[Healeys] Fried OD Solenoid

Fri Mar 25 12:21:21 MDT 2022

When the 22 Amps are flowing permanently because the contact in the 
solenoid does not open to allow only the holding current to flow, which is 
around 2 Amps, the overdrive line cable to the solenoid gets extremely hot 
and melts!!! And can cause a massive cable burning. A friend was lucky to 
realise this early enough to stop the car to catch the fire estinguisher.
I always put in a 10 Amps fuse in this line, which stands the 22 Amps for 
the 2 to 3 seconds it needs to engage the solenoid, but blows when the 
current doesn`t go back from 22 Amps to 2 Amps in short time.
Just a recommendation. I even have it in my concours cars, unvisible for 
the judges!

Josef Eckert
GERMANY

-----Original-Nachricht-----
Betreff: Re: [Healeys] Fried OD Solenoid
Datum: 2022-03-25T19:02:52+0100
Von: "john harper" <ah100tech at gmail.com>
An: "Michael Salter" <michaelsalter at gmail.com>

Simon

The overheating is likely to because the armature has not risen enough to 
break the contacts to the heavy pick coil. There is for a short while about 
22 amps is flowing which heats up the heavy coil to the point where it 
fails or the heavy contacts burn out. When operating correctly only the 
hold current should be taken; perhaps 3 amps.  The action is that the heavy 
coil is needed to raise armature until when it is at the top it breaks the 
heavy current. The hold coil is sufficient to do as it says and keeps the 
armature in place causing the overdrive to operate.

A frequent cause of the ODs with an open frame and with a rubber bottom 
stop is that this rubber button rots with oil or falls out. With the 
armature lower than it should be with the button in place the pick current 
is insufficient to lift the armature with only part of it inside the coil.  
the coil will then keep taking current. 

On mine, I have drilled and tapped the hole in which the rubber stop was 
fitted to allow a bolt and nut to be fitted that can then be adjusted as is 
possible on the enclosed versions

Best regards

On Fri, 25 Mar 2022 at 15:13, Michael Salter <michaelsalter at gmail.com
<mailto:michaelsalter at gmail.com> > wrote:
  Bluntly Simon, the operating valve was NOT set up correctly. 
  The "pull" coil was still being powered and drawing probably some 20
  amps.
  New solenoid required and some careful setup.

  M

  On Fri., Mar. 25, 2022, 10:50 a.m. Simon Lachlan via Healeys, <
  healeys at autox.team.net <mailto:healeys at autox.team.net> > wrote:

    Since we’re on the OD topic….

    I took my MkII BT7 out the other day, first time for ages, 8 weeks+/-.

    Anyhow, the OD didn’t work. I’d been to a carpet trimmer and left my
    tunnel cover with him so access was easy……

    The solenoid was very hot…too hot to touch which made me suspicious.
    Anyhow, I did my OD electrical click-test and it failed at the first
    hurdle. So, I took the solenoid out and…well, look at the picture.

    The plastic/nylon cover to the points and wiring was virtually welded
    in place. And the inside is a complete mess.

    So, the OD was rebuilt about 50 miles ago by OD Spares and I’m happy
    with the wiring. My question is this…is there a frequent or a probable
    cause to these fry ups?? These things check out at about £50:00 so I
    don’t want to be chucking them in at regular intervals. Anything in
    particular that I should look out for???

    Thanks,

    Simon

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