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Wanting to build a rectifier circuit for my lawnmower.

Discussion in 'General Electronics Discussion' started by wmrcomaniv, Apr 29, 2015.

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  1. wmrcomaniv

    wmrcomaniv

    7
    1
    Apr 29, 2015
    Ok all, here's what I have already.
    22-23 VAC out from the stator, single phase into a plug. The lawnmower has an electric clutch that I need to keep engaged in order to mow a bunch of lawns. I have tried charging the battery and it holds enough charge to keep the clutch engaged for a little while. What I want to do is build my own rectifier circuit, possibly regulate it, in order to charge the 12VDC lawnmower battery and to keep the clutch engaged. I rigged one circuit up already, but the components get REAL hot and I can't heatsink the individual diodes.

    Everything I have seen while searching today seems to show that the output from approx 12VAC thru the rectifier, and adding a capacitor across the + and - output lines INCREASES output voltage. How is this???

    All in all, I would like to take the approx 23VAC from the stator output (2 wires) and bring it to around 14.5VDC @ maybe 10 amps. I have no idea how many amps the stator can supply though... although I would bet it's enough to charge the battery! Other than the electric clutch and the battery charging, there are no other loads on the VDC side of the circuit.
     
  2. wmrcomaniv

    wmrcomaniv

    7
    1
    Apr 29, 2015
    Hell, I might even be able to get away with 5 amps if need be.
     
  3. davenn

    davenn Moderator

    13,654
    1,888
    Sep 5, 2009
    hi
    welcome to the forums

    I presume you mean 12VDC ... if AC was going into and out of a rectifier ... then it wouldn't be rectifying, aye
    without a capacitor, the rectifier output will look like a bunch of 1/2 cycles
    the capacitor smoothes that out and produces an overall higher DC output than without it

    have a look at this toturial
    http://www.electronics-tutorials.ws/blog/unregulated-power-supply.html


    cheers
    Dave
     
  4. Y2KEDDIE

    Y2KEDDIE

    259
    15
    Sep 23, 2012
    It sounds like the charging circuit is not working. Possibly the clutch coil has a shorted winding, drawing too much DC (current) discharging your battery faster than it can be charged.

    The rectifier could be shorted, delivering some AC to the clutch coil: it could be partially working but not charging your battery.

    You say the alternator is putting out 23 VAC, how are you measuring this?
    Check the DC voltage at the Clutch when engaged.

    When alternating current (sine wave in this instance) is applied to a rectifier
    the output is pulsating DC. The capacitor across the output fills in between the peaks and valleys of the pulses. The capacitor will charge to the peak of the applied AC voltage depending on the load and current capacity of the alternator. If a diode or diodes of the rectifier is shorted then the output would be reduced.

    My Toro Lawn mower has a battery operated electric start, but no provision to charge the battery other than an external charger. Maybe your mower is he same; the alternator is only large enough to operate the clutch. One charge , one mowing.
     
  5. wmrcomaniv

    wmrcomaniv

    7
    1
    Apr 29, 2015
    I'll have a look at the tutorial here in a minute...
    I should clarify... 12VAC source, rectified, approx 12VDC output from rectifier, add cap(s), and there's an increase from the output side.
     
  6. wmrcomaniv

    wmrcomaniv

    7
    1
    Apr 29, 2015
     
  7. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Yes, that is expected. The capacitor will charge to the peak of the AC wave with will be 12V * sqrt(2) minus the diode drops.

    Bob
     
  8. wmrcomaniv

    wmrcomaniv

    7
    1
    Apr 29, 2015
    Thank you, Bob... That little bit of math will be useful to me!
    I have never delved too far into the mathematics involved, so I didn't know there was a formula I could use. Knowing this will certainly help me in the future!
    Appreciate it bud!
     
  9. wmrcomaniv

    wmrcomaniv

    7
    1
    Apr 29, 2015
    Thank you, Bob... That little bit of math will be useful to me!
    I have never delved too far into the mathematics involved, so I didn't know there was a formula I could use. Knowing this will certainly help me in the future!
    Appreciate it bud!

    I measured this across the two output wires coming from the alternator into the first connector. No diodes or anything before this connector coming from the stator. AND the only measurement I can get is a VAC measurement.
    Using my DMM on the 200VAC setting: approx 23VAC between the two output wires. Less than 1VAC between either output wires and chassis/engine ground, and even less measured on the VDC setting between either output lead and chassis/engine ground. So my guess is that I'm getting AC at the connector. I more or less got a confirmation by building the rectification circuit and getting something at the output side of that circuit with it being supplied by the stator's 23VAC.

    I'm wondering if I can diffuse some of the incoming current by placing a higher watt-rated resistor (or one on each side of the incoming AC supply)... like a ceramic "box" resistor. One that's a big rectangular ceramic encasement?
     
  10. wmrcomaniv

    wmrcomaniv

    7
    1
    Apr 29, 2015
    Thank you, Bob... That little bit of math will be useful to me!
    I have never delved too far into the mathematics involved, so I didn't know there was a formula I could use. Knowing this will certainly help me in the future!
    Appreciate it bud!

    I measured this across the two output wires coming from the alternator into the first connector. No diodes or anything before this connector coming from the stator. AND the only measurement I can get is a VAC measurement.
    Using my DMM on the 200VAC setting: approx 23VAC between the two output wires. Less than 1VAC between either output wires and chassis/engine ground, and even less measured on the VDC setting between either output lead and chassis/engine ground. So my guess is that I'm getting AC at the connector. I more or less got a confirmation by building the rectification circuit and getting something at the output side of that circuit with it being supplied by the stator's 23VAC.

    I'm wondering if I can diffuse some of the incoming current by placing a higher watt-rated resistor (or one on each side of the incoming AC supply)... like a ceramic "box" resistor. One that's a big rectangular ceramic encasement?
    Thank you for welcoming me, Dave!
    I hope that this forum will be able to help me with my interest in electronics! I started building little things from schematics over 20 years ago, but a lot has changed over the years from what I was used to seeing when I opened up some piece of electronic equipment!
     
    davenn likes this.
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