Battery Powered Announcement System

[p.k.roberts]

A bit outside my normal area this, but I've been asked to assemble a portable PA/Announcement system (think 'Adastra' mixer-amp and horns) but all of the amps and other bits I'm looking at require an external 24V supply. Rather than use a pair of 12V batteries (plus two spares), I'm considering the advantages/disadvantages of using a DC to DC converter (e.g. https://www.rapidonline.com/voltcraft-12-10-240w-in-car-charger-dc-dc-converter-24vdc-10a-55-5352) along with a single, beefier battery; reasoning this is more or less cost neutral (2 batteries instead of 4), lighter to carry and easier to charge.

Seems logical to me, but I'm sure it can't be that simple - what have I missed?

[adam2]

A DC to DC converter adds an extra point of failure, and also adds losses and increases the total power demand slightly.

Some types may also add interference noise as they are a type of switched mode power supply.

 

A lot depends on how much power is required.

A single 7AH battery will be cheaper than a pair of 3,5 AH batteries.

 

A pair of 60 AH batteries or a single 120 AH battery will cost about the same. Actual prices vary a lot. What have you got already ? What will be most useful for other purposes ? In particular note that 12 volt 7 AH batteries are hugely popular and often much cheaper per AH than other sizes.

A pair of 7 AH batteries will usually be a lot cheaper than a single 17 AH battery.

[Brian]

How much power, in total, do you need and for how long?

[sunray]

How much power, in total, do you need and for how long?

And do you really need as much power as you think you do?

 

Anyway back to your question NO do not attempt the electronic version. Stick with 2 batteries for various reasons

Always try to reduce current, not increase

 

The single battery will very likely need to be more than double the capacity to cope with the potential higher discharge rate.

As batteries go flat, say to 10 volts the converter will be attempting to pull massive currents and stall/falter, whereas the amplifier may still be functioning (albeit at less than optimum performance) at 20V.

Realistically the weight difference between 2x 60AH and 1x 120AH plus converter is minimal and less fiddly.

 

Edited April 28, 2021 by sunray

[p.k.roberts]

How much power, in total, do you need and for how long?

 

I'm looking at a 60-100W (claimed output) amplifier in very intermittent use for about 8 hours; so it's basically whatever the quiescent current is with an occasional peak; so a low capacity 'leisure battery' should, I think, cover this. I realise that the converter adds an element of electronic complication, but the users of this system are likely to be not very technical, so the process of charging/replacing a single battery is, in this instance, likely to make it a lot more user friendly.

[Brian]

I'm looking at a 60-100W (claimed output) amplifier in very intermittent use for about 8 hours;...

 

 

So if you were feeding tone, at full power, and if the amp produced the claimed power, you would consume 800Whrs. So 33Ahrs at 24V. Given it's a system for occasional speech use I'd reckon that a figure closer to one tenth of that would be more realistic. I wonder what the quiescent consumption is?

[p.k.roberts]

I'm looking at a 60-100W (claimed output) amplifier in very intermittent use for about 8 hours;...

 

 

So if you were feeding tone, at full power, and if the amp produced the claimed power, you would consume 800Whrs. So 33Ahrs at 24V. Given it's a system for occasional speech use I'd reckon that a figure closer to one tenth of that would be more realistic. I wonder what the quiescent consumption is?

 

That's kind of roughly what I was thinking - this one of those 'friend of a friend' jobs which, in retrospect, I sort of wish I wasn't involved with - I won't really know what the quiescent current is until the thing is bought - but hopefully with modern design it won't be too high. I think, given the advice, I'm leaning toward a couple of 12V gel cells in series and a 24V charger - I'm assuming that they will pretty much self-balance. Sadly that means something else to box-up!

[sunray]

I'm looking at a 60-100W (claimed output) amplifier in very intermittent use for about 8 hours;...

 

 

So if you were feeding tone, at full power, and if the amp produced the claimed power, you would consume 800Whrs. So 33Ahrs at 24V. Given it's a system for occasional speech use I'd reckon that a figure closer to one tenth of that would be more realistic. I wonder what the quiescent consumption is?

 

That's kind of roughly what I was thinking - this one of those 'friend of a friend' jobs which, in retrospect, I sort of wish I wasn't involved with - I won't really know what the quiescent current is until the thing is bought - but hopefully with modern design it won't be too high. I think, given the advice, I'm leaning toward a couple of 12V gel cells in series and a 24V charger - I'm assuming that they will pretty much self-balance. Sadly that means something else to box-up!

Or you could get a 60W amp which runs on 12V. the first google hit: https://www.gear4music.com/Home-Audio/Clever-Acoustics-MA-260-60W-Mixer-Amplifier/330U?origin=product-ads&gclid=Cj0KCQjw1a6EBhC0ARIsAOiTkrFSbTg8ShpZWPSU2tHnTyyt9whkdj-wtQ2-a-SIbfy2VSRSY3tKZIIaArsoEALw_wcB

Never underestimate the battery requirement, no matter what they claim the use will be, always allow for more. One of the school sports days I've done for years with a pair of 12AH gel batteries and 120W amp with total success for 4 hrs, suddenly went flat one year and the following year same thing happened with a pair of brand new batteries. It turned out they'd started playing music through it almost constantly.

