Lipo Cell Drop Off

I am not quite sure how to phrase the question so I will give the scenario.

I am looking at the following system in C3 as an upgrade in the future which I can design in.

Power: 2X 6S 2200mAh 40C Lipos in Series = 12S, 80C & 2200mAh capacity

Control: 1x Castle Creations Phoenix Edge 160 HV ESC (50V & 160A)

Motor: 1x Align 750MX 530Kv.

If my maths is right I can average 44A over a 3 minute fight and that would drain the batteries totally. Of course you can't actually use all the power in a pack due to voltage drop off.

So...

Is an average of 44A over 3 minutes even possible with a 2.9kg weapon?
(Runs on a 3:1 reduction giving (44.4*530)/3 = 7844 lossless)

And how many amps can I drain from the Lipos before I hit the 3.2V cut off built into the ESC?

The lipos would be these: http://electriflyer.co.uk/gens-ace-6...00mah-40c-new/

160A ESC from here: http://www.castlecreations.com/produ...x-edge-hv.html

You want to ideally make sure that your not using more than 80% capacity from your packs each cycle otherwise you start to effect the life span and performance of your packs. Current wise totally depends on how well your system is built and how free it is. I think something along the lines of 3300 packs would be more suited.

If I remember right LS4 uses 2 2600mAh 5S for its weapon. As you know, more volts = less amps. I suspect you are right but I dont have the weight or the space (Unless I got a custom Lipo which would be stupid!)

I don't think more volts necessarily means less amps, as with more volts the more will spin faster so more resistance so more amps.
But if you are using a different motor which is designed to deliver same power as LS4's at a higher voltage then as you say less amps should be drawn.

That all depends on your gearing as to if you will pull more current or not than LS4. LS only has a low RPM at the disc in comparison and so draws quite a low current to keep spinning. It's hard to tell without testing.
The higher voltage/low current works if your not pulling more power. As the motors your using can give huge amounts of power it's purely down to your gearing/build and air resistance of your beater.
A bar spinner can halve its constant current draw by adding an aerodynamic edge, it's suprising how such small things make such. A give difference.

In Valkiri 2 the difference between 6S and 4S is 120A startup and 40A cont and 90A startup and 30A cont.
The increase in RPM is a lot less than you would expect.

Quote:

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Originally Posted by maddox10

In Valkiri 2 the difference between 6S and 4S is 120A startup and 40A cont and 90A startup and 30A cont.
The increase in RPM is a lot less than you would expect.

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So in that example continuous was a 3rd of the start up no matter the voltage, interesting. Do you have the 2 speeds to compare?

The two things I am balancing are do I go 8S with a standard ESC or 12S with a HV ESC. If the top speed was achievable then the 12S would spin 50% faster but I have no idea where the two will level out. The higher voltage will spin faster but the air resistance will go up. I am thinking there is no way to really know unless I try.

The potential continuous draw figure drops as, in a hard battle, you could have a few startups and a stall or two's worth in amps to get out of that maximum 44a average draw figure. If you can get more than 2.2ah, I would.

Also, is it right that C rating doubles by putting two packs in series? That doesn't feel like it should be the case? Are you certain that is actually how the math works? If not, you have a maximum of 88a continuous from those packs. At 12s the 750MX can pull beyond 160a. Looking at your battery link I see no mention at all of burst C rating. If the burst isn't great, and the C rating doesn't double when you series the batteries, you could potentially be beyond the power of the batteries in both discharge and capacity.

Someone with the knowledge, I can see how discharge would double if you parallel two packs, but not quite how that would work if they're in series... enlightenment please!

In Valkiri 2 it was a 3-1 ratio, what is consistent with most electric motors that are loaded to their rated max.

RPM of an electric motor is commanded by construction, input voltage and load.
In the spinners, aerodynamics take a serious bit of power above a certain speed, just as in cars.

I don't have direct figures, the rpm counter we used ain't to accurate, but the 4Krpm of the 4S test wasn't scaled directly to the 6S test. Maybe we reached 5Krpm.

Quote:

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Originally Posted by Ellis

Looking at your battery link I see no mention at all of burst C rating. If the burst isn't great, and the C rating doesn't double when you series the batteries, you could potentially be beyond the power of the batteries in both discharge and capacity.

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It is in the battery description: 40C they also do a 30 & 55C version.

If each pack can supply 40*2.2=88A then both will supply 176A. All that changes is the voltage or the capacity depending on how they are wired. ie 176A @ 22.2V 4.4Ah or 176A @ 44.4V 2.2Ah.

I have the weight for 2 of these... http://www.gensace.de/lipo-battery/f...tery-pack.html

I am pretty sure that would do it.

EDIT: With Davids help we looked at the readout on Binkys disc. Startup was 100A but only for half a second. The Idol was around 20A. The 2 5S 2650mAh lipos only used half their capacity in the loosers melee. I know the air resistance is less but it is far larger and 600g heavier.

They won't supply double the discharge unless they're wired such that their capacity is doubled. The C rating for each cell is the same, series or parallel. For them to be capable of 176a in series the C rating of each cell must double, and that can't happen.

You only get a higher discharge if you up the capacity, i.e., wire in parallel. But in series you aren't changing capacity, so the discharge is the same. You'd get a 12s pack capable of putting out just 88 amps. That motor at 12s, at stall, will pull double that. I'm not trying to be nitpicky, I just don't think this is right.

edit: that second battery link would probably be fine. Two in series would give 12s, 2.6Ah, 60C. That'd be safe, as the peak is claimed to be 120C. Whether 2.6Ah is enough for the job in capacity terms is a different matter.

Quote:

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Originally Posted by Eventorizon

If each pack can supply 40*2.2=88A then both will supply 176A. All that changes is the voltage or the capacity depending on how they are wired. ie 176A @ 22.2V 4.4Ah or 176A @ 44.4V 2.2Ah.

I have the weight for 2 of these... http://www.gensace.de/lipo-battery/f...tery-pack.html

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Let me put this in perspective. Each of the gensace batteries is 6S 2600mAh 60C
You can put them parallel.
This doubles the mAh value, and nothing else. Still 6S and 40C. But with 2*2600mAh=5200mah and 22.2V 60C, the rate of discharge is 312A
If you set them in series, the voltage doubles, but the rest stays the same. 2* 22.4V44.4V and 2600mAh and 40C = discharge of 156A

Ok... so I am totally wrong. Oh well. Though now I am intrigued as to how Binky lasted on only 79.5A Cont.

EDIT: Then 2 of these will definitely cut it: http://www.gensace.de/lipo-battery/f...tery-pack.html

22.2V, 2600mAh, 60C = 156A Cont.

EDIT: And now they weigh to much.

For simplicity and reliability I think I will just stick to 10S for the time being. Shame.

As long as they actually are 60C, bear in mind that the best optipower lipos are only 50C continuous.

There is a high probability that Gens Ace and Opti-power lipos actually have the same internals. The company is technically Chinese but all their manufacture takes place in Germany. When Andy did has talk last November and I asked if Gens Ace were alright he said that their supplier shipped to one other company in Germany. Since Gens Ace batteries are the packs coming out of Germany that actually do what they say and more I would believe the stats.

Note: at the champs we accidentally drained 2 of our Gens Ace packs down to a crazy 2.3-2.5V per cell... and they recovered. I have no idea what it means but it can only be good.