I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.

My experience is that fully charged AA batteries are usually 1.56
volts x 4 = 6.3 volts, which is exactly half of the resting voltage of
fully charged car batteries, 12.6 volts. I won't be watching tv when
the car is running, but maybe I would sometimes run the car to charge
the car battery, or even to warm the car** Then, iirc and I can
measure it to be sure, the voltage goes up as high as 13.2, half of
which is 6.6. Also, the label on the back of the tv says that it
uses, on average, 1.6 watts, but I will measure its current current
use and not rely on that.

Is that too high for a tv that is meant to run on 6.3? If so, I'll be
glad to make the resistor bigger and thus the voltage lower.

It also has provision for turning off the picture and only getting the
sound. I guess it would use less current then and I would calculate a
higher resistor to be needed. Maybe I should just use a resistor
substitution box and see at what resistance the tv works best? Or
should I buy a device made for this purpose. I have a spare cell
phone charger, but I don't think it wil put out a full 1.6 watts.)

Thanks


**On my best car trip, I slept in the car for 7 or 8 nights in a row.
It was very comfortable but it was a much bigger car, so I'm not sure
I can do even one or two nights this time, but I want to get some use
out of my 2 inch tv, which I got as a gift sort of, and which will be
obsolete in 36 months or so. For tht reason alone, I'd like to sleep
in the car rather than a motel. Or probably more likely, in a tent in
a state park, in late winter or early spring, in the South, where I
guess it will be warm enough. If I stay in a tent, I'll make a longer
wire.

If you are inclined to email me
for some reason, remove NOPSAM :-)

On Thu, 14 Dec 2006 23:05:16 -0500, mm
wrote:

I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of

Resistance! I don't know where I got "different".

the tv.

My experience is that fully charged AA batteries are usually 1.56

By "fully charged", I don't mean chargeable batteries, I just mean
new, non-rechargeable AA batteries. I plan to add a power-in jack via
a 3 conductor wire, and arrange it so that the batteries are
disconnected from the circuit at one end when the power plug is
plugged into the tv's new power jack. There is currently no provision
in the tv for charging batteries, and I don't want to spend the money
on 4 new rechargeable batteries, and I don't want to risk applying a
charging voltage to dying non-rechargeable batteries. I just want to
powr the tv from the cigarette lighter.

volts x 4 = 6.3 volts, which is exactly half ...

If you are inclined to email me
for some reason, remove NOPSAM :-)

mm wrote:
I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.

My experience is that fully charged AA batteries are usually 1.56
volts x 4 = 6.3 volts, which is exactly half of the resting voltage of
fully charged car batteries, 12.6 volts. I won't be watching tv when
the car is running, but maybe I would sometimes run the car to charge
the car battery, or even to warm the car** Then, iirc and I can
measure it to be sure, the voltage goes up as high as 13.2, half of
which is 6.6. Also, the label on the back of the tv says that it
uses, on average, 1.6 watts, but I will measure its current current
use and not rely on that.

Is that too high for a tv that is meant to run on 6.3? If so, I'll be
glad to make the resistor bigger and thus the voltage lower.

It also has provision for turning off the picture and only getting the
sound. I guess it would use less current then and I would calculate a
higher resistor to be needed. Maybe I should just use a resistor
substitution box and see at what resistance the tv works best? Or
should I buy a device made for this purpose. I have a spare cell
phone charger, but I don't think it wil put out a full 1.6 watts.)

Hi...

Just thinking out loud; wouldn't it be so much easier and so
much more practical to just pick up a nimh/nicad charger that
works off of 110 or 12 volts, along with 8 batteries, and use
one set while charging the other?

Take care.

Ken

mm wrote in
:

I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.

My experience is that fully charged AA batteries are usually 1.56
volts x 4 = 6.3 volts, which is exactly half of the resting voltage of
fully charged car batteries, 12.6 volts. I won't be watching tv when
the car is running, but maybe I would sometimes run the car to charge
the car battery, or even to warm the car** Then, iirc and I can
measure it to be sure, the voltage goes up as high as 13.2, half of
which is 6.6. Also, the label on the back of the tv says that it
uses, on average, 1.6 watts, but I will measure its current current
use and not rely on that.

Is that too high for a tv that is meant to run on 6.3? If so, I'll be
glad to make the resistor bigger and thus the voltage lower.

It also has provision for turning off the picture and only getting the
sound. I guess it would use less current then and I would calculate a
higher resistor to be needed. Maybe I should just use a resistor
substitution box and see at what resistance the tv works best? Or
should I buy a device made for this purpose. I have a spare cell
phone charger, but I don't think it wil put out a full 1.6 watts.)

