XL6009 not delivering enough amperage

Other Hardware General Electronics
1

Hello,

I hope I didn´t miss any previous posts about the XL6009 step-up, but couldn´t find anything that suits my problem:

I´m trying boost 2xAA batteries in series to achieve a 12V output for running a solenoid. So far so good, 12V are easy to set up. The problem is, that the solenoid doesn´t make any attempts to move. Hence, I measured the amperage and got a number around 20mA (while 300mA are needed). If I got it right, input and output follow the rule:

P[sub]In[/sub]=P[sub]Out[/sub]*efficiency

V[sub]In[/sub]*I[sub]In[/sub]=V[sub]Out[/sub]*I[sub]Out[/sub]*efficiency

The XL6009 allows an efficiency of up to 0.94. If I want to get 300mA Output, I need to supply a minimum of 1200mA Input. The batteries should easily be capable of delivering this amount. Even if the efficieny is pretty bad, there shouldn´t be any problem.

So what am I missing?

Thanks in advance,
Fosekosz

2

The datasheet of the chip states a minimum input voltage of 3.6volt.
The (unspecified) AA batteries could sag to 1volt under load.
If the chip would work on 2volt, the batteries would have to supply ~2Amp.
Only some types can, for a short time.
Leo..

3

Thanks for your fast reply.

What may be the solution for my case now?

Adding another AA to supply 4.5V? But than I run into trouble with the power supply of my Arduino Pro Mini 3v3, which I don`t want to run from RAW input for power saving reasons. Furthermore I´ll have problems with space.

Or using another Step-up?

Thanks!

4

Fosekosz:
Furthermore I´ll have problems with space.

Then go for a li-ion battery instead. A single 14400 battery (same size as a single AA)could provide 3.7 volts.

or

use 3xAAA Ni-MH and you get 3.6volts and it will only take about the same space 2xAA would.

I've used XL6009 modules and it needs above 3.5 volts to do a stable boost conversion.

5

And a 3,3V Arduino works just fine @ 4,5V.

But uhm, 3 AA's in series might still drop under load. The 300mA (and probably higher on inrush...) is already 800mA in the low side (not counting losses and assuming the full 4,5V). But under a load like that the voltage is likely to drop which results in increased current etc. I don't think a small pack of AA's can deliver enough power at once.... A lithium battery is better at that. Or if you need a small pulse you can charge some caps and discharge them at once through the solenoid.

6

Okay, Lithium battery sounds fine. I will try that, thanks for your help!

7

septillion:
And a 3,3V Arduino works just fine @ 4,5V.

The (official) ProMini has a solder jumper to separate the output of the regulator and the power LED from VCC.
Maybe wise to cut that link if you use a higher that 3.3volt supply. That could also reduce current draw by ~0.5mA.
Leo..

8

The datasheet I found says a minimum of 5V for the input side.

That solenoid wants nearly 4W, its not a trivial load, I'd ask if there's not a lower power alternative
or whether you can use capacitor boosting? What on-time and duty-cycle are you needing?

9

@Leo

Yap, heard about that already. Plan to do this when tests run fine.

@Mark

Maybe a capacitor is an option, just need the solenoid to snap back once (.5 - 1s). Another solenoid is hard to get, because of the desired dimensions. Searched a long time to find at least one that fits.

10

This page, with graphs, might be interesting.

Leo..

11

If I get it right, the last graph says - with 2.7V in and 12V out - 300mA aren't even possible. Does that apply generally or only to the Pololus?

If the former is the case, a capacitor is my only chance?

12

Of course a datasheet is for the device it's for.... Unless otherwise stated.