Easy method to measure power output to handpiece?

[kiaora73]

I need to work out how much power my tattoo machine is outputting to the tattoo hand piece as there is no display. The hand piece plugs in to the out put of the machine via a jack plug. Whats the best way of doing this? Thanks

 

[d123]

Hi,

I think you mean a plug-in Watt-meter is not what you're looking for?

Is the hand-piece part of this machine isolated from the mains? Is it a DC or an AC device? Do you know the voltage and estimated current? What measurement tools do you have available? Do you have a DMM that can measure DC current and AC current?

For a simple, home-made, rough and ready, reasonably/relatively accurate measurement you could use an intermediate cable with male jack at one end and female at the other, and solder a low value resistor in the middle of the cable, and measure the voltage across the resistor, then multiply the supply voltage by measured current to get the Watts (assuming the additional jacks, and additional bit of cable used, have negligible resistance). If you don't solder, a couple of bits of terminal strip to screw each end of the resistor to each end of the two pieces of cable is another option, and if it's a one- or two-use thing then you could possibly get away with not soldering the jack connections.

For a more permanent device, probably an idea to use a bit of PCB and solder everything, then put it in a small box with panel mount male and female jacks/sockets.

There may be much better/easier ways of doing this.

A little more information, if you can, makes it easier to suggest sensible/viable solutions.

 

[kiaora73]

Hi,

The machine has an external power supply, 15v. This plugs in to the machine where you can increase or decrease the power to the handpiece which also plugs in to the back of the machine in to a jack socket. I just need to know the power it is outputting to the hand piece from its lowest speed through to its highest setting.

Heres an example.. however not so elaborate as my machine. This one has a display which shows the needle speed. https://www.youtube.com/watch?v=GU9fkPdO0FU

 

[d123]

Hi,

Without knowing how much experience you have making circuits, I think to get an accurate measurement for AC is a pretty complicated project. I've attached a pdf (Watt_VAR_VA) which explains the difference between apparent, real and reactive power, and the reason being is that I guess what drives the handpiece needle is a solenoid, maybe I'm wrong but that must be reactive power - that, for me at least, is not a straightforward circuit to throw together at all, neither with analog parts nor a microcontroller.

If the solenoid is driven by a squarewave, maybe taking the average would give an approximation of the actual power, but still that's a circuit with quite a few parts and a fair amount of prior knowledge. Unless you especially want to make this yourself, I'd buy a plug-in Wattmeter, save a lot of work and more time, not ideal, nor will it measure power from the machine to the handpiece, only from the plug socket to the machine, but I believe it is a sensible solution.

There are two datasheets for low-priced power meters which can measure and display reactive power that are easy to install/wire for one or three phases, minimum input voltage 28V..., if you prefer that type to a plug-in one, maybe there are others which allow a lower minimum input voltage; and here's a link to about 283 different ones from an online electronic, etc. parts supplier.