Battery charging question

[steamer]

--I've got a decent battery charger but like most of the ones
I've seen it's designed to be attached to a car battery. I've tried to
rig up something that would allow me to run it from a wall socket, but
I don't have it right. What I've done is add a bridge to the output of
a Variac, so I've got 120vDC, then I've added a big capacitor to get it
to something smoother. On a 'scope the output is anything but smooth
and the charger tends to do that annoying autoatic "trip out" at
anything even a smidge above what the battery needs; i.e. a trickle
charge is the best I can do. Can someone suggest a remedy? What I'd
really like is a ripple-free DC output from the Variac. Can this be
achieved?
--TIA,

--
"Steamboat Ed" Haas : The IRS giveth refunds and
Hacking the Trailing Edge! : Blue Cross takes them away...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

 

[Lord Garth]

"steamer" <steamer@sonic.net> wrote in message
newsty4e.13425$m31.133070@typhoon.sonic.net...

--I've got a decent battery charger but like most of the ones
I've seen it's designed to be attached to a car battery. I've tried to
rig up something that would allow me to run it from a wall socket, but
I don't have it right. What I've done is add a bridge to the output of
a Variac, so I've got 120vDC, then I've added a big capacitor to get it
to something smoother. On a 'scope the output is anything but smooth
and the charger tends to do that annoying autoatic "trip out" at
anything even a smidge above what the battery needs; i.e. a trickle
charge is the best I can do. Can someone suggest a remedy? What I'd
really like is a ripple-free DC output from the Variac. Can this be
achieved?
--TIA,

Firstly, you need 12 Volts DC, not 120VDC. Why don't you use a
transformer, your bridge rectifier and filter cap and an LM7812 thus
creating a 12VDC supply. Connect this to the charger.

 

[James Beck]

In article <pty4e.13425$m31.133070@typhoon.sonic.net>, steamer@sonic.net
says...

--I've got a decent battery charger but like most of the ones
I've seen it's designed to be attached to a car battery. I've tried to
rig up something that would allow me to run it from a wall socket, but
I don't have it right. What I've done is add a bridge to the output of
a Variac, so I've got 120vDC, then I've added a big capacitor to get it
to something smoother. On a 'scope the output is anything but smooth
and the charger tends to do that annoying autoatic "trip out" at
anything even a smidge above what the battery needs; i.e. a trickle
charge is the best I can do. Can someone suggest a remedy? What I'd
really like is a ripple-free DC output from the Variac. Can this be
achieved?
--TIA,

First off, you need to stop trying to kill yourself.
There are easier ways that won't surprise you as much as what you are
currently doing.

You need to drop all that variac crap and to one of the following :

1) Get a spare car battery and use it as a power source, charging as
needed.

2) Get one of the 13.8VDC power supplies designed to do what you are
doing. A little more information about the battery charger would be
needed to determine what kind of current you will need.

Jim

 

[John Smith]

"Lord Garth" <LGarth@Tantalus.net> wrote in message
newsTy4e.1856$3z3.1091@newssvr12.news.prodigy.com...

"steamer" <steamer@sonic.net> wrote in message
newsty4e.13425$m31.133070@typhoon.sonic.net...

--I've got a decent battery charger but like most of the ones
I've seen it's designed to be attached to a car battery. I've tried to
rig up something that would allow me to run it from a wall socket, but
I don't have it right. What I've done is add a bridge to the output of
a Variac, so I've got 120vDC, then I've added a big capacitor to get it
to something smoother. On a 'scope the output is anything but smooth
and the charger tends to do that annoying autoatic "trip out" at
anything even a smidge above what the battery needs; i.e. a trickle
charge is the best I can do. Can someone suggest a remedy? What I'd
really like is a ripple-free DC output from the Variac. Can this be
achieved?
--TIA,

Firstly, you need 12 Volts DC, not 120VDC. Why don't you use a
transformer, your bridge rectifier and filter cap and an LM7812 thus
creating a 12VDC supply. Connect this to the charger.



