I just installed a brand new 200a alternator.
At idle the dash battery guage now runs LOWER than it did with the stock alternatorn (and I mean 16 yr old stock alternator!LOL).
At idle it will now drop as low as 10v!
But as soon as I rev it it'll go back to 14-15v, is this normal?

Now this MAY be because I have not put in the thicker guage battery wire yet, which leads me to another question, the positive terminal wire seems to run from the battery to the starter.
Is that the wire I have to upgrade? I can't see any other it can be but I thought the point was to upgrade the output for the alernator itself?

Any input is greatly appreciated.
Thanks.

 

a lot of the time, the higher amp alts require higher rpms to start making any power at all. You could put a bigger pulley on it, or get a replacement more along the lines of what you will be using, like a 110 amp or so.

 

Actually, a smaller pulley would make it turn faster to output at idle. I had a stocker rebuilt to put out 140 amps, and the facility put a smaller pulley on it for that reason. It doesn't have to be a whole lot smaller, I couldn't tell mine was until I put the old one next to it. Hope that helps.

 

yea, my bad. Smaller not bigger. I'm retarded in the morning.

 

sweet, makes perfect sense for the smaller pulley (I wish they'd put info like that on the product when u order it!!!)

Now I just searched around really quickly and can't find much for "alternator pulley" other than ones that don't mention being bigger or smaller...any recommendations on where I might find a smaller one?

 

When I worked at a parts store we ended up swapping pulleys quite often for customers. Consequently we had a box full of different sized pulleys just sitting under the counter. Can't hurt to ask a local parts house.

 

OK so now I have my smaller pulley and the volts still dip below 13 at idle....?????

 

If you higher the rpm like 200rpm does it bump up to around 14.4V (at 20deg celcius outside) you should charge that when around 900rpm (stock one puts out 14.2 at idle 750rpm)..

Is your battery fully charged ? an half full battery or almost empty battery will give these symptoms too..

Have you checked with an voltmeter at the battery ? or just looking at the gauge inside the car ?

 

I have had to switch the old and new alt a couple of times now and the old will still keep a 14v charge when running.
The old one only dips at idle IF I have my fogs, blower, headlights and stereo on which is why I got a high output in the first place.

The new one will still dip to 11v at idle whether I am running a lot of accessories or not, but is a good strong 15v when running over 1000rpm.

Just doesn't seem to make too much sense either way, smaller pulley made NO difference to the new alt.

(on the dash, but I have checked it before and the dash IS accurate)
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Maybe I need to adjust the belt tensioner pulley because of the smaller pulley on the alt???

Surely that would add a tiny bit of slack....or is it self adjusting....?

 

every alt is slightly different and will have a min rpm for making charging voltage, and what current it can produce that voltage at that rpm. See what yours is and what you're actually measuring and then you can start troubleshooting things.

edit: it should be like a graph or chart that is specific to your model.

 

hmmmm...maybe my idle is low, I'll check that too.

Also, I have not added the thicker guage battery wire yet...the wire I bought seems to be the wire that runs to the starter, but I thought the point was to upgrade the wire FROM the alt TO the battery??

 

When installing a new high AMP alternator you should put an new wire to the battery directly is that what you done or did you go down to the starter ?

That would also help out.