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Is this alternator behaviour weird?


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#1 Spiff

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Posted 03 December 2017 - 05:42 AM

I decided to check how my charging was so I started the car up cold(82 720) and on idle voltage across the battery was 14.5. 

I turn my headlights on and my heater fan to max. Voltage dropped to about 14.05

Still good I thought but I let it sit and idle for a little while and as it got a little hotter and the rpms dropped the voltage dropped and at idle it was about 13.5 without lights and fan and 13.03 with. I thought it was because of the lower rpm's but even when revving it to what it was when cold it wouldn't go up to more than  13.5-13.7. 

Why does it charge more at the same rpm when it's cold but not when it's warmer



#2 DanielC

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Posted 03 December 2017 - 06:06 AM

Sometimes the voltage regulator is temperature compensated.   "Normal" range is 13.5 to 14.5 volts. 

It would be OK to have slightly higher voltages in your truck, but if you are not having any problems, you could just live with it.  If you can come up with a spare alternator, I would keep one around.



#3 flyerdan

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Posted 03 December 2017 - 08:30 AM

What happened it when you started it, it took a lot of reserve power out of the battery.  The higher initial charge rate was to replenish it, and the additional .45v drop in charge was from the additional load of the lights and fan.  As the load decreases and reserve is built up, the charge rate drops.  It sounds like your system is functioning ideally.


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#4 datzenmike

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Posted 03 December 2017 - 09:37 AM

 My 720 gauge shows 6, 12 and 18v so the actual amount is kind of guesswork. I'd say around 14 but that's the point. Car makers know if too much raw info about the engine is given to owners that can't/don't interpret it, they come in asking why it's doing something different. This is why oil pressure gauges read so slowly. Real time gauges read almost instantly and on very sudden stops or hard cornering they will drop sometimes close to zero for a split second from oil slopping around. Same with the gas gauge. Temp gauges have a 'run range' and no numbers at all.

 

You need about 2.4 volts per battery cell so 14.4 charging volts. (you can charge at a higher voltage/current rate but, as the battery 'fills up' it should be reduced. Constant charging at a high rate is very bad for a battery)  But only initially, to quickly get the battery back to about 75% of it's full capacity. After that it's preferable to finish off the charge at 13.5 to 13.8 volts. 

 

Starting an engine normally takes only a minute or two to 'put back what was taken out' to start it. Usually much less.

 

So everything seems about right.


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#5 Spiff

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Posted 03 December 2017 - 10:55 AM

Great, I have a spare one but that's still just a 50A alternator. I'm researching upgrades now, found a couple of 90A and a 100A that should bolt in and I'm waiting on a measurement of a 110A. One question though: How much does a drivebelt deflection of 1mm have to say? One of the alternators I have found has the correct mounting width but the pulley is 1mm more to the rear then my stock one. (I could always make a 1mm spacer and fit behind the pulley though)

 

My rpms drop by 100-150 when I turn on my lights and fan, will a more powerful alternator prevent this? I'm also installing a stereo soon and a couple of gauges so more amps can't hurt right?? Also since I'm now running four coils and a cam sensor and standalone ecu I take it this takes some extra toll on the charging system because I can't remember it dropping that much before I switched to my current setup



#6 datzenmike

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Posted 03 December 2017 - 11:29 AM

That's only 0.040" about your thumb nail thickness... it's nothing, the belt will easily flex this amount.

 

When you turn on the headlamps the power to work them has to come from somewhere, it's not free. The alternator has to work to make up the power used and the engine has to work harder to turn the alternator. A newer alternator might be more efficient though and do it with less work. One hundred or so RPM is nothing to worry about. 

 

Four coils firing 1/4 of the time or one coil firing 4 times.... it's all the same.

 

I have a 100 amp alternator in my 710. The headlamps no longer flick when the turn signal is on and they are brighter. The heater fan blows like a tornado and does not slow even at stops and with the wipers on.


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#7 Spiff

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Posted 13 December 2017 - 12:29 PM

So today I got my x-trail diesel alternator. Bolted straight in, even the belt didn't need changing, although I'll probably go a little bit up in size to make it easier to install. I got the seller to cut the harness and include the plug also so. Yay, 90 amps :P

I also reckon I'd need a larger wire to the battery than the standard that's in my car atm.

