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Author Topic: Charge ports with pixel blades (and other high current loads)  (Read 1394 times)

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Offline jbkuma

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An item of note on pixel blades, the typical charge port most use is actually only rated for 5A.  I think it's unlikely that other makers exceed the quality or rating of the Switchcraft's jacks, if they are rated at all.  I don't know that anyone has had a problem with this, but it's something that should be kept in mind especially for those who think that 3 strip sabers are a worth while endeavor drawing up to 20A (I do not believe they are). http://www.switchcraft.com/Specification.aspx?Parent=606

All of my sabers charge through the blade socket using the aviation connector, which is similarly rated, but I use multiple pins for the power connections.

Offline Obi_1

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #1 on: April 12, 2018, 03:56:38 AM »
I personally strongly believe that 20A is a myth. Even 10A is one. You always have contact and wiring resistances. Look at it like this: 20A over 100mOhms (which is a very low resistance value) causes 2V of drop, i.e. you electronics will instantly go to undervoltage reset. The equilibrium will be reached at a much lower drain, I do not have any data to support where but my informed feeling is that even extreme neopixel builds will not exceed 10A (probably 5A-7A is a better estimate). Therefore 5A seems to me like a safe value for the RC port. Since it's purely  a mechanical Switch, I guess A.) it has a huge tolerance B.) worst Thing what can happen is that it will fuse together or slowly wears out (i.e. even with a kill key inserted it will not be fully disconnecting). A thing which in my experience happens anyway after a few years.

Offline jbkuma

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #2 on: April 12, 2018, 08:12:49 AM »
We should still be aware of it, at least. With your research it's been shown that the a lithium battery is a more ideal source and the maximum currents are less of an issue, but I've had white hot wires and slagged breadboards in early experiments at 5v.  2 strips are rated at 14.4A for 120x2 pixels or 17.28A for 144x2.  In reality, even at 5v, that would only be approached for full white.  Even if we typically use at most two fully bright colors, and that is probably closer to the 5-7 range for 120 pixel blade you mention, we have to account for edge cases, especially when designing for use by others that may not be aware of the limits.  Even many installers aren't aware of the limits of their components or even that they might have such a thing.

There are a number of components we often use beyond their ratings.  The common JST RCY connectors we often use for power are actually only rated for 3A when using 22awg wire, for instance.  In truth, that's barely in range for an tri-Cree setup.  Running all 3 at full current is already 3A, that doesn't include the power required by the board.  Most are only using 28awg which they list at 0.5A or even 30awg which isn't even on the sheet.  In truth we are using far less than the listed 250V, but we still need to be aware the rating exists.  http://www.jst-mfg.com/product/pdf/eng/eRCY.pdf

The connectors I've been using are rated for 6A, and they seem to work fine and there is no notable heating.  Many of the more recent connectors have been tested and proven useful by their creators, but they aren't truly rated, never mind tested and listed by an authority.

In my professional life I often deal with these sorts of ratings in engineering designs.  Many items are tested to 10x their rated value, but we trust those items only to their rating or risk liability if fails.  As a representative of the manufacturer I would never acknowledge by any recordable means that the equipment might be safe to use beyond it's rating.  I would instead say the tests were conducted well beyond the rated limit to ensure safe operation at the rated limit.

We trust these things at our peril, we should at least have an informed risk.

Offline ShtokyD

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #3 on: January 25, 2020, 02:04:06 PM »
I personally strongly believe that 20A is a myth. Even 10A is one. You always have contact and wiring resistances. Look at it like this: 20A over 100mOhms (which is a very low resistance value) causes 2V of drop, i.e. you electronics will instantly go to undervoltage reset. The equilibrium will be reached at a much lower drain, I do not have any data to support where but my informed feeling is that even extreme neopixel builds will not exceed 10A (probably 5A-7A is a better estimate). Therefore 5A seems to me like a safe value for the RC port. Since it's purely  a mechanical Switch, I guess A.) it has a huge tolerance B.) worst Thing what can happen is that it will fuse together or slowly wears out (i.e. even with a kill key inserted it will not be fully disconnecting). A thing which in my experience happens anyway after a few years.
It's not a myth, it's reality, it's been tested. Measure the current drain my a 20A multimeter, you will see. Here is a tested real current drain with different number of strips powered by a 15A battery, and as you can see we get exactly 9-10 Amps at full brightness White color mix with 2 strips:

