EEs step in.

Page 2 - Seeking answers? Join the AnandTech community: where nearly half-a-million members share solutions and discuss the latest tech.
Toggle sidebar Toggle sidebar
M

mrrman

Diamond Member
Feb 8, 2004
8,498
3
0
Originally posted by: PhasmatisNox
Originally posted by: FrustratedUser
Woah!!

This thread is full of useless advice. The guy is not going to use fuel cells people. He's using sealed lead batteries, also called gel cells.

Here's what you need for the simplest solution:

LM350 (take a 3A version) - linear adjustable voltage regulator
2 resistors.

16V out from 18V in means a drop of 2V over the regulator.
At 2A load this comes out to 2x2W = 4W heat, which means you need a heatsink.

Bottom of page 5 shows how to make one.
Click to expand...

When I made this thread I was thinking 18v, but now it's looking more like 24v. I want to put the whole thing in an aluminum enclosure, and use that as heatsink. I think a nice Al enclosure that looks professional would put the airport security inspectors at ease a bit, too.
Click to expand...


Until TSA finds out its a fuel cell that you are packing, consider it gone
 
F

FrustratedUser

Lifer
Aug 16, 2001
22,529
4
81
Originally posted by: PhasmatisNox
Originally posted by: FrustratedUser
Woah!!

This thread is full of useless advice. The guy is not going to use fuel cells people. He's using sealed lead batteries, also called gel cells.

Here's what you need for the simplest solution:

LM350 (take a 3A version) - linear adjustable voltage regulator
2 resistors.

16V out from 18V in means a drop of 2V over the regulator.
At 2A load this comes out to 2x2W = 4W heat, which means you need a heatsink.

Bottom of page 5 shows how to make one.
Click to expand...

When I made this thread I was thinking 18v, but now it's looking more like 24v. I want to put the whole thing in an aluminum enclosure, and use that as heatsink. I think a nice Al enclosure that looks professional would put the airport security inspectors at ease a bit, too.
Click to expand...

At 24V the heat losses with a linear regulator will be too much. In this case 16W and that will get real hot.
You need to go with a switched regulator as suggested before.
Just a note. My dad built himself a package with an external battery for his video camera. he had it strapped to his waist when going through security.........
They thought he carried a bomb.
 
D

dighn

Lifer
Aug 12, 2001
22,820
4
81
Originally posted by: FrustratedUser
Woah!!

This thread is full of useless advice. The guy is not going to use fuel cells people. He's using sealed lead batteries, also called gel cells.

Here's what you need for the simplest solution:

LM350 (take a 3A version) - linear adjustable voltage regulator
2 resistors.

16V out from 18V in means a drop of 2V over the regulator.
At 2A load this comes out to 2x2W = 4W heat, which means you need a heatsink.

Bottom of page 5 shows how to make one.
Click to expand...

but what is the dropout? that datasheet doesn't say, but the one from national says >2v at 3A, then you can't guarantee 16v. with usage the battery voltage will drop below 18 too.
 
T

TitanDiddly

Guest
Dec 8, 2003
12,696
1
0
Originally posted by: mrrman
Originally posted by: PhasmatisNox
Originally posted by: FrustratedUser
Woah!!

This thread is full of useless advice. The guy is not going to use fuel cells people. He's using sealed lead batteries, also called gel cells.

Here's what you need for the simplest solution:

LM350 (take a 3A version) - linear adjustable voltage regulator
2 resistors.

16V out from 18V in means a drop of 2V over the regulator.
At 2A load this comes out to 2x2W = 4W heat, which means you need a heatsink.

Bottom of page 5 shows how to make one.
Click to expand...

When I made this thread I was thinking 18v, but now it's looking more like 24v. I want to put the whole thing in an aluminum enclosure, and use that as heatsink. I think a nice Al enclosure that looks professional would put the airport security inspectors at ease a bit, too.
Click to expand...


Until TSA finds out its a fuel cell that you are packing, consider it gone
Click to expand...

Where the heck did people get the idea that I'm using fuel cells?

I am not using fuel cells. K? I'm using gel-cell lead acid batteries, which are safe. You can cut a good one in half with a bandsaw and have no leakage.
 
