March 15 2020, we are in the middle of the Corona virus crisis,.....

 

If you want to make a PA for 600W, you need a power supply of a bit more, because of the efficiency of the PA. And we want to have the power supply a bit over the critical dimensions. So why don't we look for a power supply of 1kW.

The next question is what Voltage ??? Well, if I look on the internet for 600Watt PA's for home use, most of them have higher voltages. In the 40-50-V range. For two reasons I guess, one is that the currents stay relatively low, and the second is that you have those power supplies available on the second hand market.

I looked for power supplies on the net and stumbled on a HP RDP120 unit. I could get it within a few days for 100 euro's including transport. Maybe I paid too much, on Amazon they are sometime offered  for less, but it is a heavy unit and transport is expensive.

So, I am happy with this unit. The specs are intriguing,...

52,4 Volt

57 Ampere

Max power 2.9kW

Well, it is far more than I need for my 600 Watt Amp, but I will use it anyway. The unit will deliver the current easily, at the rated 52,4Volt.

I was curious and opened the unit. That is easy. Put the box on a stable table, with the fans at the left, and the output connectors on the right. You will see at the top a few screws. Remove the screws. Than look for screws at the front. Remove them too.

Than look for one screw at the right, the back panel of the box. Unscrew this one too. If you did ok, than you can remove the upper/front/right part of the box. Do it gently, because you will find out that the 230V input is going through a filter, with a cable to the front end of the box. No problem. Put the removed box part in front of the box. Or loose the connector and put the box part away,...which I did on the photo,..

Now you can take a look in the box. It's impressive, big coils, big capacitors, big FETs, and nicely build.

Next thing is that I wanted to bring down the voltage to 48 Volt. I was looking for a pot-meter on the circuit boards but couldn't find it,.....but there is one ! In my PS it was covered with gray kit.

Look on the photo, look at about 40% from down to up and 85% from left to right. There it is,...

I managed to get the power down to about 50,4Volt. I didn't have the intention to un-solder the pot an try to get it lower to 48V, so I was satisfied with 50,4Volt.

I put the box together again. Some guys do slow down the fans, by putting resistors in the fan power leads, but I don't like that. The fans are there for a reason !

If I have the feeling that the fans are too loud, I can put the unit is a carton box with damping material in it, or whatever trick I may come up with.

 

So, I have a PS with 50,4Volt. Now what,....I want to draw some serious current from it. I have only a current measurement capability of 10A. That is not good enough. I looked for tools for 50-100Amperes and found them. They call it Hall-effect sensors, and you can buy them for a few euros, including Hall-sensor and digital display unit.

I got one of these and it works!. Very easy tool to measure big currents.

Well next problem,...how do I draw big currents without burning resistors or dummy loads. Well, a fellow amateur gave me a hint. Try a bucket of water and put salt in it.

Well, that's what I did. I made some wires from the output of the unit to two aluminum plates and hung both in a bucket. Make sure it is fixed tight and it doesn't short cut the power supply. Use standard water from the tap and put salt in the water. Little amounts at a time. After about 100 gram, with a good pour, the current was about 9-10 ampere. The voltage stayed on exactly the same 50,4V and the unit was producing the 10 amp easily,....500W he,...

So, I removed the 10A max measurement tool, and start using the Hall-sensor. Again I measured about 10 amperes through the water/salt bucket.

BE AWARE OF THE FACT THAT BY SENDING CURRENT THROUGH THE BUCKET, YOU START MAKING A POTENTIAL EXPLOSIVE MIX OF GASSES !! OXYGEN AND  HYDROGEN GASSES ARE COMING OUT OF THE WATER AND WHEN MIXED, IT CAN EXPLODE VERY VIOLENTLY !! SO VENTILATE YOUR ROOM AND DON'T DO IT TOO LONG.

THE WATER GETS ALSO VERY DIRTY, SO BE CAREFUL WITH IT.

 

OK, this is it for tonight. Later I will report what I managed to push with the bucket, I want to go at least to 20-25 ampere, and want to see that the voltage is not dropping significantly.

 

Good, March 20 2020. I added about 100 gram to my salty bucket of water. After poring it I put my power supply again into action. It was immediately around 21 ampere. After some more poring, I ended with 25 amperes. The drop of the voltage was about 150 mV.

I was satisfied. I have a power supply that does what I want. I can measure the voltage and I can measure the current. These values I need for my dashboard later on.

 

So, this is enough for now.

 

April 30; A lot of progress on the other items of the Amp, but I finished the work on the PS by building a wooden box around it, with a Voltage readout unit (Ali,...) en a Hall sensor current readout (yes,...Ali,...). Two big 30 Amperes connectors to bring the power to the PA. I painted the box grey. It looks nice.