Todays quiz: How many amps does a starter solenoid take?

[Nomad]

Hi folks.
I'm looking at an elderly Volvo S40 belonging to a neighbour.
Due to odd failures I'm wanting to fit a "Push to start" button to activate the starter solenoid.

The preferred choice would be to use a push button that can handle the power for the solenoid..

An alternative would be to fit a low power switching circuit with a relay that will activate the relay but that makes things more complicated.

The signal feed wire at the solenoid is a different colour to the starter circuit at the ignition switch so I suspect the car already has a solenoid...
I'm hoping I just need a low power push switch but would appreciate info from anyone who know these cars (no guesses please - I'm looking for solid info, I can make educated / uneducated guesses myself)

The question is, what amps will my new push switch need??

Many thanks

 

[Ubique]

What year S40? very few cars have a direct switched starter solenoid - especially ones with automatic transmission.
What sort of failures? fitting a push button may not be the cure, depending upon the issues.

 

[badabec]

Vehicle Wiring Products do this one which handles 50 amps.

www.vehiclewiringproducts.co.uk/products/illuminating-starter-switch?variant=52424407351632

 

[Red'n'Black]

I did this years ago, along with a toggle switch for the ignition, on my folks' Hillman Avenger when the switch block fell to bits and replacements were unobtainium. It wasn't at much risk of getting nicked anyway

From memory it was about 5 amps, I used a 10A rated switch. But I would get a DMM and measure it to be sure.

 

[BrokenBiker]

i had a 40 amp button on my 2.8 iveco that could handle prolonged cold starting conditions. i know 50 amp buttons are avaialble as well

 

[Barking Mat]

I've had failures with boat looms activating the starter solenoid, and as a solution I just stuck the first push button switch I could find in.

Worked fine for three years, and I'm sure it's still going strong.

They're generally small wires going to the solenoid.

 

[Nomad]

Thanks folks.

Age unknown but it looks like it's had a hard life, I'm guessing about 20 years old?
The owner is very attached to it, it normally does what he needs it to do so is looking for a cheap fix.
Edit: the car is a manual box not auto.

Good call about the DMM, I can check that tomorrow.

The fault is the ignition barrel. The key turns ok for position 1 "Accessories" and 2 "Run" but locks out when trying to get to 3 "Start".
I'm planning to turn the key to 2 "Run" then add a push button to activate the starter solenoid.

A new lock set will cost £££ (and given the value of the car isn't an option), a push button on the starter circuit seems to be a reasonable cheap n cheerful fix.

This :


I'll check with a DMM tomorrow to what the starter circuit pulls, and get a push button that can cope.

 

[Morris]

Solenoid coils don't pull a huge current, I would guess a few amps at most.

 

[Ubique]

The keyswitch activates a relay
Some wiring diagrams here,

VOLVO S40 Wiring Diagrams

There're some VOLVO S40 Wiring Diagrams below.

car-diagrams.jimdofree.com

 

[minimutly]

Probably a few amps, but the initial current will be a lot higher. A slow blow fuse recommended, and a 10A switch I would suggest.

 

[Ubique]

If we're talking starter motor solenoids in isolation, there are actually two sets of windings - pull-in and hold-in.
Pull-in windings take more current and are grounded through the motor terminal of the solenoid, this means that once the solenoid contacts are made, then the pull-in windings are at equal potential and no longer drawing current.
The hold-in windings share the +ve terminal with the pull-in windings but are grounded through the body of the starter, only releasing once the key is released or in later scenarios, once the engine is detected as running.

Starter relays are rated 30A, typically the pull-in current is initially 10-12A, dropping to ~8A, but to be honest, it's only energised momentarily so in practice, you'd not see the lower current draw. Hold-in current is usually in the region of ~4A, this is energised at the same time as the pull-in windings so there's no extra inrush current.
Relay switched starter circuits draw less than 0.5A, some VWG vehicles have two relays, one is switched by the safety circuit (transmission or clutch position), one by the keyswitch - both have to be energised for the starter to operate.

 

[Jack_K]

They have a big spike of lets say around 40a. One can often get away with a weak switch for a while or even decades but I always fit a relay otherwise it is just a problem waiting to happen.

