Time for a new rectifier?

[SoCalBoatGuy]

Hey Guys-

My tachometer has stopped working and I've got 15V DC across my battery with the engine at idle. This jumps up to 16V at about 1500-200 RPM. Is it pretty safe to say it's time for a new rectifier?

'87 50HP 3cyl 0B162136

 

[gm280]

SCBG, Maybe not a rectifier but a regulator. Of course if you have both of those things in one package, then yes, you need a new one. But the rectifier is doing it's job. The regulator isn't though. JMHO

 

[SoCalBoatGuy]

No Title

That's a good point. I guess I thought it was some sort of rectifier/regulator combo. This is my electrical system. It looks to be unregulated.

 

[jimmbo]

It is an unregulated system. 30 yrs ago the tach for my 84 115 quit working, a new rectifier and it was working again. Why the rectifier failed? I hooked the battery up backwards for all of 5 seconds.

 

[SoCalBoatGuy]

I ordered a new rectifier. Should be here Thursday.

 

[gm280]

I ordered a new rectifier. Should be here Thursday.

SCBG,did you test it with a DVM? You can easily test a rectifier with a DVM or even an analog meter to verify it is good or bad. Just wanted to let you know. JMHO

 

[Chris1956]

If the old rectifier is good, like it sounds, I expect a new rectifier will not fix your issue. Check the battery connections and make sure they are clean. Check the rectifier wiring and connections as well. Alternatively, your battery may be near the end of it's life.

​BTW - the charging system is not very powerful (~9A), and your battery is a large load. A little extra voltage will not mean much.....

 

[jimmbo]

I've have had bridge rectifiers test ok using a multimeter with its low current test, but fail when in operation with higher current

 

[SoCalBoatGuy]

Thanks, guys. If the rectifier is OK, what should I check next to get the tach working? The old one used to go bananas above 4500RPM. It eventually stopped working all together. The needle wouldn't go below 1000 RPM, so I figured it had some mechanical problems as well. I put a new one in and all it does drop down from about 1000 RPM to 0 when I turn the key from off to on without starting it. It doesn't move from 0 when the engine is running.

Can I check for AC voltage from the signal to ground?

 

[gm280]

I've have had bridge rectifiers test ok using a multimeter with its low current test, but fail when in operation with higher current

jimmbo, yes that can happen. But there are other tests as well that can verify a good or bad rectifier. If you check the rectifier and if it tests good via a DVM or Volt Ohm analog meter, you can always check the output voltage to see if it is DC. And then you can check it on the AC scale to see if there is a lot of AC component riding the DC voltage. If so, then replace. But part replacing as a trouble shooting method is not a great way to get things running correct again. Very costly too. JMHO

 

[jimmbo]

jimmbo, yes that can happen. But there are other tests as well that can verify a good or bad rectifier. If you check the rectifier and if it tests good via a DVM or Volt Ohm analog meter, you can always check the output voltage to see if it is DC. And then you can check it on the AC scale to see if there is a lot of AC component riding the DC voltage. If so, then replace. But part replacing as a trouble shooting method is not a great way to get things running correct again. Very costly too. JMHO

I used my old Heathkit Oscilloscope back then to see what was coming out of the rectifier

 

[gm280]

I used my old Heathkit Oscilloscope back then to see what was coming out of the rectifier

Yes an O'scope is the best way to verify any rectifier. I didn't mention that because most people don't have one or even access to one and if they did, probably couldn't understand what the signals were showing them. Please don't take that as anything but a common sense statement for most folks not knowing how to interpret O'scope readings. But unless you are into electronics really well, it is merely a fact and certainly not an insult of abilities or lack there of.

I have an old Tektronix 454 dual channel O'scope. I really like it a lot. However, since it takes up a lot of bench space I would like to go to a flat screen O'scope now but since I don't do as much electronic type work, I just can't justify buying another O'scope. JMHO

 

[jimmbo]

I really miss building Heathkits. When they were in business, I was in school and had no money, now they are out of business and I have the money to buy just about every kit they made.:blue::blue:

 

[gm280]

I really miss building Heathkits. When they were in business, I was in school and had no money, now they are out of business and I have the money to buy just about every kit they made.:blue::blue:

That is interesting to hear. I built so many Heathkit, I think they just sent me every new kit when the come out with them. TV, Stereos, Speakers, Tachometers, Radio Control Equipment, Meters, and the list goes on and on. In fact I presently have three of Heathkit Guitar Amplifiers to refurbish. Each one was one of their offerings of Guitar Amps. One single 12" speaker amp, a dual speaker amp and their top of the line combo head unit amp. I buy old Heathkits units off EBay and then rebuild them to like new. There is really nothing you can't repair with any Heathkit. They rarely used special parts for their designs. I still have a lot of Heathkits sitting around and they still work too.

 

[SoCalBoatGuy]

Well, you guys were right. Buying new parts is not a good way to troubleshoot stuff. It turns out the problem was that the wiring harness was loose and not plugged in all the way at the engine. Tachometer is working now!

 

[gm280]

Well, you guys were right. Buying new parts is not a good way to troubleshoot stuff. It turns out the problem was that the wiring harness was loose and not plugged in all the way at the engine. Tachometer is working now!

Well at least now you've learned a lesson in troubleshooting. And that is a good thing.