MTR & ARGUS help

[FMROB]

What a crappy day.
Motorola and Argus both royaly suck. Motorola has no clue about anyhting they sell. I actuallly had a MTR group engineer tell me on the phone today that I can program the MTR to proivde a lower RF wattage output when on DC as opposed to AC. He called me back after an hour and stated I was correct, it can't be done. So I spent all day on the phone talking to people who could not answer my question.

So, here is my issue. I have 6 MTR3000 units in one location. Primary AC power and need to provide 2 hours battery back-up for the 6 repeaters.

I want to use the ARGUS system L1884 and have some questions which I HOPE someone can answer.

1) Can you run three MTR's on 1 ARGUS unit or do you need one ARGUS unit per MTR?

2) What size batteries do I need to use to provide two hours of back up? Remember that it is a 24 Volt beast that lowers RF power as battery voltage drops off. I figure that I need to use at least 2 140 Ah batteries wired to provide 24 volts per MTR. Total of 12 batteries and 6 ARGUS units?

Please Help, someone.

Thanks, Rob

[kcbooboo]

There's definitely a "TX power when running on backup battery" power setting, which implies the station runs full power when running on its AC power supply, but when that supply senses lack of AC, the Argus unit provides 28VDC, and the station operates at the lower power setting.

If you setup the station for DC as the primary power source (rather than AC), then you get only one power setting - full power - at all times. I've got an MTR with a bad PS and I'm running it exclusively on 28VDC, told the station that it's DC-powered, and I'm getting full power out of it all the time. Works great. Astron makes a nice 28V 18A PS that has the Uniden brand name on it. At 75 watts on UHF the station is drawing about 14 amps, so a pair of 140 Ah batteries could provide power for 10 hours, but you'll need more than that for six stations. Of course they probably won't be transmitting 100% of the time.

The 28V DC input to the stations is fed in at the same point that the AC supply's 28V DC is created, which is why you need the Argus unit (or something similar) to disconnect the external DC power when AC power is available. Similarly, you can't put multiple MTRs in parallel via their DC connectors, because the voltage here will be different for each station, and they'll fight each other. So basically you'd need a separate Argus unit for each station.

Now, you could run multiple stations off one DC supply if that's all you had, but then you wouldn't get the high/low power settings. You could disconnect the built-in AC supply and attach a wire to the "AC Present" terminal and fake the power situation to the station, such that it would run at high power with the line grounded and low power when floating.

You could also make some kind of isolation system with big diodes or relays that would let you run multiple stations from one Argus unit, but you would probably exceed the power rating of the Argus unit. The 24V unit is only rated for 10 amps output, which would probably give you around 50 watts RF out of the MTR. Multiple units would draw too much current.

Bob M.

[FMROB]

Bob,

Thank you for the reply. After reading your post I searched the software and manual again, and I have to respectfully disagree. There is a check box for DC operation only (which indicates that it disables the AC loss alarm). I believe that the drop in RF power is directly related to available DC voltage. In other words the manual illudes that the station will run 100 watts (provided that it is programmed at 100 watts) and will continue to do so as long as the battery voltage sustains. As the voltage drops so does the RF power until it reaches drop dead voltage and the stations shuts off.

So I am going to plan to install one argus unit per MTR station with 2 140 ah batteries per station, i.e. 6 Argus units and 12 batteries. I have some reservations about running on straight DC, although it is technically the best way to do any repeater set-up. I don't know how to calculate the charger rate or how many batteries to use for all six stations?

Thanks, Rob

[Bill_G]

Rob - Have you looked at the battery manufacturers spec sheet on the batteries you are considering? Sometimes these guys like to conflate the ratings. It may state 140AH. In simple math that means 140A for one hour, or 1A for 140 hours. But, in their spec you may find they used the 1A at 140 hours to arrive at the rating, but at 10A you only get 1 hour. Look at their discharge curve, or read through their list of discharge rates to see if these batteries will deliver what you want.

Something else to consider is unifying the batteries and chargers into a single unit. Most radio systems spend the majority of their time in standby. If you can accurately determine the transmit time percentage on a busy day, and extrapolate that across the six stations, you will know the load, and how to size the batteries and charger adequately. It may actually be smaller than you think for a two hour backup.

[FMROB]

Bill,

Thank you. I have a print out of one of your previuous posts talking about battery ratings. Some of the manufacturers dont really have great data. I have used the Northstar batteries (carried by tessco) with good luck in the past.

I wouldn't mind running all of the repeaters on straight dc, but how do I charge 12 140 amp batteries (24 volt). What rate charger. Can I charge and run the repeaters at the same time?

Thanks, Rob

[kcbooboo]

On my UHF system with what should be the latest software, when I have an AC supply (i.e. the DC Primary Supply box in the Configuration page is NOT checked), the Personality->Channel Information has fields for Power Level: Normal and Power Level: Battery. When the DC Primary Supply box IS checked, the only setting available is Power Level: Normal, which on a typical station is the higher of the two settings. So besides disabling the AC Loss alarm, it also limits you one power setting.

The station will attempt to maintain that power level regardless of the battery voltage, until that voltage goes below about 24VDC. As the voltage varies, the power controller will adjust the RF drive to the PA and attempt to hold the output power at the programmed level. I tried this with my system by adjusting the output of the 28V power supply from 26V to 30V and the output power remained constant at 70 watts, which is where I programmed it.

Bob M.

[wavetar]

Under 'channel information', there is a field called 'power level'. There you can set the station to the desired power levels on AC and DC power. I've done this several times to lower current drain when running on batteries. Generally set the 'Normal' (AC) for full power (100 watts) and DC for half (50 watts).

This is only true for the 'high powered' stations...100 watt VHF/UHF and 75 watt 800MHz...30/40 watt stations do not have this capability.

(Just noticed I repeated what Bob had already mentioned, oh well)

[Bill_G]

Bill,

Thank you. I have a print out of one of your previuous posts talking about battery ratings. Some of the manufacturers dont really have great data. I have used the Northstar batteries (carried by tessco) with good luck in the past.

I wouldn't mind running all of the repeaters on straight dc, but how do I charge 12 140 amp batteries (24 volt). What rate charger. Can I charge and run the repeaters at the same time?

Thanks, Rob

The Argus batt revert/charger sold with MTR stations is a bit of a strange bird. There are several models. The one I've worked with only used AC to charge the battery. It could not supply the load. I used an separate DC supply to run the DC only station. During AC fail, the Argus would toggle it's internal relay to connect the batts to the DC load. Since you have an AC powered station, you won't need an external DC supply for that. But, you'll have to read through the Argus manual to see if it requires an external DC supply to charge the batts. Hopefully not. I know there are different Argus models for 12v batt systems, 24v batts, and dual voltages.

[Will]

And Argus was of absolutely no help.

[kcbooboo]

It's my understanding, from reading the manual, that the Argus unit is just a fancy battery charger (24V, 10A for the high power stations, 12V, 20A for the low power stations) that takes itself out of the circuit when AC fails, and it connects the batteries directly to the DC input of the station. It is not meant to run the station. It's not a battery-reverting power supply, just an expensive charger and switch.

I should have mentioned in my previous post that I've got a 100w UHF station with a dead AC power supply. When it was working (sort-of), I could get some power out of it, along with a bunch of error messages. Telling the station that DC was the primary power source got rid of the PS errors but there were other problems. When I powered the station from a pair of small 12V UPS batteries, the errors went away. A $100 28V 18A linear power supply solved all the problems.

Bob M.