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Laptop charger & Active monitor off 12v battery?

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Jack1991 View Drop Down
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    Posted: 08 February 2021 at 9:23pm
I have a 12v sound system running off its own leisure battery. But was hoping to use a seperate 12v battery to charge my laptop and power 1x active monitor speaker (just the one with its own volume knob on) I have a DJ controller which runs off the laptops usb, laptop battery doesnt last long though so needs to be on charge to last a more significant time. 

I dont know the best way to do this or if its even possible. So hoping for some pointers.

What i did think was to using a 12v to 230v power inverter, with a double adapter plug attached. Then i can plug in the laptop charger and the active monitor speaker. If that will work id need to know what size/type of inverter i would need too. Obviously if theres an easier/better way im all ears.

Photod is the laptop charger with some specs, and the back of the speaker. Thats the only information i have for both of them, i hope its ok.


Cheers


Edited by Jack1991 - 09 February 2021 at 1:18pm
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I-shen Soundboy View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote I-shen Soundboy Quote  Post ReplyReply Direct Link To This Post Posted: 09 February 2021 at 10:45pm
No mate, you need a car laptop charger.

Cheap gizmo plugs into cigarette lighter socket (yeah, I know they haven't made a car with a cigarette lighter since the 80's) and chucks out 19v dc for your laptop.

As for the active speaker...  if you have to, get an inverter with at least 100w output:  The amp uses 60w and you'll want power headroom.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2021 at 8:36am
Originally posted by I-shen Soundboy I-shen Soundboy wrote:

No mate, you need a car laptop charger.

Cheap gizmo plugs into cigarette lighter socket (yeah, I know they haven't made a car with a cigarette lighter since the 80's) and chucks out 19v dc for your laptop.

As for the active speaker...  if you have to, get an inverter with at least 100w output:  The amp uses 60w and you'll want power headroom.


Cool ok cheers mate, ill have a google of that. What my plan is is to run the sound system off its own standalone 12v leisure battery. Then run the laptop charger and active monitor off its own seperate standalone 12v battery too. Leaving the actual Van/Cars battery alone.

Out if interest why would it not work both plugged into one of these adapters and then plugged into a 12v to 240v inverter?


The laptop charger and active monitor are both UK plug 240v.




Edited by Jack1991 - 10 February 2021 at 8:37am
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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2021 at 12:49pm
It would work but your battery will run flat more quickly that way. The car charger will be more efficient than the inverter+240v charger combo. Also square multiplug adapters suck!
And if it was me (but I am an idiot who loves taking the back off things) I would open up that monitor and see if there wasn't a way to convert that to 12v input as well. Given that it's quite cheap, and only 100 watts total (for 2 channels) you might find a TPA3116 chip amp in there, which happily run from single rail DC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2021 at 5:23pm
Originally posted by studio45 studio45 wrote:

It would work but your battery will run flat more quickly that way. The car charger will be more efficient than the inverter+240v charger combo. Also square multiplug adapters suck!
And if it was me (but I am an idiot who loves taking the back off things) I would open up that monitor and see if there wasn't a way to convert that to 12v input as well. Given that it's quite cheap, and only 100 watts total (for 2 channels) you might find a TPA3116 chip amp in there, which happily run from single rail DC.

Oh okay cool thanks, that makes sense.

That would be great if it is this amp board and could run off 12v! I will check it soon and have a look. I dont know what single rail dc is though is it a complex job to change it to 12v from 240v? I assume its not just take the positive and negative and stick it to the battery. 

If i did switch it to 12v then i could have the car laptop charger and the 12v monitor speaker off the same battery couldnt i?

Also i am open to other suggestions for using a speaker as a monitor for djing other than a actual monitor speaker. It would need its own volume control really. I cant really think what else. Battery speaker with aux probably wouldnt be man enough.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2021 at 12:39pm
OK so I looked up what amp is in your monitor and it is an ST Microelectronics TDA7295. This is a dual-rail amp so you won't be able to convert it to 12v use easily. You will need to use an inverter to run it, or remove it and fit a different amp board. As the crossovers are passive after the amp outputs, this could be done relatively easily.  

Most audio electronics, including amplifiers, need a "dual rail" power supply - that means three connections: positive, ground and negative. "Single rail" means two connections, positive and ground. However, these days, there are class D chip amps (the functional heart of the amp is a single large microchip) that run from single rail. Examples include the TA2020, the TPA3116 and TDA7493. 

With the exception of the TA2020, they do need a higher voltage than 12v to work well. Depending on which chip it is that can be between 24 and 48 volts. So, you need to use a boost regulator to step up the DC voltage (a boost regulator is the DC equivalent of a step-up transformer). This is a board that takes in a lower, varying DC voltage from batteries and outputs a higher, fixed DC voltage.

