Need to charge some SLAs and other lead acid batteries for field day Im
trying to make
something work without buying a new battery charger, so here goes.
I need to charge a alot of different voltage lead acid batterys
6,8,10,12, ect. I have a
old charger that only puts out 12-14vdc, I have a 10amp 120vac
powerstat (variac) im thinking
of adding to the input of the transformer to reduce output . Will this
work?
Im not sure about the inductance & operating a transformer @ 1/2 or
2/3 the normal 120 vac
input voltage, im wandering if this will effect efficiency or if it
will work at all.

There should never be a problem operating a transformer on lower
voltage than it was designed for. The problem comes from operating on
too high a voltage (and usually that problem is core saturation at line
frequencies--or core overheating for high frequency transformers).

As for charging the batteries, you can find lots of info on "doing it
right" on the web. I've found
http://www.batteryuniversity.com/partone-13.htm to be pretty good. It
saves a lot of work if you have a circuit do the monitoring for you,
but you can do it yourself with voltage and current meters. If you get
tired of looking at the meters, check out TI's UC3906 and related ap
note.

Cheers,
Tom

In article .com,
wrote:

Need to charge some SLAs and other lead acid batteries for field day Im
trying to make
something work without buying a new battery charger, so here goes.

I need to charge a alot of different voltage lead acid batterys
6,8,10,12, ect. I have a
old charger that only puts out 12-14vdc, I have a 10amp 120vac
powerstat (variac) im thinking
of adding to the input of the transformer to reduce output . Will this
work?

Im not sure about the inductance & operating a transformer @ 1/2 or
2/3 the normal 120 vac
input voltage, im wandering if this will effect efficiency or if it
will work at all.

The transformer in your existing charger will probably function as you
expect if you reduce its input voltage with a Variac.

However, there's no assurance at all that your charger's DC output
voltage will behave. If the charger has a linear voltage regulator of
some sort inside, the regulator's not going to want to track the
reduced input voltage. It'll probably run "wide open", which means
that the charger's output voltage is going to be very critically
dependent on the Variac setting. Unless you are very careful in
setting the Variac, you'll either undercharge the battery, or hit it
with too high a voltage and end up gassing away much of the electrolyte.

You might be able to alter the DC regulation circuitry in the charger,
so that it would regulate down to a lower (switch-selectable) voltage.
You might need to do both in order to charge a lower-voltage battery
without overheating the charger - reduce the input AC voltage by about
half (to cut the raw, unregulated DC voltage) and then change the
voltage-regulator setting to produce the correct fast-charge or
float-charge voltage.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

wrote in message
oups.com...
Need to charge some SLAs and other lead acid batteries for field day Im
trying to make
something work without buying a new battery charger, so here goes.
I need to charge a alot of different voltage lead acid batterys
6,8,10,12, ect. I have a
old charger that only puts out 12-14vdc, I have a 10amp 120vac
powerstat (variac) im thinking
of adding to the input of the transformer to reduce output . Will this
work?
Im not sure about the inductance & operating a transformer @ 1/2 or
2/3 the normal 120 vac
input voltage, im wandering if this will effect efficiency or if it
will work at all.

To get battery credit, didn't the batteries need to be charged by something
other than power line current? I thought they had to be solar, wind, water
etc charged so that you couldn't just plug in a battery charger into a wall
and charge them the easy way.
Not to put a damper on your using batteries for field day, but you might
want to check the rules. Here we use a big diesel generator for the radios,
but some wanted their logging laptops plugged into the wall instead of the
generator and a spirited argument broke out whether that negated the credit
for not using lines power.
thanks, John.
KC5DWD

SLAs will be Tricky. If the supply you have is regulated, the variac is not
a very good idea. The transformer operation and efficiency is not an issue.
It will work just fine on the variac.


However, you really need a well regulated supply and accurate voltmeter and
to float them for full charge. I have two little SLAs sitting at 13.75 all
the time.

Read the lead-Acid sections of this first, then decide.
http://www.batteryuniversity.com/partone.htm

Having a good background in Lead-Acid basics, you can do some things, one
being:
For one battery at a time:
1- Measure voltage at start to determine charge state.
2- Calculate amp-hours to full charge (knowing the charge replacement
efficiency of YOUR battery).
3- Charge with known current (like a ni-cad charger) to somewhere under 90%.
4- Measure the open ckt voltage periodically, but after the required rest
period.
5- Stop before disaster happens.

OR

Just wing it. (:-)

73, Steve, K9DCI

Just kidding with the wing it thing.


wrote in message
oups.com...
Need to charge some SLAs and other lead acid batteries for field day Im
trying to make
something work without buying a new battery charger, so here goes.
I need to charge a alot of different voltage lead acid batterys
6,8,10,12, ect. I have a
old charger that only puts out 12-14vdc, I have a 10amp 120vac
powerstat (variac) im thinking
of adding to the input of the transformer to reduce output . Will this
work?
Im not sure about the inductance & operating a transformer @ 1/2 or
2/3 the normal 120 vac
input voltage, im wandering if this will effect efficiency or if it
will work at all.

