Voltage measuring
Post Reply    Forum -> Not-So-Modern
Author Message
Molto Verboso
1963 VBB2T
Joined: 07 Nov 2012
Posts: 1919

Sat Aug 01, 2020 5:09 pm quote
Hey guys I could use some help, how or what setting on our volt meters do we use to measure if we have voltage or not on the vintage Vespa AC circuits? I have no running lite but before I can tell if the yellow wire at the switch and taillite have power I need to know what Iím looking for with the bike running and voltmeter in hand ? I know how to measure across a house receptacle , resistance or just a simple 12 volt circuit but this Vespa AC stuff is a bit of a learning curve.
Thanks

77E3C0D2-86B1-4E7A-A6CE-08B46A6A85F3.jpeg

Member
Vespa 150
Joined: 02 Oct 2019
Posts: 11
Location: RI
Sat Aug 01, 2020 6:58 pm quote
Move the dial to the next item clockwise, the V with the solid line / dotted line.

put the test probes across the circuit

activate the switch, and expect to see 12V


Here's a good primer on the multimeter:

https://www.ifixit.com/Guide/How+To+Use+A+Multimeter/25632
Ossessionato
73 Rally, 74 Rally, 76 ET3, 80 P200, 06 PX150, 65 Li225 Silver Special, 86,95,96 Elite 80s, 2015 HD Road Glide Special, 2011 Ural Tourist
Joined: 18 Jan 2012
Posts: 3664
Location: Oceanside/ SF
Sat Aug 01, 2020 7:05 pm quote
AC voltage you want the V with the wavy symbol above it. DC is the V with the straight line.

Most meters have a hard time reading AC voltage so donít be alarmed if itís not a perfect 6V or jumps around a bit.
Molto Verboso
1963 VBB2T
Joined: 07 Nov 2012
Posts: 1919

Sat Aug 01, 2020 7:21 pm quote
Thanks guys thatís pretty much all I needed to know, I had always thought the line and squiggly line was used for if it was either . This is 12volt system upgraded, I know the yellow is for lites and the brake lite does work. I already got a couple zaps off the switch so I know something is working. Itís just my taillite running lite Iím trying to get working , Iím still not quite sure on the lite switch at headset which way is off or in for taillite and headlite but I have something to go on now.
Jape thanks for the primer and welcome to the MV site .
Addicted
'64 Motovespa 150S (177) , '66 Allstate SF, '64 VBB
Joined: 27 Mar 2013
Posts: 640
Location: S.Salem, NY
Mon Aug 03, 2020 4:08 am quote
Would the AC voltage on the lead from the power coil on the stator to the ignition coil be an accurate read of the coil's output or would it be affected by the points making and breaking ground ?
Hooked
PX125E
Joined: 06 Oct 2018
Posts: 173
Location: Gravesend, Kent, UK
Mon Aug 03, 2020 9:10 am quote
Moto64 wrote:
Would the AC voltage on the lead from the power coil on the stator to the ignition coil be an accurate read of the coil's output or would it be affected by the points making and breaking ground ?
Very unlikely. The volts will jump around. Those meters like to see a steady voltage.
Addicted
'64 Motovespa 150S (177) , '66 Allstate SF, '64 VBB
Joined: 27 Mar 2013
Posts: 640
Location: S.Salem, NY
Mon Aug 03, 2020 10:05 am quote
Actually, the digital meter seems to average out (?) the voltage but I am only seeing about 3.5-4.5 volts at a normal idle. It's a 6v stator and the lighting coil's doing about 9 with the battery connected through the rectifier . I think I'll try grounding the coil and spinning the flywheel with a drill at idle speed and see what it's putting out.
Ossessionato
BV350, Primavera 150, Yamaha Zuma 125
Joined: 06 Jun 2013
Posts: 3145
Location: The Twin Cities of Minneapolis/Saint Paul, Minnesota
Mon Aug 03, 2020 11:46 am quote
Moto64 wrote:
Actually, the digital meter seems to average out (?) the voltage but I am only seeing about 3.5-4.5 volts at a normal idle. It's a 6v stator and the lighting coil's doing about 9 with the battery connected through the rectifier . I think I'll try grounding the coil and spinning the flywheel with a drill at idle speed and see what it's putting out.
You have to take measurements of AC voltage from a stator like that with a grain of salt, unless it's a "True RMS" meter. Most digital voltmeters are set up to measure pure sine waves at fairly low frequencies.
Hooked
PX125E
Joined: 06 Oct 2018
Posts: 173
Location: Gravesend, Kent, UK
Mon Aug 03, 2020 11:58 am quote
Moto64 wrote:
Actually, the digital meter seems to average out (?) the voltage but I am only seeing about 3.5-4.5 volts at a normal idle. It's a 6v stator and the lighting coil's doing about 9 with the battery connected through the rectifier . I think I'll try grounding the coil and spinning the flywheel with a drill at idle speed and see what it's putting out.
I see where youíre going with this. If thereís some voltage your reading thatís all you need to know. Itís a vintage vespa and the circuit is crude by todays standards. As long as the voltage is about 7.2 V across the battery when the engine is running and You have a spark at the plug. Put the meter down and occupy your idle hands by holding a couple of cold beers.
Molto Verboso
1963 VBB2T
Joined: 07 Nov 2012
Posts: 1919

Mon Aug 03, 2020 1:15 pm quote
Ok after more troubleshooting I found out I need a pinasco regulator, easiest fix, or split and test some wires at regulator for proper voltage to use . Also apparently that first setting was the correct setting , unfortunately I got unregulated voltage . I was getting the same high voltage at the switch and everywhere else with the red/white connected to the blue at junction from stator . Thanks to Jonathan at Gick Speed , great support even years later. By the way it was explained to me a while back but of course I didn't understand , which brings me to the state I'm in.

https://www.youtube.com/watch?v=oPLB80J51LI
Addicted
'64 Motovespa 150S (177) , '66 Allstate SF, '64 VBB
Joined: 27 Mar 2013
Posts: 640
Location: S.Salem, NY
Mon Aug 03, 2020 2:58 pm quote
Excuse me , Lynnb, for interrupting.... I hope you find a simple solution to the voltage problem. These AC systems are weird .
Molto Verboso
1963 VBB2T
Joined: 07 Nov 2012
Posts: 1919

Mon Aug 03, 2020 3:48 pm quote
Moto64 wrote:
Excuse me , Lynnb, for interrupting.... I hope you find a simple solution to the voltage problem. These AC systems are weird .
No interruption, I got it straightened out. I could retire to make it work or,simply put a pinasco regulator which Iíll be doing. You are correct, these ac systems are definitely something to learn, but I have a better understanding now which is a bonus.
Missouri Loves Company Rally   Vespa Wasp Pin Badges   Yelcome Leather Top Cases and Roll Bags for Piaggio Vespa PX LX LXV GTS GTV
Post Reply    Forum -> Not-So-Modern
[ Time: 0.1594s ][ Queries: 27 (0.0380s) ][ Debug on ]