Rectifer test ??

[Way2Fast]

What is the correct procedure to check a rectifer (16 amp charging system, 2001 drag motor) with a multimeter? Thanks, Richard

[Balzy]

you swap red and black leads and terminals and follow the flow chart in the manual. don't have it with me and would be a lot to type. best you get a manual or have your local dealer copy the page for you. pretty simple test if you have the page.

[Talon2.5]

hey richard, this is the first chart of the rectifier ya use with the chart in my next post

skip

[Talon2.5]

ok now the flowchart to follow

hope it helps, skip

[Balzy]

Tols ya it would be a lot of typing.....

Like I have said before, gotta love this board !!!!!!

[Talon2.5]

ya this board is a great tool for us all to share knowledge balzy, it's great aint it!!!

skip

[Way2Fast]

Thanks guys. This board really is great. I only have one question before I head down into the garage to do the rectifier test. I have a digital gauge. When I turn it on to the Rx1000 ohmmeter scale, what should the gauge read when Continuity is indicated ? And what should the reading be if No Continuity is indicated?? I had the boat at a friends marina yesterday and he tested the rectifier and the gauge either read "1" or "0" no matter how he connecter it to the rectifier terminals. He said the rectifier was no good, then he took 2 new rectifiers from his stock and both tested exactly the same way!! I even tried 2 different gauges...same results ?? This electrical stuff is beyond me.

[JSQB]

I searched the internet for "bridge rectifier schematic" and finally found a GIF. The bridge rectifier consists of 4 diodes. A diode is an electronic device that allows electrical current to flow in only one direction (like a check valve). If it's not blowed up. The way the diodes are connected is in the GIF. Your alternator is connected on the top and bottom (where you see coils of a transformer depicted) and the battery connects to the + and - on the left and right side.
the grey triangle thingys are the diodes. With the rectifier disconnected from everything you want to test each diode to see if it has continuity one way and blocks the other.
When diodes fail (get broken) they either start conducting both ways or quit conducting altogether.
Back to the picture...current should flow from the "fat end of the diode to the skinny end. If it looked like this --|>|-- then current should flow from left to right.
As for your meter...turn it on and set it up as directed. With the leads touching it should read about 0 (this means current is flowing) and with them apart it may flash or read all nines or something like that (no current flow).
Electronic voltmeters today use very small currents to measure resistance. I like to use the lowest scale I can (like R X 1) or a continuity tester especially with these camparitively large diodes.
You can buy individual diodes from Radio Shack to practice testing with your voltmeter. An individual diode has a wire out each end of a small plastic cylinder. One end of the cylinder has a (usually white) band painted on it. The banded end coincides with the right end of the primitive drawing in the text above.
Class over.

[JSQB]

Second try to attach image:

[mercrazy]

if you only want to know if it's working just check the battery voltage with the switch on and engine not running. then start the engine and check the voltage again. if it's higher with the engine running, it's getting juice from somewhere and your rectifier is probably ok. you won't have to worry about the 1's and 0's that way.
you need to charge your start battery. it's hard for the 16amp system to keep it charged unless you do a lot of long distance running.
i charge mine 1st thing when i get back home and at least once a week.

[Jay Smith]

Mercrazy's test will work as will the other way Balsy was talking about , also remember if your tac is acting up ( reading low,high, backwards ) thats a tell tale sign the rectifier is went south too . When I raced I took 6 of them to the races always came home with none left it is a cheap piece that goes bad often. ( about $25.00 )

Jay @ JSRE

[popeyebob]

Most digital volt meter's have a diode test position on them. It look's like a little arrow pointing at a l. --->l---. Use that setting if you have it.No terminal's should show a short(0) between them.
Also, the mounting strap/stud is the negitive terminal, and there should be no short's to it either.

