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# Is this an accurate way to test laser current?

#### weidmark

##### New member
Hi I saw this method of testing how many amps of current your laser's driver is putting out. I tested this method with my yobresal lasers and got just above 1A which seems right because they are 1w-1.2w lasers. Now in the laser i built, i set the flexdrive to 1.1A (i had it set up to go for 1.5A but i couldn't seem to get the pot to get there). So now i have done this method on the laser i built but i get a reading of 1.5A. So i'm wondering if this method is accurate? Could i possibly accidentally set the driver to ~1.5? That seems pretty unlikely. Here is the test.

Thanks. Hopefully i am clear in what i'm asking

#### DTR

##### Well-known member
LPF Site Supporter
If the laser is using a linear driver you can test with this method. With a boost driver like the flexdrive it draws extra current to boost the voltage. I believe there is a way to calculate it but I have not seen the formula.

#### Drew

##### New member
Battery current draw (a) x battery voltage (v) under load = watts input. Then the driver efficiency and laser efficiency must be factored in. Flexdrives are very efficient and 445's put out in watts roughly what is put in in amps of an 18650 i believe. About 1 watt out for 3.5 in? Best way is to dummy load the driver before hooking up the diode

#### DrSid

##### New member
I think the power metering should be quite good, but you would also have to measure actual battery voltage under load, as it for sure will drop a bit.

My 445 with diode current set to 1.5A takes 2.3A at the battery (3.7V). But I did not measure the drop. Without drop it would be 8.5W at the input. On diode it would be 1.5A*4.4V = 6.6W. That would give driver effectiveness 77%. With voltage drop at battery the effectiveness would get a bit higher.