claudebadly

trust me, your alternator supplies more than enough power to run your truck. this morning i had to tow start my truck *jump start didnt work* and drove it for 2 hours to grand junction. had my battery tested, and it read 47 CCA when it was supposed to have 177 think it was. 47CCA AFTER 2 hours of highway driving.
got new battery, and no problems since

86toylet

I want to know where you guys are getting 18 volt alternators ?

abecedarian

You are correct.

pull the battery cables off of the alternator while monitoring the voltage...

and just 'cause the alt goes to 18v does not make it an 18v alternator.

It was mentioned above that there's a relationship beween volts and amps- in a nutshell, double the voltage and you only need 1/2 the amps.

bigtrucknwheels

Once again, you have demonstrated a firm grasp on what is what when it comes to electrical things. Are you an engineer?

A separately excited alternator, which is pretty common, needs that battery to make it all work. hence why a bad battery will still leave you stranded even with a jump start and a good alternator.

And, even more interestingly, most alternators actually produce a 3 phase AC output, which is then rectified to DC and then passed through a voltage regulator, which in it's most simple form, is a zener diode.

Now, my next question is why you cannot see your dash lights?

the charge and brake lights are connected together with a few diodes, that during normal operation of the charge system, blocks current through that circuit. Current from the alternator is trying to push through the diodes, but it can't and won't. But if the alternator or other component of the charging system fails, current from the battery will be able to push through the diodes in the operational direction, illuminating those lights.

This is all based on the fact that under normal operation, output from the alternator will be right around 14V, whereas the battery will be right around 12V, opposing (same polarity connected to each end of the circuit) each other in this particular circuit. The 14V from the alternator cancels the 12V from the battery and hence it maintains a 2V margin over the circuit, more than enough to keep the diodes from allowing current flow (they only require about .7V for a typical silicon diode).

Charging works the same way. Your vehicle will place the alternator and the battery under load, but the battery and alternator are hooked up positive to positive across the load. Here again, the source with a larger voltage, providing the load is not outside of the capabilities of the two sources, will be the one pushing the current through the load AND charging or attempting to charge the source with less voltage. GSGALLANT is absolutely correct in saying the alternator provides virtually all the load current, and the battery is simply charging, or used for reserve capacity.

I can explain a lot more, if anyone is curious...

Junkers88

I have no idea what any of that meant.


I couldn't see the dash lights since I hadn't turned the dimmer up. Sometimes it's the little things that baffle me.

Ed H.

Ok i see where I faulted in my statement, i would regularly jump start vehicles at work, every once in awhile i would get a car with a battery so dead that the car would not run and the alternator was charging just fine. does that have something to do with the alt. not being excited because the battery is to dead? please explain this phenomenon to me.

bigtrucknwheels

that's a self excited alternator. those are common as well, but as with everything, they have their drawbacks.

bigtrucknwheels

the dimmer is not in any way shape or form related to the indicator lamps that we are discussing. Bottom Line: If the brake and battery lamps (bright red) aren't glowing while the truck is running, your alternator is working correctly.

glad you figured it out haha. And what I said can be confusing if you aren't strong on your electrical skills. sorry for the confusion.