Need some info


#1

can someone tell me how many volts the solenoid on the starter should be putting out with the key turned into the on position


#2

You should have battery power to the solenoid. Should be 12.5 or greater.


#3

Solenoids do not put out volts. When the key is turned to the on position, that is the run position for the engine so the solenoid will have battery (engine not running) or alternator (engine running) voltage on the large terminal and 0 volts on the small terminal. The starter will not be turning.

With the key in the off position, the voltages on the terminals of the solenoid will be the same as the on or running position except it will only be battery voltage (around 12.6 volts) as the alternator will not be turning and providing alternator voltage (around 14.2 volts).

Now when you turn the key to start, it supplies battery voltage to the small terminal of the solenoid causing it to pull the contacts into the closed position. Battery voltage is then supplied to the starter coils. The starter coils conduct a lot of current because they have low impedance.

The impedance of the starter coils and the internal impedance of the battery form a Kerchoff’s loop. In most circuits of the car, the battery impedance is so low and the other circuit’s impedance is so high that the battery impedance is not significant. But because the starters impedance is so low, the battery’s internal impedance does become significant.

The two impedances are in series so each drops some of the battery voltage. Typically the starter impedance is three to four times the battery impedance, so it drops three to four times the voltage. With 12.6 volts available, that means the starter is dropping 9 to 10 volts and the internal impedance of the battery drops the rest.

So during the time the starter is turning, you would read 9 to 10 volts on the large and small terminals of the solenoid. Because the large terminal is connected to the battery with a large gauge wire, you will read the same voltage on the + battery terminal as you would read on the solenoid terminals. It is easier to take the reading off the battery terminal than to crawl around under the car to get the reading off the solenoid terminal.


#4

With the ignition switch in the on position there should be no voltage at the solenoid. The ignition switch has to be in the start position for the solenoid to see voltage.

Tester


#5

+1 for @Tester and why do you need to ask this question?


#6

Impedance means resistance in DC circuits.


#7

Impedance is the correct term here. The starting circuit has reactive components, it is not purely resistive. But for explanation purposes, the term resistance can be substituted for impedance.


#8

im·ped·ance/imˈpēdns/
noun
the effective resistance of an electric circuit or component to alternating current, arising from the combined effects of ohmic resistance and reactance.

re·ac·tance/rēˈaktəns/
noun
the nonresistive component of impedance in an AC circuit, arising from the effect of inductance or capacitance or both and causing the current to be out of phase with the electromotive force causing it.