[Healeys] Electric Draw

[Bob Spidell]

Thanks for the info, Bill.


Bob


On 6/7/2019 9:30 PM, WILLIAM B LAWRENCE wrote:
> "I don't think a generator could behave like this..."
>
> Actually a generator will act exactly like this if the cutout circuit 
> of the regulator (control box for the purists among us) fails in the 
> closed position.
>
> Bill Lawrence
> BN1 #554
> ------------------------------------------------------------------------
> *From:* Healeys <healeys-bounces at autox.team.net> on behalf of Bob 
> Spidell <bspidell at comcast.net>
> *Sent:* Saturday, June 8, 2019 3:34 AM
> *To:* healeys at autox.team.net
> *Subject:* Re: [Healeys] Electric Draw
>
> OK, folks, I gotta eat crow.  I'd never heard of it before, but I got 
> to thinking about it and realized that alternator diodes are a direct 
> path to the battery, and I did some research:
>
> /"//A leaky diode also can allow current to drain out of the battery 
> through the alternator when the vehicle is not being driven."/
>
> /- 
> /https://www.knowyourparts.com/technical-resources/starting-and-charging/starters-and-alternators-common-misdiagnosis/
>
> In my experience, diodes fail open, sort of like fuses, but if one 
> failed short--or 'leaked'--it could draw current from the battery.   I 
> think the way to test for this would be to disconnect the 
> alternator->battery lead and see if the current draw ceases (or charge 
> the battery to a known voltage, disconnect the alternator, and see if 
> the battery remains charged overnight).  I don't think a generator 
> could behave like this, but I'm gonna think about it before I press 
> 'send' before I've had my second cup of coffee.
>
> My apologies to all (including the OP's mechanic).
>
> Bob
>
>
> On 6/7/2019 9:09 AM, Bob Spidell wrote:
>>
>> Uh, I'm not an electrical engineer--but I play one on email 
>> lists--but it sounds like your mechanic isn't one either (not 
>> uncommon).  The diodes in an alternator perform the same function as 
>> the brushes and commutator in a generator; i.e. they rectify the 
>> alternating current--produced by rotating an electromagnet--into DC 
>> current, which your battery requires for charging and all your 
>> accessories require to, well, accessorize.  Hence, they aren't doing 
>> squat when the engine isn't running--when there should be no current 
>> coming to the alternator to energize the rotor--and if you had a 
>> short somewhere and your alternator was getting current with the 
>> engine stopped it would likely heat up (see if your alternator feels 
>> warm after sitting overnight). Diodes can fail by either shorting out 
>> or opening up; most alternators have 6 of them and when one fails by 
>> opening up you lose one-sixth of your charging ability (I'd have to 
>> research it, but as solid state devices--sort of one-third of a 
>> transistor--they probably mostly fail by opening up as the silicon 
>> junctions are relatively fragile).  I'm not sure if it's an open or 
>> shorted diode that causes it--maybe both--but with a bad diode you 
>> will get all kinds of radio noise, which varies with engine speed 
>> (when I used to fly light aircraft you could tell when someone had a 
>> bad diode with serious noise in radio transmissions).
>>
>> Others have offered good suggestions so I'll just add that it's 
>> conceivable your ignition switch is worn allowing some current flow 
>> when in the 'off' position (after all, it's Lucas ;)).  See if it 
>> feels warm after sitting for a while (in fact, if you can get to them 
>> see if any of the electrical devices in your car feel warmer than 
>> ambient after sitting in the shade).  Your battery ground doesn't 
>> pull a load--something has to draw current that the ground cable 
>> returns to the battery--so it isn't the problem.  A nearly half-amp 
>> current draw in a 12V system will produce 6 watts of heat (nearly 
>> half of what a 60W equivalent CFL light rated at 13W will generate).
>>
>> Bob
>>
>>
>> On 6/7/2019 6:13 AM, Michael Salter wrote:
>>> Real Healeys don't have alternators.🤣🤣🤣🤣
>>>
>>> On Fri, Jun 7, 2019, 8:55 AM Per Schoerner, <per at schoerner.se 
>>> <mailto:per at schoerner.se>> wrote:
>>>
>>>     It sounds more like your cutout switch is the culprit here.
>>>
>>>     Per
>>>
>>>     Skickat från min iPhone
>>>
>>>     > 7 juni 2019 kl. 14:47 skrev R. Lindsay <050.rpl at gmail.com
>>>     <mailto:050.rpl at gmail.com>>:
>>>     >
>>>     > For the past few weeks I have been fighting a parasitic draw
>>>     on my BJ8. It was running about .48 amps and would drain my
>>>     battery in a day or so. I was told by a mechanic that a diode in
>>>     my alternator must have blown therefore causing the draw. He
>>>     also mentioned that my ground wires in the boot were loose which
>>>     he tightened. I brought the car home, turned off the power in
>>>     the boot and 2 days later the battery was dead.
>>>     >
>>>     > So, here’s what I’ve done. I jumped the battery and started
>>>     the car and ran it for 10 minutes. I disconnected the charger
>>>     and tested the battery - 12.48 volts. I then removed the cutoff
>>>     switch and bolted the grounding wires together. I tested for a
>>>     draw and got a zero reading. That was last night. I went out
>>>     this morning (12 hours later) and the battery reads 12.33 volts.
>>>     >
>>>     > My questions are 1. Is .15 volts a reasonable drop in voltage
>>>     for a sitting car in 90 degree heat and 2. Can a diode in an
>>>     alternator work sometimes and not at others. If it’s either
>>>     “good or bad” all the time, I guess I need to presume the
>>>     alternator is not the source of the draw. If a .15 volt loss
>>>     over 12 hours is reasonable then removing the cut out switch in
>>>     conjunction with presuming the alternator is good (as it works
>>>     fine now) solved my problem.
>>>     >
>>>     > What does the wisdom of this great resource think?
>>>     >
>>>     > Price Lindsay
>>>
>>
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