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Breaktru Forum  |  eCigarette Forum  |  Modding  |  Topic: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
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Offline mamu

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Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« on: May 01, 2014, 06:58:37 PM »
Got the OKL2-T/20-W12 in yesterday and got it breadboarded this morning. 

So far, so good with testing (i.e., it's doing what it's suppose to  :laughing: ). 

Size comparison with the Naos Raptor 20A 120W board...


Min output voltage (I'm using a 1K ohm POT + 1.43K ohm resister - for a lower min voltage (~3.0v), switch to a 1.5K ohm POT)...


Max output voltage...


Testing the P-FET for reverse polarity... good to go with protection...


Wiring guide...


External parts that I have breadboarded with the OKL (all bought at mouser.com unless otherwise indicated):
20K ohm resistor (CMF5520K000FKEK)

1.43K ohm resistor (RN60D1431FB14)

2x 22uF input caps in parallel (C3225X5R1C226K250AA)

4x 47uF 16v output caps in parallel (GRM32ER61C476ME15L)

1K ohm POT (PT10MH01-102A2020) (use 1.5K ohm POT for min voltage at ~3v)

2x 10A fuses in parallel (RGEF1000)

P-FET (SUP75P03-07-E3)

1S-6S voltage reader (ebay)

3-pos slide switch (1103M2S3CQE2)
« Last Edit: May 04, 2014, 06:04:10 PM by Breaktru »

Online Breaktru

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #1 on: May 01, 2014, 07:50:15 PM »
Great mamu. Thanks for sharing.
When I looked at the datasheet the other day, I was thinking 1.5K pot and a 1k fixed resistor may push the high end a bit higher than the max 5.5v
Did you get it as a sample?

Offline Visus

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #2 on: May 01, 2014, 09:46:43 PM »
Awesome
it is priced gewd too
Party mod
Put a fan in front of a rudimentary atomizer and vapor a whole room
if only I lived in Colorado

The penguin approves


 :laughing2:

Offline david4500

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #3 on: May 01, 2014, 11:29:06 PM »
« Last Edit: May 01, 2014, 11:32:25 PM by david4500 »

Offline techguy13

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #4 on: May 01, 2014, 11:35:08 PM »
Nice work!  I've been thinking about getting the T-20 as soon as I saw it and this seals the deal for me.  Time to order a couple to tinker with. 

Offline RedLeader77

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #5 on: May 02, 2014, 12:15:13 AM »
Very nice! Being fairly new to modding, i ordered some of these by "Accident". In my attempts to actually use them, most people have told me i need to get a PCB made up for it and that soldering directly to the pads is a bad idea.  You appear to have a different opinion, whats your take?

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #6 on: May 02, 2014, 01:25:35 AM »
Great mamu. Thanks for sharing.
When I looked at the datasheet the other day, I was thinking 1.5K pot and a 1k fixed resistor may push the high end a bit higher than the max 5.5v
Did you get it as a sample?

No sample, I purchased directly at mouser.

A 1K resistor would push the max output voltage to 7.5v - that may not be good for longevity of some of the components on the converter.  The datasheet says "do not exceed the specified limits of the output voltage or the converter's maximum power rating".

I'm good with 5.5v as a max and my sons too.  We're using 1.0 - 1.5 ohm coils and running around 4.5v - 5v output.  We're a bit on the wushy side of power compared to what some are doing nowadays.  :laughing:

is this the OKL2-T/20-W12P2-C or OKL2-T/20-W12N2-C?

The one I'm using is OKL2-T/20-W12N2-C.  Thanks for asking that, I updated the wiring guide title to reflect which one I'm using.

Very nice! Being fairly new to modding, i ordered some of these by "Accident". In my attempts to actually use them, most people have told me i need to get a PCB made up for it and that soldering directly to the pads is a bad idea.  You appear to have a different opinion, whats your take?

I soldered directly to the pads on the back of the board.  Before putting it in a mod I will be putting a generous layer of gel epoxy over the pads and wiring at the edge of the board.  Just a caution if you solder directly to the pads - use low temp when soldering (< 300 °C).



« Last Edit: May 02, 2014, 09:31:40 PM by mamu »

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #7 on: May 02, 2014, 02:31:52 AM »
Note: I just realized I had pins 1 and 2 mislabeled in my wiring guide.  That's been corrected.

