Are 'balancers' even necessary?

[Solarfun4jim]

In a Lifepo4 battery pack system, whereby charging would be 0.1CA, discharging would be 0.4CA(10% of time)& 0.1CA (90%of time), running from 3.1V/cell to 3.4v/cell capacity wise....any reason to consider any balancing measures whatsoever? If pack is top balanced initially and then never taken into the knees, why would you need any balancing function?

 

[snoobler]

Currents don't matter much. It really depends on the cells. There are other factors that can impact efficiency including internal resistance, variations in cell construction, etc.

Note that with a charge voltage of 3.4V/cell, you will still get to 85%+ SoC assuming you terminate the instant you hit 3.4V. If you continue charging to low current levels, you can hit 95%.

Do you need active balancing? Absolutely not. Do you need passive balancing? Probably not. Should you engage in passive top balancing during charges only? Probably.

 

[Solarfun4jim]

Currents don't matter much. It really depends on the cells. There are other factors that can impact efficiency including internal resistance, variations in cell construction, etc.

Note that with a charge voltage of 3.4V/cell, you will still get to 85%+ SoC assuming you terminate the instant you hit 3.4V. If you continue charging to low current levels, you can hit 95%.

Do you need active balancing? Absolutely not. Do you need passive balancing? Probably not. Should you engage in passive top balancing during charges only? Probably.

@snoobler
Thanks snoobler for the reply. My thinking was, that since the cell difference(in my 24v pack) was remaining below 10mv charging up to about 3.43v and discharging down to below 3.0, then i will never be pushing these cells to the point where balancing would operate anyways. What i dont know, is whether or not over the period of say 12 months, the cells will drift such that the 10mv difference becomes 20mv?
I am only looking to run these cells/pack from approx 15% to 85% SOC capacity wise....so i was really hoping to set once and forget.

 

[snoobler]

That's why I said "probably" to just passive balance on charge. It helps to maintain the top balance you've already done meaning that no matter how long it goes, it prevents drift. It's essentially as "set once and forget" situation.

 

[Solarfun4jim]

That's why I said "probably" to just passive balance on charge. It helps to maintain the top balance you've already done meaning that no matter how long it goes, it prevents drift. It's essentially as "set once and forget" situation.

So, would you set it to activate from about say 3.3v/cell up to the 3.4v/cell cut off, with minimum cell difference value, bearing in mind i dont really want to 'bleed off' what little solar energy i'm harvesting? What do you see as the ideal trade off?

 

[snoobler]

3.35V during charging only.

Consider that something like an overkill uses 35mA of current. That's 0.3kWh per year.

 

[Solarfun4jim]

3.35V during charging only.

Consider that something like an overkill uses 35mA of current. That's 0.3kWh per year.

Cheers snoobler, thanks for the input.