Starter motors, excitation.

[tom2207]

it starts when the starter is bridged ,, so heavy side is ok , only leaves the loom as the issue. ,,, been mentioned earlier .

yes, please expand on that.

check the connections on the start switch , meter the switch its self for volt drop , and or resistance , if nothing obvious , connect a bit of two core , say ten feet or what evers needed between the big pos feed and the relay pos input on the motoor as if you were bridging it , then touch the two wires together , in effect remotely bridging the starter , if that works you know the wire length isnt an issue , then just fit a push starter button and use the new wires ,,, spend a bit of time running in the cable , as mentioned before , use marine grade cable it really does matter , waterstop if you can find it , pre tinned multistrand if you cant , solder all the joints where possible , and heat shrink everything with color coded glue lined heat shrink ,,, water ingress in cables in a marine environment is a pain in the bum ,,, wire goes black , connections develop resistance issues etc etc , get rid of the failure points by design from the start , yep it costs more in materials , time and effort , but its an investment. hth ,,,

 

[m_c]

Starter motors require quite a lot of initial current on the excitation terminal, and some starter motors are inherently more prone to needing a very good feed to fully engage.
We used to have quite a few issues with certain Merc Sprinters due to this, and we found genuine Mercedes starter motors were far less prone to the issue, compared to reconditioned aftermarket starters.

However in your case, as it's an ongoing issue, I'd just wire in an additional relay. I'd go for a 12V 70A relay (one with the larger 3/8"/10mm spade terminals), just so the contacts aren't being worked too hard.

 

[Barking Mat]

yes, please expand on that.

check the connections on the start switch , meter the switch its self for volt drop , and or resistance , if nothing obvious , connect a bit of two core , say ten feet or what evers needed between the big pos feed and the relay pos input on the motoor as if you were bridging it , then touch the two wires together , in effect remotely bridging the starter , if that works you know the wire length isnt an issue , then just fit a push starter button and use the new wires ,,, spend a bit of time running in the cable , as mentioned before , use marine grade cable it really does matter , waterstop if you can find it , pre tinned multistrand if you cant , solder all the joints where possible , and heat shrink everything with color coded glue lined heat shrink ,,, water ingress in cables in a marine environment is a pain in the bum ,,, wire goes black , connections develop resistance issues etc etc , get rid of the failure points by design from the start , yep it costs more in materials , time and effort , but its an investment. hth ,,,

Ok, give me a minute...

6mm section, you will start...starter motor.

 

[Barking Mat]

Starter motors require quite a lot of initial current on the excitation terminal, and some starter motors are inherently more prone to needing a very good feed to fully engage.
We used to have quite a few issues with certain Merc Sprinters due to this, and we found genuine Mercedes starter motors were far less prone to the issue, compared to reconditioned aftermarket starters.

However in your case, as it's an ongoing issue, I'd just wire in an additional relay. I'd go for a 12V 70A relay (one with the larger 3/8"/10mm spade terminals), just so the contacts aren't being worked too hard.

I appreciate this, and think this is thé way forward.

Although, it invités extra gremlins into thé équation.

 

[tom2207]

I appreciate this, and think this is thé way forward.

Although, it invités extra gremlins into thé équation.

if it actually was the way forwards they would have done it that way at the start ,,, its a work round but your still needing the now [ probably] failing wires in the loom from the key , or the faulty key switch or what ever isnt fixed to feed the relay to get it to start ,,,, it really isnt the way to fix it , its a way to bodge round the problem for the time being ,,,

theres no hard shoulder to pull onto at sea.

 

[Barking Mat]

if it actually was the way forwards they would have done it that way at the start ,,, its a work round but your still needing the now [ probably] failing wires in the loom from the key , or the faulty key switch or what ever isnt fixed to feed the relay to get it to start ,,,, it really isnt the way to fix it , its a way to bodge round the problem for the time being ,,,

theres no hard shoulder to pull onto at sea.

Thanks F##k it's a canal.

