MTR3K and battery revert

[FMROB]

Hello all,

Need to pick some brains out here. Working on a TRBO capacity plus design utilizing MTR3K repeater, 6 to be exact. I need to depoloy battery back up. As we all know the specified battery charging beast for these units is made by argus, and is a bit bulky and costly. Space is a premium at this site, and trying to keep cost down, so I am looking for a solution.

My thought was to power the units DC only with three seperate Samlex N+1 24 Volt Battery revert DC power supplies and connect the external batteries to the powers supply. The MTR draws about 15 amps at full load on DC, and backs down power as the voltage drops. I figure on using two Northstar 24 Volt 100 Ah batteries wired in parallel. There is TTL outputs on the Samlex that I can use to trigger an alarm when on battery, for loss of ac.

In essence we will be cutting out the need for three argus chargers and the power supplies are less money to start off with.

Am I on the wrong path, should I just utilize one argus charger per MTR3K? To me, this seems to be more streamlined.

Thanks, Rob

[wavetar]

Hello all,

Need to pick some brains out here. Working on a TRBO capacity plus design utilizing MTR3K repeater, 6 to be exact. I need to depoloy battery back up. As we all know the specified battery charging beast for these units is made by argus, and is a bit bulky and costly. Space is a premium at this site, and trying to keep cost down, so I am looking for a solution.

My thought was to power the units DC only with three seperate Samlex N+1 24 Volt Battery revert DC power supplies and connect the external batteries to the powers supply. The MTR draws about 15 amps at full load on DC, and backs down power as the voltage drops. I figure on using two Northstar 24 Volt 100 Ah batteries wired in parallel. There is TTL outputs on the Samlex that I can use to trigger an alarm when on battery, for loss of ac.

In essence we will be cutting out the need for three argus chargers and the power supplies are less money to start off with.

Am I on the wrong path, should I just utilize one argus charger per MTR3K? To me, this seems to be more streamlined.

Thanks, Rob

I know other members have done this with no issues. I believe one of our shops did for an install as well. I know the MTR2000 had a 'DC Only' option when ordering which omitted the factory PS for this purpose, and gave some savings because of it...not sure if it's an order option with the 3K or not, but your setup should still work for you either way.

Todd

[FMROB]

Todd,

Thank you. I am thinking it should work fine. If any one else has any ideas or pitfalls, please let me know.

Thanks, Rob

[RFguy]

You should have a low-voltage disconnect in place to protect the batteries.

[FMROB]

Interesting. I wonder if the argus system has this. I will also check the drop dead voltage and subsequent "turn-off" of the MTR3K repeater. I think I remember something to the affect that the MTR will shut off at a certain voltage, like 23 volts for example.

Would you consider this a low voltage disconnect? What would happen if I didn't use one?

- Rob

[wavetar]

Interesting. I wonder if the argus system has this.

I don't have the info right in front of me, but I'm 99% sure that it does & is adjustable across a range.

[RFguy]

What would happen if I didn't use one?

A couple of things come to mind.

You could permanently damage the batteries by over-discharging them.

You could also run into some weird lock-up and operational issues on the repeater. As the voltage drops below proper design limits, equipment has been known to do some strange this. Kind of like a brown out.

[FMROB]

RF Guy,

Understood. So, some things that I am thinkng about

1) If I use an argus charger or Samlex N+1 power supply/battery charger+revert, would the end result be the same. In other words, if the system stays on battery long enough to drop voltage to a repeater "off" point, what is the difference in regard to strange items happening

2) If # 1 has the same outcome argus vs. power supply/charger, would over discharge would still be an issue?

I am still not sold on the argus system. For me it is expensive, but in this application I have 6 repeaters in one, very small location. Space is the premium here, but I really don"t want the system to fail or become unstable in any fashion. The AC circuit is generated, so hopefully AC power down time will not be too long.

[escomm]

The Argus is a waste of time and money IMHO. Get the Samlex with a LVD and call it a day.

[FMROB]

Escomm, what is an LVD?

[Bill_G]

low voltage dropout

It disconnects the batteries when they have discharged to a certain level. A common battery safety option.

The Samlex BG-40/60/200 series would insert in series between the charger and load.

[FMROB]

Bill,

I am proposing to use the samlex N+1 series power supplies with intergral power supply, battery charger, and diode transfer switch built-in.

I want to run the MTR's off of DC from the power supplies. Would I be able to insert that LDV in line with the battery. Will it allow the power supply to charge the battery through the LDV, and will the LDV be able to perform it's intended function (low voltage disconnect).
The Samlex PS has a load and battery terminals.

Thanks, Rob

[Bill_G]

You may have to experiment with the BG product to see if has to go between the charger and the load, or the charger and the batts. Samlex does not discuss the internals of the BG series. They say they use a FET, but they don't say if you can charge and discharge through it, and they don't say if they pass current in one direction only, or both.

If it goes between the charger and the load, it will still protect the batts. When AC is running, the charger passes some current to the batts, but the majority passes to the load through the LVD. When AC fails, the diode in the charger passes batt current to the load through the LVD. When the voltage at the LVD drops to a level you program, the LVD opens up ceasing discharge. Once AC is restored, the charger voltage will rise, and when it reaches the pickup voltage you program, the LVD will close again.

Typically, you discharge a sealed lead acid no more than 1.75v per cell. For a 24v system, that would be 21v assuming two 6 cell 12v batts. You should read the batt manufacturers spec on allowable charge and discharge rates. Beware the amp hour ratings and discharge curve. 1Ah almost never means one amp for one hour. It usually means something ridiculously tiny like a tenth of an amp for ten hours, and one amp for ten minutes. You may need more batteries then you think depending on how long the customer wants to keep their system alive during a power failure. A few minutes until the genset kicks in is easy to build. Several hours or days of operation will get big and heavy fast. This is why the plant systems at some public safety sites are so ginormous.

[RF_Burns]

Guys, I know this is an old thread, but I was wondering if there is any issue with the LVD (Samlex BG-40) having "reversed voltage" across it. In other words, what happens if the MTR voltage is higher than the SEC2450BRM charger? (Someone pulls the plug on the SEC2450 etc).

The BG40 uses a power FET so it would see a reverse voltage applied across it.

I've got a dud Argus and looking to replace it.

thanks

[Karl NVW]

He was not planning to use the AC supply, instead running them totally on battery.