Jump to content


Photo
- - - - -

Is this alternator behaviour weird?


  • Please log in to reply
7 replies to this topic

#1 Spiff

Spiff

    Advanced Member

  • Members
  • PipPipPip
  • 200 posts
  • Location:Norge
  • Cars:720, mazda b2200, merc s320

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

DanielC

    Senior Member

  • Senior Member
  • PipPipPipPipPip
  • 4,614 posts
  • Location:West Linn,Or

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

flyerdan

    Senior Member

  • Members
  • PipPipPip
  • 260 posts
  • Location:Salem, OR
  • Cars:93 Blazer that needs parting out.

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.


Whoever said "You can't fight city hall" had obviously never met Marvin Heemeyer.


#4 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 70,321 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

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.


Posted Image

#5 Spiff

Spiff

    Advanced Member

  • Members
  • PipPipPip
  • 200 posts
  • Location:Norge
  • Cars:720, mazda b2200, merc s320

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

datzenmike

    KING RAT

  • User Administrator
  • 70,321 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

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.


Posted Image

#7 Spiff

Spiff

    Advanced Member

  • Members
  • PipPipPip
  • 200 posts
  • Location:Norge
  • Cars:720, mazda b2200, merc s320

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.

 

image.jpg
 
image.jpg
 
image.jpg
 
image.jpg


#8 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 70,321 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

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!!!
 
nlR9z1D.jpg

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...
 
olNItWV.jpg

... and put the male end of this plug on it...

QU7qygW.jpg


Now it just plugs into the stock harness.
.


Posted Image