altenator issues

[Pookapotamus]

its bolted to the back of the alt, already swapped it out with another that i had, and still no change.

[FiEND]

the new alternator yes.  the old alternator though, was external?  controlled by the ecu or pcm ?

mine i am running internal regulator and external since i did the swap to the higher amp.

the internal regulator will regulate the voltage but not sure it will turn the alternator on and off to charge (the internal relay).  that is controlled via the 2 little wires that connect to the alternator, that is the relay connection that starts the alternator charging.

so if the ECU / PCM whichever is borken, might not work even with an internal regulator.

only a voltmeter will tell you if it is charging though

[Pookapotamus]

yes it is charging, start jeep and have no accesories on and it is charging at 14v. turn on heater to full and it starts dropping, turn on lights (just headlights) and it drops further down to 12v. keep turning things on and it slowly gets to the red line. with everything on, (heater, defrost, headlights, driving lights, 4 55w spot lights, radio & amps and other misc) it holds just above red line. if i rev the engine with everything on it only comes back halfway. with just headlights and heater and defrost and i rev the engine it comes back a good 75 - 90%.

am i just being picky? i just really hate stopping at a light and all my lights dim.

[FiEND]

I guess your new alternator is toast as well.  you can really only test with load put to it as you are.

[cLAY]

What are you getting with everything on EXCEPT the heater motor? I've seen heater motors start to draw too much power when the start to fail. Although it usually shows up as a blown fuse, resistor pack or fuse.


With everything on how many volts are you seeing at the battery vs the alt post?

[Immortal]

AHA!! Dana... you were having heater problems before....

cLAY is a smart cookie!!

[FiEND]

not quite....

it's a 140 amp alternator.  if the heater is drawing enough current to severely drain the alternator (and the big fat juicy wire connecting it to the battery) then the [much smaller] wiring on the heater motor would melt and catch fire.

[mike s]

Alternator output is based on load and engine speed, at idle the pulley is turning it's slowest, so output is at it's lowest. Winter months are hard on alts cause every electrical device is on and it spends too much time at red lights idling. Bump the gearbox into neutral and pick up the idle slightly to help it out. Turn off your rear defrost and wipers till your moving again.

But 140 Amp is pretty big, try a smaller alt pulley and your dash voltmeter is at the tail end of a big load of electrics, probaly reading low. Hook up a volt meter to your alt output terminal and see what's there, if the volt on your battery is more than 0.5 volts lower, add another main wire from alt to battery

[Pookapotamus]

heater motor and fan resistor are 1 month old.
all my testing has been done with a multimeter at the batery.
wires from the alt and every other wire in that area are copper core 4 gauge wire.


@ clay i have tried many different combinations of electronics that are on, the heater motor does seem to be one of the biggest draws but like i said i just replaced it. the biggest draw seems to be the defroster on the rear windo, but i rarely use it. i am having this problem even with just headlights and driving lights on.

@ mike s i have considered a smaller pully but this seems to be a work around i would rather fix the issue instead of mask it.

a few things i am considering:
1 the alt out of the zj i got from fraser is the one that was in his jeep that got crashed. (possibly affecting the alt and it is bad)
2 the alt out of the zj is it really a 140amp alt?
3 redoing wires from the fuse block to some of the major drawing electrics.
4 i am just being picky, (jeeps are supposed to have their lights dim at lights its a sefety feature)

[Tinkerer]

Since

• you are measuring at the battery with a multimeter
• even revved up, it only comes up to half-way (what is that anyways? I presume it's half-way to 14 volts from the red line, but a voltage would be great.)

It sounds like either

• the alternator can't put out enough current
• the regulator is not providing enough field current to fully drive the alternator to capacity

Two questions / comments come to mind:

• How much voltage is at the alternator versus the battery when revved up with all accessories on?  I know you put bigger cables, so it shouldn't be there, however, this is the "acid test".
• Is there a temperature sensor on the battery for that year vehicle? It may be saying the battery is "hot" and chooses to limit the field current, and therefore the charging current. (This is typically only on ECU controlled charging.)

Is the battery good? Is it fully charged? I've seen them draw a bunch of current due to being bad, so in combination with the accessories, the alternator couldn't keep up!

[Pookapotamus]

batery is an optima yellow top not compleetly sure if it is good and i have not yet completly ruled it out as being bad. i have boosted with another battey to see if i get the same dropps and i do. so i am thinking it is good. i want to test more tonight and actually write down what i am getting instead of just going from memory.

the 95 xj does not have a batt temp sensor. it has an external regulator on the alt.

[WhiteOut]

Since the bearing in the one I gave you might have been on its way out, could you try swapping the regulator from it onto yours?

[Tinkerer]

batery is an optima yellow top not compleetly sure if it is good and i have not yet completly ruled it out as being bad. i have boosted with another battey to see if i get the same dropps and i do. so i am thinking it is good. i want to test more tonight and actually write down what i am getting instead of just going from memory.

the 95 xj does not have a batt temp sensor. it has an external regulator on the alt.

Sounds good...   sounds like it isn't the battery if that boost battery was left in parallel during some testing.

As I understand it, the regulator/alternator can put out 14V under light load (you already said so), just not under large load, even at higher rpms.

For diagnosing what can seem like an alternator issue, the 4 measurements that can be done easily with a multimeter are:

• Battery Voltage (Red to Battery+, Black to Battery-) In ideal conditions, 14V unless the battery is hot..
• Alternator Voltage (Red to Alternator output, Black to Alternator body) In ideal conditions, 14V, may be higher if measures voltage at the battery.
• Positive Voltage Drop (Red to Alternator output, Black to Battery+) In ideal conditions, 0V, but typically a very small value < 1V. Gets higher with larger load.
• Ground Voltage Drop (Red to Battery-, Black to Alternator body - could be backwards, but you'll just get a -ve voltage) In ideal conditions, 0V, but typically a very small value < 1V. Gets higher with larger load.

http://wikicars.org/en/Alternator

[Pookapotamus]

@ fraser i already swapped out the voltage regulator, twice i had three of them.

@ tinkerer i will try all your tests tonight and record the voltage.

[FiEND]

voltage regulator doesn't really do much. 

the main circuit board converts the AC from the alternator to DC 14.5 volts... or so.

the regulator reads the vehicle voltage from the battery and then either turns on charging (say at 12.5 volts or turns off charging at 14.5 volts)

so, if the regulator is not working, you will not see any voltage increase from the alternator as it will not start charging.  there is only ON and OFF.