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Alarm panel won't drive bell current

I have a DMP XR200 alarm panel with the bell output driving an MPI-11 siren driver. The panel bell output supplies 12VDC @1.5A max via an output relay.

When the siren driver is connected, I can hear the bell output relay switch on but then within about 1/2 second the relay immediately switches off -- this occurs in both pulsed and steady alarm modes.

The siren driver itself seeems to be working and the panel itself seems to have sufficient amperage, because when I connect its inputs directly to +12VDC on the panel, it properly drives the alarm speakers at full volume, drawing only about 0.4Amps. My oscilloscope confirms that the output is the expected pseudo-sine wave.

This led me to think that the problem must be with the panel bell output circuitry. However, when I disconnect the siren driver, the relay stays on and the voltage to the bell outupt is ~12VDC as it should be. I then tested it under load using a 10ohm 10W resistor and even under load, the relay still stayed closed -- using my DVM I verified that the panel was sourcing ~1.2A without tripping the overcurrent protection. So, at least with a static load, all seems to work fine on the panel.

I then noticed that the siren driver has a 2200 uF cap across its input. When I put a similar 2200uF cap across the panel bell output, it caused the relay to switch off. Similarly, when I temporarily removed the 2200uF cap from the siren driver, the siren driver board no longer caused the relay to shut off. (I also tried swapping a new 2200uF on the siren driver and it still caused the relay to shut off)

So I can only conclude that the transient current draw used to charge the 2200uF input capacitor is somehow tripping some internal overcurrent protection circuitry on the XR200 panel. Note that tripping only causes the alarm output to stop -- the rest of the panel functioning is unchanged.

Until now, my alarm has been working reliably for the past ~10 years. So, it seems like something has gone wrong in the current oversensing circuitry for the bell output.

Has anybody experienced similar issues before? Any thoughts on how to further troubleshoot & fix?

One other aside which may or may not be related. The alarm a few days ago started showing a battery trouble which by itself didn't seem worrisome since the batteries are about 9 years old. Meanwhile, I have new batteries on order.

But this still leaves me to wonder whether the two problems may somehow be related. Did the battery issue trigger the bell output issue or vice-versa? Are the batteries even bad or is the 'trouble' really just triggered by something wrong with the board. (Note: I only discovered the issue with the bell output after I noticed the battery trouble but it may have preceded that too)

(note: disconnecting the batteries did not stop the problem with the siren driver -- I thought initially perhaps that bad batteries could be drawing too much current but removing them had no effect).

Reply to
blueman
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The problem most likely is your standby batteries. They probably needed to be replaced many years ago. Replace the batteries first, then try your test again. If it still does the same thing, I would then use an external relay to trigger the siren driver board.

I do not use DMP panels, so it is hard to say why a capacitor was used other than to smooth out the DC voltage.

Jim Rojas

Reply to
Jim Rojas

Jim is probably right there. DMP panels are notorious for acting weird with marginal batteries.

Reply to
Bob La Londe

It sounds like the inrush current to charge up the 2200 mfd cap is too great. The cap looks like a short until it starts to charge up to the power source. I would consider a current limiting resistor between the output of the bell circuit and the input to the siren driver. Your 10 ohm, 10 watt will probably do, as it will limit the current to about 1.2 amps.

John Sowden American Sentry Systems, Inc.

Reply to
johnr

Change the batteries. The batteries share the load of powering the bell/siren when the panel is i n the alarm condition. A dead battery has low resistance therefore the pane l transformer is trying to provide current for the panel, the keypads the m otion detectors the smoke detectors the almost shorted bad batteries and th e bell/siren. Batteries are to be changed every three to four years NOT nin e years. Likely your bell/siren hasn't been able to ring for a number of ye ars because you ignored the low battery signal.

Apparently, one of the other short comings of DMP panels is that it lets yo u ignore a failure of a vital supporting function. Other panels give you a constant warning until the batteries have been changed.

Reply to
Jim

in the alarm condition. A dead battery has low resistance therefore the pa nel transformer is trying to provide current for the panel, the keypads the motion detectors the smoke detectors the almost shorted bad batteries and the bell/siren. Batteries are to be changed every three to four years NOT n ine years. Likely your bell/siren hasn't been able to ring for a number of years because you ignored the low battery signal.

you ignore a failure of a vital supporting function. Other panels give you a constant warning until the batteries have been changed.

Reply to
davek13815

its more likely you only have a SPEAKER for a siren ... DMP does not have a siren driver in it so you would have to get an actual alarm sounder installed ... BRINKS was notorious for speakers

Reply to
davek13815

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