12S power systems ideas and options

[rcbirk21]

my 3dhs 87 extra with the q80 that i just weighed over the weekend was 18lbs 12oz

 

[gyro]

18.5 pounds has always been my goal for the 8M and now for the DM5335 too. We were talking about power on another thread and I had to remind even myself, that we have a limit here. We want to keep the volts up above 3.6v per cell as often as possible, and with a 5000mAh capacity, we want to keep the Amps down below 120A or sacrifice flight time. Multiply 119A times 3.6v per cell, time 12 cells, and we end up with 5140 Watts. Add more capacity to increase flight time, and the added weight mean less power-to-weight. Add a bigger prop to gain more torque, and risk dropping under a 5 minute flight time.

For power hungry fliers like me, an 18.5 pound airplane means 275 Watts per pound at 5140 Watts, which will typically assure a full flight in the "silly" power range. Do you remember how many mAh's you put back after Brian's flight, Gyro?

I haven't recharged the packs as that was the last flight on them for the day. They measured 3.74 +/- .01v per cell across all 12 cells.

As soon as I have time, I'll run a charge then a storage and let you know.

What I can say, is that he wasn't shy on the throttle, and we still got a 6 minute flight on the packs 2x 5300 packs... that's kind of unheard of, isn't it?

 

[Aeroplayin]

I haven't recharged the packs as that was the last flight on them for the day. They measured 3.74 +/- .01v per cell across all 12 cells.

As soon as I have time, I'll run a charge then a storage and let you know.

What I can say, is that he wasn't shy on the throttle, and we still got a 6 minute flight on the packs 2x 5300 packs... that's kind of unheard of, isn't it?

If you are still at 3.74v per cell, that’s great. It also means that he had no need to really push the plane.

5300mAh will probably use about 70% capacity if they still come down at 3.74v per cell. That would mean you will put back 3700mAh when recharging.

If this turns out to be the case and the motor at WOT draws 125A, then he wasn’t on the throttle much at all. Here’s why….

A six minute flight is a 10C discharge rate.
If the motor is peaking at 125A at WOT, then he must be average only 30% of the power average, which ranges from zero Amps to 125A at WOT. Unless there is a throttle curved programmed into the Tx, that could easily be considered a 30% throttle average.

30% of 125A is a 37.5A average.
37.5A divided by 3.71 Amp Hours is 10C.
60 minutes divided by 10C is 6 minutes.

If you’re getting an average of 3.65v per cell, throughout the flight, which is normal, and you are peaking out at 125A, then you are peaking at 5475W.

If he was using 40% throttle (power average), and getting 6 minutes, and using 3700mAh, then the peak was only 106A, which means a peak of 4710W. Either way, he was only using an average of about 1650W over the entire flight.

 

[skibum44]

My experience with many flights on telemetry comparing time, voltage and percentage left in packs... 3.74v per cell is closer to 80% out of the pack then 70%. I run my packs down to just a hair over 3.7v (20% left) per cell and I have the timing pretty worked out when I check my voltage and it gives me 3.75v left... There isn't much left in the tank from 3.75-> 3.7v. Anyways from the video he was on the throttle probably a hair more then me and I usually get more time then the 40% figure gives me. That said I think I'll be pleased with what 5000-5300 mAh will give me with runtime.
Also to note... Just because having a higher output power doesn't necessarily mean shorter run times. If you use it, sure run times would be lower.

 

[Aeroplayin]

Even at 80%, or if you put back 4240mAhs, that's still only a 34% power average, which tells me the ~18.5 pound plane is well powered with this setup. Flying that routine in that wind at a 34% power average says a lot about the power-to-weight, and the pilot too.

 

[gyro]

Even at 80%, or if you put back 4240mAhs, that's still only a 34% power average, which tells me the ~18.5 pound plane is well powered with this setup. Flying that routine in that wind at a 34% power average says a lot about the power-to-weight, and the pilot too.

Here's what went back in on a parallel charge of both packs:

 

[skibum44]

Right in line with what I figured (closer to 80%) considering the voltage... Actually just a touch more mAh, but close.

 

[skibum44]

Finished running power system wires on my 91" extra... Still need to secure wires from the firewall back, but the time consuming part is done. Included are RPM sensor, temp sensor, and battery voltage sensor. Would have liked to monitor temp on the motor like I do on the MF4315, but the way the motor is built that can't happen so I put the sensor on the ESC.

 

[gyro]

Finished running power system wires on my 91" extra... Still need to secure wires from the firewall back, but the time consuming part is done. Included are RPM sensor, temp sensor, and battery voltage sensor. Would have liked to monitor temp on the motor like I do on the MF4315, but the way the motor is built that can't happen so I put the sensor on the ESC.


View attachment 22493View attachment 22494View attachment 22495View attachment 22496

Bryan, I used a dab of 5min epoxy to secure the temp probe to the baseplate... Seems to give me decent data so far.

 

[Enterprise]

Very clean install. Let us know how the CG works out. The 91s are notoriously tail heavy in DA-60 setups and I wonder if the electric works out well.