Posted 18th March 2010 at 11:30 AM bywintermute (Wintermutes Rantings)
Updated 2nd January 2012 at 10:24 AM bywintermute(added formula as well as a few other minor edits)
10 Feb 2011. AndrewT pointed out something really dumb I had done (in a most polite way) in the original circuit. The caps in the filter section are in series and effectively halved in value. The circuit will behave much better simply by deleting half the caps. I've uploaded the latest version of the file. Sorry to the 125 people who have already downloaded, and I hope I didn't cause too much head scratching as to why I had done that, I'm not even sure myself, and I'm surprised I never realised. I'm going to revamp this blog entry as there are some things I have realised since I first posted, but that will be over the next couple of weeks. Hopefully I will finally build it soon.
I have been spending an inordinate amount of time using LTSpice lately. The more I use it the more I like it! For someone like me who is somewhat challenged mathematically, and who's electronics theory knowledge level is well below where it should be (to be doing this sort of design anyway),...
Apply 16Vdc through 100k resistor and measure how the resistor voltage varies with time. The resistor voltage is a rough indication of the cap leakage+charging current.
Once charging is substantially over the remaioining current is predominantly leakage +-a little bit of chage/discharge current depending on the stability of the supply.
The apparent leakage is very much affected by the DC supply voltage. A good regulated DC supply that is held at constant temperature will help a lot.
You may find that 6hours at 100k gets to within 105% of the ultimate leakage current. But tell us what you find.
You can reform a bank of caps using one resistor to feed each capacitor.
Measure across each resistor to see how similar or different the caps are.
Use RG58 on all your shunts for sense wiring. Use as thick main ''force'' wiring as you like. Remember that the sense nodes are voltage nodes, don't worry about gauge. Their mission is to skip the voltage drop on the current carrying force wires and ''see'' the remote nodes directly. I believe that you will see less stuff on your scope in difficult termination situations if you shield your sense wiring. If you need extra thin and flexible enough, see about Belden (RG style) 179DT also, which I like for signal too BTW.
I have been tinkering with speaker ever sense I was a kid back in the seventies and have always been trapped in the box. My newest efforts are an improvement but remain in the box Durring the last 6 years I have visitd this site for ideas and must say thanks for all I have picked up. My system is now compiled of all dyi speakers and is a vast improvement over the commercial systems I have purchased over the years “due to lack of funds to buy the good stuff of course.” I have over the last few years tried a few open baffle approaches with little success. The back loaded horn with the fostex sounds great but it’s a little to honky for my taste. The small box using silver flutes and vifa tweets crossed at 2.5k and dampened using automotive damping pad made of polyester and kanaf “I have access to many exotic damping materials” sound good but appears to fade in and out (I need help with this one) I used decent crossover components Bennic caps and jantzen 18 ga air core ind. all connections...
Do you know what is the Vf of your LEDs? R1 should be roughly equal to (3 x Vf) / desired_current. So for testing, if your LEDs have Vf = 1.8V or even Vf = 2.1V, and we're aiming for something around 20mA, then you can use R1 = 300R.
For 1.8V LED
I = 3 * 1.8 / 300 = 18 mA
For 2.1V LED
I = 3 * 2.1 / 300 = 21 mA
The 300R resistor can be 1/2W or whatever you have around.
You will know it works well if you measure the voltage across R1 and divide it by 300 and if the result is close to about 20. Of course you should see the LEDs on.
Try to implement just the CCS portion with a 300R for R1.