George White wrote in a message to Roy J. Tellason:



 RJT> Even though it's been *ages* since I've actually seen one of
 RJT> those, 



 RJT> The other thing that just comes to mind with those is that
 RJT> underneath the mounting base were wire-wound "resistors",  maybe
 RJT> 2 or 3 of them

 GW> If you had looked closely you would have spotted that they are 
 GW> across the relay contacts. They're there to reduce (kill) arcing in
 GW> the contact as they make and break to get a decent life out of the
 GW> unit.

I did "look closely",  but at the time I was rather too young to
puzzle all of this out...    :-)



 GW>> The duty on most car batteries and the rating of the alternators
 GW>> is such that for most people by the time they've pulled out the
 GW>> drive, and certainly by the time they've reached the end of the
 GW>> street all the power taken from the battery to start the engine
 GW>> has been replaced, and that is about the only time the full
 GW>> alernator current can go to the battery.

 RJT> That depends.  I've known of some people who did *lots* of fairly
 RJT> short trips, and that ran their battery down because they weren't
 RJT> running long enough to put the charge back into it.  This may
 RJT> have been in colder weather,  may have been with the heavy use of
 RJT> a lot of accessories,  too,  I don't recall

 GW> Yes, that can happen. Usually in cold climates where you have 
 GW> heated screens, fan blowers, lighting all running all the time. 
 GW> This can limit the current available to charge the battery to 
 GW> relatively few amps even when the engine is running fast enough to
 GW> produce full output. If the vehicle was only used for school runs
 GW> and shopping and in heavy traffic (choose any big city - I'm used
 GW> to London (UK), New York (NY), Boston (Mass), Bristol (UK)) the car
 GW> spends so much of it's time in heavy traffic with the engine idling
 GW> the the alternator output falls below the accessory drain and the 
 GW> battery is being discharged in normal use.

Or around here,  in winter,  when people are just "running around town"...

 GW> (On most systems I'm used to the alternator reaches full output at 
 GW> about 25% max revs). The traditional solution is to up the engine 
 GW> idle speed - but that only works for stick shift systems. For 
 GW> automatics all you can do is cut down the power use (lower heater 
 GW> fan speed, no extra lights) or put the battery on charge 
 GW> overnight...

Not too likely for the senior citizens that are having this problem.

 GW>> In a modern car the alternator has a high current rating to drive
 GW>> all the extra things in the car (windscreen wipers, lights,
 GW>> heater/air conditoning fans, engine cooling fan, heated screens,
 GW>> heated mirrors, heated seats, in car entertainment, etc...), most
 GW>> of which only work when the enging is running anyway.

 RJT> Just so.

 GW> But you do still need to be moving along...

Yep.

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