Starter relay/solenoid for Rotax 912 or similar

[danny_galaga]

So what are you guys using for your Rotax or Jabiru starter motors? I just ordered some bits and pieces from overseas and thought I had included a Nippon Denso relay in the order. Looks like I forgot it, so if there's something thats proven amongst you guys I can get locally I'll do that. 

 

FYI, the Rotax part is a denso starter relay part number 182800-1950. It's less than half the price of a 'rotax' one. Pretty much anything around that size will do, including the knock off version.

 

BUT.... if I use a $20 relay, and the contacts fuse together, it wasn't much of a savings if my starter motor goes nuclear 😄

 

 

I tried looking at other similar relays to get a feel for what's out there, but hard to tell without specific part numbers for each. I looked at relays for Honda CB900, BMW R1200, Polaris, Harley Davidson etc 

 

When I was a sparky, the solenoids we used for cars were fairly cheap, but blowing up a Rotax starter is a different ballgame to blowing up a Cortina starter 🤣

 

[Blueadventures]

42 minutes ago, danny_galaga said:

So what are you guys using for your Rotax or Jabiru starter motors? I just ordered some bits and pieces from overseas and thought I had included a Nippon Denso relay in the order. Looks like I forgot it, so if there's something thats proven amongst you guys I can get locally I'll do that. 

 

FYI, the Rotax part is a denso starter relay part number 182800-1950. It's less than half the price of a 'rotax' one. Pretty much anything around that size will do, including the knock off version.

 

BUT.... if I use a $20 relay, and the contacts fuse together, it wasn't much of a savings if my starter motor goes nuclear 😄

 

 

I tried looking at other similar relays to get a feel for what's out there, but hard to tell without specific part numbers for each. I looked at relays for Honda CB900, BMW R1200, Polaris, Harley Davidson etc 

 

When I was a sparky, the solenoids we used for cars were fairly cheap, but blowing up a Rotax starter is a different ballgame to blowing up a Cortina starter 🤣

 

That’s where a starter still engaged warning light is a benefit and also an isolation switch to allow cutting voltage.

[danny_galaga]

I can keep it simpler by just using a good solenoid. What brand have you got? Is it the original Rotax part? 

[onetrack]

A suitable replacement solenoid for the ND 182800-1950 is the Quicksilver 8M0185622. This is a Mercury outboards solenoid, and it comes with a good marine reputation.

 

There's even a NOS one on eBay for US$29.95, but you'd have to ask the seller if he posts to Australia. Otherwise, it's on Amazon, new, for US$58.80 with free delivery, and that price equates to around AU$87.

[facthunter]

A starter energised light costs nothing and could save your life. Any solenoid can weld the contacts. I've had it happen and you need to know.  Nev

[danny_galaga]

13 hours ago, facthunter said:

A starter energised light costs nothing and could save your life. Any solenoid can weld the contacts. I've had it happen and you need to know.  Nev

I think I might do that. But 'saving your life' might be dramatic. When a starter stays engaged, it gets spun up to higher revs than it's designed for. The armature windings start to move out, and at some point they, or the commutator segments fly out and arc out against the housing. As you would probably have seen, it's a big explodey mess inside the starter, no doubt. But once everything has fallen away the arcing stops pretty quickly. 

 

I take your point though. It would be yet another one of a large number of things that can rob your engine of power on take off. In this case, the loose chunks of copper etc inside the starter can cause extra drag on the engine.

I'll pop in to Jaycar aeronautics and get a small panel mounted LED. I'll mount it where the key points at the starter position 🙂

Edited April 1, 2023 by danny_galaga

[skippydiesel]

On 01/04/2023 at 11:10 AM, facthunter said:

A starter energised light costs nothing and could save your life. Any solenoid can weld the contacts. I've had it happen and you need to know.  Nev

Seem like a simple/easy installation, that could save a starter motor - worst case scenario engine/aircraft/life.

