Thread: Getting high current 12v from 24v systems

Half tapping a 24 volt system, as you have mentioned is the best way to kill a battery - particulally if there is large current draw involved.

Why wouldn't you use a 24 to 12 volt converter? They produce a stable 13.6 volts on the output, and are readily available and you can get them in high current versions.

How much current are we talking about here - I used a couple of 40 amp units last week to run the electric legs on a semi trailer where we only had a 24 volt system on the genset that is on the trailer - we were half tapping the 24 volt system for about a year, and killed 2 - N200 batteries in the process. The converters are working fine - can't seem why they wouldn't work for a sound system - even a 'few hundred watt' unit as you have described would only draw 20 or 30 amps, and if it is a real thumper, you can buy much bigger units than 40 amp, and they aren't that expensive - less than a couple of replacement batteries.

Edit - these are the units I used the other week - 24- 12V DC-DC Converter 40A - Jaycar Electronics

If your after something bigger - DC/DC Converters, to convert voltage up or down, retail, wholesale, off-the-shelf and custom, DC/DC 5 watts to 1500 watts, voltage from 1.5V to 72V, DC/DC power supplies

Still not big enough? You can parallel several identical converters if you set the output voltages on them correctly - most have voltage trim pots. Check out this - Paralleling DC-DC Converter Outputs write up on how to properly set up and load share multiple units.

If that still isn't big enough, you just about have a set up that Cold Chisel could use live to entertain 10,000 people, and there is no way the buses alternator would keep up with a system like this.

Cheers - Gav

depending on your definition of high current and what you want to do with it.

a DC-DC converter is the way to go for upto 40ish amps. which is more than enough for your average sound system.

over that you're better off with a dedicated 12 V battery and a 24-12v battery charger which is the way I setup for car fridges in trucks

Thanks Dave, I did'nt realize the bigger ones were so reasonably priced. (Have been out of hobby Electronics for years now, so I've lost touch)

The only reason I can see for the divided battery approach is cheapness on the install. Or laziness.
One hopes that 'Incompetance' does'nt make the short-list...

I've passed on all the info to one of the bus operators, who is well into the second set of batteries in 12 months...


cheers!

urmmm, why not just buy 24v sound gear...

really the best solution by far if you want stupid levels of sound power from 12v off the shelf systems is to mount up a second alternator and set that up as 12v

40A@13.8v is only 552W by the time you fudge that down to audio realistically you're only going to be getting 400w effective worth out of your speakers....

oh and sorry, its lazyness and incompetence all in one.

Hi superquag, I deal with a company that specialises in this sort of set up.

The equip large motor homes, enormous horse floats and luxury yachts and I was talking to the owner this afternoon and mentioned what you were trying to do.

He has already done a few of these Party Buses and he has seen them need as much as a few thousand watts at 12v derived from the vehicle’s 24v system.

His suggestion was to fit 2 x 200 amp 6v batteries and run a 24 to 12 BATTERY TO BATTERY CHARGER, not a 13.8v power supply.

Where possible make sure the batteries are fully charged before the bus starts it’s nightly run and then the battery to battery charger helps to keep power going into the two 6v batteries while they supply the power as and when it’s needed.

The Battery to Battery charge he has is 40 amps input from the 24v and the 12v out put will vary depending on the draw from the 12v battery ( 2 x 6v ) but it’s able to produce a lot more than the 24v 40 amp input.

G'day Drive,

I'm not trying to do anything, apart from staying FAR away from the Noise....
It was just general conversation between a couple of bored bus-drivers, triggered when he started his bus and ran it for half an hour or so. - Then the story came out as to 'how' it was all hooked up. Not only his, but others he knows of...

My own thoughts, - apart from being a cheap & cheerful short-term solution, is to work on the basis that a battery is a storage device, to warehouse lots of Amperes and dump them out when needed. Generally a bucketload every o.6 seconds...

So yes, running a bank of ginormous A/h 12v batteries fed by an equally giant 24 to 12v charger sounds (sorry, pun just slipped in...) like the easiest way to go.

The last pair of batteries set him back over $400, so he mumbled...

On the bright side (Lasers, actually) his clients are not over-fussed about 'quality', only 'quantity' of noise.
Will be interesting to see what he does with the info.

I'm quite happy with schools and general daytime charter work...

for the cost of 2 sets of batteries he could have set up twin alternators.

Received a phone call this morning from a REDARC Techie.

I'd queried as to whether their 24/12 chargers' auto sensing circuitry would get confused when charging AND having the sound system operate at the same time. (Charger would see a rapidly varying load in time with the Booms...)
- Answer was 'no'. All would be well. Plus, he endorsed the idea of a 12v battery being fed with one of their 40 AMP chargers.

His suggestion was a nice big 12v battery, and the BCDC 1240 charger. RRP of $695.. Looks like overkill, but you get what you pay for, and in this case that includes a MPPT for a solar array !
- Add a panel or two on the bus roof....and you'd never run out of 'noise'.

"...for the cost of 2 sets of batteries he could have set up twin alternators...." - They're businessmen, - not LR owners, so they don't think laterally like us.. .besides, that means farming the work out to ??? at $? - Easier to go 'off the shelf'.

So there we have it.