Using a 12v automotive battery pack to power stomp boxes

[Steve A.]

Has anyone tried using one of these on stage in lieu of running power out to your pedal board? In particular at jams you are often just handed a cable with no AC outlet visible and no one on stage knowing where they might be. In cases like that I will just use their internal batteries but I think it would be really cool to use one of the automotive power packs instead.

To drop the 12vdc down to 9vdc could you just use a zener, or would it be better to wire up a voltage regulator?

Thanks in advance on any assistance in this matter!

Steve Ahola

[dai h.]

hi Steve,

have you seen these?

AMZ-FX Guitar Effects Blog » Blog Archive » Sanyo Pedal Juice

I wasn't sure who would have use for such a device, but apparently you might. FWIW I bought a cheap package of a couple of rechargables + charger for my digital camera("DLG" brand?), and initially they seemed to work okay but were (AFA I could tell) short lived (must be the *cheap* Chinese stuff). Later I bought Sanyo Eneloop + charger, and these seemed to perform much better (in terms of holding charge, staying useful). Even if you don't get the specific brand, it does seem important to buy "good" ones. Also, might want to beware of another similar appearing brand called "Enelong" which aren't the same AFAIK and look like an attempt to try to fool unwary buyers with a similar sounding name and appearance.

[jmaf]

Has anyone tried using one of these on stage in lieu of running power out to your pedal board? In particular at jams you are often just handed a cable with no AC outlet visible and no one on stage knowing where they might be. In cases like that I will just use their internal batteries but I think it would be really cool to use one of the automotive power packs instead.

To drop the 12vdc down to 9vdc could you just use a zener, or would it be better to wire up a voltage regulator?

Thanks in advance on any assistance in this matter!

Steve Ahola

It sounds like a great idea. For the 9V, you could solder several parallel 7509 three pin regulators into a prototype style board, using some hammond box you could then drive out several isolated 9v outputs, avoiding ground loops, etc. Any 40 Amp/hour battery should last for days, if not months, and with a 9 hour charge you're ready to go again.

[J M Fahey]

*OR* you could build a six-AA-rechargeable pack, which is permanently mounted in your pedalboard.
You have them recharged regularly, with an added "topping up" during all the night before.
You are then starting your show with a fresh, fully charged 9V supply which need no regulator and weigh nothing.
Just my 2 cents.

[Chuck H]

Six AA's... Hmmm. How long could that power a bunch of preamp devices like delay's and OD pedals? My band commonly played four sets.

If I were going to lug a car battery around, I wouldn't. I would get the smallest available rechargable marine battery. I've seen them about the size of motorcycle batteries so I would probably mount it to my board at that size. Marine batteries are built to be drained and recharged repeatedly where car batteries are more apt to fail under these conditions. They like to be recharged a little all the time they're in use. Voltage regulators come in a huge variety of applicable cases and are cheap. No point really in designing your own from parts like zeners. JMHO

[Steve Conner]

The industry term is "leisure" or "deep cycle" batteries.

There are a number of smaller sealed lead-acid batteries similar to motorcycle batteries, generically known as "SLAs" or "gel cells". We use the common 6 and 12 volt, 4 amp-hour sizes at work. You can also buy wall-wart chargers for them. They aren't really rated for deep cycles, but at less than $20 each it hardly matters. They'll last a few years as long as you don't drain them too deeply, and recharge them as soon as possible. (For that matter, all lead-acid batteries hate to be left lying around discharged, it's a sure way to kill them)

Someone mentioned isolation above. The outputs of a device like this would be isolated from the wall, but they wouldn't be isolated from each other: they would share a common ground, so ground loops would still be possible.

The 7809 regulator would be somewhat of a no-brainer for this application. Fuses would be good too, even the small SLAs can supply enough current to get wires red-hot and smoke things up. A car battery can melt a good-sized wrench.

[imaradiostar]

At work we used VRLA's- valve regulated lead acid. They charge nicely with a fixed voltage around 13.5-14 volts and a dropping resistor to limit current. Many people mistakenly call them gel-cells. They're usually available surplus for a good discount.

If you want true isolated outputs you'll need some small dc-dc converters. There are ones available that are tiny 12v to 12v supplies which would allow simple 7809 regulators at the output. The other option would be to use a 12 to 9 volt dc-dc converter.