Offline Iamthebadass

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #8 on: May 02, 2014, 02:36:53 AM »
Hey Mamu, great job. Does the Zener provide low voltage cutoff? Have you tested it?

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #9 on: May 02, 2014, 05:15:24 AM »
ok... just had a duh-oh moment while tinkering with the breadboarded setup some more - with this board I tied the switch to GND, with a zener diode as a low voltage cutoff inline with GND like this that's a no-go.  Removed the zener and corrected the wiring guide.

Offline dennis15

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #10 on: May 02, 2014, 08:24:20 AM »
 :applaude: Luv it  :yes"

Offline rrtwister

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #11 on: May 02, 2014, 08:29:57 AM »
I guess I'll have to spring for a board. Haven't heard a thing for several weeks on the sample request.

Nice going mamu  :beer-toast:

Offline wwwest

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #12 on: May 02, 2014, 08:45:37 AM »
What is your opinion on the Raptor and OKL2-T20 mamu. Which one would you prefer? To me both would be way more than I need.

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #13 on: May 02, 2014, 10:06:38 AM »
It's too early to tell what my preference would be.  Raptor has been an awesome vaping beast from the get-go.  If it weren't oos I probably wouldn't have gotten around to working with this OKL.

I'm still tinkering with the OKL though (ie., it's a work in progress - the reason the title says "tinkering").  I won't be ready to put it in a mod until I'm satisfied I've got it right and with the right components.  So the wiring guide/external components are subject to change.

I also have a few questions about this board and have contacted technical support at Murata for their advice and am waiting to hear back from them.

I've also spent some time since realizing the zener was a no go with the way it was wired in searching for an easy alternative to low voltage cutoff.  I really want that low voltage cutoff.   :yes"

So far with the testing I've done, the OKL is stable and performing really well.  I've also tested with dual 18650 batts in series and a 12V AC/DC power supply - the wiring configuration handles both aok.  With Raptor I had to change out the 7.5K pull-down resistor to a 4.7K resistor to prevent auto-firing at the higher input voltage.

Murata, manufacturer of this board, also make the OKR, and we know how well received and reliable the OKR modules are.  I wouldn't expect anything different with the OKL, so time will tell.




« Last Edit: May 02, 2014, 11:11:35 AM by mamu »

Offline CraigHB

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #14 on: May 02, 2014, 12:18:59 PM »
In my attempts to actually use them, most people have told me i need to get a PCB made up for it and that soldering directly to the pads is a bad idea.

The type of pads used on that board are actually pretty tough, they're the same ones you see on LEDs with a half via on the edge.  They bite into the board material pretty well.  They should be able to take a good amount of stress from a free hanging wire without the pad separating from the board.

I really want that low voltage cutoff.

A 6V voltage detector should be able to handle the job for you.  I did a quick look at mouser for ones that go up to 6V and found some.  Here's one;

http://www.mouser.com/ds/2/348/bd52xxfve_series-e-209417.pdf

There's some others if you search the category of Supervisory Circuits at Mouser narrowed to 6V;

http://www.mouser.com/Semiconductors/Power-Management-ICs/Supervisory-Circuits/_/N-wnws?P=1yxuc7w

I don't know if 6V is high enough, but that's as high as they seem to go.  If you need something greater, might be able to dig up an adjustable one that goes higher than 6V.  Maybe something like this;

http://www.mouser.com/ds/2/405/sbvs187c-261020.pdf


« Last Edit: May 02, 2014, 12:27:15 PM by CraigHB »

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #15 on: May 02, 2014, 01:10:28 PM »
Great info Craig. Thanks for sharing with us.

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #16 on: May 02, 2014, 02:18:44 PM »
Awesome!!  Thanks so much for sharing, Craig!!  :thankyou:

Browsing now - lol another teeny tiny part. My pieces of verobaord are being put to good use these days.   :laughing:

Offline CraigHB

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #17 on: May 02, 2014, 02:27:54 PM »
There are walls of sorts you have to get over with this stuff.  I know I have one and that's using reflow soldering for major assembly.  I'm really stuck in a hand soldering rut.  I do a little reflow for onesy twosey parts, but just can't seem to get over the wall to do a whole PCB that way.  Anywhere you guys are in working with these parts, I've been there too.  I've just been at it long enough to get over all those little walls.

