Noobie question. I have a 3.7 V battery hooked up to a DC DC boost converter. Free and clear the boost measures 7.4V output, what is needed for the remainder of my project. However, when I hook the boost converter output to the VIN/GND pins of my Arduino Nano the whole circuit drops to ~4.8V. This happens with or without other components hooked in (i.e. hooking up the Nano alone drops the voltage output across the pins of the boost to 4.8V). I'm soooo close, and SOOO fustrated. What am I overlooking?
If you apply a voltage to the Vin it will pass threw a voltage regulator of 5 volts. I don't know where you are measuring but since you said the entire circuit I assume you overlooked this voltage regulator.
Sincerly Yours,
Mike
So, lets phrase a different way. I think I just picked a boost converter poorly. Just measuring across terminals of boost, 7.4V. When hooked up to circuit, drops to 4.8V. While hooked up, turned potentiometer screw and could not get above 5V, when unhooked at that setting value across terminals of boost 20V. Hooked up another boost I had (fancier with LED readout), 7.4V unhooked up, about 0.5V drop when hooked up, circuit worked but this boost is too large for my purposes.
Specs on first boost "DSN6009 4000Khz 4A switch, module XL67009E. Input 3-30V (mine is LiPo 3.7V+/-), output 5-35V (desired 7.4V for LED array, also need about 3A). The 'good one' was about the same (input voltage: DC3-34V;Output voltage: DC 4-35V(Continuously adjustable);Max input current:3A;Max output current:2.5A). What specs should I be looking for to evaluate true performance?
[PS, 'bad' boost uses XL6009E, 'good' uses older LM2577 switch. Then I read that XL6009 must operate at 5V or more, spec'd wrong on Amazon description.]
All help and advice appreciated.
From your description, the boost regulator is not working correctly and may be defective.
Check that the battery voltage isnt sagging below 3V when you connect the load.
Its not uncommon for adjustable boost converters which have a wide input voltage range to struggle when the input voltage is close to the minimum spec.
Also seems that the converter is a buck / boost type as the output voltage can be above or below the input.
Tricky things to design for a wide voltage range.
Its better to just pick a boost converter if your output voltage is always greater than the input.
Hi,
As @mauried has suggested, measure the input volts to the DC-DC converter and see if that drops below the spec for input voltage for that DC-DC converter.
Tom.. 
Gerbe:
[PS, 'bad' boost uses XL6009E, 'good' uses older LM2577 switch. Then I read that XL6009 must operate at 5V or more, spec'd wrong on Amazon description.]
Yeh, you are right. Looks like the XL6009 is out of spec below 5V so anything could happen.
Yours,
TonyWilk
I performed a test here using a DC/DC boost converter about 2 months ago because I wanted to see what the output voltage looks like when you put a load on it. I used 2 18650 batteries in series (both 3.7V 5800mAh) I connected a computer controlled load at the output that could max draw 25W (more then the converter could provide) so I used the computer to control the load, the Amps that the converter should provide, and at it's specified max A the voltage dropped to 0 (the overload protection kicked in). Since I didn't have the components to build a voltage divider that was powerful enough to play with the input voltage I then switched to my regulated power supply (max 36V 10A) According to the specs the min input voltage had to be 5V. When turning the voltage down on the power supply to 4.85V I saw no problem on the scope concerning the output voltage with a load of 1A. When turning the load slowly up (increments of 100mA) I noticed the output voltage at 1.8A load started to change form and it went down in voltage to 8.1-8.2V (setpoint was 10V). When turning up the load to around 2.5A at some point the voltage collapsed to 2V but it looked as if it went down to almost 0V and then rather quickly go up to those 2V, to then slowly fade out to 0V again. At 4.6V input voltage the output was as good as dead, you saw a little spike at a regular interval to about 1.4-1.5V but it was very short, this was at a load of 0.2A.
To bad I didn't record this test on my scope, or took screenshots, I was just playing around a bit, also connected square waves to the input, for a project I was working on, but that was a total disaster.
I think this proves that you really need to provide the min voltage specified in the specs (5V), and if you want to power it from batteries you should keep an eye on the battery voltage drop when you connect the converter. I was only able to measure the current at the output using the computer. Maybe I should do this test again and use the Amp clamp I recently bought to connect to the scope.
I hope this has helped you,
With regards,
Mike