Hello! I have a battery powered speaker system (Carvin s600b). It is powered by an internal 12v battery. If you are running out of battery during a gig, this amp has a handy feature where you can power/charge the unit via an external 12v battery pack, it has a little input jack where you plug in the battery pack (see pic)

I'm wondering if it would be possible to power/charge the unit for a short period of time using 8 AA batteries (8AA = 12v). I have a 8AA battery carriage and the right plug which I could solder on. To the left of the little plug it reads "CHARGE - 12VDC - 2A" My question is, how does the '2A' relate to things in this situation. I know it mean '2 Amps' but does this have an effect on whether I will be able to use the AA batts? Does it give me the right info to calculate how long the AA batts will last? Would love it if someone could chime in here. Big thanks!

 

Welcome to AAC!

It would be helpful if you specified the battery chemistries and amp hour (Ah) capacities involved; and current draw by the speaker.

IMO, charging a 12V battery from AA batteries is pointless. You have to put 8 in series (more if they're rechargeable) to get 12V; to charge a 12V battery, you need more like 14V.

 

to charge a 12V battery, you need more like 14V.

Yes. To charge a battery you need more voltage than the battery being charged. Assume for a minute that your 12 volt battery has dropped down to 10.5 volts (certainly a dead battery). Putting another 12 volt battery on it WILL raise the voltage to some degree, but again for the sake of argument lets assume you're charging a 12 volt battery from another 12 volt battery of the same exact specs. One battery is sitting at 10.5 volts and the other (for this exercise) is at 12 volts. The two will average each other out so that you get 11.25 volts of charge. And that's in a perfect world. In the real world if you were to do this, the closer to the 11.25 volts the charged battery would get the slower the rate of charge. So it would take an extremely long time to charge the discharged battery to 11.25 volts. Not practical by any means.

Now, lets assume your battery that drives your system is a 12 volt 20 AH battery. That's 20 amps per hour at 12 volts. In other words 20 amps for one hour. OR 1 amp for 20 hours. Or any combination there between. And lets assume your system is using 5 AH (amps per hour). In theory your system should run for four hours on that battery starting from a full charge. If you use a dozen AA batteries that can deliver 2 AH, part of that energy will try to go to the battery being recharged while the rest goes to the system. And the system isn't going to like running on 2 amps when it needs 5.

What you CAN do is get a secondary 12 volt battery of same or greater capacity and set it up as a backup so that when the primary battery is too weak to run the system you can plug in a secondary battery. Use a plug that will disconnect the primary battery and power the system from the secondary. When your "Gig" is done you can recharge both batteries. But I wouldn't go with charging a 12 volt battery with 12 volts of AA batteries. But imagine if that were possible. I'd keep a few AA batteries in my car and disconnect the alternator so I could get better gas mileage. But again in the real world that just can't work.

 

It's better to run the system directly from the external batteries rather than trying to charge the internal battery, since that wastes energy.
But AA's won't last long. Better to go with 8 D-cells.

 

With the amp battery dead, plug in an external 12v supply and start playing some music. Measure the actual current drawn by the device through the 12v plug. Compare that against the capacity for typical AA batteries. The higher the current draw, the less total usable power you're going to get from the batteries. For example for a typical Energizer alkaline battery at 25mA draw you get 3AH. At 500mA draw you get less than 2AH. See the data sheets linked below. Your batteries will be in series, so the total AH capacity will be equivalent to 1 battery. This calculation would give you a best case. The voltage will surely drop while the batteries are discharging, so you have to consider if your device will keep running as the batteries deplete. I'm guessing you're better off buying a larger rechargeable battery to plug in.

http://data.energizer.com/PDFs/E91.pdf
http://data.energizer.com/searchresult.aspx

 

Better to go with 8 D-cells.

We still don't know the system requirements. All we KNOW is that the internal battery needs to be charged at 2 amps. That doesn't necessarily mean that the system runs on 2 amps. Could very well be. But we don't know that.

Personally I'd opt for a 12 volt SLA battery (SLA = Sealed Lead Acid) and run that as an alternate battery and NOT try to charge one from the other. Doing so will only result in two batteries under powered. Even if you put a car battery on it the charging results won't be favorable.

