Hi,
I'm planning to use an audio amp that accepts 5-12v DC and hook it up to a 12v sealed lead acid battery. Will the amp keep sucking power until it hits its drop out voltage (5v), which will then in theory ruin the sealed lead acid battery because it's only supposed to be drained to (I believe) 11.5v?
Amp
Battery
Thanks for the help!
Yes.
Amps designed to be used in cars typically have a voltage cutoff on top of the fact that the remote signal turn on wire works as a cutoff itself.
If your amp isn't car specific, it won't cutoff on its own.
How long do you need it to work unattended?
Pete
Thanks everyone. Do you know of a way to turn off the amp once it reaches the bottom limit of the battery?
Pete- I want it to operate as long as possible without killing the battery.
INTP- This won't be in a car, just a standalone amp on a battery.
Do you know of a way to turn off the amp once it reaches the bottom limit of the battery?
Use an Arduino to measure the voltage and a mosfet to turn everything off when it reaches 10 volts.
There are many ways of implementing a battery cutoff. Most would involve measuring the battery voltage and if it drops too low, shut off the power.
Google "battery cutoff circuit"
I don't see any detailed specs or graphs, but the datasheet for the "general purpose" version says:[/quote]50 - 150 cycles at 100% discharge....
...Will achieve more life cycles than standard AGM and Deep Cycle batteries.[/quote]
Your amplifier may not turn-off (at least not completely off) at low voltage. When the voltage drops you won't get maximum power out of it so it might distort. It won't shut-off completely unless there's a relay or maybe a MOSFET or some other special shut-off circuit.
It will consume less power when it's putting-out less power (when the volume is turned-down or it's silent).
...And, the battery will eventually self-discharge even with nothing connected.
Or for the non Arduino option
Have one and it works well.
There are other fancier one but this does the job.
Best to set it for 11.5v, lower and some batteries die real fast.
Best to check the D.O.D. Depth of Discharge for your battery.
E.g. car battery is around 10% and deep cycle, 60%, lithium at100%
Daz
A lead/acid battery is ok for backup, but not the best choice to charge/discharge often.
Note that the danger zone of <60% charge is already reached with a battery voltage of ~12.5volt.
Cutting the battery at 11.5volt could have discharged it to a <10% level, and it will die if you do that often.
Lithium seems far better for this project.
Leo..
You'll be fine, it's just a 20W amp. You can run it for 4 hours or so. Get a good charger.
I've pushed SLA batteries down to -2V with no immediate damage to the battery. That is a very long way from +11.5.
If you are running thousands of these batteries in some kind of business then you probably are concerned about the reliability and cost of battery replacements.
For just playing some tunes at a beach party, who cares if the battery reliability is affected?
Some thoughts and clarifications about SLA batteries to consider.
Sealed Lead Acid batteries typically come in two distinct "types"
AGM (Absorbent Glass Mat), which utilise a fiberglass mat laid between the plates to act as a wick and maintain constant electrolyte contact with the plates. AGM batteries are better for high current short duration discharges and are commonly used in standby applications (UPS, Security alarms etc)
They are normally cheaper than Gel
Gel batteries mix the electrolyte with a Silica Gel to suspend the electrolyte throughout the battery maintaining contact with the plates. Gel batteries are normally better suited to lower current longer discharge applications, when correctly specified they suit Deep Cycle applications like Solar or electric vehicles etc.
The Duracell documentation by the OP refers to both technologies in the same low cost battery which seems contradictory?
Capacity/Discharge rate:
The Dura12-9F2 listed as a 12 volt 9ah (Amp Hour) Battery with F2 Spade terminal configuration. Capacity is at the 20 Hour rate (C20)
9ah at 20hrs, contrary to apparent public opinion does NOT mean it will run 9 amps for 20 hours, or 9 amps for 1 hour or in fact 1 amp for 9 hours.
It means it will deliver a total of 9 amps over a 20 hour period to an end voltage of ?? (this end voltage should be specified but is most likely to be 1.8Volts Per Cell), which is 450 ma per hour.
Simple maths tells us that 450ma x 12vdc (nominal voltage) = 5.4 watts for 20 hours.
Without discharge curves from the manufacturer it is difficult to assess actual runtime, however looking at similar General Purpose AGM SLA batteries would suggest approximately 1 hour at 20w per channel (without considering any other losses) and 3 hours at 10w per channel.
Cycle life, Depth of discharge/end voltage and Design life.
