[jpo245]

Hi guys, in an attempt to find a cheap flexible way of getting a true linearly regulated DC supply, i thought of this.

Well ok, its not the cheapest, but its reasonably cheap, and it gives u the BEST dc source that doesnt rely on some kind oflinear regulator which isnt perfect.

Since nothing beats true DC from a battery, why not get a set of 6x3.6v li-ion cells, that are permanently inside your amp.

Then just plug in a smart charger as and when they die, or better still, leave it plugged in permanently.

I can source 6x 3.6v Liions + the smart charger for less than 50 bucks.
The smart charger is also auto switching, so ur amp is worldwide use safe.

So ur paying for portable use, auto switching, as well as the BEST DC source u can get, for under 50 bucks.

btw, the cells are 750mah each and are AA sized. so in effect, a single charge lasts about 3 times as long as 2x 9v batteries.


Anyone thought of doin this?


PS: I could have sworn i clicked "DIY DISCUSSIONS" section when i posted this. could a mod help me move this thread?

 

[Daroid]

Sounds interesting and highly doable, but how will you leave a charging circuit connected to the battery while the battery supplies power to the rest of the circuit. Wouldn't that be the same as using a battery + the charger "in parallel" (dual supply) ?

 

[jpo245]

haha hmm havent really thought abt that...
i guess u can tell im not an electrical engineer lol.

i guess to be safe, i'd just consider it a charge/use separately kinda thingy...
i suddenly thought of this idea while building a custom pack for my 3g ipod (which now hits 30hours with the addition of a 5mm thick liion polymer cell! YEAH!)


is there anyway way u can charge a battery WHILE draining it?
kinda like using it as a "filter" for crappy DC supply.

but u are right, apart from connecting them in parallel, there doesn't seem to be a way to solve this dilemma.

but i'd be satisfied for a separately charge/use device anyway.
750mah of 21volts will give me at least 48hours of non stop usage, which is not too bad considering i barely use 6 hours a day.

a better simpler idea could be to just make it in a modular fashion with 2 battery packs. just pop in a freshly charged batt pack, while the other one is charging... not that much of a hassle if u ask me. considering i'd only need to do it every week or so. would be super useful for travelling too. 96 hours of charge on the go! Lithium ion has the best energy density currently available.

One could even splurge a bit more to get lithium polymer which is OHHHH SOOOO slim....

Quote:

Originally Posted by Daroid Sounds interesting and highly doable, but how will you leave a charging circuit connected to the battery while the battery supplies power to the rest of the circuit. Wouldn't that be the same as using a battery + the charger "in parallel" (dual supply) ?

 

[jpo245]

did a bit more thinking... here's a crappy workaround.
we could house 2 sets of batteries in the Amp. one powers the amp, while the other charges. and vice versa. with a manual toggle switch to swop btw the two.

if we wanna get really funky, we could build a circuit that automatically does the toggling for u, based on the voltage differential between the 2 cells.by that time, we would probably be better off with an linear-reg elpac. lol

 

[Daroid]

The second idea is better (but as you say, it would be easier just to use a regulated power supply)... then again I'm nt an electronics engineer (We can discuss this in six years when i'm done

)

 

[mono]

I thought you wanted a "cheap flexible way"?

A cheap flexible way would be to decide what voltage you want and use NiMH cells. Stuff a minimalistic linear regulator into the portable's casing, a circuit consisting of:

- Rectifier bridge (if you want ability to run from some AC adapters/sources

- regulator w/resistor-in-series-on-output set to output barely above the peak charge voltage of the cells. Of course you need 2-3 caps and a couple resistors, all of which (excepting the resistor) can be squeezed into the space of half a AAA cell if you're creative about it, and of course you have a typical ~20-120mA portable's power requirement. You just need to decide if you want it to charge while playing from batteries or not.

That's it. $5 in parts, maybe $15 including the batteries and considering the extra size of the smart charger it might still be smaller than something using the Ion cells.

I'm not so quick to agree that linear "isn't perfect" relative to any other possible solution. It IS very nearly perfect. It can be small, inexpensive, allow vastly different power sources (just grab any adapter or even plug into your car lighter socket) and is VERY clean output relative to the part count, size and expense. You might find that the charger for the Li-Ion is very dirty output too. It is not hard to have a cheap linear supply be so nearly as good as batteries that you can't hear any difference.

The only thing sub-optimal about a linear regulator is being linear, there's the heat, but that is a rather small, manageable amount of heat unless you're trying to quick-charge the batteries. Note that most any modern linear has a thermal shutoff mechanism too, so mainly you'd just need be mindfull of what it's in contact with.

 

[Helter Skelter]

Quote:

Originally Posted by jpo245 is there anyway way u can charge a battery WHILE draining it? kinda like using it as a "filter" for crappy DC supply.

Yes, but I believe it works best with lead-acid batteries (like those found in your car or in some uninterruptible power supplies made for computers). I think other types of batteries suffer from too much of a memory effect to be very economical/useful.

Someone please correct me if I'm mistaken.

 

[mono]

Memory effect isn't much of an issue with post-Nicad technologies, unless you had a precision lab experiment going where they drained to exactly same level every time.

You certainly can charge the batteries WHILE the amp is playing from the combined series of the two (charger supply + battery supply) but don't expect the batteries to be an adequate filter, the supply will probably have to be relatively clean else switched out of the circuit when amp is on for best results.

 

[Sovkiller]

This is not new, and has been used in some designs for some manufacturers fro a while now. IIRC there is one DACK that is designed that way, on batteries, and Rudistor has one phono stage that works on sealed batteries and a chager also...