Alternative (rechargeable) battery power

[waltk]

Thanks for all the great replies.  It kind of highlights all the different ways we power and use our pedals.  Just to clarify my personal perspective on this...

I don't perform in a band, and I don't have a pedalboard.  Most of the time, I just plug in a pedal or two, and play with myself (yeah, I know how that sounds  ).  I never have to worry about a pedal cutting out in front of an audience.  I build effect circuits because it still seems like magic when you plug them in and great sound comes out.  I don't sell them or have 'customers', so there's no issue with liability, and I use reasonable care when building anything that might cause a safety concern.

There's no shortage of AC power in my shop, and I have a couple (real) OneSpots with daisy chain extensions (not to mention all the homemade benchtop power supplies).  So I guess my fascination with portable power is just a conceptual one - I like the concept of self-contained devices.  I frequently build pedals and small amps that are self-powered, and sometimes don't even bother with a power jack.

I'm also tired of putting Duracell executives' kids through college, hence the preference for rechargeable power. 

Lithium batteries pack an amazing amount of energy in a small package.  I like using lithium tool battery packs to power small amps, and usually just add a linear regulator if the voltage needs to drop a little.  So why not downsize the concept a bit to power a single pedal (my thinking went)?  That's where this idea came from.

Suppose you wanted to power a whole pedalboard with something like this?  You could use 2 of the 18650 cells shown above (@5,000mah each) for a total 10,000 mah.  Multiply the voltage by 3 at 92% efficiency and you would have a battery pack that produces 11.1V @3AH - of course you would need something beefier than a LT1054 for that kind of booster.

Question for RG - since you're here...  Could I just use pin 1 of the LT1054 to shut down the booster when the input voltage falls below 2.5 or 3V?  The datasheet says that if pin 1 is pulled down to less than about .45V, it will turn off the chip (leaving a residual current draw of about 100ua).  Would a simple resistor divider do it?

[R.G.]

Question for RG - since you're here...  Could I just use pin 1 of the LT1054 to shut down the booster when the input voltage falls below 2.5 or 3V?  The datasheet says that if pin 1 is pulled down to less than about .45V, it will turn off the chip (leaving a residual current draw of about 100ua).  Would a simple resistor divider do it?

Yes, you can turn the chip off by pulling down pin 1 (as I read the datasheet).

No, you probably can't use a resistor divider. Maybe, but I would not trust it without knowing the circuitry inside the chip better. 0.45V sounds suspiciously like the turn-off voltage for a silicon base-emitter. One possible version is that turning off the transistor right inside pin 1 shuts it down. It may work, but also may give erratic results. One situation is that the chip is operating, supplying a load, and hits threshold. It shuts down. The battery voltage rises a little since it's not loaded. The voltage on pin 1 rises and enables the chip, which loads the battery, which sags, and turns off pin 1 and the chip, over and over and over until the battery is too tired to play any more.

Until experimentation proved otherwise, I'd assume that it needs a cleaner snap off and some hysteresis to keep it behaving well.

[waltk]

Until experimentation proved otherwise, I'd assume that it needs a cleaner snap off and some hysteresis to keep it behaving well.

Thanks RG.  I see what you mean about cycling on and off.  I guess the resistor divider was just wishful thinking.  The datasheet does say:

"Any open-collector gate can be used to
put the LT1054 into shutdown. For normal (unregulated)
operation the device will start back up when the external
gate is shut off."

and it has an example of doing this.  It also mentions a "restart signal" to get it going again.  I'll have to read this section more closely and see if I can figure it out.

The new charger boards I have on order have this shutdown feature built into them, but I would kinda like to figure out how to build it into the booster so I can use up the current batch of charger boards.

[armdnrdy]

of course you would need something beefier than a LT1054 for that kind of booster.

Check the data sheet. You can run more than one 1054 in parallel for greater current.

Depending on the current required, there are other alternatives.

Here's a relevant thread:

http://www.diystompboxes.com/smfforum/index.php?topic=98225.0

[waltk]

Check the data sheet. You can run more than one 1054 in parallel for greater current.

Depending on the current required, there are other alternatives.

Thanks Larry.  I guess whether/how you want to do this depends on how much current you need.  I've noticed that many simple boost/dirt pedals only draw single-digit milliamps.  You could power quite a few of them with one LT1054.  As soon as you add something power-hungry (like a digital reverb), you have to start looking at alternatives.  I'm going to leave the higher current and/or whole pedalboard scenario for another day/topic.

[waltk]

I followed up on the idea of pulling pin 1 low to shut off the booster for low-voltage discharge protection.  Turns out it wasn't a great idea for a couple reasons...

