I've been asked to repair the central locking controller on an early Rover
SD1.

Bit of history. That car was pretty early in the UK in having electric
central locking. It uses solenoids, rather than motors which are the norm
today. Later SD1 changed to motors.

The solenoid units ain't Lucas. Not quite sure who makes them.

The control unit is pure Lucas, and very odd.

What the control unit does is provide a pulse about a couple of seconds
long to operate the solenoids, then back to zero. Even when the switch is
still made. Same as all, really.

The Lucas one uses two massive Lucas starter motor relays with 1/4" screw
termimals - rated at about 300 amps. And massive caps and a resistor box
to time them. The fuse for the entire circuit 20 amps.

I realise the early 70s was a bit early for electronic timers (although
the car has points-less electronic ignition) - but why not use the smaller
and cheaper horn type relays rated at 30 amps? They have been around since
the 50s and likely earlier.

It's not a problem repairing the thing as all bits easily available. Just
curious about the design.

--
*We never really grow*up, we only learn how to act in public.

Dave Plowman London SW
To e-mail, change noise into sound.

on 04/01/2021, Dave Plowman (News) supposed :
What the control unit does is provide a pulse about a couple of seconds
long to operate the solenoids, then back to zero. Even when the switch is
still made. Same as all, really.

I have seen large capacitors used as the power source for solenoids on
one car. Slow charging via a resistor, then fast discharge via the
solenoid when triggered.

In article ,
Harry Bloomfield wrote:
on 04/01/2021, Dave Plowman (News) supposed :
What the control unit does is provide a pulse about a couple of seconds
long to operate the solenoids, then back to zero. Even when the switch is
still made. Same as all, really.

I have seen large capacitors used as the power source for solenoids on
one car. Slow charging via a resistor, then fast discharge via the
solenoid when triggered.

Indeed - what I am curious about is the use of massive relays rated at
hundreds of amps to switch under 20. Obviously their coils have a much
lower resistance than a 30 amp one which would typically be about 150
ohms. So need much larger caps too.

--
*Rehab is for quitters.

Dave Plowman London SW
To e-mail, change noise into sound.

On 04/01/2021 14:28, Dave Plowman (News) wrote:
In article ,
Harry Bloomfield wrote:
on 04/01/2021, Dave Plowman (News) supposed :
What the control unit does is provide a pulse about a couple of seconds
long to operate the solenoids, then back to zero. Even when the switch is
still made. Same as all, really.

I have seen large capacitors used as the power source for solenoids on
one car. Slow charging via a resistor, then fast discharge via the
solenoid when triggered.

Indeed - what I am curious about is the use of massive relays rated at
hundreds of amps to switch under 20. Obviously their coils have a much
lower resistance than a 30 amp one which would typically be about 150
ohms. So need much larger caps too.

Maybe Lucas had surplus in stock and decided to "second-purpose" them.

I'm more interested in the large capacitors. I can't think of a more
hostile environment for a capacitor than a car engine compartment,
particularly if it is an electrolytic to get that long pulse. Or was the
control unit in a cooler place?

--

Jeff

In article ,
Jeff Layman wrote:
On 04/01/2021 14:28, Dave Plowman (News) wrote:
In article ,
Harry Bloomfield wrote:
on 04/01/2021, Dave Plowman (News) supposed :
What the control unit does is provide a pulse about a couple of seconds
long to operate the solenoids, then back to zero. Even when the switch is
still made. Same as all, really.

I have seen large capacitors used as the power source for solenoids on
one car. Slow charging via a resistor, then fast discharge via the
solenoid when triggered.

Indeed - what I am curious about is the use of massive relays rated at
hundreds of amps to switch under 20. Obviously their coils have a much
lower resistance than a 30 amp one which would typically be about 150
ohms. So need much larger caps too.

Maybe Lucas had surplus in stock and decided to "second-purpose" them.

I'm more interested in the large capacitors. I can't think of a more
hostile environment for a capacitor than a car engine compartment,
particularly if it is an electrolytic to get that long pulse. Or was the
control unit in a cooler place?

It's situated inside the rear wing, so temperature depends on the weather.

I doubt you'd use surplus stock on a design hoped to sell many thousands?

--
*Those who live by the sword get shot by those who don't*

Dave Plowman London SW
To e-mail, change noise into sound.

This is what happens whe a designer has no idea on how to do something and
so decides to try the first thing that comes into their head with no thought
to failure modes as the device ages, sticky solenoids, broken springs and
any detection of whether the job was done as that will cost them the cost of
another bit of wire.

Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Dave Plowman (News)" wrote in message
...
I've been asked to repair the central locking controller on an early Rover
SD1.

Bit of history. That car was pretty early in the UK in having electric
central locking. It uses solenoids, rather than motors which are the norm
today. Later SD1 changed to motors.

The solenoid units ain't Lucas. Not quite sure who makes them.

The control unit is pure Lucas, and very odd.

What the control unit does is provide a pulse about a couple of seconds
long to operate the solenoids, then back to zero. Even when the switch is
still made. Same as all, really.

The Lucas one uses two massive Lucas starter motor relays with 1/4" screw
termimals - rated at about 300 amps. And massive caps and a resistor box
to time them. The fuse for the entire circuit 20 amps.

I realise the early 70s was a bit early for electronic timers (although
the car has points-less electronic ignition) - but why not use the smaller
and cheaper horn type relays rated at 30 amps? They have been around since
the 50s and likely earlier.

It's not a problem repairing the thing as all bits easily available. Just
curious about the design.

--
*We never really grow up, we only learn how to act in public.

Dave Plowman London SW
To e-mail, change noise into sound.