use of clamp meter

	An amp clamp is a non-invasive method of checking current draw with any electrical set-up. The jaws of the clamp are spring loaded so that they can be clamped around a cable; usually the positive lead in a DC electrical set-up. It works by measuring the impedance of the current flowing through the cable. This method has many benefits. It is easy to set up; you only have to be able to access one cable to be able to take a reading. It is non-invasive because you do not have to plug anything in to the line between battery and speed controller, or between controller and motor. Plug in methods are cumbersome (shunted meters or wattmeters), especially in the field, and always have some associated power losses which make the reading a little inaccurate. On the down side, amp-clamps are expensive. However, in my experience they are so easy to use, convenient and accurate, I believe that they are worth the expense if you are serious about electric flight. One strategy I often recommend is for several electric fliers to band together to buy an amp-clamp, because you do not use it all the time and you can share one around. It is also worth a club buying one, appointing a custodian, and sharing its use. One last point - older type amp-clamps (like the Graupner variety pictured in the test set-up) require a digital multi-meter to take the reading. Leads from the amp-clamp are plugged in to the meter, and the meter is zeroed before taking a reading. The disadvantage is that your multi-meter is not free to concurrently take a voltage reading at the battery pack. Having said all that, shunting a meter is an economical way to take current readings. Click here to read an article by Phil Connolly on shunting a meter. Click here for information on an amp-clamp.
			A modern amp clamp that measures DC current, AC current and acts as a multi-meter as well. Click here for details.
			A sample test-bed for a brushless motor. Note that the amp-clamp jaws are clamped around the positive lead between the battery pack and speed controller.This is and older tpe of amp-clamp that requires a separate multi-meter to take a reading; modern types have an LCD read-out built in to the unit.