Sounds like you have a good grasp of using a resistor to drop the
voltage, and the fact that if the car's battery voltage varies, so will
the voltage dropped by the resistor.

Better way: Use a voltage regulator IC to put out a constant 6 or 6.3
volts, even if the battery voltage varies (down to 10 or up to 15). Or,
easier, buy a power adapter that does essentially the same thing.

mm wrote:
I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.
...

Are you familiar with load dump? ISO says that voltage can be 270
volts. SGS Thompson defines it at 80 to 100 volts. Your design will
make load dump irrelevant. Cheaper inverters hope you never learn why
they are cheaper - while forgetting to include load dump protection.

In article ,
mm wrote:
I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.

That is a crude method - far better to use a voltage regulator. The
output voltage may go too high under certain conditions - like standby -
if you use just a resistor as that voltage is load dependant.

Like all these things it's probably cheaper to buy a ready made one.

--
*If you think nobody cares about you, try missing a couple of payments *

Dave Plowman London SW
To e-mail, change noise into sound.

mm wrote:

I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor.

Either should be an effective way to kill the tv, though the resistor
method will do it double quick. A resistor dropper is most
inappropriate, a regulator will not generally be able to handle load
dump transients, and is liable to pass them to the tv, ensuring its
well toasted. Stick with running it off batteries.


NT

"w_tom" wrote in news:1166169455.692246.111910
@f1g2000cwa.googlegroups.com:

Are you familiar with load dump? ISO says that voltage can be 270
volts. SGS Thompson defines it at 80 to 100 volts. Your design will
make load dump irrelevant. Cheaper inverters hope you never learn why
they are cheaper - while forgetting to include load dump protection.


About Load Dumps in vehicles:

"An abrupt reduction in the alternator load causes a positive voltage
transient called "load dump." In a load dump transient the line voltage
rises to 20V or 30V in a few microseconds, then decays exponentially with
a time constant of about 100 microseconds. Much higher peak voltages and
longer decay times have also been reported.
"The worst case load dump is caused by disconnecting a low battery from
the alternator circuit while the alternator is running. Normally, this
would happen intermittently when the battery terminal connections are
defective.
"Load Dump transients also occur when heavy loads are switched off,
although their magnitude and duration will be lower. These transients are
capable of destroying semiconductors on the first 'fault event'."

On Thu, 14 Dec 2006 23:05:16 -0500, mm put
finger to keyboard and composed:

I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.

My experience is that fully charged AA batteries are usually 1.56
volts x 4 = 6.3 volts, which is exactly half of the resting voltage of
fully charged car batteries, 12.6 volts. I won't be watching tv when
the car is running, but maybe I would sometimes run the car to charge
the car battery, or even to warm the car** Then, iirc and I can
measure it to be sure, the voltage goes up as high as 13.2, half of
which is 6.6. Also, the label on the back of the tv says that it
uses, on average, 1.6 watts, but I will measure its current current
use and not rely on that.

If you are looking to do this on the cheap, then I'd modify a mobile
phone car adapter/charger. But then I have dozens of them.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

In article ,
Jim Land wrote:
"An abrupt reduction in the alternator load causes a positive voltage
transient called "load dump." In a load dump transient the line voltage
rises to 20V or 30V in a few microseconds, then decays exponentially
with a time constant of about 100 microseconds. Much higher peak
voltages and longer decay times have also been reported. "The worst
case load dump is caused by disconnecting a low battery from the
alternator circuit while the alternator is running. Normally, this
would happen intermittently when the battery terminal connections are
defective. "Load Dump transients also occur when heavy loads are
switched off, although their magnitude and duration will be lower.
These transients are capable of destroying semiconductors on the first
'fault event'."

Given the number of semiconductors in use in the average vehicle - and
have been since the first transistor radio - it seems to be a problem that
has been solved...

--
*The more people I meet, the more I like my dog.

Dave Plowman London SW
To e-mail, change noise into sound.

On Sat, 16 Dec 2006 08:48:44 +1100, Franc Zabkar
wrote:

On Thu, 14 Dec 2006 23:05:16 -0500, mm put
finger to keyboard and composed:
My experience is that fully charged AA batteries are usually 1.56
volts x 4 = 6.3 volts, which is exactly half of the resting voltage of
fully charged car batteries, 12.6 volts. I won't be watching tv when
the car is running, but maybe I would sometimes run the car to charge
the car battery, or even to warm the car** Then, iirc and I can
measure it to be sure, the voltage goes up as high as 13.2, half of
which is 6.6. Also, the label on the back of the tv says that it
uses, on average, 1.6 watts, but I will measure its current current
use and not rely on that.

