Alternator - will it fit?

[Immortality]

The charge cable isnt the standard one. I had at one stage relocated the battery to the boot (and back again). The auto elec hadnt seen the car (was a phone convo) and he said some just had a larger charge cable.

I had an elec issue a few weeks back which had me inspecting all wiring, connections and a new bosch 85 amp alt. So i can confirm the terminals are in good nick. As are the earth's and the body earths are more than adequate size.

I have a Fluke 325 MM which has been assisting me in my fault finding.

This afternoon after work i checked battery voltage before starting. 12.4v.

I started the car with the dash in test mode and the voltage showed 14v. A mate was using the mm across the battery which showed 14.5 at idle.

Lights, blower fan, engine fan on and the voltage dropped down to 11.8 at battery at worst.
11.6 on the dash.
Turn the engine fan and blower off and things looked normal again, about 13.6 on the dash.

So standard accessories dont hurt it. If the idle was brought up to about 1500 we saw the voltage come back up over 12.5.

There was about 200milli volt loss between battery and dash readout. I see that as not bad.

So we think the issue is just an underprovisioned charge system.

My question now is, would a 120amp push enough juice at idle compared to an 85amp? Im aware they dont put out their potential at idle and thats where the magic needs to happen to get things good.

Cheers for all the replies guys

That all sounds fairly normal TBH.

Alternators are normally rated at about 1500rpm. If you have a look on the body of your alternator it will show the rated output voltage 14.4 and then 2 number e.g 35/85 these are the rated outputs at minimum rpm and max output (in my example 35amps and 85 amps). the 120 amp alternator will have a greater output at low rpm. How much more exactly I don't know, you would have to check the spec's on a 120 amp alternator.

 

[EYY]

Yeah agreed; and apparently the aftermarket alternators just don’t deliver the same current at low rpm as the genuine units. That’s why I used a VT alt for my conversion and not a Chinese one.

 

[gtrboyy]

Alternators have different ratings ....good ones you want will punch out maybe 50% at low rpm. eg vt 14v 60/120a

Ebay stuff iirc are mostly cheap agricultural alternators for machinery with low amperage rates unless steep pulley ratio....basically junk for cars.

When fan comes on is it just the 1 at low speed or got both running at high speed?

Bf/fg flow alot with a matching current draw hence alternator & cable upgrade...that's why I tried vs v6 thermofan & 85a alternator setup on vp ute to avoid extra labour/expense.

Young whippersnappers!!!!

 

[Deuce]

Bet I’m younger lol

I bet you are mate. Lol

 

[shane_3800]

VT alternators were upgraded for police cars so all VT's will charge at idle with hefty load. The police were getting sick of batteries going flat on extended parked sessions with all the lights going and radios on.

 

[Immortality]

I wonder if the OP has different pulleys? Maybe a gilmer drive or something similar?

 

[Dean1985]

Hey guys.
The alternator in question is a Bosch 85 amp. Exact replacement for this vehicle. I have recently cleaned all terminals etc while i was replacing the cam. The sense wire may have an issue in the middle somewhere (worth checking).

 

[Immortality]

The sensor wire has a fusible link on the battery end but generally they either work or they don't if the fuse blows. Did you have the battery in the boot? the sensor wire really needs to be on the battery as it takes into account the small voltage drop in the main charge cable unlike when people loop it directly to the alternator output when doing battery relocations.

 

[losh1971]

Yeah x2 when my battery sensor was damaged the alt put out no charge, no reading at all from the rear post on back of alt to ground.
Did the battery check out as ok?

 

[gtrboyy]

Sense wire works or it doesn't...testlight is all it needed to check.

Even if it doesn't can loop it to alternator post it will start charging then make up another fusible link later if paranoid.

14/85a so it looks to be ebay copy or 'agricultural' meaning it's 14a at idle/low rpm....vs cop alternator bxh1250 specs are 60/120a idle/low rpm.

Had quick look at my vp couldn't see specs or part number...anyone got specs on factory bosch vn-s 85a?

*not ebay copy crap with fake bosch stickers/box