Not forgetting to use a power transistor to boost the current capability of

the poor old LM7812.

 

[steamer]

--OK here's the problem: I've added a bridge to convert the
output of my variac to DC and then I used a cap to smooth it a bit, but
according to the oscilloscope the output is anything but "smooth".
Anyway I'm just trying to use this to juice my battery charger, which
is designed to run off of a car battery, but it turns out that the
variac trick ain't working because the charger keeps tripping out; i.e.
if I try charging a 12v battery it takes *days* to get it up to snuff;
I talked to the guy at the local hobby shop and he said this is a
symptom of insufficient power being sent to the charger. I get better
results using a 15v wallwart.
--What I need is to be able to charge a couple of different
batteries, including motorcycle batteries and my 3 remaining 24-v packs
of NiMH cells. What would be nice is a benchtop power supply that puts
out 10 to 20 amps of smooth DC, but I haven't been able to find one.
--Any suggestions appreciated..

--
"Steamboat Ed" Haas : The IRS giveth refunds and
Hacking the Trailing Edge! : Blue Cross takes them away...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

 

[John Fields]

On Sat, 09 Apr 2005 18:10:01 GMT, steamer <steamer@sonic.net> wrote:

--OK here's the problem: I've added a bridge to convert the
output of my variac to DC and then I used a cap to smooth it a bit, but
according to the oscilloscope the output is anything but "smooth".
Anyway I'm just trying to use this to juice my battery charger, which
is designed to run off of a car battery, but it turns out that the
variac trick ain't working because the charger keeps tripping out; i.e.
if I try charging a 12v battery it takes *days* to get it up to snuff;
I talked to the guy at the local hobby shop and he said this is a
symptom of insufficient power being sent to the charger. I get better
results using a 15v wallwart.
--What I need is to be able to charge a couple of different
batteries, including motorcycle batteries and my 3 remaining 24-v packs
of NiMH cells. What would be nice is a benchtop power supply that puts
out 10 to 20 amps of smooth DC, but I haven't been able to find one.
--Any suggestions appreciated..

---
I'm kinda confused here. It sounds like you're saying that your
charger takes 12V from a car battery and then steps it up to
whatever's needed to charge other batteries.

If that's true and you're charging the car battery with rectified AC,
you shouldn't be able to see any ripple _at all_ on the output of the
bridge, regardless of whether you have a capacitor across it or not.
Matter of fact, you don't even need the cap, since the battery will
smooth the voltage at the outout of the bridge better than any cap
could.

So, if you're measuring any ripple at all, I suspect a high-resistance
connection between the VARIAC and the bridge or between the bridge and
the battery. Also, miswiring the bridge could do the same thing, and
remember that a VARIAC is an autotransformer, so if you've got the
output of the charger connected to mains neutral for some reason,
OUCH!!!



--
John Fields
Professional Circuit Designer

 

[Rich Grise]

On Sat, 09 Apr 2005 13:46:30 -0500, John Fields wrote:

On Sat, 09 Apr 2005 18:10:01 GMT, steamer <steamer@sonic.net> wrote:
--OK here's the problem: I've added a bridge to convert the
output of my variac to DC and then I used a cap to smooth it a bit, but
according to the oscilloscope the output is anything but "smooth". Anyway
I'm just trying to use this to juice my battery charger, which is
designed to run off of a car battery, but it turns out that the variac
trick ain't working because the charger keeps tripping out; i.e. if I try
---
I'm kinda confused here. It sounds like you're saying that your charger
takes 12V from a car battery and then steps it up to whatever's needed to
charge other batteries.

John, don't feel pregnant. I can't figure out what the OP is trying to
accomplish either. I'm guessing that he got his hands on a variac, and is
trying to use it as a 12VDC supply which would emulate a car 12V supply.

When he says "a cap", that could mean anything. Steamer, you need a big
bank of big honking capacitors to make a supply like this have a smooth
output.

