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Re: (ET) charger voltage
Than you don't understand how charging flooded series connected
batteries work. There are a number of web pages that explain it, but
those that design chargers are not a bunch of dummies. Your car
charging circuit regulates at 14.2 to 14.4 V, and charges a battery that
when new and fully charged at room temperature shows 13.8 V. Those
'extra' .6V on the 6 cells helps the battery reach equilibrium. No two
of the cells are identical; internal resistances are different. If you
tried to charge at 13.8 (all you 'need') and if one cell is 'weak', it
will prevent all of the other cells from reaching 'full' charge. The
more cells, the bigger the potential problem. Add to that battery and
cell age, temperature differences and so on, and it's easy to see why
the extra potential is used. Remember, the charger is only a constant
voltage circuit when it isn't dumping lots of current; for most of the
charge cycle it's very much current limited. If you have infinite money
you could do better with a constant current charger dumping perhaps 100A
with an automatic cross-over and detecting 'full' charge off of the
density of the electrolyte, and charging each cell individually in
parallel and then only going in series when you are running the
batteries for output. But no one is going to pay for that. The charger
circuit I did years ago equalized based on seeing each cell as an
integrator and using op-amps to equalized the cell voltage. It worked
well but added wiring and complexity. Even it cost too much to be
implemented in our electric cars.
Larry Elie
Ford Research
-----Original Message-----
From: elec-trak-bounces cosmos phy tufts edu
[mailto:elec-trak-bounces cosmos phy tufts edu] On Behalf Of Michael S
Briggs
Sent: Friday, July 28, 2006 8:54 AM
To: David C Robie
Cc: elec-trak cosmos phy tufts edu
Subject: Re: (ET) charger voltage
Dave,
Thanks for the feedback, that's essentially what I wanted to
know
- what the voltage is these 6 volt batteries will hold. As far as I see
it, if they'll typically hold 6.3 V each (so just under 38V combined),
there's no reason the charger NEEDS to put out 42-45V. That high of a
voltage will charge it quicker, but won't give a more complete charge,
since the pack itself can't stay above 38-39V or so, depending on the
batteries. My charger is putting out around 39.5V roughly, which to me
means it should be able to fully charge the pack - it will just take
longer than it would if the charger was putting out a higher voltage.
Since the Landis controller stops charging once the pack reaches
38V, it wasn't making any sense to me why people were saying the charger
needs to put out 42+ V to fully charge the pack, since presumably fully
charged is only around 38V. 42V+ will charge quicker (greater potential
difference between the charger and battery pack, so more current will
flow
into the pack), but quicker isn't necessarily better, especially when
dealing with charging batteries.
I'll measure the capacitance of the charger capacitor anyway
(have
a multimeter that can measure capacitance) to see if it's ok or not
though.
Thanks,
Mike
--
--------------------------------------------------------------
Michael S. Briggs
UNH Physics Department
(603) 862-2828
---------------------------------------------------------------
On Thu, 27 Jul 2006, David C Robie wrote:
> Depends on the age of your batteries. New batts are about 6.5 ea.
> Average batteries chg to about 6.25 6.3 (where do you think vacuum
tube
> heater voltage std 6.3 came from? 2.2V/cell). Older ones (like some
I
> got) chg to maybe 6.15. No matter how long or what rate you charge a
lead
> acid battery like we use, it will not go over this 'age and abuse
> related' voltage.
> If you find one in the string that's consistantly low, swap it outa
> there. Your tractor will thank you.
>
> Occasionally. people 'equalize' batteries by intentionally
overcharging.
> This ain't good for them. If I find a low one. I put it on a separate
> 6V charger to bring it up as far as, by experience, I know it will go.
> My packs were not bought new, they are recycles and inherently some
are
> better than others. I make sure each fall that the best ones go in
the
> tractor that has the snowblower.
>
> Charge em to the point that every cell is gassing. Then leave em
> overnite to remove 'surface charge'. Test em in the morning. That
will
> tell you where your batts are at agewise. Of course, to charge them
the
> voltage of the charger must be a little over this.
> So, depending on battery condition, anything from half a volt over
> about 36.5 to 39
> will trickle charge em, and a volt or two above will hi rate charge
em.
> (the charge voltage automatically tapers down because of the capacitor
-
> it and it's winding is called a ferro resonant circuit which is a form
of
> regulator) (therefore, open circuit voltage means little except too
low =
> bad capacitor.
>
> Dave
> Weymouth MA
>
>
>
> On Wed, 26 Jul 2006 18:50:03 -0400 (EDT) Michael S Briggs
> <msbriggs alberti unh edu> writes:
>>
>> I've been scanning through the archives, and also the Service
>> Manual, and
>> am seeing some mixed messages on this - what voltage should the
>> charger be
>> putting out to the batteries? Mine's putting out a shade under 40 V
>> (39.5V or so), and they seem to not be holding as much energy as I'd
>> like
>> (T-105s that are a few years old, bought used). According to the
>> Service
>> manual, 40-45 V is ok (well, not on exactly the same wires as I'm
>> measuring the voltage, I'm measuring across the battery pack, rather
>> than
>> at S3 and S1 directly on the charger, so there's presumably a small
>> amount
>> of voltage lost between the points the manual says and the points
>> I'm
>> measuring at, especially if some weak connections, such as at the
>> Diode
>> heat sink). According to the archives online, I've seen people
>> saying that
>> if the voltage isn't 42-45V, the charger won't fully charge the
>> batteries
>> enough (some people who replaced the capacitor when the charger was
>> only
>> putting out 39V or so, for example).
>> With mine charging, the charge meter goes slightly into the
>> white
>> section - whereas in the archives, I've seen statements that if the
>> meter
>> doesn't go all the way to the high end of the white section, the
>> batteries
>> won't get a full charge.
>> On the other hand, the Landis controller only has the
>> charger on
>> when the pack voltage falls below 38V, by default, unless you adjust
>> it
>> up. So, if charging to 38V will give you a full pack, then there's
>> no need
>> to have the charger putting out more than 39V or so (other than that
>> the
>> higher the voltage it puts out, the quicker the pack will charge).
>> So, which is it? Is 39-40V from the charger ok, or should
>> it be
>> 42-45?
>> Essentially it comes down to - what should be the voltage
>> of a
>> fully charged battery pack (I know it's higher than 36V, but how
>> much?)?
>>
>> Thanks,
>> Mike
>>
>> --
>>
>> --------------------------------------------------------------
>> Michael S. Briggs
>> UNH Physics Department
>> (603) 862-2828
>> ---------------------------------------------------------------
>>
>> _______________________________________________
>> Elec-trak mailing list
>> Elec-trak cosmos phy tufts edu
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>>
>
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