Siren and Strope current draw on ELK-M1G

richardfj

Member
I've had my security system (ELK-M1G) running with indoor only speakers connected directly to the Out1 (and the listen-in interface). I've decided to hook up a few outdoor sirens / strobes and went with 4 ELK-1RT speakers and 4 Elk-SL1 strobes, connected to a ELK-120 Voice and Siren module. Before any of the outdoor fun and games is connected to my system, I'm drawing 0.75 Amps on the system (I've got a fairly hairy and large system ... several glass breaks, smoke detectors, about 8 motion detectors and another 20 or so contact zones).

The steady and switched aux power outputs (on the left side of the control) are limited to 1.25 Amps and should be less than 1 Amp (in total) if you're following UL standards. I'm not sure what the current draw and limits are for Output 1 (where I have my inside speakers connected) .. anyone know? I was planning on connecting Out 2 (set to voltage out) to the Elk-120, but that output is current limited to 1 Amp. I'm assuming that the 1 Amp limit on Output 2 doesn't have anything to do with and don't impact the current limits on my power outputs on the left of the control (steady and switched aux) ... can anyone confirm that for me?

Even if that's true ... if I understand the current draw of these speakers (eg. http://www.ebtx.com/mech/ampvolt.htm), 50 watts and 8 Ohms ... I'll be pulling over 2 Amps when I connect all four speakers ... Watts (50 watts peak * 4) / Length (8 ohms) / Volts (12) = ~2.1 Amps ... am I doing that right????

The 4 strobes each pull 140mA ... or 0.56 Amps in total

I'm also about to hook up an Elk-M1XRF (wireless receiver), which apparently pulls 70mA as well.

Seems like I should be fine keeping my system the way it is now and connecting the M1XRF to the control without any power modifications.

However, to power the outside speakers and strobes it seems like I need to get an additional power supply. Until I started doing the calculations, I was planning on getting the 1 Amp power and battery enclosure, but I'm wondering if that's going to be enough ... seems like I need to get the 4 Amp supply ... but there is a little bit of a price difference so I don't want to go that route unless I need to.

Can someone put a second set of eyes on this and make sure I'm not missing anything?
 
I've had my security system (ELK-M1G) running with indoor only speakers connected directly to the Out1 (and the listen-in interface). I've decided to hook up a few outdoor sirens / strobes and went with 4 ELK-1RT speakers and 4 Elk-SL1 strobes, connected to a ELK-120 Voice and Siren module. Before any of the outdoor fun and games is connected to my system, I'm drawing 0.75 Amps on the system (I've got a fairly hairy and large system ... several glass breaks, smoke detectors, about 8 motion detectors and another 20 or so contact zones).

The steady and switched aux power outputs (on the left side of the control) are limited to 1.25 Amps and should be less than 1 Amp (in total) if you're following UL standards. I'm not sure what the current draw and limits are for Output 1 (where I have my inside speakers connected) .. anyone know? I was planning on connecting Out 2 (set to voltage out) to the Elk-120, but that output is current limited to 1 Amp. I'm assuming that the 1 Amp limit on Output 2 doesn't have anything to do with and don't impact the current limits on my power outputs on the left of the control (steady and switched aux) ... can anyone confirm that for me?

Even if that's true ... if I understand the current draw of these speakers (eg. http://www.ebtx.com/mech/ampvolt.htm), 50 watts and 8 Ohms ... I'll be pulling over 2 Amps when I connect all four speakers ... Watts (50 watts peak * 4) / Length (8 ohms) / Volts (12) = ~2.1 Amps ... am I doing that right????

The 4 strobes each pull 140mA ... or 0.56 Amps in total

I'm also about to hook up an Elk-M1XRF (wireless receiver), which apparently pulls 70mA as well.

Seems like I should be fine keeping my system the way it is now and connecting the M1XRF to the control without any power modifications.

However, to power the outside speakers and strobes it seems like I need to get an additional power supply. Until I started doing the calculations, I was planning on getting the 1 Amp power and battery enclosure, but I'm wondering if that's going to be enough ... seems like I need to get the 4 Amp supply ... but there is a little bit of a price difference so I don't want to go that route unless I need to.

Can someone put a second set of eyes on this and make sure I'm not missing anything?