 

I assume the LED would be wired, so as to glow when start circuit/solenoid activated - off as soon as switch/key released. In the event of a continuous starter/solenoid operation the LED would continue to glow?????

[danny_galaga]

All you need to do is run one wire out to the starter side of the solenoid, and the other to negative bus. Then it only comes on when starter is cranking. If contacts stuck, light will stay on.

 

If you wanted the reverse logic, you would have one wire on starter side, and the other on positive bus. Since a starter is almost a dead short at rest, in effect it is negative until you start it. So in that case the light would be on all the time except when starting, or contacts fused, or the internals of the motor are totally obliterated! Not really any point, I'm just showing off 😄

Edited April 2, 2023 by danny_galaga

[danny_galaga]

I should add that a light on it's own isn't going to save your starter motor. You will need a battery isolator as well. I haven't got a battery isolator in my plane, might add one later. But the warning light will tell me the contacts are fused and best not to take off. All I can do at that point is shut off the fuel. Motor will stop, and starter will keep cranking till the battery goes flat or it burns out 😃

Edited April 2, 2023 by danny_galaga

[skippydiesel]

31 minutes ago, danny_galaga said:

I should add that a light on it's own isn't going to save your starter motor. You will need a battery isolator as well. I haven't got a battery isolator in my plane, might add one later. But the warning light will tell me the contacts are fused and best not to take off. All I can do at that point is shut off the fuel. Motor will stop, and starter will keep cranking till the battery goes flat or it burns out 😃

On reflection - I agree.

 

If the solenoid is "welded/jammed" on, only disconnecting the battery will stop the starter  rotating - I will review my electrical system, with a view to installing a pilot operated, mechanical, battery isolator (will also enhance security) .

[facthunter]

Any DECENT electrical system has an isolator as well. I wouldn't fly without one. You don't want an in fight fire and if you are forced landing in rough Hit it before you flare. It's often referred to as a "Crash Bar". Cranking volts don't usually drop below about 9 fora 12 volt battery due to load till the battery is well discharged. Starter motors have an ON /off duty cycle limit a lot don't know about. A plane is not operating normally without a good condition battery with plenty of charge unless it's a very basic thing.  Nev

[danny_galaga]

Agreed. But it won't be long before either the battery is flat or starter has melted down if the solenoid is fused. The voltage will drop extremely rapidly once it's been cranking for a while. This is because at rest a starter has virtually no resistance. When it is spinning it produces back emf. So at the instant of start, it might draw 500 amps, and within a fraction of a second, it is drawing only 100 amps because it is spinning. 

 

But say it gets down to maybe 8 volts. Now there isn't enough voltage to spin the starter, or at best very slowly.so it's virtually presenting as a dead short again to the battery. Now instead of only 100 amps, it's drawing 300 amps. At 8 volts it's discharging at 3 times the rate it was at 12 volts! The figures are just ball park to illustrate, but you get the drift. 

 

I'm not saying that's a great thing to happen, just pointing out all things being equal your battery will be quite flat quickly in that scenario, or the starter will burn out, going open circuit.

 

I'm in two minds about adding a battery isolator. Yes, it could be safer but I'm also adding more and more weight and complexity. A ballistic chute thingy would make my plane safer too. Where does it all stop? 

 

But you have sold me on the warning light 🙂

[facthunter]

If the engine starts the starter just spins unchecked as it doesn't catch up with the engine speed and the back EMF will reduce the current draw but the starter will centrifuge apart in the armature windings and jamb/cook itself while still putting a high drain on the battery. By then the alternator be providing extra energy to the system. Any mechanical relay can weld points. A cable pull starter like the earlier Continentals had was far safer and easier on the accessories case internals too..  Nev

[danny_galaga]

I think I've covered all that in previous posts. If engine continues running with solenoid fused, starter destroys itself through centrifugal force because the starter will remain engaged with the engine. Ratio of pinion to ring gear is easily 20:1 so even if the engine is only running at 1000rpm, the starter is spinning at 20,000rpm!  If you stop the engine, then starter keeps spinning the engine over until battery goes flat, or starter melts down. As you alluded to before, starters don't like cranking for long..they get hot really quickly. If it has field windings, the insulation burns up causing shorts . And whatever type, the armature windings can also short out if very hot. The brush tags, if soldered can melt off. If the armature has soldered commutator segments, those can also melt. Molten solder is a saving grace in this case because everything becomes open circuit very quickly. 

