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I wanted a way to power my mobile radio inside, or on a bench. Instead of spending a bunch of money on a bench power supply capable of the amperage I need (50 watt / 13.8V = 3.62 amperes). I have friends that have done similar things for R/C equipment, battery chargers, etc. so I decided to do some googling.
I found a couple links that were very helpful when planning my power supply conversion.
First was a link a little more specific to operating a HAM on a PSU conversion. The problem with doing this directly is the power draw when transmitting. This person found that with a direct conversion, you end up right around 12V, and when transmitting the voltage would drop to 11 volts. I was concerned with this for a couple of reasons. Lower voltage = higher current draw required while transmitting, as well as the spec of the radio. My TM-V71A says it's operating voltage is 13.8V +- 15% which means the low-end should be 11.7V.
That link also mentions that there is a place on most PSU circuits that you can adjust resistance to change the output voltage. I was lucky enough to use a power supply which contained a potentiometer in that location (basically a variable resister) so I was able to change my output voltage with an easy turn of a screwdriver.
With the potentiometer turned all the way "up" my output voltage is 13.1 volts which means with 50 watts for transmit I will draw about 3.82 amperes. I used a 500 watt power supply, which claims 18 amperes on the 12V side from the sticker on the side so I have plenty of "fudge room".
Another good link for instructions is here. It contains valuable information like the fact that you need a load on the +5V side to have the PSU work, you can switch using a green wire, and what color wires are what voltages.
Here's my completed project:
Here it is with 10 awg wire to 30 amp anderson powerpoles:
Here it is powering my Kenwood TM-V71A so I can use my new programming cable on my desk!
(Sorry for the noisy cell phone pictures.)
I found a couple links that were very helpful when planning my power supply conversion.
First was a link a little more specific to operating a HAM on a PSU conversion. The problem with doing this directly is the power draw when transmitting. This person found that with a direct conversion, you end up right around 12V, and when transmitting the voltage would drop to 11 volts. I was concerned with this for a couple of reasons. Lower voltage = higher current draw required while transmitting, as well as the spec of the radio. My TM-V71A says it's operating voltage is 13.8V +- 15% which means the low-end should be 11.7V.
That link also mentions that there is a place on most PSU circuits that you can adjust resistance to change the output voltage. I was lucky enough to use a power supply which contained a potentiometer in that location (basically a variable resister) so I was able to change my output voltage with an easy turn of a screwdriver.
With the potentiometer turned all the way "up" my output voltage is 13.1 volts which means with 50 watts for transmit I will draw about 3.82 amperes. I used a 500 watt power supply, which claims 18 amperes on the 12V side from the sticker on the side so I have plenty of "fudge room".
Another good link for instructions is here. It contains valuable information like the fact that you need a load on the +5V side to have the PSU work, you can switch using a green wire, and what color wires are what voltages.
Here's my completed project:
Here it is with 10 awg wire to 30 amp anderson powerpoles:
Here it is powering my Kenwood TM-V71A so I can use my new programming cable on my desk!
(Sorry for the noisy cell phone pictures.)
My luck....
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