voltage drop measurements in run

[hotrod swinger]

1966 Valiant Slant Six

Yesterday I couldn’t get my turn signal lamps to work, caused by a serious voltage drop. This serious voltage drop was mostly a result of corroded and loose ammeter connections. That accounted for over 3 volts.

With that problem corrected, I measured voltage drop across the ignition circuit starting at the battery:

0.19 drop from battery to ignition switch

0.15 drop inside ignition switch, 0.34 cumulative

0.13 drop from ignition switch to engine side of bulkhead, 0.47 cumulative

0.17 drop from engine side of bulkhead to ballast resistor, 0.64 cumulative

0.16 drop from ballast resistor to voltage regulator, 0.80 cumulative

All of the connections are slightly corroded. I’m thinking cleaning all of the connections should bring this down.

 

[67Dart273]

I've recommended this several times. One way around this is to lessen the load on the circuit. One way to do that is to feed a bosch style relay from the starter relay "big stud." Electrically cut the "run" line after it enters the engine bay but before it branches off to loads. Use the firewall end of the wire to trigger the relay, and wire the engine bay "loads" end to the switched contact of the relay

Pay attention to coil polarity, as most auto relays have a built in spike diode

 

[hotrod swinger]

I've recommended this several times. One way around this is to lessen the load on the circuit. One way to do that is to feed a bosch style relay from the starter relay "big stud." Electrically cut the "run" line after it enters the engine bay but before it branches off to loads. Use the firewall end of the wire to trigger the relay, and wire the engine bay "loads" end to the switched contact of the relay

Pay attention to coil polarity, as most auto relays have a built in spike diode

Will the ammeter still function properly after adding an ignition relay?

 

[67Dart273]

Yes, but what you described with your ammeter I would have pulled it clear apart and inspected. There used to be a page where someone showed how to silver braze the ammeter studs to the "guts" (the shunt) so that it can NOT have a loos connection internally.

 

[hotrod swinger]

I think I’m going to install a jumper from alternator to battery, at least temporarily, and use my cigarette lighter for a voltmeter.

 

[hotrod swinger]

For what it’s worth, my measurements show no voltage loss across the ammeter.

 

[67Dart273]

You need to measure that under the worst conditions, and run it long enough and check for HEAT (Feel carefully with your fingers) Example, leave the headlights on for ?? 1/2 hour, then start it and run it and turn everything on that you can find, heater blower, lights, brake lights, everything. Measure while the battery is charging back up. I don't have a figure, but it should not be much and the important thing is, that it should NOT generate much heat Current causes drop (and heat)

I commend you for your work. You have had to have put some thought into this and made some good progress

 

[hotrod swinger]

I appreciate that. This valiant is my second build after the swinger and the electrical is my #1 priority this time.

 

[hotrod swinger]