Worn alternator brushes?

Brad

The photo shows the brushes from a 100A Denso alternator in a 94 940. Am I correct that these brushes are worn and should be replaced? The alternator doesn't seem to charging at idle as I've seen the battery voltage sitting at or below 12.3 volts.

Image description

I appreciate any help.

ramrod

Good luck finding a regulator that will work for that alternator.

I gave up, changed to Bosch

jamesinc

Yeah those contacts are pretty worn, they may well be the problem.

It may be possible to rebuild it with new contacts yourself, you can buy just about any size on aliexpress.

ramrod

The other problem with those is the diode bridge

They’re not repairable

The youngest of the denso’s is 30 years old now, I wouldn’t trust one

TL_V70

Thoes brushes are 100% replacable and its easy there not weird at all most auto Electricians can supply brushes or a complete holder ( the image you posted). Not necessarily your charge fault at idle tho

It would pay to look at the slip ring what the brushes run on inside the alternator for wear.

Does the charge rate come up above idle? And if so what voltage let's away 1200 to 1500 rpm?

Ex850R

How are the bearings on that old unit?

Brad

Thanks all

The slip rings look okay and the bearings still seem to run smooth.

Above idle the voltage increases up to ~13.8ish volts. The voltage is the same at the battery and the alternator so I doubt it's a cable issue. On going back to idle the battery voltage slowly drops back down.

As far as I know it's the original alternator, at least It still has a Volvo label on it. If it is original, the car has done 422K km.

arebee

I repaired a Denso alternator from a 940, works well now, bought the bits off eBay, quite an easy fix, provided the bearings are OK, and the rest works, which in your case definitely sounds like is the case.

https://www.ebay.com.au/itm/301222347380

John_Fraser

All alternator regulators reduce the charge voltage in hot weather to protect the battery. An important question is that voltage maintained when you turn on a bunch of loads like lights, heater blower, etc.

TL_V70

John_Fraser I disagree all alternators reduce the charge voltage in hot weather to protect the battery. I work in a very remote and hot area 45 - 50 degC and regularly see 150A-200A+ Alternators running at correct charge voltage and near on there load capacity 200A all day non stop.

Brad

I stumbled across that ebay link above on a Turbobricks post about repairing the Denso alternator. At least the parts are still available. I'll try an auto electrician for the brushes and see how I go. Thank again everyone.

BarelyRunning

I'm certain I have one of those sitting in a draw if you're unable to find one online.