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Old 12-02-2011, 18:14   #1
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Measuring Voltage Drop

Is this done by simply using a DVM and comparing voltage readings at the battery, to at the load itself, to determine the actual % drop?

Mainly for a simple way to check the actual real life drop do to the number of terminal connections, battery switch, and fuse/CB have on the circut, as opposed to a single cable w/no break run.
Thanks
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Old 12-02-2011, 18:30   #2
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Old 14-05-2011, 23:14   #3
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Re: Measuring Voltage Drop

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Originally Posted by US1Fountain View Post
Is this done by simply using a DVM and comparing voltage readings at the battery, to at the load itself, to determine the actual % drop?

Mainly for a simple way to check the actual real life drop do to the number of terminal connections, battery switch, and fuse/CB have on the circut, as opposed to a single cable w/no break run.
Thanks
To get an accurate measure of voltage drop, you must read with DVM, between both leads at the load device. Full load must be applied, motor light blower fridge ac whatever must be running at full load to cause the voltage drop if there is any.
Remember, any connection in the circuit, fuse holder, term connector, switch terminals etc can cause a drop due to high resistance connection caused by corroded or loose connection.
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Old 14-05-2011, 23:59   #4
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Re: Measuring Voltage Drop

Yes to the above (posts 2 & 3), to confirm you can place one lead of the DVM on the +ve battery post and the other on the +ve side of the load; this reading is then the voltage drop across all the positive wiring, connectors, fuses, switches etc.

Then repeat using the -ve side of the load to the -ve battery terminal to get the voltage drop across all the negative wiring and connectors etc.

The battery voltage (supply voltage) should equal the sum of the load voltage + positive wiring voltage + negative wiring voltage; if not, you have made an error in reading the various voltages .
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Old 15-05-2011, 00:12   #5
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Re: Measuring Voltage Drop

Wotname has described the most accurate way to measure the voltage drop, but if your meter leads aren't long enough (and you don't have some spare wire to make a lead extension), it is possible to make a reading at the battery (plus to minus), and a second reading at the load (plus to minus). Subtract the load voltage from the battery voltage and the difference is the voltage drop. This only works with steady loads, and the accuracy isn't usually as good, but it should be close enough for most purposes.

Whenever possible I prefer to measure as Wotname describes. Always remember that "ground" is just another node in the circuit. You need to look at the entire current loop, the ground path included.
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Old 15-05-2011, 21:25   #6
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Re: Measuring Voltage Drop

Thanks guys
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