STEP-UP, parallel, amps GET MANY?

CONNECTED Okay so, I need some diode, which?
IF YOU GET CONNECTED IN PARALLEL 5V, and 8A ??

No... The general rule is NEVER connect two or more outputs together. That rule applies to power supplies, batteries, digital Arduino outputs, audio outputs... almost everything except open collector outputs which are designed to be "ored" together. (It's generally OK to connect two or more inputs together.)

The results are unpredictable and there's a CHANCE it might work. But more likely, one will have a tiny-bit more voltage than the other and all of the current will come from that one. Or the higher (or lower) output from one will screw-up the feedback and one board will be trying to turn down it's voltage, where the voltage it's actually seeing is coming from the other one.

Or, current might flow out of one into the other... The whole thing is unpredictable and they are not designed to operate that way...

You can't put the outputs of two buck/boost converter modules in parallel - they will not agree on precisely the voltage to generate, and will fight eachother, and probably fail.

You can use schottky diodes to "or" the power sources, but the load may not be split evenly, as I said above, they will disagree on what the target voltage is, so the one with the slightly higher setpoint will get most of the current.

Use a single, larger step-up converter that can handle the full current requirement.

You can parallel the batteries, but only if they're at the same state of charge when you first put them in parallel - otherwise the more-charged one will attempt to charge the less-charged one, and that won't be good for either of them.

Also, after being stepped up to 5v, the current from the batteries will be higher (5/3.7th's, plus inefficiency in converter). I would not attempt to pull 5-6A from an 18650 battery - if you had a "fancy" 18650, like the ones people use for high-end e-Cigs, you could do it, though with poor battery life (drawing high current always lowers capacity - the rated capacity is measured at a much lower current)

Those batteries (Ultrafire 4000mAh - and more or less anything else from Ultrafire) do not meet spec. I have some that look like that, and I measure capacity of around 700mAh. I also have a batch of "6000mAh" ones that I measure capacity at 2500mAh (which I consider acceptable). Any capacity higher than 3500mAh in an 18650 battery is probably a lie.

THERE A STEP-UP, 8 A, 5V,?, NO ONE MEETING

Naruto128:
THERE A STEP-UP, 8 A, 5V,?, NO ONE MEETING

After 481 posts, you cannot express yourself any better? :o

Come on, you can do better!

// Per.

Zapro:
After 481 posts, you cannot express yourself any better? :o

Come on, you can do better!

// Per.

Is it possible that English is not his native language?

It might help if you tell us what it is for.
I remember a post like this when the user wanted to power a 5meter long LED strip.
I advised him to use two converters like that, and feed the outputs to opposite ends of the LED strip.
The resistance/voltdrop of the strip takes care of the imbalance.

You might also want to consider a (generally) more efficient buck (step-down) converter, powered by a 2C or 3C pack.
Leo..

mrsummitville:
Is it possible that English is not his native language?

I'm pretty sure caps lock is considered rude in any language.

Basic rules with power sources:

Voltage sources never in parallel, only series (and then only if matching currents and isolated)
Current sources never in series, only parallel (and only if the voltage compliance ranges are
compatible.

Think of it this way:

voltage source has output impedance approx 0, so connecting two together leads to large/damaging
currents. In practice with many voltage sources that can only drive current in one direction what
happens is one voltage source ends up doing nothing, or the whole system oscillates wildly and
produces over-voltages.

sorry, I speak Spanish.

while I made a Rotating LED Display POV (Persistence of Vision), and want to upgrade, my big problem is to energize the system is correct.

I'm using LEDs ws2812b, about 128 RGB LEDs per side.
I saw that in MOnkeyEletric use two batteries, each of 3500mah,
but it needs face 8A.
For my case would need four step-up and 4 batteries?

MY proyect

monkeyEletric

pd: You can not embed videos on the forum?

MarkT:
Basic rules with power sources:

Voltage sources never in parallel, only series (and then only if matching currents and isolated)
Current sources never in series, only parallel (and only if the voltage compliance ranges are
compatible.

Think of it this way:

voltage source has output impedance approx 0, so connecting two together leads to large/damaging
currents. In practice with many voltage sources that can only drive current in one direction what
happens is one voltage source ends up doing nothing, or the whole system oscillates wildly and
produces over-voltages.

Theoretically true. Practically it's not all that bad.
Supplies are not perfect (0ohm output impedance).
Most of them sag when loaded (bad load regulation), and sag even more when they reach maximum load.
That said, I would use several batteries in series, and use a single BUCK converter with the required current.
Leo..

Voltage regulator chips are very stiff voltage sources, the open-loop gain is large.

Naruto128:

CONNECTED Okay so, I need some diode, which?
IF YOU GET CONNECTED IN PARALLEL 5V, and 8A ??

Yes, you can combine two 5 Amp Power Supplies to create a single 10 Amp output.
But, you cannot use the parallel circuit that you proposed.

You can use something like this …
Power Supply Balancing Controller
between the two Power Supplies and the load.