Author Topic: Lucas Alternator Issue  (Read 5625 times)

dieselspanner

  • Hero Member
  • *****
  • Posts: 726
    • View Profile
Lucas Alternator Issue
« on: June 28, 2016, 12:52:38 PM »
Hi All

After 60 or more year the wiring on my Mccormick 434 is getting shabby so I've ripped it all outr and at the same time replaced the dynamo with a rebuilt Lucas A127 2 wire alternator.

I supplied the sensing / exciting wire from the ignition switch through a small panel lamp and the feed out directly to the battery. There was no output, even rev'ved to the max.

I replaced the panel lamp with a 21w indicator bulb, the alternator functions as expected.

Is this because the tractor runs at very low revs, exacerbated by the reduction in alternator revs due to the 2 pulley drive on this particular engine stepping them down, or have I missed something........

The battery was showing 12.9 volts and all connections were good and clean.

If I wire a diode into the circuit to drop the sensing current, what value should I use.....

Cheers Stef
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

38ac

  • Hero Member
  • *****
  • Posts: 2324
    • View Profile
Re: Lucas Alternator Issue
« Reply #1 on: June 29, 2016, 02:18:13 PM »
I think Glort has it right. I had the same thing happen with a 10SI Delco retrofit. Bought a little panel light and it would not excite. Replaced the panel light with a trailer side marker light and it works fine.
Collector and horder of about anything diesel

dieselspanner

  • Hero Member
  • *****
  • Posts: 726
    • View Profile
Re: Lucas Alternator Issue
« Reply #2 on: June 29, 2016, 09:54:49 PM »
Thanks for that, both,

My Barge, the Other Half's MGB, a diesel driven lash up charger I knocked up and a kit car I built years back are all wired the same way.
I've read in the past about fooling alternators into uping the output by dropping the sensing wires voltage, but knowing little about the workings wondered if there was a relationship between the alternator rpm, the sensing voltage and the out put

Big thing is It works!!

Cheers Stef
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

EdDee

  • Hero Member
  • *****
  • Posts: 773
    • View Profile
Re: Lucas Alternator Issue
« Reply #3 on: June 29, 2016, 10:53:12 PM »
Hey Stef,

If the alternator has a sepaate sense circuit, you could stick a diode into it line to up the output a bit..each diode added in series would give you about .5V increase in output. Something does ring a warning bell for me though... The symptoms you describe are indicative of too low a rpm at Alt shaft.. if you over excite to get the required output at the low revs, or adding diodes into the sensing circuit, you could be heading for the early demise of the unit due to insufficient cooling... take care... it might just be a little better to bite the bullet and change the pulley ratios if you can, to get the Alt up to its rated speed...

Incidentally, you can also elevate the output voltage of a non-sensing alternator by mounting it on insulators and using a diode in series on a grounding strap, same rule applies...

Come to think of it, ever tried to make 24V out of 2 x 12V alternators in an emergency?

Again I ramble....

Cheers
E
12/1 750RPM/9HP Roid 5kVA- WMO Disposal/Electricity & Hot Water Gen
12/1 650RPM/8HP Roid 4.5kVa - Demon Dino
Chinese Yanmar - Silent Runner with AutoStart
Classic Komatsu 1963 Dozer/Fergusson 35 Gold Belly ...
Bikes,Cars,Gunsmithing & Paintball...Oh yes, a 5Ha open air Workshop to play in!

dieselspanner

  • Hero Member
  • *****
  • Posts: 726
    • View Profile
Re: Lucas Alternator Issue
« Reply #4 on: June 30, 2016, 05:55:28 PM »
Thanks for that,

Ed,

I was going down the same road, however it's going to be difficult to change the pulley ratios, It has a 2 belt system, one drives up to the water pump, reducing rpm, and the second drives the alternator. the water pump suction side sticks out in what would be the path of a 'normal' operation, it's probably the history of the engine, the injector pump prevents the alt. going on the left side of the engine, goes back to the petrol forerunner I'd guess.

It was a free alternator and the repair kit for the whole thing, including bearings was €25 so if it fries due to overheating I'll have to come up with a better plan!

Glort,

I take the point about the hot engine bay, maybe there's a bit more free air under the bonnet of the tractor!

Cheers Stef
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

vdubnut62

  • Full Member
  • ***
  • Posts: 211
    • View Profile
Re: Lucas Alternator Issue
« Reply #5 on: July 07, 2016, 06:04:06 AM »
Dieselspanner, sounds like you have either the BD-144 or BD154 engine? I have the same setup with 2 belts in my McCormick/International B-275.
The way I got around the speed problem was to change the field windings in an old Delco 1 wire alt (10si?) It  starts charging at very low rpm, but the output suffers, I think maybe 15amps is all it will do. Beats the old Lucas generator and "Positive Earth" set up though. The belt does rub very lightly on the water pump neck, been running that way for 25 years.
Ron.
« Last Edit: July 07, 2016, 06:06:40 AM by vdubnut62 »
"The penalty good men pay for indifference to public affairs is to be ruled by evil men."   Plato.

"Remember, every time a child is responsibly introduced to the best tools for the protection of freedoms, a liberal weeps for the safety of a criminal." Anonymous