Hi all,
I probably count myself as 1 step up from total novice, but I am a noob to these forums, so be gentle!
I'm looking to build a boombox, (I know... How original!
) but I really want the power to work in a specific way. I've picked out an amp (a T2020 type thing) and what I think is a suitable battery (12v, 7Ah), and I'm happy and confident to connect it all up and make it work.
BUT, I also want my boombox to work from the mains, in much the same way a laptop does. (When it's not plugged in, it's powered from the battery. When it is plugged it works from the mains AND the battery is charging. And I want this to happen automatically, like it does in a laptop or a phone or whatever. No fiddling with charger terminals, no flicking of switches.) I've scratched my head until there's barely anything left there!! Help me please!
(Or just tell me it's a pipe dream and completely impossible!)
Thanks,
Jon
I probably count myself as 1 step up from total novice, but I am a noob to these forums, so be gentle!
I'm looking to build a boombox, (I know... How original!
) but I really want the power to work in a specific way. I've picked out an amp (a T2020 type thing) and what I think is a suitable battery (12v, 7Ah), and I'm happy and confident to connect it all up and make it work.BUT, I also want my boombox to work from the mains, in much the same way a laptop does. (When it's not plugged in, it's powered from the battery. When it is plugged it works from the mains AND the battery is charging. And I want this to happen automatically, like it does in a laptop or a phone or whatever. No fiddling with charger terminals, no flicking of switches.) I've scratched my head until there's barely anything left there!! Help me please!
(Or just tell me it's a pipe dream and completely impossible!)
Thanks,
Jon
Please don't use these as finished circuits, more as ideas how to achieve what you are proposing.
Just looking at the second schematic.
The transformer is chosen to give Vrect at about the 20V mark, so a 15V transformer will do.
Cc is a constant current regulator like the LM317, set up to charge the battery iaw its manufacturers recommendations.
Vreg is set to 12V to power the amp when mains is available.
The diodes steer the DC so that the battery is not discharged when mains is available and the one across the Vreg protects the regulator when the battery voltage exceeds the output voltage of the regulator.
This is only really suited for Lead Acid batteries which can float charge at full charging current. For any other technology the Cc reg will need to be replaced with an appropriate charging circuit.
Just looking at the second schematic.
The transformer is chosen to give Vrect at about the 20V mark, so a 15V transformer will do.
Cc is a constant current regulator like the LM317, set up to charge the battery iaw its manufacturers recommendations.
Vreg is set to 12V to power the amp when mains is available.
The diodes steer the DC so that the battery is not discharged when mains is available and the one across the Vreg protects the regulator when the battery voltage exceeds the output voltage of the regulator.
This is only really suited for Lead Acid batteries which can float charge at full charging current. For any other technology the Cc reg will need to be replaced with an appropriate charging circuit.
Attachments
Its easy with a VRLA battery such as yours. The TA2020 is rated for 16 volt operation, that's higher than anything a proper charger should apply. So all you do is connect charger input across the battery, then when you plug in the charger, its higher voltage starts to charge the battery and the amp still functions normally.
No parts required
(just make sure the charger is a proper job, i.e. it supplies either a fixed DC voltage of around 15 volts, no current limit needed for the batteries sake. That voltage is fine for cyclic use where you manually remove the charge when the battery is fully charged. If you intend leaving the charger connected for hours or days then you need a proper charger that switches from bulk to float charge)
Check out the links in post #7 and 14 here,
http://www.diyaudio.com/forums/power-supplies/240727-fully-charged-battery.html#post3594388
No parts required
(just make sure the charger is a proper job, i.e. it supplies either a fixed DC voltage of around 15 volts, no current limit needed for the batteries sake. That voltage is fine for cyclic use where you manually remove the charge when the battery is fully charged. If you intend leaving the charger connected for hours or days then you need a proper charger that switches from bulk to float charge)
Check out the links in post #7 and 14 here,
http://www.diyaudio.com/forums/power-supplies/240727-fully-charged-battery.html#post3594388
Thanks for the advice so far!