H

helpme

Diamond Member
Feb 6, 2000
3,090
0
0
I think jjzelinski wrote fuel cells instead of gel cells in his first post by accident ?
 
R

RaynorWolfcastle

Diamond Member
Feb 8, 2001
8,968
16
81
I'm an EE student and honestly, while the switching regulator business should work in theory, managing these large currents is going to require some careful planning. The next issue is that you don't really know what exactly the laptop expects in term of regulation.

Finally, Li-Ion batteries (well pretty much any battery for that matter) have a range of voltages over which they operate. The actual output voltage supplied depends on the the impedance of what you're feeding it into, how old the battery is, how charged it is etc. To give you an idea, a typical alkaline AA battery's voltage can go from about 1.6V down to about 0.9V depending on the conditions in which it's operating. This obviously means that you need to regulate this power one way or another. You're going to need to look into the battery specs and even then I don't know how much information you'll be able to dig up on what exactly your laptop is expecting.

I don't know whether the laptop manufacturers usually put the regulating circuits in the battery pack or in the laptop, so that's another consideration.

The easiest thing would probably be to buy extra batteries.
 
J

jjzelinski

Diamond Member
Aug 23, 2004
3,750
0
0
Originally posted by: RaynorWolfcastle
I'm an EE student and honestly, while the switching regulator business should work in theory, managing these large currents is going to require some careful planning. The next issue is that you don't really know what exactly the laptop expects in term of regulation.

Finally, Li-Ion batteries (well pretty much any battery for that matter) have a range of voltages over which they operate. The actual output voltage supplied depends on the the impedance of what you're feeding it into, how old the battery is, how charged it is etc. To give you an idea, a typical alkaline AA battery's voltage can go from about 1.6V down to about 0.9V depending on the conditions in which it's operating. This obviously means that you need to regulate this power one way or another. You're going to need to look into the battery specs and even then I don't know how much information you'll be able to dig up on what exactly your laptop is expecting.

I don't know whether the laptop manufacturers usually put the regulating circuits in the battery pack or in the laptop, so that's another consideration.

The easiest thing would probably be to buy extra batteries.
Click to expand...

That's exactly why I suggested that he try to incorporate the ac adapter supplied.
 
R

RaynorWolfcastle

Diamond Member
Feb 8, 2001
8,968
16
81
Originally posted by: jjzelinski
Originally posted by: RaynorWolfcastle
I'm an EE student and honestly, while the switching regulator business should work in theory, managing these large currents is going to require some careful planning. The next issue is that you don't really know what exactly the laptop expects in term of regulation.

Finally, Li-Ion batteries (well pretty much any battery for that matter) have a range of voltages over which they operate. The actual output voltage supplied depends on the the impedance of what you're feeding it into, how old the battery is, how charged it is etc. To give you an idea, a typical alkaline AA battery's voltage can go from about 1.6V down to about 0.9V depending on the conditions in which it's operating. This obviously means that you need to regulate this power one way or another. You're going to need to look into the battery specs and even then I don't know how much information you'll be able to dig up on what exactly your laptop is expecting.

I don't know whether the laptop manufacturers usually put the regulating circuits in the battery pack or in the laptop, so that's another consideration.

The easiest thing would probably be to buy extra batteries.
Click to expand...

That's exactly why I suggested that he try to incorporate the ac adapter supplied.
Click to expand...

Going from DC to AC back to DC is hardly ideal. Also, to convert to AC he's going to have to step up the voltage big time since a wall socket is 120V (IIRC) which means more heat and more complications. Seriously, buying an extra battery is probably the easiest thing.
 
J

jjzelinski

Diamond Member
Aug 23, 2004
3,750
0
0
Originally posted by: RaynorWolfcastle
Originally posted by: jjzelinski
Originally posted by: RaynorWolfcastle
I'm an EE student and honestly, while the switching regulator business should work in theory, managing these large currents is going to require some careful planning. The next issue is that you don't really know what exactly the laptop expects in term of regulation.

Finally, Li-Ion batteries (well pretty much any battery for that matter) have a range of voltages over which they operate. The actual output voltage supplied depends on the the impedance of what you're feeding it into, how old the battery is, how charged it is etc. To give you an idea, a typical alkaline AA battery's voltage can go from about 1.6V down to about 0.9V depending on the conditions in which it's operating. This obviously means that you need to regulate this power one way or another. You're going to need to look into the battery specs and even then I don't know how much information you'll be able to dig up on what exactly your laptop is expecting.

