alternator question

[kiwiwonder]

I just got my alternator rebuilt. A 3b 12v alternator from an bj60 in an fj40 with a 3b motor. I was testing the voltage at the battery and at the terminal labled B on the alternator. (I assume where the alternator power goes out to the accessories and eventually the battery. is this correct?) In idle with no accessories going the volts at the battery were about 14.05V and at the b terminal on the alternator 14.2V. It is the same with rpm's higher. When the radio is on, fan on high, and the headlights on high, and the cruiser running higher rpm's (not sure how high as it has no rpm gage) the volts at the battery are 14.05V and at the b terminal on the alternator they are 15.55V. Is this normal. Why the .15v drop between the alternator b terminal and battery in idle and 1.5v drop when rpm's are high.

 

[Radd Cruisers]

BJ60 model diagram

 

[Radd Cruisers]

We are doing the same testing today and came up with the exact same numbers you have on our 1hz.

The drop is due to the battery being charged, only explenation I could think of.

 

[kiwiwonder]

are you sure the drop is not from the accessories using voltage? does the power go from the alternator to the accessories then the battery or alt to bat then bat to accessories?

 

[Radd Cruisers]

Nope, strait back to the battery, we wired direct ourselves?

 

[s79bj40]

electricity, to use a silly example is like a big pie, its not each acc grabing a piece then the bat getting the rest, or the bat getting it first then the accs. It is like each thing in the system grabing a piece at the same time. So yes the power goes to the bat first, but the power does not actually have to physically travel through the bat before it gets to the accessories, the power goes onto the post and straight back off again reducing the amount the battery is getting. So even if something is wired a long way down the line, it will still reduce the whole system voltage the same as if it was wired directly to the alt. (depending on where the voltage regulator and sensor is)

sam

 

[lumpy70]

The more current you draw, the more heat you produce. The more heat you produce, the more resistive your wire becomes...therefore the voltage drop is higher when all of your accessories are on. Your wire in itself is like a mini-resistor.

That being said, your alternator puts out a healthy 15.5V at high idle and your battery only needs about 14V to charge, so you are fine.

Craig.