Auto-Electric Repairs Explained by Concepcion Mandy

Author:Concepcion, Mandy [Concepcion, Mandy]
Language: eng
Format: mobi, epub
Tags: Repair & Maintenance, auto-training, Transportation, automotive technician, auto-repair, auto repair, auto, obd ii, obd2, electronica automotriz, auto-technology, mechanic, computer networks, technician, Automotive, obdii, automotive technicia, electronics, auto-electric
Publisher: www.autodiagnosticsandpublishing.com
Published: 2013-06-23T16:00:00+00:00

The Parasitic Draw Amp Meter works as follows.

The circuit uses a 741 Op Amp to do the amplifying. The 741 Op Amp is a very common IC chip readily found anywhere. Use a universal PC Board to solder the 741 Op Amp to it, also found at any electronics parts store. A 10 Kilo Ohm potentiometer is also used to zero out the gadget when disconnected, and no current flows through it.

A few diodes, D3, D4, D1 and D2 are used to guide the current and protect the Op Amp and Amp Meter. A 1 milli Amp meter is also used to serve as the signaling device. The meter is a 3 dollar component, also found at any electronics parts store. This entire gadget can be built for under 14 dollars. There are some laboratory level, low current Amp Meters, but these cost a lot of money. The Parasitic Draw Amp Meter is at this time your only option.

The Parasitic Draw Amp Meter is powered by two 9 volt batteries. The reason is that it also checks negative current draw. But why? Why would you want that on a 12.6 volt DC automotive system? The answer, is loss of ground. In the event of a loss of ground, things will get dicey, and you may see negative current flow, which will never register on a normal digital DC Amp meter. 99% of all digital Amp meters are unreliable when reading low current or parasitic draw. A clamp-on Amp probe may also be used, but only as a preliminary measurement, due to unreliable readings. So, the Parasitic Draw Amp Meter is a very sensitive low current Amp Meter, and also a ground issue detector.

Last, it’s the R5 resistor. This is a 1 Ohm, very important resistor. In essence the Parasitic Draw Amp Meter is a voltmeter, made to measure Amps depending on the voltage drop across R5. We recommend a military specification resistor, since they’re more accurate. R5 color code is also odd, at Brown, Black, Gold and Gold. The last color can be White, which makes a tolerance of 2%, gold is 5%. Regardless, concentrate on the first three colors.

The Parasitic Draw Amp Meter has a maximum needle fluctuation of 100 Milli Amps. So, subdivide the meter scale accordingly. Half the needle scale is 50 Milli Amps, one quarter is 25 Milli Amps, and so on.

Basically, input current flows from negative, through the 1 Ohm R5 resistor, and it’s output is fed into the 741 Op Amp chip. The reading input at pin 3 is amplified, and the 741 Op Amp output is fed to the Amp Meter needle. At this time, you must have zeroed out the Parasitic Draw Amp Meter, and if you’re getting a higher than 20 Milli Amps reading, you’ve got a parasitic draw.

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