• even if you shut it off, there's enough current draw (~100ua) that it would drain the battery
• the issues R.G. raised, and the extra parts required to address them

...here's the good news - most of these flat Li-Po battery packs (including the one shown above), already have a tiny discharge-protect circuit attached.

[flood]

In the interest of full disclosure: I've just started my commercial project venture, some of this stuff is related to ideas I've been working with. As a fundamental principle, I do not offer batteries in my pedals. I don't have the tooling necessary to cut rectangular holes or the numbers to justify CNC routing for the same. Further, I'd like to minimize opening and closing of the pedal by the user. Most importantly, I don't think there's any reason in this day and age to use a polluting, leaky device like a regular 9V battery. 

So I've been looking at supercapacitors, Li-po cells and battery packs. Nice to see someone had the same idea as me with the LT1054, although my concern was high frequency noise - would have to try it to know for sure. I probably will soon, will chime in back here. Subscribing.

[italianguy63]

The LT1054 operates on a high frequency, and is therefore "quiet."  MC

[amptramp]

If you really want to differentiate your product from everyone else, see the picture here:



I have one of these electric toothbrushes and you will see the stand uses a non-contact magnetic charger where you sit the toothbrush on the rectangular post and plug it in and the magnetic circuit between base and toothbrush is used to transfer power to the battery charger without any electrical contact.  The base is visible a bit better here:



and here:



Placing the toothbrush on the post completes the magnetic circuit and charges the battery when the base unit is plugged in.  You would not need nearly as much power for a stompbox as you need for an electric toothbrush and you get the benefit of a charger without any electrical contacts.

[waltk]

I have one of these electric toothbrushes...

Awesome idea!  I have the same toothbrush/charger. It is just about at its end-of-life - over five years old, and the battery in the brush handle isn't taking a full charge any more.  The brush handle is sealed, and you can't just replace the battery.  I've been planning to replace the whole thing, and tear apart the old one to see what makes it tick.  I vaguely remember that the toothbrush came with a plastic tool/wrench for removing the battery from the handle - but for battery disposal purposes only (the instructions said removing the battery WOULD permanently break it).  When I get around to doing this, I'll post some gut-shots.

My guess is that the post has a little AC-powered coil.  If the receptacle in the handle has a coil, you've got a little transformer.  It wouldn't be very efficient because of the large gap between the post/primary and the handle/secondary, but I guess it doesn't need to be that efficient.  Also, all that power-level AC would probably need extra shielding/filtering for audio purposes.

It seems like I've seen a commercial product somewhere that works on the same principle - with a special charging mat that you put mobile devices on to charge.  Didn't look into it further because it was too pricey.

[R.G.]

Yeah. Those are very leaky transformers. The post in the charger is a a cosmetically enhanced post of iron that sticks through a mating donut of mag-stuff in the toothbrush, I think. This improves the efficiency a huge amount over simply having two flat surfaces, but still only up to "wretched" as compared to a normal transformer.

The primary side is set up so it does not melt down when there is no secondary or surrounding magnetic core. It just sits there making a globe of radiated power-line-frequency magnetic field radiation.

The leakiness means that the amount of power that can be transferred per time is small, but enough for a toothbrush.

This would be a Bad Thing to get near a wah pedal inductor, or a guitar pickup. Its reason for being is to have no electrical contacts exposed in a wet, splashy bathroom environment.

[italianguy63]

I have a Mini Cooper.  The key fob is rechargable in the same way.  It charges while it sits in the ignition "cradle."

MC

[amptramp]

I have one of these electric toothbrushes...

My guess is that the post has a little AC-powered coil.  If the receptacle in the handle has a coil, you've got a little transformer.  It wouldn't be very efficient because of the large gap between the post/primary and the handle/secondary, but I guess it doesn't need to be that efficient.  Also, all that power-level AC would probably need extra shielding/filtering for audio purposes.

Not if you use it to charge the battery then run the device on battery power only without the charging cradle.  You can just stick it on its post and plug in the charger after the gig.

[waltk]

Not if you use it to charge the battery then run the device on battery power only without the charging cradle.  You can just stick it on its post and plug in the charger after the gig.

Right.  Good point.

[amptramp]

I covered this in reply #63 on this page of this thread, but the entire thread is interesting:

http://www.diystompboxes.com/smfforum/index.php?topic=105617.60

Being stuck in the past with a battery design that is over forty years old makes no sense.  Are you running your copy of this forum under DOS?  DOS isn't forty years old yet, but the rectangular 9-volt battery is.