750 sport charging system

[Maico88]

I am having difficulties with the charging system on my 750 sport. Checking the system with a volt meter confirms that it is not charging( the charge light stays on 13 or less volts when runnning). There is continuity through the two yellow wires from the stator (4 ohms). The yellow wire shave no connection to ground. I tested the stator by hooking a meter (set to 200 volts ac) in circuit with the two yellow wires. I only get 50 volts ac at 4000 rpm. That seems low. The regulator tested bad. I have a new regulator, but I am hesitant to hook it up until I have confirmed that the stator is ok. Any suggestions? Thanks

[ducinthebay]

I think you found the culprit when you found the bad rectifier/regulator. 50 volts should be easily enough to rectify into 12v. My California bike had three wire coming from the alternator. Two yellow, and one red. I thought the previous owner had done something funny, as everything else was funny, and had taken out the third wire in the loom that went to the R/R. I added the wire, a red one, and hooked it up. The R/R didn't like it. I disconnected the red wire and ran just the two yellow ones. Everythings been fine since. The charging system has been rock solid for the past 4 years, and the battery never goes dead, even if I don't put the charger on it for months. Certainly better than my ST4s.

I would put in the new R/R and check it then. I think your good to go. Any of the recent single phase R/R from Ducati will work, or one from Electrex.

Cheers,

[jcslocum]

50v seems OK but I'm not an expert. I tested a bike this weekend and it had 70v at about 4k. Maybe the older bikes don't make as much juice??

[blaster]

it sounds like your stator is ok but are the two yellow connectors melted or corroded? this is a common problem for the 2 phase systems because the yellow wires are not a heavy enough gauge. ducati specified an output of 60v ac @ 3000 rpm for the 300 watt system from each yellow wire with a .2 to .4 ohm resistance between the two. the stator has to have some resistance or it's shorted. also these two phase systems have high break even points so at idle it's not uncommon to have less then 12v dc output. for the 300watt system the break even point is around 2000rpm. ducati addressed this problem by uprating to 350watts for the 900's and desmoquarttos around 93/94 but it still wasn't enough. i'm pretty sure you can upgrade to the 350watt system but check the clearance for the stator and rotor. the reg is the same. oh yea, one of the best thing you can do for your charging system is to throw that original reg as far as you can and install an aftermarket unit. i changed mine about 15 years ago and it transformed the charging system. blaster

[ducinthebay]

Connectors in a charging system are always suspect. You are much better off cutting the connectors out of the system and simply soldering the wires together. A connector is nice if you have to do assembly line work, or if you change the part frequently. Since neither is true for your bike or mine, a solder joint is much more robust and less likely to fail. Connectors in general are a bad idea, and should be eliminated whenever possible.

Cheers,

[Maico88]

This has to be the world's greatest site. I went ahead and installed the regulator. I went through and removed all butt connectors. All connections are now soldered and covered with heat shrink tubing. Duc-in-the bay, while soldering I found that mine also has the third wire from the stator. It is red and I left it disconnected. The charging system seems to work fine now. You guys rock. Thanks to all. I'm back on the road.

[jcslocum]

I fixed the wiring harness on a 95 916 this past Sunday. The harness was really burned up. Corrosion was bad at every connector. The wiring was really bad to almost 6" from the stator where the wire comes out.









It took 4 hours to strip and clean every connector and solder most of the together. Regulator was bad but the Stator was good.

[btlofrum]

Jon - it only seemed like 4 hours!

This is my first post, but I've been lurking for a while. I just picked up a '90 Sport, and today was my first day to do more than look at it. Registered it, cleaned it, replaced some bad bolts and wellnuts, and noticed some horrible wiring from the alternator, which makes this thread very timely.

I cut about six inches of horrid-looking wires off the yellowish/brown wires between the alternator and RR. Plenty of slack there, so this wasn't a big deal. I noticed the unused red wire, too. Can anyone shed a light on what and why this is? The shop manual shows a photo with three wires, but that's about all it says. The two yellow wires appear to be aluminum, which I didn't expect.

This bike, a relatively low mileage example (under 15K) has two regulator/rectifiers. The OEM one under the seat is disconnected, and there's a replacement in front of the battery. A much better location for airflow, for sure, but I'm amused no one ever chucked the old one.

I went on two brief 8 mile jaunts today (to a friend's for dinner and back a few hours later). To and fro, the red battery idiot light never went off, so I need to do some more diagnostics on the system...check today's patch job, check the AC voltage out of the alternator, and check the DC voltage out of the RR. Battery was 12.7v when I left, and that was sitting for ~10 days without a charger. I didn't check it when I returned.

