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Diode reverse protection and current limiting.

I

Ignoramus7040

Jan 1, 1970
0
Thanks to many people regarding your earlier advise on modifying my
TIG welder. The sequel to that saga is that the welder works and I use
it quite often.

Now I have a smaller modification to ponder.

After several unpleasant experiences with battery chargers (which did
not work) I want to try something different. My typical use of a
battery charger is to use it to replenish some battery that does a lot
of engine cranking.

I have a power supply that I am thinking should become my battery
charger. It is a PP-1104B/G. If you google for PP-1104C/G you will
find a description of a very similar power supply. It has a dual
range: 13-19 volts at up to 100 amps, and 26-39 volts up to 50
amps. It is a constant voltage power supply with no current limiting
other than built in breakers. I added a few not very relevalt things
to it (like handles for easier handling), but it has a few electrical
quirks that I would like corrected.

The first is that when it is turned off, it drains the battery (ie the
current flows "backwards" as opposed to current flow when charging)
and quickly consumes a lot of amps. It appears that adding a diode
with a small heatsink should take care of the issue.

My calculation is that at 100A, the diode with voltage drop of 0.7
volts would produce 70 watts, which is trivial to dissipate. I have a
number of suitable diodes and heatsinks. So, unless someone gives some
great reason why adding a reverse protection diode is a bad idea, I
will do it.

My second question is whether there is an easy way to add a current
limiting feature to this device, that is, make current limited to a
value set by a potentiometer. That would make it valuable for, say,
electroplating.

I read about current limiting today. The ones I read about were based
on the principle that there is a transistor in series with the load,
that basically acts as a variable resistor to limit current. That's
wasteful, but I can live with it, but perhaps there are more clever
schematics of a current limiting add-on. There is no space inside that
power supply to add anything, so any such circuitry would be in an
external device.

Any suggestions on more inteligent current limiting add-ons will be
gratefully appreciated.

i
 
H

Homer J Simpson

Jan 1, 1970
0
I have a power supply that I am thinking should become my battery
charger. It is a PP-1104B/G. If you google for PP-1104C/G you will
find a description of a very similar power supply. It has a dual
range: 13-19 volts at up to 100 amps, and 26-39 volts up to 50
amps.

How is the voltage varied? Why don't the rectifiers prevent back current
flow?
 
I

Ignoramus7040

Jan 1, 1970
0
How is the voltage varied? Why don't the rectifiers prevent back current
flow?

It is varied by turning a beefy knob that probably switches
transformer windings.

Second question is a good one, my guess is that there are capacitors
and a big safety discharge resistor that play a role.

i
 
H

Homer J Simpson

Jan 1, 1970
0
It is varied by turning a beefy knob that probably switches
transformer windings.

Second question is a good one, my guess is that there are capacitors
and a big safety discharge resistor that play a role.

From what I can make of the manual, yes, voltage taps. However there is a
type of magnetic amplifier which helps keep the voltage constant under load.
This is a fairly complicated gadget. I'd be inclined to add an external
'box' to do what you want rather than tinker with it. A heat sinked diode
should work fine re back flow. For constant current, maybe a big
transistor - depends on the max current you want. You could use SCR's and a
commutation circuit for more amps, but I'd look for an old GE SCR manual if
you want to do that. Or. google for (scr commutating dc).

http://www.omega.com/temperature/Z/pdf/z124-127.pdf (page 2) shows a typical
circuit.
 
I

Ignoramus7040

Jan 1, 1970
0
From what I can make of the manual, yes, voltage taps. However there is a
type of magnetic amplifier which helps keep the voltage constant under load.
Right.

This is a fairly complicated gadget. I'd be inclined to add an external
'box' to do what you want rather than tinker with it.

That would be my own approach, as well.
A heat sinked diode should work fine re back flow.

Yep. I just added a beefy 140A diode on a beefy 1/4" by 2" by 6"
copper bar, right to the + terminal, it works great (as it
should). Had to tap that bar to 3/8-24 NF thread. In testing of this,
the voltage drop varied from 0.78 to about 0.9v or so depending on
(light) load. Could not find my heatsink paste, I need to buy some or
find what I have.

So, I would say, my first problem of battery discharging through this
power supply when it is turned off, has been SOLVED.
For constant current, maybe a big transistor - depends on the max
current you want.

I would say 50A max (so that I do not exceed 15 amp single phase power
draw to not blow my house breakers), but it should be adjustable by a pot.

I do have two big transistors, not sure if I could use them or not.
You could use SCR's and a commutation circuit for more amps, but I'd
look for an old GE SCR manual if you want to do that. Or. google for
(scr commutating dc).

http://www.omega.com/temperature/Z/pdf/z124-127.pdf (page 2) shows a typical
circuit.

