Hi,

Chasing my tail againwith my 68 BB. I have replaced voltage regulator with a Standard Motors VR103T unit after a battery run down condition last weekend. Seemed to work after initial startup at low rpm. Ammeter shows a current towards battery and output voltage at alternator showed 14-just below 15V. Today I fixed a coupleof really bad electrical connection previous owner did when changing starter. I took the opportunity to install a fuse holder on the red cable that connects to the soleniod that comes from the horn relay. Just to be safe. There were no fusible link at the moment.

Then, when I though all was good and was just starting up for a testdrive I revved the engine a bit more and the ammeter climed probably towards upper half of the sweep. Then my new 20A fuse blew. Tried this one more time with same result.

My conclusion was the VR overcharging. After some more tests the new VR blew up in a small smoke cloud. Argh. This *could*however been caused by the F terminal at the alt. touching ground. Fixed that but the Chinese regulator has passed away.

Got a Delco 515 used regulator and tested. Same problem again, blew the fuse, rated at 20A, VERY good freshly charged battery.

Can these large current really be correct? Should I just upgrade my fuse to say 50-60amps? I', afraid of frying the cable harness and put the car on fire.

What more could be wrong here? Bad diode in alternator?

Or is all normal perhaps? Current might climb down after a while?

Desperation and frustration. Argh.

Thanks,

Martin

 

Martin,

An alternator will not 'overcharge' the system via AMPs anyways. AMPs are based on the "draw" (what certain circuits are pulling from the battery). Alternators are rated at say 60A or 90A, this is the max it will put out BASED on the amperage DRAW to keep the battery fully charged.

If an alternator was defective it could possibly overcharge a system voltage-wise. But this is rare. Usually when they're defective they don't put out enough voltage/amps or any at all. But you stated you read 14-15V while the car was running - this is fine.

It sounds like when you're revving the car a circuit or more than one is drawing to much current. Do you have an electric fuel pump, electric water pump? Maybe some else has some ideas here as well.

 

There is actually an electric fuel pump that takes power from the fuse box on the IGN pin.

My concern is that it appears as if the alternator CHARGES the battery very strongly just after startup. Current apparently flows towards batttery since the ammeter needle moves towards right, and then my 20A fuse blowed. I think it's suspicious that the battery can "consume" > 20A since its freshly charge, but again - my fuse is very fast acting compared to an original fusable link. As I can see it NOTHING can CONSUME current other than battery being charged when I see this condition. Key question is if the initial charge current can be that high? A fusible link as original wil be very very slow acting. Not like my fast acting fuse.

Perhaps everything is normal, but that means I must replace my fuse with a much beefier one or a piece of cable, with the risk of destroying the whole cable harness. Feels unsafe....but again...a 50A fuse is probably not going to put the harness on fire either...not immediately anyway.

I was thinking that if a diode or two were bad the VR would causing regulation to be full power to the field terminal...but that's just speculation.

Martin

 

If you are talking about the 10 ga red charge wire from the VR to the pos solenoid jug, then a 20 amp is not enough.
The protection ideally should be with a fusible link or slow blow fuse like an ANL or MAXIFUSE to protect the wire size, not the alternator output. Of course the wire should also be sized to handle the alt output.
Alt output is roughly 85% of rated output.
Depending on battery condition, your output on say a 60amp Alt would be 14.7vdc or 55amp at startup reducing to 14.0vdc or 15 amp running with the battery fully charged plus any added loads like a fuel pump.

 

Thanks for the input. Yep, I'm refering to the 10ga charging wire.

So are we saying that its normal that the current into the battery thru the "red charging wire" can be initally quite high and gradually dropping? I'm afraid that it's a bit strange to see battery charging currents in excess of 20A after a quick startup with a well charged properly functioning battery. But I have never thought of this until now either. And I have no preior experience of a properly functioning Corvette either.

I'm going to a car show tomorrow evening and are inclined to switch to a much larger fuse or fusible link. But my worst nightmare would be to fry the cable and destroy more stuff on the way, not to mention a potential fire hazard.

How does the ammeter typically behave at just after startup? Does it show a DISTINCT charge and then gradually goes towards the 0 mark?

BTW....what does the brown/white wire from the VR do?

Thanks again for all advice.

 

Put in a slow blow and you'll likely be fine. The fusible link is a VERY slow blow device. As was stated before, you can't overcharge if the voltage is set correctly, which it sounds like it is.

 

It is normal to have high charging rates after start up especially on a new battery. That rate will fall off as the battery regains its charge.

 

 

Update:

I removed the fuse and installed a short piece of fusible link instead. Hooked up DMM on alternator output and started up while also watching ammeter behaviour. Revved the engine slowly, voltage climed to 14.6-14.8V and the ammeter showed quite a large defelecton towards right, then gradually moving back towards 0 after perhaps 30 seconds. I.e. worked perfectly.

Just got back after a big carshow last night and all was perfect. Very nice to have a fully functioning charging system, first time since I have had the car. Even helped my friend jump start his 64 Mustang. Haha...

MANY thanks all for the help and guidance - truly appreciate it.

Case closed.

Martin