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General Category => General Discussion => Topic started by: Kiwi_Roy on June 29, 2025, 11:20:53 PM

Title: Drop Test
Post by: Kiwi_Roy on June 29, 2025, 11:20:53 PM
No its not dropping it on the concrete, read on.

Just reading Semper Vee's post about a shorted solenoid he indicated that his solenoid is shorted out
If you try and messure the solenoid resistance with a normal multimeter it will seem like a short circuit, that's because it's only a fraction of an Ohm (typical 0.25 Ohm)
Here's how I do it.
Take a high wattage lamp e.g. headlight bulb
Put 12 Volts on one terminal and measure the current other terminal to chassis, typically 4.5 Amps for a 60 Watt lamp.
Now instead of measuring the current to chassis apply the lamp to the trigger terminal of the starter solenoid, the lamp will light up about the same it did before.
Now measure the Voltage of the spade terminal to chassis
Note; Do not touch the Voltmeter probe to the wire from bulb, touch it on the terminal away from where the lamp is connected.
I measured ~1.2 Volts on my V7III

By Ohms law calculate the coil resistance 1.2 Volts /4.5 Amps = 0.26666667 Ohms
Now calculate the current it would like to draw at start 12V / 0.26666667 Ohms = 44.9999944 Amps
Its called a drop test because you are measuring the Voltage drop at a known current.

I learned this method many years ago as an apprentice.

Sorry now I have told you this secret electrical trick I will have to kill you LOL

BTW you can make use of the bikes own wiring to do this, disconnect the headlight ground and using a long wire ground it to the chassis near the starter solenoid thru the meter on 10 Amp range.
If you don't have a 10 Amp range calculate the current Watts / Voltage, a 60 Watt bulb should draw 5 Amps. It's always best to measure it if you can.

Roy

I kind of screwed myself here
Title: Re: Drop Test
Post by: Kiwi_Roy on June 30, 2025, 05:54:21 AM
I kind of messed up this topic by adding too much detail up front
Sorry

Roy
Title: Re: Drop Test
Post by: chuck peterson on June 30, 2025, 07:14:07 AM
Moto Guzzi..

Making electricians out of riders since 1929…

 :bow:
Title: Re: Drop Test
Post by: wirespokes on June 30, 2025, 09:40:13 PM
Making electricians out of riders since 1929…
What happened between 1921 and 1929? Did they not have electrical systems?
Title: Re: Drop Test
Post by: Kiwi_Roy on July 01, 2025, 03:36:38 AM
What happened between 1921 and 1929? Did they not have electrical systems?

They probably had a kick starter like everyone else.
Title: Re: Drop Test
Post by: chuck peterson on July 01, 2025, 06:24:31 AM
What happened between 1921 and 1929? Did they not have electrical systems?

They were in development for Startus Interruptus..
Title: Re: Drop Test
Post by: wirespokes on July 02, 2025, 04:33:33 PM
They were in development for Startus Interruptus..
:grin: :grin: :grin: