PL6 discharges lipo to 3.67V

[Jon C.]

I have a PL6 and a few 6S 3300mah packs. I plugged up one pack to cycle a few times, starting from storage charge, ~3.87v. Put about 1700mah's in at 3.3 amps. Then started the discharge at 6.5 amps. It took out 2950mah's at 3.67v/cell and wasn't finished. I stopped it there. Seems like something is wrong. Why would it take out so much? Do I have a setting wrong or something? I am using 2 DPS-600PB power supplies.

[Gregor99]

The default discharge value is 3.3v per cell for the LiPo presets unless you are using the storage preset. I always change mine to 3.67v to 3.7v depending on which pack I am discharging. You can change the preset from the console of the charger or using the software. Press and hold the INC/DEC to get into the charger and preset menu.

[Jon C.]

Originally Posted by Gregor99

The default discharge value is 3.3v per cell for the LiPo presets unless you are using the storage preset. I always change mine to 3.67v to 3.7v depending on which pack I am discharging. You can change the preset from the console of the charger or using the software. Press and hold the INC/DEC to get into the charger and preset menu.

Thank you Greg! Perfect info. I was using the high power setting (cycle), but now have it set right. Now hopefully I didn't trash my battery. My fault if I did. Thanks again!

[Gregor99]

Glad to help. I wouldn't worry about it. That was 89%. Once or twice at a slow discharge rate won't be too hard on the packs.

[sutty]

I think the issue here might be the way some, maybe all, of the newer packs maintain their voltage so well. 3.3V may no longer be appropriate for a discharge level. I was looking at the discharge curves for my 6S 5000 mAh packs and 3.3V would be almost completely drained. I'm talking comfotably past 95% here, so from the point of view of remaining capacity they would in theory be completely stuffed, and they would be on an almost vertical part of the discharge curve at this point. This having been said, they would still be above 3.0V, and maybe it is going below 3.0V which causes the damage to the cell chemistry, and not specifically the 80/20 rule with regard to its capacity.

It may be that the 80/20 rule is no longer as important as it once was. I don't know the answer to this but there is no doubt if I make a mistake with my packs, and overfly, they perform really well until the last second, and then just fall off a cliff. Even with the LVC finally kicking in, and giving me reduced power, I noticed that it was difficult to get the heli back as there was almost nothing left, even at the highest LVC setting. Haven't noticed any detriment in performance on the packs where I have accidentally done this, but they are not near the end of their life cycle yet, so maybe I have shortened their life a little. I doubt your 89% will have casued you any harm at all though, I was way past this point, though still above 3.6V when the pack was at rest. Looking at the graph, the discharge curve is virtually flat, until 95%, and then practically has a 90 degree bend in it as it plummets towards zero.

Maybe Greg knows some more in this area, regarding whether this area of potential damage is capacity related or voltage related and can shed some further light, but whatever the answer there is no doubt things have changed.

Cheers

Sutty

[Gregor99]

Its true that packs have evolved and the old values for resting voltage are not always correct for modern packs. This is the main reason the FMA AUTO modes and fuel tables worked so well years ago but have diverged from the fuel tables of today's packs.

In addition the notion of the 80% rule continues to be challenged with some interesting results. Here, TP performs a 300 cycle test discharging to 3.0v per cell with very little degradation in the cells.http://www.rcgroups.com/forums/showthread.php?t=1142882

However, many modelers still report issues with packs after repeatedly over-discharging them. While some packs may be able stand up to that in controlled tests, as a best practice I still believe that operating above 20% depleted is best for the packs.

Beyond the aged-old guidance of 3.0v minimum discharge, it is not 100% clear what the minimum cell voltage actually is. What is clear is pack health is better maintained when operated within a more narrow voltage range (not above 4.1v per cell and not below 3.7v). Put another way, the cells are under more stress closer to their voltage extremes.

Often the cycle mode and discharge mode is used for pack evaluation, where it is important to see the pack performance results all the way to the end of the charge. Because there is uniform agreement on minimum voltage above 3.0v FMA leaves it up the modeler to make the call on how far they want to go.

[Jon C.]

Another question on the same subject. I got a few more 6s 3300mah lipos and doing the break in on my pl6 using a deep cycle battery this time. I set the discharge rate for 6.6A using regenerative discharge. The max it is discharging at is 2A. I read through the manual but didn't see any setting that I missed like I did on the first post. I don't have the link for my laptop, so I'm just using the menu buttons. Is this normal or am I missing something again?

Btw, thank you Greg and Sutty for your previous responses!

Jon

[Gregor99]

Sounds like its using the internal discharge and not performing regen discharge. When your charger starts does it ask if you are using a Battery or Power Supply?

[Jon C.]

I set it in the charger options to battery as the source of power and set it to regenerative discharge. It doesn't ask me battery or dc when I turn it on though. I'm thinking the deep cycle is fully charged so its using the internal discharge? It's at 12.5v so that would be fully charged for a Pb if I have any idea what I'm talking about!

Another question, the internal discharge for the pl6 is max 8A. Why does it stop at 2? I'm probably answering my own question here, but I'm assuming it has to do with watts as well which is far beyond my knowledge of electricity and batteries. Please correct me if I'm wrong and I very we'll might be!

Thanks again,

Jon

[Gregor99]

If the Pb battery is fully charged the charger will flip over to internal discharge. Watch the supply voltage as the discharge starts. It transitions over to internal discharge when the Pb battery is 14.4v.

You are correct about the 2 amps. There's 50 watts of internal discharge. A 6s is around 25v. 25/50=2.

[dendenyc]

I always feel like a fool because I truly never understood 80/20 as it relates to economics. If I shouldn't deplete a cell less than 20% then isn't like like wasting $80 on a $100 lipo?

[Gregor99]

Originally Posted by dendenyc

I always feel like a fool because I truly never understood 80/20 as it relates to economics. If I shouldn't deplete a cell less than 20% then isn't like like wasting $80 on a $100 lipo?

My car redlines at 7000. But I usually shift at 3500. Does that mean that I'm only getting 50% of the value out of the car's motor? If I change my habits and always shift at 7000 will I get more "value" from it. Most likely I will get more pleasure, but a shorter engine life.

There is very little pleasure gained from using the last 20% of a pack. I've tried it and find the lack of power is far less enjoyable than a fresh pack. I field charge. I could lengthen my flight times and use more of the pack's capacity. But the latter part of the flight will be at reduced power. Or I can shorten my flight, walk back to the pits and swap out for a fresh pack. With field charging, there is always a fresh pack ready to rock.


The main issue with the 80/20 rule is not value. Its flight time. Are you getting your desired flight time staying above 20% remaining? If not, then are other things you can do to increase flight time without going beyond 20%.

1. Lower headspeed
2. Lower collective pitch range
3. Tune the governor and pinion to reduce massive amp draw. Switch to a proactive gov
4. Increase your collective management skills so you are easier on the power system.
5. Increase pack size as long the model will still fly well with the added weight. In general I find an increased pack size is not worth the impact to flight characteristics.