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Voltage input to BLDC inverters of tethered drone?

Flyback

Well-Known Member
Hi,

Regarding tethered drones such as the LIGH-T 4, which is rated at 1.2kW….


Do you know what voltage the BLDC motor inverters are likely to take?...presumably a lot more than a battery powered drone?

Also, do you know what is the kind of power ranges of these tethered drones tends to be?
 

Flyback

Well-Known Member
Hi

Would you agree that the old addage that “Motor torque is proportional to current” is not entirely true?....rather it is only true for an individual, particular motor.

In other words, as long as I can provide the power, it doesn’t really matter what voltage I have to drive a BLDC with. Its not the current which produces the Torque…it’s the magnetic field….and I can have a large magnetic field with a low current if I have enough motor windings…..so Torque being proportional to current is a misleading generalisation. Would you agree?

I this way, would you say that its very easy to make a 200W BLDC motor…..with a voltage input to its inverter of either 1000V, …or 20V? (assuming I have drive transistors available which can handle this high voltage)
 

alec_t

Well-Known Member
Most Helpful Member
I can have a large magnetic field with a low current if I have enough motor windings…..so Torque being proportional to current is a misleading generalisation. Would you agree?
I agree with the first part but not the second. For a given number of windings the magnetic field strength, and hence the torque for a given rotor-stator configuration, will still be proportional to current.
would you say that its very easy to make a 200W BLDC motor
There are plenty of U-Tube videos, and I daresay Instructables, showing how :).
I guess wire insulation breakdown would be a significant risk if powering a BLDC at high voltage. The thin wire could also break relatively easily under centrifugal forces.
 
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Flyback

Well-Known Member
Thanks, i am wondering if that is it, and that a BLDC with vin >48V is almost unheard of.
we are looking for a offtheshelf 200w-500w BLDC motor which takes Vin of 400V or more but cannot find one anywhere.
There are millions with voltages up to 48V, but almost none above this.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
More turns on the coils mean higher inductance so lower maximum operating speed / frequency.

A lot of machine tools use brushless DC servomotors - though in that application they are often called AC to distinguish them from older brushed DC types...

They are technically "brushless DC" regardless, a three phase style stator with a permanent magnet rotor plus some form of rotor angle feedback to allow high torque down to low or zero speed.. The drive DC bus is typically around the 400 - 600V range.

A couple of examples of small motors I've just found on ebay:


Siemens 611 series drives use 600V nominal DC.
 

alec_t

Well-Known Member
Most Helpful Member

Flyback

Well-Known Member
Thanks.
For a 56kg tethered drone consuming 12.5kW and using an 800vdc feed from the ground based power supply…what voltage would you say was chosen for feeding to the BLDC motor inverters?
(i was told it was "800v", but it may have been 800VAC of course, but i doubt it, unless it was 3 phase 800VAC)
 
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Flyback

Well-Known Member
Its a project we are bidding for...its been leaked, we shouldnt know anything about it...this is all we know for now.
Dd you reckon they are putting the whole 800v into the bldc inverters..?.or would they knock it down?..to say 400v?
 

shortbus=

Well-Known Member
Most Helpful Member
I can't imagine the weight of the cord for either of the voltages. Why on earth would you bid on something that doesn't have specifications already adopted???
 

Pommie

Well-Known Member
Most Helpful Member
Insulation being lighter than copper, there will be a most efficient voltage but I've no idea how to calculate it. As the voltage increases the copper reduces but the insulation increases, at some point the weight per unit length will be at a minimum.

Mike.
 

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