The Boominator - another stab at the ultimate party machine

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cremoire

Member
Joined 2013
Hi guys.
I have a few questions for you.

Because of the size and orientation of my battery I dont have a bunch of available space for switches, etc. on the exterior of the mini v2.

So have been looking at rotary switches. I want one that is long enough thread to fit through the 6mm (maybe 6.5mm) ply.
A lot of the specifications refer to 120v AC or 250v AC.
How does that correlate to DC at 13v? (like .125A @ 250v)

Also with the bluetooth module using so little power is it worth switching off when not being used? (when the main power switch is on)

I will put a 12v to usb adapter inside. Does that draw much when nothing is plugged into it? (And what would the draw be with a modern smart phone when charging)

I know that the whole point of these systems is efficiency so it seems a shame to waste power but if its a negligible amount it would save space/money and be more cosmetically sound to keep it simple.

And does anyone know how much the maxamp draws?
(Mine arrived today WesleyK, thanks. Its really small and def looks the part compared to my old Ta2020!)

Thanks in advance
 
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spotke

Member
Joined 2012
Switches with a higer voltage rating just provide better isolation. The current ratings will be the same fot 220V or 12V. So a switch rated for 125mA at 230V, is also only rated for 125 mA at 12V.

The 12V USB adapter quiescent current will depend on the adapter. Normally it's not very big, but I would personally still turn it off. The draw of the adapter will also depend on the adapter. If it's an efficient switching converter, you can calculate the current draw like this: (5V * charging current) / (12V * 0.90). So a smartphone with a 1 amp charging current (at 5V) will draw 463 mA at 12V using a 90% efficient adapter.

Haven't got an idea about the current daw of the maxAmp though.
 
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lutkeveld

Member
Joined 2013
You can make a hole that just fits the shaft and use the threaded piece to 'screw' it in the wood.

Bluetoothmodule uses around 20ma when in use, 5ma in idle

You want a high efficiency switching usb module so you don't waste unneccesary power when converting to 5v. Standard usb charges at 0.5A, so 0.5A*5V=2.5 watt. Taking the (in)efficiency of the usb module in account it would use around 3 watt. So to fully charge a modern phone it would take around 10 watt.

Both modules use almost no power when not in use, not 'switchworthy' IMO.

MaxAmp uses around 350mA when using it full power before clipping.
 
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spotke

Member
Joined 2012
You are messing up the units a bit though ;). Watt = unit of power, not energy. Suppose he wants to fully charge his iPhone 5S, which has a 1570 mAh battery. 1.57Ah * 3.7V (Li ion cell voltage) = 5.8Wh . With a converter that is 90% efficient, this would drain 5.8Wh / 0.90 = 6.45Wh of energy out of the battery. Likewise, a 3000mAh battery would drain 12.33 Wh of energy.

So using a 7.2 Ah, 12V battery you would be able to recharge a 3000mAh cell phone 7 times before the battery is out of energy.


And to put the current consumption in perspective: With 90dB/watt speakers, 2X 15 watt would give you ~104.7 dB at one meter. This is a bit more than twice as loud as you would get with 2 x 1 watt. (You then get 93dB of sound pressure). Given your number of 350mA @ 2x 15watt, this would mean a current draw of 23.33mA @ 2x 1 watt. So an extra power consumption of even only 5 mA would give you a ~17.6% reduction in play time if you don't go full out.

So in my opinion, it's useful to be able to turn off stuff that you don't need because it does make a significant difference in play time if you're not in full out party mode. For this same reason I dislike LEDs and stuff on my speaker. If they're fed directly from the 12V battery with a simple drop resistor, you would get an extra 20mA current draw from the battery that isn't really necessary. But the point can be made that it should be obvious when your speaker is powered on. I've left mine on after using it once for example and blew my battery because of it... (No battery protection circuit installed)
 
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KandA

Member
Joined 2014
spotke said:
Switches with a higer voltage rating just provide better isolation. The current ratings will be the same fot 220V or 12V. So a switch rated for 125mA at 230V, is also only rated for 125 mA at 12V.
...
Click to expand...

Sorry, NO. This in incorrect and important to note. When discussing 230V and 12V it normally means 230V AC and 12V DC and a switch rated for 2A AC generally CANNOT break 2A DC. You can find typical ratio between AC and DC ratings in spec sheets. Alternating current has inherent zero-current events 100 times a second (120 times for 60 Hz) and that will help break the flow of electrons. A direct current is more 'difficult to stop' and the difficulty depends on the characteristics of the load (resistive/inductive). BR
 
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lutkeveld

Member
Joined 2013
And to put the current consumption in perspective: With 90dB/watt speakers, 2X 15 watt would give you ~104.7 dB at one meter. This is a bit more than twice as loud as you would get with 2 x 1 watt. (You then get 93dB of sound pressure). Given your number of 350mA @ 2x 15watt, this would mean a current draw of 23.33mA @ 2x 1 watt. So an extra power consumption of even only 5 mA would give you a ~17.6% reduction in play time if you don't go full out.
Click to expand...

Your math isn't correct. You can't go below 55mA because that's the idle current of the MaxAmp. Normal listening level takes around 100ma of power. The extra, let's say 10mA, of current of both modules equals around 10% less play time. At full power (350mA) it's around 3% reduction. But if you really like to squeeze out the extra playtime you could indeed use a switch.

So in my opinion, it's useful to be able to turn off stuff that you don't need because it does make a significant difference in play time if you're not in full out party mode. For this same reason I dislike LEDs and stuff on my speaker. If they're fed directly from the 12V battery with a simple drop resistor, you would get an extra 20mA current draw from the battery that isn't really necessary. But the point can be made that it should be obvious when your speaker is powered on. I've left mine on after using it once for example and blew my battery because of it... (No battery protection circuit installed)
Click to expand...

Lead acid? Then use deep-charge protection :). Very rare to see a lead-acid blow up because of deep-charge. In my experience led's use only 10ma, but that's dependent on the used resistor and color ofcourse.

For a LiFePO4 PCM search ebay, they have some PCB's with balancing for around 15 dollars. For the cells you can search on AliExpress, they have 2300mah A123 cells for $8/pcs. First verify they aren't used because there are some who sell used cells.
 
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