1998 S90 alternator output

thefisch · Post by **thefisch** » Mon Sep 23, 2019 7:50 pm

Wondering what you all consider a normal output range for the alternator on a 1998 S90?

Car has been driving fine and no warning lights. But we had a dead battery due to a light being left on, and so I am checking the battery and charging system. During testing on the alternator, I am seeing voltage ranging from 12.3v to 12.9v. Most of the time the output 12.7v.

I don't have any experience with prior Volvo's and how much output is typical for their alternators. My 2010 Honda typically put out 13.7-14v and my 2011 Mercedes put out about 12.6v which was apparently normal for that car. So the S90 seems to be low output compared to the Honda but not low when compared to the Mercedes.

Post by **jimmy57** » Mon Sep 23, 2019 8:35 pm

That Volvo should have output like your Honda. The Mercedes has a controlled alternator that gets regulated by the engine control module like newer Volvos. The newer car (mid 2000's and newer for many makes) alternators will have outputs in the upper 14 V range at times and will go to very low charge at other times. If the alternator output is 12.6-12.8 then the load on engine is less and if alternator has already recharged the battery from starting the engine then no battery discharge will occur at that lower voltage. The new way of doing it is to go to a very high charge rate on lift throttle as injection is shut down and no fuel is burned and the charging then costs no fuel. That S90 has a conventional voltage regulator with none of that. Alternator output should be checked with engine at 1300-1500 RPM. Often with daytime running lights and cooling fan on the voltage will be low. A 120 Amp alternator puts out 65 or so Amps at idle and if the consumption for lights, cooling fan, blower motor is 61 A then the voltage will be lower.

thefisch · Post by **thefisch** » Mon Sep 23, 2019 9:14 pm

Ok, so if I should be seeing 13.5v or higher at about 1500rpm, then I can check for that. Thanks.

thefisch · Post by **thefisch** » Tue Sep 24, 2019 7:23 am

Just realized that the dead battery probably created additional load on the alternator and could explain a voltage drop. The testing was done after a jump start and short drive but the battery was only 10v. So to be fair to the alternator, I need to charge the battery (or replace if bad) before judging the alternator output.

I assume that the output of 13.5v or higher is the desired target without load, because with load I would expect that voltage to drop too.

Post by **jimmy57** » Tue Sep 24, 2019 8:02 am

13.7 would be target after a few minutes. Initially it should be close to 14 if not a few tenths more. When the load is 75% +/- of the alternator capacity with adequate RPM the voltage will begin to slip below 13.7. If you have lower voltage then set meter to AC V and check to see if the AC voltage is more than 100mV (.010 V). If there is a faulty diode in the alternator it will knock 25% or more off the amperage and AC voltage will be more than the 30-50 mV usually seen from normal AC waveform from diodes.

thefisch · Post by **thefisch** » Tue Sep 24, 2019 9:11 am

Thanks for the info. I will check the AC V if the voltage is lower than desired.

thefisch · Post by **thefisch** » Wed Sep 25, 2019 6:20 am

Somewhat of a related question since I am new to Volvo, I was planning to pull out the battery this weekend to charge and test it and possibly replace. But at first glance, there does not appear to be a battery hold down bracket on top. Does Volvo not use a bracket across the top of the battery? Perhaps mine is missing. The only bolts I see are the 10mm bolts on the cables but surely those can't secure the battery.

Also, I know I will have to enter the radio code, but will I lose other settings like memory seat or radio presets when pulling the battery out. Just wondering if I should bother with a tender or not.

beav700 · Post by **beav700** » Thu Sep 26, 2019 2:34 pm

There should be a rod, looking like an EYE bolt that holds the battery down with metal plate. Most rust away and break off. I drilled some holes and use metal strap to hold mine in place under and over. The metal under my battery was all rusted out. Had to do some sheet metal work.

beav700 · Post by **beav700** » Thu Sep 26, 2019 2:35 pm

Oh, and I'm getting 13.4v on mine 1998 S90

thefisch · Post by **thefisch** » Thu Sep 26, 2019 3:10 pm

beav700 wrote: ↑Thu Sep 26, 2019 2:34 pm There should be a rod, looking like an EYE bolt that holds the battery down with metal plate. Most rust away and break off. I drilled some holes and use metal strap to hold mine in place under and over. The metal under my battery was all rusted out. Had to do some sheet metal work.

Oh boy, I will be prepared to improvise then. If the original eye bolt is there, I hope it is not too rusted and will turn so I can remove the plate.

beav700 wrote: ↑Thu Sep 26, 2019 2:35 pm Oh, and I'm getting 13.4v on mine 1998 S90

Thanks for the data point on voltage