[sdiy] Combined Battery Charger / Power Supply Kit?

Fri May 7 13:47:10 CEST 2010

Hi Peter,

   thanks a lot for your elaborate answer!

> I would not use 4 rechargeable 9V blocks. I would use one battery block and generate the necessary +/- 15V via 
> a DC/DC converter circuit. This way you only have to manage the charging for one battery, and if the battery goes down all
> output voltages go down what is not garanteed with 4 batteries.
> 
> As battery the cheapest solution would be the use of battery packs for RC cars.

Well, the battery packs for rc cars mostly are utilising lithium ion polymer technology, which is pretty sensitive to total discharge and overcharging. 
I had to do some researching (my knowledge in this area is some 35 years old therefore certainly not up to date ;-)  and see that probably quite some effort is necessary to operate these packs in a safe way (safe for the pack and safe for the user).
For instance the use of additional electronics (balancer) is recommended.
I'm also looking at LiFe packs which are considered more robust but I know absolutely nothing about their pros and cons.
So I'll again have to do some reading.

The second reason is that I'm planning to get a reverb/delay pedal (stomp-box) and cannibalise it in order to put its circuits into the box.
Those pedal operate with 9V blocks. Otherwise I'd have to generate this addtional operating voltage which would cause some more overhead.

I also looked at other options like small kits providing such fx, but so far I couldn't find anything convincing.

> You can buy them for cheap in Austria
> at Schweighofer Modellbau in Corinthia. www.der-schweighofer.at
> The battery page is here: 
> http://www.der-schweighofer.at/wg/114/akkus_und_batterien

Thanks for that pointer, it appears to be a good source!

> Of course also Conrad has them, normally more expensive...

yeah, Conrad is a good place for browsing and getting inspired, but that's it IMHO.

> If you use a 12V battery pack you could use DC/DC converters that works from 9 to 36V input voltage, good quality
> DC/DC converters I can recommend are from Recom - you can buy them from www.rs-components.at .

That's indeed a neat idea!
Those converters are not cheap but I think it's pretty worthwhile to invest in such a unit.
And I don't want to re-invent the wheel. I need to concentrate on the audio circuits and the user interface and I want to get it ready asap.

> Or you can build your own DC/DC-converter using small chips from Linear Technology, Maxim or others. You can get
> a higher efficieny with non isolated designs. Isolated DC/DC converter are normally in the range of 82 to 85%, non isolated
> converters can reach up to 93 or 95%. But be careful with these 95% - they are for onw exact input voltage, so with
> batteries going down you need to have a look if these DC/DC converters can work with the battery range... the good
> efficiency converters are Point Of Load (POL) converters that work from a stabilized input voltage and convert into
> the output voltage at the "point of load" with maximum efficiency.

yeah, but in this case on the bottom line the additional stabilization also would cause less efficiency so in combination with a good battery I think I would be fine with an isolated converter.
Regarding the balancer and the total discharge protection I mentioned above such a DC/DC converter probably would be enough since
the circuits simply would stop working when the battery's voltage dropped too low.
So it only would be a matter of the DC/DC converters input voltage range, the number of cells in the battery pack and the lowest possible cell voltage (I think I read 2.6V/cell).

> For charging you need to search on Google for a solution that fits your needs.

That's quite some issue.
I can find chargers, mostly it's the same few circuits being passed around in many forums etc.
Regarding that combined charger/PSU I'm looking for I couldn't find anything.

On top of it charging that powerful packs appears to be quite some issue, individual control over voltage and current for each cell in the pack is needed. Most chargers provide lots of current which makes them bulky and requires big heat sinks.
In my case slow charging would be fine but since I'm not a developer per se quite some extra effort would be necessary to achieve decent and safe results. But maybe some intermediate steps like getting an external charger would be appropriate.
But I'm not sure about this (also because of €€€ ).

Many thoughts ... :-/

   Thanks a lot,  Michael.  :-)

PS: reading all that reviews and comments on gadgets on RC-forums (cars and planes) is big fun - it's a different world. ;-)

> Ciao
> Peter
> 
> http://come.to/synpro
> 
> ________________________________________
> Von: synth-diy-bounces at dropmix.xs4all.nl [synth-diy-bounces at dropmix.xs4all.nl] im Auftrag von Michael Zacherl. [sdiy-mz01 at blauwurf.info]
> Gesendet: Samstag, 01. Mai 2010 02:44
> An: synth-diy DIY
> Betreff: [sdiy] Combined Battery Charger / Power Supply Kit?
> 
> Hi All,
> 
>   I'm conceiving a portable synth +  fx-box which I'd like to also have battery powered.
> 
> My idea is to have 4 rechargeable 9V NiMH blocks to get +/- 15V from the charger/supply unit.
> I have no experience with such circuits and charging batteries hence I'm looking for a kit or pcb.
> 
> I want to have it this way since charging 9V batteries usually  means to have 2 to 4 chargers,
> Even my big Ansmann Energy8 provides only 2 slots for 9V batteries.
> And once it works it's much more convenient.
> 
> Basically it should be like in notebooks (this synth will be a laptop too ;-) :
> Wall-wart connected, the device is being supplied and the batteries are charging.
> Wall-wart disconnected runs the box from the 9V blocks.
> The circuit also should work as a PSU when no batteries are inserted and for backup it should
> be able to deal with Alkaline cells (w/ no charging of course) as well.
> An optional switch to prevent charging and an accurate status LED would be nice.
> 
> I'm also looking at NiMH and Li-Ion battery packs but I'm not sure if I want to go for something proprietary.
> (and adding Alkalines wouldn't be possible as well).
> 
> Since I'm located in Austria an EU based vendor would be nice.
> (but I prefer quality over shipping charges and custom fees ;-)
> 
> This is an rough idea and I'm still collecting thoughts, nothing's carved in stone.
> 
> Any hints, pointers?
> 
> Thanks a lot, Michael.
> 
> 
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