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MG MGF Technical - smoke from the boot !!! @Carl, Will or Tony

Hi,

no, no, not what you think !!!! ;-)

I _only_ have an electric related problem with the boot lid solenoid.

Installed in last year, and used only 3 or four times until it failed to work.

Got this nice from Carl but lost his instructions.
Original it is a solenoid or motor with a resistor in series. I recall, Carl said the resistor must remain in series connection ... whyever.

OK so far. This morning I had a look why it doesn't work and found this behind the mounting bracket.

http://www.mgfcar.de/boot_lid/resistor_05208.JPG

Resistor got a lttle hot, ehhhyyy ? ;)

Measures:
Solenoid resistance static is 94.5 Ohms
Resistor looks like a 2W carbon part and it currently has in this burnt condition app 8.5 Ohm, which seams to many, cause the solenoid gets to less current ??

Approved:
Voltage gets to the solenoid connector. I've crosschecked with a 12V bulb and this works half dark like connected to a 6V battery.

Question ??
What new resistor should I put in series to the solenoid ?

Thank You for taking attention to this minor matter
:o)

Regards
Dieter
Dieter

Why the resistor in the first place?
Is the solinoid rated at a lower voltage?

Note, if the light is 1/2 bright then its getting 80% of voltage!

Assuming your reading is correct (which it won't be - do you have the colour code?)

Voltage across the solonid =>
(12 * 94.5)/(94.5+8.5) = 11V

Current thru the resistor = current thru the solonid =>
V=IR
1=I * 8.5
I= 0.118 A = 118 mA

Power dissipated by the resistor
P= IV = I*I*R = V*V/R
Using V^2/R
P= 1/8.5
P= 0.118 W

So 1/4 watt would be fine.
Will Munns

Dieter,

It is strange to wire to earth via a resistor.
Earth should be as close to Zero resistance as possible.

There is no mention about a resistor here.
http://www.mgfcar.de/boot_lid/electric_boot_release.htm

I know these solenoids, and they are a standard 12v supply. Put 12volts across and the piston pulls in.
Remove 12volts and spring pops the piston back out.

One thing that does come to mind now, is that when you press and release the buttom, an electric arch can be formed on the contact points in the switch. Works like the points, distibuter and coil systems in cars. Good ol' ignition systems.
Maybe the resistor was put there to reduce the sparking?

HTH
Branko.

Branko

No diffrence in puttin the resistor between the bat and the sol and the sol and the earth. If you were trying to stop arc's you would use a cap.
Will Munns

Yes, thats exactly what I have used. :-)

What I'm trying to work out is why someone else would have used a resistor there.

The solenoid when connected directly to the car's 12v supply will operate with a loud clunk. This is a strong unit and does draw a few amps.
Now, thinking, thinking, thinking............

Bingo!! ....Add resitor so the solenoid operates with less clunk.
I think thats why the resistor is in series with the supply.

Would it hurt to try without the resistor?


Cheers,
Branko.
Branko

Hi Dieter,
sorry to se what has happend,but there is an explanation! (As allways;O)
For some reason the momentary voltage used to operate the solenoid has been more than momentary,probably there for some time! When feed directly with 13V from the pushbutton there is a too fast and "wild" action of the solenoid. To tame this I added a resistor in series ,and as there are 2 cables to the solenoid the one to ground got the resistor.
So in this way the solenoid (actually a small electric motor and gearing that gives the needed range of dragging force) moves in a more pleasant manner.

So probably there is a fault in the pushbutton OR if a relay is installed in between to handle the current it can be stuck.
IMO you will probably find continous 13Volts between the "hot" wire to the solenoid and ground.....
Or has the passenger pushed the button during your spirited driving on the Autobahn in order to try to stop the car ?? / BR ,Carl.
Carl

Forgot to mention the value of the resistor,old weak memory ;O) ,have to check on my own car. Will be back a.s.a.p / Carl.
Carl

Hi all,

thank you for comments
:o)

>do you have the colour code ?
Errr, I'd say, it's _now_ one ring only and ash gray ;) (LOL)

Branko, the solenoid on the webside was in my very first MGF. The same as used to be sold at B&G etc.
There's no resistor required, but a Relay recommended in any way. I now have this different smooth working motor from Carl.

