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Dear Collective

The overdrive solenoid on my newly installed Vanguard box has developed a fault whereby the incoming power connection is now shorted to the body of the solenoid. Fortunately, my newly installed fuse box did it's job and protected the circuit.

I am aware of the need to be careful when setting the position of the lever so that the solenoid is able to pull completely in and engage the holding coil.  I believe that I set this up properly - both by physical checking of the lever action, but also from the behaviour of the ammeter, which would flick instantaneously then return to previous position when engaging overdrive.

My two questions are therefore -

1. If I didn't set the lever properly and the pull in circuit burnt out, does this result in the symptoms I now have (i.e. short circuit between power feed and earth)? I would have thought that the symptoms would be an open circuit, rather than a short circuit? 

2. Do solenoids sometimes fail in this way (short circuit) when they have been properly installed and set up?

Thanks!

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Could it be that the pull in current was held too long and the wire got hot and melted the insulation  and is now shorted to earth.

If this was the case then a simple Multimeter check of solenoid power in to earth would indicate.

 

Roger

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I think that Roger is likely to be correct.  Here's some info which I noted a few years ago:

Today (25/05/09), I made some measurements on a brand new, spare, overdrive solenoid which I bought from Moss some time ago. I think it is fair to assume that it was built to the same specification as the original Lucas item.

Pull-in (Pull-in and Hold-in coils in parallel) 0.8 ohms, drawing about 15-17 amps.

Hold-in (pull-in circuit disconnected by plunger operating the switch within the top of the solenoid) 12.5 ohms, drawing about 1 amp.

For the technically-minded, this means that the Pull-in coil has a resistance of about 0.85 ohms, and takes about 14-16 amps.

The current drawn will depend upon the state of charge of the battery, which is usually between 12-13.4 volts.

With about 16 amps being drawn continuously by such a small item, the solenoid would get VERY HOT and would likely melt its insulation and create a short circuit.

Ian Cornish

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Hmmmm  - interesting... so I've just checked the solenoid resistances which read 0.6 ohm and 12 ohms... which leads me to suspect maybe there is nothing wrong with the solenoid after all.  I'll connect it to a battery tomorrow to see if it still pulls in.

To start with, I was using a 10 amp fuse for the solenoid power supply, then tried 20 amp which also blew... and then when I went with the feed from the ammeter, it below the 30 amp main fuse I have installed inline with the ammeter.  I can understand it maybe blowing the 10 amp and 20 amp fuses if it was running on the pull in coil continuously, but it shouldn't have blown the 30 amp fuse?

 

 

 

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8 hours ago, RogerH said:

Measure the resistance between the wire supplying current to the solenoid (disconnect it from the solenoid) and earth - it should be high.

 

Roger

Hi Roger - yes, it's really high... actually infinitely high :)

 

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Hi Roger
I may be able to get hold of a solenoid to test.  Will make some enquiries.

I have progressed with some testing today and yesterday.  I re-set the o/d actuation lever clamp and adjusted the bottom stop for the solenoid plunger to make absolutely 100% sure that it was properly set up.  I am now even more sure that the solenoid is pulling closed properly and that it is also allowing the o/d to fully disengage when switched off.  There are margins at both ends of the movement, if that makes sense.

I then went out and tested the overdrive by manually pushing the lever on the RHS of the box.  All good with that.

I then connected up the wiring and tested the electrical actuation in the garage with the engine off and the engine running (shorted one of the interlock switches on the top of the box).  All good with that, too, and I confirmed that the current draw with the overdrive engaged is 1.0 Amps. 

Then when I took the car out to test the electrical actuation on the road, the 30a fuse blew as soon as I flicked the switch.

I also checked the voltage across the battery at different engine speeds, which indicated a maximum voltage of 14v.

The resistance of the solenoid pull in circuit is approx. 0.5 Amps so that would give a current draw of 28Amps for the pull in circuit.  I am wondering if there is sufficient spike in current to blow the 30Amp fuse.  The only thing that wouldn't support this theory is that it ran perfectly ok for a long time when it was taking power from the Ammeter, which is also protected by a 30Amp fuse.  Originally, of course, the solenoid would have been on an unfused power supply.

Anyway - I am considering fitting a 0.25ohm resistor in line with the solenoid to reduce the current draw by 8amps or so.  Any drawback to that proposal that you can think of?

 

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+1

That resistor might stop it pulling in properly as you will be limiting the current to <> 18A.   Why a 30A fuse?  It should be rated to protect the cable not to just-about-carry the demand current. If you are sure that is the cause and you want to stay with 30A, the best thing to do is fit a surge-protected fuse  (a.k.a. slow-blow).  

 

Edited by RobH
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18 minutes ago, RobH said:

+1

That resistor might stop it pulling in properly as you will be limiting the current to <> 18A.   Why a 30A fuse?  It should be rated to protect the cable not to just-about-carry the demand current. If you are sure that is the cause and you want to stay with 30A, the best thing to do is fit a surge-protected fuse  (a.k.a. slow-blow).  

 

I'd obviously test the operation with the resistor, to make sure it pulls in ok.  

