13,8 V idling charging voltage ok ?

850 TDI automatic 1996 with 265.000 km

Last year in summer 2008 before a trip through countries with sparse
Volvo-support possibilities I had my mechanic change the brushes-regulator-unit
of the alternator at about 240.000 km kilometrage. I was a bit under time
pressure so he could get hold only of one from a Volvo dealer, cost about 100
Euros more than from a "normal" shop, though probably the same product. I had
bought the car with about 210.000 km kilometrage and had no idea whether the
unit had been changed before. I did not want to get stuck because of worn
brushes. Befor winter I changed the battery - put in a new 75 Ah unit.

Now during summer I have the Eberspächer engine preheater on for about half an
hour in the morning, drive to work about 1 hour 80 km, then back home without
engine preheating the same distance, headlights low beam on during driving, air
condition fan, too. In my opinion that driving should be enough to charge the
battery after the engine preheating current loss in the morning. I was curious
how "charged" my battery actually was and connected my home charging unit, 10 A
max output. I was surprised that it took about 2 hours charging until the
charging current dropped to zero, did not measure voltage, but supposedly
14,something Volts.

So I decided to check the voltage at the battery terminals - according to Haynes
manual it should be 13,5 - 14,8 V during engine operation. The reading was at
idle rpm without anything turned on - 13,8 V, after turning on the headlights
13,7. When turning on all possible stuff - seat heaters, back window heater,
fan, high beam light etc, even with highers rpms the reading dropped to 13,4 V.

I tried to increase my wisdom on battery charging voltages:
http://www.batteryuniversity.com/partone-13.htm.
13,8 V would just fit the 2,3 Volts, but still is the lower limit.

Do I have a faulty regulator unit or does it behave as it should even at the
expense of submaximal battery capacity?
Any other comment on the values measured? Any other check I should do?

Franz47

 

In our family we have another Volvo: 745 TD 1989 - I just checked the idle
voltage - 14,5.

Franz47

 

Hi,
mine is 850 TDI, manual, 11/1996, 373.600 km.

Last time I was checking the voltage was during last winter at -6 C.

Radings were the following:

-battery itself -- 12,45 V
-preheating glow plugs on -- 11,25 V
-moment of ignition/starting the engine -- 9,80 V
-idling at 1100 rpm -- 14,15 V
-idling at 850 rpm -- 14,26 V
-idling with lots of stuff -- 14,03 V

Srry, I don't know if your regulator is OK, but 13,8 V seems a little
bit low. Check the battery terminals and clean them, also check the main
cable if its corroded...

Good luck!

 

It is perhaps a hair low, but I would consider 13.8V to be perfectly
reasonable. If it's too high, the battery will overcharge while you
drive as it is constantly connected.

 

Sounds reasonabler than my values. Maybe I threw the old battery out
prematurely.

Everything is fine there, lubricated with the proper stuff. I actually put the
meter´s pins onto metal parts of the cable, too.

I think I will change the regulator again....
Franz47

 

My other Volvo, the 745 has a battery (brand Hoppecke - unfortunately they
quitted to produce car batteries some years ago) for many years working fine
with the higher charging voltage. I do not use theis745 during the winter, keep
the battery in the basement with a timer switch attached to a battery charger
for 15 min every day. The charging current drops at a voltage above 14 volts
with this charger.

Sulfatation is described as a consequence when the battery ist stored not
completely loaded for extended time. So that is what I am afraid of. The old
battery which I replaced was only about 3-4 years old. It had been bought by the
previous owner, he kept the car well in my opinion.

I think I will ask people at a local Volvo forum to measure the voltage on some
855s before buying a new regulator

Franz47

 

Also are you checking the voltage on the output terminal of the
alternator? There may be a bad connection somewhere if it is low elsewhere.

 

Good idea. Quite difficult to get there. I had a look today, no nut visible at
the alternator terminal, everything insulated. How would I get access there to
the terminal? BTW is it necessary to remove the whole alternator to change the
regulatur-brushes unit?
Franz47

 

http://www.moll-batterien.de/prod_m3_plusk2_2.html this battery has a "magic
eye" visible through a window in the cap of one cell. Should be green when
battery fully charge - shows green also. So everything is probably ok anyway
and maybe the external battery charger overcharges.

