### Power Distribution Board Selection

Need some assistance on PDB selection. Going to be running T-Motor U3 700KV motors with 40A ESC's. What will be a good distribution board for this system.

#### Replies

• MR60

Do you know my power board ?

http://www.airbotservices.com/airbotpower.html

AirbotPower | Drones
• FYI: Take a look at the Tiger motor specs. It will show thrust per motor for various prop sizes at different voltages(3S,4S,etc.). Additionally, I prefer hard case batteries. I know there is a bit of added weight, but the resistance to puncture in a crash is worth it! With the side benefit of being ROAR approved! You can also run two batteries in parallel to increase the C rating.

Oops forgot to mention an PDB! Take a look at Tiger's F55A Pro. Pretty impressive design...

• Thank you for the detailed explanation Thomas. Much appreciated!
• Hey Mergan,

First you need to determine the maximum power required for the weight of the machine; thrust and full speed movement.

Determine the thrust required to hover (defeat gravity); how much total weight is to be lifted. Thrust for each motor = weight /4.

The thrust to hover (and current draw) will be a fraction of the maximum power.

You can use the ecalc.ch web site to determine batter, motor, props...

That U3 motor has a max current draw of 25A. Note that is MAXIMUM CONTINUOUS;ie, a full throttle climb or acceleration or flat out continuous movement. While the motor may have a 25A rating, typically these products are OVERRATED and it will probably start to smoke if you continuously run 25A. I'd de-rate it 20%, lets say 20A is safe. So total through the PDB will be 80A.

At hover, only a fraction of that will be drawn. The high current draw only occurs in a short duration high speed acceleration and max speed continuous movement; how fast do you need to go?

Determine the desired max rate of climb and/or desired max forward speed, and that will determine how much power is needed.

Most of the PDBs have a burst rating for max power climb/acceleration; check the "continuous" rating.

Add some extra power capacity for reliability; perhaps 20%.

So you might have 5A per motor at hover (20A draw continuous total). 20A at full throttle climb (80A burst total).

Finally all of this is limited by the voltage and C rating of the battery. You'll never draw 80A burst for very long if the battery is too small. I've used 40C(80C burst) 4S batteries with Tiger MS2814-10 770V. (28A ) \$32 each! Similar to U3, but MUCH cheaper.Granted the newer U3 has a bit higher wattage rating.

Note that a higher battery voltage will be more efficient and reduce the current through the circuit(and the rating of the PDB required). While a 4S would be good, a 6S (21V nominal) might be best. Definitely don't want to use a 3S!

Note the U13 is only rated for up 4S(14,4) volts.Perhaps select a higher voltage motor. At \$100/motor, there are many out there!

Hope this helps!

• More like 14×4" or 13x4"
• The issue is you have not stated what props you plan on using 10x4" for 3s or 8x4" for 4s 2200 mah or larger battery 30c minimum !

• Thank you for your response Lyn. This is my first UAV build and my knowledge on this subject is limited to what I have learnt on the internet. I am building this quad for fishing; carry a minimum weight of about 4kg. I have purchased a Aquacopter bullfrog frame and the NAZA V2 flight controller. I have ordered the T- motor Air40A ESC, 14 inch carbon graphite props and the Taranis X9D radio system. I just needed some support on the power distribution board and battery selection. I would really appreciate any other advice that you may offer.
Thanks
• Hi Mergan.

When I design and manufacture a UAV the first thing I do (after obviously ascertaining what the UAV is being used for) is decide on a power train i.e, motor first. From what you say you are using a U3 (decent choice, I also use a lot of T-Motor parts) so going by the data for the 700KV unit looks like you are limited to 3s or 4s. That makes it straightforward. There is a consensus that the higher series packs are more efficient i.e. 4s is more efficient than a 3s pack etc. So I would run with that, a 4s with a decent discharge rating i.e. >25C. That being so you have a good choice of packs to go for. This is only what I do, others may have a different opinion but that's life!

Lyn.

• Thanks. Any recommendations for the battery selection
• here is 120A PDB and power sensor 120A!

Power Current Sensor Matek Distribution Board FCHUB-A 120A/200A [QA-FCHUB-A] - \$5.00 : www.brushles…
www.brushlessgimbal.ca Power Current Sensor Matek Distribution Board FCHUB-A 120A/200A [QA-FCHUB-A] - Matek Distribution Board FCHUB-A 120A/200A PDB…

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