If you are looking to do this on the cheap, then I'd modify a mobile
phone car adapter/charger. But then I have dozens of them.

Do the new ones put out 1.6 watts, which is what the back of the tv
says it uses on average? I have a spare new one.

Do even the old ones put out 1.6 watts?

- Franc Zabkar


If you are inclined to email me
for some reason, remove NOPSAM :-)

Dave Plowman (News) wrote:
In article ,
Jim Land wrote:

"An abrupt reduction in the alternator load causes a positive voltage
transient called "load dump." In a load dump transient the line voltage
rises to 20V or 30V in a few microseconds, then decays exponentially
with a time constant of about 100 microseconds. Much higher peak
voltages and longer decay times have also been reported. "The worst
case load dump is caused by disconnecting a low battery from the
alternator circuit while the alternator is running. Normally, this
would happen intermittently when the battery terminal connections are
defective. "Load Dump transients also occur when heavy loads are
switched off, although their magnitude and duration will be lower.
These transients are capable of destroying semiconductors on the first
'fault event'."

Given the number of semiconductors in use in the average vehicle - and
have been since the first transistor radio - it seems to be a problem that
has been solved...

Yes. However a resistive dropper does not solve it, nor does a simple
volt reg. A 12v vehicle system load dump onto a 6v tv would be a setup
waiting to fail.

If the OP is incautious enough to do this, it should survive longer if
you never switch heavy loads on or off while the tv's connected. The
heaviest of course being the starter motor.


NT

Dave Plowman (News) wrote:
Given the number of semiconductors in use in the average vehicle - and
have been since the first transistor radio - it seems to be a problem that
has been solved...

Yes. The problem is solved because first ISO and SGS Thompson
defined the numbers. Then electronics is designed to withstand those
numbers without damage. Do you think mobile equipment costs more just
because the manufacturers conspire to be greedy?

One designing for electronics must do what is standard for auto
compatible electronics.

In article .com,
wrote:
Given the number of semiconductors in use in the average vehicle - and
have been since the first transistor radio - it seems to be a problem
that has been solved...

Yes. However a resistive dropper does not solve it, nor does a simple
volt reg. A 12v vehicle system load dump onto a 6v tv would be a setup
waiting to fail.

I've got a few home built bits on my car with standard voltage regs with
no high voltage protection - they mostly are designed for peaks of around
40 volts, IIRC. The chances are the TV has internal voltage regulation too.

If the OP is incautious enough to do this, it should survive longer if
you never switch heavy loads on or off while the tv's connected. The
heaviest of course being the starter motor.

As I said how did a crude early germanium transistor radio survive, then?
But the quote said it was caused by the alternator. Which isn't charging
during cranking.

--
*Organized Crime Is Alive And Well; It's Called Auto Insurance. *

Dave Plowman London SW
To e-mail, change noise into sound.

In article .com,
w_tom wrote:
Dave Plowman (News) wrote:
Given the number of semiconductors in use in the average vehicle - and
have been since the first transistor radio - it seems to be a problem
that has been solved...

Yes. The problem is solved because first ISO and SGS Thompson defined
the numbers. Then electronics is designed to withstand those numbers
without damage. Do you think mobile equipment costs more just because
the manufacturers conspire to be greedy?

It costs more? Can't say I'd noticed.

One designing for electronics must do what is standard for auto
compatible electronics.

So just what are these 'standard' precautions that aren't essential
elsewhere?

--
*Procrastinate now

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
So just what are these 'standard' precautions that aren't essential
elsewhere?

Problem and solutions were defined in that previous post - ISO and
SGS Thompson products for automotive applications. Consult SAE J1455
and ISO 7637-1. Learn about National Semiconductor's harsh
environment semiconductors for automotive applications such as the
LM5005. Learn about General Semicondictors 6KA series products used in
load dump protection circuits. Read Linear Technologies design notes
and their LT3437. So much is so readily available that I am surprised
one should have to ask.

