UK Monster Owners Club Forum » .: Technical :. » Electrics » Ignition fuse blows at high revs

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Old 12-10-2019, 05:59 PM   #1
FrankenDesmo
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Ignition fuse blows at high revs

I've just replaced the RR on my M900, and I'll be honest I've replaced it with a cheapie from eBay for £25 so I'm aware this could very well be the source my problem - however:

Since wiring it in, the 'not-charging' light has gone out and the bike seems to run perfectly fine - unless I wind it out to max revs, at which point the 'not-charging' light returns and the bike dies. When this happens, the 7.5A ignition fuse has blown.

I've replaced the fuse and ridden around, keeping revs below roughly 6k, with no issue. I'm about to take it out again for another wee test ride (with a whole bunch of extra fuses just in case...) - I'll wind it out when I'm close to home to see if it happens again, and see if I can get a better idea of where the needle's pointing when the charge light pops up.

Is there anything particularly common that could be causing this? I struggle with the 'where to start' part when a new electrical gremlin surfaces, so any help is appreciated.

(I did do a reasonable search to see if this has been covered elsewhere on the forums, so my apologies if this is a common problem that's been done to death).
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Old 12-10-2019, 07:46 PM   #2
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7.5-8k rpm seems to be the breaking point. I just rode for ~20mi, at one point sitting on 7k rpm for a bit (and well within the law I might add), but it wasn't until on the way home when I purposely opened it up it went pop around there.
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Old 12-10-2019, 11:34 PM   #3
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The fuse is getting hit with too much load, the bike isn't going to be pulling significantly more amps just because the engine revs are up BUT it will be making more volts and current.
Sounds like it might be a problem with the voltage spiking which points you at the regulator
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Old 12-10-2019, 11:46 PM   #4
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Sounds about right, as it also seems that the battery probably isn't getting charged. I've pulled it out to charge it on the mains overnight, and I'll do some of the basic charging tests with a multimeter tomorrow.

I really shouldn't be shocked that this cheap regulator probably doesn't work. Might need to invest in the mosfet replacement sooner rather than later.
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Old 13-10-2019, 10:29 AM   #5
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Sounds like a regulator issue. The stanard Ducati reg/rec is ok ive found if relocated into cooling air flow as heat is the main failure mode of those shunt type.
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Old 13-10-2019, 02:54 PM   #6
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Aye, the battery is not charging

I've followed the directions on Kato's post, and come up with:

Battery voltage:
13v not connected to anything (freshly charged)
12.97v connected with nothing switched on (probably a pointless test really)
12v at idle (1k) with lights on
12v at rev (up to 6k) with lights on (well, 11.97 at this stage)

I think that safely sums up the no charging, but is the problem the RR or the Stator? To be honest, I couldn't tell, and I could have been doing these tests wrong.

This is all done on an £8 Rolson digital multimeter from Halfords, and I'll be the first to admit I'm not that clued up when it comes to testing.

First off, I set it to Diode mode, then to Resistance (on the smallest resolution - 20), and from what I can gather, when the display just shows a '1' off to the far left (instead of to the right when it's measuring something), it means there's no continuity/open circuit.

Testing the two stator output wires together I get 001 in Diode mode, 0.8ohm in Resistance mode.

Next I tested the stator input wires to the battery output wires (white & black) on the RR - in each case (Diode & Resistance) I get '1' (OC).

There is a another red wire, and I'm not sure what this one is - it's a pair from the RR which are joined together and connected to a single red wire on the bike (on a stock RR this is a spade connector). If I hold the negative meter lead to the red wire and the positive to the stator inputs, I get '1' for both tests. If I hold the positive to the red wire and the negative to the stator inputs, I get 441/436 on the Diode test (each number is for each stator wire).

Tbh, I wouldn't be surprised if I've messed up the whole test, but I think the 0.8ohms on the stator output suggests that the stator itself should be OK?

I realised after I'd finished that I didn't do an AC voltage check with the bike running, so I'll have to try that too.

Am I right, though, in thinking this is a duff RR and my Stator is probably fine?

Thoroughly confused
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Old 13-10-2019, 03:11 PM   #7
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Check this out...
https://cdn.shopify.com/s/files/1/10...29069374954073
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Old 13-10-2019, 03:20 PM   #8
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Cheers, I'll have another crack at some more meaningful diagnosis at some point during the week.
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Old 13-10-2019, 03:30 PM   #9
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To complete the picture you're going to have to do the AC test, as you said, to see if the alternator is giving a supply. The previous fuse blowing would suggest that it is (or was).

