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Lost me on the inductance issue. I assume this is about how long it takes the current to decay once you start to break the circuit.

The two cases to worry about are

1) stuck or shorted starter and engine not started. In this case you have the armature winding inductance but the voltage is 24V or (probably) quite a bit less.

2) stuck starter and engine is running. this case seems way more complicated. which side is the load now? and what is the voltage?

I looked at putting an ANL in there, thinking about case (1) and decided there wasn't one that would allow starter current AND blow fast enough to do any good. However, it would do good for case (2).

On Apr 29, 2012, at 1:18 PM, Frederick Moreno wrote:

I read it the same way you do. And at 1800 volts (!) and 300 amps, you get two shots only. I assume after that it turns into a piece of toast.

Note that there is a caveat about the inductance being 300 microhneries maximum. More inductance means more energy dissipated in the arc when the circuit is opened. I have no idea what the inductance of a starter motor would be. However, since even el cheapo units have a reasonable lifetime, I would not worry about it.

Fred

-------Original Message-------

From: Colyn Case

Fred, I haven't come across something labeled as a "starter" contactor. ....and I've become over-invested in kilovacs.

full specs for that series are here: http://www.google.com/search?client=safari&rls=en&q=kilovac+ev100&ie=UTF-8&oe=UTF-8

Now I know what the aux contact is for...

Is the relevant specification as far as coil strength/contact life, this chart showing lifetime vs. current switched?

This is from an ev200. As I'm reading it, at 28V, 110A or less, this device is good for 100,000 cycles.

The other thing I looked at on my system is can the contactor break a dead short at the max current output of

the battery. at least once. For an Odyssey 680 that is about 680 amps.

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On Apr 27, 2012, at 7:56 AM, Frederick Moreno wrote:

Responding to John's question below:

Starter solenoids switch hundreds of amps of surge current when the starter starts to crank. To assure that they make the contact with minimum resistance, the contact is pulled into the electrical circuit with a very strong magnetic field that requires LOTS of current through the coil. It is a real "wham." In turn, if there is a bit of welding at the contact surfaces, the circuit is broken by contactor bar being pushed out breaking the circuit using a big spring (which the magnetic field must also overcome). The high current draw through the coil causes a lot of resistance heating which is why the duty cycle is so restricted. A few seconds on, then minutes off to cool.

Starter solenoids are wired differently than continuous contactors even though they look the same. But look closely and they are marked differently. On the little terminals, starter contactors will have "S" (for Start, where you feed power to engage the contactor) and "I" (for Ignition) which feeds power to the ignition system (throwback to old distributor ignition systems) during the start.

The starter solenoid is energized by connecting the start switch to the S terminal, and the current flows through to the coil to solenoid frame which is presumed to be mounted on a ground thus completing the circuit. The small "I" terminal is connected to the high current outlet terminal that goes to the starter. It feeds battery power to the ignition system. Why? When distributors operated normally they were supplied with power via a resistor that limits the current when the ignition points are engaged. During the start, current from the "I" terminal goes around the resistor to the distributor to make a stronger spark when the battery voltage sags because the starter motor is engaged.

The continuous solenoid is wired differently. Feed power to one small terminal and ground the other small terminal, and the thing will energize and pull in the contact allowing current (rating typically 60-85 amps max) from one big connection to the other big connection. Nothing is connected to the case.

I just read the words above and they are too complicated. So I quickly made the ugly sketch attached. Hopefully the differences become clear.

KEY POINT: USE STARTER CONTACTORS FOR STARTERS (INTERMITTENT USE) AND CONTINUOUS CONTACTORS FOR SHIP'S POWER (BATTERY CONTACTORS) AND DON'T MIX THEM UP.

How do I know this? I replaced the el cheapo starter contactor on my Lancair IV hydraulic pump with a continuous Cole Hersee contactor rated at 85 amps, and I got fooled by the wiring change. No instructions in the box. Had to put an ohm meter on the two different contactors to figure it out. Duh. And to think I once knew the difference long, long ago. It all slowly came back as I tried to figure it out with the ohm meter. The mind is going, going, going.....

Fred

Sounds like a better choice than we’ve been using. One question comes to mind – surrounding the idea I have (is it correct?) that the starter solenoid should be intermittent because you want it to be the weak link in the starter circuit: if the starter contactors should stick, you’d have a huge amperage draw and maybe start a fire. If the contactor is intermittent, it will theoretically fail and break the contact before the starter motor burns up and catches fire or causes other damage.

Is this logic correct? If so, would the specs on this contactor from Cole Hershee still be a good choice for the starter circuit with the TSIO 550? 24059-08 UL listed

Same as 24059, but UL and CE rated.

Continuous Rating: 65A at 12V DC. Intermittent rating:750A make, 100A break. 10 sec On, 30 min Off. Circuit G1.

Thanks,
John

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