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Old 05-18-2013, 04:37 PM   #15
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This has become a very interesting thread, Thanks Scout! I checked this out on my rig and sure enough the starter relay solenoid (SRS) load side is hot at all times, even when the chassis battery switch is off & the Vansco's are dead. That's obviously not a very bullet proof design should any weakness occur in the SRS.

Here's an idea I'm going to try. My SRS is on the aft side of the rear bulkhead making up the battery compartment, & looks like this:

OEM perma-hot stud is on left, energized load out to starter Bendix unit is on right, coil ground is the black wire on middle left, coil signal is on middle right (I can apply 12V on this stud & crank the engine, good to know for hot-wiring if needed).

I'm going to take a 50A Bosch relay, take the perma-hot off the SRS & run it to the load input side of the 50A contacts, and the load output to the former perma-hot lug on the SRS. I'm going to ground one side of the Bosch coil (probably as a double tap to the SRS middle left stud), & run a double-tapped wire off the middle-right SRS stud to the other Bosch coil spade.
The net effect leaves a permahot starter input in the system, but I now have to weld two sets of contacts in parallel to engender this problem, and as long as one set is not welded it will take a full key turn to "start" position to energize. I can test the Bosch relay & SRS from time to time to see they are still doing their job. This is no slouch circuit BTW, so I wouldn't try a cheapo 30A Bosch relay, I'd look for one w/full 50A rating; these have 3/8" spades for the load & 1/4" for the coil and usually only 4 spades total, Bosch# 0 332 002 190 is one variant & the one I'll use.

For a replacement of the SRS I'd carry a Cole-Hersee 24059, any variant (they come w/a "-X" suffix so 01 or 08 or whatever), which has proved to be a reliable device for this, an HWH Pump Relay or Main Relay replacement, etc.
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Old 05-18-2013, 05:45 PM   #16
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EM--you lost me at "hello" but that is my steady state these days. I lost my way a bit during the install of the new solenoid and had to jump each of the small studs from the hot side to detect the starter switch input--sure enough, the engine will crank if you jump the switch input stud.

PS--perhaps the scariest part was that early on in the diagnostic process, we made several failed attempts turning the key to start position before we managed to get a crank-over and the engine started. I was standing by the open bat compartment door with the engine running when I heard "the whine" [ie a hung starter]. However, the whine wasnt that noticeable so it was just dumb luck that I suggested a couple of restarts. Again, I didnt really suspect a starter hang until the engine was shut-off and I heard what sounded like the starter continuing to spool on. This led to a casual check of what by then, was a very hot starter housing. At that point, we knew we had a problem.
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Old 05-18-2013, 06:59 PM   #17
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OK, to recap- the OEM setup is an in line relay (SRS) to the starter solenoid, which relay has a permanently hot input waiting for the switch to engage. If the switch engages & welds, you have a problem condition requiring disassembly of the battery connection to halt the starter.

I'm putting a second relay switch in line, so you'd have to weld two consecutive sets of contacts to have the same fault, and if you don't then turning off the key will disconnect power to the starter solenoid. I'm figuring on using the same signal & ground as the original SRS. That way the key-to-start signal still provides the same connection, but perma-hot has to go thru relay + SRS, and if either hasn't welded its contacts the circuit still works as designed. If the contacts fry (as in your original no start situation), you still have a no-start, and you have the option to correct it by identifying the bad relay or SRS & bypassing it in the circuit.

Could accomplish the same thing w/an inline manual switch to cut the perma-hot feed. But I'm thinking that's a pain that the relay makes more automatic. I'm open to suggestions on better wiring to be sure.
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Old 05-18-2013, 07:11 PM   #18
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Mike, I am sure you will measure the voltage drop across each relay so we will know that we are getting full voltage during starting with your mod. I think it is a good idea.
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Old 05-18-2013, 07:17 PM   #19
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Quote:
Originally Posted by alpinedrvr View Post
Where is the starter located on a ISC 350?

Geoff
2000 38 FDS
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Under engine on the passenger side, right on the bell housing. Big and heavy too.
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Old 05-18-2013, 07:17 PM   #20
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R&C- For that I'll need a beautiful assistant from the audience. Can't crank & measure volt drop at the same time. I'll see what I can do & post results.
Right now I don't have any insulated 3/8 female spade connectors in my collection of trash, which isn't like me as I have a pretty solid collection, so it'll have to wait for a trip to the store.
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Old 05-18-2013, 09:47 PM   #21
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Dont think voltage drop is a major issue here. Starter motor draws amps directly from the bats [hot wired] once the circuit on the starter-mounted solenoid is closed. So the amps going thru EM's inline solenoids only need to activate the solenoid on the starter motor, eg, throw the drive gear on to the fly wheel and complete the ground circuit for the starter motor. Again, amps flowing thru these inline solenoids dont actually turn the starter motor.
EM --I like your solution of preventing a hang-up vs just being notified [eg a buzzer]. This is classic risk analysis --chances of a hang-up appear small but the potential impact is significant. The fact that you: 1--have to physically disconnect the bats to kill the starter and 2--its hard to detect/hear a hung starter make prevention even more desireable.
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Old 05-18-2013, 10:21 PM   #22
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Under engine on the passenger side, right on the bell housing. Big and heavy too.
thanks Mr _D