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #18 on: May 03, 2014, 09:06:15 AM »
Looks like a decent module. Nice work

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #19 on: May 03, 2014, 04:34:52 PM »
mamu, don't forget zener diodes also have an amperage requirement, not just a voltage one, which is why this was probably failing since the draw on the remote is 3mA. Unless I misinterpreted something here...
« Last Edit: May 03, 2014, 04:38:54 PM by whoi »

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #20 on: May 04, 2014, 04:21:24 AM »
After a few days of tinkering and testing with a breadboarded setup off and on, I've run into a few glitches.

The loaded output voltage is now higher than the unloaded output voltage.  At max output, loaded voltage is 5.9v - no load voltage is 5.6v.  The load/no load voltages at lower output voltages aren't as extreme as this, but are still reading higher than no load voltage.

Load voltage higher than no load voltage just doesn't make sense. 

Although I was getting no output voltage drop under load during all this testing, I wired up a second OKL and this time connected the +Sense and -Sense pins.  Dialed the pot to max at 5.6v no load, connected an atty and the loaded voltage shot up to 6.1v with the 1st firing, then fluctuated between 5.8v - 6.0v with repeated firing of the fire switch.  It finally settled in at 5.9v.

Other than the strange initial voltage fluctuations, no difference there with the Sense pins connected vs not connected.  So the Sense is failing to compensate for the unwanted voltage increase - was curious if it would.

So... yeah I'm shaking my head by now and thinking well crap - nothing has changed here.... oh wait - the input voltage has gone from 8.4v no load to now 7.3v no load over these last few days since I initially breadboarded the OKL. 

Replaced those batts with a freshly charged set and now no load voltages match load voltage.  So then connected the 12v power supply and yup - no load match load voltage.

Put the 7.3v battery set back in and got the weird higher loaded voltage of 5.9v vs no load voltage of 5.6v.  Same results with and without the Sense pins.

Am letting this set of batts run down to 7v, then 6.5v, then 6.0v, to see what this converter does with load vs no load output voltages with lower input voltages.

This is a summary of what I'm experiencing at max output voltage:
OKL #1 - without Sense pins connected:
Input voltage-----------Output no load----------Output load
7.3v-----------------------5.6v---------------------5.9v
8.5v-----------------------5.6v---------------------5.6v
12v---------- -------------5.6v---------------------5.6v

OKL #2 - with Sense pins connected:
Input voltage-----------Output no load----------Output load
7.3v-----------------------5.6v---------------------5.9v
8.5v-----------------------5.6v---------------------5.7v
12v------------------------5.6v---------------------5.6v

What *appears* to be happening is that the OKL is not stable with regulating output when input voltage is < 7.5v.  This is not good. :(
« Last Edit: May 04, 2014, 07:37:45 AM by mamu »

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #21 on: May 04, 2014, 04:25:41 AM »
mamu, don't forget zener diodes also have an amperage requirement, not just a voltage one, which is why this was probably failing since the draw on the remote is 3mA. Unless I misinterpreted something here...

Connected to GND via the on/off control is the issue - I'm not getting the zener breakdown voltage of 5.6v.

Offline Visus

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #22 on: May 04, 2014, 07:36:43 AM »
Mamu its probably your breadboard its behavior is defined in the datas

Its also suggest trying different caps up to 188uf  for the output but says match the input as well
As the battery sags it introducing an impedance
Quote
e. Again, use low-ESR ceramic (Murata GRM32 series) or
polymer capacitors. Initial values of 188 ?F may be tried, either single or
multiple capacitors in parallel. Mount these close to the converter. Measure
the output ripple under your load conditions.

