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baby rig looking for power source(s)

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Forum Name: 12v Powered Systems
Forum Description: From Mini-rigs to ICE, all your low voltage audio needs here...
Printed Date: 12 August 2022 at 4:17am
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Topic: baby rig looking for power source(s)
Posted By: cinghiale
Subject: baby rig looking for power source(s)
Date Posted: 14 July 2020 at 12:09pm
Hey peeps!

We're a group of friends living in Berlin. We recently brought back to life an abandoned cargo bike and of course first thing we want to do is build a small sound system to have on board! we're rave enthusiasts so of course we won't stop at one sub, there's more to come Star

The bike has 2 wheels in the front with a cargo hold of approx 70x80 cm. after long research we settled on building a cubo 15 with an eminence kappa 15LF for our sub and this kit - as a top. Eventually a cubo kick will join the family but for now this is it.

the rig is of course mono, there's a thomann 4x4 mini dsp to crossover and a still open choice wondom class-d amp.

Now coming to the question! we're looking into how to power the whole thing and getting pretty confused. Initially we thought of just using a 12v gel battery but then a friend who already built a bike rig suggested we should use 48v lithium batteries, the ones aimed at ebikes.

Using a 48v battery would allow us to use an amp rated for 48v without needing a boost regulator (but we maybe still need something to have 48v stable?). For a 10Ah battery this would give us 480Wh for 2kg. The market for these batteries though looks extremely sketchy. it would be so stupid to build this beauty and then have a cheap battery explode and it all up. One possible candidate is this battery -

Using a 12v battery would mean having to find a 12v amp or use a boost regulator to up the voltage. for around 100€ we could get a 100Ah battery that would give us 1200Wh for 20kg. double run time at 10x weight. But somehow i feel more relaxed about using one of these batteries as they're probably less dangerous.

Asking u experts if you have any advice for us? is there anything we're overlooking? weight is not a big problem for us. the bike can carry 100kg and the speakers will end up being less than 50kg all together so we have plenty of payload available. money is the bigger issue.

Thanks for all the help you can throw at us!

Posted By: studio45
Date Posted: 14 July 2020 at 6:47pm
The thing about "48v" batteries, is they're not 48v. 

A "48v" lithium-ion pack is made up of 13 cells in series. When they're all fully charged, to 4.2v each, the pack voltage is 54.6v. When they're all flat, at 3.0v each, the pack voltage is 39v. So your window there is 15.6v.

An amp that is happy at 48v, may not be able to take 54.6v - my Sure Electronics boards certainly don't like anything more than 52v at their power input; they won't start up if it's too high. And by the time your pack is flattening, your available power output at 39v will be quite a bit less than at 48v; probably noticeable as a lowering of the clipping point when you give 'er some welly.

All competent power amps have a regulated boost converter inside, that steps up and *fixes* the voltage seen by the amp to a good value. I use them on my system (the 500 watt ones from Sure/Wondom). This way, as the batteries drain, as long as they can supply the current necessary, the amp voltage will not change (until the battery voltage goes below your booster's cutoff point). 

The high power booster units can normally accept 9-27v, so you *can* use lithium batteries with them - just at a maximum of 6 cells in series (25.4v --> 18v) 

The higher the voltage you can give the booster at its input, the more power it will be able to supply - as they're limited by the current capability of the input switches, so if you have one that can draw 15 amps, at 12v it will supply 180 watts, whereas at 25v it will supply 375 watts.

In conclusion, get a booster, and then use whatever batteries are handy!

Studio45 - Box Builder Commotion Soundsystem -Mobile PA

Posted By: slaz
Date Posted: 14 July 2020 at 7:37pm
All good info from Studio45 - I'd have said almost identical things .....

One point though - I'd also consider using a good 4-channel full-range class D car amplifier.
Pioneer does a decent one - there are others too.

With 4 channels you can bridge that to 2 channels and (with 8ohm drivers/boxes) - that achieves a good impedance match, and you can also its built-in filters/Xover to reasonably good effect (with a simple bass/sub + mid-top box setup).
Its a viable solution for using with a big old SLA battery setup.

SLA batteries are nice and simple to deal with/maintain and don't cost _too_ much to replace.
Obviuosly the downside is the weight.


Posted By: cinghiale
Date Posted: 06 August 2020 at 12:30pm
Thanks you for your help!
very good points, we ended up getting a 12v 50Ah AGM battery and a car amp, emphaser EA-M4x, 2x670w @ 4ohms. it can really make the baby sing with plenty of headroom!. We called it Mitzi (it's german for kitty) here's some pictures of it :) -

Now looking into building a kick cab, the expansion never stops!

I also have another question! we're aiming at having djs playing on it, so we got a vestax dj mixer that runs natively at 15v, we figured that it would work also on 12v, probably with less headroom we'll have to be careful about gain staging. And we also have 2 xdj 700 that run as well on 12v but we're worried about some components inside of not liking being hooked up to a fully charged battery around 13.2v. Do you have any experience with it? should we absolutely use a buck boost converter to stabilize the voltage or are we just overthinking it? we bought a 12dc-12dc buck boost but it heats up veery quickly so we're not sure about it.

thanks again for your help this forum is a well Yin Yang

Posted By: studio45
Date Posted: 06 August 2020 at 2:32pm
From what I can see in the service manual for XDJ700, the 12v power is not used natively for any components inside - there are a variety of local regulators on board that change it to +5, +3.3, +9 and +10v supplies to feed the various chips and LEDs. 
I would hazard a guess that all those regulators would survive an extra 1.2v at their inputs; there is a fuse right at the 12v inlet, which really ought to blow if there is a problem. So you should be fine connecting it to a full battery.

Note that it does take in 1200mA (1.2A) at 12v, which is quite a current for a small DC/DC converter - even a "5 amp" unit will get too hot to touch at a constant 1.2A output. You may want to increase the heatsinking on it, or buy a 10 amp unit.

Studio45 - Box Builder Commotion Soundsystem -Mobile PA

Posted By: cinghiale
Date Posted: 17 November 2020 at 1:14pm
Hey Y'all,
Just wanted to post an update and thanks for all the help. We took the rig out for a few outdoor test runs at the end of the summer and Mitzi really kicks ass. We added a paraflex kick cab for some mid-bass punch and it really makes it slam. Our longest run was 11 hours, at full volume, running amp, dsp, cdjs, and mixer off the 50ah battery. The cops came before the battery died :/
Big props to the cubo 15 design! We compared our rig once side by side to a small function-one stack and Mitzi had subjectively deeper, more detailed, and more pleasant sounding bass. -

Posted By: slaz
Date Posted: 20 November 2020 at 4:29pm
Nice !!

Bet that kicks up very well indeed ....

Are you using steep cut filters in the DSP (esp. for the bass LPF) ?


Posted By: Motif
Date Posted: 04 January 2021 at 6:10am
Hey! Just wondering what kind of volume you were playing at I’m looking at building something similar but I have two old quest passive pa speakers. The amp I want will power them up to 300w rms. I thought I would need an absurd battery but it seems like I’m overshooting. How many people were you playing for? 

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