Question about wiring wall cubes in series to get 30v.

[Charlie Wilkes]

Today I bought a well-used HP DJ 697c to print from DOS apps.

It came with no adapter. The label specifies 30 volts at 400ma.

I took an old plustek scanner 24v/600ma cube and a radioshack 3-12v
adjustable cube and wired them in series. I got 36v with no load, so
I figured that was probably about right. The printer powered up, but
after a few minutes the plustek power cube failed. The rshack cube is
still fine.

This group's FAQ reassured me that I wasn't doing anything too crazy,
but it mentioned a rectifier, which I don't have. I didn't get the
impression the rectifier was really essential, but I don't know much
about electronics.

Any ideas why this setup would fail?

Charlie

 

[James Sweet]

Today I bought a well-used HP DJ 697c to print from DOS apps.

It came with no adapter. The label specifies 30 volts at 400ma.

I took an old plustek scanner 24v/600ma cube and a radioshack 3-12v
adjustable cube and wired them in series. I got 36v with no load, so
I figured that was probably about right. The printer powered up, but
after a few minutes the plustek power cube failed. The rshack cube is
still fine.

This group's FAQ reassured me that I wasn't doing anything too crazy,
but it mentioned a rectifier, which I don't have. I didn't get the
impression the rectifier was really essential, but I don't know much
about electronics.

Any ideas why this setup would fail?

Charlie

Were the power adapters AC or DC output? If they're DC then they already
have a rectifier built in. Wiring wall warts in series is generally a bad
idea, particularly if you don't know the details of the output. 24v should
run the printer just fine, no need to muck around with the two adapters.

 

[NSM]

Today I bought a well-used HP DJ 697c to print from DOS apps.

It came with no adapter. The label specifies 30 volts at 400ma.

I took an old plustek scanner 24v/600ma cube and a radioshack 3-12v
adjustable cube and wired them in series. I got 36v with no load, so
I figured that was probably about right. The printer powered up, but
after a few minutes the plustek power cube failed. The rshack cube is
still fine.

This group's FAQ reassured me that I wasn't doing anything too crazy,
but it mentioned a rectifier, which I don't have. I didn't get the
impression the rectifier was really essential, but I don't know much
about electronics.

You might find one in a thrift or

http://www.allelectronics.com/cgi-bin/category.cgi?category=480&item=PS-2416&type=store

might be close enough.

 

[Sam Goldwasser]

Without knowing the details, it's hard to say what went wrong. What
were the exact ratings of the adjustable wall adapter? Many of those
are poorly constructed with limited current capability.

You might find one in a thrift or

http://www.allelectronics.com/cgi-bin/category.cgi?category=480&item=PS-2416&type=store

might be close enough.

Jameco usually has a pretty good assortment. www.jameco.com

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[Charlie Wilkes]

Without knowing the details, it's hard to say what went wrong. What
were the exact ratings of the adjustable wall adapter? Many of those
are poorly constructed with limited current capability.

The requirement was 30v 400ma. All the cubes were rated at 600ma.

I felt wantonly destructive that night so I repeated the experiment,
this time with the surviving (3-12v adjustable) cube and two others
like it. I set two of them at 9v and one at 12v. Then I twisted and
I taped and I plugged it in and it works! I've had it going for a
couple of days now, printing away like a brand-new HP printer, which
is the price I paid for it with new cartridges. I just hope I don't
end up burning down another house.

Charlie

 

[Jerry G.]

As long as their current rating is high enough, it should be very safe. The
total current output will be of the lowest rated one. The voltage output
will be the sum of all that are in series.

I personally would go around to the various electronic suppliers and try to
get a 30 Volt supply, that is rated to at least 500 ma or more. This way
only one outlet will be used, and it is a more practical way to supply your
unit.

--

Jerry G.
=====

Without knowing the details, it's hard to say what went wrong. What
were the exact ratings of the adjustable wall adapter? Many of those
are poorly constructed with limited current capability.

The requirement was 30v 400ma. All the cubes were rated at 600ma.

