Hi,

The other night I noticed that while I was idling, my voltage was dropping down to the 12.0V range. I have a Sniper EFI so on the mini-dash I could see it.
Usually at idle it is ~13.7V or so. It drops to high 12Vs when my fans come on, then with the headlights, it dropped further.

My alternator is new: GM 10si Case Style, 12 V, 140 Amps, Chrome, V-Belt Pulley
Link here

My questions are:
1) Should I be concerned or am I just paranoid?
2) Should I switch to a CS144 style instead of the 10SI or does that matter?

 

Take a reading directly off the alternator with a known working handheld VOM. Just because it's new doesn't mean it cant fail.

 

The readings jive with what I see on the handheld.

 

The other issue is pulley size and alternator design...

Most alternators put out full current at about 1500 RPM- at idle depending on design/pulleys might be only generating 50% and just because it's new- doesn't mean that it will perform to specs (made in China?!).

I do not know the extent you re-wired the car- cable upgrades and what not- that could also be an issue. When these cars were designed- GM's bean counters poopooed the idea of larger cable and just raised the voltage on the alternator to compensate for it and had NO idea that the amount of current required in a restomod would ever be seen.

Do check the output of the alternator with a "good" meter.

Think of the alternator as your income and the battery as your bank account using small wire as bank fees...spending more than you make will cause you problems!!!

Richard

 

I would be concerned. I replaced my alternator with a higher output unit when I installed a Dewitts radiator and electric fan and have had sufficient charging since.

 

Good points. I know I checked it before but I will check it again. I just got a kick *** new Power Probe just asking for some action.
When I changed the suspension, brakes, steering, engine, trans and cooling systems I also replaced every wiring harness in the car. Although it was back to stock so if they used itty bitty wires stock, I still have the same in there.

 

Did you upgrade the charging wire from the alternator to the starter? That's a recommended modification when going to a larger alternator. Somewhere on this site is a thread that talks about the Big 3 wiring improvements. If I remember correctly, upgrading the charging circuit with a larger wire is one of the 3. Grounding was one or both of the other two. Sorry, I've slept (and drank Tequila) since then.

When I upgraded to a CS144, instead of replacing the existing charging wire, I just added another one in parallel. Keep in mind that this charging wire needs a section of fusible link at the starter end. Double check me but if I remember correctly, fusible link size is two wire grades below the wire size it is protecting, so an 8 gauge wire needs a 10 gauge fusible link. Also, if you have a factory ammeter, it won't see any current flowing through a new parallel wire, it will only see the currently flowing through the original charging wire so it won't be accurate. That's why some folks just replace the charging wire entirely. I was getting rid of the ammeter in favor of a volt meter so this didn't matter to me.

I also beefed up the ground from the engine block to the frame and the ground from the new alternator to the frame.

DC

 

As DC3 said- when you upgrade the charging wire-the ammeter will not read correctly.- I've converted to a voltmeter as well.

I'm not a fan of replacing GM's cheap out protection by using a fusible link. There is too much aftermarket stuff out there that will do a much better job and a LOT easier to replace on the side of the road.

A fusable link = tow home/shop!!!

You now have three time the power as the stock wires might carry on a good day. You definitely need to upgrade the charging wire.

I don't know how you have wired the fans either- they should be connected as close to the battery as possible- WHY? The battery not only starts your car but also stabilizes the voltage and filters it ( electronics like this)

I'd go to 6GA wire from the alt to the starter terminal.- go with the "SGX" type of wire- it's designed to handle the heat under the hood.

Anding some extra grounds are good too- I like the look of the braided ones-

Another rule of thumb- when running wires under the hood- go up one size ( down numerically) due to the heat adding resistance to the wire. Wire is rated at 70º- and it's rarely that temp in the engine compartment!!!

Here's what I like- a fuse at the battery- if your alternator shorts out you will see a puff of smoke and it quits working- short the battery and you will see a fire and possible an explosion!!!




If you need to hook up say fans and the EFI to the battery- here's another neat solution-



On my car with a few added electronics- OK- a LOT- I used a marine terminal to fuse all my high current draw accessories.



I used 1/0 from the alternator-



Here's one of the many grounds I added- looks better than the cable and much easier to mount-

 

Scottjamison You are right about the Power Probe Tools. I am now using a version 3 and a version 4 of the Power Probes. This is a tool designed for working on plastic Cars and boats. I love the Power Probe set I bought the first time as it has the "Short Finder" and other valuable tools in it.

