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"Fixing" crap Harbor Freight battery charger

R

Roger Blake

Jan 1, 1970
0
Given the less-than-steller reviews and HF's reputation for electronics,
I should not have bought this thing, a 12 Volt 6 or 2 amp (switch
selectable) charger for car batteries. The problem is that instead of
providing the tapering charge and switch to trickle it is supposedly
designed for, this "charger" discharges and kills batteries instead. (In
contrast, I have a 4 amp Schauer charger that is about 40 years old
which still works just fine.)

Instead of throwing out the HF unit, I was thinking that it has a perfectly
usable case, transformer, ammeter, and wires with alligator clips. Just the
crapulent Chinese electronics are bad so I'd like to trash that stuff
and turn this into an "old school" type charger like my Schauer.

The transformer secondary is center tapped and reads about 28 volts AC
across the ends, 14 volts on each leg from the center. The original
electronics are on a small board with 7 transistors, 2 SCRs, a couple
of diodes, and numerous resistors. (That's a lot of stuff just to
kill batteries!) Searching online I'm finding a bewildering array of
home-brew battery charger circuits, everything from simply using a bridge
rectifier on the transformer secondary to more complex circuits to taper
the charge and either switch off or go to trickle when the battery is
fully charged.

The behaviour of my old Schauer is to gradually reduces current until
the battery is fully charged, where it will stay at a low level and not
hurt the battery if left on overnight or even for a few days. I have
not opened it up yet to see what's inside, but being an early 1970s unit
I'd be surprised if there is much aside from a transformer and rectifier.

Anyone have a simple circuit handy that works well for this? I've seen
a few plans online that just say to use a bridge rectifier of suitable
capacity, but I want to be reasonably sure that this thing won't kill
any more batteries.
 
K

Kalyan Ram

Jan 1, 1970
0
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C

Cydrome Leader

Jan 1, 1970
0
Roger Blake said:
Given the less-than-steller reviews and HF's reputation for electronics,
I should not have bought this thing, a 12 Volt 6 or 2 amp (switch
selectable) charger for car batteries. The problem is that instead of
providing the tapering charge and switch to trickle it is supposedly
designed for, this "charger" discharges and kills batteries instead. (In
contrast, I have a 4 amp Schauer charger that is about 40 years old
which still works just fine.)
nice.

Instead of throwing out the HF unit, I was thinking that it has a perfectly
usable case, transformer, ammeter, and wires with alligator clips. Just the
crapulent Chinese electronics are bad so I'd like to trash that stuff
and turn this into an "old school" type charger like my Schauer.

The transformer secondary is center tapped and reads about 28 volts AC
across the ends, 14 volts on each leg from the center. The original
electronics are on a small board with 7 transistors, 2 SCRs, a couple
of diodes, and numerous resistors. (That's a lot of stuff just to
kill batteries!) Searching online I'm finding a bewildering array of
home-brew battery charger circuits, everything from simply using a bridge
rectifier on the transformer secondary to more complex circuits to taper
the charge and either switch off or go to trickle when the battery is
fully charged.

It might be easier to fix the thing, unless you want a project.

I can tell from here that it's probably using some sort of half-bridge
setup. Apparently two extra diodes cost more than a smaller more efficient
transformer. Heck, it's unlikely to have the correct sized transformer to
start with, they just removed two diodes to save whatever it costs to
keep the school kids/prisoners fed.

It might be good to mod the thing to crowbar if it overshoots 13.8 or 14.1
or whatever you want your batteries charged to. There should be some sort
of rectifier to prevent the battery from discharging back into the
charger, check on that.

I can't say they're good or bad, but I've made NiMh chargers that were
just constant current sources that maxed out at the float voltage. The
charging current tapers off as the thing starts to choke itself out, but
it does work. The only reason I even had the constant current section was
to prevent the transformer from burning out if you threw a heavily
discharged cell into it. Old NiMh batteries really didnt like fast
charging either.
The behaviour of my old Schauer is to gradually reduces current until
the battery is fully charged, where it will stay at a low level and not
hurt the battery if left on overnight or even for a few days. I have
not opened it up yet to see what's inside, but being an early 1970s unit
I'd be surprised if there is much aside from a transformer and rectifier.

Anyone have a simple circuit handy that works well for this? I've seen
a few plans online that just say to use a bridge rectifier of suitable
capacity, but I want to be reasonably sure that this thing won't kill
any more batteries.