Remember the price difference is more than just the size of the power supply. With the 4 amp unit you are going from a simple transformer charger/supply to a switching power supply. Besides more capacity you are also getting more robust noise and surge protection. I use 3, and I still plan to purchse 1 or 2 more. Make sure you are thinking ahead to future expansion when making your power supply decision. Some of what mine are doing (or will soon be doing) include:

30 smoke detectors (soon to be swapped for models with built-in sounders)
8 motorized fire bells
4 strobes
8 phone mute relays
16 HA announce relays
12 Misc. relays (doorbells, garage doors, mailbox, etc.)
Magnetic door lock
4 Panasonic IP cameras
8 motion sensors
8 Elk keypads
5 Elk Input expanders
2 Elk RF receivers
8 RS-485 thermostats
4 RCS RS-485 hubs
4 Stargate I/O expanders
Stargate IR expander
4 Stargate LCD keypads
8 Stargate LED keypads

And I am thinking of replacing my 70V paging and HA announcement amplifiers with as many as 20 Elk-800 mini amplifiers.

None of this draws much power but it adds up quickly. If you think that you are likely to expand beyond your initial system, you will appreciate having the larger 4 amp supply.
 
I agree with that ... I'm not sure how much expansion I'll be adding to my security system (most of my future add-ons will likely be on the HA side ... which I'm not handling with my ELK), but either way, I probably need the 4 Amp

That said ... I am curious if I'm actually thinking about the current draw correctly. Would like to make sure I understand what the ancillary functions / features pull in terms of power.
 
I agree with that ... I'm not sure how much expansion I'll be adding to my security system (most of my future add-ons will likely be on the HA side ... which I'm not handling with my ELK), but either way, I probably need the 4 Amp

That said ... I am curious if I'm actually thinking about the current draw correctly. Would like to make sure I understand what the ancillary functions / features pull in terms of power.

The current draw for most Elk items is listed on the spec sheets at their website. For relays be sure to account for times when you might use more than one relay for something (2 relays to switch both sides of a speaker, etc.) Calculate for worst case which is usually alarm mode with all sirens and strobes drawing current.
 
The current draw for most Elk items is listed on the spec sheets at their website.

Right, but I was really trying to figure out if I understood how to calculate the current draw from the speakers ... which is the methodology I listed above, since it gets a little more tricky when you're dealing watts and cable lengths.

On that note, I wonder how much the cable length impacts the current draw on something like a 140mA strobe 100ft away from the control with let's say a 18 gauge wire ... should we worry about the additional current draw of the wire?

No worries if no one has the answer ... I was just trying to make sure I understood it right.
 
Even if that's true ... if I understand the current draw of these speakers (eg. http://www.ebtx.com/mech/ampvolt.htm), 50 watts and 8 Ohms ... I'll be pulling over 2 Amps when I connect all four speakers ... Watts (50 watts peak * 4) / Length (8 ohms) / Volts (12) = ~2.1 Amps ... am I doing that right????
I am not sure of that math/formula, since you are assuming that 50W could be produced and the voltage would be 12. This website indicates that 50 watts in 8 ohms would be 20 volts @ 2.5A, for a single speaker.
http://www.angelfire.com/pa/baconbacon/page2.html

Spanky gave some info about the current draw of their speakers and siren drivers here.
http://www.cocoontech.com/index.php?showtopic=10211

I don't think extra wire length draws MORE current from the source. Longer cables have a larger voltage drop, so the wire in a long installation takes a bigger percentage of the current, relative to the target device. Therefore, to get a perfect 12V at the device with a long run, you may have to configure the source to provide more than 12V to compensate for the voltage drop. Luckily, most security stuff doesn't require a precise 12V and the cable lengths are reasonable, so I don't think the length is an issue for your strobes.
 
"On that note, I wonder how much the cable length impacts the current draw on something like a 140mA strobe 100ft away from the control with let's say a 18 gauge wire ... should we worry about the additional current draw of the wire?"

The wire run adds resistance and drops the current. If it reduces the available voltage measured at the load, you may have to increase the size of the wire gauge. One of my strobes is about 100' from the M1, and 18awg wire handles it OK. The strobe draws about 200 mA.
 
If you run the M1 from a 4 amp DC power supply into the battery terminals, you will loose AC failure reporting. Also you will need to set the AC failure time to 255. This keeps the keypad from displaying AC failure.

100 feet of 18 ga wire at 140 ma. will drop very little voltage, so it will work OK.

Longer wire runs have more resistance in the wire, therefore more voltage drop. Voltage Drop = Current/Resistance.
The current draw will be less with a long wire run. On a speaker, a long wire run will decrease the volume slightly. Use larger guage wire to compensate for the voltage drop if you want maximum volume. Two 8 ohm speakers in parallel (4 ohms) will draw about 2 amps in alarm. Which is maxing out the M1's power supply.
 
