True voltage is lower read through accessory circuits. Why.

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Old 12-30-20, 02:02 PM
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True voltage is lower read through accessory circuits. Why.

It's about a volt more connected directly to battery than connected via my ignition relay or jump start accessory connection. Why is this?

It's an 82 Nighthawk 650 and I want to have my little voltmeter/USB charger connected and read voltage accurately if possible which would be connected via an ignition relay so it won't be on while bike is off. Connected otherwise via this jump-start kit wire connection gives even less voltage as the meter say "lo". Haven't used my multimeter to test it but I assume it's even lower than one volt less. Directly connected to battery all meters read correct 12+volts
 
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Old 12-30-20, 02:12 PM
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If it was just a voltmeter....... no additional load..... it would read the voltage correctly.

With it being a voltmeter and charger package.... it's presenting a load. Based on that load and the size of the wiring.... you will see a small drop. Increasing the wire size will reduce the voltage drop.
 
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Old 12-30-20, 02:20 PM
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So the actual size, NOT the gauge? And what about an ammeter? I want to connect a little ammeter to monitor current too with this old troublesome bike. Great bike but has electrical challenges. Will that be in accurate too? Is it the same deal with wire size/gauge here? Thanks pj
 
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Old 12-30-20, 02:37 PM
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Actual wire size is gauge. The lower the gauge the larger the wire.

When you wire your ampmeter.... you need to use the wiring size that can carry the full load.
Typically the starter motor doesn't go thru the meter.
 
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Old 12-30-20, 03:08 PM
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I understand the relationship between gauge and size but increasing the size would be the opposite of gauge. If you increase the size I'd think you'd decrease the voltage and vice versa no? And come to think of it, the wires of my jump starter kit that connect at the main fuse right between the battery cables are smaller than the battery cables so I'd think it would cause higher voltage. But maybe I got it backwards. Clarification?
 
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Old 12-30-20, 07:01 PM
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Actual wire size is gauge. The lower the gauge the larger the wire.

 
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Old 01-01-21, 01:10 PM
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Is wire size not determined by draw on the circuit? So in the jumper box the connection from source to main fuse is small because there is little draw. The bttery connection is larger because the auto will draw heavy amperage by the starter and any accessorieson at the time of starting. 12 gauge is good to 20 amp and 10 gauge is up to 30 amp whatever the voltage.Small wire on key switch is only activating the solanoid but the big wire from solanoid to starter draws more. Both are 12 volt.
 
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Old 01-22-21, 11:50 AM
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It's about a volt more connected directly to battery than connected via my ignition relay or jump start accessory connection. Why is this?

>Almost certainly there is 1 or more amps flowing through that wire.

How do you quote a post?
 
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Old 01-22-21, 01:13 PM
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All instruments have a tolerance in their reading, called accuracy. It is usually a percentage of the full scale selected on an analog meter or a number of digits in the least significant digit on a digital meter. The tolerance of the reading can be plus or minus with the plus or minus being random. The tolerance usually is published in the instrument manual. All reading in post 1 seem to be within tolerance. Don't understand what "meter says lo" in post 1 means. All meters indicate from 0 to 100 % full scale. Does it possible mean the instrument battery is low?
 
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Old 01-22-21, 01:19 PM
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If your wire is 5' of #14 you'd need 80 amps to get one volt.
"When you have eliminated the impossible, whatever remains, however improbable, must be the truth."



 
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Old 01-22-21, 05:11 PM
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"If your wire is 5' of #14 you'd need 80 amps to get one volt."
I guess what I meant to say was that 80A is unlikely so I'd doubt your 1 volt reading.
All three conditions being true at the same time is unlikely if not impossible.
 
 

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