How large are the batteries you're charging? A brute force charger may be
ok for smaller batteries, but if you're trying to charge some 2 ton off
the grid battery locker, you're going to have to smell that transformer
burn up.

What parts are on that board you have now? Can you post a photo?
 
R

Roger Blake

Jan 1, 1970
0
How large are the batteries you're charging?

12 volt lead-acid car batteries, I should have mentioned that if I didn't!
What parts are on that board you have now? Can you post a photo?

It does look like they cheaped out on a couple of rectifiers, hence
the 28V center-tapped transformer. (The transformer looks surprisingly
hefty, though.) But then again there are 2 SCRs on heatsinks and it's
surprising how many discreet transistors this thing has, enough to make
a decent transistor radio, but who knows how many are real. A bunch
of what are probably phony 1% resistors completes the components. No
ICs. No capacitors. The center tap of the transformer feeds into the
center section of the board through a circuit breaker. Each side of the
secondary then feeds into its own symmetrical section of the board.

I tried taking a picture but my camera does lousy closeups, will have
to borrow one...
 
C

Cydrome Leader

Jan 1, 1970
0
Roger Blake said:
12 volt lead-acid car batteries, I should have mentioned that if I didn't!


It does look like they cheaped out on a couple of rectifiers, hence
the 28V center-tapped transformer. (The transformer looks surprisingly
hefty, though.) But then again there are 2 SCRs on heatsinks and it's
surprising how many discreet transistors this thing has, enough to make
a decent transistor radio, but who knows how many are real. A bunch
of what are probably phony 1% resistors completes the components. No
ICs. No capacitors. The center tap of the transformer feeds into the
center section of the board through a circuit breaker. Each side of the
secondary then feeds into its own symmetrical section of the board.

I tried taking a picture but my camera does lousy closeups, will have
to borrow one...

Are these "SCRs" really SCRs or just large power transistors? Did the
thing sing or make horrible PWM sounds when it worked?

I have seen real SCRs in telecom rectifiers (giant battery chargers/power
supplies).
 
R

Roger Blake

Jan 1, 1970
0
Are these "SCRs" really SCRs or just large power transistors? Did the
thing sing or make horrible PWM sounds when it worked?

The board is silkscreened "SCR1" and "SCR2" in those locations - the
components themselves are black plastic about 3/8" square and 1/8" thick,
labeled "BT151 25J TRANSUN", metal tab at top for heat sink attachment,
3 leads on the bottom.
 
R

Roger Blake

Jan 1, 1970
0
Why would anyone use phony 1% resistors when they are dirt cheap
these days?

The Chinese are infamous for cheating on specifications. Whether these
are actually phony or not would obviously require measuring them with an
accurate meter.
Cheaped out on rectifiers? They likely paid more for that CT
transformer that they would save on two 30 cent diodes. The fact that
there are no ICs is significant in what way?

Some of the choices in the design do seem odd given that lowest possible
manufacturing cost was probably the primary constraint.

As far as the lack of ICs I was just describing the contents of the
board, though it does seem unusual these days to see a a circuit based on
discreet transistors.
 
C

Cydrome Leader

Jan 1, 1970
0
Jeff Liebermann said:
Incidentally:
<http://802.11junk.com/jeffl/pics/drivel/slides/dead-battery-chargers.html>
All of them died float charging standby and backup batteries on
mountain top radio sites. Mostly, the electronics on the PCB's (with
the numbers ground off) were what failed. I managed to fix one or two
by guessing the regulator IC that was used, but they again failed in
short order. The chargers were replaced by various Statpower/Xantrex
chargers, which have been working quite nicely for the last 7 years.

were these hunk-o-junk units plugged into those hardwired site wide surge
surpessors?
 
C

Cydrome Leader

Jan 1, 1970
0
dave said:
Physicists tell me that SCRs will work as transistors.

didn't mean to be a jerk with the last reply.

so I did about 3 seconds of searching and here's how that charger probably
works.

something is measuring the voltage of rectified DC and turning the SCRs on
and off when the input voltage is just right for charging the battery.

It's basically 120Hz PWM. They may even be using the negative or postive
voltage from the other leg of the center tapped transformer to shut off
the SCR on the opposing side. Cheap and simple. Sadly, I don't recall if
you just short the gate of a SCR to something to shut it off, or if it
needs a reverse voltage of some sort to really make "sure".

Failure modes as imagined by me are

1) SCR shorting and outputting full voltage into your now dead battery.
Seems not too likely- SCRs are pretty damn tough.

