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Old 10th July 2009, 08:24 PM   #1
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Default I need to battery power F4, F5's... Ideas?

I know that this may sound like a strange question, but...


Is there a way to power a F4 or F5 by way of batteries? Is there a way to split 48VDC into +/-24VDC for the power supply? I have no problem coming up with 48VDC or even higher. It may sound better or worse if at all possible. Some big caps is the PS and skip the rectifiers. Is this possible?

Most of you will be asking why? Simple, the land I am buying is a fair distance from the grid and it will cost a fortune for a line in and I will not use a generator. I will be using solar, therno-electric, and micro-hydro, to power the house. I am building a 12V TEC fridge/hot water heater, cold side fridge and the hot side to a water tank. I may build a DIY projector to run on 12v with LED as a light source. All other electric appliances are 12V or 24V with the exception of:

-HTPC media server
-FirstWatt amps
-Soldering iron 110V (need 220v)

The PC is easy. I would power the PC with a DC-DC smps and the Julia with a seperate battery. The soldering iron will need an inverter. I will use this inverter for guests gadgets and inevitable AC needs. However, I would like to keep it small and not have the need for the FW to be driven off it. It must be a relatively cheap solution otherwise I will just buy a big inverter or scrap the FW amps and build a set of chip amps for 12v-24v DC battery. All suggestion are welcome and if you have any wild and crazy ideas, I want them too.
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Old 10th July 2009, 09:28 PM   #2
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If you have a battery bank that is 48vdc total, it's not hard to get +/- 24vdc at all. All you have to do is tap at the 24v point of the battery bank and call that your ground for the amp. Then anything to the positive side of this tap is your +24v and anything to the negative side is -24v. However, you're probably going to need some serious current capacity to run any of the First Watt (or any other Class A power amp) off of batteries. I reality, if you do run your amps off of batteries, and the batteries are close enough to the amps, you really don't need the big filter caps that are usually in the PS.

Peace,

Dave

P.S. For the soldering iron, you can buy ones that are designed for automotive usage that run off of 12vdc. You can also get ones that run off of lighter fluid and other flammables.
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Old 11th July 2009, 12:35 AM   #3
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I like my iron, I will either mod the thing to accept 220v or sell it and buy one in that voltage which would probably be easier. However, I will need a small inverter anyway and it will be in my "mad laboratory" anyway. I have been trying to figure out how much battery I need. SLA car batteries are around 13v charged, right? How long would four 1000ah batteries last with a F5? A smps is an opton, but I still need the same amount of battery and this adds a lot to the price. They sell huge 12v and 24v batteries over there for cheap. My PS may be 3' x 2', LOL!

So aside from the battery size, how would I do it? If I have two 24V batteries, I connect them in series to make 48V. I then wire the positive rail to the positive terminal of the 48V bank, the neg to the neg and the ground in the middle where the two batteries join. It can't be that simple, can it? The extra capacitance is something I learn from my youthful car audio days. The amp likes current faster than the battery can deliver. I found this is true of unregulated PS class A/B amps anyway.

What would I do between the battery and the amp boards for protection, current regulation, and so on?

How many amps would a F5 draw off the battery? If it uses 100w per channel, or about 4A right? If that is the case a 1000AH battery should last how long?
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Old 11th July 2009, 01:04 AM   #4
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hehe

build first milliwatt amps ......

use efficient drivers and you're there ....

seriously - use smaller output mosfets and run them at 25% of Papa's projected current .

with good spks , you'll be satisfied , having most quality , combined with efficiency
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Old 11th July 2009, 01:26 AM   #5
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Quote:
Originally posted by Zen Mod
hehe

build first milliwatt amps ......

use efficient drivers and you're there ....

seriously - use smaller output mosfets and run them at 25% of Papa's projected current .

with good spks , you'll be satisfied , having most quality , combined with efficiency

