Merc 25hp Rectifier

[basserman]

G'Day all
i was hopeing that our motor gurus could help me out with a small problem

i have a Merc 25hp 2st and i have a feeling the the retifier isn't working
first what is the best way to test if it is working or not
second this is what i have done so far
first i left the battery on and tested with the test light
had earth on the earth lead and when i put pos on pos not a problem and then on the top right i had a current and when reved become stronger however nothing on the top left

then i took the battery off and the top two was the same however i now got nothing comeing from the positve lead

what should i do and what do you think is up with it

p.s. i have a pull start and the battery only runs my electronics

[basserman]

chargeing coil but thats fine as i said i have a feed that gets stronger with more revs

[NQCairns]

Hi Basserman, sorry dont know the mercs, but generically does your engine have a regulator downstream of the rectifier? if you disconnected the battery and run it, can do bad things to the charge circuit. Are there any charging volts at the battery Like 13 to 16V? Best to use a fairly drained battery for the test so the system tries harder and it is easier to get a reading.

[basserman]

thought i could reley on you NQ thanks for your input

i only started the motor for less than a min with the battery off to test the outgoing however it is straght wires to the battery anyway

went and asked on of my mates in the marine industry and he said that the 25 would only be putting out around 1amp and the test light probly wouldn't show it up and my best bet is to get a volt meter and put it on

he douts anything is wrong with it and more than liky the battery is just on it's way out from overuse
(makes sense it runs abit of electronics with only a small trickly charge going back in) ;)

[Oldyella]

While the motor is running, you should have around 14.7 volts at the battery as tested with a voltmeter.When turned off the battery should read around 12.4 -12.7 volts. Regulator and rectifier are the same thing on the Mercs.

[Oldyella]

Don't disconnect the battery with the motor running, as this will damage the rectifier.

[NQCairns]

Hi again Basserman, not sure about reliable but I do have a big net mouth :P
From what RD says if the regulator is combined then volts at the battery while running shouldn't be above 15 preferably around half a volt less.

If it is rectifier only then even 16V is common. If your system puts out only 1 amp I cannot see a need for regulation, doesn't mean you dont have regulator.

I would suspect a system with around 4-6 amps because a lot of unregulated small engines put that out, 1 amp is virtually a waste of the engines time.
.
The bad news is that if you did remove the leads while running the odds are better than even that the regulator/rectifier is now blown.

To find out for sure use a known good battery but not fully charged and check the voltage across the battery terminals (say 11.5). Then check volts again connected to the running engine, because you are using a partly discharged battery you can do the output test on the muffs without the need to rev it much past idle to get a good charge rate from the system at the battery for comparison. Best of luck with it. cheers nq

[basserman]

hmm yeh i think i was on the right though at the start and that it was alread blown
been havening alot of trouble keeping charge in the battery of lateand going by the volt meter on the sounder while sitting at 8volt when running flat out for over half a hour all i can get it up to was 8.2 volts

think i may just go order a new one luckly they aren't that dear

on the other hand got my heads from my yammy 115 back from the engine world today and was told they are now good but took 5 shave to get them square as they were a bit warped now my attionton is on the block to make sure that is still true and square (still runs fine and no scoreing in the pots)
dam it is a stupid man to own one boat and i must be insaine to own two ;D