slow to start alternator: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Jan. 12, 2010 8:41 a.m. foxtrapper SuperDork

The Volvo V70 alternator is keeping me scratching my head. Maybe some of you recognize it and can help me out.

Basically, when you start the car the alternator doesn't charge. After about 10-20 seconds, it starts slightly charging. Then it builds a head of steam and rapidly rushes up to 13.9 volts, which is where it sits. I've been watching this with a meter for a week now.

It will do this every time you turn the car off and restart it. Doesn't matter if you do it instantly, or wait overnight. Hot or cold. Rain, snow, sleet, etc.

No problem keeping up with the load. High beams, rear window defogger, etc. It never drops below 13.7 or so. It's charging.

My only real guess has to do with the field. As in perhaps it's not seeing the 12v startup it's supposed to see and is instead self-exciting from the spinning armature. I'm curious to hear what some of you think.
Jan. 12, 2010 8:43 a.m. John Brown SuperDork

Some alternators have a clutched type pulley. Inspect and replace.
Jan. 12, 2010 9:16 a.m. TJ Dork

I think it is working normally. I bet the alternator has a built in soft start feature to allow easier engine starting. If the regulator does not provide an alternator output for the first 15-20 seconds after starting then there is less load on the starter making the engine easier to start.
Jan. 12, 2010 9:28 a.m. ansonivan Reader

All new bmw alternators do the same thing, they all ramp up charging within 5-10 seconds.
Jan. 12, 2010 9:39 a.m. Dr. Hess SuperDork

Are you sure it isn't charging when it starts? Consider this: You start the car, which just sucked out a bunch of watts from the battery. The alternator is now pushing those watts back into the system, putting a load on the alternator and likely showing as a lower voltage on the overall system, as measured by wherever your volt meter is connected. After a brief period of time, the system equalizes and the voltage picks up to the regulated point. Just a theory. Before worrying too much about it, I would disconnect the alternator main charge wire and put an ammeter in series and see what the current versus time after a start looks like.
Jan. 12, 2010 10:59 a.m. xci_ed6 HalfDork

Or pickup an inductive ammeter, aka clamp meter. I got a craftsman for $50 that has peak hold and probe ports for V/O (so it is my 3rd backup DVOM). A bunch of my friends got them, probably half failed in the first month, but mine is still going 3 years later. So basically if it survives the warranty period you probably got a good one.

A very valuable time saver. It payed me back almost immediately.
Jan. 12, 2010 12:21 p.m. stuart in mn SuperDork

What happens if you blip the throttle after starting the car, say up to 2000 rpm? Some alternators won't start charging until the engine has been sped up over some threshold speed the first time; I had a Bosch alternator in my BMW that worked that way, but it was completely normal.
Jan. 12, 2010 1:26 p.m. foxtrapper SuperDork

Blip the throttle, it ignores you. Didn't realize some cars came with a soft-start type alternator. That may well be all it is. Might also be why it doesn't have a volt meter onboard.

Also see I turned myself inside out on the stator and armature with regards to who charges who.
Jan. 12, 2010 5:26 p.m. iceracer HalfDork

Should be charging app. 14.5 V.