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Multiple Parallel Power Supplies for Elk M1


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#1 kwschumm

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Posted 18 September 2019 - 04:12 PM

I'm putting together my first Elk M1 system having used HAI previously.

 

The Current Draw Worksheet that Elk has is telling me our system needs 15.66 amps.

 

This is quite a bit more than most people here seem to have, Altronix doesn't even offer a power supply that can supply that much.

 

The biggest draws are 11 COSMO-4W smoke/co detectors at .40mA each, combustible gas sensors at .8mA each, and assorted other sensors that have a max draw of nearly an amp each.

 

It is apparently unwise to have several parallel power supplies in parallel because they can fight each other, or overload one the others if one fails.

 

I could use dedicated power supplies for some purposes, such as one for the smoke circuit, another for glass breaks, another for sirens, etc.

 

There are also some lab power supplies available that offer up to 30A at 12VDC such as this one on Amazon.

 

https://www.amazon.c...aps,807&sr=8-19

 

Is there a better way? How have others solved this problem?



#2 RAL

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Posted 18 September 2019 - 04:56 PM

While there are power supplies that provide high current outputs, things will be easier to deal with if you use only Class 2 power supplies.  These are inherently power limited and make wiring on the 12V low voltage side simple and easy.  If you use a power supply with higher current output or that is not limited, then your low voltage wiring needs to follow stricter NEC wiring standards.

 

If you need 15A total current, I would recommend four (4) Altronix AL400 series power supplies. These can provide 12V at 4 Amps each.  Connect the negative terminals of all the power supplies together, and also connect them  to the M1's NEG terminal, so they all share a common signal ground.  

 

Then divide your devices across the four power supplies so that you have a load of about 4A or less on each one.  Do NOT connect the +12V outputs of the power supplies together.

 

Another possibility would be to use certain Altronix AL600 series power  supplies (such as the AL600ULPDxCB models.   Not all AL600 models are rated as Class 2 - only the CB models are.  With these, you would get 6A per supply, and would need only 3 instead of 4.

 

As an aside, It's good practice to connect the negative terminals together and to the M1.  But it is only necessary if a device powered by one of the aux power supplies needs to communicate to the M1 using signals rather than a switch contact.  So if you power a M1 databus device like an input expander from an aux supply, then connecting the negative terminals together is  required.  But for devices like motion detectors, it is not.

 

An additional complication is that if you power smoke detectors from the aux supplies, then you will need a relay there to interrupt the power to the smokes when the M1 does a smoke-reset and drops the SAUX power output.



#3 kwschumm

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Posted 18 September 2019 - 05:05 PM

RAL, Thanks very much for your clear and complete advice. It was very helpful and confirmed some of the things I was wondering about.



#4 ano

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Posted 18 September 2019 - 10:09 PM

The biggest draws are 11 COSMO-4W smoke/co detectors at .40mA each, combustible gas sensors at .8mA each, and assorted other sensors that have a max draw of nearly an amp each.

Hmmm  you might want to double-check your math.  11 X 0.40ma = 4.4ma = 0.0044 Amp.     10 sensors drawing 0.8ma each = 10 X 0.8ma = 8ma = .008 Amp.  What sensors draw an amp each? That is pretty rare. At 12V that would be 12W.  Maybe a siren draws 1A but sensors rarely do. You might want to recheck that.



#5 kwschumm

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Posted 18 September 2019 - 10:53 PM

Hmmm  you might want to double-check your math.  11 X 0.40ma = 4.4ma = 0.0044 Amp.     10 sensors drawing 0.8ma each = 10 X 0.8ma = 8ma = .008 Amp.  What sensors draw an amp each? That is pretty rare. At 12V that would be 12W.  Maybe a siren draws 1A but sensors rarely do. You might want to recheck that.

I knew there as something screwy with the numbers being so high. Operator error, off by one. I entered .4 amps and it should have been .04. Thanks for saving me a lot of money on power supplies!






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