Need someone to confirm if equation true/false, like Nm/s = Watt/Volts = A

[dejanc]

Hi,
I'm not sure if my calc is correctly. But, I want to get current for power tool which manufacturer information provide only torque + RPM or IPM (impacts per minute) + volts
Like, 190Nm = 190W/18V = 10,55A

On the other site, this equations is confusing me.
HP = Torque x RPM ÷ 5252
190Nm*1900/5252 = 67,7HP

Thanks in advance for explanation.

 

[ScottyUK]

190Nm torque is a stall torque. It certainly doesn't deliver that torque while turning at 1900rpm.

 

[dejanc]

Oh right, it is to high. I just took the highest value from tool information, and is totaly wrong.

So, another obstacle...Come on engineers, bring on your brains

 

[zeusfaber]

Formulae aren't going to be a lot of help here.

You mustn't confuse torque with energy (even though they have the same dimensions) which looks a bit like what you've tried to do.

The closest you're going to get theoretically is:

Current = Torque * RPM * 2 * π /(60 * voltage * efficiency)

Where this gets difficult is that Torque is primarily determined by the load, not by the tool - and RPM and efficiency both vary significantly with torque and with each other.

Much better either to ask the manufacturer, or take a range of measurements.

A.

 

[dejanc]

Yeap Zeusfaber, agree.
Was study over night, and it is actual impossible to get approx. current value by equation. Possible would be to get average by using measurement instrument, connected on the drill.
Example if drill is screwing the wood screw:
- to many sizes of screws (length and width), same for drill bits
- then density of material, because of the friction
- even our hands when are holding the drill in action are making the load

Anyway, thanks for brightest Picture.

 

[7anoter4]

If the torque is 190 Nm and speed 1900 rpm the power will be:
Pm=2*pi()*Tn[Nm]*rpm/60 [W]=37800 W[37.8 kW=50.7 HP]
If the torque is 190 lb.ft [ 26.3 Nm] and speed 1900 rpm the power will be:5.2 kW
However, at 18 V the current will be 290-300 A.