There *are* such things as dual-rail boost converters. However I've never been able to find a high-powered version suitable for a power amp. All you find on Google are questions from EE101 students asking how to do it! 
You can get handy-dandy little +5v to +/-15v at 100mA boards that make it easy to run small preamps, mixer circuits etc from single rail DC. Useful if you ever want to make your own audio circuits for your 12v rig. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2021 at 9:54pm
Cool thanks again for all the information. I will look into this more now i got a better base knowledge of whats involved.

I was also thinking of maybe being able to run one of those small amps off a Makita 18v 5ah battery. But noticed you said they run between 24-48v best.

Also would i need a 2 channel or mono as it has a passive crossover?

Or if your able to suggest or link me to a amp board that would be suitable to that would work in my monitor speaker. Preferably class D so its most efficient. That would be great


Edited by Jack1991 - 12 February 2021 at 7:39am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 12 February 2021 at 2:03pm
Right on, so here's an important fact about lithium tool batteries: the voltage is never what it says on the box. "18 volt" (aka "20 volt") tool batteries are made up of 5 lithium-ion cells in series (aka 5s). Each cell is 4.2v when fully charged and 3.0v when fully discharged (to a safe point). So 5x4.2 = 21v fully charged, 5x3 = 15v fully discharged. So 18v is just the voltage at one point in the middle of the discharge curve; it's not the steady voltage of the pack. 

You can run a TPA3116 amp from such a 5s pack and it will perform well. You'll get about 20 watts per channel into 8 ohms/ 40 watts into 4 ohms. With an efficient speaker that can be surprisingly loud. Performance will tail off a bit as the battery gets flattened. (That's where a boost regulator comes in handy). 

You could add a 6th cell and get a 25.2v (full) battery. That would still work well with a TPA3116. You'd get about 50 watts a side into 4 ohms. But 7 cells would be too high a voltage. The 29.4v charged voltage would fry the TPA3116 chip. 

If you want more power look at the TAS5630 chips. These run up to 52v input and can do approximately 160 watts a channel into 4 ohms/ 320 watts bridged into 8r. In theory also 600 watts bridged into 4r, with a good heatsink and fan. That's where a 48v supply would really be useful. Sure Electronics aka Wondom make some nice boards with those chips. 

All lithium batteries need to be used with protective circuits. It's not safe to discharge them below 3v per cell, or charge them to more than 4.2v per cell. Both these things can result in fire - rapidly! They are not like other cells where you can just make up a battery, put a fuse and connector on it and be done. You need a management and protection circuit suited to the number of cells you are using and the current you want to draw from them. 

If you are going to use a tool battery, my experience has been that they do not have complete protection built in - some of it is in the tool body. There is often a thermal cutout in there and sometimes over-current protection too - but *not* over-discharge protection. So if you're not careful, you can run the pack down to an unsafe voltage (less than 15v for an "18v" battery). This usually means that the charger won't charge it any more. So either use an external low voltage cutoff circuit, or monitor the voltage extremely carefully and stop using the battery when it gets near 15v. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 13 February 2021 at 9:44pm
Originally posted by studio45 studio45 wrote:

Right on, so here's an important fact about lithium tool batteries: the voltage is never what it says on the box. "18 volt" (aka "20 volt") tool batteries are made up of 5 lithium-ion cells in series (aka 5s). Each cell is 4.2v when fully charged and 3.0v when fully discharged (to a safe point). So 5x4.2 = 21v fully charged, 5x3 = 15v fully discharged. So 18v is just the voltage at one point in the middle of the discharge curve; it's not the steady voltage of the pack. 

You can run a TPA3116 amp from such a 5s pack and it will perform well. You'll get about 20 watts per channel into 8 ohms/ 40 watts into 4 ohms. With an efficient speaker that can be surprisingly loud. Performance will tail off a bit as the battery gets flattened. (That's where a boost regulator comes in handy). 

You could add a 6th cell and get a 25.2v (full) battery. That would still work well with a TPA3116. You'd get about 50 watts a side into 4 ohms. But 7 cells would be too high a voltage. The 29.4v charged voltage would fry the TPA3116 chip. 

If you want more power look at the TAS5630 chips. These run up to 52v input and can do approximately 160 watts a channel into 4 ohms/ 320 watts bridged into 8r. In theory also 600 watts bridged into 4r, with a good heatsink and fan. That's where a 48v supply would really be useful. Sure Electronics aka Wondom make some nice boards with those chips. 

