From: "Elie, Larry (L.D.)" <lelie ford com>
To: "'Neil Dennis'" <wombat RealNS com>, Elec-trak
<elec-trak cosmos phy tufts edu>
Subject: RE: (ET) batt's
Date: Fri, 10 Aug 2001 10:57:39 -0400
Harry, Neil, etc.
Sorry Harry, but I vote with Neil. 12.66V just isn't a normal voltage for
an auto charging circuit. It is even a bit low for a battery several hours
after charge for a old battery.
I work for Ford Research. I know the people who design the charge circuits
in today's cars. I have worked on the design of charge circuits in the
past. I have inventions in the area. We typically set the voltage of the
regulator at 14.2V no load and 13.8V at load. We see very large droops at
times due to wire length and gauge picked for load and weight, but these
are the targets. Typical voltage for the batter after soak (car off,
several hours to return to room temperature) is 13.2 to 13.6 depending on
age of the battery and how hot it was under hood when it was 'charged'. It
isn't quite that simple (I know someone who wants to add a wire for <$1/car
that would improve battery life by measuring without the lead resistance
drop at under hood temperature and he can't get it approved) but it's
basically the truth. Now, having said that, the ET does NOT have an
automotive battery. It is a deep-discharge design, so these values are
probably not exactly right. However, !
2.4V per cell is not unusual for a car, and most 'trickle' chargers exceed
that under some conditions, without instant damage. Remember too,
automotive batteries do NOT last more than 4 to 6 years (under hood and
vibration are the bad actors, as well as cheap regulator design and warped
plates) and the values we use are certainly not the 'best' ones you can
come up with. The people doing Ranger electric chargers do a much better
taper on their charge (but they didn't like my charge equalizer as well as
theirs... mine ended up bookshelved!) than the alternator guys do, and that
may be represented too; charging series batteries is a bit harder to do and
most people (like the Ranger guys above) tack on a few volts to make sure
every cell gets enough. This is what we call cell equalization. But
again, FAST charging is a selling feature; battery life is secondary.
Now, my best assumption is that GE knew what they were doing 30 years ago.
Batteries may have changed, but the VOLTAGE at the meter probably is still
'safe'. In other words, charge MEANS charge. If you only charge into the
green range, you are not getting the full charge the ET is capable of.
The bottom line: 42 to 45V at the end of a charge is the minimum I accept.
If the cells didn't start out equal (the lift used a lot like with the
tiller or the headlights were used) I go 45 to 47V. I never leave it above
45 for long periods. I have NEVER got good performance at 39V, period.
Larry Elie
-----Original Message-----
From: Neil Dennis [mailto:wombat RealNS com]
Sent: Thursday, August 09, 2001 9:31 PM
To: Elec-trak
Subject: (ET) batt's
Harry, sounds like an interesting idea on the voltage measurements. I
worked for years on auto and marine charging systems (alternators and
regulators), for the average use, we aimed at 14.4 +-.2 as a correct
charging level. One trucking co used 12.6 as they wanted to increase
lamp bulb life. Some tractor co's wanted 132 / 13.6 as their batteries
were in a hot location.
Agree on the "pulsing" maintainence rather than trickle.
wombat