30HP Johnson isn't charging the battery

[Vic.S]

Just a couple of points

The resistance tests on the stator wont detect shorted turns.
There may be some testing you can do described in the "Troubleshooting Guide" on the CDI Electronics website.

If the battery is in a lowish state of charge it'll take a while to get the volts up , even at WOT

Its worth charging the battery fully off the boat with a decent charger. Charge it until it still reads 12?7 ish volts 12 hours after coming off charge.

 

[atistang]

Just a couple of points

The resistance tests on the stator wont detect shorted turns.
There may be some testing you can do described in the "Troubleshooting Guide" on the CDI Electronics website.

If the battery is in a lowish state of charge it'll take a while to get the volts up , even at WOT

Its worth charging the battery fully off the boat with a decent charger. Charge it until it still reads 12?7 ish volts 12 hours after coming off charge.

I charged the battery pretty good then trickle charged it for a week before starting the boat.

also I just got back from the parts store, the battery tested good. I'll look into the CDI trouble shooting

 

[atistang]

i'll have to retest the stator, that CDI trouble shooting guide gave me some actual specs to test the stator AC voltage to

 

[F_R]

Have you considered the possibility that there may be something putting a load on the battery while it is running? The alternator puts out a maximum of about five amps. If there is a load of 6 amps going out of the battery, the result is a negative one amp. In other words you are losing ground. The motor itself doesn't require any electricity from the battery in order to run, but there may be something else turned on that is drawing current, like bilge pump, radio, cooler, etc. Or even a short in the wiring.

The real definitive way of testing the alternator for output is a lo reading ammeter connected between the rectifier and battery. If it reads current flow (amps) the alternator is working.

 

[atistang]

Have you considered the possibility that there may be something putting a load on the battery while it is running? The alternator puts out a maximum of about five amps. If there is a load of 6 amps going out of the battery, the result is a negative one amp. In other words you are losing ground. The motor itself doesn't require any electricity from the battery in order to run, but there may be something else turned on that is drawing current, like bilge pump, radio, cooler, etc. Or even a short in the wiring.

The real definitive way of testing the alternator for output is a lo reading ammeter connected between the rectifier and battery. If it reads current flow (amps) the alternator is working.

If this is the case, wouldn't I be able to turn the key on and watch the battery voltage drop over the course of 5 - 10 mins?

 

[atistang]

I figured out where the problem is

I put my leads on the battery and turned accessories on one by one and waited one min watching the battery voltage. The only one that drained the battery down any in that minute was the stern light, In one minute it went from 12.8 to 12.65.

I'm just going to buy a new stern light and run new wiring when I install it.

I also discovered that my fuel pump housing is cracked :facepalm:

 

[Fed]

Firstly a correction...

Did you properly test the rectifier yet?
The stator is very robust compared to the rectifier.
Rectifier test is with an ohmmeter, a wild guess would be about 1.5 Ohms between the yellows while disconnected and no shorts to ground.
(Happy to be corrected on this)

Where I said Rectifier I should Have said Stator.

I'd start again & retest the stator, rectifier & all connections because I don't believe it's charging properly.

 

[nphilbro]

If your lost a ground them I'd be 99% sure you blew a diode or two in the rectifier. Good batteries will recover voltage on their own. Small chance you're getting a half wave rectification but still unlikely. If it's charging at all you should see a substantial increase in voltage at the battery terminals when the motor is running. The regulator shunts or opens (depending on stator and R/R type) voltage over 14.4v and kicks on around 13.3v. If you start with a fully charged and rested battery the terminal voltage should jump over 13v very quickly even at 1500rpm. Yeah can disconnect the yellow stator wires (keep them from grounding) and turn the multi to AC voltage - 200v and you'll likely get a voltage reading around 19-28V with each meter probe connected to one yellow wire. Then rectifier just converts it to DC and the regulator controls the min/max allowed to hit the battery. The new ones use SCRs (silicon controlled rectifiers) that are fast switching to turn the phase on or off, sending current to the battery or shunting to ground. The flywheel magneto system will generate voltage regardless of load so the regulators get very hot.

 

[nphilbro]

No Title

Here's the schematic depending on whether you have a two or three phase stator. I built my own after frying a few at $250 a shot. Cooling was a problem on the motor so I had to bring the AC stator leads into the boat and rectify/regulate it there. Note: this is not like a car alternator so there's no center ground.

 

[Fed]

No regulator on this one so no need for any load testing.
Do it all with an ohmmeter.