The charger tripping out, and the output of the variac/diode not being
smooth indicates that you have nowhere near enough filter capacitance.

Do you know how to read capacitance values? For what it sounds like you're
trying to do, you need about 10,000 uF of capacitance - that's about the
size of a Foster's beer can.

Do you have a proper multimeter? Or preferably two? (or access to a
second one - I notice you got your hands on a scope.)

And, if your "charger" is designed to plug into a lighter socket, you'd
probably be better off setting your supply voltage to something like
13.5-14 volts, where they typically sit while the engine is running
and it's on float charge. I'd say a car battery that is showing a
terminal voltage of 12V is sorely in need of a proper charge.

Hope This Helps!
Rich

 

[John Fields]

On Sat, 9 Apr 2005 17:21:22 -0400, "jsmith" <juddo@ix.netcom.com>
wrote:

"steamer" <steamer@sonic.net> wrote in message
news:ZTU5e.13953$m31.136395@typhoon.sonic.net...
--OK here's the problem: I've added a bridge to convert the
output of my variac to DC and then I used a cap to smooth it a bit, but
according to the oscilloscope the output is anything but "smooth".
Anyway I'm just trying to use this to juice my battery charger, which
is designed to run off of a car battery, but it turns out that the
variac trick ain't working because the charger keeps tripping out; i.e.
if I try charging a 12v battery it takes *days* to get it up to snuff;
I talked to the guy at the local hobby shop and he said this is a
symptom of insufficient power being sent to the charger. I get better
results using a 15v wallwart.
--What I need is to be able to charge a couple of different
batteries, including motorcycle batteries and my 3 remaining 24-v packs
of NiMH cells. What would be nice is a benchtop power supply that puts
out 10 to 20 amps of smooth DC, but I haven't been able to find one.
--Any suggestions appreciated..

--
"Steamboat Ed" Haas : The IRS giveth refunds and
Hacking the Trailing Edge! : Blue Cross takes them away...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

You don't really need "smooth DC" to charge a lead acid battery. The
pulsating voltage from the rectifier is actually preferable although most
people don't realize it.

---
Hey, I'm all ears... _Why_ is it preferable?
---

Battery manufacturers are probably the least well informed in the art of
battery charging.

---
Really? I guess then, that according to you they just happened to
luck onto the chemistry and how to do it really inefficiently and you
know how to do it better. Got some examples?
---

And since most electrical engineers
are stupid and believe anything they read are were taught,

---
"are were taught"???
Yeah, just a trypo...
That is, you're not _really_ a stupid fuck, it just _seems_ that you
are, so far.
---

they continue to
revert to ancient concepts regarding battery charging just because some
moron was able to write a text book with misinformation in it.

---
If you've got some novel concepts about recharging and you want to
share them, I'm sure that there are people here who can make your
wildest dreams come true.

But...

In order to prove that you know what you're talking about, you're
going to have to show how you can charge a sealed lead-acid battery to
capacity with less loss than anyone else can and still stay within the
battery manufacturer's charging limits.

Or...

Show how you can, with your methodology, extend the life of the
battery beyond the battery maufacturer's warranty.
---

way, a fully charged lead acid battery in prime condition is fully charged
when it reaches 12.6 to 12.8 volts. Anything above that is "surface charge"
and is worthless. Once a battery is loaded with "load tester" the voltage
drops immediately to about 11.5 volts and remains there if the battery has
not suffered too much from sulfation or grid corrosion. OK you dorks and
PE's who don't agree, fire away!

---
You, obviously, are a neophyte who has wandered far from her area of
expertise. What you need to be concerned with is if two potatoes (if
you have aspirations which you think will lead you into management)
will serve about three customers.

"D'ya want fries with that" is the catch phrase and, then, if the
answer is affirmative, and you follow with "Do ya wanna supersize
that?", you've done your job.

Congratulations...

