SLA-powered pedal board PS...

[ACS]

Hi Guys

I've been asked to build a power supply that can take 12VDC from an SLA (sealed lead acid) battery and regulate down to 9VDC x10.

Plan at this point is simply to take the DC in, run it through a 7809 regulator and parallel up 10x outputs. Is this likely to create issues with ground loops?  Other option would of course be to take the 12VDC in and run to 10x 7809L regulators instead - any signficant advantages to doing it this way? 

Final question (for bonus points  ) - my assumption is that no filtering will be needed (but I'm banking on adding a 10uF cap to the regulator output/s as they seem to need this to aid stabilisation...) as the battery should be 'clean'. Is that correct thinking?

Cheers

[defaced]

Both methods are prone to ground loop problems.  This is because you have one battery.  In isolated setups, it'd be like having one battery per regulator.  That's a whole lotta SLA to drag around.  It will still probably work through, and if you have ground problem, partial ground lifts might be a solution. 

Yes, you want filter caps, but you probably already have them in your pedals, you just don't know it.  Batteries have internal resistances that make them not the greatest choice for decoupling supplies.  A capacitor does this job much better.  In this instance, you're trying to keep the power supply clean from noise created by the effect, not ripple from a rectifier.  Ideally, your pedal already has this cap inside of it.  This is the purpose of the large cap at the power supply inputs of your pedals.  If your pedals don't have them, 100u is a common value for this position. 

Read the regulator datasheets.  Most of them will have an example circuit including cap values.  Larger is not better here as the caps are for high frequency stabilization, so if the data sheet says use a 0.33u cap, use an 0.33u cap.  Often caps are specified for the input and the output terminals.  Again, consult the datasheet for the device you purchase.  

[PRR]

Many systems just daisy-chain grounds. For small simple pedalboards this usually works fine.

If it does not work, more regulators doesn't fix that. *Isolated* will mean transformers, which don't work by DC, so it gets complicated.

I'd think a "lead battery" would not need bypassing near as much as carbon/zinc cells. Mostly because it is so much bigger. And the end-life of a healthy lead cell isn't as prone to crappy connection as a cheap damp-cell.

Do your own homework. However I would just grab LM7809, put 10uFd in and out right on the pins, and wire-up.

From battery to box, use thin wire with heavy insulation. If something shorts, a lead-cell can deliver a LOT of current. 500 Amps or more! A 2A fuse *at* the battery might be good, but is awkward, and prone to trouble from acid fumes. I'd let the cable be sacrificial, but sized so it will smoke-and-die without fire or great drama.

Most lead batts have ambidexterous terminals. You WILL get them backward some day. The regulator will NOT survive. A diode *across* the input will not survive the full output of a lead cell. You need a series diode.

A diode "across" the regulator is needed to survive a shorted input with a heavy capacitance (many pedals) on the output. There is a picture in the datasheet.

[petey twofinger]

in our rigs we use fuses on the cables comin off the sla's and inside the amps . everything runs off sla's . 10 of em ...

sometimes we run into heterodyning issues if you have too many things with clocks off a single battery .

for me , a float charger is a must . also +1 on some sort of rev pol protection as this has happened a few times .

nice and quiet once you eliminate the heterodyning , i did that by having separate battery's for each amp and pedalboard , or having one persons amp (with built in 7809 going out to power pedals )  power someone else pedals and vice versa .

i got some similac bags from goodwill that are perfect size , enough room for the cell and  a scrip pill bottle that houses the v reg / heat sink . thats just how i did it , and i am very pleased as there are no ac outlets in the woods . i would think if you ran into any stick in the mud pedals you COULD get some sihm or lipo 9 volt pack and have a seperate deal for that . i know its inconvienient but sometimes everything just refuses to play together so ... its a fairly simple compromise .

there is also a low dropout vreg , that will run  longer before giving up the ghost , i used a few of those in certain spots . the video camera takes 5 volts so that v reg gets HOT . i made two units and we alternate after a while but i am getting off topic .

good luck , thats a cool idea .

https://www.youtube.com/watch?v=ujdteGw-cjQ