[ARC5] SCR274 field test

Sun Jul 19 08:10:50 EDT 2015

I have not heard it stated yet, but are you running the engine in the vehicle while running the radios? I have been running command sets and TCS sets, GRC-9s , and WS-19s from either 12 V or series up 24 volt batteries (depending on the set's power requirements) both in the shack floated across the outputs of DC power supplies, or in vehicles (specifically the GRC-9) with the engine running to keep the battery charged, and never have had a problem with sucking down a battery as long as I was using a power source that could make up for the steady state current draw of the radio, and the battery will easily handle the starting draw of the dynos. But if you are trying to run a command set system or any dyno powered radio directly off of a battery, it of course will suck down the battery voltage pretty quickly. You will obviously get more run time from a deep cycle marine type battery than a typical vehicle starting type battery but don't expect to run them the set very long. 

I have run the GRC-9 in the field for several hours off of a fully charged deep cycle marine battery as long as I switched off the transmitter dyno while receiving. In the shack, the WS-19, GRC-9 and TCS sets are run from a deep cycle marine battery that is floated across the output of two now very old Sears 12V 10 A max current chargers run in parallel, which keep up with the steady state draw just fine for extended periods. If you are trying to run your command set system off of just a battery, switch off the transmitter dyno unless you are actually transmitting. It's your biggest load by far, and all you are doing bu leaving it running is sucking down the battery during receive periods. The net current draw of that dyno idling in receive is way less than the very brief starting surges when you need to power it up to transmit. 

The voltages you quoted for key up/key down below sound low, even for a fully charged battery supplying the set without the vehicle alternator keeping a charge on the battery. A normal fully charged 12V battery should be a bit higher (I just measured my shack 24-28V bus series up deep cycle marine batteries at 13.3/13.4 volts each at full charge. The under load voltage drop at the batteries with the bus PP7333 60A DC power supply off is very little initially, even under the load of of my T-195 which draws way more current than my command sets that also run on the same bus. Your battery may have one or more weak cells. I actually have run the command set system for several hours (during Hurricane Sandy) off the 24-28V DC bus in a battery only lineup with the transmit dyno off while receiving. 

With your vehicle running and the alternator charging the battery normally, you should see around 13.6 volts at the battery terminals regardless of whether the radio is running or not. If you are only seeing 12.6 volts under load with the battery being charged by the alternator, you may have a bad cell in the battery that is holding the voltage down, or the alternator output is low for some reason. 

I run No. 10 stranded about 6 feet (for both the positive and negative leads) directly to the battery terminals in the Tacoma to run the GRC-9powered by its DY-88 power supply, The voltage drop at the radio end of the terminals under load of that set is minimal. Battery terminal voltage with the engine running is about 13.8V under load. I have 30 amp fast blow fuses in both the negative and positive leads at the battery and have never popped one on the GRC-9 DY-88 transmitter dyno start ups. 

Good luck..keep at it you will get it going eventually! I have the parts that I could make up a command set mobile system from to run on 12 volts, using either a TCS D401 12V/440V dyno, or a PE101 BC-645 IFF set dyno that someone had apparently previously used in a mobile setup. All I need is the time to put it together. Larry, NE1S, runs a nice command set mobile setup in his vintage Ford Falcon. 

73 de Chris AJ1G Stonington, CT. 
----- Original Message -----

From: "J Mcvey via ARC5" <arc5 at mailman.qth.net> 
To: "Roy Morgan" <k1lky68 at gmail.com> 
Cc: "ARC-5 List" <ARC5 at mailman.qth.net> 
Sent: Saturday, July 18, 2015 11:30:25 PM 
Subject: Re: [ARC5] SCR274 field test 

Yes the startup current is huge, I was aware of that, but the drop is after it's already running in standby under transmit load. (the dyno runs continuously in CW mode). The startup inrush current will pop a 20A fuse, but not a 30. 

I made the voltage measurements right at the battery terminals with key down. The power cable is about 6 feet of #12 AWG. The drop is nominal and there is no noticeable warmth, yet the transmitter can pull down the battery voltage quite dramatically. 

On Saturday, July 18, 2015 10:04 PM, Roy Morgan <k1lky68 at gmail.com> wrote: 

On Jul 18, 2015, at 8:28 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote: 

> ...how can 16.5 amps draw a 130AH battery down to 11v from it's fully charged resting voltage of 12.6v ? ( it recovers on key up) 

Note well where you are measuring the voltage. There may well be IR drop in the leads from your battery to the radio - if you are measuring the voltage at the radio, I’d bet on it. And especially so if you are getting the radio supply voltage from somewhere other than the battery terminal itself. 

If the wire to the radio does not come off the battery itself (and the connectors are bright and shiny inside) you’ll have voltage drop in the vehicle harness. 

Roy] 

Roy Morgan 
k1lky68 at gmail.com 
K1LKY Since 1958 

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