DC/DC Converter - fuse and capacitor QUESTIONS?

[marty]

Bought this DC/DC converter Ericsson Power Modules # PKU4511PI Really small circuit board mount.
Output Power: 50 W
Input Voltage: 36 V to 75 V
Number of Outputs: 1
Output Voltage (Channel 1): 5 V
Output Current (Channel 1): 10 A
Isolation Voltage: 1.5 KV
Package / Case Size: Sixteenth Brick
Output Type: Isolated

This is third one I bought. Long story.

Please look at Technical Specification:
http://www.ericsson.com/campaign/powermodules/archive/picov/28701-EN_LZT146308_EN_H_PDFV1R2.pdf

I copy:
It is recommended that a slow blow fuse with a rating twice the maximum input current per selected product be used at the input of each DC/DC converter. If an input filter is used in the circuit the fuse should be placed in front of the input filter.

See page 20 I don't understand all this?
My battery is 48V What is maximum input current?
____________________________________________________________________________________________________
Have not hooked this DC/DC converter up to test yet but the last 2 made some bad static on a radio about 10 feet away.
Capacitors? Take a look at pages 29 and 30 for information on:
Electromagnetic compatibility (EMC)
Electromagnetic interference (or EMI, also called radio frequency interference or RFI)

What Capacitors should I buy? And where to put them?

Thanks all for your help with Electric Bicycle Project # 2

 

[Anonymous]

.

 

[wrobinson0413]

.

 

[marty]

OK wrobinson0413,
Measure current draw on output side of DC/DC converter. See 3.8 Amps with 4 headlights all on. Go here to see lights.
http://endless-sphere.com/forums/viewtopic.php?f=3&t=3491
Add a little for rear LED that I don't have yet.

5V x 4A = 20W output
(2 - 0.9) x 20 = 22W
Lowest voltage of my battery before it cuts off is 35V according to figures from GBP Battery Co. Go here to see battery.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=1170

22W / 35V = 629mA
1.5-Amp 250V 1¼x¼" Slow-Blow Fuse DONE Thanks for the math wrobinson0413

Now the capacitor? With this DC/DC converter all hooked up with a tangle of alligator clips, my radio about 10 feet away has bad static noise.

nutsandvolts say.... electrolytic 1uF cap on input
wrobinson0413 say.... Just choose a good high frequency cap rated for your battery pack maximum voltage and size at 47uF to 220uF. These things switch around 300kHz so you don't need ultra high capacitance.

Think we need a third opinion here.

 

[Anonymous]

.

 

[wrobinson0413]

.

 

[smithinparis]

What's below might be really obvious to many, but I thought I'd throw it in for those that might be new to problems like this...

DC/DC converters are notorious for noise issues - but that's not to say they can't be controlled. What's going on, and I'm sure it's not a surprise to anyone, is that there are radiated emissions coming from the DC/DC converter and the test circuit, basically acting as a little radio transmitter. These radiated emissions are being picked up by the radio.
The DC/DC converter uses a switching frequency of 300 kHz, which is actually a square wave. So you not only have emissions at 300 kHz, but at 600 kHz, 900 kHz, 1.2 MHz and so on, at all the harmonics of 300 kHz.
The radio on the other hand can actually pick up noise remarkably well at the broadcast frequency obviously (eg 89.1 MHz for FM, or 680 kHz for AM), but also at some arbitrary local oscillator frequency (LO) and intermediate frequency (IF).
In any interference issue like this (EMI), you technically have 3 ways to approach the problem. 1) Shield or otherwise fix the source, 2) modify the coupling path (air), or 3) shield the reciever. Really the only option in this case is to fix the DC/DC converter.

Reducing EMI from a DC/DC converter
First of all, you mentioned that you have a tangle of aligator clips and probably nice long leads coming from the DC/DC converter. When you actually go to build the final setup, use a PCB and make the circuit as 'tight' as possible. This will minimize the length of the antennas that may be emitting the noise. The allegator clips and leads offer a fantastic way for the noise to couple into the air - typically, the longer they are the more efficiently they will couple. Reducing the length of the leads will make it harder for the noise to get out.
Second, in laying out the board, pay careful attention to the actual path the current will be taking, and minimize the loop areas. The idea here is that if you have any two loops, they will act like a transformer and pass noise back and forth quite well.
Third, filter the lines coming in and out of the DC/DC converter circuit. This can be a simple high frequency cap (keep lead lengths as short as possible!) or may include an inductor to ground to form a better low pass filter. This will cut back on the noise being allowed to escape your circuit.
Finally (though there are lots of other options, such as using multilayer boards $$$), if at the end of the day you are still having issues (which you may very well because you are still going to have nice antennas running from the battery to the PCB, and from the PCB to the headlights), try wrapping your long cables around a ferrite donut (torroid) which you can either buy or scavenge from an old computer power supply. Do this as close to the PCB as possible. This will increase the inductance on the line, and make it harder for the high frequency garbage to get onto the line, and otherwise into the air.

Hope this helps!

 

[Anonymous]

.

 

[marty]

Watch this...... µ Want to see that again µ Hold down Alt + 0181 µ [u with tail µ]

You guys are getting pretty deep in radio static. Thanks for the help. See 53,102 capacitors at Newark.

Lets start with what type of capacitor or capacitors would be best for what I am trying to do?

Aluminum Electrolytic
Ceramic Disc & Plate
Ceramic Multi-Layer
Double Layer
Film
Silver Mica
Tantalum&Niobium Oxide

 

[Anonymous]

.

 

[marty]

All I did was test this DC/DC converter with big tangle of test lead alligator clips. Thinking that finished product will be mounted to circuit board. Possibly something like this?

Might go back to your original suggestion of 1 capacitor on input side?

I copy from page 30

The converters are designed for stable operation
without external capacitors connected to the output. It is
recommended to use an external capacitor of minimum 1 µF
on the input.

 

[Anonymous]

.

 

[marty]

DC/DC converter connections will be soldered and mounted in a new water proof aluminum box with controller.

Yes correct - not using any input cap at all now.

For testing I am using 14G THHN wire from battery with wire nuts and 20A auto blade fuse with inline holder. All I had in my box of old parts. THHN = Thermoplastic High Heat-resistant Nylon-coated

When all done, wires from battery to controller will be 10G MTW Machine Tool Wire. Nice stuff with lots of fine strands. Looks and feels like THHN. 100A circuit breaker will be on battery box. Did not buy it yet.
Here is picture.

SERIES 187 MARINE RATED Buy at local boat shop.

 

[Anonymous]

.

 

[fechter]

I wouldn't worry about the input cap at all. It won't be connected to the line, so all the EMI will need to radiate. Unless you're trying to run a ham radio on it, I doubt you would ever cause any harmful interference. If it was a product that was going to be sold to the general public, then it may require FCC approval and in that case the input cap would be a good idea. If the input wires are really long, it might be a good idea too.

A fuse is a must. It should never blow, even if the output gets shorted. You should install the fuse close to the battery to protect as much of the wiring as possible.

 

[Anonymous]

.

 

[wrobinson0413]

.