 

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#8 datzenmike

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Posted 13 December 2017 - 05:08 PM

The 102 amp one I got, I kept the cable that crimped onto the positive battery cable on the Altima it came off of. I separated it and crimped a one? gauge lug and soldered it. This I bolted to the starter lug rather than trying to connect to the battery post. This Altima cable is heavier gauge than my 710 battery cable to the starter!!!
 
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This is my mock up engine on the ground. The ground wire went onto the engine bracket bolt. Once shaped I wrapped generously with electrical tape. Covered everything with harness shielding. You can buy or just strip it off something in a junk yard.  You could also use garden hose for chafe protection.
 
I took this plug...
 
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... and put the male end of this plug on it...

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Now it just plugs into the stock harness.
.


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#9 wayno

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Posted 22 February 2018 - 06:39 PM

Damned computer just dumped my whole post when I was just about finished.

 

I picked this thread because it was titled correct for my issue.

 

Has anyone ever heard of a Nissan alternator with a sticker on it that says "IC Internal" that doesn't need an exciter wire?

I have one I put into my truck that I had not even plugged in the "T" plug yet and it is putting out 14 volts after I rev it the first time, when I start it it pits out just over 12 volts, but when I rev it it jumps to 14 volts without an exciter wire, it does exactly the same thing with the "T" plug installed.

 

My 521 work truck has been converted over to an internally regulated alternator, I bypassed all the wiring harness except for the wire going to the light, the exciter wire comes straight off a keyed circuit in the fuse box.

 

I don't understand why it is charging 14 volts after I start it and rev it without any wire connected to it except the charge wire going to the starter post and the negative wire going to the old external regulator mount bolt, I don't need the "T" plug connected, what is going on???


 

 


#10 datzenmike

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Posted 22 February 2018 - 08:09 PM

Wayno the 'exciter' wire just kick starts the electro magnet inside. Once charging it's self replenishing, I think. What happens is there is some residual magnetism in the alternator, just a little, but when revved it's enough to get it going.

 

My 100 amp alternator was wired in with the two plug wires reversed for 3 years!!!!!! I never noticed the red charge light not coming on I just drove it trouble free this way. It wasn't till I installed a volt gauge I noticed it not charging and then charging randomly. The battery might get a little low, just about 11 volts, but it would always kick in well before it was noticeable, like hard slow starts or dim lights.


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#11 wayno

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Posted 22 February 2018 - 10:51 PM

I plugged the "T" connector in and it made no difference, I might take it off, I just don't know, I was not expecting the result I got, especially the blowing of the ign light, and that stuff is very hard for me to get to with the tilt column and all the other shit in the way, it is easier for me to remove the instrument cluster to change a bulb.

I was getting snowed on when doing this, it was 35 degrees outside, the only reason I could even work on it was because I started the engine and warmed it up checking wires before I pulled the bad alternator, and once installed I started the engine to see if it worked, I did 3 alternators, pulled the battery 3/4 times, lifted the truck several times to get to the alt mount bolts, and this was after I finished working on the hydraulic cylinder.


 

 


#12 wayno

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Posted 23 February 2018 - 04:34 PM

Here is the sticker on the alternator, this is the best photo I could get.

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It says something about "IC REG built in", is this the reason it doesn't need an exciter wire?


 

 


#13 datzenmike

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Posted 23 February 2018 - 04:57 PM

That's a '79 210 alternator.

 

Internally regulated just means solid state (transistors) used for regulating the current through the field coil attached to the spinning rotor. Current through the coil magnetizes the iron core. The strength of the field core magnetism can be increased or decreased to produce more or less current and voltage in the stationery stator windings under the outer case. As I mentioned the iron core surrounded by the field coil may still be magnetized even with the field coil turned off. (unplugged) But there may be enough residual magnetism remaining to get enough output for the voltage regulator to take over and keep going. 

 

 So the only problem of running without the plug in is no warning if the alternator craps out.


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#14 wayno

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Posted 23 February 2018 - 06:00 PM

I have a volt meter right next to the oil pressure gauge that I am always looking at, that is how I knew it was not charging, I cannot see the dash lights very well during the day, but I did notice when the ign light blew as it was very bright for that moment on the second alternator.

So it came off a 210, I wondered where I got that one, how many amps is it?


 

 


#15 datzenmike

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Posted 23 February 2018 - 06:29 PM

LR 150 so... 50amp.


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#16 banzai510(hainz)

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Posted 24 February 2018 - 02:59 PM

I would think the T connector still supplys 12volts the copper field. wen key is ON

 

IC means intrigated Circuit I believe.  Transistors ect..........(for the Volt reg)


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