Voltage input to BLDC inverters of tethered drone?

[Flyback]

Hi,

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

Ligh-T Drone Tether Station

The Ligh-T tether station can be rapidly connected to police drones and extend their endurance for continuous aerial surveillance missions.

elistair.com

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]

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]

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.

 

[Flyback]

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]

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 1FK7024 5AG21-0SG0-Z Servomotor Used | eBay

Find many great new & used options and get the best deals for Siemens 1FK7024 5AG21-0SG0-Z Servomotor Used at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

Pardon our interruption...

www.ebay.co.uk

Siemens 611 series drives use 600V nominal DC.

 

[shortbus=]

The thin wire could also break relatively easily under centrifugal forces.

I don't understand that statement. It's the permanent magnets in a BLDC that rotate not the armature coils.

 

[shortbus=]

BLDC motor which takes Vin of 400V

The Fisher-Paykel motors do it. The ones running on 220VAC.

 

[alec_t]

It's the permanent magnets in a BLDC that rotate not the armature coils.

You're right. Oops!

 

[Flyback]

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)

 

[shortbus=]

Link to what your talking about? If they told you why didn't you ask whether it was AC or DC?

 

[Flyback]

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=]

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]

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.