Will, good to get the right formulars back in mind :)

Carl, no idea what went wrong with it.
Switch and relay work fine. I daupt the relay got stuck. More realistic would be wrong access to the switch. The wiring is equal to the first installation with power to the switch contact from the handbrake light. Original rear window heater switch powers the relay and the relay contact gets +Voltage over an extra fuse.

Just got the idea to _measure_ the boot lid motor current without resistor. I have no high current Ampere instrument, but .. a heap of overstock fuses with different Amp ratings ;)
I think I start with a 4 Amp fuse and see what it does. *Fuse survival or not*.




Dieter

That will sort of work, but most fuses will be able to carry twice their rated ampage for a short amount of time, with motors you offen get a startup current which is about twice the running current, you don't get this with a soloniod.
Will Munns

Hmmm, must have a look at my unit - still in the box!
Just haven't had the time to install it yet. Hopefully on retutn from holidays.
Tony

Found what's wrong.
The Motor doesn't work as it should. I think anything mechanical broken or whatever inside.
Put it direct with the short wires to the battery and it sometimes _tries_ to work, soemtimes not. No full movement over the gear range.

Dropped it to the waste bin.

Looking for another one now. I've seen a nice small in our Smart Car rear used for opening the rear glass window ..... :)
I wonder how much it will be from MCC.
Dieter

>> I wonder how much it will be from MCC. <<

Can you spare another arm and leg Dieter? ;o) ;o)
Rob Bell

I'll sourced one ;) Not from Smart Car, even it is so nice tiny.
Check Ebay for *boot release*. I did in German with *Stellmotor*
http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=7976240399
Dieter

3..2..1. mine
http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=4551941783
Dieter

Carl ?? do you read ?

Couldn't resist and cut the broken motor :)

Found the problem, of course.
Inside is a motor with small gear. The motor drives a bigger gear with _snake_ thread.
On the snake a slide nut.
Slide nut is engaged with the pull slide between two notches on top and on the bottom.
On power the motor turns the thread, pulls slide nut and action slide. On power out the spring pulls all back.

Well, usually. But no longer at mine.
It had come off, I think cause of to long pulse from the switch (reason also for the burnt resistor, you all said this already)

http://www.mgfcar.de/boot_lid/slide_off_DSC05216.JPG

I put the slide nut back between notches and pushed the slide back aginst the spring force (assy full engaged then)

See the problem of the parts in principals if not powered with short pulse.
There is still about 10mm space for further movement and disangaging the slide nut.

http://www.mgfcar.de/boot_lid/slide_back_DSC05218.JPG

Three options with it.
- Getting some electric circuit to make a monoflop pulse.
or
- put a fitting distance pipe to restict further return movement of the slide nut.
or
Much easier for the mechanic engineer :)
- put in an additional small micro-switch and wire it in series with the motor.

All needed is there for this mod.
- space
- lever at the acting slide above the switch to cut the motor from power
Result will be a _rattling_ slide like at an electric door bell

Will see whether I can find a fitting switch and rebuild the broken part for using it until the Ascona part arrives. I think the Ascona thing will be nearly equal inside.

Regards
Dieter
Dieter

Hi Dieter,
yes, too long engagement of the pushbutton might be the problem. A piece of tubing or any other plastic part that will restrict the movement length of the slide will probably do OK. Mine has been in regular use for many years now,works fine with the "taming down resistor", but might be worth have a look inside and do an alteration...
BR, Carl
Carl

Hi Carl,

I think so. The problem is getting it proper adhered back together.

Anyway, will do a follow up in about two weeks when getting back from the Alps ride. The Ascona part should be here also when I'm back.

Electric boot release < key for later archives search
:)

Cheers
Dieter
Dieter

>> The motor drives a bigger gear with _snake_ thread. <<

The term in English is 'worm gear' - I guess in this case it is made from Nylon? Wear not that surprising if used regularly :o)

>> - Getting some electric circuit to make a monoflop pulse. <<

Another 555 chip project Dieter?
Rob Bell

Thank You for the worm gear
:)
added to http://www.mgfcar.de/mis/translation.htm

>555
??
No !!! No gears inside and they can't get fixed with hammer, knife or hacksaw !!
(Tony, Will, Carl, forgive me)
;-)
Dieter

This thread was discussed between 26/05/2005 and 31/05/2005

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