Charging system 115 HP Johnson 1981

[RickN]

My charging system doesn't appear to be working properly and wanted to know if anyone has any ideas on what to check?<br />I took a volt meter and checked my voltage before starting my motor and it was 12.5 volts. I ran the boat 1000 rpms with no change in voltage at the battery, ran it around 3000 rpms and was reading 12.5 to 13 volts at the battery and at 5500 rpms it was running around 13.5 to 14 volts. I have a brand new 100 amp battery, so it usually starts, but if I shut it off and raise the power tilt up and down, the starter clicks as it is not getting the amps to turn the motor over. I brought an extra battery and hook it up and it kicks right over. Thanks in advance for the assistance

 

[Silvertip]

Re: Charging system 115 HP Johnson 1981

It appears the charging system is working but you should remove and thoroughly clean the battery cables and terminals (both ends). Inspect the terminal ends so make sure there is no corrosion where the cable enters the terminal. Any resistance here will drop system voltage especially when starting. You may also be due for a new battery. Yes -- it may measure 12.6 volts but so will six flashlight batteries. If the engine starts fine when jumping, either the cables are bad or the battery is weak.

 

[Silvertip]

Re: Charging system 115 HP Johnson 1981

Sorry -- I missed the "new battery". However, even new batteries can fail.

 

[RickN]

Re: Charging system 115 HP Johnson 1981

I replaced the positive cable and put a gold plated termal connector on the battery. I cleaned the negative cable and it appears to be good. But will run a ohms test on it to see what the resistance is. I am with you on the cables. <br />Should the voltage output be consistant at any RPM @ approx. 13 to 14 volts on the charging system? I realize the higher the RPM the more voltage output, but the voltage regulator should provide a constant charge. I am leaning towards changing the rectifier as a test I did on my tach working and then not working indicated a possible failure on that component. Any thoughts about switching out the Rectifier. It is a 35 dollar item..

 

[MGuckin]

Re: Charging system 115 HP Johnson 1981

Have you checked the rectifier before you replace it?<br />Disconnect the rectifier leads where they hook up,(note location). 1 lead from ohm meter to 1 wire, other to ground, note the reading than switch leads should read zero one way and infinity the other. Do the same with the other wire. If the readings are not zero one way and infinity the other, change the rectifier.

 

[chuckz]

Re: Charging system 115 HP Johnson 1981

Charging systems actually rely on current for charging. The voltmeter is an indicator but doesn't tell you the full story. The best way to tell what is going on is to check the current with an ammeter. I would guess that you should have 10 - 15 amps charge current available. Install the ammeter, start the engine and turn on a load. If you don't get 10-15 amps, depending on what your system is rated at, start troubleshooting. If you get the right output current, you have a bad battery.<br /><br />You can substitude a Radio Shack bridge rectifier in place of the OEM part. Use the search feature to find additional info in these forums. There is also a detailed step by step procedure to check your bridge rectifier.<br /><br />Just re-read your post. The tach not working can be either the stator or the rectifier. Again use the search feature to find the step by step instructions for testing the bridge rectifier.

 

[Sherman]

Re: Charging system 115 HP Johnson 1981

Make sure the rectifier is grounded by cleaning mounting area. This part has an active ground requirement.