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Alternator Duty Cycle?

EMSJEEP

NAXJA Forum User
Location
Long Island
So I've fixed my recurring no-charge with a new alternator and external regulator. In addition, I have house batteries on an isolator (diode). The voltage drop across the isolator is about 1v -1.5v give or take. The question is, since the external voltage regulator is set to say, 14.5v in order to give my battery about 13.5v while running, and the regulator reads system voltage post-isolator, the regulator will always read a voltage deficiency and will essentially engage the alternator 100% of the time. As the alternator feeds directly into the isolator, if I were to connect the sensor wire for the regulator there, it would constantly read either residual voltage (like 0.4v) or the regulated output max of 14.5v. In short, I'm not sure where to connect this thing, or if it really matters...how frequently is the alternator engaged in a normal setup?
 
So I've fixed my recurring no-charge with a new alternator and external regulator. In addition, I have house batteries on an isolator (diode). The voltage drop across the isolator is about 1v -1.5v give or take. The question is, since the external voltage regulator is set to say, 14.5v in order to give my battery about 13.5v while running, and the regulator reads system voltage post-isolator, the regulator will always read a voltage deficiency and will essentially engage the alternator 100% of the time. As the alternator feeds directly into the isolator, if I were to connect the sensor wire for the regulator there, it would constantly read either residual voltage (like 0.4v) or the regulated output max of 14.5v. In short, I'm not sure where to connect this thing, or if it really matters...how frequently is the alternator engaged in a normal setup?

I am not sure about the external regulator and isolator you are using. The isolator itself will affect the voltage going into the battery/s. The documentation that came with it would be your best source of information on wiring the ground.

I once had an external regulator instead f the PCM regulator. That thing cycled so fast you could see it in the radio back lights. I did not like it and went back to the PCM. With the PCM and an accurate volt meter, I sometimes see a 0.2 to 0.3 volt drop before returning to 14.1 volt that is normal for my XJ. That voltage is displayed on the Scan Gauge mounted on the dash.
 
I am not sure about the external regulator and isolator you are using. The isolator itself will affect the voltage going into the battery/s. The documentation that came with it would be your best source of information on wiring the ground.

I once had an external regulator instead f the PCM regulator. That thing cycled so fast you could see it in the radio back lights. I did not like it and went back to the PCM. With the PCM and an accurate volt meter, I sometimes see a 0.2 to 0.3 volt drop before returning to 14.1 volt that is normal for my XJ. That voltage is displayed on the Scan Gauge mounted on the dash.

I guess a better question is, is it OK for the alternator to be engaged 100% of the time? The regulator paperwork is sparse and just directs to system voltage hookup.
 
I guess a better question is, is it OK for the alternator to be engaged 100% of the time? The regulator paperwork is sparse and just directs to system voltage hookup.

If the alternator have ignition, ground, battery and a pulse in the form of PWM from the computer (the other 12 or 14 AWG wire in the harness is the ground supplied by the PCM, the other is the ignition) and spinning at the same time it is engaged. 100% engagement or 50% engagement depends on the demand for voltage based on what the PCM reads on the buss.

Alternator engagement time is not something the average person should be worried about. Having enough output to run all the accessories, keep the engine running properly and some left over to maintain the charge/power in the battery would be only concern to most of us. As a matter of fact, adjusting the engagement time of the alternator is not something most of us are capable of doing,...well, interrupting the ignition to the alternator would do that. Or maybe building some sort of electronic device (regulator) that will supply only a short pulse regardless of battery voltage and/or power demand. That IMHO would be a bad idea.

Whether the charging is controlled by the PCM or an external regulator, having an alternator with sufficient output is the key. That is why I replaced the 85 AMP alternator that my XJ was fitted with as OEM to a 165 AMP unit so I could feed the power hungry cooling fan. I am still running the original PCM and it does a much better job than the after market external regulator I tried for a couple of weeks.
 
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