I actually started with a 10a fuse which worked for a while before blowing... then tried 20amp which also worked for a while before blowing... now using a 30amp fuse which is blowing straight away when driving the car... but seems to work ok as described above with the car ticking over in the garage at 1500rpm.  I suppose this increasing fuse rating could be a sign of something causing the resistance of the circuit to reduce over time... maybe something in the solenoid. The only other component in the system is the relay... not sure if that could have a fault that causes excess current draw. 

Yes - you are obviously correct re the choice of fuse matching the rating of the wire.

It's all a little confusing to say the least.

I'll try out the resistor but also look into getting a slow blow fuse.  Good idea!

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2 hours ago, bigmalcy said:

now using a 30amp fuse which is blowing straight away when driving the car... but seems to work ok as described above with the car ticking over in the garage at 1500rpm

So what is changing when you actually drive the car? Does the gearbox move in some way so that something shorts to earth?

Edited by RobH
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10 hours ago, RobH said:

So what is changing when you actually drive the car? Does the gearbox move in some way so that something shorts to earth?

I'll be buggered if I know!

I'll have a look over the wiring to check for any chinks in the insulation, but I think it's highly unlikely that that is the cause.

Really the only other cause that I can think of is something in the original relay that is causing a spike in current - maybe an intermittent short in the relay that is encouraged by movement and vibration.  I'll pick up a new relay today and see if that makes a difference.

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oh well - another fuse makes the ultimate sacrifice.  New relay seemed to work for a couple of engagements out on the road (worked perfectly again in the garage), but then blew on the third try. 

Tomorrow I'll rig up new beefy power cables to eliminate those as the cause... in which case I'll be looking for a new solenoid as the final piece to test...

 

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I had a similar issue with my car blowing fuses up to 50amp. In the end it was an over adjusted solenoid, at least that's what I put it down to. The solenoid was overheating and blowing the fuse. I installed a new solenoid, ignored the W/M factory setting which doesn't work anyway, and incrementally moved the adjusting lever to a position where the overdrive would just engage/disengage. It's tedious (back and fore), but it works and it's been fine since.

Rob

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11 hours ago, RogerH said:

Could the OD switch (on the dash) be shorting out top earth internally 

 

Hi Roger

The dash switch is separate to the fuse circuit that is blowing... the switch on the dash is protected by a separate fuse.

 

7 hours ago, RobTR3 said:

I had a similar issue with my car blowing fuses up to 50amp. In the end it was an over adjusted solenoid, at least that's what I put it down to. The solenoid was overheating and blowing the fuse. I installed a new solenoid, ignored the W/M factory setting which doesn't work anyway, and incrementally moved the adjusting lever to a position where the overdrive would just engage/disengage. It's tedious (back and fore), but it works and it's been fine since.

Hi Rob - I've been super careful with setting the solenoid position, and am confident that the solenoid movement is not the cause of these issues.  Having tried a new relay and established that that is not the source of the problems, the only other causes are a short in the wiring or a problem with the solenoid itself.  I'll rig up some temporary new wiring to eliminate that as the source and then see if I can get hold of a replacement solenoid to check that side of things.  

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On 5/31/2020 at 5:57 AM, RogerH said:

Can you get hold of another solenoid to test by substitution.?

 

Hi Roger

I have bought a new solenoid from our local supplier here in Aus. I haven't fitted it yet, but the resistance measurements indicate that the original solenoid has got a fault: the resistance of the new solenoid pull in circuit is approx. 1ohm, or twice what my old solenoid is... that will make a massive difference to the current and hopefully stop the fuse blowing.   Will fit and test this weekend.

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I've posted this info more than once on the Forum, but here it is again:

Today (25/05/09), I made some measurements on a brand new, spare, overdrive solenoid which I bought from Moss some time ago. I think it is fair to assume that it was built to the same specification as the original Lucas item.

Pull-in (Pull-in and Hold-in coils in parallel) 0.8 ohms, drawing about 15-17 amps.

Hold-in (pull-in circuit disconnected by plunger operating the switch within the top of the solenoid) 12.5 ohms, drawing about 1 amp.

For the technically-minded, this means that the Pull-in coil has a resistance of about 0.85 ohms, and takes about 14-16 amps.

The current drawn will depend upon the state of charge of the battery, which is usually between 12-13.4 volts.

Ha - I see that I posted it here on 30th May, but it shows that 0.5 ohms for the pull-in coil points to an internal fault.

Ian Cornish

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Hi Ian - don't worry, I read and understood your post... I thought that my old solenoid with resistance of 0.6ohms was close enough to your figure of 0.8 ohms. 

I also thought at that stage that when a solenoid failed, it would fail to the extent that the pull in function wouldn't work at all.  Mine seems to have failed such that the pull in circuit resistance has been significantly reduced, but the pull in still seems to work, but not reliably, and will sometimes draw 30+ Amps with no pull-in action.  

I'm also not sure if the solenoid issues are just due to an internal fault, or my own error in setting the position of the actuating lever.  Time will tell! 

 

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Hi malcy,

I was having a rough night of no sleep and went through Standard Service bulletin for 1954.

A couple of interesting things came from that read.  they were having trouble with water ingress on the early overdrive solenoids and also the was a setting bulletin as well.

It makes a good read if bored some night. Instructions given on how to proof the solenoid using fibre electrical tape and shellac coating.

 

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