Lipo charging questions - RC-Monster Forums

Big House · **Lipo charging questions -** 12.17.2010, 01:44 AM

I currently charge my lipos based on the mAh rating of the battery. What I mean by that is I set my charger (Hyperion 0606) to the charge rate of 5c. Now here is my question, should I base a full charge off the voltage I see through the balancer or should I be charging up to the mAh level indicated on the battery. The charger can display both.

What's_nitro? · 12.17.2010, 01:53 AM

You should base a full charge on when the charger stops and says it's full...

It's unlikely a battery would ever take it's rated mAH back in during a charge. If it did, it was probably way over-discharged prior to then...

But yeah, ALL lipo chargers will stop automatically when the battery is full. If you watch the screen it's usually when the voltage is peaked at 4.2v/cell and the charge current drops below 100mA.

simplechamp · 03:29 AM

Always base a full charge on voltage being 4.2V/cell.

My Zippy 5000mah packs will take more than 5000mah back in to reach 4.2V/cell after being fully discharged to 3.0V/cell. If I only allow the charger to put 5000mah back in they wouldn't reach 4.2V/cell and might only get to say 4.17V/cell

So I would have to disagree what's_nitro, I don't think 3.0V/cell is way over-discharged, and mine will take more than 5000mah according to the charger.

What's_nitro? · 03:40 AM

Then your packs are severly under-rated, which is not typical. If your packs were resting at 3v/cell I'd still say they were overdischarged. More props to Zippy if they hold up well to this 100+% capacity cycling...

simplechamp · 12.17.2010, 04:14 AM

You are right, they aren't resting at 3.0V/cell, I have the cutoff set there but by the time I get home and charge them up they have rebound to probably 3.2-3.3V/cell. But that would actually imply the capacity is even higher. Anyway, they definitely hold their rated capacity and then some!

So in this case the packs might be underrated, but packs can be properly rated or overrated too. That is why you rely on voltage to determine a full charge, and not rated capacity.

BrianG · 12.17.2010, 10:44 AM

Honestly, the "rebound" voltage should be closer to 3.5-3.6v/cell. I have my LVC set for 3.2v/cell and the rebound voltage is right around that. I still put pretty close to the full pack capacity back in but it provides a little extra safety margin for long cell life.

Big House · 12.17.2010, 11:14 AM

I will have to look into the program-ability of my charger if there is any to see because with all he packs I have charged, I have to watch it to make sure it does not go beyond 4.2. It does not automatically shut off. Thanks for the info though...it has been a huge help.

BrianG · 12:35 PM

What should happen is that the charger charges at a constant-current until the cells hit 4.2v/cell. At that point, the charger switches to constant-voltage mode where the voltage is held at 4.2v/cell and the current dwindles down to shutoff.

If you are stopping the charge when you see the voltage exceeds 4.2v/cell, you are missing the whole CV part of the charge and could be missing out on ~10% of the charge cycle.

If the cells are getting beyond 4.2v, it's either a charger malfunction, an error in the voltage display, the peak threshold is set to something above 4.2v, or you are in the wrong mode (NiXX instead of lipo). Either way, I would hook a voltmeter to the charge leads and watch that instead. You could even hook another meter in series to measure current at the same time. This would show you what is going on with the voltage and current simultaneously, provided the meters are accurate and/or been calibrated correctly.

I have an old Hyperion EOS7i where the voltage display shows ~0.1v higher than what it really is according to two different meters. On my Xtrema, I set the CC/CV threshold to 4.15v/cell just in case, plus it gives me a little wiggle room if the cells aren't perfectly balanced before the chargers gets to the CV point.