Opinions about a battery circuit - proposed block diagram

max72

I would like your opinion about the following block diagram:
I would like to make a small circuit to be used with two protected li-ion batteries.
The circuit should be able to switch between the two modes here described:
mode 1: the two batteries are in series, and the output is directed to the instrument
in case of external 12V nothing is affected

mode 2: there is a 12V external supply. The two batteries are disconnected and individually recharged by two max1555. The 12V input is also regulated and directed to the instrument, in place of the double li-ion supply.

Everything is driven by a 4PDT switch.
This is only the functional diagram. For sure I must identify suitable regulators, and provide a handful of caps around.

Would this approach work?

Thanks in advance
Massimo

Peter KG6LSE

Charge in para discharge in series .. The Idea works but may I recommend the same thing but in a COTS form!

http://www.parallax.com/product/28989



From what it sounds like this does the same thing .

Peter

Duane C. Johnson

Hi Massimo;

max72 wrote: »

I would like your opinion about the following block diagram:
I would like to make a small circuit to be used with two protected li-ion batteries.
The circuit should be able to switch between the two modes here described:
mode 1: the two batteries are in series, and the output is directed to the instrument
in case of external 12V nothing is affected

mode 2: there is a 12V external supply. The two batteries are disconnected and individually recharged by two max1555. The 12V input is also regulated and directed to the instrument, in place of the double li-ion supply.

Everything is driven by a 4PDT switch.
This is only the functional diagram. For sure I must identify suitable regulators, and provide a handful of caps around.

Would this approach work?

Yes it would work.

But you only need 1 charge regulator instead of 2.

Duane J

max72

Thanks for the answers
Peter: Parallax power pack has functions very close to what I'm looking for, in case I use the UPS configuration. I would need a separated regulator. I would use a 12V, so I need also an external regulator and the extra diodes. I was thinking of a stripped down version to simplify the board.

Duane: Why only one charge regulator? I thought the two batteries would require a dedicated charger..

Massimo

Mark_T

There must be a one-chip solution for charging/balancing two LiPo's in series - would be simpler than this series/parallel switchover.

Duane C. Johnson

Hi Massimo;

max72 wrote: »

Duane: Why only one charge regulator? I thought the two batteries would require a dedicated charger..

The spec for the MAX1555 does say it is designed to charge a single cell.

However, in your relay circuit the pair of cells, when in charge mode, look just like a single cell of twice the capacity. I can find no limit in the spec to the maximum cell capacity.

Another reason to use only one MAX1555 is it limits the charge current from a USB port to about 100mA. Two of these would make it 200mA which would exceed the unpowered USB port spec.

Duane J

max72

Thanks.
There are multicell solutions, but are much more complex. I like max1555 because it is so easy to use. Maybe not fast, but I don't care.
I would charge it from wall wart or 12V lead gel battery (or car battery) when on the field, but for sure a single regulator solution would simplify even more.

Massimo