--
John Fields
Professional Circuit Designer

 

[jsmith]

"John Fields" <jfields@austininstruments.com> wrote in message
news:71lg511o41uurpv0k8cnhemb19neojpbq5@4ax.com...

On Sat, 9 Apr 2005 17:21:22 -0400, "jsmith" <juddo@ix.netcom.com
wrote:


"steamer" <steamer@sonic.net> wrote in message
news:ZTU5e.13953$m31.136395@typhoon.sonic.net...
--OK here's the problem: I've added a bridge to convert the
output of my variac to DC and then I used a cap to smooth it a bit, but
according to the oscilloscope the output is anything but "smooth".
Anyway I'm just trying to use this to juice my battery charger, which
is designed to run off of a car battery, but it turns out that the
variac trick ain't working because the charger keeps tripping out; i.e.
if I try charging a 12v battery it takes *days* to get it up to snuff;
I talked to the guy at the local hobby shop and he said this is a
symptom of insufficient power being sent to the charger. I get better
results using a 15v wallwart.
--What I need is to be able to charge a couple of different
batteries, including motorcycle batteries and my 3 remaining 24-v packs
of NiMH cells. What would be nice is a benchtop power supply that puts
out 10 to 20 amps of smooth DC, but I haven't been able to find one.
--Any suggestions appreciated..

--
"Steamboat Ed" Haas : The IRS giveth refunds and
Hacking the Trailing Edge! : Blue Cross takes them away...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

You don't really need "smooth DC" to charge a lead acid battery. The
pulsating voltage from the rectifier is actually preferable although most
people don't realize it.

---
Hey, I'm all ears... _Why_ is it preferable?
---

Battery manufacturers are probably the least well informed in the art of
battery charging.

---
Really? I guess then, that according to you they just happened to
luck onto the chemistry and how to do it really inefficiently and you
know how to do it better. Got some examples?
---

And since most electrical engineers
are stupid and believe anything they read are were taught,

---
"are were taught"???
Yeah, just a trypo...
That is, you're not _really_ a stupid fuck, it just _seems_ that you
are, so far.
---

they continue to
revert to ancient concepts regarding battery charging just because some
moron was able to write a text book with misinformation in it.

---
If you've got some novel concepts about recharging and you want to
share them, I'm sure that there are people here who can make your
wildest dreams come true.

But...

In order to prove that you know what you're talking about, you're
going to have to show how you can charge a sealed lead-acid battery to
capacity with less loss than anyone else can and still stay within the
battery manufacturer's charging limits.

Or...

Show how you can, with your methodology, extend the life of the
battery beyond the battery maufacturer's warranty.
---

way, a fully charged lead acid battery in prime condition is fully
charged
when it reaches 12.6 to 12.8 volts. Anything above that is "surface
charge"
and is worthless. Once a battery is loaded with "load tester" the voltage
drops immediately to about 11.5 volts and remains there if the battery
has
not suffered too much from sulfation or grid corrosion. OK you dorks and
PE's who don't agree, fire away!

---
You, obviously, are a neophyte who has wandered far from her area of
expertise. What you need to be concerned with is if two potatoes (if
you have aspirations which you think will lead you into management)
will serve about three customers.

"D'ya want fries with that" is the catch phrase and, then, if the
answer is affirmative, and you follow with "Do ya wanna supersize
that?", you've done your job.

Congratulations...

--
John Fields
Professional Circuit Designer

And do any of your "professional" circuit designs really work?

 

[John Fields]

On Sat, 9 Apr 2005 22:24:59 -0400, "jsmith" <juddo@ix.netcom.com>
wrote:

And do any of your "professional" circuit designs really work?

---
In an effort try to see where you're coming from, I just went back and
took a look at your posting history and guess what? The kindest thing
I can say is that you're a fucking idiot.

From that first "Ohm's Law" abortion to your last pitiful attempt at
an insult, above, about the only thing you've done right is learned to
bottom post. So, there may be hope for you yet. We'll see...

