Bike won't sustain a charge. Where to look?

[BananaLover]

I'll give as many details as I can about my incident.

I have a heating jacket connected to my bike because I ride in winter. I hadn't used my bike in weeks so I had it fully charged before I head out.
I noticed that it wasn't heating me much which I found weird (might be relevant?). I rode 4.7mi and stopped at a top of a hill, this was late so I had lights on. Now I can't start my bike. I roll start it from the hill with lights off, jacket off, it starts quickly and I stop halfway through intending to wait 10 minutes for it to charge before I head off. It dies after a few minutes. I roll start it to the bottom of the hill and head off immediately (lights off from now on). It dies in a flashy way after 1.7mi, it struggles for a bit, the exhaust makes a big exploding sound before it turns off completely. Engine light comes on. I turn it off for a bit. I use my starter kit to get the bike going for another 0.8mi before the same happens. I do this a few times, I let it sit for a while and it will still die. I fully charged it when I got home a week ago (pushed it, I was close) and today morning it was sitting at 12.5V, I rode for 1.5mi and it went down to 12.2V.

Does this look like something specific? There a lot of little things that might make sense to someone. I've had my regulator changed before (2y ago) by a professional in a workshop.
I don't know much about location an issue like that, where do I start looking? I mean, with no clues, it could be anything from a corroded wire to a whole part needing replacement.
Bike: Yamaha XVS 650 Drag Star

[Polarbear]

Voltage figures when running would help. Take voltage across the battery before you start it and when running. If there is no change it definitely isn't charging. No change and I'd be looking at checking the alternator output to see if you have anything there.

If you don't, Yamaha will be happy to bend over and proceed to royally fcuk you.
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Triumph Trophy Launch Edition

[doggone]

In my experience the regulator/rectifier is more likely to fail than the alternator, however you could just have corroded connections somewhere.
They are not overly expensive
https://yambits.co.uk/xvs650-dragstar-regulator-rectifier-p-85189.html

[RhynoCZ]

Well, what does the multimeter say? If you don't have one, go and buy one, then get back to us.

Battery, engine running: 14V to 14.5V DC (no more than 15V!)

Stator, engine running: anything above 30V AC between any of the yellow wires would be nice.

Stator, engine off: measure the resistance between the wires (coils), see the service manual for specific Ohm figures.

Reg/Rec = well, you could test the diode is OK, but that's about that. Since you say it's new, I would not fiddle with it just yet.

Do NOT replace any parts before you find the faulty one! Even the cheapest multimeter will give you the answers. If you don't know how to use one, try youtube.

This should help,

https://qph.fs.quoracdn.net/main-qimg-92f6f6607cd340ffd296de7426f67081.webp
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Teflon-Mike]

It's mid Autumn, the time of year when the weather shows up the weakness in duff batteries.

I'd start there. How old is the battery? Have you checked the electrolyte level? A-N-D I'd chuck away the heated vest.... that aint gonna be helping anything!

On that note; hows the vest connected/plugs in? Is the best itself donald-ducked? Could shorted accessory garment have bludgered bike electrics? Any heated vest, like hot-grips, that actually gets warm, is going to be sucking a fair few amps. If you ride with day-light headlamps, good odds that the bikes genny barely makes enough electric anyway, without that robbing any more amps, mostly from the battery when the genny isn't making enough to power it.

When a battery is run persistently on low charge, it looses a load of its charge holding capacity through the memory effect; in worse case this results in electrolyte break down and plate warpage, that reduce the charge holding to neart nill..... but irritatingly enough to give terminal volts, and even enough to get the starter to spin, and of the engine an easy starter, even spin enough to fire up.

Your 'Bang' BTW, is most likely, ignition drop out. When the volts go too low, you get no spark, but then when it does spark, the charge that didn't get set alight, is sat in the exhaust, and hot exhaust from pot full that did catch, sets it on fire and you get what sounds like a back-fire. Some folk do it for fun, hitting the kill-switch with the throttle wide open, then back on, so that the unburned in the exhaust goes 'pop'... it's not a good practice... b-u-t..... and any inadequect in the pipe work, like an after-market can or a stubbied can, or a slash-cut etc will be far more inclined...

But start with the battery, and eliminating variables, getting rid of that hot-vest, and checking earths and fuses and connections.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[xX-Alex-Xx]

Your third sentence implies your bike was sitting for a bit. Lead acid batteries HATE being anything less than fully charged.

Sounds like you need a new battery. Keep it on a storage charger if you're not going to be riding for a while too.
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DILLIGAF

[Pete.]

Charge the battery first then use it to start the bike and put a meter on the battery to see what charging voltage you get. Charging should be 13.5-14v as a general rule. If it's less than about 13.5v your charging system is duff. If it's around that figure or better your battery has had it.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Kentol750]

Eat more pies.
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Some bikes.

[Kentol750]

Get a new battery. Then explore further. You're hardly running a massive drain on already simple electrics, what could be going wrong?
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Some bikes.

[-]

How much power does this electric heated jacket consume? Is the bike's charging system up to it?

Here...

https://www.vstarforum.com/thread-5890.html

Seems to say it only generates a realistic 250W and needs 180W of that just to run the basic needs including lights. Anything which heats via 12V is going to consume shit loads of power. What's the rating of your jacket?

[BananaLover]

Don't know why everyone has such a hate for the heating jacket, been using it for two years and would never ride at night in winter without one. Do it rarely anyways. Usually lasts for about 70 minutes with lights on before battery would start to struggle, so I always carry a starter kit and just use the vest with intervals if the journey is longer than that.

Either way, the charge in battery stays the same with the bike on so it must be charging issue.

[xX-Alex-Xx]

Do the voltage/resistance checks mentioned towards the top, and post the results.
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DILLIGAF

[-]

[MCN]

[Robby]

It'll be the reg/rec. Change it for a MOSFET type, seeing as you managed to kill a new shunt type in two years.