Need concrete help with BrianGT LM4780 battery power supply. - diyAudio
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Old 18th December 2005, 02:44 AM   #1
orpheus is offline orpheus  United States
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Default Need concrete help with BrianGT LM4780 battery power supply.

I've done a lot of searching and reading on this forum and others, but I'm still a bit confused about how I should implement a battery power supply with the BrianGT LM4780 board. There are a lot of threads about this, but nothing that is a specific basic beginner's explination, which is what I need.

I finally soldered my BrianGt 4780 kit together, but I don't have a power supply (or a chassis, connectors, etc...) I thought about building an aleph power supply and using that, and then I thought about just getting a transformer and using the diode bridges, but batteries appeal to me since I live in NYC and my power is very suspect. I have ordered batteries from Batterymart.com. 12 volt 7ah x 4, and a charger that they say can charge 4 batteries (about $60 shipped, not much more than a transformer).

I have read that 4*12 volt batteries will yield one +/-24 volt supply. This doesn't make sense to me. Couldn't I use two batteries and get two +24/-24 volt supplies? Or is each battery only capable of +12 or -12 necessitating 4 for +24/-24?

How do I wire the batteries together? I did read that the + of one battery is wired to the - of the next, but this didn't make sense to me. If anyone could be more specific and explain exactly how I should wire the 4 batteries together, I would really appreciate it, including an explination of ground with batteries.

Do I need to add anything else to the battery supply if I'm using the stock 4780 kit from Brian? Caps, regulators, anything? (I've got the stock 1500uf cap on the 4780 boards right now)

I have read that some people don't like to have a lot of capacitance with batteries, but would it work as a starting point with the stock 1500uf 50 volt cap that comes with the 4780 kit?

I decided to try batteries because they only cost a little more than a transformer, and they can be used in other applications, like DACs, t-amps, etc.

I appreciate any advice or help you might be able to give.

Thank you for your time.
-Aaron.
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Old 18th December 2005, 04:12 AM   #2
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Default battery power

4 12V batterys will give you +/- 24V's put all the batterys in series +/- /+/- the middle will be your" CT" or ground in other words first batterys + terminal with be V+24 that batterys negative will be connected to the next batterys + the - to the next batterys + this point will be your CT, center tap or ground and so on till the -24 volt tail.
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Old 18th December 2005, 04:27 AM   #3
orpheus is offline orpheus  United States
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Thanks for responding to my question.


I just want to make sure that I understand correctly. The first battery's + will be the +24, and it will not be connected to any other battery terminals, right? Then all the other battery terminals will be connected together, with the exception of the last terminal of the last battery, which will be -24. The ground will be connected to all the terminals that are connected to each other, right?

It's a bit counterintuitive, to connect all the +/- terminals together like that. Thank you for taking the time to explain exactly how it should be hooked up, I appreciate it.

Any advice on capacitors?

Thanks again-
Aaron.
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Old 18th December 2005, 01:24 PM   #4
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Default battery

This might helpClick the image to open in full size.
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Old 18th December 2005, 02:46 PM   #5
edl is offline edl  Hungary
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Hey, tiltedhalo!
What a huge pic...
My version, if you don't mind: (attached)

Regards,
Attached Images
File Type: gif 24v_batt.gif (2.7 KB, 249 views)
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Old 18th December 2005, 03:11 PM   #6
chuck55 is offline chuck55  United States
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I thought 4 12v batteries in series would give 48 volts. Or he could have 2 sets of 2 batteries in series to have (2) 24v power supplies for dual mono amps.
Also doesn't he need a diode and relay to switch between running off the charger's 24v and batteries 24v?
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Old 18th December 2005, 06:47 PM   #7
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Default battery

Most amplifiers require split power supplys V+ GND V-. with batteries you create an artificial "ground" or center tap witch is the point of zero voltage potential based on the batteries total series voltage or the center. 12V*4=48 48/2=24 the center.
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Old 19th December 2005, 06:04 AM   #8
orpheus is offline orpheus  United States
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Thank you so much Tiltedhalo, I really appreciate your taking the time to clearly explain something that is probably very obvious and simple to a lot of people on this board.

In regard to the charger, I bought the one sold by batterymart.com, and they say it can charge up to 4 batteries, so I am hoping that I will be able to connect it to all the batteries to charge when I'm not using them, and disconnect it when I am. It only costs $12, so it's not expensive.

Anyone have any thoughts on the capacitors required for a battery supplied BrianGT Lm4780 board? As I said above, I've already assembled the stock kit, so I might just try it with the 1500uf/50 volt caps at first, but I'm wondering if I need to add any to the power supply, or if changing them will be necessary for the amp to perform properly.

Thanks again for your advice and help.
-Aaron.
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Old 19th December 2005, 01:54 PM   #9
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Default battery power supply

what voltage is the battery charger?? on a split series set up you will not be able to charge the batteries without damage to the charger or the batteries, even if its a 24V charger. To use a 12V charger you will have to disonnect all the batteries and charge one by one. to utilize a single 12v charger you will have to diode isolate the batteries.
As for the capacitors the 1500uf should be fine depending on your distance from the batteries.
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Old 19th December 2005, 04:06 PM   #10
Franz G is offline Franz G  Switzerland
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Default Fuses!

My two cents:

1. Dont miss to use fuses! Shortened batteries may cause a nice incident or other damages.

2. Preload the batteries during operation (some mA, by a suitable resistor) to avoid too strong "sagging" of the voltage.

Franz
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