As I said how did a crude early germanium transistor radio survive, then?
They often did not which is why load dump was discovered. Same failure
also occurred to alternators with failed germanium diodes. The Detroit
manufacturer even overnight delivered those replacement alternators.
Load dump created by a manufacturing design defect created germium
semiconductor failure.

mm ha escrito:

On Sat, 16 Dec 2006 08:48:44 +1100, Franc Zabkar
wrote:

On Thu, 14 Dec 2006 23:05:16 -0500, mm put
finger to keyboard and composed:
My experience is that fully charged AA batteries are usually 1.56
volts x 4 = 6.3 volts, which is exactly half of the resting voltage of
fully charged car batteries, 12.6 volts. I won't be watching tv when
the car is running, but maybe I would sometimes run the car to charge
the car battery, or even to warm the car** Then, iirc and I can
measure it to be sure, the voltage goes up as high as 13.2, half of
which is 6.6. Also, the label on the back of the tv says that it
uses, on average, 1.6 watts, but I will measure its current current
use and not rely on that.

If you are looking to do this on the cheap, then I'd modify a mobile
phone car adapter/charger. But then I have dozens of them.

Do the new ones put out 1.6 watts, which is what the back of the tv
says it uses on average? I have a spare new one.

Do even the old ones put out 1.6 watts?

- Franc Zabkar


If you are inclined to email me
for some reason, remove NOPSAM :-)


Well, 1.6 Watts at 6V is nothing more than 267 mA. (1.6V / 6V = 0.267
A) I would be greatly surprised to find a cellphone charger not able
to produce that amount of current. Check the mA rating of the DC
charger you want to modify, if it provides a *regulated* output of 6V
at 300 mA or more, you will be fine.

You want to find a charger who outputs nothing more than 6V, and 300 mA
or more. The TV will take the amount of power (consumption in mA) it
needs, meaning that a 500 mA power source will not damage it, because
the TV will only draw 267 mA from the 500 mA power source. Just be
careful of the voltage produced by the charger, because that´s a
critical paramater and it shouldn´t be higher than 6.6V or lower than
5.4V under any circumstances.

To close, the idea of the dropping resistor is an awful one. Why?
Because the 1.6 Watts consumption stated in the back label of the TV
probably is an average value, or a maximum one obtained only under
worst case conditions. The consumption power of a TV, radio, or
amplifier, is really a variable one. It will vary depending on how high
the speaker volume is, and even the screen content. For instance, a
white image will demand more power than a mainly dark one. So you
can´t really obtain a fixed voltage just using a fixed dropping
resistor if your load is a variable one. Even worse, as other posters
had previously stated, the DC voltage inside a car can go anywere from
12V to 14V or more. So now you have two uncontrolable variable
parameters: a) The voltage source, and b) The power consumption of the
TV.

Don´t risk frying your TV. It´s more worth having it fuly operational
than the cost of a proper DC regulated power supply.

lsmartino wrote:

You want to find a charger who outputs nothing more than 6V, and 300 mA
or more. The TV will take the amount of power (consumption in mA) it
needs, meaning that a 500 mA power source will not damage it, because
the TV will only draw 267 mA from the 500 mA power source. Just be
careful of the voltage produced by the charger, because that´s a
critical paramater and it shouldn´t be higher than 6.6V or lower than
5.4V under any circumstances.

To close, the idea of the dropping resistor is an awful one.
Don´t risk frying your TV. It´s more worth having it fuly operational
than the cost of a proper DC regulated power supply.

A voltage regulator IC, or a modified REGULATED charger (modifying it
might be more of a hassle than it first appears) should do fine. If it
were me, I would simply use a series dropping resistor followed by a
shunt filter cap and a shunt 6.3 volt zener. The zener will probably
have to be mounted on a small heat sink - but so would a voltage
regulator IC. Pretty simple.

Bill

On Fri, 15 Dec 2006 21:09:04 -0500, mm put
finger to keyboard and composed:

On Sat, 16 Dec 2006 08:48:44 +1100, Franc Zabkar
wrote:

On Thu, 14 Dec 2006 23:05:16 -0500, mm put
finger to keyboard and composed:
My experience is that fully charged AA batteries are usually 1.56
volts x 4 = 6.3 volts, which is exactly half of the resting voltage of
fully charged car batteries, 12.6 volts. I won't be watching tv when
the car is running, but maybe I would sometimes run the car to charge
the car battery, or even to warm the car** Then, iirc and I can
measure it to be sure, the voltage goes up as high as 13.2, half of
which is 6.6. Also, the label on the back of the tv says that it
uses, on average, 1.6 watts, but I will measure its current current
use and not rely on that.

If you are looking to do this on the cheap, then I'd modify a mobile
phone car adapter/charger. But then I have dozens of them.