Mooly, I had wondered whether it might be a case of shoving the charger onto the battery terminals in parallel with the load, but thought it could possibly be as simple as that!
The battery I have in mind is a sealed lead acid cell, but I'm absolutely open to suggestions for others that might be more suitable for this application.
Mooly, I had wondered whether it might be a case of shoving the charger onto the battery terminals in parallel with the load, but thought it could possibly be as simple as that!
The battery I have in mind is a sealed lead acid cell, but I'm absolutely open to suggestions for others that might be more suitable for this application.
Thanks for the advice so far!
Mooly, I had wondered whether it might be a case of shoving the charger onto the battery terminals in parallel with the load, but thought it could possibly be as simple as that!
The battery I have in mind is a sealed lead acid cell, but I'm absolutely open to suggestions for others that might be more suitable for this application.
As long as the open circuit voltage of the charger is below 16 volts it should be fine. Lead acid batteries are an ideal, long lasting and rugged source of power as long as the size/weight is OK. Just remember to fuse it at the positive terminal for safety... you can just about start a small car off a battery that size.
Just been having a quick look around. Would, (in your opinion) this battery: Battery Masters :: Ultramax NP7-12, 12V 7Ah with 4.8mm / 0.187" Wide Male Spade connection (L(mm) W(mm) H(mm) 151 65 98)
coupled with this charger: Battery Masters :: 12V 3A Ultramax Charger for Sealed lead Acid(SLA) Batteries.
be appropriate?
coupled with this charger: Battery Masters :: 12V 3A Ultramax Charger for Sealed lead Acid(SLA) Batteries.
be appropriate?
It looks OK.
I would suggest with any battery charger you get, that you first confirm that no current flows into the charger from the battery when the charger is disconnected from the mains. If it did then a suitable series diode might be called for to prevent the battery discharging but I can't imagine its a real problem as pulling the AC mains is a valid condition and any current should be small. If it were under a couple of milliamps I wouldn't worry.
I would suggest with any battery charger you get, that you first confirm that no current flows into the charger from the battery when the charger is disconnected from the mains. If it did then a suitable series diode might be called for to prevent the battery discharging but I can't imagine its a real problem as pulling the AC mains is a valid condition and any current should be small. If it were under a couple of milliamps I wouldn't worry.
Read this page Charging Information For Lead Acid Batteries ? Battery University
The maximum charging voltage is about 14.7V
The maximum charging voltage is about 14.7V
If you will keep the charger on the battery for a long time and do not want to worry about over charging, then use a regulator and set the voltage to 13.80 V. This may need adjustment if the temperature of the room (the battery) is not "room temperature". Fast charging can be accomplished at a higher voltage, but this higher voltage must be removed at the appropriate stage in the charge cycle or damage to the battery (drying out, and possibly errosion of the plates) will result. At 13.8 V, you can keep it connected indefinitely, which is exactly what standby devices like a computer UPS or a emergency light do. The charge current should be limited to about 20% or less of the capacity/h (at 7 Ah, that would be 1.4 A).
Lead acid batteries are NOT charged by constant current, they are charged by constant voltage. The best way to describe a basic LA charger is a current-limited constant voltage. If you drive a constant current into a LA battery, the plates will go way over the safe voltage (over the "gassing" voltage) when the battery becomes close to full, and it will begin to dry up and/or the plates will deteriorate. Since an SLA cannot be topped up with water like a flooded battery, this the end of the battery.
just measure the reverse current. If there is non then a diode is in there already.
Stereo to mono just needs 3 resistors in its simplest form. One resistor in the L and R feeds (say 5K6) that then connect together. The third resistor (say 68K) just connects this point to ground. That's it. Or you could mix them in an opamp mixer type circuit which is technically a better solution.
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