Hey guys... I've spent lots of time looking over google archives for the
answer to this, and God knows this has been covered many times, but I've not
quite found my answer.

I have the following QRP power supply/charger
http://www.mfjenterprises.com/produc...rodid=MFJ-4114 .
Basically it comes standard to charge a 12 nicads, but I took out the nicad
holders and put in a 12v 5AH gel cell. I modified it to charge directly from
the 13.8v power supply instead of the 18v nicad charger circuit. I charged
the battery to about 13.8v (w/ no load) by floating. If I measure the
battery while having my radio on receive, which only draws maybe 80mA's or
so, I see the battery dropping by .10's of a V in no time. The battery is
brand new.
I've noticed that the battery only draws about 30mA's while charging at any
voltage. I even added a switch so I can switch extra diodes between the
regulator ground so I can charge it at 14.X volts.

So my question... If it measures 13.8-14v after charging, it should be fully
charged, right? Is there something going on since it is only drawing 10's of
milliamps while charging? I've read that they charge at several hundred
milli's. I'd like to use my QRP rig remotely, and at the rate its dropping,
I just don't think it will serve the purpose.

Thanks for all the help.

Jim, AB9LM

"J Shrum" wrote in message
...
Hey guys... I've spent lots of time looking over google archives for the
answer to this, and God knows this has been covered many times, but I've
not
quite found my answer.

I have the following QRP power supply/charger
http://www.mfjenterprises.com/produc...rodid=MFJ-4114 .
Basically it comes standard to charge a 12 nicads, but I took out the
nicad
holders and put in a 12v 5AH gel cell. I modified it to charge directly
from
the 13.8v power supply instead of the 18v nicad charger circuit. I charged
the battery to about 13.8v (w/ no load) by floating. If I measure the
battery while having my radio on receive, which only draws maybe 80mA's or
so, I see the battery dropping by .10's of a V in no time. The battery is
brand new.
I've noticed that the battery only draws about 30mA's while charging at
any
voltage. I even added a switch so I can switch extra diodes between the
regulator ground so I can charge it at 14.X volts.

So my question... If it measures 13.8-14v after charging, it should be
fully
charged, right? Is there something going on since it is only drawing 10's
of
milliamps while charging? I've read that they charge at several hundred
milli's. I'd like to use my QRP rig remotely, and at the rate its
dropping,
I just don't think it will serve the purpose.

Thanks for all the help.

Jim, AB9LM


It takes more voltage to charge a battery than what it is rated at. That is
the reason for an 18 volt charger voltage instead of 14 volts.

On Sun, 20 Nov 2005 19:27:49 -0600, "J Shrum" wrote:

Hey guys... I've spent lots of time looking over google archives for the
answer to this, and God knows this has been covered many times, but I've not
quite found my answer.

I have the following QRP power supply/charger
http://www.mfjenterprises.com/produc...rodid=MFJ-4114 .
Basically it comes standard to charge a 12 nicads, but I took out the nicad
holders and put in a 12v 5AH gel cell. I modified it to charge directly from
the 13.8v power supply instead of the 18v nicad charger circuit. I charged
the battery to about 13.8v (w/ no load) by floating. If I measure the
battery while having my radio on receive, which only draws maybe 80mA's or
so, I see the battery dropping by .10's of a V in no time. The battery is
brand new.
I've noticed that the battery only draws about 30mA's while charging at any
voltage. I even added a switch so I can switch extra diodes between the
regulator ground so I can charge it at 14.X volts.

So my question... If it measures 13.8-14v after charging, it should be fully
charged, right? Is there something going on since it is only drawing 10's of
milliamps while charging? I've read that they charge at several hundred
milli's. I'd like to use my QRP rig remotely, and at the rate its dropping,
I just don't think it will serve the purpose.

Just float charging at 13v8 isn't going to do a great lot for an SLA. Download
and read the following two docs from TI/Unitrode which will give you a fair
insight into the proper care and feeding of SLA's.

http://focus.ti.com/lit/an/slua115/slua115.pdf

http://focus.ti.com/lit/ds/symlink/uc3906.pdf

There's a lot of overlap, but good info, and that chip makes a fairly simple yet
elegant charger.

Me again.
Thanks for the info. I just decided to run it down to see how long it would
go. Like I said before, after fresh charge, and the battery showing 14v,
after aplying the slightest load, the voltage started dropping... it dropped
down to 12.6 in no time, but.... its been staying there. I've had the radio
on for a couple hours, and its not moved from 12.6v. I even keyed a bunch,
and that draws about an amp. Seems its holding steady at that voltage under
load.

Thanks again guys, your always more than helpful.

Jim, AB9LM

"J Shrum" wrote in message
...
Hey guys... I've spent lots of time looking over google archives for the
answer to this, and God knows this has been covered many times, but I've
not quite found my answer.

