battery protection circuits

[iggs]

This is probably the wrong place to ask this :duh2:

anyway

I noticed someone had mentioned circuits to protect batteries from full discharge on something the other day.

Does anyone know where I could find info on this? Is it relevent to only Li-Ion or also to NiMH?

I've seen posts from george80 about the maxflex cabaility of easily sucking batteries too dry oo:

 

[Szemhazai]

They are commonly used only for Li-Ion cells, you can get them there :
http://www.batteryjunction.com/licyba181417.html

 

[richdsu]

Some Info on Protected Lion Battery :->

http://www.buchmann.ca/Article5-Page1.asp

http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=461

 

[georges80]

The protection circuits for li-ion cells typically protect from overdischarge, but also from short circuits (i.e. they limit the current that can be drawn) and some also prevent overcharge.

With nFlex/bFlex or maxFlex it is prudent to set the voltage monitoring to warn you if the voltage gets below a certain threshold. This is good for not just li-ion cells but any multicell rechargeable. Even with NiMH cells you don't want to overdischarge them since you also run the risk of reversing the polarity of one or more cells. This won't typically cause a bang risk like in li-ion cells, but it will still damage your NiMH cells.

So, even though the nFlex/bFlex/maxFlex voltage monitoring is a good safety feature - for li-ion cells I'd still recommend protected cells or protection circuits (not quite as good) to reduce the risk of damage or bangs if something more catastrophic occurs like a short in the pack, or to the body, or to the driver/wiring etc.

cheers,
george.

 

[n2dsky]

What would be the "best" low voltage threshold setting on a bFlex for a 14.4v NiMH pack?

Thanks

Steve

The protection circuits for li-ion cells typically protect from overdischarge, but also from short circuits (i.e. they limit the current that can be drawn) and some also prevent overcharge.

With nFlex/bFlex or maxFlex it is prudent to set the voltage monitoring to warn you if the voltage gets below a certain threshold. This is good for not just li-ion cells but any multicell rechargeable. Even with NiMH cells you don't want to overdischarge them since you also run the risk of reversing the polarity of one or more cells. This won't typically cause a bang risk like in li-ion cells, but it will still damage your NiMH cells.

So, even though the nFlex/bFlex/maxFlex voltage monitoring is a good safety feature - for li-ion cells I'd still recommend protected cells or protection circuits (not quite as good) to reduce the risk of damage or bangs if something more catastrophic occurs like a short in the pack, or to the body, or to the driver/wiring etc.

cheers,
george.

 

[georges80]

What would be the "best" low voltage threshold setting on a bFlex for a 14.4v NiMH pack?

Thanks

Steve

Typically a NiMH cells is reasonably run down at 1.1V per cell (so that would be the med/low setting). At 1.0V per cell I'd call it quits and say it's flat.

So 12V would be the 'flat' setting assuming 12 Cells. And somewhere around 13.2V would be 1/2 discharged.

It depends on the cells as well - not all NiMH cells behave exactly the same.

cheers,
george.

 

[Darell]

This is probably the wrong place to ask this :duh2:

I assume you're asking this in regard to a bike light you're wanting to build... in the future this stuff is usually better handled in the electronics forum.