--
John Fields
Professional Circuit Designer

 

[steamer]

Rich Grise <richgrise@example.net> wrote:
: John, don't feel pregnant. I can't figure out what the OP is trying to
: accomplish either. I'm guessing that he got his hands on a variac, and is
: trying to use it as a 12VDC supply which would emulate a car 12V supply.
--Yes, that's it.

: And, if your "charger" is designed to plug into a lighter socket, you'd
: probably be better off setting your supply voltage to something like
: 13.5-14 volts, where they typically sit while the engine is running
--Yes, I've done this.

--
"Steamboat Ed" Haas : The IRS giveth refunds and
Hacking the Trailing Edge! : Blue Cross takes them away...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

 

[steamer]

--Meanwhile back at the ranch *I'm* still looking for better
ways to do what I'm trying to do..

--
"Steamboat Ed" Haas : The IRS giveth refunds and
Hacking the Trailing Edge! : Blue Cross takes them away...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

 

[jsmith]

A TOP POST. . .
Now now now, Johnny boy don't get yourself in a dither.


"John Fields" <jfields@austininstruments.com> wrote in message
news:8d0i51d1prjf006n2madusu6ibgov13cd4@4ax.com...

On Sat, 9 Apr 2005 22:24:59 -0400, "jsmith" <juddo@ix.netcom.com
wrote:


And do any of your "professional" circuit designs really work?

---
In an effort try to see where you're coming from, I just went back and
took a look at your posting history and guess what? The kindest thing
I can say is that you're a fucking idiot.

From that first "Ohm's Law" abortion to your last pitiful attempt at
an insult, above, about the only thing you've done right is learned to
bottom post. So, there may be hope for you yet. We'll see...

--
John Fields
Professional Circuit Designer

 

[Terry Pinnell]

steamer <steamer@sonic.net> wrote:

--Meanwhile back at the ranch *I'm* still looking for better
ways to do what I'm trying to do..

IMO, that's largely because your requirement was vaguely specified in
your original post. It wasn't until 4 days later that you became more
specific, with:
"What I need is to be able to charge a couple of different batteries,
including motorcycle batteries and my 3 remaining 24-v packs of NiMH
cells. What would be nice is a benchtop power supply that puts out 10
to 20 amps of smooth DC, but I haven't been able to find one."

Doesn't that imply that, smoothed or pulsed, a 12V ('120V'!) output
from your Variac will be inadequate? I'm guessing that you really want
a heavy duty DC supply capable of delivering about 26V, preferably
switchable to say 15V for charging your motorcycle batteries if they
are 12V (you still haven't specified that).

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[steamer]

Terry Pinnell <terrypinDELETE@thesedial.pipex.com> wrote:
: IMO, that's largely because your requirement was vaguely specified in
: your original post. It wasn't until 4 days later that you became more
--Yeah, well, I'm still workin' on the "basics"...

: Doesn't that imply that, smoothed or pulsed, a 12V ('120V'!) output
: from your Variac will be inadequate? I'm guessing that you really want
: a heavy duty DC supply capable of delivering about 26V, preferably
: switchable to say 15V for charging your motorcycle batteries if they
: are 12V (you still haven't specified that).
--Yes. I've been turning the dial on the Variac until the
output, as measured on a voltmeter, has been around 14 to 15v, then
I've hooked that up to the battery I'm trying to charge. I've *never*
cranked the dial past this, for fear of damaging the battery, the
house, myself, etc.


--
"Steamboat Ed" Haas : I still want to travel in
Hacking the Trailing Edge! : zeppelins and flying cars...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

 

[John Fields]

On Mon, 11 Apr 2005 15:20:15 GMT, steamer <steamer@sonic.net> wrote:

Terry Pinnell <terrypinDELETE@thesedial.pipex.com> wrote:
: IMO, that's largely because your requirement was vaguely specified in
: your original post. It wasn't until 4 days later that you became more
--Yeah, well, I'm still workin' on the "basics"...

