Regulated pedal power, in a car.

[calaverasgrande]

Okay long story short I'm building a camper van (not a tiny house grrr) and I've installed an AC power system with a couple LiFePo4 batteries, inverter etc.
Going to strap some PV panels to the roof eventually, just charging off the car now to run a fridge and keep my laptop happy.
Was looking at getting a CIOKS or similar pedal power brick to supply voltage to some pedals, drum machines etc while I'm traveling.
Then I had an idea.
Why not just take your basic pedal power supply circuit, lop off the transformer and rectifier and just wire it straight to the car 12V.
I'd assume I could do 9V this way no problem. I've a couple 12V gadgets as well. Hoping that I can squeeze in a couple of those since car volts is usually a tad higher than 12V in reality.
Is there any big gotcha I am missing here?
This just seems too easy. And well cheap compared to buying one of those CIOKS or Voodoo labs boxes.
It would be so uber nerd cool to have little barrel jack panels distributed around the van.
Heck, might get some little powered PA cabs and do some busking "off the grid".
I'll try and draw up a little diagram of my idea later. But it's pretty self explanatory.
12V and ground busses>capacitor>9V and 12V VRs hanging off the 12V and ground>barrel jacks for Boss and 3.5mm jacks for those EHX pedals.

 

[Whoops]

You can just take the 12VDC from the car battery and input that to a couple of LM7809 regulators with some filtering caps and you have you pedal power supply.
Basically 5 or 6 components only

 

[NOON]

Basic circuit as above for 9v, just make sure you have lots of diodes arranged for protection as car battery voltage can have some nasty spikes at times. Or maybe set up a system to automatically disconnect it from the car circuit when the engine is running.
12V from a car battery is a bit tricker than just a 7812 as there will be plenty of times when there's not enough headroom to keep it above the dropout voltage. You could use a zener regulator but there will be issues finding the right series resistor with the changing input voltage and unpredictable current draw from devices. There are some rather smart buck/bost regulators available these days that should be able to handle it, might need some noise filtering on the output for audio use though.

 

[calaverasgrande]

actually it will never be running from the car battery.
There is a second set of lithium batteries that are connected through a charge controller, fuses and a huge bypass switch to the cars electrical system. Basically just to parasitically charge the lithium bank. The main purpose of the charge controller is solar. But it's set up to do either charge source as is convenient. (for those cloudy days)
I'm aware of the dropout voltage. But I'm a little unclear about the details.
I know that car 12V is nominal. Actual voltage is more like 12.6-14V depending.
I'm more curious if the regulator keeps spitting out 12v at lower amperage, lower volts at same general amperage, or just folds it's arms and gets mad.
If this starts turning into buck converters and the like It would be easier to buy a retail pedal power unit.
I am just enthusiastic about being able to cut the inverter out of the loop. So I can save that juice for other devices.
Though to be realistic all my pedals and stuff plugged in probably isnt even 50 watts.

 

[Newmarket]

if using a linear voltage regulator then the output voltage cannot be greater than the input voltage.
It simply regulates down to a lower voltage by 'burning off' the voltage difference.
But there are 'low dropout' linear regulators (LDOs) that have a much lower minimum voltage drop than a 7812.
If using a switching regulator then with the correct topology you can trade voltage for current so maintain a voltage output higher than the input voltage.
Loads of solutions for this - check the TI website and tools. Of course you are then into the pros and cons of switching circuits.

 

[calaverasgrande]

Yeah I'm no golden ears who hates switching circuits. My bass amp is an Aguilar with a switching power amp.
Probably not going to be running that off the solar set up, it's 700 watts.
That said my goal here is just to make a couple simple circuits I can stuff in little hammond boxes and bolt to the frame of the van with rivet nuts. If the solution gets too convoluted it takes away the fun.
Or rather, I'm also installing water tanks, upholstering the exposed metal interior and a dozen other things over the next month. So I can't afford to let this little side project eat up too much time.
But I also haven't soldered anything in weeks and am suffering Weller withdrawal.
Thats a good idea to check out the TI site. It would stand to reason that there should be a low dropout part that fits this application. I'm not asking it to bear more than 200MA or so.

 

[JohnRoberts]

12V car systems are nominally 13.6V when engine is running, while cranking it can dip much lower.

9V battery operated gear is typically not regulated.

To get 12v from 13.6v a LDO regulator could be useful, 9V probably works from a standard 3 terminal regulator.

JR

 

[Newmarket]

12V car systems are nominally 13.6V when engine is running, while cranking it can dip much lower.

9V battery operated gear is typically not regulated.

To get 12v from 13.6v a LDO regulator could be useful, 9V probably works from a standard 3 terminal regulator.