« Last Edit: January 25, 2020, 02:23:20 PM by ShtokyD »

Offline ShtokyD

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #4 on: January 25, 2020, 02:18:19 PM »
Here are tested Recharge Ports and Kill Switches at various current loads up to 11 amps by me:



More info on this topic here: Recharge Ports and Kill Switches
« Last Edit: January 25, 2020, 02:27:27 PM by ShtokyD »

Offline Obi_1

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #5 on: January 31, 2020, 02:14:35 PM »
I personally strongly believe that 20A is a myth. Even 10A is one. You always have contact and wiring resistances. Look at it like this: 20A over 100mOhms (which is a very low resistance value) causes 2V of drop, i.e. you electronics will instantly go to undervoltage reset. The equilibrium will be reached at a much lower drain, I do not have any data to support where but my informed feeling is that even extreme neopixel builds will not exceed 10A (probably 5A-7A is a better estimate). Therefore 5A seems to me like a safe value for the RC port. Since it's purely  a mechanical Switch, I guess A.) it has a huge tolerance B.) worst Thing what can happen is that it will fuse together or slowly wears out (i.e. even with a kill key inserted it will not be fully disconnecting). A thing which in my experience happens anyway after a few years.
It's not a myth, it's reality, it's been tested. Measure the current drain my a 20A multimeter, you will see. Here is a tested real current drain with different number of strips powered by a 15A battery, and as you can see we get exactly 9-10 Amps at full brightness White color mix with 2 strips:



There is no disagreement here, only different use cases. Your test results are consistent with the golden reference (see here: https://github.com/Protonerd/DIYino/blob/master/Neopixels_Characterisation_report1.pdf ), which gives credit to your results. As you can see, with 2 stripes 143 each and full whote you can easily reach over 12Amps.

The point is, your setup is based on ideal conditions for the stripes, which is not a realistic use case for a saber. In a saber you will have losses, effectively reducing your voltage supply at the stripes, and with lower voltage the current draw will also decrease.
First of all, you want to have a decoupling with FETs. Even the most common setup with 3 of them in parallel will have an RDson of 100+mOhms, at 10Amps they alone would contribute to a supply loss of 1V. At 2.7V the LEDs have already about half the current draw. As the current of LEDs is not a linear function of voltage, the working point will be reached probably at a slightly higher voltage. Then there are the connectors, adding further, albeit small IR drops.
Plus as in the higher PWM ranges the current draw increases not in proportion to brightness gain, saber boards usually do not drive the LEDs fully, not to waste energy unnecessarily.
So it all adds up to a lower current.
Plus a full 1m blade is a kind of rare thing, most people tend to use 120 or less pixels in a blade with 80-90cm. White color is also a rare main blade color, it is mostly used for clash flash, which takes a couple of ms, therefore can be considered a pulse load, for which often other ratings apply.

In my humble experience, I never managed to trip the 10Amps, although I had a couple of saber builds with 3 stripes.

Jason is planning on supplying the community with more precise measurements, so let's wait for his results, with his many awesome builds he accomulated a lot of experience with pixel blades.

Offline jbkuma

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #6 on: January 31, 2020, 03:39:39 PM »
For some of my tests I have used a blade directly wired to a 5V 20A source with 14awg wire.

Offline ShtokyD

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #7 on: February 02, 2020, 03:17:28 AM »
I personally strongly believe that 20A is a myth. Even 10A is one. You always have contact and wiring resistances. Look at it like this: 20A over 100mOhms (which is a very low resistance value) causes 2V of drop, i.e. you electronics will instantly go to undervoltage reset. The equilibrium will be reached at a much lower drain, I do not have any data to support where but my informed feeling is that even extreme neopixel builds will not exceed 10A (probably 5A-7A is a better estimate). Therefore 5A seems to me like a safe value for the RC port. Since it's purely  a mechanical Switch, I guess A.) it has a huge tolerance B.) worst Thing what can happen is that it will fuse together or slowly wears out (i.e. even with a kill key inserted it will not be fully disconnecting). A thing which in my experience happens anyway after a few years.
It's not a myth, it's reality, it's been tested. Measure the current drain my a 20A multimeter, you will see. Here is a tested real current drain with different number of strips powered by a 15A battery, and as you can see we get exactly 9-10 Amps at full brightness White color mix with 2 strips:



There is no disagreement here, only different use cases. Your test results are consistent with the golden reference (see here: http://github.com/Protonerd/DIYino/blob/master/Neopixels_Characterisation_report1.pdf ), which gives credit to your results. As you can see, with 2 stripes 143 each and full whote you can easily reach over 12Amps.

