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PostPosted: 16 May 2017, 13:22 
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Joined: 31 Dec 2015, 06:24
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Not an audio question at all but I'm putting my faith in the goodwill of the board to stop me from doing something dumb...

Basically, there was an old 6V 10Ah valve regulated sealed lead acid (wheelchair?) battery lying around at work (this one) and I want to turn it into a multi-port USB power bank.

I know I should play it safe and step down the voltage to 5V. My question is can I attach several (4x 6x 8x?) cheap buck converters (like these) to it, in parallel? Or is the fact that each charging device will present a different load an issue?


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PostPosted: 18 May 2017, 06:57 
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Joined: 05 Aug 2016, 14:35
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deadstillstanding wrote:

I know I should play it safe and step down the voltage to 5V. My question is can I attach several (4x 6x 8x?) cheap buck converters (like these) to it, in parallel? Or is the fact that each charging device will present a different load an issue?


The loads are not relevant unless they exceed the capacity of the converter - which is not likely. Lead-Acid batteries for the purpose you describe are essentially infinite-current devices based on the anticipated loads. You will be fine.


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PostPosted: 19 May 2017, 21:54 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
I agree. You may need to consider heating in the individual converters. If you don't exceed their ratings you ought to be fine. Are you planning on using preassembled converters? If so which ones?

Good listening
Bruce

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PostPosted: 22 May 2017, 07:45 
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Joined: 31 Dec 2015, 06:24
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Peter W. wrote:
The loads are not relevant unless they exceed the capacity of the converter - which is not likely. Lead-Acid batteries for the purpose you describe are essentially infinite-current devices based on the anticipated loads. You will be fine.

gofar99 wrote:
I agree. You may need to consider heating in the individual converters. If you don't exceed their ratings you ought to be fine. Are you planning on using preassembled converters? If so which ones?

Thank you both! That's very reassuring.
This is the spec for the converters I was looking at on eBay – let me know if there's something I should be looking for otherwise I guess I'll just ensure there's passive ventilation through the enclosure:
Code:
Features:
- The max output current 3A, long time use 2.1A, enough use
- New design, 3 solid state ceramic capacitors(MCC), more safe and low ripple
- Synchronous rectification, High efficiency, 6.5V to 5V 0.7A can up to 97.5%, 12V to 5V 1A can up to 94%
- Flat copper inductor, improve conversion efficiency
- With output overvoltage protection. There is 1.5A fuse, output 5V have 300W TVS tube protect your USB device
- Using the latest USB identification circuit, perfectly compatible with IPHONE, the most of Android phones, IPAD etc
- High quality USB port
- Output voltage indicator (RED)
- Small size, 26.4 (L) * 15 (W) * 7.4 (H) mm
- Input with reverse polarity protection diode, will not damage when input connect incorrect
- Ultra-low static current, 0.85 mA only. Do not need to add swith when connected to the car battery, can be connected to car cigarette lighter cable or ACC power supply cable
Module Parameters:
Module Properties: non-isolated buck module (BUCK) synchronous rectification
Input voltage: DC 6-24V
Output voltage: 5.1-5.2V
Output current: 3A MAX (please enhance heat dissipation when full load using), the actual test result input 12V output current 2A do not need to enhance heat dissipation.
Conversion efficiency: can up to 97.5% (6.5V step down to 5V 0.7A) (after short reverse protection and fuses test value)
Switch frequency: 500KHz
Output ripple: 10mV around (12V to 5V3A) 20M bandwidth
Output indicator: Output voltage indicator is red
Operating temperature: Industrial grade (-40 ℃ to + 85 ℃) (the higher the ambient temperature, the lower the output power)
Output overvoltage protection: Yes, input 1.5A fuse, output 5V have 300W TVS tube clamp protection.
Full load temperature: 30 ℃
Static current: 0.85 mA
Load regulation: ± 1%
Voltage Regulation: ± 0.5%
Dynamic response speed: 5% 200uS
Output short circuit protection: Yes, but please do not short circuit for a long time
Input reverse polarity protection: Yes, there is reverse polarity protection diode
Connection mode: Welding
Input mode: Welding
Output mode: USB

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