Legal to sell DC-DC Converter *Kits*?

[Eeyore]

Wecan do it wrote:

BTW: Part of the UL testing regime would ( used to when I
checked it 25 years ago, require a hot cup of oil be poured
into your supply and not ignite. Fun with toasters.

I found it hilarious when I first came across UL.

I have an article on it I could perhaps post in abse.


Graham

 

On Mar 5, 6:22 pm, "David L. Jones" <altz...@gmail.com> wrote:

"Paul" <energymo...@gmail.com> wrote in message

news:1a8d8698-3f87-4096-8bbf-0b91c63288f4@s9g2000prg.googlegroups.com...





Hi,

Is it legal to sell a kit that includes all of the parts,
instructions, and diagrams so someone could build there own DC-DC
Converter kit? I believe it requires certifications (e.g., UL) to make
& sell DC-DC Converters, so someone suggested selling kits until I
make enough $ to get the DC-DC Converter fully UL listed. The kit
would also include the DC batteries and the chassis.

This seems a little iffy to me because what if there's a flaw in my
circuit design, someone buys my kit that includes all of the
directions and parts (everything) to make the DC-DC Converter, they
build it, and it burns down their house? That might be a guaranteed
lawsuit win for them, no?

Thanks,
Paul

Hi Paul
I always find it quite sad when people start getting nervous and worry about
these sorts of things.
I assume you live in the sue-happy US of A?
Really, don't worry about it. Design it properly (heat dissipation, overload
protection etc) and the chances of it burning down someone's home is zero..
How much power are we talking about here?, and what kind of batteries? Mains
power devices are another level, but if your device is not mains powered
then there is much less to worry about.

As others have said, the chances of someone suing you when you don't have
any insurance is very low, and that's on top of the chances of it burning
down someones house. What you have to worry about is people returning the
kit "under warranty" because they assembled it wrong and it doesn't work,
they'll think it's *your* responsibility to fix it. I've been selling kits
for my magazine projects for over 15 years, and that happens occasionally,
you just have to wear it.

Your chances are much higher of someone suing you when they trip and knock
their head in your front garden.

Just sell your kits and be happy.

BTW, here is my latest kit coming out shortly:http://www.alternatezone.com/electronics/ucurrent/

Regards
Dave.- Hide quoted text -

- Show quoted text -

CUTE BUT IS IT PRACTICAL

I AM PROTEUS

 

[David L. Jones]

<proteusiiv@gmail.com> wrote in message news:be775491-3c9c-4a58-8153-

CUTE BUT IS IT PRACTICAL

Yes, unlike your multimeter at measuring current accurately in low voltage
circuits.

Dave.

 

[krw]

On Wed, 11 Mar 2009 21:16:20 +1000, "David L. Jones"
<altzone@gmail.com> wrote:

proteusiiv@gmail.com> wrote in message news:be775491-3c9c-4a58-8153-

CUTE BUT IS IT PRACTICAL

Yes, unlike your multimeter at measuring current accurately in low voltage
circuits.

How is this shunt better than the shunt in the multimeter?

 

[David L. Jones]

"krw" <krw@att.bizzzzzzzzzzz> wrote in message
news:m0hgr4l2kdghr79t6rqcaucu0te43jp03n@4ax.com...

On Wed, 11 Mar 2009 21:16:20 +1000, "David L. Jones"
altzone@gmail.com> wrote:

proteusiiv@gmail.com> wrote in message news:be775491-3c9c-4a58-8153-

CUTE BUT IS IT PRACTICAL

Yes, unlike your multimeter at measuring current accurately in low voltage
circuits.

How is this shunt better than the shunt in the multimeter?

Mine has orders of magnitude lower burden voltage than a multimeter.
Almost every multimeter on the market has a high enough burden voltage at
high displayed currents (relative to the range) to be a REAL problem the
lower your circuit voltage gets. It can even be a big problem with 5V
supplies.

Dave.

 

[krw]

In article <M4Ztl.67824$aZ3.6086@newsfe01.iad>, altzone@gmail.com
says...>

"krw" <krw@att.bizzzzzzzzzzz> wrote in message
news:m0hgr4l2kdghr79t6rqcaucu0te43jp03n@4ax.com...
On Wed, 11 Mar 2009 21:16:20 +1000, "David L. Jones"
altzone@gmail.com> wrote:

proteusiiv@gmail.com> wrote in message news:be775491-3c9c-4a58-8153-

CUTE BUT IS IT PRACTICAL

Yes, unlike your multimeter at measuring current accurately in low voltage
circuits.

How is this shunt better than the shunt in the multimeter?

