Transformer without the AMP output - possible to find out how much it pushes ?

[David Zeno]

Hello,

I have a transformer that was used to power some outdoor Xmas LEDs in some icicles.

The transformer is rated at 12 volts DC output, 10 Watts output.

On the INPUT rating, it says .23 amps / 120 volts ( yes, that's point-23 of an amp ), not sure if this has any bearing on output,
I'm guessing not.

However, there is nothing marked for the AMPS the transformer puts out. Is there a way of figuring this out ?

I have a voltmeter but don't know what to do, in order to figure it out.

Thanks for any help.

 

[alexan_e]

The ratings don't make much sense, the input is 120v * 0.23A = 27.6VA
and you say the output is 12v 10W .. I would expect about 12v 2A but that is 24W and not 10W.

 

[David Zeno]

Hi alexan_e Thank you for responding. I will take a picture for you ( I have the transformer here beside me ) I'll snap a picture of the label, and post it in a few mins. Give me 10 mins please.

 

[David Zeno]

Here is the label:

 

[alexan_e]

This doesn't seem like a transformer, is it switching supply?

The output rating is 10W so this means 10W/12v= 0.83A

 

[David Zeno]

Hi again, Hmm I thought any little box like this, which converts AC power to DC power was called a transformer.

Here is another picture of it on my knee. It does seem there is a little auto-turn off and on, so it turns on the Xmas lights at night, when it gets dark
enough ( photo cell I guess u call it )

This doesn't seem like a transformer, is it switching supply?

The output rating is 10W so this means 10W/12v= 0.83A

 

[alexan_e]

A transformer is something like
https://upload.wikimedia.org/wikipe...nt.agr.jpg/220px-Transformer.filament.agr.jpg
or https://upload.wikimedia.org/wikipe...rmer.jpg/220px-Small_toroidal_transformer.jpg
Transformer - Wikipedia, the free encyclopedia

Your box seems to be a switching power supply Switched-mode power supply - Wikipedia, the free encyclopedia

The stated efficiency on your device still seems low but maybe there is a reason for it in the internal circuit, as you said it is not just a power supply but a control circuit too so there is probably some internal circuit that may consume power.

Alex

 

[David Zeno]

I'll go into why I'm so curious about the amps coming out of that AC transformer.....

I bought this battery box about 2 years ago, it worked well, and still does. It has enough power to start my car if the car battery is dead ( the battery is rated at 800 amps ) Inside
this plastic enclosure is a battery and a power inverter. You can power AC appliances with it, etc, and also it has 12 volts DC coming out if it at the side of the unit via a car lighter entry.

It also has a big port where car booster cables fit into it.

The AC transformer that charges the battery box is rated as follows ( I'm reading directly off it now ) : Input 120 volts / .03 A
OUTPUT is: 13.8 Vdc , 1 A.

Problem: - This died on me a few days ago, and now I'm trying to find a replacement, until I do... I've been using the above transformer ( the one I write about originally in this thread ) to charge
the battery box. Problem -- it won't charge it 100%, and to get it up to only 30% charge, it took 2 full days ( charging all day, and overnight 1 night )

I have a feeling, I'll eventually burn this AC transformer out also, and I may even be doing damage to my battery power box ( what you see in the picture )

 

[autx790]

That does seem pretty inefficient. I wouldn't expect the control circuit to consume much power for something like that. Must be a very poor rectifier circuit and inefficient DC/DC converters to handle driving the LEDs. You also have a night/day sensor on there so like alexan said, it's not just a transformer. What are you looking to do with this? I'm guessing it's broken and you're wanting to replace it with something else?

---------- Post added at 21:40 ---------- Previous post was at 21:37 ----------

You will not be able to fully charge the battery box with the christmas light power converter. The output of the battery box is of a higher voltage, so you will not be able to fully charge it. You would need a higher voltage output source. It's like trying to fill an above ground swimming pool that is 13.8ft tall and you only have a 12 foot tall ladder. Not sure why it got up to only 30% after two days though.

