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power for Kenwood TW-4000A

Aug 22nd, 18:14

KN6CWJ

Joined: Jul 11th, 16:40
Total Topics: 0
Total Posts: 0
Hi. I preface this by stating I am a retired software engineer not an electrical engineer. I can figure stuff out but for the moment I am in baby step mode so bear with me. I just recently received my technician license and join the local ham radio club. One of the members saw an opportunity to get rid(unload) of some of his old stuff and presented me with a Kenwood tw-4000A. He said it would be a good way to immerse myself in the world of ham radio. My thought is to set the Kenwood up as a base type unit but make it portable as well. I have no manual or any of the cables so the first challenge to to figure out the power source. My first thought was to use a booster. The Kenwood requires 13.8 volts and 7.5 amp. I purchased a WHDTS 5A Buck Boost Converter LCD Display, DC-DC 10V-50V Step Up Power Supply Module Adjustable Boost Adapter CVCC Constant Coltage Constant Current Converter with Shell. I used an old AC to DC power plug input 100 240 VAC and an Output of 12 volts 2 amps. I connected the booster output to the radio setting the volts to 15.8. The booster showed 6.6 watts .4177 amps which is not even close to the 7.5-amp requirement. So dumb questions time. What is the implication of not achieving the Kenwood volt amp levels. What do I need to learn to get the output to 13.8 volts 7.5 amps?
Aug 22nd, 20:41

WA0CBW

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Let's back up a bit. The radio requires a power supply of 13.8 volts at a current of up to 7.5 amps. On receive it will be less. The radio will draw only the amount of current it needs. On receive it may only need 1 or 2 amps but on transmit it may draw up to 7.5 amps as noted. What you need is a 12 volt power supply capable of delivering up to7.5 amps (or more) or whatever the radio needs. By the way they are typically called 12 volt even though they are voltage regulated at 12.6 to 13.8. The power supply will have a 120 volt AC cord that plugs into a regular outlet. It will have an output plus (+) and minus (-) connector.
Now 15 volts is probably nearing or over the limit of the radio so reduce the voltage to around 12 to 13.8 volts. The radio may only draw .4 amps on receive.
Hope that helps.
Bill
Aug 23rd, 12:38

KN6CWJ

Joined: Jul 11th, 16:40
Total Topics: 0
Total Posts: 0
Thanks for the explanation. As I mentioned this is all new to me. Taking what you said I connected the AC adapter (12v 2A) directly to the radio. With the multimeter it was 12 volts and .4 amps. But as you explain when I press the ptt the amp jumped up to 2.3 amp. So, one can now conclude it takes more current to send than receive. A day of enlightenment! This of course brings up the next question. How can you increase amps without increasing voltage? Does ohm law get in the way?
Aug 24th, 10:41

WA0CBW

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Simple answer is get a power supply that can deliver more current. It is generally a good idea to get one that provides a little overhead as in your case maybe 10 amps. Remember the radio will only draw as much current as it needs but the power supply has to have the capacity to deliver that amount. The power supply also has to be "regulated" meaning it keeps the voltage at a fixed value (13.8 volts) no matter how much current the radio draws. Just a reminder don't key the transmitter without connecting the proper antenna or a dummy load. Doing so can damage the transmitter.
Bill
Aug 25th, 15:16

KN6CWJ

Joined: Jul 11th, 16:40
Total Topics: 0
Total Posts: 0
Got It. Thanks

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