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Topic: 3S lipo carger (Read 989 times) previous topic - next topic

robvoi

Hi,

I have a Robot which is powered by a 3S/11.1 Lipo.
I would like the robot to dock to a charging station to charge its lipo.

Does somebody know a good solution for charging the Lipo with balancing? There are great Lipo shields. But they are for 1S/3.7V Lipos.

A solution with which the robot could stay on during charging would be perfect.

Thanks
Robert

MarkT

All multi-cell LiPo chargers should be balancing chargers, LiPo's easily catch fire if charged unbalanced.

Your main problem will be docking - a balancing charger needs n+1 reliable contacts for n cells in series,
which might be mechanically tricky.
[ I won't respond to messages, use the forum please ]

robvoi

That's why I was hoping that there is something like a multi cell lipo shield. So a balancing charger I just need to supply with two contacts.

joe mcd

How can the charger perform balance with only 2 contacts?  'Balancing' means keeping all cells at equal voltage during charge.

Chagrin

With respect to preventing overcharge / overdischarge of individual cells you can implement a battery protection circuit: http://www.all-battery.com/protectivepcbsforli-ionandli-polymerbatterypacks.aspx.

MarkT


That's why I was hoping that there is something like a multi cell lipo shield. So a balancing charger I just need to supply with two contacts.

You want a LiPo battery management system on the battery, one that takes a simple 2 wire power source
as input and that can stay connected during discharge - normally this would be called a BMS.
[ I won't respond to messages, use the forum please ]

joe mcd

An imbalance between cells can only be corrected if ALL cells are connected.

Quote
You want a LiPo battery management system on the battery, one that takes a simple 2 wire power source


That is the main charging current.  The balancing currents travel thru smaller gauge wires.
See attached image of a 3-cell LiPo under recharge on a Turnigy charger.

Look at the earlier reference closely:
http://www.all-battery.com/protectivepcbsforli-ionandli-polymerbatterypacks.aspx
You will see the multiple connections.  For example:
http://www.all-battery.com/protectioncircuitmodulepcbfor111vli-ionbatterypack3cellswith65alimit-pcb111v65a.aspx

Charging at 2 points only cannot work because the cells cannot have exactly the same capacity.  Inevitable one cell will overcharge.  Overcharging not a good idea on LiPo cells.  They contain finely divided Lithium metal and can burn vigourously when unhappy.

Trust me, I worked as a chemist with Lithium.  You not want to see it catch fire.


robvoi

Thanks for all the replies. What I then realy need is a complete Balancer and BPS - portable.
I think in this case it will be easier to build a solid five point connection for the robot and use my standard LIPO charger.

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