: Doesn't that imply that, smoothed or pulsed, a 12V ('120V'!) output
: from your Variac will be inadequate? I'm guessing that you really want
: a heavy duty DC supply capable of delivering about 26V, preferably
: switchable to say 15V for charging your motorcycle batteries if they
: are 12V (you still haven't specified that).
--Yes. I've been turning the dial on the Variac until the
output, as measured on a voltmeter, has been around 14 to 15v, then
I've hooked that up to the battery I'm trying to charge. I've *never*
cranked the dial past this, for fear of damaging the battery, the
house, myself, etc.

There's nothing wrong with that method, but you neeed to monitor a
couple of things; the voltage across the battery when it's charging
and the current going into it while it's charging, like this:


VARIAC FWB
+--------+ +-----+
ACHOT>---O--|C|<--O----|~ +|---[AMMETER]--+------< <---+
| |O| | | | | |
| |I| | | | | |
| |L| | | | [VOLTMETER] [BATTERY]
| | | | | | |
ACNEUT>--O---+----O----|~ -|--------------+------< <---+
+--------+ +-----+


If you don't have a couple of meters which you can set up to take the
readings simultaneously, and since you have a VARIAC and can use it to
adjust the current to whatever you want, you can do the readings
sequentially (without having to tear down and rebuild anything) by
substituting a resistor for the ammeter (actually, I prefer this
method) and using the voltmeter to measure the voltage drop across it
to determine the current going through it, (and into the battery) like
this, :


VARIAC FWB
+--------+ +-----+
ACHOT>---O--|C|<--O----|~ +|--+--------------------< <---+
| |O| | | | | |
| |I| | | |V O<--O----------+ |+
| |L| | | | |+ [BATTERY]
| | | | |I O [VOLTMETER] |
| | | | | | | |
ACNEUT>--O---+----O----|~ -|--+--[RESISTOR]--+-----< <---+
+--------+ +-----+


To size the resistor, decide what value of current you want the
voltage indicated by the meter to represent, and the use Ohm's law.

Let's say that you want the meter to read 1 volt when there's one amp
flowing through the resistor. Then you would write:

E 1V
R = --- = ---- = 1 ohm
I 1A


You need to be concerned about the wattage, because the higher the
current the hotter the resistor will get.

For typical motorcycle batteries I think the initial xcharging current
is in the range of 2 to 3 amps, so if you were to use a 1 ohm resistor
you'd have:


P = I˛R + (3A)˛ * 1R = 9 watts


being dissipated by the resistor when the current was first set at 3
amps. The current would decrease as charging progressed, but it would
be a good idea to have a hefty resistor in there. A really cheap way
to get 20 watts worth of resistance would be to get four 1 ohm 5 watt
"cement" resistors and wire then like this:



+-----+---->A
| |
[1R] [1R]
| |
+ +
| |
[1R] [1R]
| |
+-----+---->B

or like this:

+-----+---->A
| |
[1R] [1R]
| |
+-----+
| |
[1R] [1R]
| |
+-----+---->B

In either case, the resistance from A to B will be one ohm, and either
array will dissipate 20 W if the resistors are mounted properly. For
the cheap "cement" resistors, I'm pretty sure just letting them
radiate into ambient air will be fine.

Since your NiMH battery packs may want to be charged from a current
source, the sizing of the resistor may go differently from that for
lead acid. What can you tell us about the battery packs?
Also, what can you tell us about your VARIAC, in terms of how much
current it's rated to put out?


Also notice that one of the mains inputs to the VARIAC is labelled
"ACNEUT". That means "AC NEUTRAL" and you need to be ABSOLUTELY,
POSITIVELY, SURE that the rig is connected to the mains that way. If
you don't, you could be killed if you came in contact with what you
though was "ground" while you were grounded.