 

A 20 AH SLA will provide 20AMPS to a load for about 1/2 hour before full discharge

A 20AH SLA will provide 1 AMP to a load for 20 hours before full discharge.

Amp Hour ratings for SLA batteries are based upon discharge over 20 hours. 0.05C

 

I am going to guess that your amp uses a 12V 7-12Ah SLAB, something like this one:



Your best bet would be to carry around a spare 12V sealed lead acid battery. (Even a 12V car battery will work.)

Get a plug that fits into the 12VDC charging jack on the back of the amp. Feed the spare backup voltage into the 12VDC charging jack, making sure that you get the polarity right. You may want to put a 2 to 5A fuse on the charging cable that you create, just for safety.

 

To charge a battery you need more voltage than the battery being charged. Assume for a minute that your 12 volt battery has dropped down to 10.5 volts (certainly a dead battery). Putting another 12 volt battery on it WILL raise the voltage to some degree,

The charging jack is labelled 12V 2A. That seems to imply that it will charge with 12V and 2A. If the battery is indeed a 12V battery, they probably have a boost converter internal.

Bob

 

The charging jack is labelled 12V 2A. That seems to imply that it will charge with 12V and 2A. If the battery is indeed a 12V battery, they probably have a boost converter internal.

Bob

I don't think so. Usually, the amplifier is supplied with a charging adapter. The adapter would be labeled as 12VDC output but most likely puts out 15VDC.

 

That seems to imply

"Imply" being the key word. Truth is - we don't KNOW anything beyond what little we've been told.

You charge a 12 volt battery with a 12 volt charger. Not a 12 volt source.

The adapter would be labeled as 12VDC output but most likely puts out 15VDC.

This I would agree with 100%.

 

Hello! I have a battery powered speaker system (Carvin s600b). It is powered by an internal 12v battery. If you are running out of battery during a gig, this amp has a handy feature where you can power/charge the unit via an external 12v battery pack, it has a little input jack where you plug in the battery pack (see pic)

I'm wondering if it would be possible to power/charge the unit for a short period of time using 8 AA batteries (8AA = 12v). I have a 8AA battery carriage and the right plug which I could solder on. To the left of the little plug it reads "CHARGE - 12VDC - 2A" My question is, how does the '2A' relate to things in this situation. I know it mean '2 Amps' but does this have an effect on whether I will be able to use the AA batts? Does it give me the right info to calculate how long the AA batts will last? Would love it if someone could chime in here. Big thanks!

I would say if it needs 12V to charge it, then it will be a 7.5 to 9V battery, best to take the cover off and look at the battery type.

 

I would say if

Again, we don't know.

 

Now, lets assume your battery that drives your system is a 12 volt 20 AH battery. That's 20 amps per hour at 12 volts.

What the heck is an "amp per hour"?

Ah = amps · hours

which is NOT the same as amps / hours

BTW: AH would be amperes times henries.

In other words 20 amps for one hour. OR 1 amp for 20 hours. Or any combination there between.

Only combinations there between?

So 40 A for 1/2 hour or 0.1 A for 200 hours aren't possibilities?

An amp-hour is merely a unit of charge (3600 coulombs, to be precise). In theory, a 20 Ah battery has the ability to provide a total of 72 kC of charge as it goes from fully charged to fully depleted -- although what constitutes "fully depleted" is a matter of definition since there isn't some instantaneous transition that occurs. The faster you draw the charge out, the less time it will take to deplete it.

In reality the actual amount of current a battery can supply before being considered "depleted" is a factor of many things. One of those is the rate at which the charge is withdrawn. In general, the higher the current draw, the lower the total amount of charge that the battery can produce.

In addition, there is an upper limit on the current that a battery can deliver, even with brand new and completely charged.

As you point out, trying to use 8 AA batteries to charge the amplifier's internal 12 V rechargeable is almost certainly a fool's errand. The nominal capacity of a typical AA alkaline is about 2000 mAh to 2500 mAh. But that is at a low current draw (somewhere around 25 mA). As current draw goes up, that goes down considerably. At 0.5 A (which is considered a "heavy load") the available capacity is about half of that. At 2 A, the capacity is probably well below 1 Ah and possibly below 0.5 mAh. Plus, as the internal resistance rises as the battery drains, it probably won't take long before a AA couldn't deliver 2 A of current, even into a dead short.

