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Class D Switching Power Amplifiers and Power D/A conversion

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Old 28th March 2013, 07:18 AM   #71
Mooly is offline Mooly  United Kingdom
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Well done

If its all working it must be right... with the proviso that I would just check that the battery voltage doesn't rise when you plug the wall wart in.

If it did then it indicates the battery is being charged... which would explode... hello ! are you still there
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Old 28th March 2013, 09:14 PM   #72
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xrk971... Haha, I wish i could claim to be a mp3 box builder. I am learning so much from this forum. I didn't take photos of the few that I have done, oopsie! I will make sure to take some of my upcoming projects. All my friends want one now.

Mooly, yes nothing has exploded yet, YAY!!! It sure seems right, but I am still a little nervous. Can you ease my mind by checking out the simple schematic I did.
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Old 29th March 2013, 07:13 AM   #73
Mooly is offline Mooly  United Kingdom
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That's it
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Old 31st March 2013, 09:35 AM   #74
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Just an update. I was able to run this amp at full volume for 4 hours on a new 9V duracell battery. It wasn't even dead, it just started clipping a little bit and the LED started blinking when the bass would hit. I am gonna see how long it lasts til it is completely dead. It still sounded pretty good at a lower volume.

I thought 4 hours was pretty good, what do you guys think?
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Old 31st March 2013, 09:35 AM   #75
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I was also thinking about buying rechargeable 9v. Any suggestions on a good brand to go with?
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Old 31st March 2013, 10:57 AM   #76
xrk971 is offline xrk971  United States
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I don't think they make rechargeable 9v's that are very cost effective. The 9v isn't critical, you can probably run with rechargeable NiMH AA's snapped into 6 cell holder from Radio Shack. Another cost effective option is to use powertool battery packs.
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Old 31st March 2013, 12:13 PM   #77
Mooly is offline Mooly  United Kingdom
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What fits is obviously critical and perhaps weight is a factor ?

If you have the battery voltage below the level of the wall wart then you have an easy way of recharging. We can come to that later

A small VRSLA (gell lead acid type) could be an option. Totally spill proof, can be used any which way up and offer good capacity. Weight is the downside but there are small 12 volt 2AH ish capacities available.

And NiMh as xrk971 suggests. All are do-able.
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Old 31st March 2013, 12:23 PM   #78
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If you're running the 9v battery so the LED drops out occasionally, you're dropping below the 5v supply needed to keep the chip going. That's basically a dead battery.

6- or 8- AA battery packs are, IMO, the way to do it. You can use rechargables (as many as you like), and replace with ordinary batteries once the rechargables are done.

Other types of battery can offer good performance, but will need a dedicated charger to make the system work again. With AAs, just bring more of them.

A couple of 9v rechargables could be useful, but I'd keep them as back-up rather than the main power source. Their capacities are often ~200mAh, whereas the AAs come in at 1800-2800mAh. Granted, you'll need 6 of the AAs to get it working nicely, but they'll last much longer than the 9v ones.

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Old 31st March 2013, 06:27 PM   #79
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xrk971, Mooly, Chris thanks for your insight! These are all very good suggestions. Mooly hit the nail on the head..

Quote:
Originally Posted by Mooly View Post
What fits is obviously critical and perhaps weight is a factor ?
Both the fit and the weight is a huge factor for me. I play guitar, one of the acoustic/electrics uses a 9V, the battery compartment is very easy to access. It is setup like this one. I like the fact that I can cut a hole in the enclosure and mount the battery compartment on the outside and have easy access to change it out.

The downfall obviously is the battery life, however I don't stay at the beach longer then a couple of hours anyways. So a 9v would last me 2 days, when I write that it doesn't sound like much LOL.

I do like the idea of 6AA for longer battery life and is probably doable if I find a bigger enclosure for my next project. I also really love the idea of the small VRSLA (gel lead acid type). That is really intriguing to me! It can be wired so the wall wart can charge the battery?

Quote:
Originally Posted by Mooly View Post
If you have the battery voltage below the level of the wall wart then you have an easy way of recharging. We can come to that later
Care to elaborate?

I love this forum so much, you guys get my wheels turning like you wouldn't believe. Thanks so much for all your input!
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Old 31st March 2013, 06:53 PM   #80
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by kittygirl View Post
...........I love this forum so much, you guys get my wheels turning like you wouldn't believe. Thanks so much for all your input!
No answer to that

To recharge either an NiMh or lead acid battery involves applying "more" voltage than the battery voltage across the battery and limiting the current to a safe value. All that can be achieved with as little as a diode and resistor for the NiMh and same for the lead acid with the proviso that the final voltage doesn't exceed around 15 volts (which is OK for "cyclic" use on lead acids).

Lets keep it simple. A 9 volt NiMh pack and around 13 volts ? from the wall wart. So 13 - 9 is 4 volts. Add (or rather subtract) the volt drop of a diode and you have 3.3 volts to play with. A 9 volt battery pack probably rises to around 10 volts full charged... so that leaves 2.3 volts. The resistor would be 2.3/I (I= the charge current that is safe to leave as a float or trickle charge) and that would allow a correspondingly higher initial charge current when the battery voltage is lower (when its discharged). The resistor would have to be chosen such that the max charge current for the battery is never exceeded and so to the max current from the wall wart.

The bad news is that NiMh PP3 type batteries are hopeless compared to say an alkaline PP3. You would need something like the AA's as a minimum I think
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