Century 600+ motor questions!

[mx400]

Hey guys I would like to try to run more than 6 cells but I noticed on the century website it says 6s maximum on this motor, what are my options? Is a 7s a123 setup possible or maybe 8s? Sorry guys but large electrics are new territory for me. Thanks guys

[kgfly]

7s A123 is no problem for a 6s-rated system. The nominal max voltage is identical (7 x 3.6 = 6 x 4.2 = 25.2V). The nominal voltage is close (7 x 3.3 = 23.1V vs 6 x 3.7 = 22.2V) and the loaded/operational voltage is lower, (7 x 2.8 = 19.6V vs 6 x 3.5 = 21V). Even 8s A123 *might* be OK (28.8/26.4/22.4) for the motor but will burn out an ESC only rated for 6s. If you are thinking of 8s A123 or higher get an HV ESC.

I think the 600+ is similar to the Z30-1100 which is rated for 6s-10s according to this site: http://www.wattsuprc.com.au/product_detail.asp?pid=ZP30

[mx400]

Everyone says it is the same but on century's website it says 6s. Which seems low IMO but I'm not up on all the electric stuff as much. Is there a way to assemble the a123 cells to get more flight time? Again I dont understand how wiring in parallel like 7s2p is different from wired in a series. More help please! Thanks

[ping]

A123's have a lower voltage then Lipos. The Z30 and Century motors are basically the same, they are made by the same supplier. I guess the claim is the Z30 has a different endbell that increase efficiency.

7S A123's seems to be the limit for the non-HV controllers. I might try 8 A123's on my PHX80, the nominal voltage on an 8s is 26.6 (about 29v off the charger) and the MOSFETs on the controller are all rated to 30 volts.

[exceljay]

Ping
Did you use A123 battery?

[ping]

Yea I fly 7 A123's at the moment and performance is really good. I get about 5 minutes of sport flying. I'm looking into trying out 8 A123 in the near future it should increase the runtime a bit and provide power greater then 6 cell lipo packs.

For what it's worth I think the benefits of A123's far outweigh the lower energy density. You can charge them in 15 minutes, abuse them, and charge them without worrying about lighting your garage on fire or melting your helicopter.

[exceljay]

Did you make it or did you buy it.
I searched some forum. and know the howto make it. but i didn't try.
if you make it. How easy it is?

[kgfly]

Everyone says it is the same but on century's website it says 6s. Which seems low IMO but I'm not up on all the electric stuff as much. Is there a way to assemble the a123 cells to get more flight time? Again I dont understand how wiring in parallel like 7s2p is different from wired in a series. More help please! Thanks
How are you with plumbing ? There is a reasonable water-based analogy to grasp simple electrical concepts. It is not perfect but it might help you.

Voltage = Pressure
Amps = flow rate
Charge = volume
Internal resistance = diameter of hole in bottom of bucket

So consider a single cell as a bucket of water. The greater the volume of the bucket, the more water (charge = energy = capacity). The taller the bucket, the greater the pressure. The bigger the hole in the bottom of the bucket, the smaller restriction to water flowing out.

Now placing cells in series is like stacking buckets on top of each other. The total pressure (voltage) increases. So does the total energy available however the maximum flow rate remains the same (all the water has to drain through the one series of holes all the same diameter).

Placing cells in series is like standing buckets side by side and connecting their outputs to a larger hose. Total pressure remains the same, total energy available increases and the maximum total flow rate increases too (sum of the flow rate from all the parallel buckets).

So, placing cells in series increases voltage and total energy at the same max current.
Placing cells in parallel increases max current and total energy at the same voltage.

Since Power = Voltage x Current and PowerLoss = Current x Current x Resistance, for any given target Power, a higher voltage solution will be more effecient as there will lower current and hence much lower resistive losses.

Brushless motors are limited primarily by their maximum designed RPM. Exceed the max RPM and bad things can happen, like magnets coming unglued and windings deforming and shorting. RPM is proportional to Voltage, hence why there is a recommended max number of cells (remember, more cells in series = higher voltage).

ESCs (and BECs) are rated for max voltage across their transistors. They use a kind of transistor called a "FET" (FIeld Effect Transistor) as the primary switching element. The full voltage of the battery is applied across the FETs so their max voltage rating is what limits the number of cells they can support. Going above the FET's max voltage will let the magic smoke out.

If you are not comfortable with this stuff, then stick to 7s A123 which is certain to work safely with any components rated for 6s lipo.

Note that elements of the above are simplifications but overall it is good enough for starters. I hope it is some help.

[bstock]

Wow Ken - as always... Good Stuff!!

[mx400]

Yes, that was a huge help! Thanks