split power supply (+/-30V) from a single 36V battery - Page 1
Forum section: electronics / beginners

author: ri
author_rank: Newbie
timestamp: September 24, 2022, 05:43:14 pm
content: 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 inverterwith 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 videowhich explains how to use a pair of cheap LM2596-based buck converter boardshttps://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=yto 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 advanceRiccardo

author: ledtester
author_rank: Super Contributor
timestamp: September 24, 2022, 06:13:02 pm
content: Quote from: ri on September 24, 2022, 05:43:14 pmWhat amplifier circuit are you trying to power? The solution might be a different amplifier circuit.

author: ri
author_rank: Newbie
timestamp: September 24, 2022, 07:05:26 pm
content: Hi,I am looking at a class A amplifierhttps://sound-au.com/project27.htmalthough I have also considered a class D oneRiccardo

author: rdl
author_rank: Super Contributor
timestamp: September 25, 2022, 08:15:25 am
content: 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.

author: Vovk_Z
author_rank: Super Contributor
timestamp: September 25, 2022, 09:17:51 am
content: 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.

author: rdl
author_rank: Super Contributor
timestamp: September 25, 2022, 12:25:42 pm
content: Quote from: Vovk_Z on September 25, 2022, 09:17:51 amGood 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.

author: ri
author_rank: Newbie
timestamp: September 25, 2022, 03:40:18 pm
content: 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?ThanksRiccardo

author: ledtester
author_rank: Super Contributor
timestamp: September 25, 2022, 04:34:36 pm
content: 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/Reviewedhttps://youtu.be/bK-yif8qqscThat 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.

author: Vovk_Z
author_rank: Super Contributor
timestamp: September 25, 2022, 06:24:37 pm
content: Quote from: ri on September 25, 2022, 03:40:18 pm1) Only if they are isolated, or one of them is inverting.3) LM2596 seems too weak to be used for the power amplifier.

author: strawberry
author_rank: Super Contributor
timestamp: September 25, 2022, 07:55:12 pm
content: for enough power TL494 Push-Pull SMPSI wonder if that module actually run at 150kHz