Re: (ET) charger voltage

["harry landis" <hlandis hotmail com>]

I guess there's nothing like a battery charging question to get the list 
active. My charger controller (it's a charger controller, not a charger) 
does exactly what the stock timer does, except it measures battery resting 
voltage, not time. The timer turns the stock charger on and keeps it on for 
a set time, then turns it off. My controller turns on the same stock charger 
for a set time (about 4.5 minutes) and then turns it off. During the on 
time, the voltage is not controlled or measured by my controller. So the 
voltage will rise to 40 or 45 volts just like it would have with the stock 
timer.  After the set time elapses, my controller measures the battery 
voltage. If  the battery rest voltage drifts down to 38V, it turns the 
charger on again for another 4.5 min. Therefore, the 38V setpoint is not a 
cutoff voltage, but a start voltage.
Full details are on the elec-trak.com website in the Classifieds section 
here:

http://www.elec-trak.com/bin/classifieds/classifieds.cgi?search_and_display_db_button=on&db_id=15&query=retrieval

It's a great site. Thanks, Don!

Harry Landis



From: Michael S Briggs <msbriggs alberti unh edu>
To: "Elie, Larry (L.D.)" <lelie ford com>
CC: elec-trak cosmos phy tufts edu
Subject: Re: (ET) charger voltage
Date: Fri, 28 Jul 2006 19:28:14 -0400 (EDT)


On Fri, 28 Jul 2006, Elie, Larry (L.D.) wrote:

> Actually, the more cells, the greater the likelihood of one bad actor.
> I've seen them actually reverse charge.  Let's see how well you can
> bring the pack up when one cell is at -2.3V....  You are lucky to get
> the others to 60% charge.

I'd think though that if that happens, you should just replace the
battery. :)

> Mr. Landis and I have disagreed on this in the past.  His charger works.
> The ET charger works.  They don't work in exactly the same way.  If the
> ET charger stopped at even 40V you will not get a full charge.  Harry's
> charger will pump it up again a number of times after the battery cools
> which gets the job done.  It won't be as fast, but if you want to just
> leave it on for months it's superior.  There are other techniques

That's sort of what I'm saying - that a higher voltage will let you charge
faster, but you *could* get a complete charge with a lower voltage
(as long as it's still a good bit above the voltage of a fully charged
pack). But, that may not be convenient for most people.
        That said - I checked the capacitance of the cap on my charger
about a half hour ago, and it is indeed toast (read no capacitance at all
- which now has me wondering how the charger is putting out a fairly
stable 39.5V with an apparently dead cap). So, I'll be replacing it.
        But, I still am looking to find out exactly what the voltage of a
fully charged pack should be, so I can decide whether to up the set point
voltage on the Landis controller, and if so, to what. I don't want to
leave it plugged in permanently when not in use - so I'd rather not have
it shut the charger off *right* when the pack first hits 38V, if it can
charge up higher than that.

> available as well.  Remember, the ET charger can put out lots of current
> when the batteries are low because it is a simple constant voltage
> design; you dropped the peak voltage the current it would put out at
> lower voltages is also reduced.

Yup, thus slower charging.

> Another factor you are leaving out is that 38.2V is the room temperature
> voltage 90 minutes or more after charging.  The voltage at the pack at

I'm not leaving that factor out - I don't know that factor. :) My initial
question on this was asking what the voltage of a fully charged pack
should be. If it only drops to 38.2V 90 minutes after charging, then
apparently a fully charged pack just after charging should be higher - and
that's what I want to know. I figure I could bump the set point on the
Landis up to a smidgen under that fully charged voltage, at least for
during the summer, and if I don't use the Elec-Trak in the winter, I could
move the set point back down to 38V.

> the end of the cycle on an ET charger will be over 42V, with the
> batteries well above room temperature.  If you really want to see where
> to cut off, measure each battery with a DVM and see if they are all at
> least 6.4+V.  Frequently, you have one still at 5.9V with others at 6.5V
> at the 38V level.  By the time you are at 42+V, the worst battery is
> usually near 6.4V.  Try it yourself and see.

Can't try it right now, since my charger is only putting out 39.5V. :) And
of course the Landis is shutting off the charger when the pack is at 38V.
So, what should I bump it up to? 39V? 40V? 42V? Of course, I'll need to
replace that capacitor first....

Mike

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