10. #10
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    Default Re: Measuring impedance in anode connections

    Quote Originally Posted by VicS View Post
    Some may be aware that there is a difference but most probably do not know the difference................. You had better explain .
    I am sure Vic understands the difference but for those who do not. Alternating current will effectively pass through a capacitor. However the impedance exhibited depends on the amount of capacitance and the frequency. So impedance is expressed by Xc (in ohms) = 1/2pi FC where c is in farrads. It is expressed in ohms and resists current flow a bit like DC ohms. Likewise an inductor can carry DC easily but tends to resist alternating current so impedance Xl =2piFL where L is in henries. (pi is the 3.14 one).
    Now to confuse things we also use the term impedance to describe characteristic impedance of coax cable. This relates to the fact that coax cable (or any transmission line ) has a ratio of current to volts which exhibits minimum loss. The ratio is expressed in ohms. The transmitter likewise will have an apparent impedance relating to the ratio of voltage an current which it can best supply. Too much load impedance will not accept all the power, too little load impedance can "short" the amplifier damaging it. The antenna likewise has an "impedance" ie best for power transfer.
    The term is somewhat similarly used to express the impedance of a loud speaker. There is a best ratio of volts to current which can be fed into a speaker to give the loudest sound. This depends on the number of turns in the coil of the speaker. Now an amplifier likewise will have a best ratio of output volts to current to give max power. The load and the amplifier should match their characteristic impedance to get max power.
    The above concept is not much different to a boat where the engine has a preferred RPM and torque for max power the propeller is then chosen to best convert that torque and RPM to thrust. A prop too course or too fine will work but not best power transfer. or is Vic pulling my chain? ol'will

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