Starter solenoid current draw?

[sp838]

How much current does the starter solenoid draw? Not for the actual starter motor, just need to know the current draw for the switch. Thanks!

[Kiwi_Roy]

About 50 Amps but just for a split second, as soon as the contacts close it drops down to 10 Amps

 

There are 2 coils in the solenoid the heavy current one (~40 Amps) that's in series with the armature, this does the lion's share of the work then when the contacts are closed it has the same Voltage on both ends so current drops to zero.

 

The lighter one (~10 Amps) helps to pull the solenoid in but then it holds it in place as long as the button (relay) is closed.

 

BTW this is the main reason other model Guzzis suffer from "Startus Interuptus" they have the current run through the ignition switch and miles of spaghetti, too much resistance for the current required.

See if you can find a Guzzi schematic that shows 2 coils, I wonder if they are aware of it? If you were to measure the current with a meter you would only see 10 Amps because the heavy current only lasts about 1/4 second, if it goes much longer the 15 Amp fuse will pop.

 

The relays are rated for an inrush of 60 Amps.

If you are thinking about doing away with the relay keep in mind Voltage drop due to the high current, keep the wires short, a 20 Amp fuse is appropriate.

[sp838]

So you are saying that this line coming from the starter relay jumps to 50A then drops to around 10A when the starter button is pressed?

 

[Kiwi_Roy]

That's correct.

I took a careful reading of coil Ohms doing a drop test (Valeo starter)

1.05 Ohms for the holding coil - the upper one in the sketch

0.25 Ohms for the heavy coil -  the lower one going to the armature

By Ohms law at 12 Volts it works out at 50 Amps

In reality when I measured mine with a scope it was 37 then 10 Amps.

I attributed the lower current to the wiring resistance and the armature resistance

 

The Bosch starter has a much heavier winding on the armature but the solenoid coils draw a similar high current.

 

BTW the Valeo starter on my bike draws 170 Amps, the Bosch ones seem to draw a bit less, around 150

 

Where did you find that sketch?

 

I'll send you a PM

[sp838]

That sketch is from one of your wiring diagrams

 

So, how does the fuse not blow every time the starter button is pressed, if that circuit is 15A but the solenoid switch is pulling ~50A? Is it really just getting away with it because it happens so quickly?

[Kiwi_Roy]

Yes,

       I simulated the contact not closing by removing the fat wire on LH side of the contacts, the fuse blew in about 1/2 second.

As I said before as soon as the contact closes the current drops to 10 Amps

Some owners have found the 15 Amp fuse pops so increase it to a 20, more so on other Guzzis I think where they have too much resistance and the solenoid sits and thinks about pulling in. I don't know what the cut-off is between pulling in or sitting there, I suspect 25 - 30 Amps but it's just a guess.

 

BTW if you look at the sketch you posted you will see when you take the finger off current can flow backwards from the armature side of the contact thru both coils in series to chassis, In this case the strength of one solenoid is supposed to work against the other to cancel out the field. I have seen one Bosch where it wouldn't let go until the battery lead was broken

 

[sp838]

In your opinion, can the starter, neutral and clutch switches handle this current if I was to rewire the starter button to go through them and to the starter solenoid directly instead of through all the relays?

[gstallons]

This will work until it stops working.  That relay is not in this circuit just for entertainment . A relay is there to handle the current the other components shouldn't .

[gstallons]

I know they make slow blow fuses for glass tube type fuses . Does anyone know if they make them for ATO { blade type } fuses ?

[Kiwi_Roy]

You won't be able to wire thru the neutral switch, it's only 1 terminal to ground.

If you are thinking about having a start button close to the starter it would probably be ok. Some ignition switches have a spring loaded contact that may be man enough.

Think about using one of the older cube relays mounted right beside the solenoid that would keep the heavier wires really short. The relay coil wires only pass about 100 mA so they can be tiny.

Think about the safety aspect, the starter should be disabled by removing the key, kids love to push buttons.

 

 

Sent from my shoe phone!

[sp838]

Thanks Roy. I will not attempt to route it directly, will use switched power through the clutch switch only, to a relay, which will send full juice through to the solenoid.