Cycle life is simply defined as the number of cycles to a specified end voltage, at a defined temperature, with a defined temperature controlled recharge rate. The reason Duracell list such a large range is possibly because they have not defined any of these parameters.
Depth of Discharge is a little more complex, 100% DoD is NOT zero VPC it is when the battery has discharged to a design end voltage.
As an example small UPS's typically discharge to 1.70VPC (10.2 volts at 12 volt nominal) but may go as low as 1.6VPC
End voltage is the voltage that the system should disconnect from the load to either prevent damage to the load or the battery.
Design life is more relevant to larger batteries and systems and again is tied to the operating parameters and duty cycle of the system.
The Duracell battery selected by the OP is designated as General Purpose and will run the sound system but won't last too many seasons.
My strong advice to any SLA battery user is to use a battery charger designed for SLA's, they are very voltage sensitive, leave the battery on float charge at about 2.25 - 2.6VPC @ no more than 25 degrees Celsius
This link is for a battery company that supplies more information regarding the battery design, this is the sort of information needed to design a commercial battery system.
https://checkout.na3.netsuite.com/c.ACCT90786/site/downloadlibrary/HZS.pdf.
Thanks everyone.
I bought one of these to cut off the battery at a set voltage, thanks for the recommendation Daz.
Kiwi_Bloke, amazing info, thank you. For more background info, I have a small UPS that I'll be borrowing the battery from when I want to play the amp at BBQs. After each session I'll plug it back into the UPS. I'll use it once or twice a month during the summer. I'll set the battery cut off device to 10.2 volts per your message, unless you recommend higher.
Since this is for a low current long run time project rather than high current short run time, should I buy a different battery and a separate charger? Would I get much more play time out of it? If not, I may just go the cheap/easy route and stick with my original plan.
Hi bryanz,
Try before you buy is always a good idea.
In ref to the UPS battery, from pratical experience the batteries in them usualy only last for 3 to 4 cycles of power outage.
This is due to how far the are discharged, the usually enormous discharge amperage and the fact that the sit around alot.
I tend to find the batteries DOD of 10%, 60% or what ever the manufactures recomend is 12v at anything below that causes damage be it 0.1% or higher and most use 10.5 volts as the 100% discharged point.
This all varies depending on the manufacture (as mentioned rightly by "kiwi_bloke") but the above are a good rule of thumb for the good old lead acid.
Every cycle of a battery brings it one step closer to death, so is the life of a chemical battery.
Best way to work it out in the real world is try it. With the voltage cutout try it at 12v, 11.5v and 10.5v and see how long the radio goes.
Street buskers i see are usually running a 12 lead acid on their amps and run it all day (most seem to have an old car battery or a SLA).
Few words of caution!
Check that the UPS is not running batteries in series or when you put it back in you will have an unbalanced set because the UPS charges inseries.
Eg. 24v UPS charges at 24v across the 2 12v batteries so if one is at 12 and the other is at 10v then the end result after charging could be one at 13 and one at 11.
Also remember (although sealed) seawater in contact with lead acid on the batteries produces a nasty gas (chlorine (disputed by some)) but definitely produces corrosion so be careful putting it back in the UPS.
Daz.
bryanz:
For more background info, I have a small UPS that I'll be borrowing the battery from when I want to play the amp at BBQs. After each session I'll plug it back into the UPS. I'll use it once or twice a month during the summer. I'll set the battery cut off device to 10.2 volts per your message, unless you recommend higher.
Given the very low usage I would follow Daz'z advise and do some testing, but take into consideration the very low recharge current available from the UPS. I would recommend allowing at least 4 - 5 days back in the UPS to recharge the battery between uses.
bryanz:
Since this is for a low current long run time project rather than high current short run time, should I buy a different battery and a separate charger? Would I get much more play time out of it? If not, I may just go the cheap/easy route and stick with my original plan.
If you were using it every day of every weekend I would look at a good deep cycle Gel option, but for your usage? No, just be aware that the battery will probably only last the summer.
Daz1712:
Also remember (although sealed) seawater in contact with lead acid on the batteries produces a nasty gas (chlorine (disputed by some)) but definitely produces corrosion so be careful putting it back in the UPS.Daz.
I can't comment on Seawater + Battery acid = Chlorine, I am not a chemist, however I have sold a number of low voltage, high current rectifiers for the production of Chlorine gas for water purification.
Industrial water treatment plants bought our 10 - 15 volt, 5 - 10,000 amp rectifiers to release Chlorine (or Hydrogen) gas from Brine.
I personally doubt even emptying the battery into the ocean would cause any issues except localised pollution, but don't try it please.