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Topic: voltage converter? (Read 538 times) previous topic - next topic

sarf2k4

Hi,

I have quite a number of questions about voltage converters that is boost, buck and linear regulator types.

I have these:


A. lithium charger
B. LED Strip
C. boost converter
D. Boost/Buck Converter

I wanted to drive a small segment of led strips on B a short strip consists of 5 segments, typically about 15 leds. They are 12v leds and I wanted to drive them using a rechargeable 18650 battery that uses the A to protect the battery and also act as a charger. The wiring dagram are as follows:


A >>> C >>> B
A >>> D >>> B

Both C and D were boosted to ~12v max and also observed from multimeter. When I connected that led strip to either C or D, the voltage dropped to 8.5v and highest I could go is 8.8v then it will go down for some unknown reason.

Actually I tried to search via google about the voltage drop phenomenon and such but unfortunately I'm unable to find specific information about this issues.

Power consumption as I measured after either using C or D, highest was about ~80mA before it starts to drop.

My question was:

1. Is it normal to have a voltage drop let's say 3.7 boosted to ~12v, under load with the above small led chunks, it drops down to ~8v?
2. What about D while I was trying to adjust the voltage range, the minimum I could go was 12v, max is 50v, could it be already busted?
3. While was wiring with D as the boost to ~12v, I tried to ramp up the voltage, multimeter didn't show any changes, neither do the leds shows the sign of getting brighter, after I taken off the led from the contact, multimeter straight shows the max voltage which is 50v prior to question no.2. What really happened here?
4. While using C, initially set to ~12v, under load it dropped to ~8v, took the led off and multimeter shows roughly about ~9.5v when no load. Is this normal?

p.s
I am not sure where to post my question, as this applies to arduino general, arduino motor/power and this general of general discussion. Also I have no background in EE stuffs as I am slowly learning my way through. It is kind of confusing and too much thing so I'm trying to learn what I can digest but I too, considered the safety precaution about my projects

westfw


Quote
1. Is it normal to have a voltage drop let's say 3.7 boosted to ~12v, under load with the above small led chunks, it drops down to ~8v?
4. While using C, initially set to ~12v, under load it dropped to ~8v, took the led off and multimeter shows roughly about ~9.5v when no load. Is this normal?
neither of those would be "normal" behavior for a properly working switching regulator used within its rated power output.  And while your regulator "C"  looks awfully tiny to provide the 2A that the sell page claims, I'd think the 250mA or so you need for a 15-LED segment would be "possible."
OTOH, if something is limiting the input current from the battery to ~500mA (the supposed limit for USB), that might explain it.



Quote
2. What about D while I was trying to adjust the voltage range, the minimum I could go was 12v, max is 50v, could it be already busted?
3. While was wiring with D as the boost to ~12v, I tried to ramp up the voltage, multimeter didn't show any changes, neither do the leds shows the sign of getting brighter, after I taken off the led from the contact, multimeter straight shows the max voltage which is 50v prior to question no.2. What really happened here?
Who knows?  Undocumented modules of unknown quality using unnamed chips (that are probably undocumented  as well (there might be documentation written in Chinese that you can't access.))  Those Aliexpress/eBay/etc modules are great bargains when they work the way you expect, and/or someone else has figured out their quirks.  When they don't appear work... you need a lab to tell why.)
Try putting some big-ish electrolytic caps (47-470 uF?) on the inputs and outputs of the step-up converters.  A lot of the tiny "complete solution" converted modules from US manufacturers are "complete solution.  Except for several rather large capacitors on both input and output."  (ie http://www.linear.com/product/LTM4661)


sarf2k4

What I haven't tried yet is to wire the 18650 directly to the converter and check the voltage. I used the 18650 battery holder that typically has thin wires probably around 24-26awg.

I also might try the electrolytic capacitor hooked to the input and output of the converters. Small electronic components are hard to source in my area, almost everything had to order online and China =\

jremington

When boosting voltage from 3.7 to 12 V, the current draw from the 3.7 V source can be excessive. You have to obey the input current limits of the booster and of the low voltage source.

Pololu has a great selection of voltage buck/boost converters, and unlike most other manufacturers, they carefully document the limitations of their devices, explain how to use them and support their products.

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