Do you mean something as pictured in Figure 6? What would be the
point, to turn current on and off like that? Or are you suggesting
high frequency switching? I would rather regulate it, that is my
first, unstudied thought, than switch on and off? I apologize if
my comment is off base.
 
H

Homer J Simpson

Jan 1, 1970
0
Do you mean something as pictured in Figure 6? What would be the
point, to turn current on and off like that? Or are you suggesting
high frequency switching? I would rather regulate it, that is my
first, unstudied thought, than switch on and off? I apologize if
my comment is off base.

The point is to handle large currents without large heat losses. SCRs were
used for such tasks before large transistors or FETs were common. One use
was as a speed control for a battery golf cart. Basically you fire the first
SCR to turn the current on. At a certain point you fire another SCR across
it with a capacitor in series. This shunts the first SCR which turns off and
the capacitor then charges and turns the second SCR off. Then repeat.

A more modern design might have transistors cycling on and off to control
the current with lower heat losses than remaining on. Basically this is a
form of switch mode power supply, perhaps without the transformer and
Schottky diodes.

As I say, it depends on how much current you want to use for electro
plating. 50 A at 12 V drop (say) is mighty hot.
 
Ignoramus7040 said:
Thanks to many people regarding your earlier advise on modifying my
TIG welder. The sequel to that saga is that the welder works and I use
it quite often.

Now I have a smaller modification to ponder.

After several unpleasant experiences with battery chargers (which did
not work) I want to try something different. My typical use of a
battery charger is to use it to replenish some battery that does a lot
of engine cranking.

I have a power supply that I am thinking should become my battery
charger. It is a PP-1104B/G. If you google for PP-1104C/G you will
find a description of a very similar power supply. It has a dual
range: 13-19 volts at up to 100 amps, and 26-39 volts up to 50
amps. It is a constant voltage power supply with no current limiting
other than built in breakers. I added a few not very relevalt things
to it (like handles for easier handling), but it has a few electrical
quirks that I would like corrected.

The first is that when it is turned off, it drains the battery (ie the
current flows "backwards" as opposed to current flow when charging)
and quickly consumes a lot of amps. It appears that adding a diode
with a small heatsink should take care of the issue.

My calculation is that at 100A, the diode with voltage drop of 0.7
volts would produce 70 watts, which is trivial to dissipate. I have a
number of suitable diodes and heatsinks. So, unless someone gives some
great reason why adding a reverse protection diode is a bad idea, I
will do it.

My second question is whether there is an easy way to add a current
limiting feature to this device, that is, make current limited to a
value set by a potentiometer. That would make it valuable for, say,
electroplating.

I read about current limiting today. The ones I read about were based
on the principle that there is a transistor in series with the load,
that basically acts as a variable resistor to limit current. That's
wasteful, but I can live with it, but perhaps there are more clever
schematics of a current limiting add-on. There is no space inside that
power supply to add anything, so any such circuitry would be in an
external device.

Any suggestions on more inteligent current limiting add-ons will be
gratefully appreciated.

i

This is the kind of thing I just buy. I have a lot of gel cells I use
for power in the field. I use
<http://www.batterystuff.com/battery-chargers/12-volt/11-20amps/JAC1212.html>
They have other smart chargers at
<http://www.batterystuff.com/battery-chargers/12-volt/21amps/>

The problem with charging batteries is you can't sit there and watch
the damn thing charge. Thus you need protection circuitry in the
charger. I suppose you can spend you time designing such circuits.
Generally I only build what doesn't exist off the shelf. I can tell you
the Japlar Schauer I bought is a good product.

Getting back to your situation. Lead acid batteries tend to self limit.
I don't have my Gates Energy book handy, but I think the limit is
generally around 25% of capacity. This means your 100A charger is set
up for a 400AH battery. I am presuming your battery isn't 400AH, so you
really should current limit the power supply just to be on the safe
side.

Seriously consider buying an off the shelf product.
 
M

Michael A. Terrell

Jan 1, 1970
0
Ignoramus7040 said:
It is varied by turning a beefy knob that probably switches
transformer windings.

Second question is a good one, my guess is that there are capacitors
and a big safety discharge resistor that play a role.

i


A 100 amp contactor in series with the output would be the simplest
way to go. Wire the coil across the transformer primary to turn it on,
when the supply is on.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
I

Ignoramus31174

Jan 1, 1970
0
The point is to handle large currents without large heat losses. SCRs were
used for such tasks before large transistors or FETs were common. One use
was as a speed control for a battery golf cart. Basically you fire the first
SCR to turn the current on. At a certain point you fire another SCR across
it with a capacitor in series. This shunts the first SCR which turns off and
the capacitor then charges and turns the second SCR off. Then repeat.

