Battery Sag

[coyote_dc5]

So i was having a good think about what actually causes the sag aside from cell fatigue if you push beyond the C rating. If the connector is only rated to say 20amps like the PH2.0 is likely to be as the XT30 = 30amps, XT60 = 60 and so on then I'm wondering if the voltage drops instead as a result. I decided to upgrade my Emax cells to GNB ones because they stated a higher C rating but now I'm wondering if this is pushing the PH2.0 now and thus voltage drop is now being seen.

The Emax supplied lipo's are:

Cell/Mah	Constant Amps (C)	Burst Amps
1S 450 80c PH2	36	72
2S 300 50c PH2	15	30

The GNB/Tutto one's I'm now running are:

Cell/Mah	Constant Amps (C)	Burst Amps
1S 520 80c PH2	42	83
2S 300 75c PH2	23	45

I was going to replace my 2S with a higher C rating again to rule this out but I'm curious whether that's not the issue and actually pulling the C rating down to match that of the plug capability will keep the voltage stable.

My options are either 600mah 50c or 550mah 80c as viable replacements.

Any experts out there can help straighten this out?

 

[coyote_dc5]

I've just read this on a post somewhere


The biggest factor is usually internal resistance (IR), it limits the max current of a LiPo battery.

Ohm’s Law: Voltage (V) = Current (I) x Resistance (R)

Energy that is lost to resistance will turn into heat, and this is what causes the battery to get warm when discharging at high current. The pack can even become swollen in extreme cases

I have noticed the 2S cells are very hot when they are removed so I'm still going with C rating not being high enough then as it seems voltage is being dropped because of the internal resistance of the cell itself. I'm going to give the 550mah 80s a go and see if this helps as that will kick out 44 constant amps or 88 bursts so maybe the issue will then be moved to the Ph2 socket next. I'll post findings on here when I've tried it.

 

[HighTechPauper]

JST-PH2.0 does not mean it is a 20 amp connector, it means there is 2mm between pins, just like a JST-PH1.25 has 1.25 mm between pins. You are never actually getting anywhere near 20 amps on the quad and the 40 amp reading is even more questionable, the current meters on the quads are never calibrated, and to actually figure it out, strap one down, put an ammeter on the positive leg and go full throttle and see. The C rating has ZERO basis in fact, and only hints at a better or worse battery. This is a way more complex subject than the few links in the chain you are focusing on. The connector doesn't limit the current, it is a matter of how much it can take before heating up too much and melting or catching fire. Still I am interested to see what you learn over time.

 

[coyote_dc5]

I might do that actually and see what the actual amps are. The integrated ESC is only capable of 5amps a corner so that's 20amps and then add vTX, FC and receiver etc so it's probably 25amps or so max. I'll go ahead and get the more capable lipo to see if it's cooler after a blast and if the voltage sag is better or not. I find it a really interesting topic and if you can fully understand and maximise then you can get the most out of your flying performance and experience

 

[HighTechPauper]

Perhaps you should run the amp test first, so you can work from a point of fact.

 

[Deleted member 3641]

So i was having a good think about what actually causes the sag aside from cell fatigue if you push beyond the C rating. If the connector is only rated to say 20amps like the PH2.0 is likely to be as the XT30 = 30amps, XT60 = 60 and so on then I'm wondering if the voltage drops instead as a result. I decided to upgrade my Emax cells to GNB ones because they stated a higher C rating but now I'm wondering if this is pushing the PH2.0 now and thus voltage drop is now being seen.

The Emax supplied lipo's are:

Cell/Mah	Constant Amps (C)	Burst Amps
1S 450 80c PH2	36	72
2S 300 50c PH2	15	30

The GNB/Tutto one's I'm now running are:

Cell/Mah	Constant Amps (C)	Burst Amps
1S 520 80c PH2	42	83
2S 300 75c PH2	23	45

I was going to replace my 2S with a higher C rating again to rule this out but I'm curious whether that's not the issue and actually pulling the C rating down to match that of the plug capability will keep the voltage stable.

My options are either 600mah 50c or 550mah 80c as viable replacements.

Any experts out there can help straighten this out?

What doesn't make any sense to me here is if a XT30 carries 30 amps constant, how would a PH2.0 carry anything like the amps you are showing constant? Is it possible that the battery is heating up because of the resistance in the connector?
This is from BetaFPV:
"BT2.0 260mAh 1S Battery supports 9A continuous current, while the PH2.0 connector supports 4.5A continuous current."

 

[coyote_dc5]

@brettbrandon yep this is why I got confused so it has to be an inaccurate reading on the OSD. Have you ever added to your OSD and looked? I'd be interested to see what others experience here too. From what i understand with electricity, a soldered wire presents very little resistance so amps will flow and the amp limit is there as a guide to prevent melting and fire. The IR of the cell itself is what's causing the heat in the cell which is why I've opted to up the mah and C rating to see if that helps with sag. Itll be interesting to see if that then pushes the heat to the connector

 

[coyote_dc5]

Ok I've managed to calibrate the onboard amp meter in BF. It's now showing around 8amps and the mah output is perfect against 1s cells too. Issue i have now is when I use a 2s because the voltage is double the amps climb twice as fast. Is there a compensation tool somewhere in BF so it knows you've changed the lipo?

 

[coyote_dc5]

A larger 650mah 60/120c lipo has made a massive difference. It came with xt30 so I've soldered a PH2 back to it and I'm now getting over 4mins flight time and no real noticable sag. The battery is a lot heavier though so I think I'm going to get a 550mah 80/160 which will be the sweet spot for a tinywhoop