On Tue, 7 Feb 2006 15:56:18 -0600, "john graesser"
wrote:


wrote in message
roups.com...
Need to charge some SLAs and other lead acid batteries for field day Im
trying to make
something work without buying a new battery charger, so here goes.
I need to charge a alot of different voltage lead acid batterys
6,8,10,12, ect. I have a
old charger that only puts out 12-14vdc, I have a 10amp 120vac
powerstat (variac) im thinking
of adding to the input of the transformer to reduce output . Will this
work?
Im not sure about the inductance & operating a transformer @ 1/2 or
2/3 the normal 120 vac
input voltage, im wandering if this will effect efficiency or if it
will work at all.

To get battery credit, didn't the batteries need to be charged by something
other than power line current? I thought they had to be solar, wind, water
etc charged so that you couldn't just plug in a battery charger into a wall
and charge them the easy way.
Not to put a damper on your using batteries for field day, but you might
want to check the rules. Here we use a big diesel generator for the radios,
but some wanted their logging laptops plugged into the wall instead of the
generator and a spirited argument broke out whether that negated the credit
for not using lines power.

If he's using batteries and not recharging them with a motor generator
or the power line, then he's running battery power and gets a
multiplier of 5. Where they were previously charged isn't an issue.

He can still charge them:

6.9. Batteries may be charged while in use. Except for Class D
stations, the batteries must be charged from a power source other than
commercial power mains. To claim the power multiplier of five, the
batteries must be charged from something other than a motor driven
generator or commercial mains.

But doesn't get the multiplier.

The spirit of the thing is that the contest is a test of emergency
preparedness. If he had the foresight to have a bank of batteries
charged when the power failed, then he is "prepared."

Considering that it's a bit warm at the end of June in Tucson and half
the mountains in the state were on fire (wait till this year, 110 days
without rain and counting), I stayed home and ran 1E. I could actually
(and did) run for quite a while on just battery power but I
periodically ran the Honda generator to charge it.

Still didn't do to badly. One man, one band and only 17 hrs on the air
and still third highest number of QSOs in my category in the nation.

Doesn't that rule only apply to batteries being charged DURING the
event? If this is to charge BEFORE the event, it would (obviously) be OK...



To get battery credit, didn't the batteries need to be charged by something
other than power line current? I thought they had to be solar, wind, water
etc charged so that you couldn't just plug in a battery charger into a wall
and charge them the easy way.

On Tue, 7 Feb 2006 15:56:18 -0600, "john graesser"
wrote:


wrote in message
roups.com...
Need to charge some SLAs and other lead acid batteries for field day Im
trying to make
something work without buying a new battery charger, so here goes.
I need to charge a alot of different voltage lead acid batterys
6,8,10,12, ect. I have a
old charger that only puts out 12-14vdc, I have a 10amp 120vac
powerstat (variac) im thinking
of adding to the input of the transformer to reduce output . Will this
work?
Im not sure about the inductance & operating a transformer @ 1/2 or
2/3 the normal 120 vac
input voltage, im wandering if this will effect efficiency or if it
will work at all.

To get battery credit, didn't the batteries need to be charged by something
other than power line current? I thought they had to be solar, wind, water
etc charged so that you couldn't just plug in a battery charger into a wall
and charge them the easy way.
Not to put a damper on your using batteries for field day, but you might
want to check the rules. Here we use a big diesel generator for the radios,
but some wanted their logging laptops plugged into the wall instead of the
generator and a spirited argument broke out whether that negated the credit
for not using lines power.
thanks, John.
KC5DWD


There are two different multipliers at work.

If it's battery then how they were charged is unimportant. All that
counts is your running on battery. If you charge them while on the
air then how you charge them counts. If off generator its differnt
than off the mains. There is a special class if you charge them using
neither generator(gas/diesel power) or mains for that see alternative
power.

If your going for the alternative power source multiplier then how the
batteries are charged counts. I think the rule says non-petropower
(gas oil or pertro byproducts) IE: Solar, unless you have a really
big solar array it's diffictult to run a radio directly from the sun
(it's possible) but the rules do allow you to charge batteries from
the sun and run from them. I believe you get both solar power and
battery scores for that. Other sources are allowed such as water
power, wind, someone peddling a genny, a old military handcrank gen
would be valid examples. I was told steam powered genny running off
wood or waste and a internal combustion engine running off a wood
gassifier also qualifies. I suspect a diesel gen running of
greasoline (used cooking grease or vegetable oil) may also qualify.

Running aux equipment like fans, lights and computers(not connected
to radios) do not negate the battery or alternate energy
credit/nultipliers.

Allison
KB!gmx

Field day is along way off, I just wanted to keep them alive until
then. After it starts i have a large array of solar cells & Im sure
the
sun will be out, hope so anyway.

N4aeq