 

[Barking Mat]

if it actually was the way forwards they would have done it that way at the start ,,, its a work round but your still needing the now [ probably] failing wires in the loom from the key , or the faulty key switch or what ever isnt fixed to feed the relay to get it to start ,,,, it really isnt the way to fix it , its a way to bodge round the problem for the time being ,,,

theres no hard shoulder to pull onto at sea.

Well, yeah, you would have thought so, but.......

 

[sparkysy]

This is sounding like a loom fault as @tom2207 says either rubbish cable gone and degraded or a faulty crimp or contact somewhere, disconnect them both ends and do a low resistance test, you can then check that this corresponds to the reading you should be expecting. Also worth doing an insulation test on the cable if you can. disconnect it first this will prove if it's rubbed through or the insulation has failed.
Do you have a insulation and low ohm continuity tester, unfortunately a multimeter won't cut it for the tests I'm proposing.
Last resort if you end up having to rewire it just use a heavier gauge twin core if the length is an issue with 3mtrs of 1.5 try 2.5 instead as it's resistance will be lower!
I love fault finding, if you were closer I would be there like a rocket to find it, just to know what it was!
Sy

 

[tom2207]

Thanks F##k it's a canal.

Ive sailed on some of those canals ,,, may as well be at sea. lol
size does matter.

 

[m_c]

The probable actual problem is the original loom being underspecced.

We've got some equipment with Perkins engined power packs, and most problems are around how the equipment manufacturer has interfaced to the power packs.
As soon as you add in that extra layer of design, the finer details get lost, so although the power pack may use 1.5 wire for the starter which works fine when the switch is on the side of the power pack, when you then extend the wiring using 1.5 to have the switch say 3 metres further away, it's then borderline voltage drop for the starter to engage. The engine manufacturer would probably have guidelines on the required wiring, which the power pack provider doesn't forward on, as they're not expecting somebody to move the switch.

If it's easy enough to upgrade the wiring, then that is likely the easiest option, but adding an extra relay may be the easier option. Provided it's installed well, there's no reason for it to be any less reliable than running heavier cable.

 

[Barking Mat]

This is sounding like a loom fault as @tom2207 says either rubbish cable gone and degraded or a faulty crimp or contact somewhere, disconnect them both ends and do a low resistance test, you can then check that this corresponds to the reading you should be expecting. Also worth doing an insulation test on the cable if you can. disconnect it first this will prove if it's rubbed through or the insulation has failed.
Do you have a insulation and low ohm continuity tester, unfortunately a multimeter won't cut it for the tests I'm proposing.
Last resort if you end up having to rewire it just use a heavier gauge twin core if the length is an issue with 3mtrs of 1.5 try 2.5 instead as it's resistance will be lower!
I love fault finding, if you were closer I would be there like a rocket to find it, just to know what it was!
Sy

I appreciate the offer.

 

[Barking Mat]

The probable actual problem is the original loom being underspecced.

We've got some equipment with Perkins engined power packs, and most problems are around how the equipment manufacturer has interfaced to the power packs.
As soon as you add in that extra layer of design, the finer details get lost, so although the power pack may use 1.5 wire for the starter which works fine when the switch is on the side of the power pack, when you then extend the wiring using 1.5 to have the switch say 3 metres further away, it's then borderline voltage drop for the starter to engage. The engine manufacturer would probably have guidelines on the required wiring, which the power pack provider doesn't forward on, as they're not expecting somebody to move the switch.

If it's easy enough to upgrade the wiring, then that is likely the easiest option, but adding an extra relay may be the easier option. Provided it's installed well, there's no reason for it to be any less reliable than running heavier cable.

Yes, yes and yes, I thoroughly agree.

 

[hunter27]

Older Yanmar marine diesels have a similar problem including my last boats 1GM10 and my newer boats 2GM20 I have had the same thing happen occasionally, press the start button and nothing is heard from the cockpit a second or third press and it starts as normal. There is loads about this on the internet, the general thinking is that the wiring loom fuse fitted by the engine is a rubbish plastic housing with a copper clip on both ends and a standard fuse. A common fix is to replace the fuse with a bolt in mega fuse which I have done in both cases but I also think that the wire size is barely adequate and being a loom has several connectors.

