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Thread: Rechargeable 9v battery and low charge indicator?

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    Old Timer olddawg's Avatar
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    Rechargeable 9v battery and low charge indicator?

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    I picked up one of these to go to weeknight bar jams and bring minimal equipment. 4 effects in one small package, analog, no digital menus, the size of about 3 packs of cigarettes. It’s a VERY sturdy steel case. The problem is that it uses an external 9vdc supply so the wire and finding an outlet is always an issue. So... I was thinking about modding it with an internal rechargeable 9v battery. I would also like to add a “low battery indicator” led and don’t want to reinvent the wheel. Has anyone ever done this? Got a circuit diagram?

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    Last edited by olddawg; 06-12-2019 at 01:24 AM.

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    Old Timer olddawg's Avatar
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    Guess I’ll build this on a square of perf board and order a battery or 2 that will fit.
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    Last edited by olddawg; 06-12-2019 at 06:56 AM.

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    Lifetime Member Enzo's Avatar
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    If you didn't already, google "low battery indicator" and get much information.

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    Old Timer olddawg's Avatar
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    Yeah Enzo.. I did. I was just wondering if the pedal makers out there use a ďstandardĒ circuit. Iím surprised there arenít more rechargeable pedals out there.

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    Don't forget the joker g1's Avatar
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    That enclosure looks a lot like the Tech21 fly rigs.
    Hope it's not the same as those boards are a nightmare to get out of the steel case.

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    Old Timer J M Fahey's Avatar
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    What current does your pedal need?
    Absolute worst case, measure when you get it, being analog power consumption "should" be reasonable .
    Battery indicators use power for themselves, so one old Boss solution on some pedals was to wire a red "test" Led in series with a resistor, say 1 or 2k to limit current, and a 5.6V Zener PLUS a temporary normally open "Battery test" switch, so Led eats current *only* for a few seconds, while you push the button

    Since Red leds drop some 1.9V ; LED would NOT turn on below 7.5V , which shows a well used battery but still with enough juice to finish the night well.
    So now and then you push the test button; if Led lights, fine; if not , finish your show but first thing in the morning replace that battery.

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    Old Timer olddawg's Avatar
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    Yeah.. Iím assuming, since it has 4 analog effects, that it will draw roughly 5X what a stand alone pedal does on average. I just need the charge to last 4 hrs. So I thought a larger or a couple of rechargeable 9v batteries will work and be able to be recharged from the included power supply... and also be able to power it off of the supply of course.

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    The (chemical) discharge process of a battery is different from discharging a capacitor. A weak battery primarily shows increased series resistance while no-load voltage may still be nominal. So testing of a battery is preferably done with a load (current) similar to the application - or connected to the designated load.

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    Old Timer olddawg's Avatar
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    While sourcing batteries I found this: Pedaltrain PT-VT3 Volto 3 Power Supply w/Polish Cloth and 2 Patch Cables https://www.amazon.com/dp/B07R8PLGBW..._Rk8jDbHS93CE1 and others available. The cheaper ones are around $40. When you factor in the time and grief designing and building your own.. it seems a better option. From the reviews the problem seems to be reliability. Anybody used one?

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    Old Timer olddawg's Avatar
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    Or this one.. even a better price. I donít really need on this complex.
    https://www.amazon.com/Joyo-JP-05-Re...89870181&psc=1

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    Old Timer tedmich's Avatar
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    heres a 2S Lithium meter from the US
    https://www.ebay.com/itm/1S-2S-3S-4S...sRKyU3sQFxFcLA
    I'd wire it across battery leads with a momentary push button just for checking.

    For batteries they make USB charged Lithium "9V" batteries (really 2s=7.4V) that you could mount internally with a hole cut to allow USB charging without disassembly, and replace them when one gets weak.
    https://www.amazon.com/gp/product/B0...0E6XJT18&psc=1

    Some 9v applications really must have 9V and some draw so much current theres no real substitute for fresh alkaline 9Vs, since cheap circuits often have real bad parasitic current draws. Its difficult to design battery powered devices with very low passive discharge (why mitutoyo calipers >> the clones)

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    Last edited by tedmich; 07-14-2019 at 08:51 PM.

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    Old Timer olddawg's Avatar
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    Quote Originally Posted by tedmich View Post
    heres a 2S Lithium meter from the US
    https://www.ebay.com/itm/1S-2S-3S-4S...sRKyU3sQFxFcLA
    I'd wire it across battery leads with a momentary push button just for checking.

    For batteries they make USB charged Lithium "9V" batteries (really 2s=7.4V) that you could mount internally with a hole cut to allow USB charging without disassembly, and replace them when one gets weak.
    https://www.amazon.com/gp/product/B0...0E6XJT18&psc=1

    Some 9v applications really must have 9V and some draw so much current theres no real substitute for fresh alkaline 9Vs, since cheap circuits often have real bad parasitic current draws. Its difficult to design battery powered devices with very low passive discharge (why mitutoyo calipers >> the clones)
    Good advice.. thanks.. evidently these have charge indicator leds on them. I canít see a problem with paralleling the output terminals. May try this.. The current draw on the pedal is 105ma if it can be trusted. Probably will last a couple of hours with these at least. Better than taking a chance on a questionable $100 battery block that may or may not crap out in a month.

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