Do the new ones put out 1.6 watts, which is what the back of the tv
says it uses on average? I have a spare new one.

Do even the old ones put out 1.6 watts?

The majority of mine are switchmode PSUs based on an MC34063 IC (I
also have some linear supplies).

The application circuit on page 7 of the MC34063 datasheet shows a
5V/500mA design example:
http://www.onsemi.com/pub/Collateral/MC34063A-D.PDF

In a typical car charger you will need to recalculate R1 and R2 to get
the desired output voltage.

FWIW I've adapted one of these chargers to supply 7V to a 12V fan in a
DVD player.

If you are worried about the load dump problem being discussed
elsewhere in this thread, then you might like to place a transorb or
transil (transient voltage suppression diode) across the 6V output.
However, I suspect that a SMPS of this type is largely immune to
supply transients (due to the series inductances). You may still want
to add the diode for overvoltage protection in the event that the IC
fails.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Dave Plowman (News) wrote:
In article .com,
wrote:

re load dump

As I said how did a crude early germanium transistor radio survive, then?

filtering on the power input. Its not too difficult, just needs to be
not missed out if you want reliability.


NT

w_tom wrote:
Dave Plowman (News) wrote:

So just what are these 'standard' precautions that aren't essential
elsewhere?

Problem and solutions were defined in that previous post - ISO and
SGS Thompson products for automotive applications. Consult SAE J1455
and ISO 7637-1. Learn about National Semiconductor's harsh
environment semiconductors for automotive applications such as the
LM5005. Learn about General Semicondictors 6KA series products used in
load dump protection circuits. Read Linear Technologies design notes
and their LT3437. So much is so readily available that I am surprised
one should have to ask.


As I said how did a crude early germanium transistor radio survive, then?

They often did not which is why load dump was discovered. Same failure
also occurred to alternators with failed germanium diodes. The Detroit
manufacturer even overnight delivered those replacement alternators.
Load dump created by a manufacturing design defect created germium
semiconductor failure.

Its a long time since I opened a geranium car radio, but typical
practice decades ago was an LC input on the power line.

For load dump proof reg ccts, check out National Semiconductor's app
notes series, now online.


NT

wrote:

Its a long time since I opened a germanium car radio, but typical
practice decades ago was an LC input on the power line.

For load dump proof reg ccts, check out National Semiconductor's app
notes series, now online.


Delco used a very thin double sided PC board at the input as a "Spark
plate", followed by a large filter choke. Anything over the voltage
rating of the gap arced over from the input lead, directly to the
radio's case.


--
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

In article om,
wrote:
re load dump

As I said how did a crude early germanium transistor radio survive,
then?

filtering on the power input. Its not too difficult, just needs to be
not missed out if you want reliability.

Or even half decent performance on a car radio?

--
*Errors have been made. Others will be blamed.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Michael A. Terrell wrote:
Delco used a very thin double sided PC board at the input as a "Spark
plate", followed by a large filter choke. Anything over the voltage
rating of the gap arced over from the input lead, directly to the
radio's case.

And this was used to protect against voltages of 50 or so? I really can't
see that being a reliable method in the hostile environment of a car.

BTW, the first transistor car radio I had was a hybrid kit where only the
AF was handled by transistors. Early '60s. No sign of anything like that
on it. Perhaps Lucas electrics couldn't produce much over 14 volts. ;-)

--
*On the other hand, you have different fingers*

Dave Plowman London SW
To e-mail, change noise into sound.

On 15 Dec 2006 18:55:15 -0800, wrote:

Dave Plowman (News) wrote:
In article ,
Jim Land wrote:

"An abrupt reduction in the alternator load causes a positive voltage
transient called "load dump." In a load dump transient the line voltage
rises to 20V or 30V in a few microseconds, then decays exponentially
with a time constant of about 100 microseconds. Much higher peak
voltages and longer decay times have also been reported. "The worst
case load dump is caused by disconnecting a low battery from the
alternator circuit while the alternator is running. Normally, this
would happen intermittently when the battery terminal connections are
defective. "Load Dump transients also occur when heavy loads are
switched off, although their magnitude and duration will be lower.
These transients are capable of destroying semiconductors on the first
'fault event'."

Given the number of semiconductors in use in the average vehicle - and
have been since the first transistor radio - it seems to be a problem that
has been solved...

Yes. However a resistive dropper does not solve it, nor does a simple
volt reg. A 12v vehicle system load dump onto a 6v tv would be a setup
waiting to fail.

