• New Sponsor: ShipNerd, Ship Your Gear with Us... for less! Click Here.

DIY Rechargeable 9V DC Battery Pack for Pedal Board

M Brown

Member
Messages
14
I created an account so I could ask you electrically inclined types some questions about battery power for my pedalboard.

First, here's a link to the original thread that I'm drawing info from...

https://www.thegearpage.net/board/index.php?threads/building-a-battery-powered-pedalboard.1131722/

and Mike Bland's blog post about pretty much the same thing...

https://mike-bland.com/2013/01/11/rechargeable-9v-power-supply.html


So I got two of the 8 AA cell packs..

http://www.ebay.ca/itm/272374318721

and instead of switching and re-soldering the wires to get the correct polarity, I bought a Trutone CYR reverse polarity adapter (tested with multimeter and it does convert every plug downstream back to center negative). I already have two 8-plug daisy chain cables designed for the One Spot.

The idea is that 8 x 1.2V NiMH AA cells = 9.6V DC power

I'm not an electrical techie, but I metered the battery pack with 8 brand new, freshly charged NiMHs and the reading was 11.15V with no load. Compare this to a brand new 9V cell which reads 9.87V and a regulated AC/DC wall wart which reads 9.85V.

My question to you guys is this - do you think 8 cells would be safe to not fry any pedal components via over-voltage, or should I replace one of the cells with a dummy cell and go with a 7-cell pack that should be 8.4V DC theoretically?

Here's my proposed signal chain in order for my new board that I'm putting together...

TC Polytune Mini Noir 9V DC 45 mA

EHX Freeze 9V DC 140 mA

EHX POG2 9V DC 160 mA

AMT Japanese Girl 9-12V DC 7 mA

EHX Crayon 9V DC 10 mA

Suhr Jack Rabbit 5-18V DC (9V nominal) 20 mA

AMT Little Loudmouth 9-12V DC 6 mA

EHX Deluxe Memory Boy 9V DC 100 mA

TC Hall of Fame Reverb 9V DC 100 mA

Total current draw: 588 mA

using 1900 mAh batteries: 3.23 hours

Let me know what you guys think - thanks.
 
Last edited:

amz-fx

Silver Supporting Member
Messages
1,763
The idea is that 8 x 1.2V NiMH AA cells = 9.6V DC power

I'm not an electrical techie, but I metered the battery pack with 8 brand new, freshly charged NiMHs and the reading was 11.15V with no load. Compare this to a brand new 9V cell which reads 9.87V and a regulated AC/DC wall wart which reads 9.85V.
You have to test them with a load on the output. This will give you a more accurate reading.

8 x 1.2V NiMH AA cells giving 9.6V DC will not hurt any pedal that I know. Even pedals with a crappy charge pump chip will take 10v. :)

regards, Jack
 

M Brown

Member
Messages
14
Thanks for the response, Jack - load testing is what I had in mind, but not sure how to do it. Where would you place the meter leads - do you have to open up the pedal(s) and put the leads on different components on the PCB? Any risk of damaging components by touching them with meter leads?

Any downside to running the 7-cell 8.4V setup?
 

amz-fx

Silver Supporting Member
Messages
1,763
It usually doesn't take much of a load to get a more accurate reading - a 12v open circuit reading might be 9.5v when you connect an LED to it, for example. As a first step, I usually just connect an LED (with series resistor) to a circuit to see what happens to the voltage under a load. A red LED with a 390 ohm resistor in series will give you a load of about 20 ma. This should be adequate.

I would go with the 8 cells.

regards, Jack
 

underdog726

Member
Messages
1,645
i made one with the same battery pack you bought, (in fact i have about six extra battery packs if i known i would of sent u one for shipping cost only) It actually worked quite well on my nano board. I was gonna try to make a charger that would charge the battery pack without removing the batteries but never got around to that.
 

