Cheap way to split 48v battery into 36v and 9v? - Page 1
Forum section: electronics / beginners

author: UCYT5040
author_rank: Newbie
timestamp: August 03, 2024, 05:32:52 pm
content: So I have a 48v battery, a 36v motor, and a 9v micro controller. Is there a way to split that into the 9v and 36v cheap? I'm trying to do this very low budget, so any part recommendations are great.I'm totally new to this stuff, so I'm not sure if watts apply here, but I don't think they do.Thanks all!

author: squadchannel
author_rank: Frequent Contributor
timestamp: August 03, 2024, 05:41:46 pm
content: Linear method cannot be used because the voltage difference is too large.A DCDC converter module from Amazon or Aliexpress and smoothing with capacitors would be the lowest cost.I think it would be better to combine a DCDC module that can input more than 48V with a module using XL6009.

author: UCYT5040
author_rank: Newbie
timestamp: August 03, 2024, 05:50:56 pm
content: Quote from: squadchannel on August 03, 2024, 05:41:46 pmReally looking for the lowest cost option here.But I don't really understand what you are saying.I would need one DCDC for 48v to 36v, right? I couldn't find anything on aliexpr that does this.And then use resistors to take it from 36 to 9? I'm not sure, but I think that's too much of a difference.Sorry to ask this of you, but could you clarify your response?

author: Grandchuck
author_rank: Super Contributor
timestamp: August 03, 2024, 06:11:05 pm
content: Found this:https://www.amazon.com/dp/B07DMV5KB5/Have no idea of quality or reliability?

author: themadhippy
author_rank: Super Contributor
timestamp: August 03, 2024, 06:13:53 pm
content: open up the battery and tap the individual cells at the required voltage,maybe not the safest way,but its cheap

author: Andy Chee
author_rank: Super Contributor
timestamp: August 03, 2024, 06:37:11 pm
content: Can you tell us more about the 36V motor?Without any information, I would suggest that the 36V motor would run directly from 48V with no problems.

author: magic
author_rank: Super Contributor
timestamp: August 03, 2024, 07:20:05 pm
content: Cheapest if not necessarily most power efficient:motor: add a 12V zener in seriesMCU: use a linear regulator like 7809, MCU is low current so not a big problem with thatBy the way, 9V for an MCU? Aren't they all 5V, 3.3V or even less?

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 03, 2024, 07:25:32 pm
content: Quote from: Andy Chee on August 03, 2024, 06:37:11 pmThat still leaves the 9V.But 33% over voltage on a motor might be a bit much.If the battery is based on separate accessible cells then tapping the individual cells could be an option but leaves some of the cells unused, unless you can live with a positive and negative power supply. Otherwise it would require to separate the batteries, but that might cause problems with the battery management system in case of lithium ion cells.The easiest option would be to use two buck converters. One to make the 36V and another one to make the 9V. It does depend on current draw which buck converter suits the bill. A motor can draw quite a bit of current certainly at startup and the converter needs to be able to handle this without dying.So to make better suggestions more information about both parts of the system are needed. (So info about the motor and the microcontroller system that is)Edit: Forgot to mention to also include more information about the battery.

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 03, 2024, 07:28:06 pm
content: Quote from: magic on August 03, 2024, 07:20:05 pmMight be that the OP is using something like an Arduino board which takes 7V to 12V on the power input.

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 03, 2024, 07:37:07 pm
content: Quote from: squadchannel on August 03, 2024, 05:41:46 pmThere is always a possibility to make it work, but a lot of heat needs to be dissipated when the current is high.Quote from: squadchannel on August 03, 2024, 05:41:46 pmThe one problem with this is the high input voltage. A XL6009 can only safely handle 32V at the input. (Absolute max. 36V) So it is a bit of a search to find one that can handle the 48V and the needed current for that matter.

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 03, 2024, 07:41:03 pm
content: Quote from: Grandchuck on August 03, 2024, 06:11:05 pmSame module on Aliexpress for half the price:https://nl.aliexpress.com/item/1005006771384010.htmlBut indeed no idea about quality and performance.

author: UCYT5040
author_rank: Newbie
timestamp: August 03, 2024, 08:01:51 pm
content: Okay, so here are some links to help out here. Sorry they are so long.BatteryMotor:MotorAlso this controller for the motorI also bought these parts, but let me know if I should return/cancel them if they wont work:48v to 9v:https://www.aliexpress.com/item/3256805929589243.html?spm=a2g0o.order_list.order_list_main.20.611c1802eE8cMg48v to 36v:https://www.aliexpress.com/item/3256804736367166.html?spm=a2g0o.order_list.order_list_main.10.611c1802eE8cMgThat last one was pretty expensive, so if it's true that I can send 48v to the motor, I can happily return that.One other thing: I think it's too dangerous to use individual cells from the battery and also I need this to be weather proof, so it would complicate thatThanks everyone for the help

