Charge a 12V SLA while using the amplifier. - diyAudio
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Old 4th July 2011, 09:05 PM   #1
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Default Charge a 12V SLA while using the amplifier.

I have the standard AMP6Basic powering a boombox. It has a 7.2aH 12V batteri. I would like to charge the batteri while still playing. Worry free.

After much research it seems like a quite complicated task. Until i thought about the solar panel charge controllers. Like this cheap one for instance:

http://cgi.ebay.com/Solar-Panel-Char...item5199daf3e3

From what I understand it provides the following functions, all of which I would love to have on my boombox:

Over-load protection
Short circuit protection
Protection from the lightning strike
Under-voltage protection
Over-charging protection

Isn't it possible to connect a simple power supply instead of a solar panel? I was thinking around 15V and 1A. Is there any problem in this configuration? Or is there a much simpler solution I have overlooked?

/PalleRaa
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Old 4th July 2011, 09:40 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

AFAIUI its not complicated for a SLA battery. The battery will act as a regulator,
so all you need is a standard SLA charger, whether current is being drawn from
the battery or not should not make any real difference to what is going on.

rgds, sreten.
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Old 12th December 2011, 06:34 PM   #3
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Quote:
Originally Posted by sreten View Post
Hi,

AFAIUI its not complicated for a SLA battery. The battery will act as a regulator,
so all you need is a standard SLA charger, whether current is being drawn from
the battery or not should not make any real difference to what is going on.

rgds, sreten.
Excuse my lack of knowledge on the matter, but can anyone elaborate on this? I'm designing my circuit like so:

Click the image to open in full size.

I know if the power switch is off then there won't be any issues charging (I think), but what if I leave the switch on? Will the charger increase the power flowing to the amp? Could it possibly damage the amp or battery? If so, is there a better way to build the circuit?

The battery in question is a 12v SLA and the charger specs say 12v at 0.75 amps. The amp accepts 9-14v input.
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Old 12th December 2011, 06:41 PM   #4
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Think of the battery as (roughly) a constant voltage device.

Under all normal circumstances its voltage will not exceed 14V under charge. So your amp will receive 12v (ish) when not charging, and about 14v (ish) under charge and when fully charged.
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Old 12th December 2011, 06:42 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

Power to the amplifier will not be affected by the charger.
13.8V is the no load output voltage of a 12V SLA battery.

The charger needs 14V to fully charge the battery.

The charger is current limited to 0.75A when the battery is low.
As the battery fully charges the supply current dwindles to a trickle.

rgds, sreten.
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Last edited by sreten; 12th December 2011 at 06:48 PM.
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Old 12th December 2011, 06:46 PM   #6
Mooly is online now Mooly  United Kingdom
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Is your charger specifically for SLA batteries ? By that I mean one that "bulk" charges and then switches to a lower "maintenance" charge.

If so, then as drawn it should work fine.

When the amp is turned on the fully charged SLA voltage will fall from around 13.8 volts to around 13 or less pretty much instantly instantly. The charger will detect this as a battery that needs charging and will attempt to put 13.8 or slightly higher across the battery. If the amp draws little current then the charger will be able to increase the voltage across the battery maybe to as high as 15 volts. If the amp draws current above what the charger can supply then the battery voltage will fall again (which is OK) and the charger will be supplying it's maximum output into the amp/battery combination.

Points to watch. It must be a purpose designed SLA charger and NOT just a transformer and rectifier.

The charger must be able to cope with delivering its full output continuosly.
A situation could occur if the amp pulled the battery voltage down (discharging the battery by playing loud for hours) below say 11 volts which might increase dissipation in the charger as that would be trying to charge a battery that (while the amp was on) could never be brought back up to 13.8 volts with the current available from the charger.
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Old 12th December 2011, 06:59 PM   #7
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Yes, the charger is designed for SLA batteries. Specifically it's a Battery Tender Junior.

I'm not actually planning to use the amp while charging for the most part, I'll just probably forget to turn the power switch off every once in a while, in which case the amp won't be amplifying and so should be drawing very little power. Sounds like I'm good to go as drawn. Thanks!
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Old 12th December 2011, 08:15 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

FWIW an SLA battery charger is very simple, its basically a current
limited 14V DC regulator, simply that, and nothing more much. It
will automatically drop voltage in current mode, and trickle charge.

Most do not use a higher voltage to maintain the charging current,
the current simply tapers off to the trickle level towards full charge.

rgds, sreten.
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Last edited by sreten; 12th December 2011 at 08:25 PM.
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Old 13th December 2011, 06:22 AM   #9
Mooly is online now Mooly  United Kingdom
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This is worth a read,
Attached Files
File Type: zip Little Red Book Of Batteries.zip (745.5 KB, 84 views)
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Old 13th May 2013, 04:53 PM   #10
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puje avoir le schema electrique de l'ampli
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