Leccy advice please

[Rodbr]

Given that I have already had two failed overdrive solenoids, I want to protect the solenoid before it goes into melt down!

I have a blade fuse holder installed on the only line to the solenoid so what fuse well work but also protect at the same time given the way it operates with pullin load and holding load.

I have the relay fitted but this is a "known" issue.

Looking at alternative weather protection/shroud as I would rather be driving than pulling it apart to fix it.

 

BR

Rod

[Lebro]

You would need to know what the two current values are - pulling in, & holding.

I could measure later today on mine. the fuse rating needs to be higher than the holding current, but lower than the pull in current, & have somting of a delay in blowing to allow time to pull in.

 

Will try to post suggestions later.

 

Bob.

Edited September 5, 2018 by Lebro

[Nigel Triumph]

See Ian Cornish's post#2 in this thread:

 

https://www.tr-register.co.uk/forums/index.php?/topic/60058-a-type-overdrive-solenoid-adjustment/

 

Pull in current 15-17 amps, holding current around 1 amp.

 

Hope this helps.

 

 

Nigel

[Lebro]

OK that sounds about right, so a fuse rated to blow at around 5 - 10 amps then.

The unknown part is the time delay in blowing with 15 amps. maybe worth experimenting with a selection of fuses, starting high (say 15A), & working down until one blows on O/D activation, then add a couple of amps.

 

Bob.

[RobH]

A fuse will only provide protection against an additional heavy current such as would be caused by a short-circuit. As I understand it the solenoid fails through overheating, not through over-current. It's just that the necessarily high pull-in current is applied for too long but you cannot really make a fuse arrangement which will protect against that in a reliable way.

 

You could perhaps do something with a timer-relay so that the high current is only present for a few seconds each time the overdrive switch is operated. That would save the solenoid from overheating should the internal disconnection switch fail to operate but it would be complicated by having to allow also for the lower hold-in current in normal operation.

 

If the solenoid supply was a current-limited feed at (say) 2 amps with the current limit bypassed for a few seconds when the switch was operated, that would do it. Fairly easy with a few electronic components I think.

Edited September 5, 2018 by RobH

[Lebro]

But as the pull in current is at least 10 times the holding current, & the problem is when the pull in current does not switch off after the < 1 sec time to pull in. surely a suitable value of fuse (with some delay action) would differentiate between the two currents.

Yes, the problem is overheating, but this is only caused by the much greater current being drawn continuously instead of momentarily.

 

Bob.

[RobH]

The key is the reliability. Fusing times for fuses is very variable depending on several factors including ambient temperature. You might find a particular slow-blow fuse which will give a long enough delay but still blow fast enough to prevent the overheating but as it ages the fusing characteristics will change so you might then start to get premature failures.

 

 

 

If the solenoid was fed via a low-current fuse - 2A - which was bridged by a relay for a few seconds when selecting o/d, that would do it. If the solenoid internal switch had not operated then when the timer contact drops out the fuse will blow immediately.

Edited September 5, 2018 by RobH

[Rodbr]

Guys, I thank you for the debate and suggestions but I am more used to setting up cranes, heavy specialist haulage, and construction works so the discussion about electrical smoking rope is a bit above my pay grade. I understand the principals and what you are suggesting but not how to build such a device.

The idea appeals greatly but I don't have that skill set to make such a device.

Perhaps a drawing/sketch might be possible and I could persuade my electronics Guru to make it as a test bed.

 

The main issue that seems to cause the overheating problem is that the plunger does not fully engage and shut off the pull in power switch, this is caused by many things, water, oil mist, debris.

I can coat the internal of the solenoid but the issue seems to be where the plunger exits into the switching section and moisture seems to cause the plunger to stick partway with resultant failure to reduce load leaving the pullin coil activated,

Given that this seems to be a known issue I am surprised that a solution has not really come up before.

Rgds

Rod

[stuart]

TBH in many years of running overdrives on Jaguars and Triumphs unless you go fording rivers a lot or driving off road then a properly set up solenoid just keeps on working, possibly the new repro green box Lucas arent made to the same type of tolerances that originals where maybe more the problem..

Stuart.

[RobH]

Rod - unless someone else comes up with something in the meantime, I will post a schematic this evening when I have more time to draw it.

[Rodbr]

I spoke to a very nice man at Overdrive services and he advised me accordingly.

I have never stripped an original o/d gearbox so was unaware that there should be a cork gasket between the solenoid and the mounting as well as the specific way to install the rubber. The rubber cylinder seal rubber comes according to him with it fitted in the wrong position. Who knew! Not one of my three rebuilt gearboxes has a gasket so no clues there.