The claimed current on these sort of amps will usually be about double expected so 10A@12V for 60W my battery target will always be at least 25% so 2.5A x8Hrs =20Ah. The Toa 512 (24V) runs about 0.75A quiescent (I imagine more modern versions are more efficient but not checked) 0.75Ax 8 =6Ah Total 26Ah. If it really is just an ocassional few words a 17Ah will probably suffice but just leaving the mic open will make a significant difference.

 

[sandall]

I started using a car battery with 12V amps many years ago, & have never thought of using anything else - the battery charge always outlast the gigs by a wide margin. The only problems come when nobody has noticed that the amp is now in full sun, & too hot to touch.

[sunray]

I started using a car battery with 12V amps many years ago, & have never thought of using anything else - the battery charge always outlast the gigs by a wide margin. The only problems come when nobody has noticed that the amp is now in full sun, & too hot to touch.

Yes too hot... I had one where the microphone cable laid over the amp and the outer shealth melted on the black surface.

I've used car batteries since 1977 and to date never had any go flat on me, at one point I had 16, mostly 95Ah. on manned jobs I like to take 100% spares and 4 jobs at 24V= 8 plus 8 spare.

Historically I've done a decent number of very short jobs such as remembrance service, road openings and similar where I have to manhandle kit to location and a couple of 7Ah gels plus a 2Ah for radio mic is perfectly adequate and a fraction of the weight and size. That equates to an ali tool box containing batteries mic/radio mic, all connecting cables/speaker cables, media player, tools etc. Then amp, horns, tripods, mic stand amounts to 2 trips carrying or one trip with sack barrow.

 

The school sports job went past a RA and they would not accept wet batteries so I did a couple of test runs and established a pair of 12Ah gels would be OK, and it was until they started playing music.

It never ceases to amaze me how long a 2Ah gel will run an S4.4 radio mic receiver, I've had 10am Friday to 5pm Sunday several times - 55hours

[electronicsuk]

If you're not set on horns and quality isn't a major issue, how about a couple of the self-contained 10 or 12" plastic cabs that buskers tend to use? I've got a few QTX QR12PA's in my stock and they're fine for vocal announcements, battery and radio mic receiver is all internal to the cab. The receivers are all tuned to the same frequency and if you're sensible about positioning relative to the mic then you should easily be able to get 50m separation between a pair of boxes. I suppose if you wanted to spend a bit more money then you could buy something like one of the MiPro systems, but the QTX stuff is almost disposable so it doesn't matter if, for example, it gets left out in the rain.

[sunray]

If you're not set on horns and quality isn't a major issue, how about a couple of the self-contained 10 or 12" plastic cabs that buskers tend to use? I've got a few QTX QR12PA's in my stock and they're fine for vocal announcements, battery and radio mic receiver is all internal to the cab. The receivers are all tuned to the same frequency and if you're sensible about positioning relative to the mic then you should easily be able to get 50m separation between a pair of boxes. I suppose if you wanted to spend a bit more money then you could buy something like one of the MiPro systems, but the QTX stuff is almost disposable so it doesn't matter if, for example, it gets left out in the rain.

I used to have a couple of the 8" version but with a different badge and TBH I found the radio mic range was nowhere near 50m, in fact if it was not absolute line of sight I'd say it was down to 10m. The radio mic systen is common across the range so I'd expect the same performance but otherwise I'll describe the 8" with the silly gimmicky leds (which I disconnected) etc as a toy compared with the bigger units. Having said that I've had no working experience of them.

 

 

Without knowing more about the required use and coverage area etc of OP, I'll avoid offering advice over and above that requested for the current proposal.

 

 

EDIT: I've read your post again and realise you're suggesting 25m range, not 50m.

 

Edited May 3, 2021 by sunray

[sunray]

I've got a few QTX QR12PA's in my stock and they're fine for vocal announcements, ... but the QTX stuff is almost disposable so it doesn't matter if, for example, it gets left out in the rain.

Dec 2019 We went to christmas market in Edinburgh and the whole complex was covered by a lot of those, running on mains and linked by XLR cables(and running far too loud) one day it poured down and I was surprised they made no attempt to cover/protect them, you've probably explained that now. Edited May 4, 2021 by sunray

[electronicsuk]

Dec 2019 We went to christmas market in Edinburgh and the whole complex was covered by a lot of those, running on mains and linked by XLR cables(and running far too loud) one day it poured down and I was surprised they made no attempt to cover/protect them, you've probably explained that now.

 

Just for the record, nothing to do with me! I can't say I approve much of the idea of running them on mains without making any effort to waterproof them. I'm not sure why anyone would do it this way when the passive version of the same cab is about half the price and would be a lot safer in the rain.

[sunray]

Dec 2019 We went to christmas market in Edinburgh and the whole complex was covered by a lot of those, running on mains and linked by XLR cables(and running far too loud) one day it poured down and I was surprised they made no attempt to cover/protect them, you've probably explained that now.

 

Just for the record, nothing to do with me! I can't say I approve much of the idea of running them on mains without making any effort to waterproof them. I'm not sure why anyone would do it this way when the passive version of the same cab is about half the price and would be a lot safer in the rain.

Total agreement, however using powered speakers makes it very easy to control the volume at each location. Secondly I find it almost impossible to convince people not accustomed to using 100V lines that it works for music quality.