JR

I understood that the OP is not intending this to run off the same battery that is running the vehicle ignition etc but not crystal clear on that.
If that was going to happen then I'd strongly suggest an automotive qualified regulator and associated transient/fault precautions. From memory, it was a while ago, the nominal 'datasheet test voltage' for these was 14.4V (for a '12V' battery - obvs more for 24V systems) and then there the "auto nasties" to guard against - Load Dump , Reverse Voltage with two batteries in series, heat, transients...

 

[JohnRoberts]

Yes, lots of noise sources in automotive power.

JR

 

[calaverasgrande]

The intent is for there to be two 12V systems.
One is the car's starter battery,
the other is a Lithium Iron Phospate battery bank
which also powers an inverter.
They are both connected through a charge controller which will also eventually be fed by a few PV panels on the roof.
So in a sense they are one system. But the purpose of the charge controller is to prevent you from running down the starter battery when you aren't driving. As well as to provide optimum volts and current for the type of battery bank you have connected.
Right now I'm waiting on my 12V fuse block to show up before I can start on that end of it.
I'm starting to think this might be worth doing a couple PCBs for durability sake over my usual veroboard or handwired approach. Once I settle on the specific circuit.
Since the footprint is much the same for 9v, 19v and 12v, would make sense to try and come up with something that can be configured for any of those. Probably the good old resistor lead shorting two through holes method.
Looked up 12V regulators on Digikey and there are indeed a few with .5 or so dropout voltage

Sounds like I'm going through a lot of trouble to avoid buying a regular pedal power brick?
But I have a mental image of little boxes bolted to the walls around the van, with 9v+ 12v+ etc labeled on them. Maybe 4 jacks each? I could power almost everything but the Elektron boxes and the mixer off just 9v and 12v.

 

[calaverasgrande]

So this is what I'm thinking right now. Except probably 4 or 5 outs per each.
Looked up the battery specs for the model I have and it's 12.8V.
These 12V regulators have a .6V dropout at 150ma, should be good.
Going to have to go jot down the current draw for all my 12V boxes to see if that's good enough.
Since I'm already scraping the edge there on volts wouldn't want to push it on current draw.
Thinking of throwing in a polarity flipper as well? Easier than having to worry about polarity of power cables.

 

[Bo Deadly]

You're not going to be able to regulate down from 12.8V to 12V. A 78L12 would need about 14V+ to regulate properly. But a LiPo pack should be pretty noise free already. It's not like you have massive rectifier noise. If something else is running on it or if you try to charge it from the car with the car on, noise could be injected into the system that way. But presumably when you're using this stuff the car will not be running. So for 12V you could just use a capacitance multiplier which is only ~0.6 drop. It's a poor-mans LDO.

But, for the record, the proper way to do this would be to use DCDC converters. Specifically I would get a couple units like MeanWell SCWN03A-15 and then put two regulated outputs on each to make two outputs of 12V and / or 9V. For example, if you have two SMPS that each have two regulators and each of those has two outputs, that 400mA distributed across 8 outputs. One of the main reasons for doing this would be because the SMPS are isolated. SMPS like that have transformers inside so the output's are floating. And it would be very low noise. Using LiPo > SMPS > Regulator > Capacitor is going to have the greatest chance of being noise free in a hostile environment like a mobile rig.

But I would not bolt things to the inside of the van. One of the bigger problems with this is the grounding scheme. You will want to have a central supply that provides a single sturdy ground point. If anything gets grounded elsewhere, especially to the chassis of the van itself, you will likely get noise.

Another issue is how to ground the overall system. If you are playing instruments with pickups, the shields of those need to find their way to earth ground. Otherwise, your pickups are going to pickup EMI and hum like crazy more or less depending on where you are and which direction your facing and where your hand is on the fret board and so on. Not good. So you will want to optionally have a metal spike that you can run outside and stick into the ground. However, this raises a safety issue. Normally a vehicle is isolated from the earth through it's tires. This is good if there is lighting and such. If you connect the negative side of your LiPo pack and everything attached to it to the ground through said metal spike, that is no longer the case. If you're standing out in a field thrashing out your interpretation of Ride the Lightning, you might literally ride the lightning that now has a path through the guitar (to which you are very well attached), down the cable, into the supply ground and down into earth.

 

[Newmarket]

You're not going to be able to regulate down from 12.8V to 12V. A 78L12 would need about 14V+ to regulate properly.

Another issue is how to ground the overall system. If you are playing instruments with pickups, the shields of those need to find their way to earth ground. Otherwise, your pickups are going to pickup EMI and hum like crazy...

If you look at the sketch it has a 750L12 LDO for the 12V not a 78L12
https://www.ti.com/product/TL750L?keyMatch=TL750L&tisearch=search-everything&usecase=GPN

The pickup shield/screen does not need to go to the planet earth.
It needs to go to a low impedance reference. In this context this is essentially the battery negative (0V/'GND').
There is nothing 'special' about the planet itself. It doesn't magically absorb charge or current although many past texts would have you thinking along those lines.
Indeed, one leading EMC author/consultant has half-jokingly 'banned' the use of the term 'Ground' due to this area of misconception.
Obviously in pro-audio and much other instrumentation we are dealing with standard earthed mains kit and so the PE is inherently part of the scheme.
But battery powered setups - eg your local electric guitar wielding blues busker with an amp and battery on a sack trolley - are not inherently noisier than mains powered setups.

