Installing a relay on the starter

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kendall

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Aug 2, 2005
374
pearson ariel grand rapids
Many (Chrysler primarily) had a 'ballast' resistor in the ignition circuit, the 5th pin allowed bypassing the resistor to get full voltage to the points. The resistor limited current flow and preserved the points.

In the circuit shown in the original post, the starter will run all the time because it's connected directly to the battery. the starter (+) terminal connection is made internally through the starter solonoid only.

Ken.
 
Dan Johnson

Dan Johnson

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Oct 14, 2005
2,191
1983 Hunter H34 North East, MD
Good catch, Ken...

My bad as I missed that in looking at the relay part of the schematic.

In real life that is not likely to occur as the battery wire is connected to the solenoid and the solenoid is connected to the starter with the short stub coming out of its casing. It would be quite difficult to actually wire it as in the schematic.
 
K

kendall

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Aug 2, 2005
374
pearson ariel grand rapids
Timo42 said:
The solenoid draws far more current than a relay because it is pulling the bendix as well as closing the contacts, don't have the numbers in front of me. Using a relay in the starter solenoid ckt has become almost universal in the automotive world in the last 10 yrs, several mfgs have even had recalls to retrofit a relay. Chevy cavalier and Hyundai come to mind. I am adding one to the starter ckt on the Push, hotrodders commonly use them.
Click to expand

Most often the reason for the recall is that on cars that dont have the firewall/fender mounted solenoid, the cable from the battery to the starter is ALWAYS live. Abrasion, touching a hot exhaust etc can cause it to ground and start a fire., installing the upper solenoid makes it so the cable is only live while the starter is actually in operation.

The old Fords all had fender mounted solenoids, If the wire abraded, the only issue noticed was that the starter stopped working. With a chevy (starter mounted solenoid) if you were LUCKY, the car would die, and the battery would discharge, if you weren't so lucky the jacket would start to smoulder and burn.

That's also why offroaders and racers make the mod, it's for safety

With newer cars and their tighter engine compartments, the cable often has to run all the way around the engine passing very close to the exhaust and potential abrasion points, so a long live wire is a fire just waiting to happen.

Ken.
 
Hermit Scott

Hermit Scott

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Sep 25, 2008
2,288
C30 Event Horizon Port Aransas
kendall said:
Many (Chrysler primarily) had a 'ballast' resistor in the ignition circuit, the 5th pin allowed bypassing the resistor to get full voltage to the points. The resistor limited current flow and preserved the points.

In the circuit shown in the original post, the starter will run all the time because it's connected directly to the battery. the starter (+) terminal connection is made internally through the starter solonoid only.

Ken.
Click to expand
The starter is always connected with a heavy gauge cable to the battery. That's how it is now. If you take a starter apart, the connection is made when the solonoid pushed the pinion gear forward to engage the flywheel. Then the electric motor is energized and starts to spin. If you don't have that cable hooked up and you energize the solonoid the pinion gear slams forward but doesn't spin.
The diagram I drew doesn't show that, I know.
 
K

kendall

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Aug 2, 2005
374
pearson ariel grand rapids
In the circuit shown, the (+) terminal of the starter should be connected to the solenoid, not the battery.
the solonoid is the only thing that should have wires connected from the battery. The starter should only be connected to the solenoid.

Ken.
 
Hermit Scott

Hermit Scott

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Sep 25, 2008
2,288
C30 Event Horizon Port Aransas
I see what you guys mean about all wires to the solonoid. I have an always live cable running to the starter which is also attached to the solonoid, that's why I drew it that way.
I was wondering about the amps needed to handle the starter.
In a post maine sail displayed the data on his zantrex battery monitor when he starts his engine. It went up to 130 amps momentarily. Most of you here use 30 or 40 amp fuses?
 
Timo42

Timo42

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Mar 26, 2007
1,042
Venture 22 Marina del Rey
Hermit, found the relay last night, while looking for something else.:dance: I also found the taillight, I am on a roll now.:D One of the wires is undersized, so I will change it before I send it out. The 30a fuse is on the solenoid, not the motor, so the 140a starter draw doesn't go through it. Kendall, this type of relay only reduces the current flow through the ignition switch, and the voltage drop to the solenoid, it doesn't relocate the battery cable. The Cavalier recall was for what GM euphemistically called an "ignition thermal event" if the car didn't start and the driver held the key in the crank position for an extended period, the switch could catch fire. :eek:
Tim
 
Hermit Scott

Hermit Scott

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Sep 25, 2008
2,288
C30 Event Horizon Port Aransas
Timo42-I received the bosch solonoid today. I will install it when I go down this week end to pull the forestay. I appriciate it very much. If there is ever anything I can do for you let me know.
 
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