And all of this is using a cutoff voltage of 0.8 V, so those 8 batteries in series will be down to 6.4 V. Unless there is a built in DC-DC converter in that amplifier, any charging will stop LONG before then. But let's say that it does have a 100% efficient DC-DC converter, you'd probably be lucky to get more than 15 minutes of use out of them and very possibly considerably less.

 

OUCH. OK, I have the wrong understanding of it. 20 AH is 20 amps for one hour? 20 x 1 = 20? Or 1 amp for 20 hours; 1 x 20 = 20? 2 amps per hour on a 20 amp battery wouldn't equal 10 hours of service? Well, I don't claim to be the smartest whip. Maybe even as sharp as a fuzzy tennis ball, but that's the way I've always understood AH from high school. Maybe I misunderstood something.

And why you gotta bring Henry into this? Isn't Henry something to do with coils?

I can be wrong. I can admit it when I am. Still not sure I am, but if so - - - .

 

OUCH. OK, I have the wrong understanding of it. 20 AH is 20 amps for one hour? 20 x 1 = 20? Or 1 amp for 20 hours; 1 x 20 = 20?

20 A · 1 h = 20 Ah

1 A · 20 h = 20 Ah

2000 A · 0.01 h = 20 Ah

2 mA · 10,000 h = 20 Ah

Notice the multiplication involved. amps TIMES hours yields A·h or Ah.

2 amps per hour on a 20 amp battery wouldn't equal 10 hours of service?

Again, what is "amps PER hour"?

Answer: "amps per hour" is a rate at which a current is changing.

For instance, let's say that you had a current that was steady at 100 A and then over the course of the next six minutes increased steadily to 102 A and then stabilized at that level. During that six minutes, the current was changing at (102 A - 100 A) / 0.1 h = 20 A/h, or 20 amps per hour.

One place where you see current per unit time is with inductors.

V = L (di/dt)

Notice that the units on (di/dt) are current per unit time, or amps PER hour.

With a battery we are talking about charge, which is related to current by

I = dq/dt

or

Q = ∫I·dt

Notice here the units are current TIMES time, or amps TIMES hours.

I think you are thinking of this as "amps FOR AN hour", but this is NOT the same as "amps PER hour". The "FOR AN" translates to multiplication while "PER" translates to division.

And why you gotta bring Henry into this? Isn't Henry something to do with coils?

I'm not the one bringing henries into it. YOU are when you use a unit of AH. A capital 'A' is the symbol for amperes. A capital 'H' is the symbol of henries. The symbol for hours is 'h'.

 

I don't think so. Usually, the amplifier is supplied with a charging adapter. The adapter would be labeled as 12VDC output but most likely puts out 15VDC.

In other words, I assume the manufacturer has labelled the power jack correctly, and you assume he has labeled it incorrectly.

I agree that a wall wart might be labelled 12V at 2A, and read 15V open circuit, but that label is still correct because it is an unregulated supply that will be at 12V when it is supplying 2A.

Bob

 

In other words, I assume the manufacturer has labelled the power jack correctly, and you assume he has labeled it incorrectly.

I agree that a wall wart might be labelled 12V at 2A, and read 15V open circuit, but that label is still correct because it is an unregulated supply that will be at 12V when it is supplying 2A.

Bob

I now see that the Carvin S600B comes with an AC power connector and will internally charge the 12V battery (appears to be 7Ah) from AC mains power. Carvin supplies a 12V adapter cable that is intended to be plugged into the 12V automotive charging system (even though the auto charging voltage greater is than 14V).

I have not said that the manufacturer has labeled it incorrectly. That is the your way of interpreting it.

 

See DISCHARGE Page 8.

http://www.power-sonic.com/images/powersonic/technical/1277751263_20100627-TechManual-Lo.pdf

 

I think you are thinking of this as "amps FOR AN hour"

Yeah, that's what I was thinking. But thanks for taking the time to explain it more fully. It's going to take a while for me to get my fuzzy head around all the math.

And my reference to Henry was meant jokingly. "What's Henry got to do with it? He never did anything to me." Guess it was a failed joke.