 

The only way the starter would keep spinning for any length of time is if the pinion clutch failed, or didn't engage the ring gear. Then the starter would spin quite happily for ages. Although that would give you plenty of time to disconnect the battery 🙂

Edited April 2, 2023 by danny_galaga

[facthunter]

IF the starter pinion stays engaged with any engine revs on it will demolish the clutch very quickly and extra damage will ensue. This is  one of your "worst case scenarios"  Not all starters use a car type ring gear It's often into the accessories drive case and bits dropping off in there will ruin the engine.  Nev

[onetrack]

I've run multiple hundreds of engines over 57 years of owning and repairing vehicles and equipment, and I cannot ever remember a solenoid welding the contacts on me.

Starter manufacturers go to great pains to develop copper alloys that resist welding. I think there's probably a much greater chance of a short circuit creating problems, and as a result, attention to wiring design and security has to be a far more important area to focus on. A smoke-filled cockpit will ruin your day very quickly.

[danny_galaga]

59 minutes ago, onetrack said:

I've run multiple hundreds of engines over 57 years of owning and repairing vehicles and equipment, and I cannot ever remember a solenoid welding the contacts on me.

Starter manufacturers go to great pains to develop copper alloys that resist welding. I think there's probably a much greater chance of a short circuit creating problems, and as a result, attention to wiring design and security has to be a far more important area to focus on. A smoke-filled cockpit will ruin your day very quickly.

Agreed. I've seen it, having been an auto electrician, but it's not common. But what I'm driving at I guess is you increase the risk of it happening if you get a cheap solenoid. The contacts might not be as good a grade of alloy, or not very well aligned etc. So the original thrust of this thread was to find a reputable solenoid brand I could go with that is available in Australia. The mercruiser one was mentioned, but hard to know if I'm getting the real deal or not. But everyone can stop looking, because I've discovered a popular Rotax engine that uses the same Denso solenoid 🙂

 

https://www.rotax.com.au/shop/item/starter-relay-evo

 

Which you can get from Go kart shops etc. My journey is done, and I'm also fitting a starter indicator light as well thanks to this thread. Thanks guys!

 

[Blueadventures]

1 hour ago, onetrack said:

I've run multiple hundreds of engines over 57 years of owning and repairing vehicles and equipment, and I cannot ever remember a solenoid welding the contacts on me.

Starter manufacturers go to great pains to develop copper alloys that resist welding. I think there's probably a much greater chance of a short circuit creating problems, and as a result, attention to wiring design and security has to be a far more important area to focus on. A smoke-filled cockpit will ruin your day very quickly.

Agree, heard of a loose connect on a keyed start switch that closed circuit for starter to the on terminal.  This is why I always encourage the starter on warning light and the isolation switch as necessary and a must have. Also include a fuel off valve just before the firewall cabin side not just at the tank feed area. There could be times need immediate or as quick as possible method of stopping engine.  The feed for light is starter side of solenoid. Cheers

[skippydiesel]

1 hour ago, facthunter said:

IF the starter pinion stays engaged with any engine revs on it will demolish the clutch very quickly and extra damage will ensue. This is  one of your "worst case scenarios"  Not all starters use a car type ring gear It's often into the accessories drive case and bits dropping off in there will ruin the engine.  Nev

Rotax 912 range use a SPRAG clutch

[danny_galaga]

Received my solenoid from the kart shop ok. I was going to buy one from Ecclestone aviation in the UK where I bought my Rotax fuel pump from but I forgot. Hence my mad scramble to find something in Australia 😄