I am stumped on this curcuit

S

Scott Wiper

Guest
am stumped on this curcuit:


I am trying to make a simple battery float charger for a 12V lead acid
battery into a simple power supply. I have a test design that you can veiw
at;


http://www.travel-net.com/~swiper/test.gif


I am stumped on the following facts.

1. Can you adjust a emitter voltage to 14.40 volts from ground plus .6 volts
of the reverse protection diode. The transister will be a 2n3055 that can
handle large currents? Q1 in the test design


2. Can you also put a seconf transister to turn off a 12v relay when the
battery reahes 10.40v with a trim pot so it does deep discharge to protect
it from damage?


The plan is to keep the battery floating at 13.8 volts when this not
finished project is under A.C. power. But when it loses A.C. power it will
run on the battery until the battery dicharges to 10.40 volts indicating
that the battery is dead and will turn off until A.C. power is restored and
the battery will aauto recharge at about 3 amps until it reahes full charge
is reached and it will float down to just a few milliamps.

Any help would be appreciated.

Please direct replys to the URL; (Because my e-mail is munged because of
spammers)

http://www.travel-net.com/~swiper/email.htm


--
My Cat Tigger says every morning...
Before my morning coffee I might as well be a DOG!
Insert ' NO SPAM ' when responding or it wiill be trashed
http://www.travel-net.com/~swiper
 
"Scott Wiper" <nobody@devnull.spamcop.net> wrote in message
news:f9U%b.3110$mx4.73810@nnrp1.uunet.ca...
am stumped on this curcuit:


I am trying to make a simple battery float charger for a 12V lead acid
battery into a simple power supply. I have a test design that you can veiw
at;


http://www.travel-net.com/~swiper/test.gif


I am stumped on the following facts.

1. Can you adjust a emitter voltage to 14.40 volts from ground plus .6
volts
of the reverse protection diode. The transister will be a 2n3055 that can
handle large currents? Q1 in the test design
Click to expand...
Yes, this isn't hard. Your scheme won't be very stable, in that if there is
any fluctuations after the transformer (which there will be under load) the
transistor will wobble around with them. A better way would be to use a
Zener diode to set the voltage more precisely, rather than using a voltage
divider. (Note that in your circuit, if you assume an amp gets drawn out of
the transformer, your 2N3055 will be dissipating about 20W, so use a big
heat sink.)

Also, the 2N3055 already is a diode, so you don't need the extra one;
current won't flow in the other direction.

2. Can you also put a seconf transister to turn off a 12v relay when the
battery reahes 10.40v with a trim pot so it does deep discharge to protect
it from damage?
Click to expand...
The best way to do this kind of stuff is to use a comparator and a voltage
reference. Use a divider to get a percentage of Vbattery, and compare that
to a voltage reference. Set the comparator to go high when the voltage gets
below the reference by connecting the reference to the + input, and the
divider to the - input. Then, set up the relay to stay closed unless the
comparator goes high.

Use some positive feedback from the output to the V+ input to set
hysteresis.

The plan is to keep the battery floating at 13.8 volts when this not
finished project is under A.C. power. But when it loses A.C. power it will
run on the battery until the battery dicharges to 10.40 volts indicating
that the battery is dead and will turn off until A.C. power is restored
and
the battery will aauto recharge at about 3 amps until it reahes full
charge
is reached and it will float down to just a few milliamps.

Any help would be appreciated.

Please direct replys to the URL; (Because my e-mail is munged because of
spammers)

http://www.travel-net.com/~swiper/email.htm


--
My Cat Tigger says every morning...
Before my morning coffee I might as well be a DOG!
Insert ' NO SPAM ' when responding or it wiill be trashed
http://www.travel-net.com/~swiper
Click to expand...
Take a look at

http://home.comcast.net/~rcmonsen/misc/batbackps.GIF

There isn't any current limiting, so its not really a very good supply.
However, it sketches out how to do the battery backup charging, and also how
to do the cutout circuit.

Regards,
Bob Monsen
 
Hi Scott,

Robert already hit most of my objections.

