Tach Pulse

[bobandpeni]

Re: Tach Pulse

Hey!<br /><br />Now you guys are making me think I'm gonna need an ammeter!!! <br /><br />Next thing I'll be out buying an oil pressure guage for my 2 cycle!<br /><br />Joking aside, you can never have too many instruments and I've been debating putting voltmeter, ammeter, tach, etc. I'd just like to run my boat once in a while instead of working on it all the time. I did find it amusing that there is no discharge idiot light or ammeter on this boat. I've always prefered voltmeters over ammeters, so I'll probably go that way shortly.<br /><br />If it is possible that there is something else causing my tach to read incorrectly I sure would appreciate any ideas.<br /><br />Thanks all!!!

 

[Basscat 1]

Re: Tach Pulse

Just crank the boat up and bring the idle up to what you think 2500-3000 rpms should sound like, and check your charging using a multimeter. It should read 13.0 volts or higher at the battery.<br />If it is, that will eliminate the rectifier.<br /><br />Bob, what 2500 rpms sound like and 5000 plus is totally different. Let your ears do the math as to weather your tach is working or not.<br />Speedometer's on boats are not very accurate, but GPS is.

 

[Boilermaker]

Re: Tach Pulse

I'm no expert on outboards, but the rectifier is a bridge rectifier>>>both input sides come from the stator (charging) and ONE COULD be bad and still provide 13volts, but would cause a false reading on his tach. I'm NOT saying that is the case>>>its just a possibility. Easy to check with a $10 RadioShack multimeter.

 

[mjash]

Re: Tach Pulse

All the rectifier is doing is letting current flow one way..It's flowing because his tach is working. If one of the diodes was open...It wouldn't flow. If shorted you would get reverse current that would smoke something else. I think anyway! Pretty sure it isn't the rectifier though.

 

[bobandpeni]

Re: Tach Pulse

Boilermaker,<br />I would like to examine all possibilities before I go and buy a new tach. I'd really be bummed if I spent the money for a new tach and it did exactly the same thing the the present one does. <br /><br />That said, I've got the multimeter but not sure where to start looking for the rectifier.<br /><br />Any suggestions?<br /><br />Thanks

 

[Tacklewasher]

Re: Tach Pulse

Just curious. I had one wire busted on the rectifier and it was the wire that the tach connects to (I think yel/gry). The other wire was fine. My tach didn't work at all.<br /><br />Would my tach have worked if the other wire was busted?

 

[mjash]

Re: Tach Pulse

I think it would....I believe that one wire is for the tach and the other is for the battery charging. I think if one leg was bad and you switched them you would swap the problem.

 

[Basscat 1]

Re: Tach Pulse

Heres a hint. The rectifier is either good or bad. <br /><br />

posted July 26, 2005 08:25 PM<br />--------------------------------------------------------------------------------<br /> Just crank the boat up and bring the idle up to what you think 2500-3000 rpms should sound like, and check your charging using a multimeter. It should read 13.0 volts or higher at the battery.<br />If it is, that will eliminate the rectifier.<br />

 

[Boilermaker]

Re: Tach Pulse

I'm NOT saying that this is what is wrong with your tach...but here is an electrical schematic of a bridge rectifier<br />

<br /> <br />This is a bridge rectifier....just like on your engine. The stator would be the the transformer coils to the left (AC input), the output would be on the right side (where the capacitor and load resistor are in this picture). The bridge rectifier is made up of four diodes that can only conduct in one direction NORMALLY.<br /><br />

<br />This shows the flow thru 1 half of the AC wave cycle. <br />If one side of the bridge was bad>>>open or shorted...1/2 the ac pulse should still pass thru the bridge. IF it was shorted...it should contain a pulsed DC wave and an AC wave riding ontop...a digital volt meter set to DC volts would ONLY read the DC waveform & could show a charging voltage as normal.<br />AGAIN ... I am not saying that this IS what is wrong...just a possability.<br />

 

[Boilermaker]