Try with a lipo would be my suggestion and then if same  I would change caps..  But 1st I would make an "air" wired breadboard lol



Quote
Output Current Limiting
Current limiting inception is de? ned as the point at which full power falls
below the rated tolerance. See the Performance/Functional Speci? cations. Note particularly that the output current may brie? y rise above its
rated value in normal operation as long as the average output power is
not exceeded. This enhances reliability and continued operation of your
application. If the output current is too high, the converter will enter the
short circuit condition.
Output Short Circuit Condition
When a converter is in current-limit mode, the output voltage will drop
as the output current demand increases. If the output voltage drops too
low (approximately 98% of nominal output voltage for most models), the
magnetically coupled voltage used to develop primary side voltages will
also drop, thereby shutting down the PWM controller. Following a time-out
period, the PWM will restart, causing the output voltage to begin ramping
up to its appropriate value. If the short-circuit condition persists, another
shutdown cycle will initiate. This rapid on/off cycling is called “hiccup
mode”. The hiccup cycling reduces the average output current, thereby
preventing excessive internal temperatures and/or component damage. A
short circuit can be tolerated inde? nitely.


I like troubleshooting

Quote
Due to large stray capacitance (from 2-25pF per contact point), the inductance of connections, and a relatively
high and not very reproducible contact resistance, solderless breadboards are limited to operate at relatively
low frequencies, usually less than 10 MHz, depending on the nature of the circuit. The relatively high contact
resistance can also be a problem for some DC and very low frequency circuits.
Source http://en.wikipedia.org/wiki/Breadboard

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #23 on: May 04, 2014, 08:24:57 AM »
It would be easy to explain voltage drop under load at lower input voltage, but I'm not getting an output voltage drop, Visus, I'm getting an output voltage increase under load with < 7.5v input voltage.

At first I thought well I need to wire in the Sense that would compensate for that voltage increase, but that didn't have any effect.

Full charge batts = no problem
12v power supply = no problem
<7.5v input = problem with unwanted increase in voltage under load

Maybe when Craig checks in he'll be able to explain how a voltage increase under load would happen when input voltage is low.  I have no idea other than its internal to the converter.


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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #24 on: May 04, 2014, 09:38:34 AM »
The data states a +1% rise if short circuit or drop/impedance
your seeing a +1% rise loaded

Its weird that it would do that but that what it says lol

when no load it is free flowing electrons, happy, when loaded it goes in the short circuit condition +1% or your chip is faulty may be also condition..
« Last Edit: May 04, 2014, 10:13:16 PM by Visus »

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #25 on: May 04, 2014, 02:41:08 PM »
Maybe when Craig checks in he'll be able to explain how a voltage increase under load would happen when input voltage is low.  I have no idea other than its internal to the converter.

I'm not sure I understand the problem, but if you're saying output voltage is higher than input, that's a really odd one.  It should not be physically possible for a step down converter to output a voltage higher than input...however...if a converter has a wiring error or some other input-output anomaly, it can do some screwy things. 

Since there is a good amount of inductance inline with the circuit, there can be large voltage spikes that occur during the high speed switching a converter performs (at several hundred thousand Hertz).  In some cases, superfluous voltage spikes can actually fry components within the converter, I've had that happen and it's a major bummer.  When building your own converters, you have to design so those don't happen.

Basic DMMs filter spikes and arrive at an average voltage.  A high end DMM will actually add the influence of those spikes to an RMS reading which will accurately represent perceived voltage.  In some cases, voltage spikes can overcome what a basic DMM can average resulting in an erroneously high reading. 

For situations where noise or voltage spikes are involved, I can't recommend highly enough a decent oscilloscope.  T-Equipment.net has a nice Rigol DSO (digital storage scope) for $329.  If that's not do-able, even an old analog scope can cover you there and you can find decent ones on eBay for less than $100.

Otherwise, if you're seeing output voltage go up when input voltage goes down, that's not that strange really.  There is an amount of regulation error involved wth these switching converters.  It's actually pretty liberal.  Input voltage does have an effect on output regulation error.  It wouldn't be unusual for output voltage to increase or decrease as input voltage drops, but it shouldn't be more than a tenth or two of a Volt.  If it's more than that, there's something wrong.

Don't forget about a converter's drop-out.  For a step-down converter, you need input voltage a Volt or two above output at all times.


« Last Edit: May 04, 2014, 03:50:00 PM by CraigHB »

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #26 on: May 04, 2014, 05:23:23 PM »
ok... been tinkering again and *think* I've now got a stable OKL.