I wouldn't use a 28V trany, the full wave rectified voltage in the
2200uF filter cap will be way too high!, ~39V, which requires a huge
heat sink on the 2N3055.

There is nothing in your circuit which would limit the current, either,
except
the transformer winding resistance.

Figure that there are times when this thing will want to deliver 5 or
more Amps. The dissipation in the 3055 will be
(ThirtySomeThingV-12V)*5A = ~100W,
which requires several square feet of heatsink...

Try to find a tranny that has a secondary voltage something like 15V.
Even with
loss in the diode bridge, it would charge the cap to a peak voltage of
~(1.414*15- 1.4) = ~18v which still leaves plenty to charge the battery
to ~13.25V

Why did I say 13.25V? That is the required "float" voltage for a flooded
cell lead acid storage battery.

You want your circuit to work like this:

Bat V Current
10V Full
11V Full
12 Full
13 Full
13.1 Full/2
13.2 Trickle
13.25 Smaller Trickle
13.3 zero
.... zero


In other words, when the battery voltage is less than 13V, you want your
charger to
behave like a constant-current source such that for all voltages below
13v, it delivers
its "full" current, say 3A. Limiting the current in this way prevents
burning up
the 3055 in case your battery is nearly fully discharged.

For battery voltages from 13 to 13.3V, you want it to taper from "full"
to zero current.
This means a high-gain control loop, which requires something more
complex than
your pot tied to the gate of the 3055. Robert has it right; this reqires
a reference
voltage source, and a feedback amplifier to drive the 3055. Since the
3055 requires
a lot of base current, it would also be useful to add a smaller NPN
ahead of the 3055 and
make a Darlington connection.

A crude way of limiting the current that your charger might deliver into
a discharged
battery is to put a "ballast" resistor in series with the primary (on
the 120V line side).
A 120V lamp can be used. Try 25 to 150W bulb to get your desired max
"full" current.
The lamp will glow dimmly; its brightness is an indicator of how much
current the
charger is putting in the battery.

MikeM, PhdEE
 
You might also want to add something to limit the current through the 3055
when a flat battery is connected?




"Scott Wiper" <nobody@devnull.spamcop.net> wrote in message
news:f9U%b.3110$mx4.73810@nnrp1.uunet.ca...
am stumped on this curcuit:


I am trying to make a simple battery float charger for a 12V lead acid
battery into a simple power supply. I have a test design that you can veiw
at;


http://www.travel-net.com/~swiper/test.gif


I am stumped on the following facts.

1. Can you adjust a emitter voltage to 14.40 volts from ground plus .6
volts
of the reverse protection diode. The transister will be a 2n3055 that can
handle large currents? Q1 in the test design


2. Can you also put a seconf transister to turn off a 12v relay when the
battery reahes 10.40v with a trim pot so it does deep discharge to protect
it from damage?


The plan is to keep the battery floating at 13.8 volts when this not
finished project is under A.C. power. But when it loses A.C. power it will
run on the battery until the battery dicharges to 10.40 volts indicating
that the battery is dead and will turn off until A.C. power is restored
and
the battery will aauto recharge at about 3 amps until it reahes full
charge
is reached and it will float down to just a few milliamps.

Any help would be appreciated.

Please direct replys to the URL; (Because my e-mail is munged because of
spammers)

http://www.travel-net.com/~swiper/email.htm


--
My Cat Tigger says every morning...
Before my morning coffee I might as well be a DOG!
Insert ' NO SPAM ' when responding or it wiill be trashed
http://www.travel-net.com/~swiper
Click to expand...
 
your problem is that a relays holding current can be low compared to
what it requires to pull in.
what you need is to add a simple OP-amp to form as schmitt trigger.
that is a Voltage comparator with a feed back to the + side to forward
bias the comparator so that is off set..
this offset can give you the desired window you need for the turn on
point and turn off point, this Op-amp will drive a 2n2222 or any
switching transistor that can handle the current of your relay as long
as you saturate the transistor.
what your doing now is most like not switching the relay when you want
due to relays wide windows and also q2 maybe getting alittle warm at
times ..
if you need more help on that idea i am sure you can get it from
some one here. there are allot of schmart guys here! :)



Scott Wiper wrote:

am stumped on this curcuit:


I am trying to make a simple battery float charger for a 12V lead acid
battery into a simple power supply. I have a test design that you can veiw
at;


http://www.travel-net.com/~swiper/test.gif


I am stumped on the following facts.

