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Radio requires 13.8 volts, I only have a 12 volt battery system

old goat 321

old goat 321

Well-Known Member
Dec 31, 2015
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I was going to operate as 1E this field day. After I hooked up my ftdx 1200 to my battery bank I realized my radio shuts off when transmitting. Here are the particulars.

I have 10 Trojan T 105 6 volt batteries. They are 225 amp hour @ 20 hrs. They are wired in series and parallel, making a 12 volt system.

Radio is a Yaesu Ftdx 1200 requiring 13.8 volts plus or minus 10%.

I ran a 100 foot length of 10 gauge from the batteries directly to the radio. I was only running qrp, 10 watts on ft8. Everytime the radio keyed it shut off and restarted. I shut down immediately. I checked the batteries. They were fully charged. I think 12.91. Could I have that much loss with the 100 foot run of 10 gauge? How can I utilize my battery bank to operate my radio at the full 100 watts during emergencys? Can i somehow ramp up the voltage? Should I arrange the batteries to a 24 volt system. And if I do that, can I use a 24 volt battery backup to run minor household items, lights, tv, etc.?
 

old goat 321 said:
I was going to operate as 1E this field day. After I hooked up my ftdx 1200 to my battery bank I realized my radio shuts off when transmitting. Here are the particulars.

I have 10 Trojan T 105 6 volt batteries. They are 225 amp hour @ 20 hrs. They are wired in series and parallel, making a 12 volt system.

Radio is a Yaesu Ftdx 1200 requiring 13.8 volts plus or minus 10%.

I ran a 100 foot length of 10 gauge from the batteries directly to the radio. I was only running qrp, 10 watts on ft8. Everytime the radio keyed it shut off and restarted. I shut down immediately. I checked the batteries. They were fully charged. I think 12.91. Could I have that much loss with the 100 foot run of 10 gauge? How can I utilize my battery bank to operate my radio at the full 100 watts during emergencys? Can i somehow ramp up the voltage? Should I arrange the batteries to a 24 volt system. And if I do that, can I use a 24 volt battery backup to run minor household items, lights, tv, etc.?
Click to expand...

You could for sure have that much loss with that long of a run.I have an ICOM 910H & it drops that badly with a regular power cord so it's suggested that it have only a 3 ft maximum length power cord & my technician tested the radio & says it needs 14.8 volts even then for full output.The ICOM 7000 is another one that is power hungry but as with the 910H it's an AWESOME transceiver.You can always purchase a power booster that will keep the voltage up but they cost over $100 but they do work.

SIX-SHOOTER
 
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Thanks six shooter. I like my 1200. Its my first ham rig. I'm going to do some searching for a booster. I did a quick search and found some elcheapos on
Amazon . They only had a max of 3 amp output. The radio needs at least 23 amp to operate at full power. So says the manual. I kind of have a hard time believing that.. Do you know of a specific booster that hams use in my situation?
 
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old goat 321 said:
Thanks six shooter. I like my 1200. Its my first ham rig. I'm going to do some searching for a booster. I did a quick search and found some elcheapos on
Amazon . They only had a max of 3 amp output.
Click to expand...

The radio needs at least 23 amp to operate at full power. So says the manual. I kind of have a hard time believing that..
Click to expand...

Believe it. Why would you doubt the manufacturer? These rigs aren't some piece of class C CB crap with false ratings. My FT-857D requires 22 amps to run as do pretty much all 100 watt class amateur radios. Running that rig at QRP levels is extremely inefficient and likely still requires at least 10-12 amps even at QRP output levels. True QRP designed rigs are MUCH more efficient at low power levels than simply dialing back the power on a 100 watt rig.


Do you know of a specific booster that hams use in my situation?
Click to expand...

Hams don't use battery boosters as a general rule. There are far better options than a band aid. Get rid of that 100 foot length of wire to begin with. It's killing you. That's 200 feet of wire taking both + and - into account. 10 gauge has a resistance of about 1 ohm per 1000 feet so that makes 0.2 ohms for all 200 feet of wire. At 10 amps that is 2.0 volts lost so now you are down to only 10.9 volts on your fully charged batteries. WAAAAY below spec.
 
