I store a car through the winter with the negative cable unhooked.
This last winter I decided to just hook the charger up to the battery,
and shut off the power to te building at the fuse box. That way, when I
do go into the building now and then, and turn on the breaker, the
battery will get a shot of charge during that time, keeping it topped
I just went in there and turned on the breaker, and it looked like the
battery was drawing a surprisingly high amount of amps, almost as much
as a dead battery would draw.
The charger is a decent booster/charger, a Schauer I believe, not
really a cheapo.
Battery's not very old, maybe a 2 year old Die Hard Gold, and I
suppose the battery could have gone bad.
But is it possible that leaving the charger on the posts all the time
was giving some continuity between positive and negative terminals,
drawing it down the whole time?
Some do, some don't. Most don't... Use an ammeter to measure any current
draw with the charger disconnected, and see what you get... Anything
over about 10 or 20 MA (careful that you don't damage your meter, start
on a high range and work down) is too much.
The charger outputs through rectifier diodes, similar to the ones in
your alternator. With the charger off (or alternator not running), these
diodes are the only thing preventing reverse current flow.
A 'leaky' diode in your charger (or alternator), a 'parasitic' current
draw in the car somewhere (glove compartment lights were bad about this
on some makes/models through the years), or just a bad battery could all
explain the issue.
Get out you amp meter, and have at it!
 In my limited experience with battery chargers I've learned that
they usually use the absolute cheapest diodes available... it's amazing
they work as well as they do. But then again, charger diodes often have
good size heat sinks, and aren't subjected to heavy use, large thermal
shocks, vibration and all that like alternator diodes...
For a point of reference, my Schumacher XC-103 (which is a semi-automatic
SCR instead of diode based charger with an LED display) draws 1mA from the
attached 12v battery whether plugged in and not charging or unplugged.
On 18/03/2012 10:46 PM, Daniel who wants to know wrote:
Look at a SCR as an upscale diode with a third lead to control current
flow. Some "cheap" chargers might use the SCR gate to control current
and that is the only real regulation they use. Cheap chargers rely on
line voltage as the voltage reference.
I am not up on the models, but hope your XC-103 has more than a center
tap transformer and just two SCRs. While good enough to get a car
going, they are not good to really properly charge up a boat battery to
RECESSION is when your neighbor loses their job.
DEPRESSION is when you lose your job.
Wonder who told you that bit of swill? An SCR only works on an AC
circuit, is never intentionally used as a diode, only as a switching
device. Since an SCR won't turn off unless all power is removed, it
cannot control a DC circuit (with the exception that SCRs are often used
as a crowbar to short the output of a power supply when the voltage
exceeds a design threshold.
Bullsh1t. SCRs can be used with AC or DC on input, but granted, more
often AC to rectify 1/2 wave of the AC. You can use the gate to
regulate AC or DC current, but the AC is 1/2 wave rectified.
An example is a DC to AC converter, putting 60 hz into the gate to chop
the input DC into a transformer to step up to 120 VAC. Makes for dirty
output but works and is common in DC to AC converters you might use on a
SCR is a three lead device, it will do whatever the gate tells it. It
is in essence a diode with a current limiter controlled by the gate.
Feed in DC, oscillate the gate and you have chopped alternating on the
SCRs are NOT only for AC input. Just more BS on your part.
RECESSION is when your neighbor loses their job.
DEPRESSION is when you lose your job.
Once an SCR is turned on, it remains on until the current passing
through it goes to zero. It cannot be turned off, an SCR works as an
'ON' switch that once turned on cannot be turned off. Therefore it is
only useful in AC circuits or in applications where it must (or should)
conduct until power is removed such as a power-supply crowbar protection
The fact that a battery is connected makes an SCR useless in a battery
charger's DC circuit.
Post a schematic of one (an automotive battery charger with an SCR on
the output) and I'll apologize, until then, I stick with my point.
