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I have an alarm board from Paradox, model SP6000. I power it with 16Vac/2.2A from a 40VA transformer which is connected to the electrical circuit from my house(230V 50Hz). The board has an AUX power line where I can connect multiple consumers(eg. keyboards, motion sensors, exterior siren). In the manual it says that the typical current consumption on the AUX line is 600mA, maximum 700mA and fuseless shutdown at 1.1A.

I connected 2 keyboards(power consumption at max of 250mA based on the manual), 10 motion sensors(8mA idle - 10mA max power consumption for each sensor), external siren(35mA idle + whatever power is needed to charge a 12v/7A battery attached to it) and a communication module which has a max power consumption of 100mA. Based on my calculations the max power consumption on the AUX terminals is 735mA. The alarm board has a separate circuit where used to charging a second battery with 350mA. According to the manual the max power consumtion for the entire board is 1.7A.

The transformer was heating up a lot after 1h of running so I turn it off.

Any advice on what to do? Could it be cause I had too many consumers?

Thank you.

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    \$\begingroup\$ You say "based on my calculations" but did you try measuring the current draw? It could be more than you think. \$\endgroup\$ – Steve G Feb 12 at 12:31
  • \$\begingroup\$ I only have a simple multimeter. How can I measure the current drawn with it? \$\endgroup\$ – Sitram Feb 12 at 12:46
  • \$\begingroup\$ my calculations are based on the theoretical values from the manual of each consumer. For example the keyboards consume in theory 250mA when their display is set at maximum intensity \$\endgroup\$ – Sitram Feb 12 at 12:58
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    \$\begingroup\$ Connect your multimeter in series with the 16vAC and set it to AC Amperes on a 5A or 10A range. It should show less than 2.2A. Multply the 16VAC*2.2A = 35.2VA, 35.2/40 = 88% capacity used. Transformers get warm, and it is not uncommon to size them up to twice as large as the actual demand. \$\endgroup\$ – rdtsc Feb 12 at 13:35
  • \$\begingroup\$ @rdtsc I apologize in advance for my noobines when it comes to electrical engineering. My background is in programming and I struggle with everything that is related to electricity. The transformer has 3 output wires, yellow(0V), blue (~16V/2.2A) and brown(~18V/2.0A). On the alarm board there are 2 pins marked with ~ and beneath them AC. I connect the blue wire in one of the pins and the yellow on the second one. It might be a dumb question but how do I connect the red and black wires of the multimeter in series? \$\endgroup\$ – Sitram Feb 12 at 13:47
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I was able to figure out why the transformer was heating. I was mislead by the yellow color of one of the output wires from the transformer, thinking it was ground. I connected it to the ground pin on the board and to the ground wire from the metal casing. Even with all consumers disconnected, the transformer was still heating and this is what made me thinking that maybe there was a problem with the power wires.

As soon as I disconnected the yellow output from the ground and connected it only to the second AC pin from board everything was OK and the transformer didn't heat over night.

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