2) the gate circuitry getting botched up and the SCR NOT being shut off
before the voltage hits the overvoltaged and killed battery zone. SCRs
latch so if that's the case, your battery is basically being murdered 120
times as second because the gate shutoff circuity is failing 120 times a
second.

The of course, maybe the thing is a GTO, but the idea is the same either
way.
 
M

Michael Black

Jan 1, 1970
0
didn't mean to be a jerk with the last reply.

so I did about 3 seconds of searching and here's how that charger probably
works.

something is measuring the voltage of rectified DC and turning the SCRs on
and off when the input voltage is just right for charging the battery.

It's basically 120Hz PWM. They may even be using the negative or postive
voltage from the other leg of the center tapped transformer to shut off
the SCR on the opposing side. Cheap and simple. Sadly, I don't recall if
you just short the gate of a SCR to something to shut it off, or if it
needs a reverse voltage of some sort to really make "sure".

Failure modes as imagined by me are

1) SCR shorting and outputting full voltage into your now dead battery.
Seems not too likely- SCRs are pretty damn tough.

2) the gate circuitry getting botched up and the SCR NOT being shut off
before the voltage hits the overvoltaged and killed battery zone. SCRs
latch so if that's the case, your battery is basically being murdered 120
times as second because the gate shutoff circuity is failing 120 times a
second.

The of course, maybe the thing is a GTO, but the idea is the same either
way.
You saw that sort of thing in the early days of SCRs. There seemed to be
much more use of SCRs (or at least much more application for them) when
they came out, and then that faded. Not sure if there were problems, or
other things came along or what.

Michael
 
C

Cydrome Leader

Jan 1, 1970
0
Jeff Liebermann said:
Sorta. All the sites were on some form of backup or emergency power,
such as an autostart generator. The switching transitions are
anything but graceful, with no provisions for zero voltage switching.
The resultant glitches, spikes, surges, and over-voltage hiccups could
easily have blown up the chargers. However, all the sites also have
big MOV surge protectors and LC line filters just after the circuit
breakers, which does a fine job of protecting against glitches and
such. There was plenty of other equipment in the buildings, including
commodity networking hardware, scanners, computahs, weather station,
etc all of which are somewhat sensitive to glitches. Nothing failed
except the battery chargers.

It's pretty sad lead acide battery chargers were the most sensitive
devices out of that mix of hardware.

Any interesting lightining strike stories?
 
C

Cydrome Leader

Jan 1, 1970
0
Jeff Liebermann said:
I still don't know exactly what killed all the chargers. I would
expect such high power devices to be built rather rugged, but
apparently, that's not the case.

Very odd. Some sort of fatal design flaw with the regulation parts is what
it sounded like.
Nope. I live on the left coast, where we don't have much lightning.
I've had some nearby hits blow up various antennas, radios, and
assorted boxes, but nothing spectacular. We've eliminated most of
those type of problems with careful grounding, lighting arrestors, and
ritual sacrifice to the lightning god. Lighting is one problem that I
don't have to deal with (much).

The only interesting horror story I've heard was from another service
company, where copper thieves axed the big ground wires from the tower
legs to the ground rods. When lightning hit the tower, it went into
the building instead of directly into the ground. I didn't see the
carnage, but was told it was huge. I'm considering adding a ground
wire integrity test to the SCADA alarm panel.

I just gave this a few minutes of though and drew a blank. How do you
directly test to make sure nobody stole your ground?

The only thing I could come up with was run a thin wire along your ground
system in a loop and assume scrappers will steal that too. If that guard
wire of whatever you'd call it opens or goes missing you've triggered an
alarm?
 
L

Leif Neland

Jan 1, 1970
0
Cydrome Leader formulerede spørgsmålet:
I just gave this a few minutes of though and drew a blank. How do you
directly test to make sure nobody stole your ground?

The only thing I could come up with was run a thin wire along your ground
system in a loop and assume scrappers will steal that too. If that guard
wire of whatever you'd call it opens or goes missing you've triggered an
alarm?

Measure the resistance between the tower and a separate ground
connection.

Leif
 
C

Cydrome Leader

Jan 1, 1970
0
Leif Neland said:
Cydrome Leader formulerede sp?rgsm?let:


Measure the resistance between the tower and a separate ground
connection.

Leif

That still sounds tricky as there may be multiple grounds all connected to
your ground busbar. I just took a peek at the telecom room on this floor
and the plate on the wall had nearly a dozen connections, of which 3
seemed to be going back to the electrical riser for the floor. You could
remove most of those connections and everything would still be grounded,
enough that nobody dies from a frayed power cord, but just not able to
take a lightning strike or some major electrical contractor screw up.