 

[Turbo]

I would suggest that the 1.5mm2 cable you used to test it is a bit too weedy, some starter solenoids can take a fair few amps to pull them in. At 240v 1.5 flex will handle up to 13a but at 12v it's a whole lot less!
Vehicle flex is usually measured in swg & you'll find a conversion chart online between swg & mm2 plus a chart giving current capacities of swg cable at 12v.
Also note that due to the low voltage (12v) you get more voltage drop so on long runs you need thicker cable.

 

[Neilj]

If you only have 10.5v at the starter excitation terminal, then I'd say you've got a bad connection somewhere. It could be between the ignition switch and the starter solenoid or it could be in the feed TO the ignition switch from the battery. Inline fuses are a likely candidate if you have any; a bit of water ingress and corrosion play havoc with them.
The solenoid on a starter like that has two windings; a high current one and a low current one. When energised, both windings are activated (lots of current) and once the solenoid has pulled in fully and contact made the high current winding drops out, leaving the low current winding energised to simply hold the solenoid in place. They take quite a few amps to pull in but not a lot to hold in place.

 

[Guineafowl]

Newbie here, but I’ve done a fair bit of this.

You’ve identified a voltage drop, and the next stage is to locate it with (+ to +) and (- to -) voltage drop tests, with the circuit loaded. You’ll need someone to hold the key on.

With one meter probe held on the +ve battery post (the lead post, not the clamp), put the other on the +ve clamp. You should see close to 0V. Now, ‘walk’ this second probe to the next available measurement point, and carry on till you reach the starter excitation terminal.

You should see pretty much 0V all the way along, however, if your 2V or so shows up, your probe just crossed the bad connection.

Repeat the above with the negative side of the circuit. Starting at the lead battery post, etc. It’s possible that, rather than having voltage drop along the +ve leg of the circuit, a bad earth connection is causing the starter body to float up by a few V. Doing these tests will find it.

Easier to show you than describe, but this should solve the mystery.

 

[Justme]

The volts on the feed might show as 12.7 but under load it will drop due to a feed cable issue.
Replace main feed with new cable direct to bat.

 

[500e]

The +to+ -to- is a simple test that tells you so much would use tinned copper cable as @tom2207 suggests have seen newish plain copper wire just fall apart in virtual dust.
Link

2.5mm/14 AWG Oceanflex Tinned Single Core Thin Wall Cable - 50M Reel (29 amps)

High temperature thin wall low voltage wiring cables suitable for use in the automotive, marine and other harsh environments. The tinned copper conductors make this cable more resistant to corrosion. Manufactured in accordance with ISO 6722-1:2011 (class B) 105°C. Suitable for 12v and 24v...

www.furneauxriddall.com

You only need single core as the - side should be the engine casing starter body ( dont ignore earth between starter and engine) direct to battery
Presume the start cable comes off the ign sw is it fused, (a suspect) doing @Guineafowl,s test will show any high resistance, start the + test at battery Post and check for voltage between there and starter solenoid.
Surprising how often I have found 2/3 volts drop on - to engine dirty connections, under speck wire from battery to engine, the Mk5 Cortina was a prime example
Battery volts drop to under 9V for split second as the SM takes MAX amps been here with numerous vehicles and boats

 

[Red'n'Black]

do it right once , its hard to bump start a boat.

 

[CKJDJK]

I have had similar issues. Each joint in the cable gives a volt drop. as does the length of the cable. Add to this, the switch will give a volt drop and you soon get below the required volts to energise the starter relay. just measuring with a test lamp shows the circuit working but closer look with a meter shows the lack of volts when under load.
Fit a Lucas plant type ingnition switch with new cable 2.5MM from battery positive and new cable 2.5mm to starter solonoid all with soldered connectors and I am sure your starting problem will be fixed.