Using a 12v automotive battery pack to power stomp boxes

[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]

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.

[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

[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.

[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.

[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.

[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