Well, I ignored that in my post because I am open to the idea of modding, have a few parts lying around. It would be no big deal to me to tack on some capacitors across the battery rails. I looked up the datasheet for the regulator, at least the IC model # used on past revisions of BT-C3100, and it does allow for an output smoothing capacitor.
Heh, I hate vagueness in posts so I should elaborate. EUP3484 regulators (or just stamped āP3484ā) are on each charging bank. A datasheet for that shows a typical app circuit with 22uF on the output, but goes on to elaborate with equations and alternates like tantalum or lower ESR electrolytic, so you could choose the capacitance and ESR to arrive at the ripple reduction you want. Itāll never be a purely linear charge, but at some point you could consider it shades of gray how little ripple there is.
However, I must confess that I have not reviewed the details of HKJās analysis, so I donāt know how bad the pulse is.
You might find that eventually it needs some capacitor attention anyway, as the generic little 220uF caps they have on each bank could be considered a āwear itemā with a finite lifespan shorter than the otherwise viable life of the charger. I mean something is going to fail first (after the !@#$ fan) , and if itās something you can fix for a couple bucks costā¦
I donāt agree about any 25mm x 10mm (or thinner) fan being adequate for (any) use, unless weāre talking about the highest precision fan that mankind could build at extreme cost. Iāve bought top shelf fans in the past and no brand or model that tiny has good lifespan. Granted I tend to think in terms of extreme duty, for someone running a charger only a handful of hours a week, it may not matter, but I am very much a fan (pun intended) of āfix it once then forget itā, to do a mod that never fails again, or at least not for a couple decades.
This mod you did is similar to some mod thoughts I had, except I would either use a lower diameter fan and cut an open hole in the bottom, OR make a reinforcement plate out of aluminum so a larger fan didnāt structurally weaken it too much, so there was a larger opening instead of little holes that catch dust and restrict airflow, and then I could just fold down the sides of the aluminum into an inverted āUā shape to form two leg-rails to elevate it.
However I have several fans of different sizes lying about, so almost too many options if Iām willing to fabricate a plate too. Iām leaning towards two 50mm x 10mm or one 50mm x 20mm fan on the bottom. The 10mm thick have a shorter lifespan, is the main reason Iād go with two 10mm thick instead, as one moves enough air if thereās an unobstructed opening to allow it, well that and I have about 4X as many new 10mm thick.
I get the concept but the electronic specific is out of my league. Are you willing to be a more specific about a cap? I can solder and have replaced bad caps in motherboards and TVās but I just put in what is recommended.
^ Depends on if youāre trying to only fix a failure and promote longer life, in which case you could just do similar, pick the same voltage rating, capacitance value in a major brand with āvery low ESRā and 105C temperature rating, like a Panasonic FM (or whichever newer series they came out with that lowers ESR even more), or for higher cost, one of several brands of polymer capacitor. NCC, Rubycon, et al make suitable models of capacitor. I would advise against use of a generic (or any, really) Chinese brand, though some people have had luck with those too, but I donāt see the point for a few cents cost difference, and the higher quality major brands tend to have lower true ESR.
Larger diameter, height, and voltage rating (up to a point) will give beneficial ESR reduction but as it is the cap is already shoehorned in there at an angle instead of proper mounting on a PCB. For best results a ruler may be needed to measure clearance.
As far as changing for performance, the conservative answer would be choose same diameter, taller since lying sideways that could fit, and go with a higher voltage rating to drop the ESR and no more than double the capacitance. At some point the capacitive load could be too high but I donāt know what that limit might be. If youāre measuring with a scope you can experimentally arrive at an ideal capacitance value to get closer to your ripple target.
You may try the 40mm fan like mine first, as in my experience itās just powerful enough to keep the batteries just lukewarm, needed for nimh termination just in caseā¦and as to durability, our charging needs is just way shorter than the time a ānormalā psu fan is subjected in its lifetime. And you can always pull out the 40mm and go for a bigger fan as you see fit.
And btw, those rectangular protrusions in the base surrounded by the holes I drilled have openings in its entire length as original design for air to pass through.
l have yet to see someone declare with certainty and with concrete evidence that a cell NOT charged through pwm outlast or outperform a cell charged through other means.
I also have 2 vp2 chargers, iCharger, Pila, MC3000, C9000 and some really cheap ones and l for one never noticed any advantage of one over the other except the user-friendliness of the Opus (and the C9000).
Sometimes I wonder if pulse charging is just an evolution in marketing, a throwback to the NiCd era where people used pulses to blow away dendrites that shorted out cells, that if a charger did that for you automatically, it could create the perception that it was a more versatile charger in being able to charge near dead cells that others refused to.
Iām not suggesting that it should be avoided, only that like any other circuit, the level of peaks to the pulses are higher current that requires the whole circuit to be more robust to handle it, though I question if itās a good idea to pulse past 4.2V/etc on lithium chemistries since their lifespan so dramatically drops the closer you get TO 4.2V, let alone going over it.
Itās another thing that makes me wonder how far a mad modder would goā¦ they do make a thing called zeners that could shunt voltage, but then how far do you want to go to fix a design? It does make sense in that it saves a lot of time to get something with a custom display and features built in, then you just correct its shortcomings. Heck, half the time when I do a project, it takes me as much time to figure out and fab a custom enclosure that doesnāt look ghetto. :laughing:
The internal switcher uses PWM to regulate output current, all switchers do that and in most cases there is a filter on the output to remove the PWM and give a smoother current and voltage.
The internal switcher usual works at 300000Hz to 60000kHz, not the <100Hz that Opus and other analyzers uses for PWM.
@ HKJ: Thanks for explaining altough I donāt really understand it. @Gaus: well you mention safety, so I would say that putting a high current in a bad worn out cell might be dangerous.
My opus arrived and Iāve used to charge and test a few cells. I like it so far but Iām not sure bout the full test, I seem to be getting quite low mAh. But I have to play with it a little more. Some cells got warm on 700mA charge rate but not hot. They never got this warm on my VP2 or VC2 on a 1A charge rate. I wonāt be using the opus to charge smaller cells unless I really have to.
Your Opus will not use your chosen charging rate if the cell cannot handle it. It will just automatically go down to what is the level it deems safe for the cell, which is a good feature when charging salvaged cells that has remained in low state-of-charge for quite a while. You will see the display not āfollowā your chosen rate, but will eventually go higher, or may not at all if the cell is really in bad shape.
The four individual displays of the Opus is one major advantage over the Littokala and Dragon, for you see whatās happening to ALL four cells at the SAME time, regardless of mode chosen in each bay.
I donāt worry about those pwm or pure CC/CV or whatever thing, for as I posted before, I have owned or am using those ALL those type of chargers and until now have not noticed any advantage of one over the other to my cells in real usage, just perhaps a smoother graph presentation of one over the other.
With salvaged cells, just be around ALL the time when charging them as some of them can and will suddenly get abnormally hot anytime. Most of these cells have had a tough life, or have stayed in a very dangerous low voltage already. It happened one time to me. I salvaged Sanyo cells that was given by a friend from an unrepairable laptop. It was 4.2v after charged, but suddenly got hot when put into the charger in a discharge mode.
In an open cell (SLA battery) environment this can matter, but in a sealed cell, humidity can only matter with hygroscopic flux residue present, or if the cell itself was defective so the seal, wasnāt one.
The world will need a mechanism for the change relative to humidity. This is science, not a social game of putting the burden on someone else who screwed up their findings.
Donāt be deluded by one study where the participants were desperate to show they didnāt waste the money spent on it. This happens all the time.