1. Can you adjust a emitter voltage to 14.40 volts from ground plus .6 volts
of the reverse protection diode. The transister will be a 2n3055 that can
handle large currents? Q1 in the test design


2. Can you also put a seconf transister to turn off a 12v relay when the
battery reahes 10.40v with a trim pot so it does deep discharge to protect
it from damage?


The plan is to keep the battery floating at 13.8 volts when this not
finished project is under A.C. power. But when it loses A.C. power it will
run on the battery until the battery dicharges to 10.40 volts indicating
that the battery is dead and will turn off until A.C. power is restored and
the battery will aauto recharge at about 3 amps until it reahes full charge
is reached and it will float down to just a few milliamps.

Any help would be appreciated.

Please direct replys to the URL; (Because my e-mail is munged because of
spammers)

http://www.travel-net.com/~swiper/email.htm


--
My Cat Tigger says every morning...
Before my morning coffee I might as well be a DOG!
Insert ' NO SPAM ' when responding or it wiill be trashed
http://www.travel-net.com/~swiper
Click to expand...
 
Now watch it.
i got kicked out of an Electronics Forum
on IRC "Undernet:Electronics" for using the
term "Trany" it seems that some
take this field so seriously that
they can't get their heads out of the clouds
,do a little R&R and throw in some slang
phrases now and then! it sure saves on typing
and getting the point across!
Now i know that some would feel insulted
getting caught communicating with such people using
short cut slang phrases. so these people (some of which
are channel Op) would rather Banned you from the rome then
let you help some one on live chat that is understanding you
very well. now if this OP thinks i am a moron then more power
to him ;)
How ever, i can tell you a little story of an individual years
ago walked in my shop and asked me if i could replace the pills in his
amplifier ?, well after thinking about it for a moment and then coming
to the conclusion that he must of been talking about the ceramic RF
power transistors i then ask him if he had a subscription. he looked at
me for a moment thinking about my question verses his and said he
changed his mind and walked out. i did get a kick out of it how ever!
:))



MikeM wrote:

Hi Scott,

Robert already hit most of my objections.

I wouldn't use a 28V trany, the full wave rectified voltage in the
2200uF filter cap will be way too high!, ~39V, which requires a huge
heat sink on the 2N3055.
Click to expand...
 
Hi Jamie,

I'm one of those "old farts" that has earned a special dispensation to
call things what I want; you know, like

Transformer = Tranny
Bush = Idiot
Cheney = Crook

MikeM


Jamie wrote:

Now watch it.
i got kicked out of an Electronics Forum
on IRC "Undernet:Electronics" for using the
term "Trany" it seems that some
Click to expand...
 
"mikem" <mikem@bogus.adr> wrote in message
news:c1vmiv$4vm$1@coward.ks.cc.utah.edu...
: Hi Jamie,
: I'm one of those "old farts" that has earned a special
dispensation to
: call things what I want; you know, like

: Transformer = Tranny
: Bush = Idiot
: Cheney = Crook

: MikeM

No one "earns the right" to be a FOOL! It comes naturally!
You sound like a Demon_Rat to me!
Learn to use the Language or be ridiculed frequently!
 
Roger Gt wrote:
"mikem" <mikem@bogus.adr> wrote in message
news:c1vmiv$4vm$1@coward.ks.cc.utah.edu...
: Hi Jamie,
: I'm one of those "old farts" that has earned a special
dispensation to
: call things what I want; you know, like

: Transformer = Tranny
: Bush = Idiot
: Cheney = Crook

: MikeM

No one "earns the right" to be a FOOL! It comes naturally!
You sound like a Demon_Rat to me!
Learn to use the Language or be ridiculed frequently!
--------------
Click to expand...
Roger the Git, above, doesn't appear able to handle the Truth!

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public
 
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