checking a rectifier

[scotssandy]

i did a voltage test on the rectifier on my 50hp merc as it does not seem to be charging, on the yellow wire iam getting 26 acv and on the grey output wire ian getting only 1.4 dcv , could anyone advise me on this please .

 

[DHPMARINE]

Re: checking a rectifier

I can't help there,as I don't test them that way. Where did you learn how to test this way ?<br /><br />The way I do it is with an ohm meter.<br /><br />DHP

 

[Barnacle_Bill]

Re: checking a rectifier

If you are getting just 1.4 VDC out, chances are it is bad. To be sure, check it with an ohm meter per your manuals instructions.

 

[rodbolt]

Re: checking a rectifier

the gray wire is an AC output to drive the tach, never looked at it with a DC setting.<br /> the red lead is DC out.<br /> a seriel number or at least a year model would help. <br /> some of the 50hp motors used a non regulated rectifier and some used a regulator/rectifier assy. the test procedure is different on the two.<br /> however if you have 26Vac input and no or very low output on the red DC line odds are the rectifier is fried. but the gray wire is a tach signal.

 

[scotssandy]

Re: checking a rectifier

tks, the model number is 9414656 it is a 4 cyl i was told it is a 1979 model

 

[phatmanmike]

Re: checking a rectifier

very simple....<br /><br />with boat OFF, place volt meter across battery, reading should be about 12.6V DC<br /><br />with boat on and running, if its charging, same reading sould now say about 13.5 or so or maybe more.<br /><br />done

 

[scotssandy]

Re: checking a rectifier

tried that and it is just the same, does this mean the rectifier has blown? or could it be something else, iam getting 26 acv going into the rectifier

 

[ricksrster]

Re: checking a rectifier

For continuity test on a rctifier, connect the RED lead from an ohm meter to one of the alternater terminals of the rectifier and the BLACK lead on the posistive teminal of the rectifier. you should have continuity. Reverse the leads, BLACK on alternator terminal and RED on positive terminal. Should show no continuitity. Do the same test on the other alternater terminal.

 

[rexa1925]

Re: checking a rectifier

Let me know too?<br />Never hurts to learn something.<br />Thank You<br />Rex

 

[scotssandy]

Re: checking a rectifier

tks checked all that and iam getting no continuity no matter what way i try it, does this mean the rectifier is fried ??

 

[ricksrster]

Re: checking a rectifier

Doesn't look good for that rectifier. The cost for a new one is between $25 and $40.

 

[phatmanmike]

Re: checking a rectifier

radioshack.com sells 25amp full wave bridge rectifiers for 3 dollars ! its far superior to OEM in every way and its only 3 bucks. i use them on all my outboards, as do many other people on this board!

 

[scotssandy]

Re: checking a rectifier

tks for the info, could someone let me know if these rectifiers from radioshack are easy to instal??? and would i get one in the uk ??

 

[Texasmark]

Re: checking a rectifier

Been retired for 1 year after 45 years in the electronics business. Can't believe how fast you can go brain dead.<br /><br />Most ac voltmeters read rms voltage (root means square.....square root of (1st element squared plus 2nd element squared plus 3rd squared... thing). Fancy term for the same heating effect for the same voltage in dc.<br /><br />To convert from rms to dc you multiply by the square root of 2 (1.414) to get the peak value, then start subtracting your losses..... half wave vs full wave vs bridge recification (your diodes we're talking about here) diode drops, source impedance (resistance), line losses and all. The result is the dc that is sitting on top of your battery when your engine is doing a couple thousand rpm's. <br /><br />In short your 26 vac is great. Your alternator is alternating like it is supposed to.<br /><br />Problem looks like your diodes are defective. Doesn't matter what's wrong.....they just aren't getting 14+ ish volts dc delivered to your battery like you are supposed to have.<br /><br />Radio shack rectifiers may seem like a good idea, but you are in a marine environment and you need to have your connections sealed and your diodes sealed against moisture and all. You need to get the right type to get the necessary voltage (half wave, full wave, or bridge type rectifiers)<br /><br />The $25 to $40 may be cheap in the long run. Bite the bullet and go for it.<br /><br />HTH<br /><br />Mark

 

[Nos4r2]

Re: checking a rectifier

Scotsandy- The Radio Shack franchise used to be owned by Tandy over here and now appear to not exist. There's plenty of Maplins stores over here though -try them... BUT...<br /><br />Honda 250 and 400 Superdream (motorcycles) use a sealed rectifier/regulator unit with a heatsink. Their alternators put out 27vAC at full output so I'd bet you could use one of the reg/rec units and get a decent regulated system on there if it fits inside the case (the unit is approx 3 inches square by an inch deep)and they are easy to find at motorcycle breakers. The wiring should be coonnected as follows:-<br /><br />2 of the 3 yellow wires on the reg/rec should be connected to the 2 AC wires from your alternator.Tape off the 3rd yellow-it's not needed. <br /><br />The GREEN wire is the earth wire-a Honda peculiarity<br /><br />The red and the black wires from the rec/reg unit should be joined-(red is main +ve feed, black is auxiliary +ve feed) and should go to the wire that currently goes to the positive terminal on your dead rectifier.<br /><br />That should give you a nice regulated 14.5v when running.

 

[phatmanmike]

Re: checking a rectifier

i klnow you're an engineer and all, but the work. and no they dont rust away. they are made of alloy. and for a total of 5 bucks, you get a rectifier, connecters and sealer for the connections.

 

[Texasmark]

Re: checking a rectifier

Still say it's risky; but for $5 what have you lost? Other than some time and if the wrong type a potentially shorted alternator or dead battery cause you didn't get enough voltage output to charge it.<br /><br />Now if I was involved in the process (seeing things there) I might think it's a super Idea.<br /><br />My 2c,<br /><br />Mark