Although the datasheet says input and output caps are optional and not necessarily needed, I feel they are necessary for a stable input and output for our application.  The datasheet says if using caps, use 44uF for input and 188uF for output.  You're not going to find 44uF MLCC caps or 188uF MLCC caps, so the best option is to parallel a lower value to add the capacitance for the total we need.

Also, with my testing without an output cap it makes no difference whether the Sense pins are connected or not - I'm not getting a stable output with or without the Sense when input voltage drops to <7.5v.  It is important then to use both an output cap and connect the Sense pins to get a stable output voltage else you'll be back to an unstable output under load.

Added 4x 47uF 16v caps (soldered together in parallel) to the output, connected +Sense to Vout and connected -Sense to GND and am now getting stable voltage out under load no matter the input voltage level (min voltage should still be ~6v).

I'm still going to be doing a few more days of testing, but hopefully this wiring is now good to go.  I've updated the OP with the latest wiring guide, but can't edit the parts list to add the output caps.

Here's the parts I've now got breadboarded in addition to the OKL:
20K ohm resistor (CMF5520K000FKEK)

1.43K ohm resistor (RN60D1431FB14)

2x 22uF 16v input caps in parallel (C3225X5R1C226K250AA)

4x 47uF 16v output caps in parallel (GRM32ER61C476ME15L)

1K ohm POT (PT10MH01-102A2020) (use 1.5K ohm POT for min voltage at ~3v)

2x 10A fuses in parallel (RGEF1000)

3-pos slide switch (1103M2S3CQE2)

P-FET (SUP75P03-07-E3)

1S-6S voltage reader (ebay)

This has been a rather *fun* project and a great learning experience for me (I say that with a bit of sarcasm) :laughing: but I think we're good to go.  I'm checking in to adding a voltage detector for low voltage protection for the batts per Craig's recommended parts (thanks Craig!) so will update that when I get the parts in.
« Last Edit: May 05, 2014, 01:12:40 AM by mamu »

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #27 on: May 04, 2014, 06:06:43 PM »
Great mamu. Persistence paid off. Well done. I edited the O.P. w/ the output caps included.

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #28 on: May 04, 2014, 06:28:41 PM »
Thanks, breaktru.

This one has been a challenge for sure and has def abated my need to tinker with new toys... at least for a loooong time.  :laughing:

Offline Visus

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #29 on: May 04, 2014, 10:17:46 PM »
Woot
Glad you got it
Read and misinterpreted the rise wrong on the +1v 
Quote
Short Circuit Current (17) Hiccup technique, autorecovery within ±1%
of Vout     0.02 A

I look at what we do,  then look at what it says about it.  We short circuit a wire for tasty occurrence.  It said short lol..

Well I got a D+  here must do more school less watching outrageous acts of science lol,,,

 Awesome if it remains stable...

Offline Visus

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #30 on: May 04, 2014, 10:36:44 PM »
Thanks, breaktru.

This one has been a challenge for sure and has def abated my need to tinker with new toys... at least for a loooong time.  :laughing:

Nooooooo  ya cannot stop we love ya tutorials.    Mucho thanks from so many people..   :thumbsup:


With your popularity--- maybe sky is the limit...

The FDA has approved an ecig manufacturer -- .
Finally medically approved and its the only one and to my knowledge nobody knows this guy.. 
His device is badarse tho, its totally unique..
http://news.yahoo.com/u-e-cigarette-experiment-inspires-medical-device-120928130--finance.html
http://thermovape.com/

Offline CraigHB

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #31 on: May 05, 2014, 03:27:35 PM »
One thing to keep in mind is that step down converters really load the hell out of the input caps.  Boost converters load the hell out of the output caps.  So in this case, additional input capacitance is where you should see improvement in stability.  I would give it a try with no additional output capacitance and the two 22uF MLCC caps in parallel on the input. 

The C3225X5R1C226K250AA MLCC caps you're using are the best ones I've found so far, I use them on the output for my boosters, really good performance.

Offline Iamthebadass

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #32 on: May 05, 2014, 04:33:38 PM »
So I have one of these on its way right now. I only have 22uf caps so I'm gonna have to tinker and figure out how many works best.

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #33 on: May 05, 2014, 06:26:07 PM »
I have been doing testing with 2x 22uF (soldered together in parallel) input caps all this time.

