Power Supply Problem

[kaohao]

Hi Cocooners, complex problem here. We have a system consisting of an omnipro II and five expansion enclosures. We have frequent power outages and a generator that kicks in when an outage occurs.
    The generator powers our main board, one expansion enclosure and an altronix auxiliary power supply unit. The idea was that we would power the expansions not covered by generator power with the altronix. Unfortunately we only have cat5 running to two of the more distant expansion enclosures and it doesn't seem to adequately carry the necessary amperage to those expansions. They run, but the battery starts to show a lower value on the PC access after a short period. Also we have kinda limited cabinet space so we're trying to avoid using larger or additional batteries.
    So, the question is twofold: how can we power these remote expansions during our long and frequent power outages, and is there a way that we can program our omnipro to ignore those expansions when the batteries run down?
    Also, we are unable to power the two expansions in question with our generator using the wiring currently in place. Thanks!  

 

[RAL]

The generator powers our main board, one expansion enclosure and an altronix auxiliary power supply unit. The idea was that we would power the expansions not covered by generator power with the altronix. Unfortunately we only have cat5 running to two of the more distant expansion enclosures and it doesn't seem to adequately carry the necessary amperage to those expansions. They run, but the battery starts to show a lower value on the PC access after a short period. Also we have kinda limited cabinet space so we're trying to avoid using larger or additional batteries.

 
 
You've got me confused.  Don't the remote expansion units normally get their power from the Altronix through the Cat5?  And didn't you say the Altronix is receiving power from the generator?
 
It would be normal to see the battery voltage decrease when the AC power goes out.  It's going to follow a predictable curve from about 13.5V down to 10.5V or so.
 
If the voltage is dropping too quickly, that suggests that the battery is too small for the load and the time you need it to maintain power.  It's also possible that the resistance of the Cat5 is resulting in a voltage drop (say 1V) that doesn't cause a problem when on AC power and the Altronix is putting out 13.2V. But when running on battery, as the battery voltage drops, it causes the expansion units to fail sooner than you expected.
 
I don't know of a way to have the OP2 ignore the loss of the expansion units.

 

[kaohao]

Normally the remote expansion units get their power locally, but those outlets aren't covered by the generator. My idea was to power them all the time from the altronix, but shortly after hooking these two expansions up to the altronix using the cat5, I started getting these declining battery readings.

 

[cobra]

You say you used cat5 for power, but how is it wired?  I would use 2 or 3 of the cat5 wires in parallel for your 12V and return lines each, depending on how many you have available in the cat5.
 
How old is the battery?  You may just need to replace it.  It sounds like it may be unrelated to your changes.

 

[kaohao]

I actually used 2 cat5's (8 conductors for each terminal). Each output from the altronix supplies 3.5 amps so I figured that would be plenty for my two expansion enclosures and 3 sirens. It's about 200 ft. from the Altronix to the expansion enclosures.

 

[kaohao]

My 2 cat5's do seem to be powering one of the expansion enclosures somewhat adequately. The reading on the battery from the PC access dropped quickly from 230 to 216, however, but that was with the siren sounding. I have since disconnected the siren.

 

[RAL]

I actually used 2 cat5's (8 conductors for each terminal). Each output from the altronix supplies 3.5 amps so I figured that would be plenty for my two expansion enclosures and 3 sirens. It's about 200 ft. from the Altronix to the expansion enclosures.

 
A single 24AWG conductor of Cat5 cable has a resistance of 25.67 ohms per thousand feet.  With 8 conductors in parallel, that would reduce it to 3.2 ohms.  Over a distance of 200 feet, you'd have a total loop resistance of 1.28 ohms.  
 
The expansion unit draws 0.08A (typical) to 1.6A max with all outputs active. That would give you a voltage drop in the range of 0.1V on up to 2.0V. 
 
If you are running both expansion enclosures over the same Cat5 cable, then double those numbers.
 
A single outdoor siren could easily be drawing 1A when it is active, dropping the voltage another 1.28V.  If it's just a piezo "screamer" the current is more like 175mA, which would give you a voltage drop of 0.25V.
 
I'll guess that you probably don't have all the expansion outputs active, so your voltage drop with 2 expansion units and no siren is probably about 0.2V or so.  But with the siren(s) active, you could be getting into trouble.
 
The best thing to do is put a multimeter on the DC input terminals on each expansion enclosure and measure the actual voltage and compare that to the voltage you measure back at the battery.

 

[Del91574]

Pay attention to which Altronix. Some offer 0V loss upon cutover, some lose 1-2V on cutover....combined with the battery float voltage, it's very easy to get into trouble.
 
Doubling or tripling up conductors to make up for being undersized is a bad idea in practice.

 

[kaohao]

What's cutover? Also, for a run of 200' is there an ideal conductor? Maybe I can pull something else through the conduit.

 

[RAL]

What's cutover? Also, for a run of 200' is there an ideal conductor? Maybe I can pull something else through the conduit.

 
Cutover is the switch from AC power to battery power.  In some power supply designs, the circuitry that does the switching reduces the battery voltage.  I think elsewhere, you said you have an AL600, which has a 0V loss.  So not something you need to worry about.
 
The ideal conductor size will depend on how much current your hardware can draw under worst case conditions.  If you have 3 sirens at 1 Amp each, plus two expansion units with all outputs active, you're looking at something over 6 Amps.  With a high current like that, to limit the voltage drop to something modest, say around 0.5V, you'll need a very heavy gauge wire. Probably not practical, in my opinion.
 
On the other hand, if you don't have the sirens, and don't use the outputs on the expansion units, your current draw would be much more reasonable - say 0.2A.   In that case, 18AWG would give you a drop of 0.51V on a 200' run.

 

[kaohao]

DEL, why is doubling up conductors bad? sorry, total newb here. 

 

[RAL]

why is doubling up conductors bad? sorry, total newb here. 

 
The problem of using multiple conductors is that if one or more of the conductors breaks or comes loose, you may not be aware that there is a problem right away.  If things are running at less than maximum current load, everything may continue to run and appear normal with the current being carried on the remaining conductors.  But under higher loads, the conductors won't be able to properly handle the current, which will cause a voltage drop.  That in turn can cause system errors, possible overheating of the conductors, and perhaps even a fire.
 
At the voltage and current you're talking about in this specific case, a fire would be unlikely.  But still, you could run into the other problems.