Well, I think I could totally solve this problem by not running the
engine when I'm watching tv. I wasn't planning on actually driving
and watching tv, a fully charged battery should last a long time at
only 1.6 watts. Plus I have a Battery Buddy that disconnects my
battery when it is getting pretty low, while leaving enough to start
the car. It works great.

If the OP is incautious enough to do this, it should survive longer if
you never switch heavy loads on or off while the tv's connected. The
heaviest of course being the starter motor.

But I won't be starting the car, nor running the heater fan, or
anything more than the courtesy lights.

NT


If you are inclined to email me
for some reason, remove NOPSAM :-)

On Sat, 16 Dec 2006 09:43:11 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article .com,
wrote:
Given the number of semiconductors in use in the average vehicle - and
have been since the first transistor radio - it seems to be a problem
that has been solved...

Yes. However a resistive dropper does not solve it, nor does a simple
volt reg. A 12v vehicle system load dump onto a 6v tv would be a setup
waiting to fail.

I've got a few home built bits on my car with standard voltage regs with
no high voltage protection - they mostly are designed for peaks of around
40 volts, IIRC. The chances are the TV has internal voltage regulation too.

Maybe not since they only provided for 4 AA battery operation.

If the OP is incautious enough to do this, it should survive longer if
you never switch heavy loads on or off while the tv's connected. The
heaviest of course being the starter motor.

As I said how did a crude early germanium transistor radio survive, then?
But the quote said it was caused by the alternator. Which isn't charging
during cranking.


If you are inclined to email me
for some reason, remove NOPSAM :-)

On Fri, 15 Dec 2006 04:25:14 GMT, Ken Weitzel
wrote:

mm wrote:
I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.
.....
Hi...

Just thinking out loud; wouldn't it be so much easier and so
much more practical to just pick up a nimh/nicad charger that
works off of 110 or 12 volts, along with 8 batteries, and use
one set while charging the other?

This wouldn't work for me.

At the company Xmas party a few years ago, I won the raffle at the end
and won the boom box our boss had bought for music during the party.
He gave me the receipt too, with the suggestion there might be
something else I want more. The only thing the small store sold in
the same price range ($100) was this tv, so even though I didn't pay
for it, I have 100 dollars invested in the tv.

I don't want to spend the money for 8 rechargeable batteries for a tv
I have barely used in 10 years, and which will be obsolete** in 2 1/2
more years, PLUS a charger, plus the nuisance of connecting the
charger enough to have charged set when the other ones die, and
interchanging the batteries every time. I know you're helping, but
really, even ignoring the cost, I don't consider that easier at all,
compared to building something from parts I have around the house.

**Maybe I would find some other use for these batteries when the tv is
obsolete, but I haven't had such a use in all these years.

Thanks for the suggestion, though.

Take care.

Ken


If you are inclined to email me
for some reason, remove NOPSAM :-)

On Fri, 15 Dec 2006 05:35:38 -0000, Jim Land
wrote:

mm wrote in
:

I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.
....

Sounds like you have a good grasp of using a resistor to drop the
voltage, and the fact that if the car's battery voltage varies, so will
the voltage dropped by the resistor.

Better way: Use a voltage regulator IC to put out a constant 6 or 6.3
volts, even if the battery voltage varies (down to 10 or up to 15).

This sounds great but complicated. But something I would like to do.
OK, I looked into it during the intervening period and it's not
complicated. Mouser has the parts for under 3 dollars. Radio Shack
had the voltage regulator for 2.50, but Mouser wants about 90 cents
iirc. Shipping is free because I"m already ordering things.

Or,
easier, buy a power adapter that does essentially the same thing.

So far all the power adapters I've found with google are dedicated to
particular devices, like GPSes etc. I've seen them in the past.

If you are inclined to email me
for some reason, remove NOPSAM :-)

On 14 Dec 2006 23:57:35 -0800, "w_tom" wrote:

mm wrote:
I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.
...

Are you familiar with load dump?

No, I'm not. I googled load dump and read three of the sites, but I
picked wrong I guess and didn't learn much.

ISO says that voltage can be 270
volts. SGS Thompson defines it at 80 to 100 volts. Your design will
make load dump irrelevant. Cheaper inverters hope you never learn why
they are cheaper - while forgetting to include load dump protection.


If you are inclined to email me
for some reason, remove NOPSAM :-)

On Fri, 15 Dec 2006 09:24:40 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
mm wrote:
I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.

That is a crude method - far better to use a voltage regulator. The
output voltage may go too high under certain conditions

If I decide never to use the tv when the car is running, would that
prevent the high voltage problem? I don't see how it can go over 12.6
when the car is not running.

