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Author Topic: 120 vac and 220 vac  (Read 2059 times)
W8JI
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« Reply #15 on: April 11, 2010, 03:46:24 AM »

>What you must never do when running 240 volt supply is to connect the the midpoint of the two primary windings (the jumper that puts them in series) to the safety ground or neutral. It should simply float.

How's it wired at the distribution transformer?

He is correct.

If the mid-point of the power transformer is grounded or connected to the neutral, it can burn up the transformer.

Also nothing that uses power should return to the chassis.

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N6AJR
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« Reply #16 on: April 11, 2010, 10:50:27 AM »

so a typical amp at 1200 watts will draw ( in a perfect world) about 10 amps on a 120 volt circuit.  (10 amps times 120 volts is 1200 watts)  now in the same perfect world you would only draw 5 amps on 240 volt  circuit. ( 5 amps times 240 volts is 1200 watts.

now if you add the typicld load for an amplifier, such as filiment power and light and meter circuits and all the other juisee using items that it takes to make it operate and then factor in all the power that is lost as heat, you find the typical amp at QRO levels dras 20 amps or more on 120 v and about 10 amps on 240v.

typical house wiring is 15 amp circuits, so you ar eover loading them at full power.  they may also have other items on the circuit, ( lights , clocks, tv's etc.)

most 240 v wiring is either 15 or 20 amp circuits so 10 amps is less load percentage wise.  most houses have a dedicated line to the kitchen for a stove, and possibly a dryer, and maybe an air conditioner, and thats about it.

I had an electrician run  a dedicate 240 line and 2 new 120 v lines to the shack from the panel and It was only a little over $300 for the whole thing.  I find that a cheap price for the peace of mind.

another some what moot point is that if your house is around 30 years old you may have aluminumiminuminum wires in the walls and if older than that yo could have  10 amp circuits or even knob and tube.  so a dedicated line or two is easy and cheap.
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W3LK
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« Reply #17 on: April 11, 2010, 01:39:39 PM »

When I was living in Baltimore, my 80A was on a 120v, 15a circuit. There was nothing else on the circuit.  Now, in my retirement home, the amp is on a 240v, 20a circuit.

There is no significant difference in the output or the voltage drop in the HV when keyed.

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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
NA0AA
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« Reply #18 on: April 11, 2010, 02:36:53 PM »

Lon:

You were fortuate to have a very stiff [high quality] 120 supply in that house - the one-tube 3-500Z amps are about the very limit of a 120 circuit.
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W8JI
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« Reply #19 on: April 11, 2010, 03:03:21 PM »

When I was living in Baltimore, my 80A was on a 120v, 15a circuit. There was nothing else on the circuit.  Now, in my retirement home, the amp is on a 240v, 20a circuit.

There is no significant difference in the output or the voltage drop in the HV when keyed.



That is very typical for amplifiers in the 1000-1300 watt input power range or less.

That's why AL80's, since they were born, have been shipped wired for 120V.

 
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AA4HA
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« Reply #20 on: April 11, 2010, 03:23:09 PM »

Here are a few other factors to consider;

The standard duplex wall outlet is either rated for 15 amps or 20 amps. If there are no other devices attached to that circuit (other duplex outlets, lights, etc...) the maximum rating would either be 1800 or 2400 watts at the outlet (E*I=W). Amplifiers are only efficient to a much lesser degree than the total AC power coming in on the line.

Bad things can happen to duplex outlets that are chronically overloaded, they get hot and can catch fire. If you decide to stay with a 120 volt connection you need to check out the wire gauge from the panel to the outlet, the current rating on the breaker and the current rating of the outlet. Even if things do not get "gonna catch fire" hot the voltage sag may be unacceptable. Put a voltmeter into the other plug on the duplex outlet and measure the line voltages when not transmitting and then when transmitting. The voltage drop can be converted into the amount of watts that is dissipated as heating losses between the panel and the outlet.

If voltage drops are excessive (>10% of line voltage) you may find your gear acting oddly or tripping out because the current goes up in proportion to the voltage sag (some equipment behaves this way, this is what happens during a brownout).

Putting in a dedicated 240 volt circuit will require two vacant adjacent slots in the breaker panel. The 240 volt breaker is two 120 volt breakers with a locking bar bonding the handles together so if one leg trips it opens up the other leg. The outlet is different and usually you do not use standard Romex wire. The typical 120 volt Romex line as a white neutral, black hot and a bare ground. For 240 volts the Romex has three wires (red, black and white).

One thing it will complicate a little is if you have an emergency generator for backup power. If you want to run the amp you will need to make sure to provide 240 VAC to this outlet. Most generators of any decent size will support this connection.

Tisha Hayes, AA4HA
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
VK1OD
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« Reply #21 on: April 11, 2010, 03:29:23 PM »

... Put a voltmeter into the other plug on the duplex outlet and measure the line voltages when not transmitting and then when transmitting. The voltage drop can be converted into the amount of watts that is dissipated as heating losses between the panel and the outlet.

That would assume that:
1. there is no voltage sag upstream of the panel; and
2. voltage drop is entirely resistive.

Neither of which is true.

Owen
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