Inga my faithful 1986 245DL has an 100 amp alternator out of a 740. I have noticed that the voltage output is always 14 volts starting up in the morning, but as you make your stops to get gas and coffee by the time you get on the road the voltage would be down near 13.3 volts. On a long drive of 300 miles with a couple of stops the voltage dropped to 12.6 volts.

That put me on a crusade to find the source of the voltage loss and having an 86 wiring was my first suspect. The power cables from the alternator and starter, and battery are new. Still the voltage dropped as the car warmed up. Lots of fuse cleaning, connection checks, and other tests without any real change.

Did the kick butt light modification per Dave Shannon, well I used new relays and spliced the old wiring. But the lighting was improved and it did seem at first the voltage did not drop as fast. But checking the voltage showed that that as the car warmed up, the voltage dropped. There have been many of modifications to the wiring also. The one constant is the voltage drops and the car heats up.

Make all sorts of charts with various grounds and at places like fuse 13, fuse 3, the alternator excite voltage, and the plus terminal of the battery. After all the measurements and I felt like I was not really finding a source of the drop.

Today on the way home at highway speeds and the swamp cooler sucking air across the coils I noticed something I should have much sooner. The voltage when you start the car cold and get up to highway speeds along at highway speeds resulted in 13.8 volts for 25 miles. When I exited the tollway and reached stop and go speeds the voltage dropped down to 13.2 volts. Got ready to take some more readings at the house and when I reaches in to measure the alt excite voltage when my arm felt all that heat off the exhaust manifold.

The light went on and I went to the garage and got the electronic freeze spray. Gave the regulator assembly a good long shot of the spray and quickly measured the voltage across the battery. The voltage had climbed to 13.8 volts. Just for luck let the alternator warm up and the voltage drop on down again. A hit with the freeze spray (I miss R12 for doing this) and the voltage climbed back up.

Heat from the manifold seems the source of the drop, at least that is the way I am headed. However how to stop the heat from reaching the alternator is going to take some sort of heat shield to deflect the heat

Anybody have something like that installed? I was thinking about a a simple shield between the regulator and the the manifold. Reflect the heat and allow the swamp cooler to pull air over the unit more efficiently. Has to be stiff enough to hold it's shape rolling down the road of course.

The thought that the 100 amp Alt is on the other side of the 740 and is not subject to the heating that it is on the 240 is also a thought. The regulator assembly could also be more sensitive to heat than the one used on the 240 units. This is a lifetime part and they will give me another unit, but this is my third unit in the last seven or eight years, and they have all done the same thing voltage wise. That is why I am headed towards blocking the heat.

Any other thoughts and tests, please let me know.

Regards,

Paul

The charge voltage is reduced with ambient temperature to prevent boiling the electrolyte in the battery. All voltage regulators have a temperature sensor and some have a remote sensor mounted on the battery. There should also be a difference in charge voltage in hot verses cold weather. You can find charge voltage verses ambient temperature diagrams in most repair manuals including our green manuals.

Right on the money. I thought the 240's placement of the alternator made an extreme example out of it in this regard, but it has not yet become a problem for me - meaning the battery is charged and the lights "work".

But if one is performance minded, or trying to get the utmost from the headlights, an external regulator would be my suggestion. I believe Dave Barton recommends one on his page http://www.davebarton.com/AdjustableVoltage.html which might reach to a cooler area of the engine compartment.

Here's the chart you probably have in the books for your 81, back when some 240's had externals.



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Art Benstein near Baltimore

I totally take back all those times I didn't want to nap when I was younger.

Well first of all Inga is an 86, must have released the mouse button too soon. What I get for adding a post late at night.

The issue is on hot days and this has been a long hot summer. The 90 degrees on Sunday felt really nice and cool, and that is sadly not a joke.

The voltage drops below 12.8 volts and the battery is not getting charged. I know because of a long drive in the upper 90's two weeks ago. Stopped a couple of times and the voltmeter was just above mid range on the 12 when I stopped the engine at the kids house. I had a feeling that the battery was doing some of the work and had my son in law hook up a battery charger. The needle went to almost 60% and the battery charged right up. Did not have a problem going back,it had rained, the temps were in the mid 80's, and at night. Did the same check the next morning and the battery had a full charge when I hooked up the charger

That 100 amp alternator does not like being under the heat lamp is my bet. Was going to heat sink the regulator and install some sort of heat shield but I like your idea Art.

Seems IPD sells an adjustable external regulator, anybody installed one of these? Anything other parts required to do the job right? Where would you mount it (far away from that manifold of course)?

Regards,

Paul

Oh, Paul, I feel as if I know Inga like one of my own stable, even though I've never owned a 85-88 Volvo. You probably read what I edited out here.

I'd use the common sense I wasn't born with to find a cool spot to locate Dave's external -- anything would be better than below the exhaust manifold, right? One of them Bosch designed was meant to be sensed at the battery, which is the device the regulator is meant to protect! Sorry, I can't offer any advice on IPD products -- no experience. None whatever, except the feel of driving on their bars - exquisite! Go for it.
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Art Benstein near Baltimore

Mother Superior called all the nuns together and said to them, 'I must tell you all something. We have a case of gonorrhea in the convent.' 'Thank God,' said an elderly nun at the back. 'I'm so tired of chardonay.

Art, did you edit that post? Or was I hallucinating the first time I looked at it?
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'80 DL 2 door, '89 DL Wagon

Don, I absolutely did edit it. Even admitted that in the post. The rant isn't fit for this forum, and wasn't meant personally, so I excised it.

Where is your regulator temperature taken?

:-)
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Art Benstein near Baltimore

There are two theories to arguing with women. Neither one works.

Missed that edit mention. Must still be seeing things. Or not seeing things.
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'80 DL 2 door, '89 DL Wagon

I believe the original Volvo external regulator can be made adjustable by replacing one of the resistors with a pot. I have the schematic somewhere if anyone is interested.