Micro Motor Community

Max Amps on Lipos

#1

Is the min voltage under load for a lipo 3.5V or 3.3V not to damage them?

Also, I’m thinking about building my second brushless (hopefully much better than my first since now I know what not to do haha) and I have a couple battery questions.

In your experiences, for 3S/4S lipos, what’s the voltage drop vs mah and amp draw?

For example, my Emax 1106 4500KV with a 3045 prop and Tattu 3S 450mah 75C lipos drop to 3.5V/cell during punchouts. My OSD says that the four motors draw 40A during punchouts, so under a 3 Second 40A load my lipos drop to 3.5V.

Obviously increasing my batteries mah will decrease the voltage drop under load, but I wonder if anyone has any advice as to what’s a good combo? I’d be willing to get with 4 inch props if I can get the total weight less than 250g and the thrust to weight over 10.

Maybe those of us with current monitoring can post their total max amp draw during a 3 Second punchout and their cell voltage during punchout and we could make a table so we’d know what mah to pair with what amp draw?

#2

3.3v is a good line.
The tricky part is deciding how much damage is damage, there’s some damage with any discharge cycle.
More amps means more damage, but there is a steep curve up in the amount of damage if you pull the cell voltage under around 3v, and 2.7v is about immediate death.

Way I figure, generally, is that if they aren’t puffing or hot, it’s all good.

For reference purposes my 5" is the only one with an amp sensor, depending on various things it pulls 105-120 amps and brings a china Hobby Line 1300mAh 100c to around 3.5 to 3.6v.

Any charting done will have to be with specific batteries, as a 500mAh 100c from Tattu won’t behave the same as a 500mAh 100c from GNB, etc.

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#3

IMHO, it also depends on the lipo. If you get a bad lipo, it will puff at, say, 10c. Also, how does one really calibrate a currrent sensor? For me, all the numbers seem to be way too low…
I abuse my micro packs and bring them down at 3v a cell, but only because they are cheap. But for 5", i take better care, usually bringing them down between 3.5-3.3v per cell.

#4

Ah. So I’m being overly careful with my lipos. I got worried when I saw 3.4V on one of my recent flights. They feel a bit warm, but not hot, especially since I was flying in 85F weather. Really, I just want ~200 good flights with each lipo, since I do buy the more expensive Tattu brand.

I’d be fine organizing by battery type, if I can get my hands on more data. I’m using the Omnibus Nano V2 on my 3” for current sensing and it seems decently accurate. I draw around 420mah from my 450mah packs and get a resting voltage of 3.74V/cell.

The motors I’m looking at (Emax 1306 4K KV) (If I remember correctly a 4 inch prop did something like 670g thrust) Engineer X says draws about ~164A on a 3 inch prop and ~204A on a 4 inch prop. That seems awfully high compared to my current motors ~8*4A draw. So by your data maybe I’ll need an 850mah lipo?

I thought the values are 25-30% lower than thruststand data because the air is already moving so less thrust and less amp draw?

#5

Sorry, when I said the numbers seemed low, I meant on my OSD. I figure the multiplier value is off. Also, I would caution against thrust stand data. It is good for bench testing, but not super great for a quad flying. I have used them as a baseline, though. What pitch was the 4" prop? 4k kv seems a bit high for even a 4030 prop… But what do I know, never tried 4"

#6

It was a 4040 prop.

Here’s the vid. He did put caution next to the prop though.