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Author Topic: Can I attach 12v to 13.8v SS power supply?  (Read 4878 times)
W9KDX
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Posts: 770




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« on: December 29, 2011, 12:35:57 PM »

I wonder if I can attach my Ameritron ATR-20, it calls for a 12 volt DC power supply, to my 13.8 volt power supply?

I have plenty of amps in reserve and I have seen a lot of "12v" AC transformers which range from 11-20 volts so I am assuming that there is some tolerance, plus I am hoping that Ameritron understands that almost all of us have 13.8v supplies in the shack.  Most of the other ham gear that needs power has called for 13.8v, but of course the way MFJ does things........

I figured I should check before 1.8v destroys my $500 equipment.
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Sam
W9KDX
N6AJR
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« Reply #1 on: December 29, 2011, 12:46:22 PM »

a 12 volt power supply puts out a nominal 13.8 volts, which will work fine  for any thing designed for 12 v.  also there is usually an adjustment inside a power supply to tweak the output voltage, but 13.8 is really what we use for 12 v. I have everything in my shack that uses 12 v into 13.8 v power supplies. no problem.
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W9KDX
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« Reply #2 on: December 29, 2011, 12:54:46 PM »

a 12 volt power supply puts out a nominal 13.8 volts, which will work fine  for any thing designed for 12 v.  also there is usually an adjustment inside a power supply to tweak the output voltage, but 13.8 is really what we use for 12 v. I have everything in my shack that uses 12 v into 13.8 v power supplies. no problem.

Thanks for the assurance.  My Astron measures spot on at 13.8; if that is what my Ameritron expects I am good to go.

Happy New Year
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Sam
W9KDX
AC5UP
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Posts: 3834




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« Reply #3 on: December 29, 2011, 02:52:58 PM »

If anyone wants to look at the schematic, http://www.ameritron.com/pdffiles/ATR-20.pdf

I don't see anything that looks voltage critical and the 12 volt line powers the meter circuit and indicator lamps. If someone was truly anal about it they could mod the unit with an LM-350K or LM-7812 three pin regulator and power it with 15 vdc, as three volts of headroom is rule of thumb for a series regulator, but I would have no reservation about shooting 13.8 vdc straight into the power jack.

Hell, they have a 1N4xxx diode in series with the power line so the net voltage is closer to 13-ish anyway..............   Wink
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N4NYY
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« Reply #4 on: December 29, 2011, 02:57:18 PM »

I build Astrons!  Grin
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W9KDX
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Posts: 770




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« Reply #5 on: December 29, 2011, 06:52:03 PM »

I build Astrons!  Grin

I thought I saw your call sign on the quality control sticker!

Nice power supply, by the way.  I bought it because of the reputation.
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Sam
W9KDX
AC5UP
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« Reply #6 on: December 29, 2011, 07:27:28 PM »

I build Astrons!  Grin

Another good reason to stock up on batteries..............................  Tongue
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K2OWK
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« Reply #7 on: December 29, 2011, 09:08:14 PM »

Hello, Even your fully charged car battery reads 13.8 VDC. I use a 13.8 volt DC power supply for all my station equipment. I have never had a problem in more then 50 years. Just about all manufacturers of ham equipment that requires a 12 volt DC supply, call for 13.8 volts DC. I am not sure why, maybe someone out there knows?
73s
K2OWK

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W5DQ
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« Reply #8 on: December 29, 2011, 09:39:09 PM »

I wonder if I can attach my Ameritron ATR-20, it calls for a 12 volt DC power supply, to my 13.8 volt power supply?

I have plenty of amps in reserve and I have seen a lot of "12v" AC transformers which range from 11-20 volts so I am assuming that there is some tolerance, plus I am hoping that Ameritron understands that almost all of us have 13.8v supplies in the shack.  Most of the other ham gear that needs power has called for 13.8v, but of course the way MFJ does things........

I figured I should check before 1.8v destroys my $500 equipment.

