Kaidomain 8x7135 driver question

I recently found out that my KD 8x7135 driver doesn't draw 3A at high from a fresh set of cell (dmm reading 4.18V). The highest it went was 2.2 to 2.4A.

I later used an external power supply to check; in order for the driver to draw 3A the voltage must be at 4.8V...

Is this normal?
Thank you.

I tested on 2 of my flashlights with the same driver & both have the same issue

How are you measuring the current? Some DMM leads are very thin and have a significant voltage drop.
This is not normal behavior, that's for sure, but it doesn't have to be caused by the driver.

Use thick leads (0.25mm2 at least and 0.5mm2 for DMM) and try again.

I mentioned the ways of measurement in my OP...
As for the lead, i was using the original probe from the DMM

No offence, but the way of measuring current is not in the OP?

DellSuperman said:

I recently found out that my KD 8x7135 driver doesn't draw 3A at high from a fresh set of cell (dmm reading 4.18V). The highest it went was 2.2 to 2.4A.

I later used an external power supply to check; in order for the driver to draw 3A the voltage must be at 4.8V...

Is this normal?
Thank you.

Click to expand...

You are measuring the voltage with a DMM, that's obvious. But no word on the current. I used to measure the current with my DMM, but I now have a dedicated measuring device (not sure about the name in English): http://tweakers.net/ext/f/5wgu2dI3DWKrkYv8oB6SUedm/full.jpg

But, I presume that you are measuring current by connecting the DMM in series with the driver. Try using the same method, but with thicker leads instead of the the leads from the DMM.
Also, measure the voltage difference from the Battery + and Led +. It should be near zero.

Epsilon said:

I used to measure the current with my DMM, but I now have a dedicated measuring device (not sure about the name in English): http://tweakers.net/ext/f/5wgu2dI3DWKrkYv8oB6SUedm/full.jpg

Click to expand...

I'm not sure all English-speakers would agree, but in the US we would call that a clamp-on ammeter, sometimes abbreviated to clampmeter. For anyone who isn't familiar with these, they are a great tool for this measurement, as they will measure current without adding any resistance to the system. Using a DMM with leads will ALWAYS add resistance, and will often change the current it's trying to measure. If anyone is thinking of getting one, make sure you get one that will work on DC. 99% of these (including all cheap ones) measure only AC with the clamp-on part. If they measure DC, it's with leads.

To the OP: Try measuring the voltage between the input and output of the driver. This is the 'overhead' of the driver. You should be able to get full output current with an overhead as low as 0.2V or less. This should be measured at the terminals of the driver.

If you have more than 0.2V overhead and less than full output, something is wrong with the driver. If you have less than 0.2V of overhead and 4.2V of input, you have some excessive voltage losses somewhere outside the driver.

As Epsilon has pointed out, the overhead and current measurements have to be made without changing the system. You can't measure the overhead, then move the meter to the output line and change it to read current. This would result in two measurements that while both accurate, do not represent the same system.

Epsilon said:

No offence, but the way of measuring current is not in the OP?

You are measuring the voltage with a DMM, that's obvious. But no word on the current. I used to measure the current with my DMM, but I now have a dedicated measuring device (not sure about the name in English): http://tweakers.net/ext/f/5wgu2dI3DWKrkYv8oB6SUedm/full.jpg

But, I presume that you are measuring current by connecting the DMM in series with the driver. Try using the same method, but with thicker leads instead of the the leads from the DMM.
Also, measure the voltage difference from the Battery + and Led +. It should be near zero.

Click to expand...

Sorry, my 1st method of measurement is using the DMM set to read amperage up to 10A.
2nd method is using an external power supply with variable voltage & current settings.
With current at 3A & voltage at 4.2V, the max current draw was 2.2A.
Only when i raise the voltage dial slowly to 4.8V, the current draw was able to hit 3A