A more modern design might have transistors cycling on and off to control
the current with lower heat losses than remaining on. Basically this is a
form of switch mode power supply, perhaps without the transformer and
Schottky diodes.

As I say, it depends on how much current you want to use for electro
plating. 50 A at 12 V drop (say) is mighty hot.

OK, I see now. 50 A at 12V is not that much -- it is just 500
watts. Nothing that a 10 inch long heatsink could not handle. I have a
heatsink with 2 transistors assembly, would be nice to try to make it
into a variable voltage limited and current limited supply using them.

i
 
I

Ignoramus31174

Jan 1, 1970
0
This is the kind of thing I just buy. I have a lot of gel cells I use
for power in the field. I use
<http://www.batterystuff.com/battery-chargers/12-volt/11-20amps/JAC1212.html>
They have other smart chargers at
<http://www.batterystuff.com/battery-chargers/12-volt/21amps/>

Hm, thanks. That's interesting. If you vouch for them, that means a
lot to me. The "smart chargers" that I tried were basically all very
poorly programmed, had a lot of software bugs, and would not charge my
deep cycle batteries correctly and would "hang" while continuing to
charge etc. (that is, they would continuously display 88% charge
whereas the battery was at 15V or something).
The problem with charging batteries is you can't sit there and watch
the damn thing charge. Thus you need protection circuitry in the
charger. I suppose you can spend you time designing such circuits.
Generally I only build what doesn't exist off the shelf. I can tell you
the Japlar Schauer I bought is a good product.

Getting back to your situation. Lead acid batteries tend to self limit.
I don't have my Gates Energy book handy, but I think the limit is
generally around 25% of capacity. This means your 100A charger is set
up for a 400AH battery. I am presuming your battery isn't 400AH, so you
really should current limit the power supply just to be on the safe
side.

My batteries are about 180 AH rated.

Yes, so this comes back to current limiting discussion.
Seriously consider buying an off the shelf product.

So, let me ask you then, the charger that you are describing, charges
all sorts of batteries well and does not hang or misbehave in any way?

I have a 1.5v smart trickle charger/battery maintainer, these ones
work VERY well, but they charge too slowly when I need to charge a
battery quickly.

Oddly enough, when I clicked on enlarge image, it showed a 24v
charger, but I suppose it is their mistake and that's all.

i
 
I

Ignoramus31174

Jan 1, 1970
0
A 100 amp contactor in series with the output would be the simplest
way to go. Wire the coil across the transformer primary to turn it on,
when the supply is on.

Mike, I put in a diode yesterday, it works just fine. I just need to
find heatsink paste, I misplaced it. Otherwise it is great.

i
 
J

John Fields

Jan 1, 1970
0
The point is to handle large currents without large heat losses. SCRs were
used for such tasks before large transistors or FETs were common. One use
was as a speed control for a battery golf cart. Basically you fire the first
SCR to turn the current on. At a certain point you fire another SCR across
it with a capacitor in series. This shunts the first SCR which turns off and
the capacitor then charges and turns the second SCR off. Then repeat.

A more modern design might have transistors cycling on and off to control
the current with lower heat losses than remaining on. Basically this is a
form of switch mode power supply, perhaps without the transformer and
Schottky diodes.

As I say, it depends on how much current you want to use for electro
plating. 50 A at 12 V drop (say) is mighty hot.

---
What you've described isn't a constant-current supply, but rather
one where the _average_ current into the bath can be controlled by
varying the duty cycle of the waveform into the tank. Still, for
plating that should be adequate.

The controller can take the form of either a fixed cycle time,
variable-width pulse or a fixed-width pulse, variable cycle time
supply.

In either case the current into the bath would have to be measured
and then either the pulse width or the cycle time adjusted in order
to get the right number of electrons into and out of the bath in the
allotted time.

I'd go the fixed pulse width, variable cycle time route myself
because it would be easier to figure out how long to wait to pump
another load of charge through the bath after I knew how much I'd
just pumped through it than trying to figure out how much to pump
through it on the fly.

Google "pulse electroplating" (no quotes) for a lot of folks who
have already done it.
 
H

Homer J Simpson

Jan 1, 1970
0
Oddly enough, when I clicked on enlarge image, it showed a 24v
charger, but I suppose it is their mistake and that's all.

I believe this can be jumpered for 14 V or 28 V.
 