I don't know whether the laptop manufacturers usually put the regulating circuits in the battery pack or in the laptop, so that's another consideration.

The easiest thing would probably be to buy extra batteries.
Click to expand...

That's exactly why I suggested that he try to incorporate the ac adapter supplied.
Click to expand...

Going from DC to AC back to DC is hardly ideal. Also, to convert to AC he's going to have to step up the voltage big time since a wall socket is 120V (IIRC) which means more heat and more complications. Seriously, buying an extra battery is probably the easiest thing.
Click to expand...

You know the whole 120v thing somehow never occured to me :eek:

I'll be leaving now :D

 
F

FrustratedUser

Lifer
Aug 16, 2001
22,529
4
81
Originally posted by: dighn
Originally posted by: FrustratedUser
Woah!!

This thread is full of useless advice. The guy is not going to use fuel cells people. He's using sealed lead batteries, also called gel cells.

Here's what you need for the simplest solution:

LM350 (take a 3A version) - linear adjustable voltage regulator
2 resistors.

16V out from 18V in means a drop of 2V over the regulator.
At 2A load this comes out to 2x2W = 4W heat, which means you need a heatsink.

Bottom of page 5 shows how to make one.
Click to expand...

but what is the dropout? that datasheet doesn't say, but the one from national says >2v at 3A, then you can't guarantee 16v. with usage the battery voltage will drop below 18 too.
Click to expand...

The drop out is what you set it to be with a minimum for a normal regulator of 1.5V
To generate 16V he will need a minimum of 17.5V on the input. The output voltage is programmed with 2 resistors.
If you set the output to be 12V with an input of 16V the drop out will be 4V.
 
R

RaynorWolfcastle

Diamond Member
Feb 8, 2001
8,968
16
81
Originally posted by: FrustratedUser

The drop out is what you set it to be with a minimum for a normal regulator of 1.5V
To generate 16V he will need a minimum of 17.5V on the input. The output voltage is programmed with 2 resistors.
If you set the output to be 12V with an input of 16V the drop out will be 4V.
Click to expand...
Right, but regulators have minimum dropout voltages.
 
D

dighn

Lifer
Aug 12, 2001
22,820
4
81
Originally posted by: FrustratedUser

The drop out is what you set it to be with a minimum for a normal regulator of 1.5V
To generate 16V he will need a minimum of 17.5V on the input. The output voltage is programmed with 2 resistors.
If you set the output to be 12V with an input of 16V the drop out will be 4V.
Click to expand...

it was a rhetorical question. what i meant is that at 3a, the dropout is at least 2v, so 18 -> 16 is not going to work with the component you suggested
 
S

sciencewhiz

Diamond Member
Jun 30, 2000
5,885
8
81
Originally posted by: FrustratedUser

The drop out is what you set it to be with a minimum for a normal regulator of 1.5V
To generate 16V he will need a minimum of 17.5V on the input. The output voltage is programmed with 2 resistors.
If you set the output to be 12V with an input of 16V the drop out will be 4V.
Click to expand...

The national datasheed for the lm350 shows the dropout voltage to be 2.5v at 3a. That's too high to be comfortable going from 18v to 16v.
 
F

FrustratedUser

Lifer
Aug 16, 2001
22,529
4
81
Originally posted by: sciencewhiz
Originally posted by: FrustratedUser

The drop out is what you set it to be with a minimum for a normal regulator of 1.5V
To generate 16V he will need a minimum of 17.5V on the input. The output voltage is programmed with 2 resistors.
If you set the output to be 12V with an input of 16V the drop out will be 4V.
Click to expand...

The national datasheed for the lm350 shows the dropout voltage to be 2.5v at 3a. That's too high to be comfortable going from 18v to 16v.
Click to expand...

You can use a LDO regulator like the MIC 29300 from Micrel. They have dropout of <400mV.
I thionk you can buy them from Newark.
 
You must log in or register to reply here.

TRENDING THREADS

COMPANY
RESOURCES
FOLLOW
Top Bottom