[JSQB]

Let's see 6 X$ 25 = lots
I don't know where the rectifier moiunts but it must be getting too hot or be under sized. You can buy rectifiers at least as big as 50 amps and individual diodes way more than that. I'd think you could save many $ with a permanent fix.

[DBK]

Mercrazy, Balzy, Jay Smith:
Also have charging system problems I think. '94 2.5 EFI. Have the stator test procedure...not finished with it yet. Before I gutted my engine it would read 12.6 V on the battery at rest and 12.6 V with it running....including taking it up to about 6000. Doesn;t move a bit. Doesn;t seem right. Just printed the rectifier test procedure and will run through that as well. Shouldn't the battery V go to at least 13 V with the engine running? Even with a wimpy ass 16 or 18 Amp charging system?

Balzy: How are those Z-pistons working out for you? Got a decision to make with my engine.....all holes presently empty. # 3 and #5 were @ 50%...no wonder it wouldn;t start or idle worth a ****....still ran 90 though. Old rings are worn right through the chamfer...mostly over the exhaust port....sharp as a razor. Holes look good.....got it in time. Got a decision to make. New Z-pistons w/rings or re-ring and re-bearing my Mahles and hope for the best. RP told me you are running a new set of Z-pistons and he has had zero failures on about 6 or 8 motors in the field vs about 50:50 coin flip with the Wisco****. Also some other guy who ran Eagle River w/you has new Z-piston 2.5 I guess. Comments?
Dyno Don
Hastings MN
Allison w/empty 2.5

[Balzy]

I have now, they are in great shape. I'm not sure what RP meant by Z-pistons or when you talked to him, but the ones I have now are the new 2002 Merc 2 ring pistons. Side pins but the rings captures it. If it came loose it could not get out. So far so good. About 35 to 40 hours on them and just took a peek at #5 and #6 when I had the powerhead off last week and the rings look great. The whole surface is still gold. These are the Tit-Nite rings with the newer poly side coating. I am also running Merc performance blend at 32/1 this year. Amsoil at 40/1 last year. That might be why they look so good right now too, although 40 hours is not that much time.:cool:

[Cp]

.....will usually result in EXCESSIVE voltage (14-18v) when charging. No change in the voltage when you should be charging sounds like something bad under that flywheel. Cp

[sosmerc]

Which particular Amsoil were you running at 40:1? They have 3 different 2 stroke oils and I'm curious as to which you might have been using...and your thoughts about why you switched to Merc's Performance Blend.
Thanks.

[Way2Fast]

Yesterday I tested my rectifier as per the diagrams provided by Talon2.5 With the multimeter in the diode ( -->I-- ) position everything checked out OK as per the left branch of the diagram. I assume the rectifier is OK. The reason I wanted to check it was because the charging system on my 2001 drag does not appear to be working. Voltage is 12.6 with motor off and 11 volts with motor running at idle up to 5000rpm+ Next I checked the stator as per instructions given me by MERCMAN. Using an ohm meter set at r x 2K (he said to set it at r x 100 but my meter does not have such a setting) the red to black and red/white to black both came in at .071 which I think is OK. When I tested the blue and red leads they read .548 the blue/white and red/white read .557 MERCMAN said these readings should be 3900-4400@r x 100 I don't know if the reading difference was caused by my meter not having a r x 100 scale?? Or is the stator no good? Are there any other stator tests? Thanks, Richard

[Tranzman]

I'm wondering if anyones experiencing their engines shutting down revs due to the rectifiers or stators being faulty? I have a twin rig that dropped from 8,000 rpm to 4,000rpm then picked up to 6,000 rpm and dropped again to 4,000 rpm. Did the rectifier test and they seam OK. Will now do the charging test. I'm running 2 x S3000 motors. Why do both drop off?

[wrechin2]

You would probably do better starting your own thread. Not many people are going to read a post that is 8 years old. JMO....... If they see s3000 motors losing rpm's , they are alot who are going to read and be able to help.

[YELLOWSS]

Wow!!!