The cheapest German made alternator available would drain my pocket by about 300
Euros. The new battery was about 100 Euros. So I will go ahead without doing
anything and just regularly check the battery voltage, bull eye and idling
charging voltage.
Franz47

 

As usual James is right!

I took the time now to have a closer look. The voltage at the alternator
terminal was 14-14,1 Volts, exactly as it should be according to the regulator
specs. There is a 0,3 V voltage drop between the alternator terminal and the
cable terminal at the battery.

Although I removed the cable from the alternator terminal, sprayed it with
electrical contact spray, cleaned it with fine sandpaper, the same with the
surface of the nut pressing the cable terminal to the alternator terminal -
nothing changed. The cable terminal on the alternator is connected with the
cable in a way I cannot do much about. Maybe there is a resistance. On the
battery side the cable turns into a terminal without much to do either. The
voltage drop is already at the battery cable terminal. There is no more voltage
drop between cable terminal and battery terminal. The cable disappears form the
alternator into the depth of the space - is there a connection at the starter
which could be the culprit?

Franz47

 

There will always be a voltage drop over a length of conductor when there
is current flowing, The drop (V) depend on the current (A) and the
resistance (Ohm).
Do not forget the negative part of the cirquit.
I am not familiar with all Volvo solutions at the alternator end, but at the
battery end we have the cable from the negative battery terminal to the
ground (chassis or transmission). That should be checked at both ends.
And for the positive part you probably could run an additional cable
directly from the alternator to the battery terminals, that is what the
experts did on my Toyota.
Any comments James ?

Asbjørn

 

I did not measure current to the battery plus, then I could calculate the
resistance. 0,3 V voltage drop still eems to be quite a lot for a thick copper
cable connection of such a short distance. I will measure on another car.

I could measure a voltage of 0,3 Volts between positive alternator terminal and
positive cable/battery terminal at the battery. Any resistance on the negative
side of the circuit cannot influence this result.

I think I will have a look at a possible connection at the starter between
alternator and battery, if it is accessible from above.

Franz47

 

There's a black cap that pops off the back of the output terminal where
the big red wire attaches.

Depends on the car, 740 you can easily change the brush pack/regulator
with the alternator in place. Most 240s you can too, but the turbos are
a lot tighter down there.

I've never had to replace the alternator itself, they're quite dependable.

 

0.3V is not very much given the current potentially involved. The wire
does connect to the starter, along with another wire that goes to the
battery.

 

The connection at the starter should be accessible, you'll have to
refresh my memory as to what sort of Volvo this is. You also might see
if you can get a probe in to the exposed copper wire immediately before
the terminal and measure between that and the terminal to see if you
have a bad connection there.

 

855 TDI 1996 December (in VADIS I find it only under 1997) with
D5252T MSA 15.7 diesel engine and
AW 50-42 automatic transmission.

Franz47

 

Thanks for the tip. I found that, when I had a look yesterday under better
illumination.

In the 855 one has to pay the price for front wheel drive and engine mounting 90
degrees to driving direction.
I still have another 745 TD 1989, which I have used many years and my wife now
ses in the countryside. I have changed the brush-regulator there, really a
breeze. Plenty of space around the engine.

Not me either since my first car with an alternator, a Citroen 2CV in the
seventies last century. Not even mechanical parts have failed. I just changed
the brushes once a while in these alternators, nowadays including the regulator
unit, making it much more expensive. The regulators are overpriced, for the
money the tiny little, probably very primitive circuit costs, I can get a b/w
laser printer with duplex unit...

Regards Franz47

 

Ah, I'm not gonna be much help with specifics then, unfortunately the
last Diesel powered Volvo to reach this continent was the '86 760.

I'm actually surprised I haven't heard of anyone importing an 850TDI,
but I've yet to see one in the US.

 

At least in the case of the older Bosch alternators, you could get a
brush pack meant for even older ones that work with an external
regulator. I've seen late 80s 700 series cars retrofitted with late 70s
style external regulator. I don't know what sort of alternator an 850
uses though.

 

I don´t know which kind of gas guzzlers the gasoline versions of the 850 are,
but the 2,5 l Audi TDI diesel runs on about 6,5 - 7 liters/100 km (makes 36 -
33,6 mpg), which was good fuel economy at that time for that car size.
Franz47