Mine has orders of magnitude lower burden voltage than a multimeter.
Almost every multimeter on the market has a high enough burden voltage at
high displayed currents (relative to the range) to be a REAL problem the
lower your circuit voltage gets. It can even be a big problem with 5V
supplies.

You're going to have to explain this one.

 

[Nobody]

On Thu, 12 Mar 2009 06:49:44 -0500, krw wrote:

CUTE BUT IS IT PRACTICAL

Yes, unlike your multimeter at measuring current accurately in low voltage
circuits.

How is this shunt better than the shunt in the multimeter?

Mine has orders of magnitude lower burden voltage than a multimeter.
Almost every multimeter on the market has a high enough burden voltage at
high displayed currents (relative to the range) to be a REAL problem the
lower your circuit voltage gets. It can even be a big problem with 5V
supplies.

You're going to have to explain this one.

The current passing through the shunt causes a voltage drop. This only
occurs when the multimeter is in-circuit, so inserting the multimeter
changes the behaviour of the circuit. If the voltage drop is significant,
then the current displayed by the multimeter could bear little or no
resemblance to the current in normal operation (without the multimeter
present).

 

[krw]

In article <pan.2009.03.12.18.28.49.516000@nowhere.com>,
nobody@nowhere.com says...>

On Thu, 12 Mar 2009 06:49:44 -0500, krw wrote:

CUTE BUT IS IT PRACTICAL

Yes, unlike your multimeter at measuring current accurately in low voltage
circuits.

How is this shunt better than the shunt in the multimeter?

Mine has orders of magnitude lower burden voltage than a multimeter.
Almost every multimeter on the market has a high enough burden voltage at
high displayed currents (relative to the range) to be a REAL problem the
lower your circuit voltage gets. It can even be a big problem with 5V
supplies.

You're going to have to explain this one.

The current passing through the shunt causes a voltage drop.

Obviously, since this is what is needed.

This only
occurs when the multimeter is in-circuit, so inserting the multimeter
changes the behaviour of the circuit.

Sure (uncertainty, and all that).

If the voltage drop is significant,
then the current displayed by the multimeter could bear little or no
resemblance to the current in normal operation (without the multimeter
present).

So this box becomes a permanent fixture of the DUT? It is never
removed, permanently changing the behavior of the DUT? Hardly
seems like a reasonable explanation.

 

[David L. Jones]

"krw" <krw@att.zzzzzzzzz> wrote in message
news:MPG.2422b2d46c3c431c989a8d@news.individual.net...

In article <M4Ztl.67824$aZ3.6086@newsfe01.iad>, altzone@gmail.com
says...
"krw" <krw@att.bizzzzzzzzzzz> wrote in message
news:m0hgr4l2kdghr79t6rqcaucu0te43jp03n@4ax.com...
On Wed, 11 Mar 2009 21:16:20 +1000, "David L. Jones"
altzone@gmail.com> wrote:

proteusiiv@gmail.com> wrote in message news:be775491-3c9c-4a58-8153-

CUTE BUT IS IT PRACTICAL

Yes, unlike your multimeter at measuring current accurately in low
voltage
circuits.

How is this shunt better than the shunt in the multimeter?

Mine has orders of magnitude lower burden voltage than a multimeter.
Almost every multimeter on the market has a high enough burden voltage at
high displayed currents (relative to the range) to be a REAL problem the
lower your circuit voltage gets. It can even be a big problem with 5V
supplies.

You're going to have to explain this one.

No problem.
Best way is with a cut'n'paste example from next month Silicon Chip article
that should explain it:

QUOTE:
"Let's look at how the supply voltage can impact your current measurement,
or vice-versa as the case may be:


Lets say you want to measure the supply current of a chip or circuit taking
200mA using say a 4000 count meter on the 400mA range. A not uncommon
scenario, and one you would think would be pretty easy for any mutlimeter to
handle right? - Hold on.



A typical high end "accurate" multimeter will have a "low" 1mV/mA burden
voltage (about as low as it gets), so this means the meter will drop 200mV
across its shunt resistor at 200mA. This represents an almost tolerable 4%
(200mV / 5V * 100) of a 5V supply voltage. This may not be a big deal if
your supply voltage is spot on 5V, as your chip will get 4.8V and still be
within spec. But what if it's already say 4.8V?, your chip or circuit is now
getting 4.6V and may be outside of its operational spec. This already shows
the limitation of the current range on a typically mid to high end
multimeter. Not to even mention the circuit current can differ when you
lower the rail by 0.2V.