Maybe it will turn out that it won't work, but I can test the tv with
various images on the screen, all black, all white, or with no picture
and just sound, and find the minimum current that it uses, and choose
the resistor accordingly.

If the higher value resistor prevents the tv from working with a
mostly white screen, then I can go to a more expensive or more
complicated solution.

- like standby -
if you use just a resistor as that voltage is load dependant.

Like all these things it's probably cheaper to buy a ready made one.

It couldn't be unless your attributing a cost to my relaxation time,
which this would be part of.

Well I have all the parts now (for the resistor plan, not yet for the
votage regulator plan), and I do allocate time to relaxation and
projects like this.

If you are inclined to email me
for some reason, remove NOPSAM :-)

In article ,
mm wrote:
I've got a few home built bits on my car with standard voltage regs
with no high voltage protection - they mostly are designed for peaks of
around 40 volts, IIRC. The chances are the TV has internal voltage
regulation too.

Maybe not since they only provided for 4 AA battery operation.

Not much these days will work efficiently on raw volts from alkaline cells.

--
*Sleep with a photographer and watch things develop

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
mm wrote:
Are you familiar with load dump?

No, I'm not. I googled load dump and read three of the sites, but I
picked wrong I guess and didn't learn much.

I'd not bother anyway. It's a red herring now. Might have been relevant 50
years ago.

--
*Don't squat with your spurs on *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
Michael A. Terrell wrote:

Delco used a very thin double sided PC board at the input as a "Spark
plate", followed by a large filter choke. Anything over the voltage
rating of the gap arced over from the input lead, directly to the
radio's case.

And this was used to protect against voltages of 50 or so? I really can't
see that being a reliable method in the hostile environment of a car.

I dont think 50v would jump that. The LC is what does the work. The L
limits how much i will flow during load dump, and the C means that i
flow results in little v change.


BTW, the first transistor car radio I had was a hybrid kit where only the
AF was handled by transistors. Early '60s. No sign of anything like that
on it. Perhaps Lucas electrics couldn't produce much over 14 volts. ;-)

I presume it had an LC power filter.

Last time I had Lucas electrics it boiled the battery.


NT

Dave Plowman (News) wrote:
In article ,
mm wrote:

Are you familiar with load dump?

No, I'm not. I googled load dump and read three of the sites, but I
picked wrong I guess and didn't learn much.

I'd not bother anyway. It's a red herring now. Might have been relevant 50
years ago.

Far from. Alternators are still as inductive as they were, and a read
of National's app notes explains the whole thing and gives load dump
proofed circuits. Your kit may survive if you ignore it, but I'd say
the risks are significant.


NT

In article . com,
wrote:
I'd not bother anyway. It's a red herring now. Might have been
relevant 50 years ago.

Far from. Alternators are still as inductive as they were, and a read
of National's app notes explains the whole thing and gives load dump
proofed circuits. Your kit may survive if you ignore it, but I'd say
the risks are significant.

I'm trying to think how many home made electronic additions I've got on
the old car - but it's lots. Things like a PDC. Electronic charge
indicator (useful with Lucas alternator) Timer for rear window. Better
controller for the central locking. 'One touch' electric window mods - and
sunroof too. And plenty others (I have a new car too and want some of the
toys on the old one and it's a hobby).

And none of them containing anything other than the usual smoothing and
decoupling. All using just basic op-amps, timers etc. And not one has
blown up. Perhaps it's because I didn't know about 'load dump' Now I do
they'll all start failing...

--
*Why is it considered necessary to screw down the lid of a coffin?

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article . com,
wrote:
I'd not bother anyway. It's a red herring now. Might have been
relevant 50 years ago.

Far from. Alternators are still as inductive as they were, and a read
of National's app notes explains the whole thing and gives load dump
proofed circuits. Your kit may survive if you ignore it, but I'd say
the risks are significant.

I'm trying to think how many home made electronic additions I've got on
the old car - but it's lots. Things like a PDC. Electronic charge
indicator (useful with Lucas alternator) Timer for rear window. Better
controller for the central locking. 'One touch' electric window mods - and
sunroof too. And plenty others (I have a new car too and want some of the
toys on the old one and it's a hobby).

And none of them containing anything other than the usual smoothing and
decoupling. All using just basic op-amps, timers etc. And not one has
blown up. Perhaps it's because I didn't know about 'load dump' Now I do
they'll all start failing...