An SCR battery charger has a dual secondary winding, one center tapped, one
standard. The standard secondary powers the electronics, the center tap of
the other is connected to the ground (-ve) of the electronics and to the
battery via a current sense resistor and optional ammeter. Each of the ends
of the CT winding is connected to the anode of an SCR, the cathodes are
connected to the battery +ve and a voltage sense lead to the electronics.
The electronic circuit "fires" the gates on the SCRs at the proper moment
each half cycle to regulate the output voltage and current, IE for full
output the gate is triggered at the beginning of that alternation, for less
output it is triggered near the end.
The 0 crossing twice each cycle turns the SCR off.
As said this is exactly how the several hundred dollar Lester 24v charger
that came with many Invacare electric wheelchairs functions.
A democrat is one who would take an academic position and say it would
work in a real world application! You took a circuit that was made to
demonstrate exactly what I was saying, and tried to make it look like it
supported your position...
It is in fact a CT transformer and 2 SCRs controlled by a microprocessor,
but so what? So is the stock Lester charger that comes with Invacare
Many electric pallet jack and forklift battery chargers are also SCR based.
True that an SMPS charger is easier on batteries but the SMPS Schumacher
chargers don't have a jump start capability either.
The only problem with the XC-103 and I suspect all other models in the same
line (XC-75, etc) is that the voltage setpoints are too high. For instance
the book (which covers the 75 and 103) and my own testing confirms that it
From the book:
Charge Voltage: Usually 14.7 volts (Gel Cell), if not, then 15.4 volts
(AGM), otherwise it will be 16.0 volts (Standard battery).
The problem here is that it should be 14.1 for gel, 14.4 for lead-antimony
flooded, and 14.9 for AGM or lead-calcium flooded, hence whwnever I use it
on car batteries and AGM I set it to gel, and I don't charge gel batteries
with it at all.
The only rhyme or reason I can think of for this voltage discrepancy is that
it has no temperature compensation and they wanted it to work even in
freezing temperatures where the required voltage is higher. To the
charger's credit it does shut down and show an error code if it thinks the
battery is going into thermal runaway, which it would likely do on a hot
summer day at those voltages if it were set to "normal" on a flooded
YES, Power flows back through the chargers transformer windings and will
discharge the battery.
Get a float charger, that's the best for the battery. All my stored
vehicles, toys and mowers with batteries are stored with a float charger on
them. Got 10 yrs. out of my bikes battery, it still cranked fine when I
changed it, just didn't want to trust a battery that old on a long trip.
BTW I don't even disconnect the vehicles from the battery when the float
chargers on them. Quick discon. plug setups on the float chargers.
Repairman54 wrote, "Get a float charger, that's the best for the
battery. All my stored vehicles, toys and mowers with batteries are
stored with a float charger on them. Got 10 yrs. out of my bikes
battery, it still cranked fine when I changed it, just didn't want to
trust a battery that old on a long trip. BTW I don't even disconnect the
vehicles from the battery when the float chargers on them. Quick discon.
plug setups on the float chargers. "
What exactly is a "float charger?" I presume that's not the same as a
Could you post a link of where to get what you are using, or similar?
It's also called a battery maintainer.
Harbor Freight sells one for $9.99 and I have one on all my stored battery
equipped toys and mowers, etc. .
Also use a battery maintainer/conditioner by BatteryMinder that I rotate
around the batteries during storage time.
Repairman54 wrote: "Also use a battery maintainer/conditioner by
BatteryMinder that I rotate around the batteries during storage time. "
Thanks for the info, I googled Battery Maintainers and saw many which
claimed to be able to "de-sulfate" batteries. I wasn''t aware that
could be done -- but I'm inclined to think it's legit since so many
battery maintainers claim to be able to do it, one of which was made by
A comparo indicated the BatteryMinder was the best one.
But how is it possible to de-sulfate a battery? I thought they were
toast once sulfated.
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