Let's now say you need to do the same thing on a modern circuit or chip with
say a 1.2V power supply. That same 200mV burden voltage is now a whopping
17% (200mV / 1.2V * 100) of the supply voltage. Your circuit will likely
fail to function correctly and this is clearly not acceptable, not to
mention inaccurate.



Think this is only a problem with "cheap" meters? Think again. The Fluke
87-V, probably the most popular high-performance meter available has a
burden voltage of 1.8mV/mA (which is still pretty good). So the above
numbers are even worse - a 360mV drop for a 200mA current.



Sure, you can switch up a current range, using the 10A jack, with its burden
voltage of say 10mV/A, giving you a very nice drop of only 2mV. But your
display is now showing 0.200 or 0.20 instead of 200.0 - you've just lost a
valuable digit or two of resolution. And the higher 10A current range is
likely much less accurate than the mA range too!"

/QUOTE



And that's the same with virtually every multimeter on the market,
regardless of price.

Some are a LOT worse. Try the above example on a Fluke 77 Series III or a
Meterman 37XR for example.

They will drop so much your 1.2V circuit will get ZERO volts. The Fluke
79-III is so bad Fluke decided to remove the 400mA range entirely.



And that's of course not even mentioning that the current accuracy on almost
all meters is a lot worse than the basic DC voltage accuracy. Try 5 times
worse for an average.



So my uCurrent provides a much lower burden voltage and uses the more
accurate voltage range to measure current. So it solves two rather annoying
prolems in one hit.

Nothing tricky about it at all, it's just that no one has bothered to do it
before as a multimeter add-on (that I am aware of). But it's carefully
considered and done all the time in in-circuit current shunts.



I suspect the article will be a real eye-opener for some people.



Dave.

 

[David L. Jones]

"Nobody" <nobody@nowhere.com> wrote in message
newsan.2009.03.12.18.28.49.516000@nowhere.com...

On Thu, 12 Mar 2009 06:49:44 -0500, krw wrote:

CUTE BUT IS IT PRACTICAL

Yes, unlike your multimeter at measuring current accurately in low
voltage
circuits.

How is this shunt better than the shunt in the multimeter?

Mine has orders of magnitude lower burden voltage than a multimeter.
Almost every multimeter on the market has a high enough burden voltage
at
high displayed currents (relative to the range) to be a REAL problem the
lower your circuit voltage gets. It can even be a big problem with 5V
supplies.

You're going to have to explain this one.

The current passing through the shunt causes a voltage drop. This only
occurs when the multimeter is in-circuit, so inserting the multimeter
changes the behaviour of the circuit. If the voltage drop is significant,
then the current displayed by the multimeter could bear little or no
resemblance to the current in normal operation (without the multimeter
present).

Correct, and the drop gets higher the closer you get to full-scale on your
current range.
Virtually every meter on the market will have between 1mV/mA and 10mV/mA
burden voltage for the mA ranges, so do the math for the 200mA range and
then ask if your circuit can handle (or be affected by) that drop.
Similar but often not as bad for the uA ranges.

Dave.

 

[Clifford Heath]

David L. Jones wrote:

Correct, and the drop gets higher the closer you get to full-scale on your
current range.

What'd be useful is a momentary-action pushbutton that
applies a dead short, so while your clip leads are in
circuit and you're testing it, you can hit the button
to see if the behaviour changes. That way you know if
the meter matters.

Clifford Heath.

 

[David L. Jones]

"Clifford Heath" <no@spam.please.net> wrote in message
news:49b9911e$0$7377$afc38c87@news.optusnet.com.au...

David L. Jones wrote:
Correct, and the drop gets higher the closer you get to full-scale on
your current range.

What'd be useful is a momentary-action pushbutton that
applies a dead short, so while your clip leads are in
circuit and you're testing it, you can hit the button
to see if the behaviour changes. That way you know if
the meter matters.

Nice idea, but it's not just the circuit behaviour that matters it's also
the current accuracy of what you are measuring. Your circuit might still be
within spec and fully functional, but when you put that meter in series it
can change the actual circuit current. Makes an already inaccurate current
range even less accurate.
If you are not concerned with high accuracy then a regular multimeter will
usually suffice of course.

Dave.

 

[David L. Jones]

"Clifford Heath" <no@spam.please.net> wrote in message
news:49b9911e$0$7377$afc38c87@news.optusnet.com.au...

David L. Jones wrote:
Correct, and the drop gets higher the closer you get to full-scale on
your current range.

What'd be useful is a momentary-action pushbutton that
applies a dead short, so while your clip leads are in
circuit and you're testing it, you can hit the button
to see if the behaviour changes. That way you know if
the meter matters.

