Charging issue?

[elorenzof]

Good morning,

I have a 70 C10 which i rebuilt from the ground up. I have dakota digital gauges, and Sniper 2 with the Hyperspark ignition. I've only about 30 miles on the engine, it's a 383 stroker. New everything. CVF serpentine belt system with the 1 wire alternator. The alternator is grounded to a clean spot on the frame, and I'm running 6 gauge wire from the alternator to a 200amp fuse, then to the battery. Which is a new battery.

When i start the truck it puts out (the alternator) 14.3v according to the sniper handheld, and to the dakota digital gauge. after the truck "warms up" i guess you could say, maybe even after a mile or so, the sniper shows the volts at 12.8 during idle sitting, (the dakota digital gauge confirms w the same reading) but when i accelerate it goes to 13.8 to 14.3 voltage.

I thought i had a bad alternator so i called CVF racing and they sent another one out. Installed it yesterday, same result.

what am i missing? I was wondering if anyone else has come across this issue and how they solved it, or is it really even an issue?

Lorenzo

[MySons68C20]

Sounds normal to me...the alternator is supposed to put out 14.2 volts.
My guess the voltage drop is due to pulley size or a low idle.
If the battery isn't becoming discharged you have no problem.

[weq92f]

.

When the EFI and your gauge in dash show the lower voltage, put your DVM on the battery. My guess is you'll have higher numbers there.

-Kevin

[Rust_never_sleeps]

Normally, one-wire alternators will “cut-out” below a given voltage, typically 1200 IIRC, so voltage below that will be drawn from the battery IF you rev it back and forth above that cut-in speed, you should see it switching on and off

If you dig, the spec on your alt will probably have this listed somewhere as CIS or cut-in, or similar so you can verify it’s behaving as expected. THey do make units with lower CIS, like 880RPM

It’s kind of an annoying behavior because it’s so easy to forget about
Service trucks backinaday often had a hand throttle for PTO, but also to keep from draining the battery sitting at idle

IDK if more modern charging systems have similar behavior or their switching is more sophisticated

[RustyPile]

This "low voltage at idle" is typical of one wire alternators.. That's why I don't like them.. Install a 100 amp 12SI and connect the voltage sense wire to the main power distribution wire somewhere near the firewall connector.. The low voltage at idle problem will magically disappear.

[EDIT]
Read all about it here:

http://www.madelectrical.com/index.shtml

[PbFut]

Low RPM greatly affect alternator output. My Powermaster SI alternator came with a bench test card. Amps were 107 idle, 139 cruise, 156 top end.
If you test your voltage at different points in the system, you will see different results even with a no change in alternator output. The voltage your sniper is reading is at it's point of connection. Within your electrical system there are varying resistance (Ground connections, wire size, length) and loads at different points in the harness. You will get different voltage readings at different locations in the harness. A one wire alternator will adjust to load, but it is reading at the head of the well so to speak. A SI alternator will adjust as a result of the reading it gets at whatever point in the system you attach the wire used to read voltage. Main splice is often used. The main power at fuse block another. So depending on connection point of that sensor wire load will affect output as well as RPM. Connecting the sniper direct to the battery will read the voltage at the battery terminal. Voltage will be that of the battery or higher if the harness lead to the battery is getting higher voltage from the charging system.
Another way of looking at this is: Think about your water system at the house. Turn on a large faucet or hose bib, and all of a sudden the pressure drops in the shower. Same idea applies for a electrical system. Put a pressure gauge at the water meter in the street, not a big change. Put the gauge at your shower head, big change. Generally not as dramatic, your electrical system does the same thing.. It is why the EFI companies are adamant in their instructions you connect direct to the battery both positive and negative terminals. Not to some point mid wire harness or ground to the closest ground point. There is also the issue with harness line noise and magnetic cross over messing with the electronics in the ECU. Holley recently updated the sniper to reduce this from happening so much. Aces EFI is very sensitive to this.

[Accelo]

Not a fan of one-wire alternators for the above reasons.
Consider retrofitting to the GM configuration. If GM could have made this work satisfactorily, they would have for cost reasons.
Especially important if you have high electrical loading at idle, like AIR conditioning.

[HO455]

You might investigate the pulley sizes on that CVF serpentine belt set up. I've seen several aftermarket versions that come with an underdrive pulley on the crank which slows the alternator down making charging at idle an issue.

There several online pulley speed calculators that can help you determine what RPM your alternator is spinning at idle.

https://www.blocklayer.com/pulley-belteng