The point is, your setup is based on ideal conditions for the stripes, which is not a realistic use case for a saber. In a saber you will have losses, effectively reducing your voltage supply at the stripes, and with lower voltage the current draw will also decrease.
First of all, you want to have a decoupling with FETs. Even the most common setup with 3 of them in parallel will have an RDson of 100+mOhms, at 10Amps they alone would contribute to a supply loss of 1V. At 2.7V the LEDs have already about half the current draw. As the current of LEDs is not a linear function of voltage, the working point will be reached probably at a slightly higher voltage. Then there are the connectors, adding further, albeit small IR drops.
Plus as in the higher PWM ranges the current draw increases not in proportion to brightness gain, saber boards usually do not drive the LEDs fully, not to waste energy unnecessarily.
So it all adds up to a lower current.
Plus a full 1m blade is a kind of rare thing, most people tend to use 120 or less pixels in a blade with 80-90cm. White color is also a rare main blade color, it is mostly used for clash flash, which takes a couple of ms, therefore can be considered a pulse load, for which often other ratings apply.

In my humble experience, I never managed to trip the 10Amps, although I had a couple of saber builds with 3 stripes.

Jason is planning on supplying the community with more precise measurements, so let's wait for his results, with his many awesome builds he accomulated a lot of experience with pixel blades.
My test results are realistic to saber usage, because these tests are made in an actual saber powered by a single charged Li-Ion 3.7V 15A high drain battery and wired by a proper wire gauges (18-20 AWG for power wires). There will be no major voltage or current losses in the saber if it's wired with proper wire gauge and use proper components.
« Last Edit: February 02, 2020, 03:27:40 AM by ShtokyD »

Offline ShtokyD

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #8 on: February 02, 2020, 03:21:18 AM »
For some of my tests I have used a blade directly wired to a 5V 20A source with 14awg wire.
In sabers we use 4 Volts maximum (Li-ion battery voltage is from 2.5 volts to 4.2 volts and under load voltage drops to at least 4 volts or lower) for Neopixel blades, so need to do tests with Li-ion batteries but not a 5V bench power supplies for realistic results.

Offline jbkuma

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #9 on: February 03, 2020, 11:43:07 AM »
I meant even with 5V and essentially unlimited power I never saw current over 10A for a 120x2 blade, the only thing it did was make things hotter faster than a 3.7v or battery.

All of my testing is done with a battery unless there is a specific reason I am using a regulated supply.

Offline ShtokyD

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Re: Charge ports with pixel blades (and other high current loads)
« Reply #10 on: February 04, 2020, 03:03:57 AM »
I meant even with 5V and essentially unlimited power I never saw current over 10A for a 120x2 blade, the only thing it did was make things hotter faster than a 3.7v or battery.

All of my testing is done with a battery unless there is a specific reason I am using a regulated supply.
8-10A current is when you drive the strips at White color full brightness (Red + Green + Blue mix): 2 x 120 x 11mA x 3 = 8 Amps. That's for the 120 pixels, but some people use more pixels in their blades - 130-140.
6-7A for dual color mixes (Cyan, Purple, Yellow etc..): 2 x 120 x 12mA x 2 = 6 Amps
3-4A for pure single colors (pure Red, Green, Blue): 2 x 120 x 13mA x 1 = 3 Amps

- thats real world measurements, and as you can see the less total current drain from the battery -> the more current each individual pixel gets (the more brighter it is) because of the voltage drop in the strip and wires and battery. Thats for the regular 12mm 5050 WS2812B flexible strips, in "skinny" 3535 8mm strips the situation is worse because of the thinner "power rails" Positive and Negative traces, these strips create a bigger voltage drop -> total current drain gets lower and strip brightness gets lower. The new KR-sabers custom strips with 5050 pixels I recently tested are brighter than regular 5050 flexible strips and have less voltage drop, which means each individual pixel gets more current.
« Last Edit: February 04, 2020, 03:18:58 AM by ShtokyD »