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PostPosted: Sat Apr 13, 2024 1:00 pm 
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Supercharged
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Joined: Wed Oct 12, 2005 9:00 pm
Posts: 2817
Location: kankakee IL
Car Model: 80 volare, 78 fury 2 dr, 85 D150
Not terrible, at the high end of the "ok" range, but temperature, current state of charge, and current load on battery should cause that number to vary a bit. If you have access to an amprobe or n old style alternator/battery tester like a vat40 and see what kind of amps you're getting both just idling and under a load.
Run it a bit and see what it does.
And you won't get any more amps from it than what it calls for at any time.


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PostPosted: Sun Apr 14, 2024 12:15 pm 
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4 BBL ''Hyper-Pak''

Joined: Thu Nov 09, 2023 5:12 am
Posts: 32
Location: Hudson Valley, NY
Car Model: 1964 Dart 270 4-Door
SpaceFrank wrote:
The battery is currently ~12.5 V with the key off. Voltage at the battery goes up to about 13.8 V after starting the engine and idling, but when you rev it up the voltage increases to about 14.5 V, and it stays there until you turn the engine off. This is definitely better than it was with the old regulator, but I'm wondering if I need to adjust the screw on the back.

What do y'all think?

Based solely on experience and a bit of internet reading over the years (there are reliable sites showing ideal float voltages for different types of lead-acid batteries), but not on any professional expertise, I would say that you are just a bit high.

"Flooded" lead-acid batteries have different ideal voltages from AGM batteries and from fancier (Odyssey) batteries.
I use an adjustable regulator on my motorcycle with an AGM, and generally go for about 14.2v, which is the highest I think I'd venture as a set point.
Theoretically wet-cells should sit somewhere between 13.6v and about 14v, if I recall.

The 14.5v is unlikely to cause any problems just doing a little bit of local driving (and may be good if the car sits for long period in between), but if you take any highway trips in hot weather, you could hurt your battery.

If you've got an adjustable regulator, I'd just turn it down half a volt (Use that ground jumper, as recommended earlier).

Your volt meter is accurate, and you're measuring at the battery, right?

- Eric


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PostPosted: Sun Apr 14, 2024 1:29 pm 
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Joined: Thu Oct 31, 2002 5:39 pm
Posts: 24254
Location: North America
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Light bulb lifespan changes exponentially to the power -13 (negative 13) with input voltage. Let's do some math.

Take a bulb rated 500 hours at 12.8 volts. Put it in that vehicle. We probably aren't going to run it at 14.5 volts, because there's going to be some voltage drop along the wires and switch contacts, but the bulb could easily see 13.8 volts.

(13.8 ÷ 12.8)^-13 = 0.376. Our bulb fed at 13.8v will lose over 62 per cent of its rated lifespan.
0.376 × 500 = 188 hours.

Voltage regulators are temperature-compensated, too, because a cold battery has higher internal resistance than a warm one, so it needs higher charging voltage. What's this 14.5v going to turn into next winter? I had a car ('91 Dodge Spirit R/T) with the voltage regulator built into the engine control module. Its temperature compensation was faulty, such that when it got cold out and the car had been sitting a couple hours so there was no heat in the engine bay, it drove charge voltage as high as mid 15s to low 16s. If I didn't let the car run long enough to warm things up underhood a little so the voltage regulator would back off a bit, turning on the headlamps resulted in two bright flashes and no more light from up front until I put in new bulbs; the dead ones had little globs of tungsten at the filament ends. All caused by the overvoltage.

Okeh, a turn signal bulb is easy to change, and you might appreciate the increased headlight brightness (the exponent for output is 3.4, so running a 12.8v bulb at 13.8v gives 29% more light). But think of the bulbs that are a PITA to change (dashboard…) and while you're in that neighbourhood, spare a thought for other fragile, voltage-sensitive components like the instrument cluster voltage regulator.

In reasonably mild ambient temperatures, and with a battery in good health, 14.5v is pushing it. You might want to do some deeper digging. Try putting a hot hairdryer on the voltage regulator and watch what (if anything) happens to the line voltage with the engine at a fast voltage. Try the same thing with an upside-down canned-air duster in place of the hairdryer.

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Last edited by SlantSixDan on Tue Apr 16, 2024 7:23 pm, edited 1 time in total.

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PostPosted: Tue Apr 16, 2024 7:10 pm 
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Turbo EFI
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Joined: Fri Dec 30, 2005 2:49 pm
Posts: 1154
Location: Houston, TX
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Thanks for the replies, y'all! Especially Dan with the screenshot of what I assume is a later FSM. Yes, my reported voltages are all at the battery terminals.

I'll do some more troubleshooting. If I need to adjust the screw on the back of the regulator, which way is which? It didn't come with instructions.

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