C

Chris Jones

Jan 1, 1970
0
Ignoramus31174 said:
OK, I see now. 50 A at 12V is not that much -- it is just 500
watts. Nothing that a 10 inch long heatsink could not handle. I have a
heatsink with 2 transistors assembly, would be nice to try to make it
into a variable voltage limited and current limited supply using them.

i


If you are thinking of any kind of switching regulator, and given that you
have low voltage DC already, I would definitely avoid SCRs since they
always drop quite a lot of voltage and are difficult to turn off. I would
either use MOSFETs in a switching constant current source, or get a big
heatsink with a fan, and build a linear regulator with either NPN bipolar
transistors or MOSFETs. The switching regulator would be more intersting
and more efficient, and an inductor to handle 50A DC could probably be
scavenged / built up from some computer power supply parts.

Chris
 
I

Ignoramus31174

Jan 1, 1970
0
If you are thinking of any kind of switching regulator, and given that you
have low voltage DC already, I would definitely avoid SCRs since they
always drop quite a lot of voltage and are difficult to turn off. I would
either use MOSFETs in a switching constant current source, or get a big
heatsink with a fan, and build a linear regulator with either NPN bipolar
transistors or MOSFETs. The switching regulator would be more intersting
and more efficient, and an inductor to handle 50A DC could probably be
scavenged / built up from some computer power supply parts.

Chris, you know me. I am basically looking to see what would it entail
to make the cheapest/easiest solution to making a more versatile power
supply out of this PP-1104B/G. If the power converter is lossy, I
think that in the end it is not a huge consideration.

Is it true that a linear transistor based regulator is basically an
extremely simple solution?

i
 
I

Ignoramus31174

Jan 1, 1970
0
Chris, would I be able to make a linear voltage and current regulator
with these transistors

http://yabe.algebra.com/~ichudov/misc/ebay/ups-stuff/PRX-KS624530/

I have two, conveniently mounted on a heatsink. Would be great to put
them to some use. Ignore the for sale verbiage, whatever I sold was
sold a long time ago. That heatsink also features a 150A current shunt
and some SCRs, which I do not thinkI would need fora linear regulator.

i
 
H

Homer J Simpson

Jan 1, 1970
0
Chris, would I be able to make a linear voltage and current regulator
with these transistors

http://yabe.algebra.com/~ichudov/misc/ebay/ups-stuff/PRX-KS624530/

I have two, conveniently mounted on a heatsink. Would be great to put
them to some use. Ignore the for sale verbiage, whatever I sold was
sold a long time ago. That heatsink also features a 150A current shunt
and some SCRs, which I do not thinkI would need fora linear regulator.

One would give you up to 30 A assuming dissipation was not a limit. You need
to drop enough voltage to make the regulation work, but not so much as to
create excessive dissipation.
 
I

Ignoramus31174

Jan 1, 1970
0
One would give you up to 30 A assuming dissipation was not a limit. You need
to drop enough voltage to make the regulation work, but not so much as to
create excessive dissipation.

Actually one would give me 300A, not 30A. (I just double checked). My
question is, are they a suitable type transistor for both voltage and
current regulation with pots.

Ie can use them to I make a device to convert incoming 14VDC with no
current limit, to a power source with voltage up to some limit below
14 VDC and with current up to some limit below 50A. (the limits being
settable)

i
 
H

Homer J Simpson

Jan 1, 1970
0
Actually one would give me 300A, not 30A. (I just double checked). My
question is, are they a suitable type transistor for both voltage and
current regulation with pots.

I was going by the speciication on the auction document..
Ie can use them to I make a device to convert incoming 14VDC with no
current limit, to a power source with voltage up to some limit below
14 VDC and with current up to some limit below 50A. (the limits being
settable)

Seems doable.
 
Ignoramus31174 said:
Hm, thanks. That's interesting. If you vouch for them, that means a
lot to me. The "smart chargers" that I tried were basically all very
poorly programmed, had a lot of software bugs, and would not charge my
deep cycle batteries correctly and would "hang" while continuing to
charge etc. (that is, they would continuously display 88% charge
whereas the battery was at 15V or something).

15V is way too high. I don't know if that is dangerous, but it probably
damaged the battery. The smart charger I bought uses a bi-color LED to
indicate the charging.
My batteries are about 180 AH rated.

Well, that is a serious battery. I would contact the company at the
link I provided and see if you can agree on an acceptance criteria for
whatever charger you determine fits your need.
Yes, so this comes back to current limiting discussion.


So, let me ask you then, the charger that you are describing, charges
all sorts of batteries well and does not hang or misbehave in any way?

I have charged a very narrow range of 12V batteries, 50AH to 70AH. Thus
far, no problem. These are not deep discharge, but SLA.

My issue with home brew battery charging is the fecal matter can really
hit the fan if you screw up. Nothing like burning down the house to
save $50 on a commercial charger. When I was designing chargers, I'd
run the charger in an environmental oven, just in case something bad
happens.
 
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