 

[David Zeno]

Hi autx790,

yeah doesn't seem like this thing is pushing much of anything out. This came with some Christmas LED icicles that I bought at Costco. I think it was a set of 8, so a total of 8 LEDs, which we know don't need much electricity to run, so I guess they didn't need a powerful transformer thing.

The battery box is what I want to charge with that power brick ( the one I'm calling a transformer ) that Alex said is putting out .82 of an amp.

Funny thing though - the real power brick ( transformer ) that came with my battery box is pushing out only 1 amp total.

here is a picture of the "tranformer" that came with it.

That does seem pretty inefficient. I wouldn't expect the control circuit to consume much power for something like that. Must be a very poor rectifier circuit and inefficient DC/DC converters to handle driving the LEDs. You also have a night/day sensor on there so like alexan said, it's not just a transformer. What are you looking to do with this? I'm guessing it's broken and you're wanting to replace it with something else?

---------- Post added at 21:40 ---------- Previous post was at 21:37 ----------

You will not be able to fully charge the battery box with the christmas light power converter. The output of the battery box is of a higher voltage, so you will not be able to fully charge it. You would need a higher voltage output source. It's like trying to fill an above ground swimming pool that is 13.8ft tall and you only have a 12 foot tall ladder. Not sure why it got up to only 30% after two days though.

 

[David Zeno]

well, that picture I just posted doesn't show the info very well... here's a better image.. sorry about the other one.

so this is the power brick or transformer that charges that battery box inverter thingie I bought.

you can see it only pushes 1 amp of power. I'm assuming it's the amperage that gives the battery box what it needs in terms of "charge" power ? would that be
correct ?

p.s. - the other side of that power brick plugs into the wall outlet.

 

[kak111]

The AC transformer that charges the battery box is rated as follows ( I'm reading directly off it now ) : Input 120 volts / .03 A
OUTPUT is: 13.8 Vdc , 1 A.

Lead acid battery charging voltage is 13.4...14.4V

These are general voltage ranges for six-cell lead-acid batteries:

Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10–2.13V per cell)
Open-circuit at full discharge: 11.8 V to 12.0 V
Loaded at full discharge: 10.5 V.
Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells

All voltages are at 20 °C (68 °F), and must be adjusted −0.022V/°C for temperature changes.
Float voltage recommendations vary, according to the manufacturer's recommendation.
Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) which is almost as detrimental as excessive voltage (causing corrosion and electrolyte loss)

Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)
Equalization charging (for flooded lead acids): 15 V for no more than 2 hours. Battery temperature must be monitored.
Gassing threshold: 14.4 V
After full charge, terminal voltage drops quickly to 13.2 V and then slowly to 12.6 V.

Source : Lead

Time To Full Charge = Battery Capacity [Ah] / Charge Current [A]
( Add 10... 20% for Efficiency Loss )

 

[autx790]

Hey David,

It is the current that will charge your battery, as the equation above indicates, less charge current means longer charge time. However, in order to get a full charge, you will need to be able to achieve the full voltage with your charger. Think of current as water flow (kinetic energy) and voltage as the potential energy. So if you have a bucket that is 13.8 gallons and you're trying to fill it from a bucket that has 12 gallons, you can have a hose that flows 1 gal/min or 0.83 gal/min. The latter will take longer to fill the other but it will eventually get there, except the bucket you're trying to fill the other from doesn't hold as much so it wont fill up all the way. Sorry, my analogies may not be the best technically. Hope this helps.

 

[Syncopator]

The first item you mention, David, may or may not be a simple transformer, but I suspect that it is (although it may have some circuitry in it which flashes the l.e.ds on and off?). A switch-mode power supply would be much more efficient than a cheap transformer.

As has been pointed out, the power in to the device is over 27 watts yet it delivers only 10. I bet it gets hot doesn't it?

The second device you mention, the charger for your battery box, has an input power of 36W (the current is 0.3A, not 0.03), and the output a little over 13.8. Another cheap transfomer - which also gets hot doesn't it?

None of the figures are remarkable. They are to be expected from transformers of dubious pedigree.