Nice idea, but it's not just the circuit behaviour that matters it's also
the current accuracy of what you are measuring. Your circuit might still be
within spec and fully functional, but when you put that meter in series it
can change the actual circuit current. Makes an already inaccurate current
range even less accurate.
If you are not concerned with high accuracy then a regular multimeter will
usually suffice of course.

Dave.

 

[Nobody]

On Thu, 12 Mar 2009 13:39:37 -0500, krw wrote:

How is this shunt better than the shunt in the multimeter?

Mine has orders of magnitude lower burden voltage than a multimeter.
Almost every multimeter on the market has a high enough burden voltage at
high displayed currents (relative to the range) to be a REAL problem the
lower your circuit voltage gets. It can even be a big problem with 5V
supplies.

You're going to have to explain this one.

[snip]

Maybe you should elaborate on exactly what you want explaining. I took it
as "why does it matter that it has orders of magnitude lower burden
voltage than a multimeter?". If that wasn't what you were asking, then my
reply is of no use to you.

 

[Stuart]

In article <DEeul.3931$0E.1639@newsfe15.iad>,
David L. Jones <altzone@gmail.com> wrote:

Virtually every meter on the market will have between 1mV/mA and 10mV/mA
burden voltage for the mA ranges, so do the math for the 200mA range and
then ask if your circuit can handle (or be affected by) that drop.
Similar but often not as bad for the uA ranges.

Also, don't ignore the volt drop in your test leads - unless you abandon
your standard leads for something considerably thicker - and shorter. You
will also have to replace the 4mm input sockets on your meter with
adequately rated screw terminals.

Don't forget the power dissipated in the shunt either. If you're measuring
20A and your volt drop is 200mV, your shunt has to dissipate 4W. This is
Ok with a properly designed external shunt but not if you're going to
stick it inside the average multimeter case.

 

[Twayne]

Paul wrote:

Hi,

Is it legal to sell a kit that includes all of the parts,
instructions, and diagrams so someone could build there own DC-DC
Converter kit? I believe it requires certifications (e.g., UL) to make
& sell DC-DC Converters, so someone suggested selling kits until I
make enough $ to get the DC-DC Converter fully UL listed. The kit
would also include the DC batteries and the chassis.

This seems a little iffy to me because what if there's a flaw in my
circuit design, someone buys my kit that includes all of the
directions and parts (everything) to make the DC-DC Converter, they
build it, and it burns down their house? That might be a guaranteed
lawsuit win for them, no?

Thanks,
Paul

It appears you don't know the UL/CSA safety specs. Without those, you
are truly lost. And you won't learn them in a day or two. Do not sell
anything with any voltages greater than 42V. Design to UL/CSA specs,
advertise it thusly and be certain you actually did that correctly.
Many labs around the country would do a test suite for you for a
reasonable price, and then you could use those in your adverts too.
Note that many cities, counties and town around the country won't
allow a product to be sold unless the safety approval is in place,
though. All of Ca, NYC, Chgo, DC and FL are a few of them.
Also be certain that every component has a UL or CSA listing also.
It doesn't guarantee you'll USE them correctly, but if you do, at least
the components are listed.

Burn down my house and yes, you have a guaranteed law suit on your
hands. But then, I would never purchase anything that was not UL
approved, including kits. It's difficult to get approvals on kits, too.
Lot of hoops to jump thru.

Go talk to UL; they will talk to you and give you some good info.

 

[Twayne]

Paul wrote:

On Mar 5, 8:41 am, Paul <energymo...@gmail.com> wrote:
Hi,

Is it legal to sell a kit that includes all of the parts,
instructions, and diagrams so someone could build there own DC-DC
Converter kit? I believe it requires certifications (e.g., UL) to
make & sell DC-DC Converters, so someone suggested selling kits
until I make enough $ to get the DC-DC Converter fully UL listed.
The kit would also include the DC batteries and the chassis.

This seems a little iffy to me because what if there's a flaw in my
circuit design, someone buys my kit that includes all of the
directions and parts (everything) to make the DC-DC Converter, they
build it, and it burns down their house? That might be a guaranteed
lawsuit win for them, no?

Thanks,
Paul


Sorry, I should have been more clear. It's not just a DC-DC Converter,
but an entire mobile battery powered power supply package with
variable DC voltage up to 12V DC.

Regards,
Paul

You're missing the point: What is its source? The output itself is
almost irrelevant. Don't do this; you are not prepared to handle it.

 

[Mr.Eko]

On Wed, 18 Mar 2009 13:18:12 -0400, "Twayne" <nobody@devnull.spamcop.net>
wrote:

It appears you don't know the UL/CSA safety specs.

It appears that you are nothing more than a mouthy little bitch.