Re: (ET) Duracell Batteries

["David Roden" <etpost drmm net>]

On 17 Jun 2015 at 12:17, bushman165s aol com via Elec-trak wrote:

> most GE chargers that I repair put out about 42VDC. 

Is that measured open circuit, or when it's connected to the battery?  It 
makes a difference, because of the way voltmeters average pulsating DC.

You want to read the voltage it fires into a fully charged battery.  
That's 
what matters, and most likely it'll read higher than the open-circuit 
voltage. For gels, this voltage should be between 42.3 and 42.9 volts.

If it's too high, you might be able to adjust it somewhat by changing the 
value of the capacitor.  I've never tried this, so I don't know if you 
could 
get enough wiggle room.

Even if the GE charger does produce the right output voltage, you also 
need 
to eliminate the battery taps that imbalance the batteries, so you don't 
have to beat them over the head to equalize them on every charging cycle.  

Converting the lights to run on 36v would be pretty easy; just use 
forklift 
bulbs. The lift is more of a challenge.  A big honkin' regulator might 
work, 
burning off the excess voltage as heat.  I'd have to see how much current 
the lift draws at peak.  A more efficient but more expensive solution 
would 
be a DC:DC converter with a 14-18 volt output.

Still another idea : give the lift its own smaller onboard battery.  If 
you 
replace the GE charger with something more modern and smaller, you might 
have enough room for an extra 12v deep cycle battery up front.

> I think I could use one of the Landis controllers with the setpoint at
> 42.5VDC or so to keep them from overcharging. 

Ehh, not so fast!  I'm not so sure that's going to help much with gel 
batteries.  The Landis controller doesn't quite work that way; it's a bit 
oddball.  

To explain what I mean, first a little about basic battery charging 
control, 
that is, ways that chargers fill up a battery right to the brim, not 
either 
undercharging or overcharging.  If you already know this stuff, just skip 
ahead.

One of the simplest methods is to just regulate the charger's output 
voltage.  If you limit it to the battery's theoretical fully-charged 
voltage 
(ideally compensated for temperature, because a battery's fully charged 
voltage depends on its temperature), it *can't* overcharge the battery.

As long as the battery voltage is less than the charger's voltage, current 
flows into the battery.  As the battery charges, its on-charge voltage 
rises, and the charging current tapers off.  Thus this is called a taper 
charger.  

When the current falls to about 0.05C (2% of the battery's 20 hour amp 
hour 
capacity expressed as amperes), we consider the battery fully charged.  

If properly set up, taper chargers are pretty safe for the battery.  Their 
main fault is that they can be maddeningly slow.  It can take days or even 
weeks to completely fill up a big battery.

So the engineers have developed ways to increase the current in the bulk 
phase (up to 80% SOC, gassing voltage), without overcharging later.

Generally they use some kind of electronics to monitor and regulate 
voltage 
and current.  From there they diverge on best strategies to do the job; 
this 
is where you get such alphabet soup as IU, IUI, and DV/DT.  (Look them up 
if 
you're interested.)  What they all have in common is the electronics, 
which 
of course adds to the charger's cost and complexity.

At the bottom end of these smarter chargers, carrying a C+ average, we 
find 
a relatively simple design that I've seen called a "cycle dropping" 
charger.

A cycle dropping charger starts with an output voltage high enough to 
charge 
the battery fairly rapidly during its bulk phase (up to gassing voltage).

To prevent overcharging with this higher charging voltage, the controller 
monitors the battery's on-charge voltage.  When it reaches the fully 
charged 
voltage (for our purposes, let's say 42.6 volts), the charger shuts off 
its 
output.   The battery's surface charge dissipates, and its voltage falls.  
When it falls below some lower threshold voltage (there's some hysteresis 
in 
these voltages; let's say it's 42.1 volts), the charger restarts.  

This cycle repeats many times.  As the battery approaches full, the on 
time 
shortens and the off time lengthens, eventually reducing the average 
charging current to the value I mentioned above (0.05C).  

At this point the charger *should* turn off, but I've never seen a cycle 
dropping charger that actually does.  Instead, the manufacturers will 
usually tell you that it "maintains the battery at full charge." You 
should 
read this as "overcharges the battery if you leave it for very long."  Ask 
me how I know this.  

As I said before, cycle dropping is kind of crude as charging algorithms 
go. 
But if it's used carefully (I always put these chargers on timers), it 
actually can work tolerably well for many applications.

So now we come to Harry Landis's controller.  I may have missed some, but 
I've never seen any other charge controller like it in the marketplace.  
The 
best way I can think of to describe it is that it's a cycle dropping 
charger 
in reverse.

It uses a threshold voltage, but it defines a *minimum* voltage to turn 
*on* 
the charger, instead of a *maximum* voltage to turn it *off*.  Any time 
the 
battery falls *below* some voltage value, the charger turns on and runs 
for 
a fixed time (5 minutes, IIRC).  

You can see that this isn't what you really need for your gel batteries, 
because there's no actual top limit on the voltage.  In fact the Landis 
controller is more of a battery maintainer than a cyclic charge 
controller.  
I know some folks here use it for a charge controller, but that's not what 
it's really designed for.  If it works for you, great, but I personally 
wouldn't (and don't) use it that way.  

That gives me an idea.  Are you up for building your own charge 
controller?  
Here's a schematic diagram of the charger used in Comuta-Cars in the early 
1980s.  

http://www.evdl.org/docs/c_car_charger.jpg

This circuit is for a 48v battery, but it should be easy to adapt to a 36v 
battery.  I'm not an EE, but I think all you'd have to do is change the 
value of R4, and maybe of R6.  In fact I just might try that for my New 
Idea 
rider.

A nice feature of this circuit is that L1 (a small 12v indicator lamp) 
lights up when the charger is off, so you can see how the charge is 
progressing.  You could replace this lamp with a resistor and LED.

Anyway, to finally cut to the chase, if you want to go with the gels, I'd 
recommend you either addd some smarts to the GE charger, or replace it 
with 
a modern smart charger.  If you do neither of these, at least make sure 
the 
GE stays below 43 volts when charging the battery. 

Either way, I also recommend getting rid of the battery taps to fix the 
battery imbalancing problem.


David Roden - Akron, Ohio, USA

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