I have the following QRP power supply/charger
http://www.mfjenterprises.com/produc...rodid=MFJ-4114 .
Basically it comes standard to charge a 12 nicads, but I took out the
nicad holders and put in a 12v 5AH gel cell. I modified it to charge
directly from the 13.8v power supply instead of the 18v nicad charger
circuit. I charged the battery to about 13.8v (w/ no load) by floating. If
I measure the battery while having my radio on receive, which only draws
maybe 80mA's or so, I see the battery dropping by .10's of a V in no time.
The battery is brand new.
I've noticed that the battery only draws about 30mA's while charging at
any voltage. I even added a switch so I can switch extra diodes between
the regulator ground so I can charge it at 14.X volts.

So my question... If it measures 13.8-14v after charging, it should be
fully charged, right? Is there something going on since it is only drawing
10's of milliamps while charging? I've read that they charge at several
hundred milli's. I'd like to use my QRP rig remotely, and at the rate its
dropping, I just don't think it will serve the purpose.

Thanks for all the help.

Jim, AB9LM

J Shrum wrote:
(top-posting fixed)
"J Shrum" wrote in message
...

Hey guys... I've spent lots of time looking over google archives for the
answer to this, and God knows this has been covered many times, but I've
not quite found my answer.

I have the following QRP power supply/charger
http://www.mfjenterprises.com/produc...rodid=MFJ-4114 .
Basically it comes standard to charge a 12 nicads, but I took out the
nicad holders and put in a 12v 5AH gel cell. I modified it to charge
directly from the 13.8v power supply instead of the 18v nicad charger
circuit. I charged the battery to about 13.8v (w/ no load) by floating. If
I measure the battery while having my radio on receive, which only draws
maybe 80mA's or so, I see the battery dropping by .10's of a V in no time.
The battery is brand new.
I've noticed that the battery only draws about 30mA's while charging at
any voltage. I even added a switch so I can switch extra diodes between
the regulator ground so I can charge it at 14.X volts.

So my question... If it measures 13.8-14v after charging, it should be
fully charged, right? Is there something going on since it is only drawing
10's of milliamps while charging? I've read that they charge at several
hundred milli's. I'd like to use my QRP rig remotely, and at the rate its
dropping, I just don't think it will serve the purpose.

Thanks for all the help.

Jim, AB9LM





Me again.
Thanks for the info. I just decided to run it down to see how long it
would go. Like I said before, after fresh charge, and the battery
showing 14v, after applying the slightest load, the voltage started
dropping... it dropped down to 12.6 in no time, but.... its been
staying there. I've had the radio on for a couple hours, and its not
moved from 12.6v. I even keyed a bunch, and that draws about an amp.
Seems its holding steady at that voltage under load.

Thanks again guys, your always more than helpful.

Jim, AB9LM

I was going to suggest that you do this. If you have the patience keep
it up until the battery voltage really starts doing a nosedive. Radio
Shack sells (or used to sell) a DVM with a serial output and a little
scope program that was nice for collecting this sort of data.

"Rechargeable Batteries Application Handbook" by the "Technical
Marketing Staff at Gates Energy Products" indicates that a SLA battery
isn't really discharged until it's down around 1.8V per cell. I'm not
sure that I'd take it that low, but 12.6 - 12.8 is what you expect from
a six-cell lead-acid battery that's not being charged, and it will hold
that voltage for 70-80% of the time that it's discharging.

It's a good book, by the way. It's no more technical than the ARRL
Handbook, and it has slews of information about NiCd and lead-acid
batteries. It's a bit light (and a bit out of date) on NiMh batteries
and it came out before Lithium Polymer batteries were on the market, but
other than that it's a fine resource.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

These SLA =Sealed Lead Acid batteries usually have a charging rate for 2
types of usage The YUASA battery I have in front of me has the following
instructions (applicable at 20 degrees Celcius ) :
Standby Use : Voltage regulation 13.50 -13.80 V Initial current :
No Limit
Cyclic Use : voltage regulation 14.4 - 15.00 V Initial current:
1.75 Amperes max.

I also use a number of SLAs without such instructions , which I (safely)
charge at 0.1 C (for example a 7Ah battery is charged at 700 mA ) and
limiting the Voltage to 13.5 V ,bearing in mind that 12 V lead acid
batteries are still 70 -80 % charged when voltage has dropped to 12.6 V
To test (charged )12 V lead acid batteries I discharge them at a constant
0.1C current and check the time until the voltage has dropped to 11.9 V
(at that voltage the battery might not as yet be fully discharged ,but below
that voltage they are of no use to me )

Frank GM0CSZ / KN6WH

+++++++++++++++++++++++
So my question... If it measures 13.8-14v after charging, it should be
fully charged, right? Is there something going on since it is only drawing
10's of milliamps while charging? I've read that they charge at several
hundred milli's. I'd like to use my QRP rig remotely, and at the rate its
dropping, I just don't think it will serve the purpose.

