Re: (ET) charger voltage

[David C Robie <mycroftxx1 juno com>]

Capacitor;  These open circuit when they go.  If they short it will
sometimes trip the house circuit breaker.  'Run' capacitors are built
with an internal fuse link so if they short, they open.

Speaking on same subject;  As your batts age and get down in 'max
possible volts' the charger don't know that. A deep discharge such as
mowing a lot of lawn with older batteries will heavily load the charger
when you plug in (say charging into perhaps 32V  takes more current than
charging into 36 or higher).  So it  takes over max power from the AC
line. Essentially it will draw more current from the wall, even to the
point of blowing those 15A auxiliary breakers in multi outlet strips. 
Charge very seldom on AC, mostly solar chg with 3 12V solar panels in
series - byt when I do, sometimes got to reset that breaker 3 or 4 times
before th AC input curent is down enough so it will hold.
       In the fullsize EV's we have better regulated charges.  Same ferro
resonant system in many of em (old golf cart type Lesters) but more money
and thought spent on it.  
      To get away from a traffic light in my EV, foot to the floor the
controller is limited to 400A.  As the batteries get weaker they can no
longer supply this as a weak battery essentially is one with an internal
dropping resistor in series with it.  So what happens?  The worst ones of
an unbalanced pack go down to zero on these heavy draws and when at zero
under load, the polarity reverses.  Then you got a boiling hot ruined
battery (instead of the more normal 'kinda hot one)  the next tromp on
the accelerator is instantly generated high pressure steam and an
explosion.  Some just blow the caps off.  But most blow the top of one
cell off or if the case is old and weak, the entire case. I have blown up
a couple at traffic lights and wrecked a couple more through reversal
before learning why and how to equalize em, and not to drive em down that
deep.
    At least the learning process of restoring an older EV using old
batteries is not as expensive as that of doing the same thing with a gas
driven car and blowing a con rod or something.  In most of the newer plug
in EV's,  the controller won't let you get down that low to damage the
batteries.  It's like that automatic cutout on 12V inverters that kill
the power at 10.5V .  But mine is a 1970s controller.
   Relating to the charger, this is 120V not 36VDC and 220VAC in with
bout 28A DC at full charge of a weak pack tapering down to perhaps 5a
when it's full. Regulation is purely ferro resonant.
      Ths is how it happens in the big ones.  We are using much smaller
currents in the Etraks,  with less peak draw at turn on and I doubt
seriosly if a battery could get that hot to make 'flash steam' in an
Etrak.  But here's a warning to anyone reading this email.  If the
tractor will barely move due to low batts, don't run it or you may
reverse a cell and ruin it.  Charge the pack first before running.
  
Dave
Weymouth MA







On Fri, 28 Jul 2006 08:53:50 -0400 (EDT) Michael S Briggs
<msbriggs alberti unh edu> writes:
> 
> 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
> >> ---------------------------------------------------------------
> >>
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> >
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