The converter is stable with regulating output and no issues when input voltage >7.5v - with and without the Sense and with no output cap - the converter is aok as long as input voltage is >7.5v. 

With Sense connected and with output cap, no issues.  I removed the output cap and I get issues with loaded output voltage being higher than no load output voltage - more especially so when set output voltage >5v.

I have never seen loaded output voltage higher than no load output voltage until now so is weird.

If I set the no load output voltage at 5.6v, I expect to vape at 5.6v, not 5.9v.   It's like the converter is overcompensating and maybe the feedback loop or whatever is off, especially at higher set output voltages.

Someone else may find different results, but this is what I'm getting with my breadboarded setup.


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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #34 on: May 05, 2014, 06:38:36 PM »


Wire in a button and have a turbo option..  :laughing2:

Good news thats a powerful mod fer sure

Have you run it down to specs @100+W
Not like anyone can vape it there but inspections..


Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #35 on: May 05, 2014, 06:48:57 PM »
lol no I haven't maxed it yet.  I should and see what happens.

Offline Iamthebadass

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #36 on: May 05, 2014, 07:34:12 PM »
I vaped a raptor at 120. It was not fun.

The juice instantly vaporized. All of it. Flooded wicks, still a dry hit.

Offline CraigHB

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #37 on: May 06, 2014, 02:28:28 AM »
With Sense connected and with output cap, no issues.  I removed the output cap and I get issues with loaded output voltage being higher than no load output voltage - more especially so when set output voltage >5v.

I have never seen loaded output voltage higher than no load output voltage until now so is weird.

If I set the no load output voltage at 5.6v, I expect to vape at 5.6v, not 5.9v.   It's like the converter is overcompensating and maybe the feedback loop or whatever is off, especially at higher set output voltages.

Okay I get it now, you're getting excessive regulation error, but the error is positive as load increases instead of negative as you would expect to see. 

I've actually seen this with my boost converters, but not to that degree.  I've seen no load voltage a tenth or two lower than it is with a light load, but then after that, regulation error goes negative as load increases. 

You're right, it's something going on with the feedback loop and how the converter handles no load.  In my case, it's because the converter goes into a low power mode which causes negative regulation error.  I've since changed the controller configuration to disable that low power mode so it doesn't happen anymore. 

In your case, increasing output capacitance reduces no load regulation error, but I can't tell you why.  Maybe I could tell with a scope.  On my own converters I actually run a 1k resistor from output positive to ground to eliminate the possibility of a zero load condition.  You might try that.  Some parts actually require a minimal loading to stay within specified regulation error.  A 1k resistor will usually cover it.

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #38 on: May 06, 2014, 04:44:57 AM »
...I've seen no load voltage a tenth or two lower than it is with a light load, but then after that, regulation error goes negative as load increases. 

That's exactly what is happening with this converter.

I did some high amp testing with the OKL.  I didn't max it out - I did 5.5v with 0.4 ohms (76W and 14A) and the converter handled the load aok and I got the expected loaded Vdrop.

But I feel like I'm in the twilight zone with this converter.  I thought the output cap stabilized it, but now with/without Sense and with/without output cap, at around 3-5A Vout loaded is running up to 0.3v (it varies) higher than Vout no load with Vout set >5v.  And this is no matter the input voltage level.  With the high amp testing I just did, there is the expected Vdrop under load.

I tried the 1K resistor across Vout to GND and no effect - with/without output cap and with the 1K resistor no change.

I give up - it is what it is.   :laughing:
« Last Edit: May 06, 2014, 06:09:09 AM by mamu »

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #39 on: May 06, 2014, 02:04:22 PM »
If you're connecting the adjustment pot through a breadboard, you might try hard wiring it to the PCB with connections as short as possible.  Maybe try a leaded resistor instead.  See if that makes any difference.  But yes, it's a mystery.  You mentioned you emailed Murata technical support about that.  Maybe one of the engineers will get back to you on it.  I have had strange things happen with parts and actually received a response from engineering after sending a query.  Though more often than not, it ends up in the black hole of support requests.  You kind of get what you get with this stuff. 

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #40 on: May 06, 2014, 02:32:51 PM »
I'll do that.  In fact, I think I'll wire up all the parts and see what's what.

Still waiting on Murata rep to get back to me.  I've sent him 3 emails now lol.