I'd love to see the AT&T manual not on how to sweep floors, but on
grounding everything.
 
S

Shaun

Jan 1, 1970
0
"Roger Blake" wrote in message

Given the less-than-steller reviews and HF's reputation for electronics,
I should not have bought this thing, a 12 Volt 6 or 2 amp (switch
selectable) charger for car batteries. The problem is that instead of
providing the tapering charge and switch to trickle it is supposedly
designed for, this "charger" discharges and kills batteries instead. (In
contrast, I have a 4 amp Schauer charger that is about 40 years old
which still works just fine.)

Instead of throwing out the HF unit, I was thinking that it has a perfectly
usable case, transformer, ammeter, and wires with alligator clips. Just the
crapulent Chinese electronics are bad so I'd like to trash that stuff
and turn this into an "old school" type charger like my Schauer.

The transformer secondary is center tapped and reads about 28 volts AC
across the ends, 14 volts on each leg from the center. The original
electronics are on a small board with 7 transistors, 2 SCRs, a couple
of diodes, and numerous resistors. (That's a lot of stuff just to
kill batteries!) Searching online I'm finding a bewildering array of
home-brew battery charger circuits, everything from simply using a bridge
rectifier on the transformer secondary to more complex circuits to taper
the charge and either switch off or go to trickle when the battery is
fully charged.

The behaviour of my old Schauer is to gradually reduces current until
the battery is fully charged, where it will stay at a low level and not
hurt the battery if left on overnight or even for a few days. I have
not opened it up yet to see what's inside, but being an early 1970s unit
I'd be surprised if there is much aside from a transformer and rectifier.

Anyone have a simple circuit handy that works well for this? I've seen
a few plans online that just say to use a bridge rectifier of suitable
capacity, but I want to be reasonably sure that this thing won't kill
any more batteries.

--
Roger Blake
Change "invalid" to "com" for email.
Google Groups killfiled.

Harbour Frieght products are crap! You get what you pay for! Why don't you
just go out a buy a new one from a reputable store. The rest of the parts
in your dead battery charger are probably crap too.
 
W

William Sommerwerck

Jan 1, 1970
0
"Michael A. Terrell" wrote in message

WTH is 'Harbour Frieght'? Another of your drug induced nightmares?

Harbor Freight is a chain selling cheap tools. Some of their stuff is good,
and/or good value for the money.
 
S

Shaun

Jan 1, 1970
0
"Michael A. Terrell" wrote in message

Harbour Frieght products are crap! You get what you pay for! Why don't
you
just go out a buy a new one from a reputable store. The rest of the parts
in your dead battery charger are probably crap too.


WTH is 'Harbour Frieght'? Another of your drug induced nightmares?


If your so fucking stupid that you can't figure that out, you shouldn't be
posting. "Harbour" is the Canadian way of spelling that word, and Frieght
is just a typo, nobody is perfect, we all make mistakes - look at your
parents; they had you ASSHOLE. What do you get out of critiquing someone
else's spelling? Does it make you feel superior to other people, do you
need to do that for your low self esteem. You are a pathetic excuse for a
Human being!
 
S

Shaun

Jan 1, 1970
0
"Michael A. Terrell" wrote in message

"Michael A. Terrell" wrote in message


WTH is 'Harbour Frieght'? Another of your drug induced nightmares?

If your so fucking stupid that you can't figure that out, you shouldn't be
posting. "Harbour" is the Canadian way of spelling that word, and Frieght
is just a typo, nobody is perfect, we all make mistakes - look at your
parents; they had you ASSHOLE. What do you get out of critiquing someone
else's spelling? Does it make you feel superior to other people, do you
need to do that for your low self esteem. You are a pathetic excuse for a
Human being!


Your the one who is brain fucked. There is no US company named
Harbour Frieght, so go **** yourself.

Splitting hairs proves nothing. I think the content and general idea of a
message to be important unlike some anal retentive prick like you that looks
for problems.
 
R

Roger Blake

Jan 1, 1970
0
Just as a followup here, for the moment I've solved my need for a
second automotive battery charger by picking up another 35-40
year old charger at a flea market. It works great! There's something
to be said for simplicity.

I'll play around with the Harbor Freight unit when I have a chance,
there are a lot of possible circuits out there to play around with.
 
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