Re: Could two relays overload door-unlock output?

[mm <NOPSAMmm2005@xxxxxxxxxxx>]

On Mon, 7 Mar 2011 07:35:46 -0800, "Bill"
<billnomailnospamx@xxxxxxxxx> wrote:

>"mm"  wrote in message
>>I have a car alarm, Excalibur, AL-1510-EDP.   It has been installed
>>in
>> my Chryler LeBaron for about 3 years and had always worked fine.
>> (In
>> a previous car, I had an AL-1000-E for several years)
>>
>> The alarm included a separate relay to unlock the two doors** and
>> another separate relay to unlock the trunk.  The standard automotive
>> relays used with car alarms.
>>
>> Since the trunk lid doesn't pop up anyhow, and I often wanted the
>> trunk open when I unlocked the car, I changed the wiring, I moved
>> the
>> trunk relay wire, so that when I unlock the car doors, it also
>> unlocks
>> the trunk.
>>
>> Everything was fine for a week, but then the remote, both of them
>> would no longer arm the alarm, or lock or unlock the locks.**
>>
>> Did I overload the circuit by connecting two relays to the same
>> output?
>>
>> **Alhthough it's not totally dead.  I think there are 3 fuses in the
>> setup and none are blown.  When the battery dies (as it did often in
>> the cold winter, I have a Battery Buddy that disconnects the battery
>> when it gets too low, and when I push the button on the battery
>> buddy
>> to reset it, or sometimes after that, when I then turn the ignition
>> key (one or the other and always), the alarm sounds for 4 or 5
>> seconds
>> and stops.
>>
>>
>> If I overloaded it, or not, is there any chance of repairing it?  I
>> have many years of very part time amateur tv repair.   If the
>> problmee
>> is in an IC, I'm stuck, but if there's an internal relay I
>> overloaded,
>> I should be able to fix that, for example, and maybe even something
>> more difficult.
>>
>>
>>
>> **And another one to look the doors. There is also the other usual
>> features like a current sensor, a starter motor interrupt, Echo II
>> two-way remote, plus a regular remote.
>>
>
>Usually outputs, like the relays in this case, are sort of a separate
>thing which can go bad, but then just the output no longer works, but
>everything else works like normal. In technical terms, there would be
>a transistor output driving the relay(s) and that, if overloaded,
>would act like a fuse and the output only would no longer work.

That's what I would have thought.
>
>I suppose an output transistor could fail so that it was always
>shorted "on". If that is the case, try powering it up and see if the
>relays activate when you power it up. And if this was shorted on, then
>it could overload other things in the electronics.

Neither the trunk nor the locks do anything when I reconnect, after
the Battery Buddy disconnects (which has happened probably 20+ times).

>Anyway I would suspect some other problem. Try using a voltmeter to
>see if the unit is getting a good 12 volts power.

But it does set off the siren every time the battery buddy disconnects
the battery and then I reconnect it.
>
>As to how many relays the output could power, this would be the
>amperage rating of the output (transistor or whatever). If you don't
>have a schematic diagram of the unit, call the manufacturer and ask.

I don't want to bother them just for myself.  I'm not a dealer, and I
think they'd prefer me to take it to a dealer or just buy another one.
>
>If you do have schematics, then search for the data sheet for the
>output transistor and see the max amperage rating. And also find the
>data sheet for the relays and see what their amperage draw is. Here is
>an example of a data sheet...
>http://www.nxp.com/documents/data_sheet/BUJ105A.pdf
>
>Also relays sometimes have a "flyback diode" which is a backwards
>diode. When a relay turns off, it can send a high voltage back into
>the electronics and "zap it". That diode prevents this. So it could be
>important that you used the provided relays and wired them correctly.

I did put in the diodes, as the installation manual said to.
>
>On flyback diodes and relays...
>http://www.physics.unlv.edu/~bill/PHYS483/relay.pdf

I delayed posting until I read these.  Thanks.

>As to adding the 2nd relay, I would have connected that to the output
>of the 1st relay rather than in parallel.

DA

 Then the alarm output would
>only be driving one relay, then that relay would drive the doorlocks
>*and* the 2nd relay. Thus you would not be placing an additional
>amperage load on that output.