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 03, 2024, 08:08:48 pm
content: Quote from: magic on August 03, 2024, 07:20:05 pmWhat? That zener will burn in 0.0001 seconds

author: tunk
author_rank: Super Contributor
timestamp: August 03, 2024, 08:34:29 pm
content: The motor draws up to 10A (360W/36V) - I assume you ordered the 10A step down converter?Specs of the motor controller: Voltage Input, 6.4v - 16.8vEdit: Assuming a 13S li-po battery, the battery voltage range is something like 56-39V.

author: langwadt
author_rank: Super Contributor
timestamp: August 03, 2024, 08:41:44 pm
content: Quote from: UCYT5040 on August 03, 2024, 08:01:51 pmthat's a brushed motor, and a brushless controller, that won't workto use that motor just get controller for a brushed motor that can handle 48V and limit max throttle

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 03, 2024, 09:10:19 pm
content: Quote from: tunk on August 03, 2024, 08:34:29 pmIf the motor draws 10 A then any converter hooked up to it should be a min of 15 A. 20-30A would be better.

author: UCYT5040
author_rank: Newbie
timestamp: August 03, 2024, 09:15:48 pm
content: Quote from: JustMeHere on August 03, 2024, 09:10:19 pmSo a 10A won't work? Will it burn up or just be inefficient?

author: radiolistener
author_rank: Super Contributor
timestamp: August 03, 2024, 09:37:40 pm
content: 48V battery consists of 14 cells, each cell 3.6V.So, you can use 10 cells to get 36V and 2-3 cells to get 7.2-10.8V for microcontroller.But this way to use battery may lead to unbalanced discharge for cells, so some cells lifetime will be much shorter than other.Another way is to use DC/DC, but it will have about 10-20% power loss on heating during conversion.

author: langwadt
author_rank: Super Contributor
timestamp: August 03, 2024, 09:46:57 pm
content: Quote from: radiolistener on August 03, 2024, 09:37:40 pma brushed motor controller is already a dc-dc converter, no need to add another, just limit the max output to ~75%

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 04, 2024, 05:41:36 am
content: What I don't get is why the OP bought (At least I assume he already bought it) a 48V battery pack when the target voltage for the motor is 36V. (Actually rated for 24 with a max of 36 according to the Amazon page) Can't see the prices of the battery packs due to not shipping to France, but the page also lists 36V battery packs using LiFePO4 which are saver then Li-ion.They also have higher current ratings and those are needed for the chosen motor with a max 14A rating.To control the motor something likethismight do.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 04, 2024, 09:55:23 am
content: Quote from: UCYT5040 on August 03, 2024, 09:15:48 pmIt won't last long. You should derate your power components. If they are expected to do 10A continouts duty then design them to handle 20A. Make the workload a breeze instead of a challenge.

author: UCYT5040
author_rank: Newbie
timestamp: August 05, 2024, 03:20:15 am
content: Quote from: pcprogrammer on August 04, 2024, 05:41:36 amI got the high voltage battery so I can also power my microcontroller. Do you think I should be returning that battery and getting a different one? A lot of the batteries I saw were to unreliable based on reviewsAnd yeah I got that motor control already.

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 05, 2024, 05:24:06 am
content: Quote from: UCYT5040 on August 05, 2024, 03:20:15 amYes return it if you can and get one for 36V. Why, because that will give you a longer run time as there is no need to reduce the voltage for the motor so less loss and the microcontroller needs to have it's ground at the same level as the motor ground. Therefore no need for a higher battery voltage to make up for the microcontroller supply.The buck converter for the microcontroller will also have less stress due to the lower input voltage.

author: perieanuo
author_rank: Frequent Contributor
timestamp: August 05, 2024, 05:25:23 am
content: cheap means a 9v1 zener with a regulating transistor for micro

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 05, 2024, 05:36:16 am
content: Quote from: perieanuo on August 05, 2024, 05:25:23 amYou forgot the resistor that is also needed.And then produce heat in the resistor, zener and transistor while for just a little bit more money you can get a simple buck converter to do the job. By reducing the 48V battery to a 36V one the choice of buck converters becomes wider, so easier to find a cheap one.

author: Sagar
author_rank: Contributor
timestamp: August 06, 2024, 11:17:02 am
content: I will suggest to use 9v500mA zener for MCU and for 36 volt you can use any buck converter which suits the current requirements. I did not find any currentratings in the post, if you can mention that I suugest you a cheap option. Because voltage can be divided even by using resistor divider network but please mention the application, where you want to use it.