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Old 05-19-2013, 08:04 AM   #23
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Mike,

If you want to add redundancy to prevent a single failure of the SRS in either the stuck closed or stuck open position, you could duplicate your series connected relay pair and put another series connected pair in parallel (Then you would have 4 relays total). In normal operation, this will also split the load current between the 2 parallel circuits and extend the life of all the relay contacts. Probably overkill but just a thought.

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Old 05-19-2013, 02:07 PM   #24
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EM - Is it possible to feed the permanent hot connection on the solenoid from the chassis shut-off switch? My thought is to have a direct means of killing the power as opposed to grabbing a wrench in a panic situation and disconnecting the battery. I don't have my chassis diagram handy but if the chassis cut-off is fused then perhaps the additional solenoid/starter amps would pull too much for that fuse. Otherwise, it seems like a simple approach. You could still wire a buzzer to the solenoid output for problem detection.
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Old 05-19-2013, 05:31 PM   #25
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Dave- now that you mention it, the failure appears attributable to arcing of contacts, a fairly instantaneous issue related to energizing & mechanical delay aspects of each device; no way to predict which part(s) will experience the arcing, but some will. While the load would be split in run mode by making parallel redundancy, the arcing load would fall to one, two or three of the 4 parts you describe, with either 2 or 3 of them arcing at half the amps when the fastest circuit is already completed. So whether we go 2-stage-series, or 2-stage-series-parallel, the first stage is still vulnerable, we've just eliminated the perma-hot direct to a single output that would fry a starter or at least give the owner a heart attack trying to kill the circuit quickly.
So since the problem is arcing, we could replace the arcing device w/a better suited component that is a non-arcing type device, a solid state relay. These tend to be spendy, and need to be tailored to the use, it'd have to be a potted type and sufficiently robust to handle the initial spike amps.

I just put my recording amp probe on the SRS, tickled the signal post using my Power Probe 3, & recorded spike & run amps while cranking; I'm getting 20A run, 30A peak draw on the SRS contacts. Now I need to look for a solid state replacement part meeting those specs. I can leave the SRS mounted in place to use as a spare in case of replacement part failure. Much better solution.
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Old 05-19-2013, 06:24 PM   #26
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BC- yes, you could rewire the input from the Chassis disconnect & use that manual switch as a cut-off. However, in the event you are in the driver seat & start as usual not knowing the SRS contacts are welded, you'll get to your first pit stop at lease before you know there is an issue, absent a fail safe buzzer. Rewire + buzzer makes for a semi-manual solution.
One thing's obvious- carry a spare SRS in any case, whatever you are using for that switch function; no point in having that failure then needing to hunt down parts.

Another solution would be a 1/2 second delay in energizing the load circuit. You could have the SRS make contact, then energize the load path and eliminate the arcing.
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Old 05-20-2013, 11:12 PM   #27
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Mike,
Any electromechanical relay will eventually fail primarily due to the contacts going bad. The contacts can fail to close, get welded shut, or totally disintegrate. The failure happens over time and is caused by arcing that results in metal transfer and oxidation each time the contacts open and close. This causes the contact resistance to rise which in turn causes the contacts to get hot and eventually burn up or weld shut.

Switching an inductive load, such as with a starter solenoid coil, makes the arcing much worse due to the huge counter EMF spikes encountered when the contacts open or bounce during closing. As an electrical engineer early in my career, I designed a few power systems for fault tolerant applications. We always included arc suppression circuits across the contacts of any relay. These consisted of a combination of capacitors, resistors and diodes designed specifically for each application. I am not familiar with the internal design of automotive starter solenoid relays, but I always assumed that they included arc suppression circuitry. If not, the simplest way to greatly increase the life of the relay would be to design and implement an external arc suppression circuit.

That said, a properly designed solid state relay would have even a longer MTBF. In your last post you talked about measuring the current spikes, but you did not mention voltage spikes. The solid state relay would either have to be designed to suppress voltage spikes from an inductive load, or an external suppression circuit would need to be added. If not, the solid state relay could become toast very quickly.

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Old 05-21-2013, 08:38 AM   #28
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As mentioned in an earlier post, I have rewired the SRS power feed to the chassis disconnect switch and wired a backup beeper to the load side of the SRS. I listen for the beep during start and after. If I hear it with the engine running I know there is a problem Works for me.
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