[Rovernet] Geoff - electrics

Fri May 23 14:49:17 EDT 2014

Thanks again. The NAPA alternator replacement is for the SD1 and...the Jag
XJ12!

AvMedSafe
Geoffrey W. McCarthy MD MBA DipAvMed
677 NW Melinda Ave Portland OR USA 97210
503-241-8468(h) 503-799-3809 (mobile)

-----Original Message-----
From: Rovernet [mailto:rovernet-bounces at rovernet.org] On Behalf Of Fletcher
Millmore via Rovernet
Sent: Friday, May 23, 2014 10:29 AM
To: Rovernet
Subject: Re: [Rovernet] Geoff - electrics

Geoff-
To expand a bit
The bulb is a balance between Alt output and battery voltage, but of course
that is only true AT the bulb. So, any broken wires or bad connections make
the bulb not light, or light very dimly.

If the Alt is not charging, but everything else is good, the bulb lights.
Once the Alt starts charging, there is system voltage on both sides of the
bulb, so no current flows = no light. If Alt voltage goes very high from a
fault, or if Batt voltage at the bulb is low, then the bulb lights again,
but it is "backwards" light, as current flows from the Alt to the system
backwards through the bulb.

If the bulb gets very bright at high RPM and blows, you definitely have an
Alt fault, which also means charging output will be a bit low and the Alt
will run hot.

However, Your description sounds as if you have several or many bad
connections in the system. These can in and of themselves cook the Alt,
among many other noxious effects. The limit of this is the sticker all these
cars used to have "Do Not disconnect battery with engine running", and
defective batteries can do the same. I had an MGB customer whose car sat all
winter, leaving the Batt dead, so he had AAA come and put in a new one - it
lasted 60 miles, when the defective new Batt caused the Alt to literally
melt everything inside.

I have written a long doc re my adventures in really figuring this out (on
an XJ12), what goes wrong and how to diagnose and fix it. On that car, I had
about 15V at the Alt, but 9V at the battery, as the electrons tried
frantically to get through all the bad spots. In the process, I fixed a
bunch of stuff, like erroneous instrument readings (low fuel, temp, OP),
poor to no start, poor performance, etc. Two solid weeks of measuring and
cleaning connections, used more than a tank of fuel in the driveway!

E mail me, ask for "Electrobabble"  gofanu at usachoice.net

FRM

On 5/23/2014 12:17 PM, GeffMcCarthy via Rovernet wrote:
> Thanks!  I noted that it charged slowly and we made it all the way to 
> San Jose (there is an old song with those words, I think...) but in 
> city traffic the battery slowly died. Will seek and replace bulb!
>
> AvMedSafe
> Geoffrey W. McCarthy MD MBA DipAvMed
> 677 NW Melinda Ave Portland OR USA 97210
> 503-241-8468(h) 503-799-3809 (mobile)
>
> -----Original Message-----
> From: Rovernet [mailto:rovernet-bounces at rovernet.org] On Behalf Of 
> Fletcher Millmore via Rovernet
> Sent: Thursday, May 22, 2014 10:51 PM
> To: Rovernet
> Subject: Re: [Rovernet] Another set of rare bits required.
>
> The bulb supplies the excitation current for the alt to start working, 
> which is why it stops charging if the bulb goes. But, the bulb only 
> blows if there is a bad diode in the alt, which causes voltage to go 
> way high. The bulb gets real bright before it blows. So, the bulb is a 
> sort of fuse - you have a defective but not totally fried alt.  Some 
> systems (GM I think) use a resistor in parallel to the bulb to supply 
> the current even if the bulb fails, but you lose the safety aspect. I 
> had an Austin America with this problem (and no money for an alt), and 
> as long as I kept it under 6000 rpm, the bulb - and the headlights - 
> would be bright, over 6000 pop! Got really good at changing the bulb along
the road in the dark.
>
> Some alts will charge without the excitation current, as there is 
> enough residual magnetism to get things started once the engine is 
> going fast enough, after which it keeps charging even when the engine
speed drops.
> We used to get that on Delco alts replacing other things (because we 
> did not know how to wire it correctly)- once you punched it up to 3500 
> it would work and put the light out. All depends on the fine detail of 
> the alt/reg circuitry.
>
> If the bulb NEVER lights, even when you turn the key on, it or some 
> wiring is dead. The alt should supply enough power at idle that the 
> light does not come on with engine running, even with low battery.
>
> FRM
>
> On 5/22/2014 7:23 PM, GeffMcCarthy via Rovernet wrote:
>> Re NADA fuel pipes:  I removed all the charcoal canisters and lines 
>> in my 3500S, but may reinstall to limit the fuel odor after every 
>> partial
> fill.
>> Does the charcoal deteriorate?  Can it be restored or refilled?  Thanks.
>> PS:  The SD1 which I acquired in LA made it to Portland with only 1
>> snag: an alternator fault traced to the small alternator wire.  The 
>> previous owner related that if the charging light bulb burns out, the 
>> alternator stops charging.  I have not seen the bulb lit, even with 
>> 9V on
> the battery.
>> Interesting design fault, no?
>> AvMedSafe
>> Geoffrey W. McCarthy MD MBA DipAvMed
>> 677 NW Melinda Ave Portland OR USA 97210
>> 503-241-8468(h) 503-799-3809 (mobile)
>>
>> -----Original Message-----
>> From: Rovernet [mailto:rovernet-bounces at rovernet.org] On Behalf Of 
>> Kent Kinard via Rovernet
>> Sent: Thursday, May 22, 2014 1:14 PM
>> To: Rovernet
>> Subject: Re: [Rovernet] Another set of rare bits required.
>>
>> Yes.
>>
>> JULIAN BARNARD via Rovernet wrote:
>>> Hi there - I am in the middle of restoring a1969 NADA Rover 3500S Auto.
>>> Unfortunately the previous owner removed the fuel tanks and although 
>>> the
>> main fuel tank is easy enough to get in the UK, it seems impossible 
>> to find the Fuel Spill Return tank and associated fixings and pipework.
>>> Has anybody in the Rovernet group got access to a set of parts such 
>>> as
>> these?
>>> Julian Barnard.
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