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Author Topic: Tinkering with the OKL2-T20 20A 110W dc/dc converter...  (Read 3817 times)

Offline mamu

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Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« on: May 02, 2014, 02:32:54 AM »
Well crap - thought I posted about my new toy here yesterday and came to check and it's not here then realized I must have hit Preview instead of Post or maybe I thought I posted here and didn't.  *sigh*

This is the OKL2-T/20-W12N2-C 20A 110W DC/DC Converter.

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

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 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)
« Last Edit: May 04, 2014, 05:31:51 PM by mamu »

Offline Blewt

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #1 on: May 02, 2014, 06:53:29 AM »
Awesome as usual.  Too bad it's Greek to me :D
No oral or dirty trombone and I am in.
I will give you a taint massage though.

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #2 on: May 04, 2014, 03:44:20 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, 06:38:57 AM by mamu »

Offline mj

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #3 on: May 04, 2014, 10:11:01 AM »
Hmmmm..  Data sheet says nominal Vin is 12....  Apparently I haven't had enough coffee to decode the revision level code on that chip label.
Fortune favors the bold.  Leave it all on red and hold my beer.

Offline junquedujour

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #4 on: May 04, 2014, 11:20:13 AM »
maybe this is the issue MOC is having. heh.

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #5 on: May 04, 2014, 03:08:34 PM »
That is common, mj, with these dc/dc converters.  Performance specs, efficiency, etc are referenced at 12v so that is referred to as nominal.

Offline mj

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #6 on: May 04, 2014, 03:27:20 PM »
Well, hell, I'm sure you rechecked all your parts and connections and shit.  Anybody else working with this board?
Fortune favors the bold.  Leave it all on red and hold my beer.

Offline mamu

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Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #7 on: May 04, 2014, 04:25:13 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 and parts list.

This has been a rather *fun* project and a great learning experience for me (I say that with a bit of sarcasm)  :cheesy: 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, 12:16:31 AM by mamu »

SpaceCiggysForum

Re: Tinkering with the OKL2-T20 20A 110W dc/dc converter...
« Reply #7 on: May 04, 2014, 04:25:13 PM »

 



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