Just thought I would pass this information on for those it may help.

I always seem to have a low charge rate on my car and it gets worse over extended driving periods. Its wired up correctly if you take what you read and understand as fact. IE "S" terminal is the live sense feed, "ign" terminal goes to the battery an the "L" terminal to the lamp.

So mine is wired up so the S & IGN are put together and connected to the big B terminal on the alternator as this becomes live from the cut off switch and passes directly to the battery.

I got talking to a friend of mine who is a loom maker for a living, he makes for F1 and WRC clients as well as us mere mortals so he knows what he is talking about.

I told him my problem and he said do the following:

Run an earth from the chassis to the alternator. Regardless of if you have one on the engine etc.

The IGN is fine connected to the B terminal on the alternator as I don’t have a key.

Connect the “S” wire to something with a load, best thing is the high pressure fuel pumps live feed, as this is the most important thing really and varies under load.

He said you should see bout 15Volts + if everything is correct and the alternator is up to the job.

So I connected it as per his instructions and I replaced all the wiring other than the Lamp feed.

Fired the car up and its now charging at 15.9volts at just over tick over. Exactly spot on to what he said.

He also said so many problems are caused with the mapping and running of a car because the fuel pumps don’t see 13v constantly or under load, this causes low fuel pressure and a performance drop under pressure.

So if you think this would help you give it a try, it does seem the voltage is a tad high, I will get my meter out again in the light and test it at various load sites on the car, as the pumps are now the sense I guess there should be 13v on them now and the stack dash is just reading the charging rate voltage without a true load.

For information purposes I use an 80amp racing alternator, an Edge type one.

He also said if alternators get heat soaked they can run at a 60% reduction so if you can duct some air to them do so.

The duct of air should go in the back and only needs to be small in diameter.

James

I work at an alternator factory and our test paramaters for voltage reg switching are 14.2-15.4 volts at a constant 10A load so that does seem too high. Mid to high 14s are perfect.

As for efficiency they do run a hell of a lot worse when they are hot, this is very true. Air on a compact alternator though is designed to be ducted in at the front and rear then pushed out of the centre via the 2 fans inside, on a topf, the old ones with the external fan it's in at the front and through so your ducting can go to the front or the rear depending on space constraints. Running it cold means less torque required for any given load so technically you are gaining power too, not a lot though........

HTH
Stott

Hi Scott

Thanks for the reply, I agree it is high, but I have in my hand the dyno sheet that came with the alternator and it says

"Voltage Regulator set point is 14.5v"
Max Output Power 1183 watts
Max under full load 91amps

So I am guessing the stack dash is reading slightly high and I will test the true voltage on the fuel pump terminal and the batery.

Before I was getting 11.9 when hot and 12.5 coldish.

I have had continual electrical problems untill I sorted out a VR sensor connection and got an alternator built by SC in Harlow.
I recomend Steve he knows what he is doing, built an alternator specifically for me and is VAT free

"Voltage Regulator set point is 14.5v"

That's bang on, mid 14s, and that's what you want to be measuring. If you're getting a true 15.9 the reg isn't switching properly due to fault or the sensing circuit not being connected correctly.

Before it would seem you had no charging at all, just battery voltage.

Cheers
Stott

Edit: Just re-read our post. If that voltage was taken at your fuel pump terminal it's possibly low due to volt drop in the cable, if it was at the battery or alt b+ I'd say it wasn't charging

[Edited on 27/5/10 by Stott]

15.9v is simply far too high, it will cook your battery in short order.

The sense line is designed to sense battery voltage, in order to compensate for the voltage drop across the high current cables. Connecting it directly to the alternator output will bypass this function and give you the lower charge rate that you were seeing before.

However, connecting the sense line to a high current device some distance from the battery makes it look to the alternator like the battery is at a lower voltage than it really is, which is why your charging voltage is now far too high. The sense line should be connected as close to the battery positive as possible.

Your charging amps should drop off after running for a few minutes it is because the battery is approaching full charge.
After starting the engine initially you will always see a high current showing because the starting the car has taken charge out the battery. This current will slowly drop away as the charge is replaced until after 20minutes or so only a small number of amps will be getting pumped into the battery.

I should point out reading the voltage directly from the fuel pump terminal will always tend give a silly reading --- the fuel pump is a large inductor that is getting switched on an off.


Charging voltage is always measured across the battery terminnals at 2,000 to 3,000 rpm -- A charging voltage anything more than 14.9 volts across a lead acid battery on or off load is seriously bad news. The ideal range is 13.4 to 14.7 volts depending to some extent s on electrical load and state of charge of the battery and size of alternator. Some modern calcium doped lead acid batteries might show 15.1v.

I had another word with my man this morning and I am going to put the sense wire on the ecu feed and take a Reading.

He did explain why it was Reading so high, I need to balance the sense feed so I get 13.5 to 14.5 volts.

He said it should run better when sorted. Good though isn't it this electricary!!!

Had a go at it last night and tried the sense wire on various pickups, I now have it so its charging between 13 and 14,5 depending on the revs and load.

So I am happy.

That's more like it, happy days

Stott