Wiring a Rectifier

[Ding123]

I wired my 4 prong rectifier ,to my gennie. I want to know if it is ok to have

a reading in AC and a reading in DC , as well. If this is a normal occurance can someone please let me know.Thank you.





Editor thinks you should try to provide more info, your pictures don't say much about how the bridge is wired [see only its back side] , the readings you see, etc [ they are too blurry for me to read]. Comment  with more info and try to give as much info as possible or it is futile trying to get help.

[seanchan00]

What you show seems to be a bridge rectifier. Two opposing prongs are for AC wires from the alternator and you will see AC if your alternater is generating AC. The remaining two prongs will be your required DC output. One is usually labelled + and the other neg( - ). This will be measured DC. I am not sure how you measure AC in your rectifier. I measured my alternator AC by connecting one of the STAR leads to the three leads wired together. I have never tried to measure AC at the rectifier.

SeanChan.

[Shadow]

You should get AC up to the rectifiers, Then DC with you positive and negative outputs.

[stop4stuff]

if you're measuring the dc output and get an ac reading, this is because the output is a pulsed dc, to get a true dc reading, you need a capacitor across the +ve & -ve of the rectifier

[Ungrounded Lightning Rod]

I'm assuming you have something like this:

 - Genny hooked to the AC terminals of the rectifier.

 - Meter across the DC (+, -) terminals

 - No battery or other load connected.

 - Spinning the genny by hand or something.

 - DC and AC readings taken with no changes

   to setup except for switching between a

   DC and AC voltage scale.

If that's the case it's fine to have readings

on both the DC and AC scales - and for them

not to match.

Your bridge rectifier's output is pulsing DC.

Your multimeter's DC scales are just the meter

movement connected to the probes through a big

resistor (selected by the scale you chose) to

turn the voltage into a proportional current.

The meter movement responds to the current -

averaging it out over the cycle.  Pulsing DC

has a non-zero average DC voltage and that's

what you read.

The AC scale will be similar, with three changes:

 - A capacitor is inserted in series, to eliminate

   any response to the DC component of the input.

   (Now it only responds to the CHANGE in voltage.)

 - A pair of diodes are inserted - one in series

   with the meter coil, one (pointed the other

   way) in parallel with the series connected diode/

   coil combo.  This causes the meter to respond to

   one half-cycle of the voltage change and ignore

   the other.  (A bridge rectifier would let it

   respond to both half-cycles but that's unnecessary).

 - The scaling resistors (and scale markings) are

   different - so that when connected to a sine wave

   of power line frequency (or pretty much any frequency

   above that) the meter will show the RMS equivalent.

Since your DC is pulsing, the meter will show a non-zero

value when set to the AC mode also.

Hang a bigcapacitor across the bridge and the DC reading

will go up somewhat - from the average to the peak -

while the AC reading just about goes away.

Hang a battery (of a value below the peak) across the

bridge and it will be charged by the genny-bridge

combo - and will drag the peak voltage down.  Then the

AC reading will show the small ripple from the charging

current's voltage drop through the battery's series

resistance, while the DC reading will show the battery's

voltage plus the average of the ripple.

[Ding123]

Thank you very much Editor,Sean Chen,Ungrounded Lightening Rod and Shadow, and to anybody else who took time to answer this question.WOW! you guys really got it together....thank you