Re: Tach Pulse

BOTH legs from the stator provide AC pulses, just like a transformer would. IT is NOT one leg to charge & one leg for the tach...<br /><br />A bad ground at the Rectifier could also cause faulty readings. The first thing to do would be to remove the rectifier and clean its grounding points.<br /> To TEST the rectifier, ground one ohmmeter test lead to the rectifier case and connect the other lead to the yellow/gray rectifier lead. NOTE the meter reading. Reverse the test leads and note the reading. One reading should be ZERO, and the other should be INFINITY.>>if both readings are close to the same...that side of the rectifier is bad.<br />REPEAT the test with the YELLOW wire & rectifier case. <br />Then with the RED wire and Yellow/Gray rectifier leads. <br />Then repeat with the Red & the Yellow rectifier leads.<br />ALL should read close to ZERO resistance in one direction (forward current flow)and INFINITY in the opposite (reversed current flow).<br /> >>>It is a lot simpler & quicker to do the test then to discribe it! <br /> BE SURE YOUR GROUNDING AT THE RECTIFIER CASE TO THE ENGINE BLOCK IS A GOOD ELECTRICAL CONNECTION!<br />Good Luck <br /><br /> <br />

 

[ddbyrd3]

Re: Tach Pulse

That was VERY educational........

 

[Basscat 1]

Re: Tach Pulse

IF it was shorted...it should contain a pulsed DC wave and an AC wave riding ontop...a digital volt meter set to DC volts would ONLY read the DC waveform & could show a charging voltage as normal.

Has anybody ever seen a rectifier that wasnt completly fried, especially since it is all contained in one housing? Possible, but doubtful. Besides he says his tach does read, I would bet the engine charges too.<br />Do a rectifier search, and you will find the Joe Reeves method of testing the rectifier.

 

[Boilermaker]

Re: Tach Pulse

I think its still worth checking>>>doesn't cost anything to check. I bet you have seen bad grounds causing problems??? And bad rectifiers giving Tach problems>>>> Right???<br />And yes ...I have seen rectifiers that are incased in one unit, that have 1 bad side>>>thats why I suggested checking.<br /> Its just a suggestion, not a challenge of your outboard expertise.....

 

[Basscat 1]

Re: Tach Pulse

Its just a suggestion, not a challenge of your outboard expertise.....

Trust me Im no expert. I just use common sense.<br />22 years mechanic, its not rocket science.

 

[Boilermaker]

Re: Tach Pulse

Basscat1 ... no problems <br />I am an Operating Engineer for over 30 years, and an electronics tech. as a hobbie for over 35 years>>>> I studied electronics in school for 4 years and I hold an Extra Class Amature Radio License from the FCC.<br /> I see a lot of weired stuff in electronics...stuff you would think logicly couldn't happen...but it does.<br />I was just trying to present an idea to check out. Something outside the box that is easy to check one way or the other. I still think its worth checking. And some of the rigs I see around here....IT IS ROCKET SCIENCE!!!<br />

 

[mfinucan@sympatico.ca]

Re: Tach Pulse

Easy boys, you get away from what we are here for, help, not to put each other down. All advice is good advice.

 

[jahughes]

Re: Tach Pulse

Great exchange IMO, this is the kind of info that can be priceless for today and for the future (for those of us who use the search feature)!

 

[Basscat 1]

Re: Tach Pulse

Well I know who to call when I need help with my radio.

 

[Boilermaker]

Re: Tach Pulse

ANYTIME Brother!!!<br /> Its all in good fun & I have respect for Basscat1...its all about the exchange of ideas (just as we have done)!<br />

 

[Boilermaker]

Re: Tach Pulse

I just re-read the whole thread, and also looked in TELEFLEX website for tech setups. <br /> Is it possable that Bob Kopicki's 12 pole stator is a 10 pole stator with 2 ignition pick-up coils being counted by him as alternator coils???<br /> Teleflex site says omc less then 70 hp is 10 pole, and should have tach set at 5P.<br /><br />Also, Bob K, if you turn your ignition switch to the ON position, without starting the engine>>>does your tach read zero???