I felt wantonly destructive that night so I repeated the experiment,
this time with the surviving (3-12v adjustable) cube and two others
like it. I set two of them at 9v and one at 12v. Then I twisted and
I taped and I plugged it in and it works! I've had it going for a
couple of days now, printing away like a brand-new HP printer, which
is the price I paid for it with new cartridges. I just hope I don't
end up burning down another house.

Charlie

 

[jakdedert]

Today I bought a well-used HP DJ 697c to print from DOS apps.

It came with no adapter. The label specifies 30 volts at 400ma.

I took an old plustek scanner 24v/600ma cube and a radioshack 3-12v
adjustable cube and wired them in series. I got 36v with no load, so
I figured that was probably about right. The printer powered up, but
after a few minutes the plustek power cube failed. The rshack cube is
still fine.

This group's FAQ reassured me that I wasn't doing anything too crazy,
but it mentioned a rectifier, which I don't have. I didn't get the
impression the rectifier was really essential, but I don't know much
about electronics.

Any ideas why this setup would fail?

There is no info given as to the nature of the voltage: AC or DC. Two
adaptors in series? The adjustable wall wart would have to be AC to pass
any current at all through the second one, but I've never seen an adjustable
*AC* wall wart. I suppose they could exist, but every one I've seen was DC.

If it's the case that the OP needs 30 volts *AC* then a simple transformer
should suffice. Finding a ~30v transformer might be difficult, but I'll bet
the tolerance is not all that close. If the unit accepts AC, then there's a
complete power supply inside which probably includes some degree of
regulation.

I certainly wouldn't mess around with cascading wall warts....

jak

 

[Asimov]

"jakdedert" bravely wrote to "All" (08 Feb 05 10:41:45)
--- on the heady topic of "Re: Question about wiring wall cubes in series to
get 30v."

ja> From: "jakdedert" <[email protected]>
ja> Xref: aeinews sci.electronics.repair:9852

Today I bought a well-used HP DJ 697c to print from DOS apps.
It came with no adapter. The label specifies 30 volts at 400ma.
I took an old plustek scanner 24v/600ma cube and a radioshack 3-12v
adjustable cube and wired them in series. I got 36v with no load, so
I figured that was probably about right. The printer powered up, but
after a few minutes the plustek power cube failed. The rshack cube is
still fine. [,,,]
Any ideas why this setup would fail?

ja> There is no info given as to the nature of the voltage: AC or DC. Two
ja> adaptors in series? The adjustable wall wart would have to be AC to
ja> pass any current at all through the second one, but I've never seen an
ja> adjustable *AC* wall wart. I suppose they could exist, but every one
ja> I've seen was DC.
ja> If it's the case that the OP needs 30 volts *AC* then a simple
ja> transformer should suffice. Finding a ~30v transformer might be
ja> difficult, but I'll bet the tolerance is not all that close. If the
ja> unit accepts AC, then there's a complete power supply inside which
ja> probably includes some degree of regulation.

ja> I certainly wouldn't mess around with cascading wall warts....


jak,

A device that requires 30 VAC might still work with DC if it contains
its own rectifiers. However recall that 30 VAC is actually about 42V
peak, so the supplied input DC should really have this higher value.

The problem is if 30V DC is too little voltage for any internal
regulation to function properly. If it is a switching supply then it
might not be a problem other than it getting a bit warmer due to the
inceased duty cycle.

A*s*i*m*o*v

.... If plugging it in doesn't help, turn it on.

 

[Sam Goldwasser]

There is no info given as to the nature of the voltage: AC or DC. Two
adaptors in series? The adjustable wall wart would have to be AC to pass
any current at all through the second one, but I've never seen an adjustable

Huh? Think: two DC power supplies in series.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

 

[jakdedert]

Huh? Think: two DC power supplies in series.

Okay, I finally get what the OP was talking about when he said 'series'. If
I understand, what he actually did was commoned one leg of the OUTPUT of
each device and used the two remaining leads as the output....

I agree with James. Try it on 24 volts (one adaptor: unfortunately, the one
he blew out), or else obtain a suitable supply (or buy a transformer and
build one). While what he's doing is not cascading supplies, it still
sounds like a recipe for disaster...not a huge disaster, to be sure, but....

At the very least, I wouldn't leave this kludge plugged in when not
attended.

jak