 

I understand from the "nice man" that there are varying quality in the three suppliers so I suppose you pays your money and takes your chance. The repro one I bought was not made to any indentifible tolerence and things fitted where they touched like a bad suit. It melted like a goodun!

 

I will await the delivery of the replacement and see about fitting it as per his spec. Will have to make a gasket.

 

RobH,

That would be great, many thanks.

 

BR

Rod

Edited September 5, 2018 by Rodbr

[ianc]

In 55 years of owning TRs with overdrive, I've never seen a cork gasket between the solenoid and its mounting. One just screws it hard down, metal to metal, which means it is bound to be in the correct position and there will be good electrical contact.

If the solenoid's plunger is unable to rise to the full extent, it will fail to open the contact which disconnects the feed to the pull-in coil - in that case, it will cook itself, as it will be drawing some 15 amps all the time.

I see Nigel has pointed already to my post concerning pull-in and hold-in currents, which has saved me having to post it here.

Ian Cornish

[RobH]

As promised this is the first schematic showing how a delayed relay could be used to protect the solenoid. I am still working on the block called 'delay circuit' as I don't want to post it until I have made a prototype to be sure it will work properly. A job for tomorrow.

 

 

Edited September 5, 2018 by RobH

[stillp]

As promised this is the first schematic showing how a delayed relay could be used to protect the solenoid. I am still working on the block called 'delay circuit' as I don't want to post it until I have made a prototype to be sure it will work properly. A job for tomorrow.

 

 

solenoid schematic.jpg

Wouldn't it be simpler to use a current sensing timed relay?

 

Pete

[RobH]

Not sure how that would work Pete - the circuit has to pass the high current first, not just switch off when a certain level is exceeded which is what most current-sensing relays seem designed to do. Plus the ones I am aware of seem to be very expensive. Had you a particular one in mind?

[Rodbr]

Hi Ian,

I only reported what the technician at Overdrive Services told me and in his 30 years no one had had the issue I am having,

I must confess that I fitted the repro one first and it failed ( perhaps just bad luck) and then a used Lucas one which may have been on it's last legs when fitted.

My gearbox has only done 3000 miles since a full rebuild by a reputable expert known to most on here so I have no doubts it is set up properly. I understand why one might have a gasket between the solenoid but I have never seen one either. He tells me that it is included in their supplied gasket set.

 

Rob H

Many thanks for your obvious efforts and I await following up on the solution.

 

Thanks to all who have taken my issue on to help find a solution.

BR

Rod

[RobH]

Here is the delay circuit for the previous schematic. Pretty simple, all analog, and it works !

 

[RobH]

On reflection I realise I haven't provided protection for the above circuit from back-emf from the solenoid coil, so here is an update with a couple of additional components:

 

[ChrisR-4A]

Hi Ian,

I only reported what the technician at Overdrive Services told me and in his 30 years no one had had the issue I am having,

I must confess that I fitted the repro one first and it failed ( perhaps just bad luck) and then a used Lucas one which may have been on it's last legs when fitted.

My gearbox has only done 3000 miles since a full rebuild by a reputable expert known to most on here so I have no doubts it is set up properly. I understand why one might have a gasket between the solenoid but I have never seen one either. He tells me that it is included in their supplied gasket set.

 

Rob H

Many thanks for your obvious efforts and I await following up on the solution.

 

Thanks to all who have taken my issue on to help find a solution.

BR

Rod

Hi Rod, as mentioned above your problem appears to be very rare (30 years rare) and you mention yourself that the two solenoids you tried were of doubtfully provenance.

I would suggest getting a good solenoid from ORS and fitting and adjusting it as per the WSM.

Although the additional electronics suggested could eventually be made to work and provide additional protection they add unnecessary complication which in itself could fail.

TR electronics are fairly basic but robust and there is a lot to be said for keeping things simple save for the odd additional relay to protect existing/extra circuits.

In 22 years I have had one replacement solenoid on my car which has now been on for about 20,000 miles.

I would definitely not use a gasket as it is important to set the free play on the actuating lever and a gasket could compress and result in reducing this and stopping the solenoid engaging.

Chris

Edited September 6, 2018 by ChrisR-4A

[stillp]

Not sure how that would work Pete - the circuit has to pass the high current first, not just switch off when a certain level is exceeded which is what most current-sensing relays seem designed to do. Plus the ones I am aware of seem to be very expensive. Had you a particular one in mind?

My last employer used to sell one that could be set to pass a set current for a certain time, then switch off. I'm not sure if there's a 12V version, I'll try to check.

 

Pete