You have met Mr Murphy, have you not?

Ken

"Dave Plowman (News)" wrote:

In article ,
Michael A. Terrell wrote:
Delco used a very thin double sided PC board at the input as a "Spark
plate", followed by a large filter choke. Anything over the voltage
rating of the gap arced over from the input lead, directly to the
radio's case.

And this was used to protect against voltages of 50 or so? I really can't
see that being a reliable method in the hostile environment of a car.


It was paper thin phenolic PC board, and Delco claimed that it would
arc over below 50 volts when I went to the factory school. I asked the
engineers so many questions that they stopped answering. They thought
that I was after their jobs. ;-)


BTW, the first transistor car radio I had was a hybrid kit where only the
AF was handled by transistors. Early '60s.


Delco was building hybrids in the late '50s with a DS501/2N441
doorknob germanium output transistor:

Industry Number : DS501
NTE Device Number: NTE105
T-PNP, GERMANIUM AUDIO PO, TO-36 Case

Other companies used tubes designed for 12 volts on the plates in the
aerly '60s while Delco was building all transistor units.


No sign of anything like that
on it. Perhaps Lucas electrics couldn't produce much over 14 volts. ;-)


From what I've heard about Lucas you were lucky it didn't go up in
flames the first time it was turned on.



--
*On the other hand, you have different fingers*

Dave Plowman London SW
To e-mail, change noise into sound.


--
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

"Dave Plowman (News)" wrote:

In article . com,
wrote:
I'd not bother anyway. It's a red herring now. Might have been
relevant 50 years ago.


50 years ago there were no semiconductors in a car's electrical
system to worry about.


Far from. Alternators are still as inductive as they were, and a read
of National's app notes explains the whole thing and gives load dump
proofed circuits. Your kit may survive if you ignore it, but I'd say
the risks are significant.

I'm trying to think how many home made electronic additions I've got on
the old car - but it's lots. Things like a PDC. Electronic charge
indicator (useful with Lucas alternator) Timer for rear window. Better
controller for the central locking. 'One touch' electric window mods - and
sunroof too. And plenty others (I have a new car too and want some of the
toys on the old one and it's a hobby).

And none of them containing anything other than the usual smoothing and
decoupling. All using just basic op-amps, timers etc. And not one has
blown up. Perhaps it's because I didn't know about 'load dump' Now I do
they'll all start failing...


If your battery develops an open cell, or the cable falls off you'll
lose lots of electronics. Go to news:sci.electronics.design and tell
them that "Load Dump" in automotive electrical systems is a myth. They
will tell you just how wrong you are.


--
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

mm wrote:

If the higher value resistor prevents the tv from working with a
mostly white screen, then I can go to a more expensive or more
complicated solution.


The current load will vary with brightness and volume changes. Not a
good idea, unless you want to damage the TV.


--
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

mm wrote:
I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.

My experience is that fully charged AA batteries are usually 1.56
volts x 4 = 6.3 volts, which is exactly half of the resting voltage of
fully charged car batteries, 12.6 volts. I won't be watching tv when
the car is running, but maybe I would sometimes run the car to charge
the car battery, or even to warm the car** Then, iirc and I can
measure it to be sure, the voltage goes up as high as 13.2, half of
which is 6.6. Also, the label on the back of the tv says that it
uses, on average, 1.6 watts, but I will measure its current current
use and not rely on that.

Is that too high for a tv that is meant to run on 6.3? If so, I'll be
glad to make the resistor bigger and thus the voltage lower.

It also has provision for turning off the picture and only getting the
sound. I guess it would use less current then and I would calculate a
higher resistor to be needed. Maybe I should just use a resistor
substitution box and see at what resistance the tv works best? Or
should I buy a device made for this purpose. I have a spare cell
phone charger, but I don't think it wil put out a full 1.6 watts.)

Thanks


**On my best car trip, I slept in the car for 7 or 8 nights in a row.
It was very comfortable but it was a much bigger car, so I'm not sure
I can do even one or two nights this time, but I want to get some use
out of my 2 inch tv, which I got as a gift sort of, and which will be
obsolete in 36 months or so. For tht reason alone, I'd like to sleep
in the car rather than a motel. Or probably more likely, in a tent in
a state park, in late winter or early spring, in the South, where I
guess it will be warm enough. If I stay in a tent, I'll make a longer
wire.

If you are inclined to email me
for some reason, remove NOPSAM :-)
Radio Shack has a cig adaptor that is voltage selectable and has many
pugable jacks that fit most everything for around 20 bucks