Discussion in 'How To' started by OneOneNiner, Nov 30, 2009.
The battery is what powers everything anyway. Why bother upgrading the alternator?
Hmm... I will read through the FSM again, but the consensus on here seems to be that its computer managed. I know troubleshooting alternator problems on the KJ is a pain after reading threads on it and guys giving up and going to the dealership.
Thanks! Its a labor of love, just like my KJ.... lol
This is the biggest misconception of vehicle electrical systems. The alternator provides power to run everything, the battery is merely a storage system for starting power and to handle surges and for convenience items like having your radio and lights on without the engine running, its like the big capacitor you put on a car stereo amp to smooth out the power and handle large short duration current draws when the engine is running.
Why do you think that you can jump start a vehicle with a dead battery?? Because your providing power to get the engine running until the alternator is up and running and supplying power. Now granted the newer vehicles won't always run after a jump start if the battery is dead because the PCM senses the low voltage, or the battery might be internally shorted and overloading the alternator.
But the battery DOES NOT power everything. I had an old Chevy Scottsdale with a dead battery, disconnected the positive battery cable and wrapped it in tape, it was a manual so i just got it rolling and popped the clutch in fourth to crank and start the engine, now as long as i didn't shut it off i could use it normally. I ran it like that for two months back in high school, couldn't afford a new battery.. lol
Good website for charging and electrical basics like this... The above quote is from that page.
KB-ThunderbirdJunkie slightly misspoke.
The bulk of the power still travels through the battery, even if the battery is not directly powering it. Yes, the alternator DOES power everything, but it has to travel through the battery for it to act as a capacitor as you described. If it travels through the battery then the battery is powering it
Yes... Thats the main thing, the battery is like a big capacitor...
Sorry if i came off harsh, i get idiots all the time who like to argue electrical stuff like that!
From the FSM, the other wires from the alternator go to the PCM actually, i even double checked the wiring diagrams in the FSM...
The charging system consists of:
² Electronic Voltage Regulator (EVR) circuitry
within the Powertrain Control Module (PCM)
² Ignition switch
² Battery (refer to 8, Battery for information)
² Battery temperature sensor
² Generator Lamp (if equipped)
² Check Gauges Lamp (if equipped)
² Wiring harness and connections (refer to 8, Wiring
The charging system is turned on and off with the ignition switch. The system is on when the engine is running and the ASD relay is energized. When the ASD relay is on, voltage is supplied to the ASD relay sense circuit at the PCM. This voltage is connected through the PCM and supplied to one of the generator field terminals (Gen. Source +) at the back of the generator.
The amount of DC current produced by the generator is controlled by the EVR (field control) circuitry contained within the PCM. This circuitry is connected in series with the second rotor field terminal and ground.
As you can see.... The PCM controls the field of the alternator. So if the PCM is programmed for the smaller rating alternator you could put in a 300 amp alternator and it wouldn't matter, it would still charge at the stock rating. The problem is the KJ alternator doesn't contain the regulator, thats all handled by the PCM. Its not like the good old days where you can slap in a huge alternator to carry the loads. I don't know why they went with such a small alternator either. Even the minivan we used have was a 160 amp.
It kind of sounds like it is only controlling the voltage as standard external voltage regulator would in an old car. The amperage output, from the description, does not sound like it is being managed. From my limited, non engineer standpoint of electrical control, you would need some pretty hefty parts to control the amperage output.
Need to find out more.
Regardless, I think having a dual battery system when powering a lot of lights etc. would give more of a buffer for longer night time wheeling trips. When I noticed the dimming I turned off one set (each set has own switch) of my overhead lights and the rest brightened slightly. I don't think my alternator could keep up with all the power for the lights and recharge the battery at the same time at the slow speeds my engine was at.
You should see the octopus I have created under my dash. screwy.gif
ITBJRC the VOLTAGE regulator is internal to the alternator. Troy can probably shine some light on the subject if he sees this
Not that long ago I was driving my YJ through the woods on a snow run when I discovered my "Check Engine" lamp on and my dash's voltage gauge reading low. I had burnt off the charging post off of my alternator. It's a 1995 vehicle so the alternator is much simpler then the Liberty's.
I got a boost/charge off of another Jeep and managed to drive my YJ out of the woods. Unbelievably it would run about four or five miles before the engine computer died.
So I guess both statements are true, you can drive a vehicle with only a battery or only an alternator.
On the topic of dual battery setups, I'd like to set one up in my YJ to power the winch. I feel when winching like I'm straining the alternator.
Separate names with a comma.