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Multiple output isolated DC/DC supply

D

dt

Jan 1, 1970
0
Hi, I need to charge lithium batteries (3 to 12 cell packs) and
prevent individual cells from exceeding the desired voltage (4.2v
each). This is most commonly done in hobby circles using a charger
that takes the overall pack up to the desired total voltage (eg: 12.6v
for 3 cells) and a separate balancer circuit to try to keep each cell
the same.

What I would prefer is a charger than can charge each cell
individually to 4.2v and eliminate the need for the balancer circuit.
Single cell lithium charging chips are readily available, and if I
were to supply each of these from separate 5v mains power supplies I
could daisy chain any number together and achieve my objectives. An
example of what I mean is shown in this post if I'm not clear: http://
www.rcgroups.com/forums/showpost.php?p=6049417&postcount=4

However, I would like to do this from a single 12v car battery source.
So I need a step-down design with up to 12 isolated outputs (~5V
each). I need at least 3A each, preferably more. Does anyone know of a
elegant way of achieving this please?
Thanks, David.
 
L

linnix

Jan 1, 1970
0
Hi, I need to charge lithium batteries (3 to 12 cell packs) and
prevent individual cells from exceeding the desired voltage (4.2v
each). This is most commonly done in hobby circles using a charger
that takes the overall pack up to the desired total voltage (eg: 12.6v
for 3 cells) and a separate balancer circuit to try to keep each cell
the same.

What I would prefer is a charger than can charge each cell
individually to 4.2v and eliminate the need for the balancer circuit.
Single cell lithium charging chips are readily available, and if I
were to supply each of these from separate 5v mains power supplies I
could daisy chain any number together and achieve my objectives. An
example of what I mean is shown in this post if I'm not clear: http://www.rcgroups.com/forums/showpost.php?p=6049417&postcount=4

However, I would like to do this from a single 12v car battery source.
So I need a step-down design with up to 12 isolated outputs (~5V
each).

Usually, that for isolating AC. Very difficult to isolate DC in this
situation.
I need at least 3A each, preferably more. Does anyone know of a
elegant way of achieving this please?

Alternative is to switch cells in/out of charger or to switch by-pass
loads.
 
Y

Yzordderrex

Jan 1, 1970
0
Hi, I need to chargelithiumbatteries (3 to 12 cell packs) and
prevent individual cells from exceeding the desired voltage (4.2v
each). This is most commonly done in hobby circles using a charger
that takes the overall pack up to the desired total voltage (eg: 12.6v
for 3 cells) and a separate balancer circuit to try to keep each cell
the same.

What I would prefer is a charger than can charge each cell
individually to 4.2v and eliminate the need for the balancer circuit.
Single celllithiumcharging chips are readily available, and if I
were to supply each of these from separate 5v mains power supplies I
could daisy chain any number together and achieve my objectives. An
example of what I mean is shown in this post if I'm not clear: http://www.rcgroups.com/forums/showpost.php?p=6049417&postcount=4

However, I would like to do this from a single 12v car battery source.
So I need a step-down design with up to 12 isolated outputs (~5V
each). I need at least 3A each, preferably more. Does anyone know of a
elegant way of achieving this please?
Thanks, David.

Off the top of my head I think thats 180w. You could probably get
that with one of those Topswithc GX controllers from Power
Integrations. 12 secondary windings would track reasonably well.

Although I think you said a car battery for the input.

Then I would probably just use a homebrew open loop half-bridge to get
the isolated supplies.

then drive some battery charger chips. I think TI has benchmark or
use a simple switcher and homebrew the output side too.

many ways to skin this cat.
 
M

me

Jan 1, 1970
0
Off the top of my head I think thats 180w. You could probably get
that with one of those Topswithc GX controllers from Power
Integrations. 12 secondary windings would track reasonably well.

Although I think you said a car battery for the input.

Then I would probably just use a homebrew open loop half-bridge to get
the isolated supplies.

then drive some battery charger chips. I think TI has benchmark or
use a simple switcher and homebrew the output side too.

many ways to skin this cat.

why use separate supplies? just use one high current source....
 
D

dt

Jan 1, 1970
0
why use separate supplies? just use one high current source....

The 12 cell pack is my biggest problem. Its not practical to parallel
them for charging purposes.
You've given me a few ideas to pursue.
Thank you, David.
 
Y

Yzordderrex

Jan 1, 1970
0
The 12 cell pack is my biggest problem. Its not practical to parallel
them for charging purposes.
You've given me a few ideas to pursue.
Thank you, David.- Hide quoted text -

- Show quoted text -

I'm fast becoming an expert on these chargers. I didn't know what a
Li-ion battery pack was two weeks ago. This stuff is great fun. Have
you tried those A123 systems batteries. I have wallpaper on my work
machine of a guy doing a burnout on a 9 second electric bike powered
by Li-ion.

Check it out.

http://www.electrifyingtimes.com/a123/KillaCycle.html

regards,
NEO
 
D

dt

Jan 1, 1970
0
I'm fast becoming an expert on these chargers. I didn't know what a
Li-ion battery pack was two weeks ago. This stuff is great fun. Have
you tried those A123 systemsbatteries. I have wallpaper on my work
machine of a guy doing a burnout on a 9 second electric bike powered
by Li-ion.

Check it out.

http://www.electrifyingtimes.com/a123/KillaCycle.html

regards,
NEO

Yes I'm using A123's and LiPo's. The A123's are more forgiving but
still need balancing if taken to their boundary voltages. Regards,
David.
 
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