Like Jon said before, we were getting 70 v AC at 4000 rpm off a 916 (350 watts) last weekend, and my '92 750SS was also in that range when I tested it last year. My SS has the same 300w alternator as the Sport, so I expect this bike to generate about the same. I'll post my results tomorrow, assuming I get back to it.

Thanks.

Ben

[jcslocum]

Welcome Ben. I can't wait to see the Sporty on the road and compare it to my F1!

It wasn't 4 hours??

[btlofrum]

Yeah, me too. Also want to ride it back to back with my '92 and your (gasp) Paso, since the engines are nearly identical. Does it have the Webers, or were those replaced?

Anyway...Jim gave me a proper pair of SS clipons last night and I'm going to go install them now and then play with the charging system.

The alternator puts out about 45 at 4K rpm and peaked around 65 when I goosed it. This is slightly lower than my 92 750SS, but within a reasonable range. It's also close to the 50 volts AC that the earlier bike in this thread was getting...

Ben

[ducinthebay]

Ben,
That 'second' R/R under you seat is most likely the computer for the ignition. Its a cast aluminum housing with fins, about the same size as the R/R. Does it say Magnet Marelli Digiplex 2S on it by any chance? If it is disconnected, and your bike still runs, you bike may have been retrofitted to the Kokusoan ignition system from later models of the SS or Monster. The correct placement of the R/R is in front of the battery, for air flow.

I don't really know why they added the third red wire from the alternator. The schematic shows that it is a tap from between the two coils.

Bad wiring can kill a R/R quickly, so if your wiring is fried, your R/R may be also. Refresh the wires, hook it all up, and see what you got. Hope for the best.

Good to have you on board.

Cheers,

[btlofrum]

Thanks - I guess the box under the seat is the ignition module, then. It looks suspiciously like a regulator.

I haven't pulled apart the regulator's wires to see if the incoming/outgoing wires are in good shape, nor to see whether the output from the regulator is strong. I did put a meter on it while running, and the battery isn't getting properly charged.

I was working on the clip ons this morning. Got the upper triple off, removed the old clip ons, and installed the SS clipons. While aligning them, I managed to strip a bolt head, which is when I stopped for lunch. I have some errands to do before I'll get back to it.

I'm off tomorrow, too, but I am supposed to take a short bike trip Fri/Sat. If the weather forecast continues to be shitty, I'll have two more days to work on the bike. There's still a shitload of things I need to do.

Ben

[blaster]

ah,i love a good mystery. i always wondered about that third red wire. the factory manual showed it but it also showed the kokusan ing. the owners handbook wiring diagram shows the correct diagram for the us model so i just thought the workshop diagram was for a earlier or other market model. the correct diagram shows the wire from the reg ,which the factory diagram shows as connected to the mystery red wire from the stator ,as spliced to the wire that connects to the battery + terminal. has anybody checked the red wire for any kind of reading? do 750 paso's have this wire? anyway, the two yellow wires and their connectors always fail because they are just too lightweight for the job. the model that seems to suffer the most from this is the early 916's. i also own a 1995 916 and am trying some fixes right now. one fix i heard of looks like it should solve the problem permanently. remove the yellow wires from the stator at the connecting plate on the stator and solder heavier wires,10 or 12ga, it their place. two areas of concern are, one, finding someone who knows how to do this type of work, and two, make sure the wires fit through the outlet on the sidecover without leaking. the connector i want to use is a mil spec unit i saw when i worked in the aerospace industry. i am looking in aircraft surplus outlets for it or anything close. the heavier wires may solve this problem as well. blaster

[jcslocum]

Blaster,

I think the wire size is sufficient (just) for the 916 but the connectors create enough heat over time that they just melt down. As I cut back the wire sheath from the stator the further from the connector the less melted and better it all got. I wouldn't change the full wire out but remove the connectors.

The other areas of concern, was the main fuse down next to the battery. The connectors were corroded and the legs of the fuse were corroded creating quite a bit o heat. I disassembled the socket, cut the connectors off and resoldred them in. Once this was done, the charging system worked normal again with no overheat.

[blaster]

the formula that determines the wire gauge for a specific load, which i can't find at the moment, stated that the wires on the 350watt stator should be at least 12ga but they are 16ga. add in some corrosion,dirt, and road grime which builds resistance and produces heat and ,voila, well done connections. as to that fuse holder, if i remember correctly, ducati supplied a uprated unit to replace that one but it was an undocumented fix which ducati did sometimes. as you said, soldering the connections,whether they are connectors or wires, builds reserve capacity into the circuit and helps to halt the damage. i think this problem goes back to the old days when ducati put most of their effort into performance and not into things like fit and finish or lights or any other thing that didn't help the bike to go down the road faster. i like that thinking but it does have its drawbacks. o-well, these bikes are just like beautiful girls, they hurt you and you just don't care. pain is so subjective. blaster