Surge in Voltage - DC to DC Boost Convertor

I have a spare headway cell I am trying to use to power small LED lights. It is a 8amp high power cell, and it is behaving normally.

I have connected this to a boost convertor module from ebay a http://www.ebay.co.uk/itm/XL6009-DC...e=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649. I have the following problem:

I set the output voltage to 12v to power the lights, I check the input voltage it is 3.5V freshly charged.

However, after a while I see that the lights switch off, and I see that the voltage is surging up to 28v and then back down to the 12v. This cycle repeats itself over and over again about every 15 seconds.

What is going on here?

Thank you in advance.

Sounds like a defective or poorly designed DC-DC.

It could be shutting off due to insufficient input (current or voltage) then turning back on with a spike in voltage that then settles down, etc.

Or it could just be broken. :/

When it is doing the cycling, what do you see for voltage on the input, at the battery? does it vary at all?

if it does, what is the amount it varies?

If it is more than a tiny amount then the cell may either not be fully charged (despite the voltage you're reading on it with no load) or it may be low capacity, and dropping in voltage as it runs out below the DC-DC's LVC.

Thanks Amberwolf, very helpful as always.

I will try your suggestions.Have a nice day.

I just checked, the IC used is not the original LM device, it is now XL6009.

This device is specified as operational down to 5V only. What is likely happening is the ic tries to start, storing energy in the inductor. The increasing current causes the battery voltage to droop, and the IC goes into under voltage lockout UVLO. It may even go into a mode, the technical term for this is "stupid", in that there is not enough voltage for the IC to make good decisions.

Switch to an IC rated for operation down to 2.5V. Sadly the LM2577 is not pin compatible.