Battery Charge Voltage - Old 860GT

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Old905Duc
Mariana
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Battery Charge Voltage - Old 860GT

Post by Old905Duc » Thu Apr 07, 2016 8:36 pm

I was suspicious that the battery was not charging properly on my original 1975 860GT. The electrical system is original other than horn and turn signal deletes, and the addition of Lucas RITA ignition and a halogen headlight (no electric starter). The bike has the original 150 Watt generator and original regulator. I measured battery voltage with my crusty old analog voltmeter (50 volt scale) and saw ~12 volts at idle and no voltage increase under easy Revs. So I was a little concerned (actually, maybe I did not rev the engine high enough in this quick test).

I then disconnected the regulator, cleaned the regulator contacts, and measured the generator winding continuity and resistance to ground and found no problems. I did find a slightly high resistence measurement (<10 ohm) on the brown wire between the regulator and the fuse box. I re-crimped the conector at the fuse box and got back down to zero ohms (BTW this is not an original fuse box ..... I already went through the melt-down scenario and replaced with Radio Shack parts a long time ago).

I then repeated the battery voltage measurements with the headlight off with the following results ......
o Idle to approx 3000 RPM ......... ~ 12 volts
o approx 3000 RPM .................. voltage begins to increase above 12 volts
o 3000 RPM - 4000 RPM ............ voltage increases to about 14.5 volts max

I was about to buy a new voltage regulator, but the results now look pretty normal to me. I would appreciate the advice of the forum concerning my results and your experience with the electrical charging system of a 860. At this point I am thinking that it does not make any sense to replace the voltage regulator. Your thoughts?

Thanks and happy riding !
Old905Duc

ducadini
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Re: Battery Charge Voltage - Old 860GT

Post by ducadini » Fri Apr 08, 2016 11:57 pm

With the old 150 watts You'll have to keep revs over 4000 to charge the battery while driving with the lights on.
The standard ignition worked on itself so this wans't a big issue then.
It WAS on the 750s with points robbing a lot of juice.
You could shop around for a 200 version ?
But it still IS better to keep revs over 4000 to save bigends.

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

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Old905Duc
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Re: Battery Charge Voltage - Old 860GT

Post by Old905Duc » Sat Apr 09, 2016 12:48 pm

Ducadini, thanks for your thoughts. When my Ducati ignition failed for the 2nd time (many years ago), I decided to go with the Lucas-RITA ignition as an alternative that might last longer. At that time I didn't realize that the Ducati unit was self energizing. Now I understand how the RITA ignition places an additional load on the charging system compared to the original Ducati ignition. I agree that this makes the 150 Watt generator even more marginal, and makes the 200 Watt generator much more desireable. That being said I will look around a bit to see what is available and at what cost. In the mean time I will mind my RPM.

Thanks and happy riding.
Old905Duc
Last edited by Old905Duc on Sun Apr 10, 2016 7:43 pm, edited 1 time in total.

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Old905Duc
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Re: Battery Charge Voltage - Old 860GT

Post by Old905Duc » Sun Apr 10, 2016 7:37 pm

I have been looking into upgraded alternator options with respect to electrical charge improvement and value. At this point my favorite option is shown at the link below. I am still working to get more details on the power rating and the applicability to an early 860 engine. Based on Steve's online parts manuals, the same stator and rotor were used for the 750GT/SS and the early 860GT. So, I think this will work in my early 860, and it is also compatible with the original voltage regular!
http://www.mdinaitalia.co.uk/cgi-bin/co ... ey=1X00060

The shop that sells this is on holiday for the next 1-1/2 weeks, but when they get back I will try to get their assessment for use on an early 860GT.

Happy riding!
Old905Duc

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Old905Duc
Mariana
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Re: Battery Charge Voltage - Old 860GT

Post by Old905Duc » Fri Jan 06, 2017 8:54 am

Just an update to close on this posting ......
I did purchase the upgraded 750 alternator from Mdina Italia. It has been installed for a while and is working. However I haven't really put on too many miles. So, I can't give a full conclusion yet. The parts seem to be of high quality. Note however that the length of the cable (too short) and the connectors are not correct for an old bevel Ducati. I simply spliced the new cable into the old one. Removal of the old alternator was straight forward except that the rotor nut was really TIGHT :doh: !!! BTW, I did not have the rotor locking tool and instead engaged high gear and locked the rear wheel. Installation of the new alternator went without hitches, although I was a little concerned about how to best separate the new rotor and stator due to the much stronger magnets. I ended up making a simple mandrel out of wood which worked well to slide out the rotor with full control. Installation of the alternator cover (containing the stator) was a little challenging as the much higher magnetic forces tended to cock the cover making it hard to properly engage the alignment pin. Patience however prevailed ultimately and it all slipped together :Uwin: . Short rides so far with the headlight on have not drained the battery. So, so far so good :vroom: .

Happy Riding.
Old905Duc

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