Not sure who the OP is here...

I gave some relevant info in another thread (Below), but here's some
additional info.

The lead acid chemistry's voltage goes from just under 12 volts at dead, to
just over 12 V at full charge (Don't remember the exact, but the idea
holds). HOWEVER, this is ONLY after "RESTING" for some time. I never found
out (or perhaps remembered) what this resting time is, but think it is
perhaps half to one hour.

Float voltage is around 13.8 (I have some Yuasa SLAs and they say give a
range of around 13.7-13.9 for float). At the float voltage, they will "take
what they need" to stay charged, but that is NOT the terminal voltage after
resting, or when delivering current. This is what I say above.

In addition to the constant voltage float, you MUST also limit the current
to some maximum (specified my the mfr) when a dead battery is first put on
the charger. With a high current 13.8 supply, you can damage (explode, or
whatever) the battery with too much current at this time. Once the battery
gets up to the 13.8 float voltage, the current will begin to drop and the
constant current part of the charger will fall out of use and you have a
constant voltage, where the battery top itself off thing going on.

Steve

================================================== ==========================
=
previous post


Looks like you have some good info from others. Here's a little more.

What you will be doing is not "trickle" charging, but it is called "float"
charging. Lead acid chemistry, similar to Li-ion (unlike in-Cd & Ni-Mh) has
the characteristic that it has a voltage chrematistic such that the terminal
voltage rises between dead and full charge. You can safely put a constant
voltage (but also with a current limit) on the battery and it will seek its
own full charge and the current will taper off, when it gets enough, to what
it needs to stay at full charge. CAUTION -- This voltage is typically
around 13.8, HOWEVER you MUST consult the manufacturer's specs. This
voltage also changes slightly as the temperature of the battery changes.

A commercial device designed for this service is recommended.

73, Steve, K,9.D;C'I







"Highland Ham" wrote in message
...
These SLA =Sealed Lead Acid batteries usually have a charging rate for 2
types of usage The YUASA battery I have in front of me has the following
instructions (applicable at 20 degrees Celcius ) :
Standby Use : Voltage regulation 13.50 -13.80 V Initial current :
No Limit
Cyclic Use : voltage regulation 14.4 - 15.00 V Initial
current:
1.75 Amperes max.

I also use a number of SLAs without such instructions , which I (safely)
charge at 0.1 C (for example a 7Ah battery is charged at 700 mA ) and
limiting the Voltage to 13.5 V ,bearing in mind that 12 V lead acid
batteries are still 70 -80 % charged when voltage has dropped to 12.6 V
To test (charged )12 V lead acid batteries I discharge them at a constant
0.1C current and check the time until the voltage has dropped to 11.9 V
(at that voltage the battery might not as yet be fully discharged ,but
below
that voltage they are of no use to me )

Frank GM0CSZ / KN6WH

+++++++++++++++++++++++
So my question... If it measures 13.8-14v after charging, it should be
fully charged, right? Is there something going on since it is only
drawing
10's of milliamps while charging? I've read that they charge at several
hundred milli's. I'd like to use my QRP rig remotely, and at the rate
its
dropping, I just don't think it will serve the purpose.

Can anyone comment on the merits of the Schumacher 1562A charger?

Tom

"J Shrum" wrote in message
...
Hey guys... I've spent lots of time looking over google archives for the
answer to this, and God knows this has been covered many times, but I've
not
quite found my answer.

I have the following QRP power supply/charger
http://www.mfjenterprises.com/produc...rodid=MFJ-4114 .
Basically it comes standard to charge a 12 nicads, but I took out the
nicad
holders and put in a 12v 5AH gel cell. I modified it to charge directly
from
the 13.8v power supply instead of the 18v nicad charger circuit. I charged
the battery to about 13.8v (w/ no load) by floating. If I measure the
battery while having my radio on receive, which only draws maybe 80mA's or
so, I see the battery dropping by .10's of a V in no time. The battery is
brand new.
I've noticed that the battery only draws about 30mA's while charging at
any
voltage. I even added a switch so I can switch extra diodes between the
regulator ground so I can charge it at 14.X volts.

So my question... If it measures 13.8-14v after charging, it should be
fully
charged, right? Is there something going on since it is only drawing 10's
of
milliamps while charging? I've read that they charge at several hundred
milli's. I'd like to use my QRP rig remotely, and at the rate its
dropping,
I just don't think it will serve the purpose.

Thanks for all the help.

Jim, AB9LM