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Lead battery problems

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Smonjirez

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Hello there, im just new here btw so i don't know if this is the best place to post my question.
I've lately built a music box to play music in the open air, and added some 12v LEDs to it. Now my problem is: If i've just charged up my (lead) battery (12v, from a scooter) everything works fine. Music and LEDs simultaneously. But after about half an hour, the lights won't go on again. The music just keeps on playing fine. When I turn off the music for about 5 mins and turn it on again, the music won't play. Instead, the volume drops by about 90% and cracks like hell. If I dont turn the music off it'd keep playing for at least 5 hours. And when I charge the battery for just even 5 minutes after I've turned it off, it will keep playing for 5 hours again (of course not if it's empty.)

So it seems I have to "kickstart" this lead battery =S That's very inconvenient if you're out in the open air where there is no possibility of "kickstarting" the battery. Does anyone know a solution for this? plz? (Amplifier is also just 12v (160w max))
 
160W amp? Sounds more like an electrical problem with the amp more than anything with the battery. Probably discharges the filter caps, gets into some odd power-up oscillation with low voltage. You might try a seperate switch just to the music generator or amp, see if delaying turning one on will stop affecting the other.
 
Yeah well it doesn't pull that much, i always have the volume below 30% and it's not RMS.
I've already got 3 seperate switches, 1 to turn the main power on for the amp, 1 for the signal power, 1 for the LED's.
I also read that the voltage of lead batteries is about 1 - 1.5v higher just after charging than after half an hour.
Isn't there something I can put between the circuit to "kickstart" it or something:confused:
 
Doesn't matter how much it pulls, it's what they did to the amp to get it to put out 160 watts that's the problem. See, 12V on a 4Ω speaker is good for maybe thirty watts or so. To get more power, they step up the voltage with a voltage booster that uses an inverter. A typical inverter design runs the base of the drive transistors off a tap in the transformer. So long as it's doing its thing, it's generating enough voltage to drive the transistors. Kill the power, and now it can't get started again. If you always have the volume below 30% anyway, you might try using a smaller, simpler amp.
 
Well, the point is, this was the smallest amp i could find in the local store.
It's originally designed to build in scooters, where you always have the engine to power up the battery.
Can't i do something stupid like connect a battery in serie (with a switch) with the accu to the amp so it's generating a high enough voltage to start it up?
or would the amp pull so much amps that the battery would explode / melt or something
 
Sure, try it if you want. Use a couple of D cell nicads (not NiMH, not alkaline) they can handle a good 30 amps without exploding.
 
Hmm still sounds kinda dangerous to me.
Is something like this possible?

I put a bunch of condensators in series with the battery itself
when I shut down the music, the energy stored in the condensators remains there for some time right?
Now I add a kickstart button, which redirects the energy from the condensators back to the battery and when I release the button the current flows through the condensators to the amplifier again.
Would this work the same as charging the lead battery for a very short time?
 
Yes, but use capacitors (they are much easier to find than condensators) and put them in parallel with the battery to charge it, then in series with the battery to "kick start" your device. You only need one unless you are using low-voltage "supercaps". Putting capacitors in series reduces the total capacitance.

This approach is actually probably more dangerous to the electronics than a couple of "D" cells. With this, you could potentially apply up to +24V to the electronics instead of +15V, but it would take a pretty big capacitance to actually get the voltage up that high.
 
Okay nice, then I won't have to concider changing batteries or something all the time, that'd be convenient.

So in the circuit, just AFTER the amp switch i'll pull a wire to one side of the capacitor and the other end leads directly to the negative of the battery.
Next there is also a switch between the positive side of the battery and a wire that goes directly to the positive side of the capacitor.
That way, I'll first kill the switch leading to the amp (meaning the negative side of the amp, capacitor and battery are still connected) and then Ill switch on the switch so the current flows from the capacitor to the battery creating a closed cirquit. After a few seconds or so I'll first switch on the switch leading to the amp and then Ill switch off the switch from the battery directly to the capacitor (still connected via the other wire)

am i getting it right now? =P
thanks btw
 
Not sure I follow you. The cap needs to be in parallel with the battery, then in series. Here's a schematic. D1 powers the amp through the battery after the cap has discharged. Use a big cap for C1, like 10,000µF or more. It must have a voltage rating of 16V or higher. The switch is shown in the "charge" position, and the cap is in parallel with the battery. When you throw the switch, it puts the cap in series.
 

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Ok I think I understand.
But if i'm correct, the amp won't go off wether the switch is in position 1 or 2?
I'm not very good at electrical schemes
What about this one?:
in the shown position the amp is turned on and the condensator is connected paralel (+ connected with +?)
and in the "off" position the current flows the opposite way, not going through the amp because of the diode, and the battery is in series with the condensator's minus.
Correct? =P
 

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Doesn't matter how much it pulls, it's what they did to the amp to get it to put out 160 watts that's the problem. See, 12V on a 4Ω speaker is good for maybe thirty watts or so.
Amplifier and speaker manufacturers lie about power.
Instead of RMS at a low distortion, they quote PEAK or MAXIMUM or MUSIC POWER with the volume control turned up way too high so the output is severely distorted square-waves.
A bridged car radio amplifier IC has a max output of 20V p-p (or less) with a supply of 12V which is only 12.5 Watts (or less) into 4 ohms at clipping. It is 160 Whats.
 
That sure makes more sense than an inverter in a scooter.

What about this one?:
in the shown position the amp is turned on and the condensator is connected paralel (+ connected with +?)
and in the "off" position the current flows the opposite way, not going through the amp because of the diode, and the battery is in series with the condensator's minus.
Correct?

No. Dumb. Might make the cap explode. You have a voltage reversing switch, it's not going to boost anything. My original circuit is doing what you asked for.

And it's not "condensator", FFS, it's "capacitor".
 
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Ok well thanks for that I dont want acid / other not-human substances in my face =). I'll give it a shot soon and will let you know if it worked.

Thanks
 
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