18v question

alparent · February 07, 2015, 03:33:21 PM

I'm building an effect that needs 18v I'm going to use a max1044 charge pump. Feed it 9v from my power supply and get 18v. This I know how.

My question is, I also want this to run from batteries. I don't want to use only one battery as this charge pump deal will drain it to fast. (I think ?) I can ether use 2 batteries in series to get 18v (but this is complicating me power switching and the complexity all together) The other thing I was thinking was to wire 2 batteries in parallel (keeps my wiring simple and should double me battery life?)

What is the pros and cons of each setup?

I've been on this forum long enough to know that I've probably thought of only 30% of the full question!

anotherjim · February 07, 2015, 03:49:53 PM

Well, you can't win with batteries...
You put them in parallel for more current. Since you don't want to change the wiring too much, you have pretty much talked yourself into doing just this anyway

Perfect, so long as one battery doesn't die early with a low resistance, when it might become a load on the good one, shortening it's life. A way to reduce risk of this is feed each battery + out via a schottky diode (1N5457?). Each diode prevents a good battery feeding back into a bad one. Some volt loss from the diode of course.

alparent · February 07, 2015, 04:45:36 PM

Thanks for that diode tip.
It does sound as if I already decided on doing it this way.....but if you have other ideas, I'm a teacheble guy!

Mark Hammer · February 07, 2015, 04:53:19 PM

Hi Alain, from the other side of the river. Miss our chats.

That diode tip is an excellent one. I was just about to caution against using two batteries in parallel and Jim's diode made me realize the differences between batteries didn't HAVE to be a problem.

alparent · February 07, 2015, 10:54:52 PM

So long since we spoke! Grasshopper is missing is mentor. Any idea when you will be back?

Mark Hammer · February 08, 2015, 03:43:10 PM

Could be another year or more, but I hope to come by for some meetings in a couple of months. I'm on GEDS, now, but we have cells instead of "proper" phones. I leave mine locked in a desk drawer, so best to e-mail.

Brisance · February 08, 2015, 03:47:53 PM

If you use 2 batteries anyway, why not do away with the charge pump and just wire them in series?

reidk1960 · February 08, 2015, 06:24:21 PM

I don't know if this is applicable to your situation, but it's not too hard to make an 18V drop-in replacement for a 9V. You just wire 6 2450 coin cells in series and attach a 9V clip (remember to swap polarity on the clip so that it goes the right way when you plug it in). You get 620 mAh, so it's equal to or better than two alkaline 9Vs in series.

It's cheap if you buy your 2450s from a place like this: http://www.allelectronics.com/make-a-store/item/lbat-2450/cr2450-3v-lithium-button-cell/1.html.

Assembly details are left as an exercise for the reader, but here's a hint: two stacks of three.

Reid

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18v question