Low voltage

[panalukes]

Here is one for the electrons.

I am having issues with my stereo cutting out while the engine is running and I'm stopped in drive. The rpm is 700ish at this point. My volt meter shows it drop to 11.7 volts, this with the engine running. If I put the engine in park the rpm will climb enough that the voltage climbs and stereo comes back on, Stereo doesn't cut out while the engine is off and it's just running on the battery. I only get the low volts when the engine is running. it's been like this ever since I got the vehicle. I don't have any problems with dead batteries though so I'm puzzled. Could my alternator be putting a load on the battery at low rpm? I have multiple grounds. I haven't had the alternator tested. I believe it's a newer type alternator setup. Pictures to follow. Sumtin ain't right.

 

[Viperwolf1]

It takes some current to drive the ignition system and alternator field. Your alternator isn't keeping up at that slow speed.

 

[Steve83]

I'd check for other key-on draws. You need to put a LOT of details about the truck into your profile & signature: every original component, everything that has been replaced, every upgrade, every modification, maintenance, damage, repairs... Hell - just the model year & engine would be a good start, but don't spare the camera, either.

 

[panalukes]

photos of the alternator

I had the same issue before I changed engines and ignition systems from a stock engine/ignition. I don't have low volts while the ignition is ON and the engine is not running. All the keyed 12V things would be powered at this point. I too thought that there must be some big draw on the system. Its only low volts when the alternator is turning at low rpm. This leads me to believe that the alternator isn't putting out enough juice, or it's wired incorrectly, or both.

The situation is exacerbated when I had the headlights running (more draw) so I swapped them for LED lights. That helps a little but still having the issue.

I also considered a grounding issue so I added an additional ground from the block to the frame during my engine swap.

Part of my post was really a theory question of whether the alternator could somehow be drawing a huge load on the battery at "idle" rpm.

 

[Broncobowsher]

Alternators can be half dead. Actually 2/3s dead. So a stock 60A alternator that has lost some diodes or windings can be limited to very low output. I had this once where daylight driving would keep up and top off the battery, but the headlights would put enough load that I would be driving at a loss. Careful planning of driving routes could keep me driving on the 20A that I still had. Just no long drives at night, and no heater use (blower fan too much).

 

[Jdgephar]

I don't have low volts while the ignition is ON and the engine is not running. All the keyed 12V things would be powered at this point.

Depending on what ignition you have, and/or where the distributor is stopped, you may not have the ignition load when the key is in the run position.

 

[DirtDonk]

Is that a standard 3G or a 1-wire 3G like we sell? Is that a local alternator rebuilder's decal? If the alt came with the truck, maybe you can call them to find out if you don't already know.

Where does the Black wire go from the 3-wire connector on the alternator?

And even though your charge wire is theoretically large enough to be somewhat safe (looks like 10ga from here?) over that short of a distance, I would still use a larger wire.
At this point it's just to make sure that it's not a bottle-neck to higher amperage when it's needed.

How old is the alternator? You say it was doing this before, so is this the same alternator? Maybe it's just tired? As said, it happens.

Good luck.

Paul

 

[JAFO]

I wonder if your battery is weak? The alternator is charging the battery. The battery should be able to supply 12 volts DC for a bit of time before dropping below 12 volts. Actually, a charged 12 volt battery should be a little more than 12 volts.
Plus you must have a finicky radio that has to have a full 12 volts. I see my alternator drop low when I am a very slow idle, but nothing in my truck turns off. I can put my foot on the accelerator pedal and speed the engine slightly and the charge jumps up normal. I just like a real slow idle.
In the old days you could figure on driving 100 miles off the battery if the charging system failed.

 

[panalukes]

Thanks guys.

The black wire goes to my ron francis fuze box.
I googled SVA thunder but couldn't find anything. Called the number, no joy. I will try a different battery. And take the alternator in to get tested.

 

[panalukes]

the phone number on the alternator tag is associated with a member of this forum...looks like he hasn't been active in quite some time. RRRAAAYYY2. Anybody know him?

 

[broncodriver99]

AFAIK Ray got out of the biz, and SVA the manufacturer went under.

 

[Steve83]

That's a common 3G with all 4 normal wires, though I can't see if the brown S wire is connected to anything, or what size frame it has (small 95A or large 130A). The charge wire is certainly undersized, by about 2 gauge numbers, and it lacks any circuit protection (fusible links). But what catches my attention is the STACK of spacers between the alternator case & the head, clamped down by a dirty steel bracket & an old bolt. I'd start by pulling it out and cleaning ALL those mating surfaces so there's clean metal from the alternator housing to the head, AND from somewhere on the engine to the battery (-) post along a good black battery cable.



If that's too much work, at least add a clean cable from the battery (-) to the alternator case until you have time to clean up the rest.



It needs to be AT LEAST the same size as the (correct) charge wire.

 

[Steve83]

Post your questions here so everyone can help answer them. The black/brown wire should not be connected to the fuse block, though it CAN have an inline fuse.

.

 

[panalukes]

brown wire

Here is the pertinent diagrams I have from Ron Francis for my kit. What I don't have is instructions for a 3G alternator with 4 normal wires. If I don't run the brown wire to the fuze panel then were would I run it?

 

[Broncobowsher]

Have you done the simple thing of just pulling the alternator and having the local parts store test it yet?

 

[panalukes]

haha. No, but I'm about to!

 

[Steve83]

What I don't have is instructions for a 3G alternator with 4 normal wires. If I don't run the brown wire to the fuze panel then were would I run it?

Click the thumbnails in my previous post & read them. The first one (the diagram) lists each wire, its function, and how it's connected. The 2nd is an easy bolt-on/plug-in way to install a 3G in an eB.

You don't need to remove it or take it anywhere to test it. The diagram also explains that simple process.

Your attachments won't open - they'll only download. Do you have links to their online addresses?

 

[panalukes]

Unfortunately, no I don't have an online link to those diagrams. That's what Ron Francis sent me direct as a PDF. I did see the diagrams you posted, thank you. And they confirm that the brown wire connected to my fuze panel is correct. That's the 12V keyed power source on my panel.

 

[panalukes]

Changed out the alternator. Now I get 14.5 volts at 800rpm. Yay. Case closed. When they tested the old alternator it failed the initial check, ground check of the voltage regulator I think it was. In any case, I picked up a few good tips from you guys in the process and I appreciate the feedback.

 

[Timmy390]

I take it the brown wire is the Green/Red wire on my 3G.

If so, that wire should hook into the Green/Red (mine is more yellow/red/pinkish due to fading) on the old Bronco harness at the old external voltage regulator plug is or should be. That wire is hot in Run and Start

Tim