[Rovernet] Geoff - electrics

Fletcher Millmore via Rovernet rovernet at rovernet.org
Fri May 23 13:28:34 EDT 2014


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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