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old goat 321 said:
I ran a 100 foot length of 10 gauge from the batteries directly to the radio. I was only running qrp, 10 watts on ft8. Everytime the radio keyed it shut off and restarted. I shut down immediately. I checked the batteries. They were fully charged. I think 12.91. Could I have that much loss with the 100 foot run of 10 gauge?
Click to expand...

The voltage drop will depend on the current demands of your rig.

I don't know anything about ft8...but its near constant current, isn't it?

I can only guess what your radio is using, but if the ampere draw at that output level is near 5 amps, you would easily have a voltage drop that would put you well under 13.8V - 10%.

And actually, your 12.91V is already less than that before the voltage drop. So yes, you're likely well under.

Problem is, arranging your batteries into a 24 volt system would put you well over 13.8 + 10%.....so don't do that.
 
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old goat 321 said:
And if I do that, can I use a 24 volt battery backup to run minor household items, lights, tv, etc.?
Click to expand...

Just one other note. 24VDC isn’t going to provide you anything useful as far as appliances. True, some things can run on DC...but generally not 24 volts. But even if you did run DC to appliances and etc, the switches, relays and etc would not be happy with you.

The most realistic way to get household power from your battery bank is with an inverter.
 
2NC995 said:
Just one other note. 24VDC isn’t going to provide you anything useful as far as appliances. True, some things can run on DC...but generally not 24 volts. But even if you did run DC to appliances and etc, the switches, relays and etc would not be happy with you.

The most realistic way to get household power from your battery bank is with an inverter.
Click to expand...
yes, i mis spoke. I have an inverter to run the household items.
Thanks CK and 2N. I didn't think the 10 gauge would have that much loss. I really only need around 40'. I could also go with a 40' run of 8 or 6 gauge. Keep it just for emergency power for my radio. But now for the Elephant in the room. How do I get 13.8 volts out of my 12 volt system. Please keep in mind this only happened because I wanted to run on my batteries for field day. Now, I want to ensure that I have the capability to operate when we lose line power. As always, I very much appreciate all of the knowledge and expertise of the people on this site.
 
old goat 321 said:
I didn't think the 10 gauge would have that much loss. I really only need around 40'. I could also go with a 40' run of 8 or 6 gauge.
Click to expand...

Just running the numbers again in my head...I was wrong that you’re starting below the req’d voltage. But...you’re right on top of it and that’s with open circuit voltage, topped off batteries, and no load.

It’s entirely possible that this rig won’t run with the batteries right next to it, or if it does, then maybe not for very long.

I’d personally be hesitant to invest in 40’ of larger conductors. That’s still far for a 12VDC system.

I would get the batteries within a few feet of the rig, and see if the voltage holds up like that before committing further.
 
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Moving the batteries would be near impossible for me. I could put a 12 volt marine battery next to my rig and see how that works. But just a question . Is there a way, a device that I can buy that may be able to up the voltage to required levels at the radio. Or am I challenging the laws of physics? I'm beginning to think I may not be able to run on a generator? Have to try it out.
 
old goat 321 said:
But just a question . Is there a way, a device that I can buy that may be able to up the voltage to required levels at the radio.
Click to expand...

I'm sorry, but I don't know enough about DC-DC converters to be of assistance with that question.

Maybe CK, Six-shooter or others will pop in and advise.
 
I'm thinking about and looking for a variable dc to dc converter. Something that i can manually adjust for 13.8 volts. Just really became aware of dc to dc converters. I completely forgot about stepups and step-down.
 
I found some dc stepups on fleebay. They have some that go from 9.5- 12 input to 13.8 output. Personally, i have a self imposed moratorium on buying anything Chinese. But this may solve my challenge. Now to find a product made in Japan with Chinese parts.
 

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