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Radio Shack 25 amp Switching Power Supplies - running in p..

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Anonymous
a b ) Power supply
January 2, 2005 9:44:16 PM

Archived from groups: rec.audio.tech (More info?)

Is it possible to run two radioshack 25 amp (13.8 volt) powersupplies
in parallel? I want to run some powerful car amplifier amps in my
house and need all the amperage I can obtain :)  The main problem is
that every time I try to run them together, one shuts off *I'm sure it
is some sort of circuit they put in it to keep people from bonding them
together. Any advice on bypassing it? Thanks for your help or
instructions!

-Matt
Anonymous
a b ) Power supply
January 2, 2005 10:26:12 PM

Archived from groups: rec.audio.tech (More info?)

so you think that using two rectifier diodes and then running their
output in parallel will stop them from shuting off? (maybe) I know
that rectifiers do have some backward current or something like that...
Anonymous
a b ) Power supply
January 2, 2005 10:53:31 PM

Archived from groups: rec.audio.tech (More info?)

<Chesteta@gmail.com> wrote ...
> so you think that using two rectifier diodes and then running their
> output in parallel will stop them from shuting off? (maybe) I know
> that rectifiers do have some backward current or something like
> that...

I'm surprised that you haven't experienced a catastrophic failure
somewhere here already. I hope you have good medical coverage
and be sure to wear protective gear whenever trying your dangerous
experiments. And be sure to keep an appropriate fire extinguisher
(one rated for electrical fires) within arms reach.

What you are trying to do is A VERY BAD IDEA!!! You are
experimenting with high power in a most clueless manner and
are running a higher risk of injury or fire than you realize.

Using high-power battery-operated equipment in a stationary
application is in itself highly questionable. Cobbling together
power supplies, and SWITCHING SUPPLIES IN PARTICULAR
is just a disaster waiting to happen.
Related resources
Anonymous
a b ) Power supply
January 2, 2005 10:59:29 PM

Archived from groups: rec.audio.tech (More info?)

what is bad about switching power supplies?
Anonymous
a b ) Power supply
January 2, 2005 11:16:16 PM

Archived from groups: rec.audio.tech (More info?)

<wrote ...
> what is bad about switching power supplies?

If they become unstable, they often fail in a spectactular
chain reaction of blown components. They are far less
forgiving of use outside their design parameters than old-
fashioned linear supplies. They are far more dangerous
to debug and repair as much of the active circuitry is
connected directly to the power/mains.

http://repairfaq.ece.drexel.edu/sam/smpsfaq.htm and many
similar sources of info.

I have been hacking electronics for >30 years, but still
treat switching supplies (including HV ones around CRT
displays) with the utmost respect and maximum deployment
of protective gear and procedures. There are few areas of
amateur electronics experimenting that are more dangerous.

Paralleling even linear power supplies is tricky, particularly
at high powers. Paralleling switchmode power supplies is
something rarely done even by the people who design them
and undesrstand them best.

You'd be far better off getting a big RV deep-cycle battery
to run your equipment, and keep it charged with a trickle-
charger designed for such use.
Anonymous
a b ) Power supply
January 2, 2005 11:21:45 PM

Archived from groups: rec.audio.tech (More info?)

Chesteta@gmail.com wrote:

> Is it possible to run two radioshack 25 amp (13.8 volt) powersupplies
> in parallel?

Yes, but its a non-trivial problem.

> I want to run some powerful car amplifier amps in my
> house and need all the amperage I can obtain :) 

Maybe, maybe not. This is one of those cases where a stiffening
capacitor can help. Switching power supplies have very rigidly enforced
limits. Audio power amps have peak current requirements that are far
greater than their average current requirements. A stiffening capacitor
can vastly increase the peak current capacity of a power supply with a
rigidly-enforced current limit.

> The main problem is
> that every time I try to run them together, one shuts off *I'm sure
it
> is some sort of circuit they put in it to keep people from bonding
them
> together.

Not really. The problem is the rigidly-enforced current limit. Power
supplies like these have output voltages that are also tightly
controlled, but the exact output voltage that is the target being
controlled to, varies slightly from unit to unit due to normal
component value variations. Therefore one power supply puts out
slightly more voltage than the other. It tries to carry the entire
load, including the other power supply. This results in excess current
drain which of course causes that power supply to trip out.

> Any advice on bypassing it?

The usual solution to a problem like this is to isolate the two power
supplies from each other by hooking a small value resistor, such as
0.01 ohm in series with each power supply. Normal output voltage
variations such as 0.1 volt will be balanced out by the resistor before
the 25 amp current limit is reached.

