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Re: Battery Chargers, Pulse Units
- Subject: Re: Battery Chargers, Pulse Units
- From: roden ald net
- Date: Sat, 12 Dec 1998 13:33:36 -0500
- In-reply-to: <19981212171227.FVS17685@LOCALNAME>
- Sender: owner-elec-trak cosmos5 phy tufts edu
vic garza <vtr-garza worldnet att net> wrote:
> I have found
> some of those used for charging SLA in cordless tools are at least semi
> "smart" chargers and much cheaper than the purposely built kind. They
> usually don't contain the sophisticated electronics and are slower to
> charge a battery but are often built for long term seasonal trickle
> storage and so won't overcharge ... maybe the 36V cordless push mower
> chargers (Roybi?)
> could be used for tractors converted to SLA?? Charging would take longer
> of course...
These are constant voltage chargers, probably set up for float charging.
That means they put out a regulated voltage at the level specified by
the battery maker as appropriate. This is the voltage at which a fully
charged battery will accept no more charge. So you can (theoretically)
plug 'em in and forget 'em.
This sounds good, but "Charging would take longer of course" is right.
Much longer. Probably weeks. Maybe even longer than that.
A constant voltage charger (also called a taper charger) will start off
with its full charge current, but the current will fall about linearly as
battery charges. So the first 20% of the charging goes quickly, but
from there on things slow down in a big way. It can take weeks to put
in the last 20% of charge. Many of these little wall-wart charged tools
never actually get there. Their batteries ultimately die of
On the other hand, a constant current charger will keep pounding in as
much as it can from start to finish. It goes *real* fast, but it will
sealed battery and isn't so hot for a flooded battery either.
The GE charger is a constant voltage charger set much higher than
float voltage, so it is a compromise between the two. It will charge
faster than a float-voltage CV charger, but still has a low enough final
rate that it won't destroy flooded batteries.
Here is what a 3-stage charger does.
Stage 1: constant current to 80% charged.
Stage 2: constant voltage (above float voltage, typ. 14.2-14.7 volts)
until charge current falls below some value, usually 2-3 amps
Stage 3: either float voltage (around 13.8v) or a final short constant
current equalizing charge. Which one it uses depends on your battery
maker's recommendation and/or the charger maker's philosophy.
Because it combines the methods, a 3-stage charger is the fastest
and the best for your batteries. It is also the most complex and
All this by way of suggesting that these small tool chargers would take
a *very* long time to fully charge a tractor's batteries. In fact if they
designed for the low capacity batteries in a push mower, they might
*never* fully charge the ET's batteries.
Unfortunately, in chargers, you pretty much *do* get what you pay for.
Especially with sealed batteries, if you go cheap, you will spend the
saved money on more frequent battery replacements.
Don't be too quick to dismiss the combination of the ferroresonant GE
charger and flooded golf car batteries. Yes, it's ancient technology
(most modern 3-stage chargers use microprocessor control), but for its
intended purpose, this combination works very well. While it's not the
ultimate in convenience, nothing can touch it for cost-effectiveness.
David Roden THE VIRTUAL PD
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