Want to convert from 9v alkaline to solar rechargeable

A 9V alkaline battery produces a low continuous power. Then an ultrasonic producer will not be loud enough to shoo pests away. A pest that hears one ignors it. About 40 years ago the US government fined companies who made ultrasonic repellers for false advertising. Ask Google if ultrasonic pest repellers work.

Choose high-quality 9V rechargeable batteries, preferably NiMH (Nickel-Metal Hydride) or Li-ion (Lithium-ion). Select solar panels that can provide adequate power to charge the 9V batteries. You also need a solar charge controller, battery holders, diodes etc.

Can you provide me with an example of a solar charge controller for NiMH or Li-ion batteries?

Just a voltage regulator with a series diode at the output to the battery. The solar cell maximum current will act as a current limiter.

For NiMH, use six cells and set the voltage at full charge to around 8.7 - 9V

For lithium, you would need a two cell combined protection and balance module connected between the cells and everything else. Do not use internally protected cells with those.

Use a solar cell panel just big enough to prevent the device shutting off from low voltage; with a simple system like this, the batteries should occasionally reach full charge, but not be held there continuously. Setting it up so the cells partly discharge frequently will give the longest cell life.

(Ideally, they should charge with current monitoring to100%, then the charge shut off until they are down to around 20%, then charge again. Using a barely large enough cell should allow some cycling and avoid them being held at full charge, which can wreck them quickly).


NiMH are really better for a minimal system such as this. They can be held at full charge just about forever, as long as the voltage is not too high.

What is the power requirement of the device?
Over what voltage range will they operate?

I have my own slug-o-cuter (my circuit design) in our garden. I bought a "Newpowa" 30W solar panel, a "Huine" charge controller, and a "Neptune" 7 A-H 12V sealed lead acid battery, all from Amazon. I suppose I could have designed the charge controller but buying one was much cheaper and easier. I don't believe in making my own unless there is a good reason.

I think that one very good option would be to use something like I did, but add a 9V voltage regulator powered from the (to the load) output of the charge controller. The controller has 6 wires: Two to the panel, two to the battery, and two to the load.

The size of your solar panel and battery, and the type of voltage regulator (switching or linear) would depend on the amount of current you need. If the present 9V batteries are the small rectangular "transistor radio" type then it sounds like you do not need much.

If the current is less than 200 mA (for example) then an LM317 linear voltage regulator ought to work well.

Keep in mind that the solar panel power rating applies to new and ideal conditions which happen seldom if ever. I guess my average power consumption might be a couple of watts.

It is my observation that SLA batteries may be better for fixed low-moderate power applications because I think the "care and feeding" of them is easier than Li-Ion. Comparison is difficult because SLA batteries do not like to be deep discharged, but I think SLA batteries are significantly cheaper. My battery was $20 in 2022. A few pounds of battery is not a problem for my situation. This is all now working for its third year in the garden.

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UPDATE to the above: I have second thoughts about the LM317: I love that IC but one drawback is that it will drain a continuous 5 mA or so minimum from the input. So if your ultrasonic gizmo is designed to work on conventional 9V batteries, this could be a big number compared with that from your ultrasonic device. In that case the LM317 could represent a significant load current. Anyway this is just a note of caution; there are plenty of other ICs around which can do the job but the LM317 is inexpensive and is available from several different manufacturers.

audioguru said:

A 9V alkaline battery produces a low continuous power. Then an ultrasonic producer will not be loud enough to shoo pests away. A pest that hears one ignors it. About 40 years ago the US government fined companies who made ultrasonic repellers for false advertising. Ask Google if ultrasonic pest repellers work.

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Just like barking dog suppressors and rat repellers don't always work. It depends on the assumptions. I got 3 cheap AC wall units and put one in each bedroom upstairs as the subfloor had those little noises. Eventually, they were gone and never returned after the winter and next year. But with fresh food, it's hard to deter free-loaders.

But slugs love beer .

Solar Lithium management system :



Regards, Dana.

rjenkinsgb said:

For lithium, you would need a two cell combined protection and balance module connected between the cells and everything else. Do not use internally protected cells with those.

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Bear in mind, this is NOT a charging circuit, you still need a properly designed Li-Ion charger as well as the protection circuit.

But as you also suggested, NiMh is probably the easiest option - and needs nothing other than the solar panel, a reverse blocking diode, and perhaps a series resistor?. Depending on the power requirements of the load, a sensibly sized solar panel will be unable to over charge the battery or cause any issues.

However, do these units actually do anything?, there seems little evidence that they work, and certainly ones powered by PP3 batteries are going to be exceptionally low power (if not just a complete scam).

There are new Chinese no-namebrand 9V Lithium rechargeable batteries (charged from 5V USB) available at VERY low prices. no specs, I do not recommend them.

Have you considered interfacing solar powered ground lights to the battery charger - on by day, off at night?
I realize you'll need several of these lights to recharge the 9V battery, but may be more affordable depending on your setup and situation.

shokjok said:

Have you considered interfacing solar powered ground lights to the battery charger - on by day, off at night?

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I am not the original poster, but I do not understand what you are describing. Lights that are ON during the day? The original question does not deal with lights. I suspect that I am not the only person who does not understand what you are proposing.

Yes, 9V batteries are quite expensive.

You can easily convert 9V to 6 x R20/AA batteries which are probably cheaper than a 9V and last (wait a minute check my notes here... ) at least 20 times longer.

It is actually the case that if you "open" a 9V battery, there are 6 small batteries inside.

netrunner_sw said:

You can easily convert 9V to 6 x R20/AA batteries which are probably cheaper than a 9V

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That sounds like a good idea. But while you are at a solution that does not physically fit in the original case, why not go to C cells or D cells? I think that the $/(mA-hour) goes down as the size goes up. Of course I do not want to get ridiculous about this....

The OP would be better off with proven technology like, fences, netting, traps and pesticides. Even better would be to get vegetables from the market. If ultrasonics worked, farmers would be building solar or wind powered gadgets all over their fields.

Karklebapper said:

I am not the original poster, but I do not understand what you are describing. Lights that are ON during the day? The original question does not deal with lights. I suspect that I am not the only person who does not understand what you are proposing.

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Removing the light bulbs and connecting the solar light bulbs socket wiring in series to attain a 9V output directly connected to the battery. I use two 12W solar panels connected in series to recharge my 19.2-volt Craftsman cordless tool batteries. My Craftsman batteries do not force an overcharge condition - too little sunlight during the setup time.

audioguru said:

There are new Chinese no-namebrand 9V Lithium rechargeable batteries (charged from 5V USB) available at VERY low prices. no specs, I do not recommend them.

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Indeed.
Too cheap to be legit.

schmitt trigger said:

Indeed.
Too cheap to be legit.

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The price of lithium is down more than 85% from 2-years ago and the mining & extraction companies put a bunch of money into more capacity so they expect to move some product. Get ready for inexpensive EVs and cheap rechargable batteries - especially from China.

So more of this?