This is one of the tools I recommend to folks who want to work on their Corvettes. Mine save my butt when I had fuel pump issues allowing me to verify the pump's operation at the pump and followed it all the way back to a faulty connection on my Fuel Pump relay. I love being able to apply either battery voltage or battery ground at the tip simply with the rocker switch. It makes finding voltage drops easier as well!

I was so impressed with my 3rd generation that I bought the fourth generation so I would have one available more often. I keep the 3rd gen in my RV as it gets lots of use there. I have let people use my Power Probe only to see them buy their own very quickly afterwards.

My C3 has a 120 AMP alternator on it and it seems to be enough for my Corvette. I have a pair of 11" SPAL fans, an electric fuel pump and MSD ignition system and other gadgets but don't have any issues with low voltage. I ran a 4 gauge Marine Cable from the alternator output to the starter motor's Battery cable. This allows the charging system to work without damaging the ammeter. Both my Fuel Pump and cooling fans are controlled by controllers using PWM so I avoid spikes doing this. My cooling fans start up slowly and you don't hear a constant electric fuel pump running.

A lot of people forget to hook a good ground strap from the alternator body to the engine or frame of the vehicle. It is very important to have a clean ground connected to the alternator for it to function properly.

Best regards,
Chris

 

Wow that is some awesome info from you and DC3. Much appreciated.
One quick question, does the ground go from the alternator body to ground? I always thought the alternator grounded through the body and mountings to the engine/frame.
Do you still run the charging wire through the Horn relay?

 

Thanks Chris.
You just answered my previous question about where to hook up the ground.
Based on what I am reading, I do need to increase the gauge of the wires to the starter and also add the ground strap to the alternator body.

My fans and fuel pump are on relays so we should be good there.

 

If you are completely replacing the existing charging wire, then yes. I just added a new wire in parallel and bypassed the horn relay. Figured one less connection was better in that instance.

I recalled a bit more information about the Big 3 wiring upgrades I mentioned in an earlier post. Traditionally the Big 3 was related to mobile audio installations with alternator upgrades and the 3 upgrades were a larger charging wire, upgraded ground from battery to frame and upgraded ground from engine to frame. For our Vettes, the negative battery cable is pretty hefty (and short) and may not need to be upgraded. Where it attaches to the frame does need to be inspected to make sure the connection is solid.

I used a pre-made battery cable of the right length to connect the engine to the frame. There are several choices of these pre-made cables at parts stores. If I remember correctly, the alternator grounds to the radiator support or somewhere near there. I added another pre-made battery cable from the alternator down to the frame and just checked that the existing alternator ground was good. Originally, I did not upgrade the alternator ground but ended up chasing a very slight alternator whine in the stereo at low volume. Adding the better alternator ground lessened the noise somewhat but it's still there. Can't hear it at normal volume so I quit worrying about it.

DC

 

Sounds good. I just ordered the wire and fittings and will do like you did to run the bypass directly to the started, but also the existing line to the horn relay. I have a new set of battery cables that I am going to put in also. Damn those weren't cheap!

 

I would NOT run the charging wire to the horn relay AND run a wire from the alternator to the starter terminal.

That DEFEATS the fusible link to the horn relay from the starter terminal...

Then the terminal at the horn relay becomes UNPROTECTED directly from the battery.

Best is to put a fuse at the battery- let the horn relay be protected by fusiblelink from the starter terminal and the wire from the battery to the alternator be protected by a fuse.

Richard

 

There are multiple posts with this confusing information. The alternator in a C3 is not grounded by the black wire connected to it's case. That is the ground wire for the radiator support so the headlights and such up front work. The alternator is grounded through the brackets to the engine block and the engine block is grounded by the large cable on the passenger side going between the engine and frame.

 

I added a fusible link to the new charging wire I ran so both wires are protected.

DC

 

Good info to have. Thanks for the input.

DC

 

I will say that when I went back to the instruction manual last night out of curiosity, they actually did recommend grounding it with the same gauge as the power wire. Definitely not stock, I agree.

 

and if thats the case I would think adding additional grounds can actually create a ground loop situation and create noise. Which is normally the source of a whine in a car stereo.

 

Ground loops in car audio are a completely different thing-

The "whine" in car audio is due the AC ripple not filtered by the alternator entering the AC -speaker level or most often pre-amp 500mv level. Quite often due to different impedances between the radio and amplifier- and most of the time due to a lesser quality amp and or cheap unshielded RCA cables-

Extra grounds on the car cause no problems at all- electricity not only follows the path of least resistance but ALL paths... If the extra grounds were a problem then the battery would NOT be connected to the chassis-