 

[knighty]

instead of wiring it to the starter.... wire it to the back of the ignition

might as well use a decent sized switch anyway... but that means if it was using a relay to activate it, it'll keep doing that

 

[eddie49]

From memory it was about 5 amps, I used a 10A rated switch. But I would get a DMM and measure it to be sure.

Solenoid coils don't pull a huge current, I would guess a few amps at most.

Probably a few amps, but the initial current will be a lot higher. A slow blow fuse recommended, and a 10A switch I would suggest.

A few amps is what I expected when I helped a neighbour diagnose a "faulty" starter motor on his 2007 Honda Accord.
However, as Ubique said, modern vehicles initially pull a lot!
I was testing directly at the solenoid, and melted a high quality Hirschmann test probe because the solenoid initially took 30 Amps.
The "pull-in" coil measured 0.6 Ohms to the motor terminal, taking 30 Amps to engage the pinion and close the motor contacts. The "hold-on" coil was 1.8 Ohms to earth and drew less than 10 Amps whilst the starter motor was spinning - which would be until the ignition switch is released from the spring-loaded "Start" position. The original Honda wiring uses a relay and a decently-thick cable to connect to the solenoid.
So be careful what wires you use to jumper and test solenoids, and use a DMM with an adequate DC Amps range!

 

[Jack_K]

This question has come up a few times on forums I go on. I've been meaning to scope some starters and record the data. A Typical amp meter is unlikely to give the correct reading. An oscilloscope is normally what would be used for this test.

This image from https://usbautoscope.eu/library/elpower-script-manual/ shows one example of a starter solenoid current and how short the spike is.

 

[Morris]

Not all starter motors are dual coil. The Ford one In wifey's Pop isn't and I'm fairly sure they weren't on the zetecs either.
The immobilizer is rated at 20A on the starting circuit and is quite happy.

 

[Pigeon_Droppings2]

Been a while but I think Volvo auto models have a key lock safety system which prevents the key from being removed if it's not in park. I don't recall it preventing starting though.

It physically locks the key in the ignition...prevents anyone leaving it in neutral I guess.

 

[Nomad]

The plan now is to connect the new push button at the ignition switch not at the starter motor (this will make use of the existing starter circuit which I’m fairly confident already has a relay in the circuit - a good result).

Last night I opened up the wiring harness connector from the ignition switch and teased out the wire from the switch to the starter. All I need to do now is add a push button to give that wire 12v for starting. Easy

The dmm I used should have shown me the current being drawn when starting but the meter isn’t working on the amps range (is ok in volts & resistance so I’m guessing the dmm fuse has popped..)

My local motor shop didn’t have any big red buttons with “Do not press” logos so I got a boring black push button
It feels sturdy but there’s no rating on it so I can gamble it’s ok or I can fit a relay even tho’ I’m fairly confident the original wiring already has a relay. Descisions..


It should be working by tomorrow night

 

[bricol]

Disconnect the starter power cable - link your starter wires, and listen for the "click" of a relay...or not.


Many years ago, K-series engined Caterhams had start issues - would refuse to start, usually when nicely warm, after filling up in petrol stations etc.

Many solutions suggested by owners club - new, expensive, starter motors, new, expensive cables, new relays in the ECU box...I simply took a new fused supply to suitable terminals on the existing ign switch, a new wire to a new relay, which switched power to the existing starter motor's existing cables. By-passed the many interconnections between Caterham and Rover looms. Still working perfectly 24 yrs later.

 

[Nomad]

Disconnect the starter power cable - link your starter wires, and listen for the "click" of a relay...or not.

Many years ago, K-series engined Caterhams had start issues ... I simply took a new fused supply to suitable terminals on the existing ign switch, a new wire to a new relay, which switched power to the existing starter motor's existing cables. By-passed the many interconnections between Caterham and Rover looms. Still working perfectly 24 yrs later.

Good suggestion about listening for the relay, thanks

My citroen xsara had a similar problem to your caterham (key always turned ok, starter sometimes engaged sometimes didn't), easily fixed by adding a "push to start" button and a new wire from there direct to the starter motor solenoid...

The problem with the volvo starter isn't my first rodeo