Suggestions for devices? The other option is BIGGER batteries! In the tropics I will have a lot of sun, I am on a river and a black piece of metal gets really hot in the sun for thermo-electric.
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Old 11th July 2009, 03:11 AM   #6
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Surprise, but yes it is that easy to get the +/- 24vdc you need for the amp. In regards to the need for caps to buffer the amp from the battery, this is largely due to the distance between the battery and the amps. The longer the cable run, the more resistance and inductance between the battery and amp. This causes voltage drops and power response lags. If the batteries are in a central bank, away from the amp, then yes, you should have caps for each channel, each voltage rail (or you could have a sub battery bank near the amps) . But if the batteries are setup near the amps, and are only used for the amps, then you shouldn't have issues with this sort of lag. Soon others will disagree.
Don't bother with an SMPS in the path. Any sort of power conversion provides a further loss of available total power, thus efficiency loss. If you have the correct voltage already available, use it directly.
I don't recall if the F5 is a constant current design, but if it is, and each channel uses 4A, then you will draw 8 amps total for a 2 channel system. If you divide 1000Ah by 8 this will tell you the total amount of time you could run the amps, assuming that nothing else is running off of the batteries. Also keep in mind that you don't want to discharge the batteries too much, it will permanently damage them.
I can't answer for Zen Mods suggestion of going smaller in your current demand, or in regards to particular transistors, but I understand what he is saying. Lower your power demands for each amp channel and the batteries will last for a longer amount of time before they need a recharge.

Peace,

Dave
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Old 11th July 2009, 03:24 AM   #7
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Quote:
Originally posted by dave_gerecke
If you have a battery bank that is 48vdc total, it's not hard to get +/- 24vdc at all. All you have to do is tap at the 24v point of the battery bank and call that your ground for the amp.
You could do that,BUT,you will have to consider the 'ground' points for the rest of the system.
Often RE battery banks are grounded at the negative end (0V),if you tap the center of the bank and use that as the amp ground,then the 'ground' of the amp will be floating at 1/2 of the battery bank voltage. If you were to connect the amp,to say,a preamp that's grounded at 0V,you're gonna have 1/2 of the battery bank voltage flowing through your interconnects! And we all know BIG batteries can supply BIG currents.

Just be sure to consider all of the current paths,before you start connecting things together.
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Old 11th July 2009, 03:33 AM   #8
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Quote:
Originally posted by DigitalJunkie


You could do that,BUT,you will have to consider the 'ground' points for the rest of the system.
Often RE battery banks are grounded at the negative end (0V),if you tap the center of the bank and use that as the amp ground,then the 'ground' of the amp will be floating at 1/2 of the battery bank voltage. If you were to connect the amp,to say,a preamp that's grounded at 0V,you're gonna have 1/2 of the battery bank voltage flowing through your interconnects! And we all know BIG batteries can supply BIG currents.

Just be sure to consider all of the current paths,before you start connecting things together.
Good point, I didn't think that one fully through before making the comment. If you do setup your power supply to the power amps this way, you would want to setup the rest of the system this way, otherwise you will have problems like those mentioned by DigitalJunkie. UH OH, Magic Smoke!!!!


Peace,

Dave
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Old 11th July 2009, 03:48 AM   #9
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My set-up will be a Buffalo-ish DAC from Twisted Pear to Lundahl LL1674 trannies for I/V to Aikido 24V preamp, to the F4 or F5, to Audio Nirvana 12". The DAC is easy for batteries, the preamp all DC inside and easy for batteries and the only hiccup I can see is the amount of battery I will need. So what should I be doing then to avoid this "current" problem?

How do you avoid this with a normal "Virtual ground" PS?


Could I wire each on their own batteries and isolate each component completely except the signal?
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Old 11th July 2009, 10:07 PM   #10
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Hello khundude, not knowing the schematics of the various equipment you mention, it's hard to say the proper way to wire things up. If you can post links to the schematics for all of your equipment, people can look at the power supply demands for each and recommend proper wiring from that.

Peace,

Dave
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