Rectifier Testing - Yamaha 9.9 4 Stroke

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priestp

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Whilst wondering why my batteries were slowly discharging, I checked the output line of the regulator on my 1989 Yamaha 9.9 4Stroke and only found 6V. My assumption is that the rectifier is u/s but I can't find anything anywhere on how to really test it. Any advice from an boat electrics guru would be welcomed.

Also, if it is defective, apart from paying top-whack Yamaha prices, can someone advise where I might find a cheaper substitute part (if it's not a false economy)

Thanks
 
As I understand it - its basically a set of diodes to 'cut' one direction of the AC current created by the outboard.

I know one guy who used a rectifier (from an old small inboard boat engine which had been removed) that was still bulkhead mounted .... he fed the outboard supply to that and voila got DC charging out ....

Maybe a chat with a local electrician / Maplins guy may provide a good alternative.
 
Depends on whether it is full wave or half wave. Half wave will have only one diode but full wave will have two! if you are getting 6volts I would think it is full wave and and one diode has gone. Don't know the construction of the rectifier, but, you should have two connections marked with a sine wave, like an S on its side (ac input). There should be another two connections marked + & - .
(dc output). If you put a multimeter, set to OHMS, across one of the input and one of the output terminals you should get a high reading, or a low reading. Reverse the meter leads and the reading should also reverse. They should be opposite for each Pair of I/O terminals.
Don't forget to disconnect the rectfier before testing, and mark the connections to make sure you get them back in the right order.
 
On my Honda it must be connected to the battery for the output to be present, auspect the battery is engergising the field coils. So best bet is to test the output of the outboard by measurng the battery voltage. ie does it go up when the outboard is running and what to?

I find that to get up to around 13.5V I have to rev my outboad like crazy way more than I would normally use when pushing the boat along.

Gave up on trying to chage from outboard and bought a 10w solar panel instead.
 
Thanks, will disconnect tomorrow and do some more investigation. From what I can see and from what you guys have told me I think it will be a full wave 4 diode unit and my guess is that one diode is open circuit..
thnks
 
If your rectifier is a full wave rectifier (aka bridge rectifier) then it will have 4 connections; two being the AC input the other two being the DC output. It is possible that the negative side of the output is the case as it will probably be "grounded".

If you use a digital multimeter use the diode test range rather than a resistance range as the latter do not necessarily work for diode testing.

From each of the input connections in turn you should get a circuit (lowish reading) to one of the ouput connections but not to the other until you reverse the meter then you will get a circuit to the other but not to the first. If you get a reading both ways then that diode is shorted but if you don't get a reading either way then that diode is open circuited.

A word of caution not all outboard rectifiers are simple bridge rectifiers. The Evinrude/ Johnson ones are more or less full wave 3 phase ones having three input wires, a positive DC output wire with the case being the negative. The testing is the same though just one extra input wire to take into account. There are six diodes inside as opposed to four.

All this assumes that the O/B has just a lighting/charging coil and a rectifier rather than a "proper" alternator with a regulated output as that will involve field diodes and a regulator as well, just like a car alternator.
 
I think one of the problems with many small outboards is that the lighting coil is designed to be used directly to lights without rectifier or regulator so voltage when used with a rectifier is not enough for real charging. My 6HP Johnson give .7 amp into a battery when used with a bridge rectifier.
Yours may be more sophisticated of course. You mention regulator. Does it really have a regulator.
Presumably it has charged better in the past. If you can't be sure it has never done better in the past it may simply be running at it's best. On the other hand it may have a fault.
To connect a digital voltmeter across the output in lieu of a battery is a sure source of confusion. Digital VM can sniff a voltage through large resistance giving very confusing results. Further the waveform will be rising from zero to a peak and then falling to zero again each AC cycle so Digital VM sample the volts at a small instant of time not necesarily giving an average. A moving coil analogue meter is a bit more honest in this way.
The only way to test for performance of the system is current into the battery.
Given that it sounds like it is not giving anything. Then the most likely problem is in corroded connections. You should be able to measure resistance of the coils under the flywheel. There should be low resistance less than 5 ohms between any of the wires concerned.
If that is ok and you are convinced it is the rectifier (regulator) You could simly buy another bridge recifier for a quid or so from Maplins RS etc and substitute. AC to 2 terminals and +&- from the other 2. This will be s system without regulator and use an ampmeter to measure actual production. So it is all a bit difficult not knowing your particular system.
good luck olewill
 
Thanks for your help everyone. Disconnected and metered the unit (which is has 4 diodes) and one of the diodes is duff - short in both directions.

Time for a new one...

Peter
 
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