Sorry to go on - but 'Earth' misconceptions get to me ! I'll stop before I mention aeroplanes...

 

[Bo Deadly]

The pickup shield/screen does not need to go to the planet earth.
It needs to go to a low impedance reference. In this context this is essentially the battery negative (0V/'GND').
There is nothing 'special' about the planet itself. It doesn't magically absorb charge or current although many past texts would have you thinking along those lines.
...
Sorry to go on - but 'Earth' misconceptions get to me ! I'll stop before I mention aeroplanes...

I have to challenge you on this one. If everyone is wearing platform shoes and standing on dry logs (or yes, if everyone was in an airplane), then yes, maybe it would work just fine. But if one guy on the other side of the van at the end of another long cable has his toe in a mud-puddle, that provides a path for the electromagnetic radiation that is raining down all around us to induce currents in all those cables through said guy's toe and to earth. Those currents across the inductance and resistance of various wires could easily produce noise in places that are not desired. Of course this stuff is highly unpredictable. It all depends on the specific arrangement of devices and impedances and wires and how shields are wired and so on.

 

[calaverasgrande]

Correct I did go find the lowest dropout 12V regulator a Digikey.
It's not critical that it be exactly 12V.
The drum machine and keyboard I use that take 12V have been happy on wallwarts that are anywhere from 11 to 13V (no load).
As far as earthing.
The standard for a lot of folks is to just treat the whole vehicle like one big ground.
Again since I'm dealing with two systems, starter battery and house battery, and since the amps are a lot higher than I'm used to playing with on these things. I'm doing ground wires for everything. Just to be safe.
Got my 12V fusebox and a ground distribution block with 0 and 4 gauge inlets and outlets in the mail today.
Not really hyped on the idea of SMPS or DCDC converters.
I actually have a pretty decent AC inverter that can power everything.
I'm only doing this to free up plugs and in theory, to be more efficient. Avoiding the conversion to AC, then back to DC.
Not sure if I would do such an elaborate power setup for just the 2 12V boxes.
But who knows, after I do a better survey of my gadgets I might want to do a bunch of power sources.

 

[calaverasgrande]

Thought I should add why I am looking at regulated power.
I have a few older drum machines, pedals and synths that act up a lot in terms of noise sometimes.
My Korg KPR77 is an especially notorious offender. It's actually not noisy itself.
But it has a habit of inducing noise in it's neighbors.
The fun part is that it's been pretty difficult repeating these noise events. Even had me thinking of cracking open the Korg and rebuilding the power section.
And yeah my single coil basses and guitars are the worst.

 

[Newmarket]

I have to challenge you on this one. If everyone is wearing platform shoes and standing on dry logs (or yes, if everyone was in an airplane), then yes, maybe it would work just fine. But if one guy on the other side of the van at the end of another long cable has his toe in a mud-puddle, that provides a path for the electromagnetic radiation that is raining down all around us to induce currents in all those cables through said guy's toe and to earth. Those currents across the inductance and resistance of various wires could easily produce noise in places that are not desired. Of course this stuff is highly unpredictable. It all depends on the specific arrangement of devices and impedances and wires and how shields are wired and so on.

Ah - I'll admit I hadn't considered the "Toe in mud-puddle" scenario
I think the way I'd solve that would be to consult learned texts than shout across:
"Oi Mate. Get out of the mud and put some proper footwear on ! It's muddy you know" (add expletives to taste)

But yes it's 'unpredictable' with stray impedances and currents and all that.
But I'd still start from the point of view of keeping any intended Earth connection out of it where there is no mains voltage consideration.
I guess we could look at how mobile and OB trucks generally operate but I'm guessing there is mains and/or inverters involved.

 

[Bo Deadly]

I guess we could look at how mobile and OB trucks generally operate but I'm guessing there is mains and/or inverters involved.

With electric cars becoming common I could see a mobile rig that runs off your car. Recording in a big open field has desirable acoustic qualities.

 

[calaverasgrande]

Suppose I should mention that there are other things like a car fridge, fans and LED lighting which could potentially dirty up the power. This whole dang project has gotten dragged out longer than anticipated thanks to the good old global supply chain slowdown.
Can't get half the stuff I need in a timely fashion.
House power should be installed soon though. Then I can worry about the fun stuff.

 

[CJ]

i built a battery operated pedal board, the D cells are underneath that sliding panel section.
batteries can melt stuff so obviously a fuse is in order.

most 9 volt effects will take 12, a tube screamer can take from 9 to 18 etc.

yes some gear generates a lot of noise, i had to wind a 1 to 1 iso xfmr on a Neve core to keep the looper happy.