Perfecting the USB Isolator

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hey i'm not discounting them when compared to linear supplies, if they are dynamic enough for your application; but I am discounting them when compared to lifepo4. sure if they are convenient and you cant get or afford the lifepo4, but when given a choice I dont see ANY reason to use them. your one may not be huge, but that is not the norm
 
but those packs are not designed for audio, there is quite a bit of extra metal messing with the output impedance, crappy steel leads and connectors designed for RC and not audio. even the RC guys that are serious about their sport make their own to get better performance. its really not difficult to make your own
Where did you get this info on the construction of the A123 Racing battery packs? This guy shows the construction of his packs and they don't seem to have any steel or extra metal. How do they strike you?

EP Buddy 3S1P 9.9V 2300mAh LiFe battery pack USA A123 - eBay (item 230442131487 end time Oct-22-10 17:40:21 PDT)

This A123 thing is getting me excited. I'm having a HUGE problem with noise in my AC lines. I've done a ton of research and bought some gear but the solutions don't seem to completely eliminate the problem. What I'd love to do is power an amp with a big pack of A123 batteries. My speakers are Magnepan MMGs which are power-hungry, but I live in an apartment and I keep the volume low. Do you know of an amp that could drive the MMGs and could be powered by A123 batteries?
 
what do you mean, I have 24 of them here ;) I dont need to get any info, the solder tabs they use to connect them are massive and steel or alloy of some kind. I would be a little bit wary of these packs. not because I know anything about the seller, but because I would doubt very much that A123 would allow an official battery pack that isnt their own when they have their own racing team. its possible they have bought the cells some other way in bulk and made them unofficially I guess.

so yeah the end tabs are nothing great they are chunky alloy or tin or something and designed to give a solid connection, not one made for audio, same with the cables and connectors on them; even hardcore RC guys not interested in audio will make their own packs and use better materials. i'm sure it still works fine, but given some small measure of skill you could do better yourself. for some reason I cant find the pic with the full size solder tabs, you can see it kindof in the first pic

tabs.jpg


soldering.jpg


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


hmm mate i'd love to be able to help you with a rec for an amp, but i'm mainly a headphone geek. I run active monitors and my next project is a better set of actives with class D for bass and Class A discrete solid state Pass amps. so not really efficient. you'de be best asking in the chipamp section. but if your speakers arent efficient, I dont know how much luck you'll have with batteries unless you fill the room with them. I would be looking at grounding problems given your experience that you speak of, I would bet you have a ground loop somewhere, because AC usualy isnt that noisy in and of itself, usually tere is a root cause in the way the power supply is wired up.
 
HobbyKing RC has them for reasonable prices. they will never be cheap for the legit ones if you need heaps, but since the hiface only uses around the 200ma mark, a 2 cell pack will last a good 8-10 hours at least.

dunno about cheap chargers, people say you can just use a regular type CC/CV charger, but I bought a TP-610 6 cell digital balance charger so each of the cells in my packs is charged to optimum charge each time and they will last longer. they are quite safe, but I would still hesitate using them with any old charger as there is a pretty serious energy density. and if things went wrong, I would expect they go quite wrong
 
"if things went wrong, I would expect they go quite wrong"

Yes, they have a tendancy to explode if overcharged. The protected type are a lot safer.

hehe yes i'm the king of understatement. :D i'm well aware of the issues with lithium cells, lifepo4 are much much safer than lipoly and they will take much more abuse. I wouldnt bother with the protected type, as that comes with extraneous circuitry that we dont need and treated with respect there is no problem

that being said, I have noticed a worrying trend on here and elsewhere in audio of using them with trickle chargers, this is tempting fate in a big way IMO. yes they are safe in comparison to lipo, but thats akin to saying they are quite safe compared to packing a BOMB in your entertainment system. just google 'lipo overcharge accident video' or something like that and you will see

I have done quite a bit of research for this, because I started using these cells in a portable buffalo II dac/headamp and wasnt keen on losing my ***. the most important thing is to use them with a charger that is quoted as having lifepo4 or A123 charge mode, lipo charge to a higher voltage per cell (4.2v) than the 3v3 nominal (3.65v at totally full) and if you use them with a lipo charger, good chance something bad is gonna happen.

if using and charging single cells its not quite so dangerous using a CC/CV charger, as long as the cutoff charge level is correct, but once you start making batteries (groups of cells) you face the problem of one cell becoming more deeply discharged than another in the pack before you charge them and if you just charge them all together, then 1 or more may become overcharged and you might be in for a surprise :eek:

now in answer to your email Shaman, it really depends on how many cells you want to use ie, how many in series (voltage) and how many in parallel (capacity/runtime) with the hiface, you will want to be running 2 or 4 cells I would think, depends on whether you are powering the whole thing, or just the XO supply. so pick one that will charge a 4. i'm sure the cheaper chargers you linked me will work, but I hesitate to recommend such cheap stuff. if you cannot see yourself going higher than 2 cells needing charging simultaneously, I would go with the 2 cell A123 charger there on the second page. you will need a power supply for the chargers you linked, none come with one, as most are designed to be used at the field and therefor use car battery. I use a thunderpower TP-610, but thats a 6 cell charger and way over the cost of those. the way I see it you get what you pay for.

of the ones you linked I would go with this one but you will need a power supply

you might check out ebay for used ones, or even on RC forums
 
oh one thing, if you decide to go ahead and remove the tabs as I recommended for best current transfer, use the biggest iron tip you have and turn the iron all the way up, the cells are as you would expect, good conductors and this includes heat, so that will suck the heat out of the iron and we need to do this well and quickly, because the more you heat it, the more charge capacity you lose. if you are quick the loss can be ignored, but to long and you will effect battery life.

so remove the tabs as quick as you can, then add some flux and tin the area you will solder, do it in a staggered manner, so heat and tin a touch, then stop and wait for it t cool, then again quickly and stop. same with connecting the wires; make sure they are tinned well, add a touch of flux, then quickly join.
its a good idea to insulate the other end of the wire you are connecting to protect from shorts, you do NOT want to short these babies, they kick like a mule for a battery
 
Do you know of an amp that could drive the MMGs and could be powered by A123 batteries?

Any of the tripath amps can run off batteries. Depending which chip and output power you require. Whether you will like the tripath sound I cant tell you. They are fast and detailed, but being class D, the HF might not be your cup of tea.
2*100W 4? TK2050 Class-D Audio Amplifier Board-improved - eBay Power Amplifiers, Amplifiers, Home Audio, Electronics. (end time 10-Oct-10 01:29:41 AEDST)

Here is a board for sale on ebay.
There are many forums about these tripath chip amps.
 
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