12v Transformer to 12v Rechargeable Battery?

[CCinPA]

Can I connect a 12v transformer to a 12v rechargeable battery to recharge the battery?

 

[hj]

NO!!!! The transformer is AC current and the battery is DC.

 

[Sponsor]

 

[CCinPA]

Suggestions?

 

[Reach4]

Buy a battery charger with automatic control. What kind of battery? If it is a 12 volt lead-acid, I would consider a Battery Tender charger made for motorcycles if it is fast enough. It is easier on the battery than faster chargers.

 

[CCinPA]

Buy a battery charger with automatic control. What kind of battery? If it is a 12 volt lead-acid, I would consider a Battery Tender charger made for motorcycles if it is fast enough. It is easier on the battery than faster chargers.

Isn't a battery-tender 110v in? If so, the source I have is the 12v transformer.

 

[Jadnashua]

You have a steep learning curve before you can get something to work. As HJ noted, you CANNOT apply acv to a battery. A battery requires dcv, and you don't get that directly from a transformer. You need to first rectify that voltage and have some sort of regulation and some means of ensuring you don't overcharge the battery which can literally blow it up or start a fire if done incorrectly. FWIW, if the full charged level on the battery is 12vdc, typically, you need to feed it a higher voltage. Too high, it doesn't work. Applied too long, you can destroy the battery. There are different chemistries of 12vdc batteries, and they each have their own charging curve and actual fully charged value.

And, yes, a typical 12vdc battery charger is plugged into the 120vac wall socket, but, that does not mean it even uses a 120-12vac transformer (10:1), the output would need to be higher than 12vac to be able to regulate it to where it needs to be.

 

[CCinPA]

You have a steep learning curve before you can get something to work. As HJ noted, you CANNOT apply acv to a battery. A battery requires dcv, and you don't get that directly from a transformer. You need to first rectify that voltage and have some sort of regulation and some means of ensuring you don't overcharge the battery which can literally blow it up or start a fire if done incorrectly. FWIW, if the full charged level on the battery is 12vdc, typically, you need to feed it a higher voltage. Too high, it doesn't work. Applied too long, you can destroy the battery. There are different chemistries of 12vdc batteries, and they each have their own charging curve and actual fully charged value.

And, yes, a typical 12vdc battery charger is plugged into the 120vac wall socket, but, that does not mean it even uses a 120-12vac transformer (10:1), the output would need to be higher than 12vac to be able to regulate it to where it needs to be.

You are correct... I am very uneducated on this subject!

So... Are you stating I can't do what I want to do?

If there is a solution, can you provide a link to a recommendation?

 

[Reach4]

Isn't a battery-tender 110v in? If so, the source I have is the 12v transformer.

How do you have 12 volts AC available and not 120 volt AC? Usually a 12 volt transformer has 120 VAC on its input side.

There is a solution, but we need more clarification.

Edit: For a while I was wondering if this was a homework problem.

 

[Jadnashua]

You need a bunch more components than just a transformer. You need to build a DC voltage power supply, which often will contain a transformer, when you want to plug it into a wall socket. Do a search on DC power supplies. Unless this is an educational project, it's much better to just buy yourself one off the shelf.

A power supply will usually have a transformer, a rectifier, a voltage regulator, and usually at least one capacitor. To charge a battery, you may need a current limiter, and a sensing circuit to determine when the battery is charged. Commercial ones often include a voltage readout and a current meter.

 

[JerryR]

You cannot charge a 12v dc battery with a 12v ac transformer. If it’s a small battery that is used to backup say an alarm system then there are solutions that can use 16-24vac/100VA transformer input to feed a charger board such as an Altronix SMP5.
https://www.altronix.com/library/pdf/installation_instructions/SMP5_DIP.pdf

What is the input voltage source for the 12vac transformer?

What kind of battery are you trying to charge? Motorcycle: automobile, small tool battery? How many Amp hours is the battery? What is it going to be used for? Alarm system gell cell? Too many unknowns for anyone to give you good advice.

You could perhaps use a solar charger. That’s what I’m planning on using to charge a lead acid battery to supply occasionally 12 volt lighting in my barn.

 

[CCinPA]

Well... You will either appreciate my honesty... Or shut me down.

Instead of asking for a solution, I will explain the need.


I am an avid garden hobbyist; With the need of challenges, then a solution.


Currently I have a garden-ornament that is powered by a AA(1.5v). As you might expect, the battery only lasts a couple days.


Therefore, I am searching for a solution to power the ornament during daylight-hours.


I read a suggestion of solar… Yes.

 

[WorthFlorida]

You are not going to find anything less than 3 volts are the market. How many batteries does this thing use? One or two? You may have draw full of of chargers from old mobile phones, electric shavers and just about anything that was powered by ni-cad's or metal hydride. Cannot use one for lithium battery. Look at the label or stamping on it. Some were AC output and others DC output.

If you search on solar panels, you find the lowest voltage is 3 or 3.2 volts to power. Any battery powered device like you have for a garden probably wouldn't last more than a few weeks with continuous use. They are usually cheap devices and not designed for continuous use.

 

[CCinPA]

Yeah... I had the below connected with an reducer-pod attached. But, the charge didn't last very long.

So... Me the simpleton, thought I could re-charge it by tapping into my 12-volt low-voltage landscape-wire/lights/transformer.

12V-3.4AH_B12-3 12 Volt 3.5 Amp Sealed Lead Acid Battery

 

[Reach4]

Currently I have a garden-ornament that is powered by a AA(1.5v). As you might expect, the battery only lasts a couple days.

OK. That describes the load. If we presume 2.4 amp-hours from an alkaline battery and the battery lasts 48 hours, that would be about a 50 millamp load. Sound like it might be 1 or more LEDs, but it could be something else.

That should be quite doable. A bridge rectifier fed by 12 vac will give you around 16 vdc (volts DC) with some amount of ripple with load. An LED will not require ripple-free power. No battery needed if the 12 vac is continuous.

1. The 16 vdc could feed a DC-to-DC converter (which I am not selecting for the moment) to produce the 1.5 volts. https://www.digikey.com/products/en/power-supplies-board-mount/dc-dc-converters/922 would be one source of such devices.
2. Alternatively, the load might be powered with pulsed DC. That is fine for LEDs but not some other things. That could be produced by a step-down transformer powered by 12 vac, and producing a between 1 and 2 volts AC (better calculations would be needed). That would feed a rectifier, which could be a bridge (4 diode) rectifier. More efficient would be a center-tapped transformer feeding 2 diodes. With no filtering, each will pulse the light at 120 Hz (pulses per second). That will be mostly perceived as a steady light.

 

[CCinPA]

If I may re-address Solar? I have a solar-panel, output 12VDC/1.5W. Is this a possible solution for me? I understand the output is 12v... But it would provide power to the 1.5 during daylight without the need of charging?

 

[Jadnashua]

You'd need to regulate the 12vdc to 1.5vdc. That's still, essentially, a power supply. If you found a power supply with a 12vdc input that had a 1.5vdc output, that would work. Something like this would probably work for you https://www.amazon.com/Valefod-Effi...vdc+to+1.5vdc&qid=1566874413&s=gateway&sr=8-1

On second thought, I'm not sure that would work well if the inlet voltage varied. Solar cells' output can vary not only in voltage but in current as the light level changes. I don't know how much it varies, or how well that device I linked would track it. It might work fine, I just don't know.