While I cant find the specifc data I had done some testing over a year ago with the voltage drop on 2 wire smoke zones using different gauge wire. At 18 awg I dont think you will see more than a .5 V drop at 100 feet or so (slight difference solid/stranded). In most applications that is insignificant and you would never see a difference. In the case of 2 wire smoke zone you MIGHT on SOME panels under extreme conditions (prolonged AC failure where the battery was dying and you had an alarm on that zone).

From what I remember of some testing I did years ago on ZN 16 of the M1 the 100 feet of wire is no problem at all (I think you could go MUCH MUCH further if I remember correctly) . On other brands of panels it could be a concern for 2 wire smokes in some cases. If wire length is a concern usually the mfg installation instructions would have a notation not to exceed a certian length in order to maintain their UL Listing etc.

There seems to be more and more awareness by code authorities for the proper loading of alarm panels. I know the state of MA has started making the installers submit their calculations in writing in order to get approval of the installation. The code authorities are becoming more and more educated each year.

Edit: All UL Listed devices are tested at under and overvoltage conditions as well. 85% to 132% of the rated voltage range of the device. This helps insure proper operation.
 
Excellent conversation ... thanks for the insights.

Since it's been a couple of years since I studied this in school ;-) ... I might be drawing the wrong conclusions, but it seems that since amps = watts / volts as voltage drops over longer cable runs, amps increase ... in has to no? So I completely get that the devices will function perfectly well within a range of volts supplied ... but if a long run causes the voltage to drop, the total current (amps) flowing through the circuit has to increase ... in other words, a device closer the the panel will draw less current than the same device further away from the panel ... this is the same reason we use 240V circuits for things like ranges and A/C's ... it enables us to get the current draw lower because the voltage is higher ... anyone with some actual knowledge, feel free to correct me

BTW - I've already figured out that I need the power, so the 4amp supply is on the way ;-)

To Spanky's point above (2 speakers in parallel drawing 2amps) ... can anyone confirm how much a series / parallel setup of speakers will draw? I currently have three of the indoor 20W speakers connected in series / parallel to my Out 1 (... so 6 ohms), but was intending on connecting a few more ... will the 8, 4 and 5 ohm options for 4, 5 or 6 speakers draw more or less current? Or is it just a matter of how many speakers I have? Is the ohm of the series / parallel setup simply to balance out the resistance across each speaker as much as possible?
 
Excellent conversation ... thanks for the insights.

Since it's been a couple of years since I studied this in school ;-) ... I might be drawing the wrong conclusions, but it seems that since amps = watts / volts as voltage drops over longer cable runs, amps increase ... in has to no? So I completely get that the devices will function perfectly well within a range of volts supplied ... but if a long run causes the voltage to drop, the total current (amps) flowing through the circuit has to increase ... in other words, a device closer the the panel will draw less current than the same device further away from the panel ... this is the same reason we use 240V circuits for things like ranges and A/C's ... it enables us to get the current draw lower because the voltage is higher ... anyone with some actual knowledge, feel free to correct me

BTW - I've already figured out that I need the power, so the 4amp supply is on the way ;-)

To Spanky's point above (2 speakers in parallel drawing 2amps) ... can anyone confirm how much a series / parallel setup of speakers will draw? I currently have three of the indoor 20W speakers connected in series / parallel to my Out 1 (... so 6 ohms), but was intending on connecting a few more ... will the 8, 4 and 5 ohm options for 4, 5 or 6 speakers draw more or less current? Or is it just a matter of how many speakers I have? Is the ohm of the series / parallel setup simply to balance out the resistance across each speaker as much as possible?

The error in your logic is assuming watts stays constant. In reality the source voltage is constant for these calculations. As wire resistance goes up then amps go down according to amps = volts/ohms. Since watts = volts X amps, as amps go down so do the actual watts produced (volume gets lower). The reason we use 240V for ranges is to get the same amount of watts (heat) with half as much current as would be needed at 120 volts.

For your speaker calculations remember the watts rating of the speaker tells you how much it can handle NOT how much it will draw. To calculate draw you need to use the impedance. If Spanky says 4 ohms will draw 2 amps then according to A = V/R 8 ohms should only draw 1 amp and 16 ohms should only draw 500 mA. The actual watts generated at each speaker will depend on how you series/parallel them together and is a separate issue. The total load, that is the impedance that the panel sees from the total series/parallel speaker combination, is what determines the current that will be drawn from the panel.
 
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