Alright peeps. This engine swap im working on has gotten so close to being complete its frustrating, yet one more issue has arisen. The alternator on the engine that we bought was not charging. As in, engine running you can take the positive battery terminal off and the engine dies. Wired as correctly as I could see (factory plug still plugged in from before when it was pulled from a running car and the one wire to the + side of the battery). Replaced the alternator with a new one from oreilly and still the same. no charge and it dies when you disconnect the battery. bad new alternator or problem with my wiring? Or am I missing something?

edit - I looked around here and it was suggested that the small wire needs a 470 ohm resistor and 12v. Thats fine, but did I miss putting power to a certain plug/pin/wire in the original LT1 wiring harness (95 camaro) or should I just run the power with resistor?

Thanks for your help.

 

You probably damaged the new alternator.

Go get another one and don't remove a battery cable while it's running anymore. Use a voltmeter to tell if it's changing or not. Not running = about 12vdc. With engine running check the battery voltage and it should be about 13.8vdc.

Here's a cut and paste from an article I quickly found so I wouldn't have to type too much. In short the battery is a huge, necessary filter. I hope you didn't damage any electronics on the car.

cut and paste:
The moment he disconnects either lead from your battery, it's entirely possible he caused thousands of dollars in damage. Here's why...

Your battery does more than just provide electricity. It also shorts AC, spikes and transients to ground. Removing the battery from the circuit allows those spikes and transients to travel around, endangering every semiconductor circuit in your car. The ECU, the speed sensitive steering, the memory seat adjustments, the cruise control, and even the car's stereo.

Even if your computers and stereo remain intact, in a great many cases removing the battery burns out the diodes in the alternator, necessitating a new alternator. If disconnecting the battery interferes with the voltage regulator's control voltage input, it's possible for the alternator voltage to go way over the top (I've heard some say hundreds of volts), frying everything.

Even the initial premise was wrong. If you disconnect the battery and the car conks out, you don't know if it conked out due to insufficient alternator current, or whether the resulting transients caused your ECU (the car's computer, which controls fuel mixture, timing, and much more) to spit out bad data, shutting down the car.

Nobody should EVER run your engine without a battery.

And yet when you tell them not to, they'll roll their eyes. "I'm a professional. I do this every day. It's fine!" They'll sound so authoritative. So commanding. So in charge. So intimidating. But they're wrong.

The problem, of course, is that disconnecting the battery doesn't always damage something. It does it only sometimes. Less experienced jump start professionals and automotive technicians figure if they got away with it a few times, it must be OK.

Don't let them do it on your car. When you call for roadside service, or take the car in for possible electrical problems, or have your battery and charging system checked at a "battery shop", give them

 

With engine running take your meter and check voltage at the battery cables. With a properly operating alternator you should have 14-15 volts DC, 12-12.5 volts engine not running. I would not recommend disconnecting the battery cables while the engine is running, you could possibly damage some of your sensitive electronics.

Are you sure the battery is charged?

 

before I disconnected it, voltage was around 10 or 11 volts running. Same as old alternator. I'm thinking I'm not giving power to the field. Several others have posted on this same thing about not giving power to the plug.

Concerning your post, I'm not disagreeing as I dont know exactly to whats up, but I've had Lt1's before (carb conversion) and many other chevys and have never had a problem with taking the positive lead off the battery. Thats kinda been the go-to way to check them for 60 years or more. Are you sure I could have damaged it?

 

battery was charged enough to start it, (11 volts ish) but there is less voltage in the system when running as opposed to before starting. The engine running pulls the voltage down in other words.

 

Just because the engine started, dosent mean that the battery is not the problem. Try charging it. Like I said 14-15 volts with engine running is normal. Disconnecting the battery cables may have worked in the 1970's but cars from the 80's on have ECM's and other electronics that are sensitive to voltage spikes. The battery absorbs voltage spikes and maintains a constant 12 volts.

The first thing I would do is make sure I had a good properly charged battery.

 

Your CS144 is likely a 3 wire so you need to find and use a wiring diagram for a CS144 using that connection type OR one that matches the wiring of your particular CS144 pigtail. It might be easier to help if you mention which terminals of the alternator are actually used in your connector and of course the number of wires.

You will rewire the charging circuit completely with your particular install.

 

I had to do that with my track car when I removed the stock dash. I added a small light bulb. I think it was only 50 ohm but it was enough to activate the alternator charging. You can also make a small circuit with a resistor in case the light bulb burns out.

 

yes, but I'm not sure you did.

 

You may be onto something regarding the field winding. I'd get a wiring diagram and check wiring to the field, without it the alternator will not put out.

My plane has a instrument panel breaker for the field winding. My operating checklist calls for it to be off during starting and after the engine is running push the breaker in and then my demand (amp) meter reads the current draw from the alternator.

 

ya'll were absolutely right. I hit the alternator plug with 12 volts with a 470 ohm resistor in it and it shot to 13 volts right off when it was 10 before starting. It would go to 9.5 or 10 before, so its charging! Thanks for the help. I'm charging the battery fully tonight so I can make the wire permanent tomorrow (its 38 outside now where the truck is!) and test drive again.

 

Make sure it is a 1/2 watt or larger resistor, I would suggest at least 1 watt. My calculation shows it will dissipate just over .4 watts at 14 volts.

 

it is a 1/2 watt. radio shack didnt have anything larger.

 

Make sure you don't shrink wrap it or do anything else that would reduce the heat dissipation of that resistor. Worst case if it stops working at some point you replace it with a 1 watt or larger resistor.

 

dont shrink wrap it? too late. I've covered every connection in this thing as best i could. more aggravating yet, after it started last night just fine and charged, today after charging the battery and starting it the idle got slower and slower till it died, now it wont restart. It'll fire a couple times but wont run. So, yeah. nearly dead battery and it starts - charged battery and it wont. go figure.