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Jul 21st, 2025 | | | | Joined: Sep 2019 Posts: 62 'Bolter | | 'Bolter Joined: Sep 2019 Posts: 62 | I just put on a new 6 volt alternator on and connected the shot wire to the battery connection on the starter and the exciter to the hot side of the coil. I went for a decent ride and when I went to restate the battery was down. what is the best way to determine if the alternator is charging? 235 on a 48 Chevy. thanks.
1948 3/4 ton Chevy Pickup
| | | | | Joined: Jan 2016 Posts: 631 'Bolter | | 'Bolter Joined: Jan 2016 Posts: 631 | Measure the voltage at the battery with the engine running..........should be about 8 volts +/- . | | | | | Joined: Sep 2019 Posts: 62 'Bolter | | 'Bolter Joined: Sep 2019 Posts: 62 |
1948 3/4 ton Chevy Pickup
| | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | 8 V is too much. Look for 7.5V against a fully-charged battery. This is vitally important, as the condition of the battery is what determines what the voltage regulator does. Setting or checking regulator settings against a partially-discharged battery is an impossible task.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Nov 2007 Posts: 190 Shop Shark | | Shop Shark Joined: Nov 2007 Posts: 190 | stick a screwdriver or something to the rear bearing on the back of the alternator. If its putting out it will be magnetized and stick.
What kind of alternator is it? Delco 10SI with internal regulator maybe? If so it would have either been built with a 6 volt self exciting regulator that excites when your alternator rpms increase or a 6 volt non-self exciting regulator and you will need an exciter wire to the alternator to excite the regulator. | | | | | Joined: Sep 2013 Posts: 1,288 'Bolter | | 'Bolter Joined: Sep 2013 Posts: 1,288 | Lee, I suspect this thread is fully linked to your thread on you truck not starting with it's new Optima 6 volt battery. My truck had a 6 volt alternator already installed when I bought it. However, due to the slow speed required on a lot of my rural country roads in the winter with headlights on and heater blowing it would not keep the battery charged. Problem was the alternator needed to operate at higher rpm. Well, that wasn't gonna happen and my net searches led me to install a 6 volt taillight bulb under the dash (used a old taillight socket) to act as an exciter. Now if the engine is running no matter how slow, the alternator is charging. No more problems.
I trust someone here can talk about this in detail, if I can find the info detailing exactly how to do the above, I'll post it. It's been so long ago I really don't recall the details.
Good Luck,
RonR
1951 3600 with Clark flatbed, T5, 4.10 rear
1970 340 Duster
1990 5.0 V8 Miata (1990 Mustang Gt Drivetrain)
1964 CJ5
| | | | | Joined: Sep 2013 Posts: 1,288 'Bolter | | 'Bolter Joined: Sep 2013 Posts: 1,288 | OK, this is the thread with details on what made my alternator charge at low rpm. Lots of information in general on the challenges of getting our old truck doing what they should electrically speaking. Good Luck, RonR
1951 3600 with Clark flatbed, T5, 4.10 rear
1970 340 Duster
1990 5.0 V8 Miata (1990 Mustang Gt Drivetrain)
1964 CJ5
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