Can Ammeter Run Parallel?

[baskin]

TheMonkey; your theory is correct, to be more exact, you’ll find a wire resistance chart here http://www.stealth316.com/2-wire-resistance.htm What you’ll need to do to calculate the split is to first find the resistance of each path, then convert that resistance to conductance (1/R) and then find the percentage of conductance for each path. As an example, let’s say you have 10 feet of 10 gauge bypassing the ammeter, giving a resistance of .0102 ohms, and 15 feet of 12 gauge running through the ammeter path, giving a resistance of .0243 ohms. The conductance of the bypass path = 1/.102 = 98.4 S, the conductance of the ammeter path = 41.15 S, and the percentage of current through the ammeter = 100* 41.15/(41.15+98.4) = 29.49%. The resistance given is at 77F and will rise about 6% for every 20 degrees F but, given both paths are at relatively the same temperature, it won't change the final numbers much.

For safety reasons, you'll want to use a fusible link on both paths, the correct gauge for that should be 4 gauge numbers higher than the wire being used, eg; 10 gauge wire would require a 14 gauge fusible link. Finally, remember that the function of the link is to get hot enough to melt the copper on overload, which will also melt solder, so although you can solder the connections to the link, they need to be primarily attached mechanically (crimp connector)

[TheMonkey]

baskin: you rock . that's the information i was looking for. resistance is something i can measure, and that formula seems straight forward.

i was thinking about using a 40 amp circuit breaker before going through the firewall to the ammeter, but i'll check that against the math for the wiring.

cheers,
Scott.

[baskin]

baskin: you rock . that's the information i was looking for. resistance is something i can measure, and that formula seems straight forward.

i was thinking about using a 40 amp circuit breaker before going through the firewall to the ammeter, but i'll check that against the math for the wiring.

cheers,
Scott.

The lowest resistance you can accurately measure with an ohmmeter is about an ohm, below that, the lack of resolution and contact resistance makes for a pretty inaccurate reading. What you can do is essentially build your own ohmmeter, just go down to radio shack and pick up a couple of 20 ohm, 20W resistors. Connect them in parallel to ground, connect the other ends of them through the wire you want to measure to the positive side of the battery. With a battery voltage of 12.6v applied, each resistor will draw 12.6v/20 ohms = .63A, for a total of 1.26A. Measure the voltage across the wire and divide it by the current in order to get the resistance. This is exactly how an ohmmeter works, but with a far lower current which limits the accuracy in measuring low resistance loads.