If the alternator checks out satisfactorily, then it does point to the RR. But don't write it off straight away. Check all the connections in and out of the RR for good continuity and LOW resistance.
I mean check that current is passing from one side of the connection to the other. Just because the connector is together, doesn't always mean that current is going through.
If you can get your meter probes onto a bit of bare wire where the cable goes into the back of the connector, so much the better. Or push into the conductor through the insulation, close to the connector, where the puncture can be re-sealed with heat shrink.

If the RR does prove to be the problem, then seek a refund from the seller immediately and put it towards a better item.
As you will have already read, the connections from the alternator to the rectifier (three or two yellow cables) must be good electrical connections with LOW resistance and good weather protection. I use Gold connectors on these.
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Old 02-11-2019, 02:02 PM   #10
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Wow new month already - I still haven't found the time to properly diagnose the RR & Stator!

I've just SORNd the bike for the winter as finances have been too tight to do this properly with decent parts, so I'm going to take my time and use the winter to fix a few things.

First up I'll need to check the output of the stator to make sure that is OK - if it's a dud, then that's the first bit to replace.

One thing I have noticed on my stator wires when I strip them is that the exposed strands are sticky with some kind of glue-like residue. Possibly something from the inside of the sheathing? I'll give the ends a good clean with some petrol or similar before testing the output / crimping new connectors.

I'm also going to put in one of the MOSFET RRs supplied by roadstercycle.com, and get a proper crimping tool at the very least. I will try to find some gold connectors Gazza, I know you've mentioned RC hobby shops, so I will see what I can find around Glasgow (or online). I'll likely mount this in the stock location, as the higher-quality connectors in the kit should pose less of a problem with the weather.
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Old 02-11-2019, 05:55 PM   #11
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Sticky residues don't bode well for good connections. My first thoughts are that it's the result of melting insulation from overheated cables, but that would probably re-set hard again when cool?
You would probably be better off cutting back to clean cable, than trying to clean what you have (contaminant unknown), provided there is sufficient length.

I use 4mm soldered Gold bullets, which I think are good for 50amps. RC model shops are a good source, or like everything else, just order online.
GWS is one such online source, but they never let go once they get your email address, so be warned.
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Old 02-11-2019, 06:12 PM   #12
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That was after cutting back, though not far from the old connectors (don't want to run out of wire!). I guess if they have overheated (outside of the sheath looks fine to the engine case), then there's a good chance of seeing problems with the output tests (assuming it's got hot enough to melt through inside the stator and start shorting the wires together).

Having a look online at the moment, can't find a GWS though?
I'll be looking for some crimp connectors (ideally just butt connectors as I'd like the wiring to be more or less permanent), have read that solder can cause problems with corrosion, not to mention that I don't have a soldering iron, nor can I solder very well!
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Old 02-11-2019, 06:21 PM   #13
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Something like this might be a goer: https://compassaudio.co.uk/product/c...speaker-cable/

Edit: wait, that's just a plug - need the corresponding socket.
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Old 24-11-2019, 02:22 PM   #14
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I have finally gotten around to measuring the stator output (no excuse, pure laziness).

First I did the resistance check from stator wire to engine ground - open circuit when both running and shut down, so no probs there.

Next I checked the AC voltage output while running (stator not connected to anything besides the meter):

1k rpm (idle): ~15V
3k: ~45V
5k: ~65V

So that all appears to be in order (phew!), and I just need to slap a decent RR on. Like I've previously said, I'll be going for the Shindengen unit from roadstercycles (he also supplies a mount adapter with the correct spacing for the standard RR mount holes). The kit he supplies will just require the two stator wires to be connected, so I think I'll use a pair of Deutsch pin contacts (no plug housing) and heatshrink them. The rest of the kit wires direct to the battery, replacing the stock wiring.

At some stage I'll see about tracing the stock wiring through and removing it from the loom, but that might end up with the whole loom apart.

On another note, I noticed what appears to be a wee bit of blue smoke puffing from the top cylinder's exhaust at idle & when revving Oh well... as I keep telling myself as I find issues on this bike "It was an absolute bargain Jase, it's a forever bike, you can always rebuild it..."
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Old 11-03-2020, 08:25 PM   #15
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Just thought I'd put a final update in here - stator was absolutely fine, as evidenced when I hooked up a good quality RR (Shindengen unit from roadstercycle). It's all charging fine now and not blowing fuses!
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