--
John Fields
Professional Circuit Designer

 

[John Fields]

On Mon, 11 Apr 2005 12:12:18 -0500, John Fields
<jfields@austininstruments.com> wrote:

Also notice that one of the mains inputs to the VARIAC is labelled
"ACNEUT". That means "AC NEUTRAL" and you need to be ABSOLUTELY,
POSITIVELY, SURE that the rig is connected to the mains that way. If
you don't, you could be ABSOLUTELY, POSITIVELY killed if you came in contact with what you
though was "ground" on the rig and you were inadvertently grounded.

---
P.S. After making sure that mains NEUTRAL is really NEUTRAL, and
before you plug in the VARIAC, you need to make sure that the rig is
connected to the VARIAC _EXACTLY_ as shown, that the VARIAC's output
is set to 0V, that the Variac's ON-OFF switch is set to OFF, and that
the switch on the rig is set to measure current. ( That it's in the
"I" position). Once that's done, connect the battery to the rig,
plug in the VARIAC, and if there's no smoke and the lights are still
on, place the VARIAC's ON-OFF switch to the ON position. If there's
still no smoke and the lights are still on, SLOWLY rotate the VARIAC's
output control while watching the voltmeter which is displaying
current. If it starts to rise, then things are probably working!
When you get to whatever the initial charging current is, the VARIAC's
knob should be somewhere between 10 and 15 volts. Now, change the
range on the voltmeter to read the battery voltage and flick the
switch on the rig to the "V" position. You should be reading
somewhere between 10 and 13V if the battery was fully discharged when
you put it on the rig. If it is, then just monitor the battery voltage
(checking current occasionally) until the battery's fully charged and
you're done.

There's a little more detail to it than that, depending on whether you
want to let the batteries float after they've been charged, but the
best place to get that information is from the battery manufacturer's
website, since they all use slightly different chemistries and their
terminal voltages and currents are all a little different.

Once you've finished charging the battery, turn the VARIACS's knob
down to 0V, turn it OFF, unplug it, and then (and only then)
disconnect the battery from the rig.

Good luck.


--
John Fields
Professional Circuit Designer

 

[steamer]

--Thanks very much; that's going to help me a lot!

--
"Steamboat Ed" Haas : I still want to travel in
Hacking the Trailing Edge! : zeppelins and flying cars...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

 

[jsmith]

"steamer" <steamer@sonic.net> wrote in message
news:ZTU5e.13953$m31.136395@typhoon.sonic.net...

--OK here's the problem: I've added a bridge to convert the
output of my variac to DC and then I used a cap to smooth it a bit, but
according to the oscilloscope the output is anything but "smooth".
Anyway I'm just trying to use this to juice my battery charger, which
is designed to run off of a car battery, but it turns out that the
variac trick ain't working because the charger keeps tripping out; i.e.
if I try charging a 12v battery it takes *days* to get it up to snuff;
I talked to the guy at the local hobby shop and he said this is a
symptom of insufficient power being sent to the charger. I get better
results using a 15v wallwart.
--What I need is to be able to charge a couple of different
batteries, including motorcycle batteries and my 3 remaining 24-v packs
of NiMH cells. What would be nice is a benchtop power supply that puts
out 10 to 20 amps of smooth DC, but I haven't been able to find one.
--Any suggestions appreciated..

--
"Steamboat Ed" Haas : The IRS giveth refunds and
Hacking the Trailing Edge! : Blue Cross takes them away...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

You don't really need "smooth DC" to charge a lead acid battery. The
pulsating voltage from the rectifier is actually preferable although most
people don't realize it. Battery manufacturers are probably the least well
informed in the art of battery charging. And since most electrical engineers
are stupid and believe anything they read are were taught, they continue to
revert to ancient concepts regarding battery charging just because some
moron was able to write a text book with misinformation in it. And by the
way, a fully charged lead acid battery in prime condition is fully charged
when it reaches 12.6 to 12.8 volts. Anything above that is "surface charge"
and is worthless. Once a battery is loaded with "load tester" the voltage
drops immediately to about 11.5 volts and remains there if the battery has
not suffered too much from sulfation or grid corrosion. OK you dorks and
PE's who don't agree, fire away!