1980 Darmah SS Won’t Charge Battery - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 7 (permalink) Old Aug 13th, 2019, 11:33 pm Thread Starter
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1980 Darmah SS Won’t Charge Battery

My 1980 Darmah SS won’t charge the battery. It goes dead 30 miles or so in. The red charging light is always on. This is the model with a Bosch ignition.

When the original ignition switch broke, Bevel Heaven sold me one for a later model that has the headlight always on.

I don’t know much about electrics. Can anyone help me troubleshoot this and find parts?
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post #2 of 7 (permalink) Old Aug 14th, 2019, 2:49 am
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I don't know much about electrics either but here are one or two thoughts: Running the headlamp on all the time will not flatten the battery - I run mine like that and have no problem. I would guess that your regulator/rectifier has packed up, which they all do eventually, and this is why the red warning light is on.

Do you have a test meter? If you place the probes onto the battery terminals and rev the engine you will see if any charge is generated; a simpler test is to turn on the headlight and rev the engine from idle and it should show noticeable brightening.

I would expect that your regulator/rectifier is toast. They are readily available from Bevel Ducati spares outlets.

Ducati GT1000, Ducati 900S2 Bevel
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post #3 of 7 (permalink) Old Aug 14th, 2019, 10:42 pm Thread Starter
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Any ideas on how to troubleshoot and determine the problem? The rectifier is a $150 or so part and I’d hate to replace it just to find out that’s not the problem.
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post #4 of 7 (permalink) Old Aug 15th, 2019, 12:09 am
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On a bike that old, the rectifier is a good investment anyway and as for the price - is this a Concours d'Elegance show winner bike where you have to have oem everything? Get something modern for $50 new or less used and it will work more than fine.

I had a similar alternator to yours on my bike and got it rewound by a BMW guy in Denver to take it from about 175 watts to 300 - made a lot of difference on modern batteries and I live in a temperate climate unlike you. Yes, you should check and clean the main ground point before pulling out your wallet but non mosfet rectifiers just do not last as long as yours already has.

1991 900SS
1995 900SS SP #746

Last edited by RockAZ; Aug 15th, 2019 at 12:15 am.
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post #5 of 7 (permalink) Old Aug 15th, 2019, 1:00 am Thread Starter
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That’s interesting. Any specific suggestions? Will any rectifier/regulator work? A Honda/Kawasaki/Yamaha part? Any particular spec or capacity? For instance, I use accessory solid state rectifier/regulators on all my British bikes. Would that work? And what does “non mosfet rectifiers” mean? I’m pretty uninformed on electrical matters.
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post #6 of 7 (permalink) Old Aug 15th, 2019, 1:37 am
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Here is a guy who can advise you:https://www.ducati.ms/forums/14-vint...-question.html

You can test the regulator and alternator with a small voltmeter across the battery terminals, if the charge exceeeds 14 - 14.5 volts then the alternator is working but the regulator has failed. You will probably need a new battery as the old one will have been damaged by the overcharge.

A MOSFET regulator is new technology that controls the charge to the battery without producing heat. I fitted one to my modern Ducati a few weeks ago as a precaution, because of the reputation of normal regulators to pack up.

Check this out:https://www.electrexworld.co.uk/cgi-...2ehtml#SID=439
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post #7 of 7 (permalink) Old Aug 15th, 2019, 5:24 pm
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I recently went all the way with a Sacshe ignition, DynaTek coils and a Shendingen regulator (https://www.roadstercycle.com/).

Before jumping to conclusions, give your wiring a really good inspection and make sure your grounds around the battery and regulator are all clean and conducting. Then move to your fuse box; again check everything and make sure all is clean and conducting. I have an old analog multi meter with a buzzer function for continuity checks. Love it; perfect for these jobs.

A very typical failure point is the insulation of the 2 yellow leads from the alternator at the regulator connectors end; I think the wires are too small in diameter and simply get too hot at the regulator plug end. When there's no insulation left, the exposed wires are not supported and can flex and break so check. I replaced the last 6 inches of wire with a slightly heavier gauge on my bike.

Next test the alternator output; disconnect the two yellow wires from the regulator and hook them up to a multimeter set on alternating current and anything over 100V. Start the bike and see what you get; alternator stators typically either work or don't, so if you see nothing, then either one or both of the wires is broken or the stator itself has a broken wire or short. Check each yellow for continuity to ground; you should not see any; if you do there's probably a short in the alternator stator. Alternator stators can be repaired so don't rush into buying a new one.

If you do see an output from the alternator and your yellow wires were good then the regulator is the next likely culprit. I'm pretty sure that all Darmahs have 12V, 28A regulators to handle the electric starter. There are some simple tests you can perform to test a regulator; just Google it. You will need a multimeter with a a diode test function. If your regulator is toast then you have the choice of replacing it with the same or going my route with a more modern Mosfet style but be warned; the one I got, a FH020AA, is slightly bigger than the original. I was able to fit it on my MHR on the same frame plate with a few tweaks. I'm not sure where the regulator lives on a Darmah. If you do go this route, tell me and I'll send you my wiring updates for this mod.

I should have started with the battery; if your battery is tired then you will have charging problems, starting problems and a weak spark. Weak batteries are often blamed for wrecking sprag (starter) clutches too. Batteries do not live forever and have a finite lifetime even when babied. You could take your battery to a local auto shop for a test; a good idea to put this possible issue to bed.

Please post back as you proceed and good luck.

Your Motopiat voltmeter looks like it is actually working. It's supposed to give you a "Gen" warning when the bike is running but not charging

Rick 81 MHR
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