Optional Starter Relay, Add a relay to protect the ignition switch |
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Optional Starter Relay, Add a relay to protect the ignition switch |
Artfrombama |
Feb 23 2024, 03:01 PM
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#1
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Member Group: Members Posts: 51 Joined: 21-January 24 From: Alabama Member No.: 27,870 Region Association: South East States |
On a previous 914 I had many years ago I experienced a "no crank" condition that I traced back to my ignition switch. It seems that in the start circuit on the switch, when the key is released a tiny "backfeed" of current from the starter solenoid arcs across the terminals on the ignition switch, and over time damages the contacts.
After a little research I determined there are two ways to stop this "current backfeed", one is to install a diode to ground in the starter wire, another (which I did) was to install a simple 5 pin relay. Hope this is of some help, please disregard or delete if this has been discussed before. |
Superhawk996 |
Feb 24 2024, 12:40 AM
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#2
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914 Guru Group: Members Posts: 5,876 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
42 (IMG:style_emoticons/default/stirthepot.gif)
Typical Bosch aftermarket automotive relay is rated 30A. The generic Ford starter relay is rated for 150A or a little more depending on who’s making and rating them. Starter solenoid draws around 25A nominal at 75F ambient temp. That’s not a lot of margin in the Bosch relay. The standard Bosch 30A automotive relay doesn’t have an integrated flyback (freewheeling) diode. Bosch requires that diode on an inductive load (i.e. solenoid) in order to achieve their rated life cycle for the relay. As mentioned previously the lack of a flyback diode will lead to burned relay contacts that eventually malfunction. Note: the Ford solenoid doesn’t have an integrated diode either which is why those can malfunction too despite the much higher current rating. I measured the starter solenoid current draw a while back using a 50A, 75mV shunt resistor. This was on a properly operating starter. My bet is that solenoid draw is even higher in cold weather. I’d also bet there are a statistical population of solenoids out there that draw more current than my random sample of one. (IMG:style_emoticons/default/welcome.png) |
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