M Brown

Member
Messages
14
A red LED with a 390 ohm resistor in series will give you a load of about 20 ma. This should be adequate. I would go with the 8 cells.
This might sound like a dumb question, but does this involve soldering these components to a PCB to make the circuit? Would you have to install a barrel outlet to accept the plug from the pack? Where would the meter leads go? Any easier way to do it without soldering?

i made one with the same battery pack you bought
Have you used it a lot? Any ill effects? What pedals were you running?


Another question for Jack - I've read that when you plug in a higher voltage supply than a pedal is rated for, it either dies right away or it's fine. Conversely, I've read that pedals may run, but the useful life of components is shortened. Which is true, or are both statements kind of true? I powered a Big Muff Pi TW for a few seconds with the 8-cell pack and switched it on and off, but didn't run a guitar signal through it - everything lit up, though. Being cautious at this point.

I ask because I'm obviously nervous about making any of my expensive pedals guinea pigs in this experiment, hence all the questions.

Thanks for the helpful responses!
 

underdog726

Member
Messages
1,645
No ill effects. I dont play out much anymore so i eventually just used a fuel tank jr underneath. I used the home made battery pack for about a year tho. I had about 5 pedals usually on my nano. I switch around a lot but i know i had a mini tuner a ts type pedal a mxr delay and rotated some others. Always worked fine thats why i bought like 10 battery packs and was gonna make some for friends.
 

amz-fx

Silver Supporting Member
Messages
1,763
This might sound like a dumb question, but does this involve soldering these components to a PCB to make the circuit? Would you have to install a barrel outlet to accept the plug from the pack? Where would the meter leads go? Any easier way to do it without soldering?

I've read that when you plug in a higher voltage supply than a pedal is rated for, it either dies right away or it's fine. Conversely, I've read that pedals may run, but the useful life of components is shortened. Which is true, or are both statements kind of true? I powered a Big Muff Pi TW for a few seconds with the 8-cell pack and switched it on and off, but didn't run a guitar signal through it - everything lit up, though. Being cautious at this point.
If you do not want to solder, here is a way to test it. You measured your battery pack at 11.15v under no load so the voltage is going to drop when you apply a load. The Suhr pedal can take 18v so it is safe to power with the batteries. Open the pedal and measure the voltage at the power jack with the pedal on (LED lit). It doesn't matter if you reverse the leads of the meter; it will only display a negative voltage and won't affect the pedal. If your reading is less than 10v, then the battery pack will be safe to use with most any fx pedal. If the voltage is still more than 10v, add the two AMT pedals and the Big Muff to the daisy chain power and read the voltage again. You are just trying to see that the voltage will sag to a nominal level under load (10v or less).

Both statements about component life are sort of true. Higher voltages might quickly kill a pedal that has 10v capacitors, but those are rare. If you see 6v capacitors in a pedal, they are probably situated after a voltage regulator so it doesn't matter if the input voltage is a little high, though heat dissipation of the regulator can come into play as the input voltage increases.

Powering a pedal that has 16v capacitors with an 18v adapter most probably will be okay, but the life will be shortened. Capacitors with a 16v rating are common in certain vintage pedals. I wouldn't power them with 18v but 12v is okay.

A very few pedals have a charge pump chip that can only take 10v but most builders are wise to this and now use charge pumps that can stand 12v.

regards, Jack
 

M Brown

Member
Messages
14
I was thinking the same thing about using the Suhr and AMT pedals as Guinea pigs because they're rated a bit higher. Still waiting for the AMTs to come in the mail but I have the Suhr so I can test that. Instead of opening it up, couldn't I just meter one of the daisy chain plugs that's downstream of the pedal(s)?
 

M Brown

Member
Messages
14
The battery pack powers the Jack Rabbit and it switches on - haven't tried to run a signal through it. Here's the inside of the Jack Rabbit (I've circled the barrel jack area). Where do I put the meter leads? I tried metering the daisy chain plugs downstream of the connected pedal - same voltage as with no load, so I'm obviously not getting it.