0.1 ohm resistors are not readily availble. You can make one of your
own using lengths of fairly heavy wire. For example, 12 gauge wire has
a resistance of 0.0017 ohm per foot. About 6 feet of 12 guage wire has
about 0.01 ohm resistance. Hooking both power supplies to the load
through 2 3 foot 12 guage copper wire cables should sufficiently
isolate the two power supplies from each other, and provide up to 50
amps to the load. Try this instead of tying the two power supplies
together with short lenghts of heavy wire. There will be about 0.25
voltage loss through the two pieces of wire at maximum current drain.
Anonymous
a b ) Power supply
January 2, 2005 11:26:17 PM

Archived from groups: rec.audio.tech (More info?)

well if its been working for five months, i should be fine right? this
is currently set up as a powersupply powering one amplifier, the way it
is meant to work (no rectifier trying to get 50 amps or anything like
that)
Anonymous
a b ) Power supply
January 3, 2005 1:11:30 AM

Archived from groups: rec.audio.tech (More info?)

In article <1104720256.053031.247360@f14g2000cwb.googlegroups.com>,
Chesteta@gmail.com wrote:

> Is it possible to run two radioshack 25 amp (13.8 volt) powersupplies
> in parallel? I want to run some powerful car amplifier amps in my
> house and need all the amperage I can obtain :)  The main problem is
> that every time I try to run them together, one shuts off *I'm sure it
> is some sort of circuit they put in it to keep people from bonding them
> together. Any advice on bypassing it? Thanks for your help or
> instructions!
>
> -Matt

The Rat Shack power supply is probably very low in quality; maybe some
obsolete mainframe computer component that's repackaged.

Any switching power supply that cuts off for an overload can't be
paralleled. Even the slightest imbalance of voltage will cause only one
to provide current at a time. You need one that has current limiting
instead.

Try
http://www.meanwell.com/
I don't know if it the site will load. It appears to be totally broken
after a redesign.

Meanwell has power supplies that deal with abuse gracefully. I use them
for 12V systems with battery backup because I can fine tune the voltage
and they current limit while a low battery is drawing all available
power. Some Fry's Electronics sell them.

Like all switching power supplies, you will need a stiffening capacitor.
The regulation feedback loop is slow so they can't deal with rapidly
changing currents. A car battery works too if you maintain it with
proper charging.

You should also look into replacing your car audio equipment with home
audio equipment. Car audio equipment is usually extremely inefficient
and lower in quality. Large enclosure subs for a home can be 10 times
as efficient as small car subs. It makes a 150W amp very useful.
Anonymous
a b ) Power supply
January 3, 2005 9:50:17 PM

Archived from groups: rec.audio.tech (More info?)

Al wrote:
> > It is possible that this isn't possible to do. You might get
> > it to work by putting diodes on the output of each power supply.
>
> I suspect the forward voltage drop would be a problem though :-(
Think Shottky diodes.
January 3, 2005 10:11:04 PM

Archived from groups: rec.audio.tech (More info?)

> It is possible that this isn't possible to do. You might get
> it to work by putting diodes on the output of each power supply.

I suspect the forward voltage drop would be a problem though :-(

Al.
Anonymous
a b ) Power supply
January 4, 2005 3:48:36 AM

Archived from groups: rec.audio.tech (More info?)

In article <1104807017.933916.149010@z14g2000cwz.googlegroups.com>,
"Arny Krueger" <arnyk@comcast.net> wrote:

> Al wrote:
> > > It is possible that this isn't possible to do. You might get
> > > it to work by putting diodes on the output of each power supply.
> >
> > I suspect the forward voltage drop would be a problem though :-(
> Think Shottky diodes.

The voltage drop is comparable. Schottky diodes are mostly used for
their speed. It still won't help the poster. It's an imbalance of
voltage/current in power supplies that don't have current limiting. If
one supply is 13.85V and the other is 13.75, then the 13.85 supply shuts
off, followed by the 13.75V supply shutting off.

A regulator would work but that costs 1 - 2 volts and maybe $50 to
build. This would work for small voltage imbalances:

+12V 25A +12V 25A
| |
+----R----+----R----+ 0.1 Ohm resistors
| | |
C | C
B--------+--------B NPN, fairly well matched
E E
| |
| |
+---------+---------+
|
v


I'd just replace the whole thing with home stereo equipment, or at least
get better power supplies.
Anonymous
a b ) Power supply
January 4, 2005 10:33:39 AM

Archived from groups: rec.audio.tech (More info?)

Kevin McMurtrie wrote:
> In article <1104807017.933916.149010@z14g2000cwz.googlegroups.com>,
> "Arny Krueger" <arnyk@comcast.net> wrote:
>
> > Al wrote:
> > > > It is possible that this isn't possible to do. You might get
> > > > it to work by putting diodes on the output of each power
supply.
> > >
> > > I suspect the forward voltage drop would be a problem though :-(
> > Think Shottky diodes.
>
> The voltage drop is comparable.

Tell that to MIT:

http://fab.cba.mit.edu/classes/961.04/topics/power.pdf

page 4, figure near middle of page.


> Schottky diodes are mostly used for
> their speed. It still won't help the poster. It's an imbalance of
> voltage/current in power supplies that don't have current limiting.

