Alternator charge

[itchyfeet]

Drop your trousers next time - it may get excited then

Is Wechselstromgenerator masculine or feminine or neutral?

[Oldiebut goodie]

Who cares duckie!

[CJH]

Ahem. Stop messing about and pay attention.

Measurements:

With all three of my relays still connected, and my meter connected in circuit between the blue wire and the alternator's binding post, I get 2V and 23mA

With the blue wire reconnected to the binding post, and each relay disconnected and measured in turn, I get:
- Fridge relay: 1.6V and 16mA
- Towing Relay #1: 1.4V and 16mA
- Towing Relay #2: 1.4V and 16mA

With all three relays disconnected and the meter back in circuit at the alternator's binding post, I get 75mA. The voltage is at virtually battery voltage because the current through the voltmeter isn't enough to light the dashboard LED now (it remained lit for all the other tests though).

That 75mA is satisfyingly close to the sum of the original measurement and the three relays (23+16+16+16=71).

And the acid test - with the relays removed the dashboard light goes out at a noticeably lower rpm than with them connected. That must be the impact of the increase from 23mA to 75mA for the exciter current.

Now, where's that master cylinder...

[itchyfeet]

What are you calling a binding post?

[CJH]

What are you calling a binding post?

The threaded stud (6mm?) where the blue wire connects to the alternator via a ring terminal.

[itchyfeet]

(E D I T now I understand what you did)

With blue connected I get 1.5V blue to earth ( field windings and any diodes) and 160mA flowing ( sure I saw 185mA when first switched and batt voltage good) 90A bosch.

I may never have tested the 90A bosch for self excitement I tested the old lucas for sure, job for tomorrow, not revving the nuts off when cold

[CJH]

How are you measuring current if not by disconnecting the blue and putting the meter in the circuit? Have you got a really fancy ammeter that clamps around the wire?

[itchyfeet]

No edited it now I understand what you did, your measurements were with it connected via ammeter.

still a long way short of 160mA, different resistor in dash or high resistance in connections.

you could find a high resistance coil relay and use that to trigger all the other relays

[CJH]

you could find a high resistance coil relay and use that to trigger all the other relays

That's an idea. It would mean a bit of rewiring, or perhaps two high resistance relays, as my fridge relay is by the fridge and my towing relays are in the wardrobe. Or maybe I could just replace all three of them with high resistance versions. Maybe I could add suitable resistors to the three existing relays instead. I've got all the numbers I need to figure out what power and resistance values they'd need, and I can probably find out what's the minimum voltage the relays need to trigger reliably. But actually you know, I think I'm happy enough the way it is - the alternator works perfectly at normal driving rpm.

Plenty here for the OP to go at though if he's interested in lowering the rpm at which the alternator kicks in. :tongue in cheek:

[itchyfeet]

Yes as you say hardly worth bothering
good to discuss though sure we all leaned something

[CJH]

Definitely, yes. I love things like this. Mind you, there's no guarantee I'll remember any of it when my alternator stops working due to a fault with that little blue wire.

[itchyfeet]

I may never have tested the 90A bosch for self excitement I tested the old lucas for sure, job for tomorrow, not revving the nuts off when cold

Just tested the 90A Bosch with blue wire disconnected and it self excited at a little over 3000rpm engine revs (alt will be lower revs) voltmeter shows when it starts producing voltage hight than the batt, let engine revs drop and it continues.
It had been run so it's just possible it still had some residual magnetism (if thats possible), maybe from cold it doesn't do it but I'm not revving it cold.

[CJH]

Oh, well that's different from mine. Different model numbers perhaps? Mine's an 0120 469 727, which, according to the Bosch Automotive Catalogue, was discontinued in March 1992. It was superseded by the 0120 469 734, and then by the 0120 469 863.

What model is yours?

[itchyfeet]

No idea, where is ths number? I can't see one
looks like this but they probably all look the same.

[CJH]

Mine has a red sticker on the end cap. if that's gone I guess there's no way to tell. Oh well. Was yours always on your van, or have you sourced it from another vehicle?