I tied Sense directly to the atty pos and neg - still same results.

And exact same results with and without Sense connected.  So the Sense doesn't appear to be doing anything.

Of course that's all breadboarded so will wire everything up directly and with short lines.

Offline techguy13

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #41 on: May 06, 2014, 05:22:57 PM »
I'll do that.  In fact, I think I'll wire up all the parts and see what's what.

That same sort of thing happened to me when I breadboarded the UVT020A0X3-SRZ the other day.  The voltage under load would go high, low and just jump around but once I wired it all together into a small package it started to perform perfectly under load.  I hope it works out the same for you!

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #42 on: May 06, 2014, 10:43:51 PM »
Thanks techguy.

I'm curious - with the converter you're working with, did you wire Sense (VS) directly at the atty connector?  Or connect to Vout at the board?

Offline techguy13

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #43 on: May 06, 2014, 10:56:14 PM »
I wired VS as close to the atty connector as possible just to be sure it would work properly.

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #44 on: May 07, 2014, 12:12:12 AM »
That's what I was thinking of doing for best results so will do.

GE puts out a much better complete and descriptive datasheet than Murata.  Some areas of the Murata datasheet is vague, confusing (to me anyway) or just no info at all.

Hope you posts pics of your build and mod when you get yours done!!  :yes"

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #45 on: May 07, 2014, 12:32:22 AM »
That's why I decided to go with the GE converter instead of the Murata one, it just seemed to have a more comprehensive datasheet to it.  I will post some pictures of my build as soon as I get enough posts to be able to create a thread.

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Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #47 on: May 07, 2014, 10:11:08 AM »
A Murata technical engineer finally got back to me this morning.  I sent another email yesterday evening lol - that makes 4 now.  He probably got tired of the repeated emails and thought he better respond to get me off his back.  :laughing:

There were a few questions I had that didn't get answered.  But he said there are 10 ohm resistors internal connecting the Sense pins to Vout and GND, so the DC-DC will work ok if left open circuit but you sacrifice a small amount of output voltage regulation if left open circuit.   

He also said with or without an output cap, should not affect the Sense.  He also said "We guarantee our output voltage regulation at the point where the Remote Sense lines connect into the Vout and GND busses."

I took everything off the breadboard and wired all components directly to the converter and also tied +Sense directly to +atty connector and -Sense directly to -atty connector.

and... success... no more funky Vout... max unloaded = 5.5v, loaded = 5.5v (this was with a load of ~4A) and with higher loads the expected Vdrop.

I'm going to still monitor input voltage level and Vout load/no load just to make sure I don't re-visit the twilight zone with this, but I think I'm finally ready to put it in a mod.  It took me a while to get there and to get it right, but all is good in the end.  :yes"

I updated the wiring guide in the OP (you may need to clear your cache or hit refresh).



« Last Edit: May 07, 2014, 10:33:49 AM by mamu »

Offline CraigHB

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #48 on: May 07, 2014, 12:43:50 PM »
Sounds like a case where you got hit with the parasitic effect of breadboarding.  The feedback circuits can be sensitive to that.  Good to hear you got it worked out though.

I agree the data sheet is sketchy on that part.  Knowing the function of the sense pads and that they are internally connected would have been nice information to have.  For my own circuits, I'll often pass on parts that don't have a comprehensive data sheet.  Big ding on that one.

Offline Visus

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #49 on: May 07, 2014, 02:17:33 PM »
Breadboard and those crappy meters all wreck havok on precisional.

A good meter, thats mandatory..

Craig said he will sell you his for like 10 bucks in a deleted post but I was upset so he sold it to me for 15 lol...
I am now proud owner of  a  sebastian omnitrix ben 10 meter..
Its in the mail.  lol

 
No really at least freak yourself out confiding with knowing,  it aint your equipment..

Inductance is a tricky unit just ask a joule thief.   :yes"
So ya know your routed wiring is perfect now with two of  those in-line..
If you saw how fast they drain caps you know what I are chats about, its uber fast
that loss cannot be good for holding down the volts stable
using caps on the output if using meter I would say since golden here
if not using a meter none are needed
but ya need a good DMM to know if true

I would bet a margarita in Monaco thats whats what




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