Well, sorta but you've missed the point that these are regulated power
supplies with low output impedances. If there is no isolation between
them, the power supply with the higher voltage will overstress itself
trying to pull up the voltage of the supply with the lower voltage.

Driving the load though diodes prevents either power supply from
delivering current to the other one.


> If one supply is 13.85V and the other is 13.75, then the 13.85 supply

> shuts off, followed by the 13.75V supply shutting off.

Hence my recommendation of low value series resistors. The power supply
with the higher voltage carries the bulk of the load until the drop
across its series resistor drops the voltage of its contribution below
that of the the power supply with the slightly lower voltage.

> I'd just replace the whole thing with home stereo equipment, or at
least
> get better power supplies.

Given the requirement, I went with the larger power supply - a 25 amp
linear supply from the local non-RS parts and ham supplies store.
Didn't cost that much more than just one of the RS supplies.

Later on I also picked up an even larger switching supply via eBay for
far less money.

I've also used scrapped laptop switching supplies with current storage
caps. It can work amazingly well because of the relatively high peak to
average current needs of audio.
Anonymous
a b ) Power supply
January 4, 2005 11:34:01 PM

Archived from groups: rec.audio.tech (More info?)

Using diodes will keep the two supplies from seeing *each other* but they'll
still both see the load. The supply putting out the highest voltage will
still carry the bulk of the load. The only way I know of to get them to
share the load equally is to *separate* the load into two equal parts, and
use each supply to drive each load separately. Provide a good common ground.

Or, here's a fun project: Wire up a car battery, alternator, and regulator
and connect it to your stereo. Connect a 5 HP Briggs & Stratton engine to
the alternator with a fan belt. Crank up the engine and enjoy! Important
safety tip: Route the exhaust to the outside. Oh, and play the music really
loud. The engine will add some background noise.
Anonymous
a b ) Power supply
January 5, 2005 4:18:52 AM

Archived from groups: rec.audio.tech (More info?)

In article <1104852819.393992.316590@f14g2000cwb.googlegroups.com>,
"Arny Krueger" <arnyk@comcast.net> wrote:

> Kevin McMurtrie wrote:
> > In article <1104807017.933916.149010@z14g2000cwz.googlegroups.com>,
> > "Arny Krueger" <arnyk@comcast.net> wrote:
> >
> > > Al wrote:
> > > > > It is possible that this isn't possible to do. You might get
> > > > > it to work by putting diodes on the output of each power
> supply.
> > > >
> > > > I suspect the forward voltage drop would be a problem though :-(
> > > Think Shottky diodes.
> >
> > The voltage drop is comparable.
>
> Tell that to MIT:
>
> http://fab.cba.mit.edu/classes/961.04/topics/power.pdf
>
> page 4, figure near middle of page.

It depends on the diode's optimizations. I've seen Schottky diodes with
0.3 to 1.1 forward voltage and standard diodes with 0.6 to 1.3 forward
voltage. IRF is a good source of high-grade semiconductors.

>
> > Schottky diodes are mostly used for
> > their speed. It still won't help the poster. It's an imbalance of
> > voltage/current in power supplies that don't have current limiting.
>
> Well, sorta but you've missed the point that these are regulated power
> supplies with low output impedances. If there is no isolation between
> them, the power supply with the higher voltage will overstress itself
> trying to pull up the voltage of the supply with the lower voltage.

A switching power supply won't draw more than a few mA if forced to a
slightly higher voltage. The only load is its feedback circuit. Maybe
you can trigger a crowbar by forcing it too high but that's a different
story.


> Driving the load though diodes prevents either power supply from
> delivering current to the other one.
>
>
> > If one supply is 13.85V and the other is 13.75, then the 13.85 supply
>
> > shuts off, followed by the 13.75V supply shutting off.
>
> Hence my recommendation of low value series resistors. The power supply
> with the higher voltage carries the bulk of the load until the drop
> across its series resistor drops the voltage of its contribution below
> that of the the power supply with the slightly lower voltage.
>
> > I'd just replace the whole thing with home stereo equipment, or at
> least
> > get better power supplies.
>
> Given the requirement, I went with the larger power supply - a 25 amp
> linear supply from the local non-RS parts and ham supplies store.
> Didn't cost that much more than just one of the RS supplies.
>
> Later on I also picked up an even larger switching supply via eBay for
> far less money.
>
> I've also used scrapped laptop switching supplies with current storage
> caps. It can work amazingly well because of the relatively high peak to
> average current needs of audio.
August 25, 2011 3:27:29 AM

I purchased a 650 watt psu capable of doing 53amps on the 12 volts rail. It's safe and easy to use, just buy some molex to 6 or 8 pin connectors, strip them and use em! never mind using more than one psu, i tried it and ended up making one fail on me, spend about 100$ on a corsair 600+ watt psu and your good to go.
!