alt not charging batt. 8.5v at idle

davbra1171

Recruit
Joined
Jun 22, 2007
Messages
3
I have a 91, tohatsu 70. my battery wont charge, I'm getting 8.5v at idle and around 15v at 3/4 throttle. what should I be getting? checked all wires/connections, look good.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: alt not charging batt. 8.5v at idle

8.5 volts at idle says the battery is not charged. It should read 12.6 or thereabouts with the engine off. 15+ volts at 3/4 throttle is pretty normal for an engine with an unregulated charging system. Don't know if your Tohatsu has a regulator or not. What may be going on is that you actually have a battery that this on the way to battery heaven. Have it load tested at any auto parts store. It may also be that your voltmeter is not reading correctly. A battery that is fully charged should read 12.6 volts whether the charging system is working or not. It should not immediately drop to 8.5 volts.
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: alt not charging batt. 8.5v at idle

I agree 8.5 volts normally says the battery has 2 bad cells. So has 4 good cells and 2 bad cells. I would fully charge the battery with a battery charger then let it sit for a couple of hours then check the battery voltage before starting. It should be 12.6 volts. 6 cells at 2.1 volts per cell or 12.6 volts.
Turn on the navigation lights for a light load and check voltage before starting.

Did you keep your battery charged over winter and spring?
 

davbra1171

Recruit
Joined
Jun 22, 2007
Messages
3
Re: alt not charging batt. 8.5v at idle

sorry, I didn't say that I'm not checking the battery, im checking the cable with the battery disconnected. battery is good, thanks for the replies
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: alt not charging batt. 8.5v at idle

I would never check with the battery not connected.
With an alternator most of the time it will blow tha alternator.
Outboards many times do not use alternators but instead stators.
Better and safer to check at the battery with the motor connected.
 
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