split power supply (+/-30V) from a single 36V battery

[ri]

Hi all,
my first post in the forum.

I am have some electronics experience in microcontroller based projects, for home automation and AC motor control.

For a change I am now looking to build a guitar amplifier just for the fun of it, and I am having problems figuring out how to build the split power supply.

I want the amplifier to be portable so it needs to be battery powered. Researching the subject I found that a common way to go is to power it would be to power a mains inverter
with a 12V battery and then feed the 220V AC to a standard split power supply.


It seems to me quite a convoluted andheavy way to go, so I started exploring ways to use a battery instead.

One simple way would be to connect two batteries in series and use the middle terminal as ground.

Since I would like to have a +/-30 V, 3A supply that would make it quite a heavy solution.

Instead I would like to find a way to use a single 36V battery from a disused electric bike, to feed a DC converter to obtain both the positive and negative voltages.

I found a video



which explains how to use a pair of cheap LM2596-based buck converter boards

https://www.aliexpress.com/item/1775868763.html?_randl_currency=GBP&_randl_shipto=GB&src=google&src=google&albch=shopping&acnt=708-803-3821&slnk=&plac=&mtctp=&albbt=Google_7_shopping&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=17858129175&albag=&trgt=&crea=en1775868763&netw=x&device=c&albpg=&albpd=en1775868763&gclid=Cj0KCQjw1bqZBhDXARIsANTjCPLXrgUE0LYsPUFdY_YrmfSV0Xj1iU_wHESnRS_fZhrTy01sY3UBfywaAnIpEALw_wcB&gclsrc=aw.ds&aff_fcid=c54da1cb57f1457ab9b76bc03c2550ce-1664040760183-01841-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=c54da1cb57f1457ab9b76bc03c2550ce-1664040760183-01841-UneMJZVf&terminal_id=0be153833cec4022b7927a1df14d8c94&afSmartRedirect=y

to get the positive and negative rails. One of the LM2596 would take care of the positive voltage, and the other would regulate the negtive. I have them on order andI will be experimenting with them.

However, their specs are not ultimately suitable for my project, since they can't reach neither -30V nor the desired current output.

I have a few questions:

1) Is the method above (two sparate buck converters) a good one or there are better ways to solve the problem?
2) If the method is good, is it feasible to achieve +/-30V, 3A supply?
3) Any recommendations for switchers with more muscle than the LM2596?

Thanks in advance
Riccardo

[ledtester]

For a change I am now looking to build a guitar amplifier just for the fun of it, and I am having problems figuring out how to build the split power supply.

I want the amplifier to be portable so it needs to be battery powered.

What amplifier circuit are you trying to power? The solution might be a different amplifier circuit.

[ri]

Hi,

I am looking at a class A amplifier 

https://sound-au.com/project27.htm

although I have also considered a class D one

Riccardo

[rdl]

The project linked is intended to run from mains power and it includes a power supply schematic. My guess is using two of those 36v batteries in series would be the way to go.

[Vovk_Z]

Class A with a battery power is not reasonable. It is much more reasonable to use Class-d amplifier with unipolar power supply.
You can buy ready-made 200-400-800 W rated amp (at ebay etc) which may be powered directly from 36V battery.

[rdl]

Class A with a battery power is not reasonable.

Good point. I overlooked that. I have a NAD integrated amp that has a Class A pre-amp. It uses over 30 watts just sitting there doing nothing.

[ri]

Thank you for the advice. I understand the need to make the battery last is in conflict with Class A.  Using a unipolar class D makes things simpler.

It still would be useful to have an answer to the questions below, as I haven't been able to find them anywhere:

1) Is the method above (two sparate buck converters) a good one or there are better ways to solve the problem?
2) If the method is good, is it feasible to achieve +/-30V, 3A supply?
3) Any recommendations for switchers with more muscle than the LM2596?

Thanks
Riccardo

[ledtester]

Consider:

1. Those boards do not use a real LM2596 and their specs are very inflated. For that board in particular see this video:

LM2596 2v-37V 3A Voltage Step Down converter Module Tested/Reviewed
https://youtu.be/bK-yif8qqsc

That channel has reviewed other cheap buck/boost converters you can get from aliexpress/ebay.

2. In the video around 4:20 it is explained that for the negative switcher V_IN - V_OUT- must not exceed 40V. In your case 36V - (-30V) = 76V which exceeds this limit.

3. The video then explains that the max output current of the negative switcher will be a fraction of the 3A possible. For converting 36V to -30 that fraction is approximately 1/2 so you'll only be able to get 1.5A at best.

[Vovk_Z]

1) Is the method above (two sparate buck converters) a good one or there are better ways to solve the problem?
2) If the method is good, is it feasible to achieve +/-30V, 3A supply?
3) Any recommendations for switchers with more muscle than the LM2596?

1) Only if they are isolated, or one of them is inverting.
3) LM2596 seems too weak to be used for the power amplifier.

[strawberry]

for enough power TL494 Push-Pull SMPS

I wonder if that module actually run at 150kHz