The Rat Flasher - Efficiency Measurements for Boost Convertor

It all seemed so straight forward. Move from two cob leds in series to 4 cob leds orientated every 90 degrees around a case, each with their own boost convertor. How hard could that be?

Trivial, until you try to get every last drop out of the boost convertor. The boost converter data sheet never really envisaged hitting leds so hard for such a short pulse. So when I measured efficiency I found the absolute best I could get was 72% at which point I was hitting the cob led with 250mA with a power dissipation of 2.1W. 

Four of those flashing together was going to be really bright. However, that meant a peak supply current of around 4 x 1 Amp, or 4 Amps.  And a 4 Amp surge meant I had to add larger decoupling capacitors and consider the micro browning out from the voltage dip.

I found the efficiency was dependent on the battery voltage. A drop of 0.5V meant efficiency fell from 72% to 64%. Which means I will have to revisit the PCB at some point to use some bigger traces and eliminate the headers used to connect the battery.  A voltage drop of 0.5V when drawing 4A is just 125mΩ!

A slight tweak in the code means it is now easier to lengthen the time between sets of pulses. The rat flasher had not been in the ceiling for 3 nights, and no vermin had returned, so I applied a cautious tweak. With the adjusted timing I expect I can get 3 nights of solid flashing before the LiFePO4 battery goes flat. Over 24 hours the average current drawn should be around 40mA. I have a solar cell ready to go on the roof which should re-charge the battery during sunny days. With the arrival of spring there will be plenty of sunshine.

Longer term I need to move to a better boost converter. The boost converter this project evolved from uses a NMOS switch with a Rds of 0.5Ω. I expect a step change in efficiency by moving to a boost convertor with on resistance of 80mΩ. And a revised circuit that essentially charges a large capacitor and dumps that through the leds at much higher current, and hence brightness. 

There's no point in showing you a circuit of how not to do this. Another iteration is warranted so please be patient. If your desperate to drive those critters out of your roof and are happy with a less than optimal solution then by all means contact me.

The Rat Flasher - Is it actually killing Rats?

The premise behind the Rat Flasher was it would scare rats off leacing our roof space free of vermin. For some time now there hasn't been any noticeable activity. However, two dead rats have been detected by the smell. 

While I would prefer eviction over death I'm not concerned by the rats death. But I am puzzled by the deaths. Are the rats having a seizure? Are there still old baits in the ceiling?  I don't know but I am certain of one thing: the Rat Flasher has in practice eliminated rats in our ceiling. 

A version with 360 degree coverage is being constructed and a suitable solar panel found to recharge the battery. This should allow for a permanent maintenance free installation. Pictures in a few days.

The Rat Flasher - Evolution continues

So I got tired of recharging the Rat Flasher every couple of days. A software tweak so it only runs at night with 16 seconds of flashing followed by 16 dormant seconds stretched the battery life out to 5 nights. It still seems to be deterring the rats.

After a fair amount of thought I have devised a way to make it easy to install and keep running several of these giving me better coverage of the roof space. More on that in a few weeks when I can show you a picture of a prototype.

The Rat Flasher - Adventures with Roofspace Vermin : Trial Results

Results

Night     Result

1              Reduced activity but at least one critter still present.
                Appeared to move along a "sheltered" recess.
                Noticed again shortly thereafter active in an area the strobe was blocked by air conditioner .

2              One instance of brief activity noticed by wife. Dark part of roofspace

3              No activity noticed

4.             No activity noticed

5              Brief activity noticed in southwest corner of roof

Yellow dot : approx position of Rat flasher

White arrow : direction of flash

Conclusion:

A suitable strobe light appears to deter rats from entering an area. One "Rat Flasher" does a good job but 300m2 of roof space is a big ask. I am surprised that it worked as well as it did.

 

Description of Rat Flasher prototype:

Powered by a single 26700 LiFePO4 battery.

STM8S003 running STM8 eForth which allowed timing parameters to be quickly updated.

 2 x 3W White CoB leds facing in same direction, about 180 degree coverage

Leds dissipating 3.5 Watts 

Yes, it's very bright and annoying. 

I was recharging every day but every second day would suffice.

Next Step

Double the number of leds and orientate for 360 degree coverage

Adjust circuit for additional leds and revise PCB

Bigger battery!

 

 

The Rat Flasher - Adventures with Roofspace Vermin

 

Image by https://www.furaffinity.net/user/mrweirdo6472/

 

 

Not that kind of flasher! The kind with really bright LEDS.  

I've been playing around with backup lighting for my workshop and house. That led me to test a few LED COB's in a torch. One night I was banished to my office recliner with my cold where I lay awake. When I hold the button down on my torch it flashes. I didn't have to do this often to realise how annoying it is. 

Tonight, the Rat Flasher get's a proper test in the roof space. A super bright 60ms flash once per second. All night. I'll report if I hear any critters after testing for a few nights.