 
Last edited:

amz-fx

Silver Supporting Member
Messages
1,763
Testing on the daisy chain is okay since the outputs are all in parallel. I was going to suggest adding the Big Muff but the admin on the EHX forum says that 18v will blow it up (not sure I agree with that) though you are much lower volts than that. Wait for the AMT pedals to come in.

regards, Jack
 

M Brown

Member
Messages
14
OK, thanks - I tested on the daisy chain plugs with the Jack Rabbit plugged in and activated and the reading was the same as if nothing was plugged in.

I'll see if I can pull down the voltage rating when the AMTs arrive.
 

M Brown

Member
Messages
14


So yeah, this is still a work in progress. The new board is about half done - just positioning pedals with plugs, no cabling yet because I'm still waiting for the two AMT pedals to come from Russia (never order parcels by Russian Post before or during the holidays, btw). In the meantime I decided to wire up all the pedals I have with a 1-Spot daisy chain and also test the battery pack voltage under different conditions. This setup allows me to switch between the 1-Spot wall plug and the battery pack easily. Here's some background on test parameters...

- I bought some dummy AA cells from China that are basically just conductors with no electrolyte inside so I could experiment with bringing down the voltage of the AA pack
- I let the NIMH AA's in my pack sit uncharged ("stale") for a few weeks so I could observe their voltage drop during that time (also I was busy and couldn't work on this anyway)
- I tested both 7 AA (+1 dummy cell) and 8 AA configurations with no load both in "freshly charged" and "stale" states
- I tested the 7 AA configuration in "fresh" and "stale" states under load with all the pedals pictured above powered on and activated (but obviously no signal passing through because I haven't made patch cables yet)
- For all tests the battery pack is switched on with a Trutone CYR reverse polarity converter attached to the pack's barrel connector, making it safe for standard centre negative pedals
- No-load tests were metered at the end of the CYR cable's barrel connector
- Load tests were metered off the + pole of the first AA and - of the last cell (either battery or dummy, depending)
- The pedals currently on the board draw around max 575 mA.

and the data...

- 7 AA stale, no load = 9.18V
- 8 AA stale, no load = 10.6V
- 7 AA stale, loaded = 8.78V
- 8 AA fresh, no load = 11.93V
- 7 AA fresh, no load = 10.4 V
- 7 AA fresh, loaded = 10.0V

Oh, and I didn't test the 8 cell configuration under load at all - felt it was too risky with all my pedals in the daisy chain. When the pedals are all switched on they only pull down the voltage by about 0.4V, which would probably put the voltage of 8 AA's in the 10.2V to 11.5V range, which makes me a little nervous.

So, I suppose being the cautious person that I am, I'm still leaning toward a 7-cell, 1 dummy configuration just because I'm paranoid about going over 10V under load. Of course, I witnessed the voltage slowly and steadily drop the longer I had all the pedals running. The picture above shows a rating of 8.69V under load with 7 stale batteries after just a few minutes of running the rig (down from 8.78V when I began) It's anyone's guess whether running 7 cells vs 8 would shorten the useful life of the pack between charges - would depend on a lot of factors. All the pedals light up and seem to be functioning properly from a visual standpoint with the 7 cell setup.

Jack, you had said the AMT pedals would be a good choice to test higher voltages because they can handle 12V, but their current draw is very low (around 6 or 7 mA) - would you really see a meaningful voltage sag just from those pedals alone?

Any feedback is welcome.
 
Last edited:

amz-fx

Silver Supporting Member
Messages
1,763
The 7-cell configuration looks to be the way to go, at least for now.

regards, Jack
 

M Brown

Member
Messages
14
Thanks for all the responses. Once I'm done wiring up the patch cables I'll see if the daisy chain creates any excess noise (waiting on the last pedal to be delivered). I may end up going with an isolated brick power supply like the 1 Spot Pro CS12 in which case the daisy chain will be retired and the battery pack won't be compatible. It's been educational, though. I'll post proper photos once the board is done.
 






Trending Topics

Top Bottom