TRY THIS

A bunch of those would give true isolated outputs- you could use a mix of both depending on the need for isolated supplies. I haven't needed isolated supplies on my pedal board- I've just lifted the ground connections where needed so I don't create loops.

Jamie

[Steve Conner]

Yeah, those are the ones, VRLAs is yet another name for them. It is technically correct, because they aren't quite sealed, they have valves to relieve any pressure inside.

DO NOT buy them surplus. They have a shelf life of only a few years, so get fresh ones. The cheap surplus ones are tempting, but every one I've ever bought has been shot. That's why they are so cheap.

The DC-DC converters are nice, but each one costs as much as a smaller SLA battery.

[Ronsonic]

Just go to somebody like batteryspace.com and buy a 9.6V or so battery pack of NiMH cells and a charger. Total cost will be low and you'll have the mA/Hs to run pedals for days. The entire battery pack and charger won't be as large as a lead acid cell of any type and it will weigh a hell of a lot less. For a long time I had repurposed a mountain bike lighting battery pack (in a water bottle format) to run my board.

[R.G.]

Laptop computer battery packs

[jmaf]

Someone mentioned isolation above. The outputs of a device like this would be isolated from the wall, but they wouldn't be isolated from each other: they would share a common ground, so ground loops would still be possible.

You're right, I stand corrected about the regulators and ground loops.

A car battery can melt a good-sized wrench.

Here where I live you'll still find old school car electricians who measure battery charge by how big the spark is. Who needs a multimeter. There are wrenches and screwdrivers just for this purpose, high tech specialized tools with carbonized and dented ends.

[Steve A.]

Thanks for all of the suggestions! The "automotive battery pack" is used for jump starting your car, some with a cigarette lighter jack and some with a bright light. I have a big one which is pretty hefty and then a smaller easy-to-carry one I picked up at Kragen/O'Reilly's when it was on sale in 2008. I didn't get around to labeling the power wall wart and haven't been able to figure out which one it is. :-(

I got some of those Eneloop rechargeables and they work great! They are rated at 2000mAh compared to regular cells with up to 2700mA, but their selling point is that they hold their charge for several months. Also because of their design they handle heavy loads better. I bet the Eneloops would last for quite awhile. An suggestions for battery holders for 8 AA's? Mouser?

BTW I'm drawing a total blank about how to wire up the zener. In series with the positive lead or from the positive to the negative? 3 volt or 9 volt?

Thanks again for all of the help!

Steve Ahola
"If it ain't broke, I think I can do something about that."

[Mark Hammer]

I have a 2W battery-powered amp that I made. Runs on 8 rechargeable C-cells. Runs for a long time, too. Not sure how they got there, but the rechargeables were purchased for peanuts at a dollar store.

[Steve A.]

Mark: I suspect that it was aliens from outer space who teleported down something actually useful and not total crap to your dollar store.

I was browsing on-line for sources of 9.6vdc NiMH battery packs and chargers. The nice ones run about $60 with shipping. I found a Tenergy 2000mAh 9.6vdc battery pack and cheap charger for about $30 (or get a 2nd battery pack for another $12). One of the reviews on Amazon mentioned that the charged packs put out around 11vdc, which is okay for RC cars but could cause problems when used with electronic circuits. Scratch that one off the list. And then it occurred to me to put a 9vdc zener diode between the two leads to keep that under 9v. With 2 packs I could have one with a zener for sensitive pedal and one with for the ones that will work with 12vdc.

Or I could get 8 AA eneloops for about $24 and use my own chargers. Either way I expect them to be good for quite a few hours (with the Eneloops lasting longer). One advantage with a battery pack (or a battery) is that you have no potential AC hum or noise from them.

Thanks for all of the suggestions!

Steve Ahola

[Teleman55]

Steve,it's about time this came up.I dabble in RC airplanes and rechargeable batteries are the hot fuel source.I have some 9.6v 3800mh NiMh battery packs that I have used for my effects.They worked fine and I have used a single battery pack for 5 hours of practice.I know that my RC plane will draw 20 amps for 8 to 10 minutes-.Places like- ALL Battery -sell pre made packs for a variety of uses.