Propeller size tunning / new 18650b batteries cells

[Kisssys]

You have to parallel enough to get the discharge rate you require.

[Max]

[LPR]

Max

I started to think I might be able to slip the batteries inside the heli tail booms but there a little to big. I had to take the DELL laptop battery to measure the batteries and of course I'm charging the batteries in the laptop pack with an RC charger, set to charge lithium ion batteries. I'll find out if the batteries are bad or the charging circuit bad. I just might have my first 6 batteries.

Larry

[afernan]

I see, those 18650B looks promising, with the drawback of the max discharge limitation.
I've made some numbers on that.
One cell 3400mA weights 45gr, so a 3S pack weights 135g. Compared with a lipo 3Sx2200mA, 200g means that 18650B are less than half the weight for same energy than lipo: very good!
So we need a configuration compatible with the max discharge value.

Angel

[leopold1]

Some extra info

[afernan]

Looking to the Panasonic spec for 18650b and some detailled testing:
http://www.candlepowerforums.com/vb/sho ... 28Green%29

They are sensibly better for low current draw, but it drops a lot for high discharges. In the tested curves, maximum tested current is 5A per cell (<2C) while we normally need more discharge than that value.

For instance, for a light copter (like mine, 1Kg) I need 120W for hovering. So, I need to go to 6 cells (22v) to get 2C discharge. In that case the total capacity also drops to about 2800mAh (from 3400 nominal). This package weights 284gr. A first estimation is that we can double the flight time compared with a classical Lipo. Our AQ anyway is limited to 18v (5cells), which makes the things a bit worst.

But this is only theory...
Anyone wants to try?

Angel

[LPR]

Angel

Good information on the 18650B batteries. Did you see that Bill used 40 18650A batteries to get 1 hour and 20 minuets. The watts used to hover goes up as you add the weight of the batteries. The 10% gain going from 18650A to 18650B will make a differience in how many batteries you'll need. Getting an hour is a big step forward for multicopters, over an hour is gas helicopter territory.

Larry

[afernan]

Larry:
table below shows a simulation based on real data froom my copter and data from the 18650b tests mentioned before.
As you can see the watts increase with the batt weight (based on my own tests). Probably ratio discharges >2 may not be realistic for this batteries.

[LPR]

Angel

Great chart. With cells costing between $11 and $15 and the fact they can take around 500 recharge cycles there not out of line for cost. A 5s, 1p battery could get a quad in the air but wouldn't have enough watts for good maneuvering.
I'm thinking that making up 18650B battery packs starts to make sense when you fly a lot and need over 30 minuets flight time.

Larry

[bn999]

For comparison, the same machine that did the 1h 20m with 18650B's would stay in the air for 45 mins using 3 5000mAh 4S lipos. The overall weight was slightly lower with the lipos.