OKR-T/10 Voltage Drop Issue

[whoi]

So I put a .6o coil on my build @ 5.4vout which should be possible and the voltage is dropping to 4.6vout when I attach the atomizer.  The batteries are at 7.15v and I have 18awg runs from the battery and to the atomizer. Anyone know why the drop is so low?

[CraigHB]

You normally get some error in regulation when going from no load to a heavy load, but it shouldn't be that much, a tenth of a volt or two is maximal.  You should measure and adjust under load to get the best accuracy.

At .6 Ohms and 5.4V, you're right up against that regulator's output limit of 50 Watts.  If your atomizer measurement of .6 Ohms is not accurate and you are in fact running somewhat less, then the regulator is bumping up against its output limit.  Typically DC-DC converter based regulators use "hiccup mode" over-load protection which means the regulator reboots in a sense.  It will do that at a frequency of a couple thousand Hertz and a meter will average output somewhere between zero and the voltage setting.

The regulator should be able to handle a maximal output of 50 Watts, but it's right on the edge so the regulator may be destabilizing and failing to regulate output properly.  There's a host of issues that can cause a regulator to destabilize at high outputs.

Excessive input or output impedance would be a likely cause.  If you've added input and/or output capacitors, verify they are within specifications defined in the data sheet.

Verify you're not getting big losses in input voltage.  For those high outputs you need high quality connections to the battery and the cells need to have low internal resistance.  From your description that does not sound like your issue, but even so, impedance that may not be obvious with a simple voltage measurement can still cause problems for the regulator.  You would actually need to check that with an oscilloscope.

The feedback circuitry is sensitive to electrical noise.  If you are using unusually long wire runs to the adjustment pot, that can cause the regulator to destabilize at high outputs.

If you're relying on a simple LED voltmeter, it could be the meter is not accurate.  Double check your output with a proper DMM.  Switching regulators get noisy at high outputs and a simple LED meter may be in error due to a noisy power supply.

[whoi]

I have a feeling its my battery sled. It has coil springs and they are bit jenky.

I built another one in a box with short runs and a different battery sled and it works like a champ.

Thanks again for the input Craig. Your always in point.

[djboa]

5.4V out
7.15V at batteries

you need a minimum 2V difference per okrt10 specs .... charge your batteries and try again

[mamu]

We've been seeing this a lot lately.

Using only Keystone contacts and batt holders is highly recommended.

[djboa]

I agree that the contacts will play a part running at the upper end of the range

- but testing on fully charged batteries, and within spec is the only way to beeing able to draw any conclusions. Below 3.6V per battery is a long way from a full charge, and the 2V difference minimum is real as per my experience.

[CraigHB]

Found the spec in the data sheet, note 16 below the specification section;

Vin must be 2V or higher than Vout for 3.3 to 6V outputs: Vin >= (2V + Vout)

So if you're not meeting the dropout spec, the regulator will fail to provide the desired output.  Since input voltage drops an amount under load as a function of input impedance, you need to use cells with low internal resistance and use quality connections with minimal resistance.  Even so, you need an input voltage of at least 7.4V to provide maximal output at 5.4V.

I was under the assumption dropout on that regulator was closer to 1V which would be the case for a step-down converter with a maximal 95% duty cycle.  Evidently, this one uses a 90% maximum duty cycle which is a big ding against it.  Usually step down converters have a max between 90 and 100%, but the higher the better.  There are 100% duty cycle step-down converters that have almost no dropout, the OKR is definitely not one of them.

[mamu]

The OKR datasheet on Vin to Vout is misleading.  2v higher Vin than Vout is a margin for maximum efficiency.

The OKR does not require 2v higher voltage to operate as it appears the datasheet is saying.  It requires ~.5v overhead (6Vin for 5.5Vout), but efficiency will drop from ~97% to ~90%.  The same thing happens with the TI Evercool converter.

CapeCAD did side by side comparison testing and this was his results:
TI minimum input voltage = Vout/0.83
OKR minimum input voltage = Vout/0.86

Based on his results, the OKR will give longer vape times before cutoff.

[CraigHB]

That's good then.  Nothing like bench testing to nail those specs down.

[whoi]

I tested with full charge batteries as well. I am pretty sure its the sled. My second OKR is using http://www.digikey.com/product-detail/en/BK-18650-PC4/BK-18650-PC4-ND/2330513 works great.

[Breaktru]

I tested with full charge batteries as well. I am pretty sure its the sled. My second OKR is using http://www.digikey.com/product-detail/en/BK-18650-PC4/BK-18650-PC4-ND/2330513 works great.

I use that same holder for my bench testing

[Madmanmacguyver]

I use the 3 cell version of those...they meet my needs very well just watch out for the wrappers on the batts, on some I wind up having to use a chopped credit card to extract the batts safely...