13.8 volts DC is what 12V standard automotive batteries will read when fully charged. Your reference to 12V AC transformers is a bit misleading. I'm not sure if you are referring to a 12VDC wall wart which is NOT a 12V AC transformer or referring to an AC transformer used to build a 12V power supply.

Be careful and do NOT use 12V AC on an amateur radio transceiver. I highly doubt it will be a very nice thing to do to it Huh

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
KA4POL
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Posts: 1962




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« Reply #9 on: December 29, 2011, 10:53:20 PM »

Interesting to see that the manual does only talk of 12VDC where usually you find a specification with min and max limits. Huh
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W9KDX
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Posts: 770




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« Reply #10 on: December 30, 2011, 06:23:50 AM »

I wonder if I can attach my Ameritron ATR-20, it calls for a 12 volt DC power supply, to my 13.8 volt power supply?

I have plenty of amps in reserve and I have seen a lot of "12v" AC transformers which range from 11-20 volts so I am assuming that there is some tolerance, plus I am hoping that Ameritron understands that almost all of us have 13.8v supplies in the shack.  Most of the other ham gear that needs power has called for 13.8v, but of course the way MFJ does things........

I figured I should check before 1.8v destroys my $500 equipment.
I'm not sure if you are referring to a 12VDC wall wart which is NOT a 12V AC transformer or referring to an AC transformer used to build a 12V power supply....

Gene W5DQ

Sorry, poor wording.  I meant an AC adapter designed to put out 12v DC.  In any case, the Ameritron can connect to the standard ham 13.8v power supply with no problems.  Thanks all.
« Last Edit: December 30, 2011, 06:25:22 AM by KD0PLD » Logged

Sam
W9KDX
N6AJR
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Posts: 9913




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« Reply #11 on: December 30, 2011, 12:18:53 PM »

 bit off subject, but...

If all the manufactures would put a full wave rectifier at the input of the 12 volts into the radio, you could never hook up the power leads wrong.  feeding 12 v into a full wave rectifier will always put out the same + and - to the rig regardless of how it was fed.  I remember a while back having a rig or two with a full wave  bridge on the input, but can not recall what it was.  I guess the extra couple of dollars it would cost are not worth the protection they would give.
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KB1GMX
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Posts: 745




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« Reply #12 on: December 30, 2011, 02:54:52 PM »

<<If all the manufactures would put a full wave rectifier at the input of the 12 volts into the radio, you could never hook up the power leads wrong.  feeding 12 v into a full wave rectifier will always put out the same + and - to the rig regardless of how it was fed.  I remember a while back having a rig or two with a full wave  bridge on the input, but can not recall what it was.  I guess the extra couple of dollars it would cost are not worth the protection they would give.<<<


Good reason they don't.  The two diodes in series in the bridge is 1.4V voltage drop. 
the circuit cannot anywhere have a DC ground the chassis.

That drive up cost a lot.  Also things like 100W radio and amplifiers would have to develop full power at 12.4V or less, that drives up distortion.

For low power apps that works fine.   

I use a diode to the coil of a SPST relay.  If the polarity is right the relay connects the
red wire to the radio if not nothing happens.  The benefit of that is there is no voltage
drop from the diode.  Still requires a hefty relay for some amps and radios.

Allison
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KA4POL
Member

Posts: 1962




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« Reply #13 on: December 30, 2011, 11:38:07 PM »

Instead putting the diodes into the input you might consider the output of the power supplies and correct the voltage to the required 13.8V. And for the voltage drop there are Schottky diodes which have a drop of about .3V only.
The driving factor is of course cost.
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K1CJS
Member

Posts: 5981




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« Reply #14 on: January 01, 2012, 07:26:25 AM »

Sure you can!  Just don't let the electronic fog out of the radio components.   Grin

Seriously, though, yes.  That extra volt or so isn't going to harm your '12 volt' equipment.
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