All lithium batteries need to be used with protective circuits. It's not safe to discharge them below 3v per cell, or charge them to more than 4.2v per cell. Both these things can result in fire - rapidly! They are not like other cells where you can just make up a battery, put a fuse and connector on it and be done. You need a management and protection circuit suited to the number of cells you are using and the current you want to draw from them. 

If you are going to use a tool battery, my experience has been that they do not have complete protection built in - some of it is in the tool body. There is often a thermal cutout in there and sometimes over-current protection too - but *not* over-discharge protection. So if you're not careful, you can run the pack down to an unsafe voltage (less than 15v for an "18v" battery). This usually means that the charger won't charge it any more. So either use an external low voltage cutoff circuit, or monitor the voltage extremely carefully and stop using the battery when it gets near 15v. 

Cool perfect thanks Studio45 for all the information. Im going to take 1 of the monitors apart soon and have a look inside. See how daunting it looks for me to mess about with it. Im hoping it says the ohms on it somewhere to see what it is. 

Is there a particular amplifier board you would suggest? One that runs from 12v and up. Would i need a mono board i guess seeing as the crossover is passive? 

Id prefer a board that runs from 12v and up so i can experiment with different voltages like using a car battery and then a makita '18v' battery too. Just to try and understand it all a bit more too.


Edited by Jack1991 - 13 February 2021 at 9:45pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 14 February 2021 at 2:59pm
OK here's a TDA7498 board that will do 2x100 watts into 4 ohms from a 32V supply: 

https://www.ebay.co.uk/itm/TDA7498-TDA-7498-Stereo-Amplifier-Board/114653635580?hash=item1ab1e3a3fc:g:xwQAAOSwpHxfR8yo

And here's a boost converter to get that 32v from whatever battery you like:

https://www.ebay.co.uk/itm/400W-DC-DC-Step-Up-Boost-Buck-Voltage-Current-Converter-Power-Supply-Module-UK/224214901303?_trkparms=ispr%3D1&hash=item34343fe237:g:DIUAAOSw9wZe8xJf&amdata=enc%3AAQAFAAACcBaobrjLl8XobRIiIML1V4Imu%252Fn%252BzU5L90Z278x5ickkgCVySCgrNFPU8Iu85TabMKWc7KjlyHL5DMvF5WPes2Zj%252F7lZt3Mjn42K%252Bl%252BqQ5SUWqGUDAhJvu84CPZ%252B%252FrIkKurdcJKdISFlRUKGXd3FCFzHUZrNLJEfKmhxSdgn5l%252Bj872yFZinNVm5CuheFZfQz4UgT%252FekiiPDQKB26Ku4nmU4mj4Tq7I%252BqfkPttuTwMGbQbr%252BbiyMSqwt6FowrJDSvo2q4CltFNULTKHXx9Oys7hZe9mIg3YP7HuN6sRaCAMknrcSgcSAA%252FLRGeQP0hJASbcb4GKSeDCyTzAxAfTDS6OyNoLmQ8CaNputqV4Id34X1%252F0vwLjIvPWXj2uCuu9jO4Pj1ROybYvF78EDQNko7mDet5m70HaPk18Tc23TAPdRthqkYY%252F%252BJknf4kAq6W1iY1bLYlsE0%252BrxBmrs3nqBmfdCywIS6%252FGXktSCZJLmR8Ri1moQTn3Z34Es9XVo3SvItmUham83MvSNO2sHgtOORpvPY4h0ARMPG1WV5KrC3KwA0UYft1cC0V%252BPDgPOVC5Ljo7YdtDfC6UQbLeScNLy%252Bx9K0sEEMRgTXL%252FxNqRiHwabSGLXZy1gNV2aiJ5dU20AwR%252BfmRsICSEOCTy3r%252BYxhePcPZkNl8TFqCZfaqJBe4JP6t8AzImhcYZ%252BD4e6dgX53F14C48uGiCUTQduoIb2Lc3%252FZy2p3LyoCbbhMl4cyq5iO8MBqJEXZLn1LrVJzhbme2fPosTd3v2QDJHWlReBgxezHr9PtjvdsDKqV81LlijhipzR3XOh5OszLym6yf%252Ff7w%253D%253D%7Ccksum%3A2242149013032d3f2c2357dc4967bde1f688877ac4fb%7Campid%3APL_CLK%7Cclp%3A2334524

You'll also want a 15 amp fuse on the boost converter input, and appropriate connectors. Anderson Powerpole 30 (PP30) are pretty good, I use them. You can probably re-use the switch on the monitor. 

There are about three main groups of class D chip amp boards: 12-24v, 24-36v and 36-48v. AFAIK there aren't any boards that would power up and work from 12v, but still accept the higher voltage ranges. You can turn that boost converter up and down of course to see what the amp does at lower voltages. Don't go over 36v though or it will fail ;)
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