charging???

[bruce conway]

not sure if my '87 90HP 3 cyl Mercury is charging. <br /><br />Voltage measured at rectifier is only 12.8 volts at 2500RPM. 12.5 at idle 800RPM.<br /><br />Because the rectifier output goes directly to the battery the battery acts like a regulator<br />(electrical sponge) and may be keeping the voltage low.<br />This engine has no regulator that I can see. I have a volt gauge on the console but <br />it is not very accurate. the gauge also reads the voltage at the end of a long engine harness<br />with relatively small gauge wires. My fish finder (Lowrance) reads the voltage as 12.4 to 12.8 <br />and drops to 11.8 with the lights on and 3500RPM. Again this is at the console.<br />bottom line is I have 3-4 hours use on this (new but used) engine and the battery seems fine.<br />trim works, cranks fine, just worried being stuck far from home.

 

[wilde1j]

Re: charging???

You should read ~ 14.5 v at the battery @ 2500 RPM if charging is taking place. If you check the battery cells w/ a hydrometer, what do you get? Less than fully charged?<br /><br />If you confirm charging is not happening, start checking terminations, starting at the battery. If all are OK, rectifier is probably bad.

 

[oldboat1]

Re: charging???

If the voltage goes up with an increase in rpms, I would think the charging system must be working. An ammeter would be nice -- I don't have one either. <br /><br />I have one of those little hand-held battery testers that indicate the level of charge as a percentage. I find it also works to get an indication of whether the system is charging. If the battery shows 80% charged at rest, and climbs to 100% with the engine running, I know it is charging. It's inexacting -- but there is a variation between engines. My Chrysler Sailor, for example, pushes the needle up into the 100% range very quickly at idle, or a little above. My Evinrude Yachtwin, on the other hand, moves the needle up slower indicating less output. I used the gauge to determine initially that the Evinrude wasn't charging, and then that the system was working again after repair (replaced rectifier). These are 10/9.9 hp motors with 4 to 5 amp systems, but my little tester also works on my inboard (51 amp alternator).<br /><br />But it won't tell you if the system is producing the amperage it is designed to produce, only that it is working (and to some degree, how strong the output is). I guess I've always operated with the notion that outboard charging systems either work or they don't, and don't go much beyond that.<br /><br />(kind of a windy response just to say it sounds like your system is working)

 

[suzukidave]

Re: charging???

Busted rectifiers can sometimes put out an irregular charge. Mine is like that -- it is definitely broken and gives irregular charge, usually 14.5 volts wot, but sometimes lower or none. I live with it since I don't use it to start the boat (rop[e start) and use minimal electrical. If your tach works properly it's a sign the rectifier is working but I would definitely take a hydrometer to the battery and also do an isolation test on the rectifier (check old posts on the subject here for how to do it).

 

[oldboat1]

Re: charging???

The easiest thing to do is probably to fully charge the battery, and then perform the same test you did earlier. With a fully charged battery (and no accessories on), you might see the 14/14.5 volts.<br /><br />You might want to run with two batteries if having a good starting battery is a concern (not unreasonable).

 

[sloopy]

Re: charging???

hey, you might have a dead battery it can suck up voltage and it goes no were!