Small solar powered DIY project - advice please

[dogfonos]

I have a raised garden vegetable bed fitted with an electrical slug & snail deterrent. This deterrent consists of two bare conductors spaced about 1cm apart that run around the bed's perimeter (around the outside, a few cm's down from the top edge). Currently, I power it with a 9V battery connected to the wires via a resistor that limits current flow to 180mA when the conductors are shorted. This does a great job of keeping the bed slug & snail free.

I'm looking into replacing the battery with a solar panel powered setup. Clearly, as most slugs & snails visit at night, I would require battery backup and this is the bit I don't understand. Could I simply connect a sealed lead acid battery, of suitable voltage, directly to a solar panel (maybe a solar panel designed to trickle-charge batteries?) then also connect battery, via resistor, to the two 'electric fence' conductors? Or do I need some sort of controller?

Advice much appreciated, thanks.

 

[JohnW2]

.... Could I simply connect a sealed lead acid battery, of suitable voltage, directly to a solar panel (maybe a solar panel designed to trickle-charge batteries?) then also connect battery, via resistor, to the two 'electric fence' conductors? Or do I need some sort of controller?

Essentially 'yes'. IF you have a rechargeable battery and a "solar panel designed to trickle-charge a battery (of the type in question)_" (which may mean that the panel includes some sort of 'controller') then, yes, you could then treat the battery just as you currently dowith a non-rechargeable one.

Kind Regards, John

 

[winston1]

Put a diode in series with the panels output to stop the battery self discharging through the panel at night.

 

[JohnW2]

Put a diode in series with the panels output to stop the battery self discharging through the panel at night.

I thought that solar panels usually had built-in diodes to address that potential issue?

 

[Astra99]

I use a 25W solar panel for lighting and small amounts of power in my garage. The panel itself has built-in diodes to prevent discharging at night, but does not have voltage control. In the height of summer the panel voltage can rise to over 20V open-circuit, and 16V plus when connected to the battery. This caused my inverter to shut down as the input voltage was out of range. If you are not using an inverter, or anything which may be voltage sensitive, you may well get away without using a voltage regulator on the solar panel output.

 

[SFK]

Suggest you Use a solar panel controller. Many out there. This is an example one.

https://www.amazon.co.uk/Controller-Topcloud-Parameter-Adjustable-Regulator/dp/B08FCQB173/ref=asc_df_B08FCQB173/?

 

[dogfonos]

Appreciate the advice and guidance.

Just like everything in life, the more you look into things, the more complicated it gets - not to mention expensive. My preferred choice of battery, sealed LA, has fussy charging requirements for a long service life - constant voltage is most important, I think - so I'd need a controller to limit/manage voltage from the solar panel feeding into the battery as well as to prevent battery discharging through the solar panel at night (assuming panel doesn't have suitable circuitry/diodes built-in).

I'll need to Google some more when I have time. I can't justify spending too much on this small project just to replace a standard 9v battery which does the job anyway and has been working fine for a few months already. Current draw on the battery is zero almost all of the time and only 180mA max. when loaded (which I would imagine is for just a few seconds per 24 hours).

Thanks again.

 

[ericmark]

You can get MPPT or PWM controllers/regulators for solar panels, the controller uses some power, so it depends on the size of the solar array as to which is best.

The MPPT turns DC to AC transforms it and back to DC so it can gain power sooner and latter than with a simple zenor diode and a diode to stop battery feeding solar panel, but this means a 50 watt solar panel with one controller can supply a different amount of power as same panel with a different controller.

Also use wise, it depends on the size of the invasion force, so need to at least fit an energy meter to it for a day to get some idea.

 

[JohnW2]

You can get MPPT or PWM controllers/regulators for solar panels, the controller uses some power, so it depends on the size of the solar array as to which is best.

I think this discussion may be forgetting about context.

As I understand it, in the OP's case, the required 'power' (to the load) is effectively zero, since he merely wants to establish a pd between two bare conductors as a slug deterrent (a bit like an 'electric fence'). When things get wet, there will be a tiny current but, when dry, current (hence 'power') will be zero.

The OP's requirement therefore reduces to wanting a solar setup which will safely maintain full charge in a battery which is supplying essentially no current (i.e. 'trickle charging'), and (as I said at the start) I thought that there were small solar panels designed for exactly that purpose, hence presumably with some sort of in-built 'controller' to limit the 'trickle charge current' to what one wants for the battery concerned?

Kind Regards, John

 

[dogfonos]

Also use wise, it depends on the size of the invasion force, so need to at least fit an energy meter to it for a day to get some idea.

"Invasion force" - I like it. That's what it feels like in our garden.

At present, I'm gradually adding extra resistors into the circuit to establish an optimum max. current flow (i.e. enough to deter the large invaders yet not enough to kill the small ones). Presently, 180 mA max. is killing the odd small slug yet still deterring the large snails & slugs so I can reduce max. current further still. Not surprisingly, I can't find any info. on this topic so it's trial & error all the way!

When things get wet, there will be a tiny current but, when dry, current (hence 'power') will be zero.

I haven't actually measured this current but it must be low because it's been wet lately and the small PP3 battery hasn't drained. A prototype wooden veg bed - with electric fence - I constructed many years ago suffered badly in this respect and ate batteries, hence the change from wood to recycled plastic 'lumber' (which I forgot to mention previously).

The OP's requirement therefore reduces to wanting a solar setup which will safely maintain full charge in a battery which is supplying essentially no current (i.e. 'trickle charging'), and (as I said at the start) I thought that there were small solar panels designed for exactly that purpose,

Indeed there are, however it seems to me that the ones I've seen are designed to trickle charge standard lead acid batteries and I'm unsure if they'd suit SLA batteries. I agree that the amount of power required from the solar panel must be really low. The invaders are not consistent. On some dry, cold nights they may not trouble my defences at all whereas it's the opposite on warm, damp nights, so trying to get an idea of average energy used would be tricky.