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newbie question

Andy Street

Nov 23, 2015
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Hello folks,

Please excuse what is probably a silly question, but I would rather ask silly questions than catch something on fire.....

My wife has recenty purchased 5 sets of solar powered garden lights.

These work fine when fully charged, but the UK winter does not give enough light to charge the small internal batteries.

I was looking to connect the internal batteries ( 1.4V dc, 1000mAh, AA size ) to a small power supply to trickle charge them during the day & night.

I think that connecting them in parallel should give me a capacity of 5000mAh, so a charge of 500mA shouldnt cause any problems.

I want to leave in the current solar panels, as there is a light sensor built in to switch them off in the daytime, and I was looking to keep that.

I have a number of assorted low voltage power supplies with outputs of around 500mA.

Can I just wire the batteries together in parallel and feed them from one of these ?

I can put am ammeter in the circuit to make sure I'm not pulling more than 400 - 600 mA

I am sure there are lots of better ways to do this with circuits and transisters etc, but I'm afraid my skill level with electronics is limited to a miss spent youth bodging car electrics back together and fixing children's toys :)

Many thanks for your help.

Andy
 

Martaine2005

May 12, 2015
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Hi Andy,
If you are going to leave them connected day and night, why not just disconnect the batteries and power them as you described.
They are probably LEDs and a100ma adapter would more than likely be fine for all 5.

Martin
 

Andy Street

Nov 23, 2015
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I did consider that, but I was unsure if it would be safe to run it during the day, with the LEDs off without the battery as a "buffer "
 

Martaine2005

May 12, 2015
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That would make no difference what so ever. If the LDR is still in circuit, it wont switch on until dusk.
Replicating the original circuit, without the battery.
You might want to clip the solar panel wire too.
Other than that, it will work the same way for British summers ...

Martin
 

Arouse1973

Adam
Dec 18, 2013
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I think most modern lamps like this use the solar panel as the light detector as well as charging the battery, but I might be wrong. You may also need to find out if the circuitry inside has a little boost convertor to take a single cell battery up to a voltage high enough to drive the white LED at the specified brightness. So you may have to have a mains timer for the PSU and disconnect the solar cell as already mentioned.

Can you take one apart and take some pictures of the PCB, we may be able to see what type it is.

Adam
 

Andy Street

Nov 23, 2015
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Pictures enclosed
 

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Andy Street

Nov 23, 2015
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It does look like the solar panel is used as the light sensor, as there seems to be no spare wires to the front plate.
I cant imagine it is very complex, it runs 100 led's and the entire unit, including battery & led's only costs £7.99 ( about $12 )
 

Arouse1973

Adam
Dec 18, 2013
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The 4 pin device might be a little booster for the LEDs? Can read any markings on the device?
Adam
 

Andy Street

Nov 23, 2015
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I will take it apart again tonight and have a look.

From what has been commented above, no one seems to see a problem with connecting these units in parallel across the batteries and wiriing in a small power supply, as long as I keep the current down to below say 1 amp ?

I'm not looking to make myself lots of work, I just want to make sure i'm not going to blow anything up :)
 

BobK

Jan 5, 2010
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There are many things wrong with what you are proposing:

1. These are likely NiMH batteries and they can be overcharged and vent, though they will not likely catch fire. C/10 is too high to trickle charge them, C/20 is recommended for trickle charge of this type of battery.

2. Putting 5 batteries in parallel will not guarantee that they all receive the same charge current.

3. Simply connecting them to a supply rated at 500mA will not guarantee that only 500mA is drawn and (see point 2) that each will receive 100mA. The rating of such a power supply is not the max current it will provide, it is the max it can provide safely without damage.

If you are going to power them off a power supply, as others have suggested, the batteries are only a complication. Remove the batteries and power them with a 1.5V power supply. This is far safer and likely to work for a longer time. Leaving in the batteries will result in failure, probably within a year or two.

Bob
 

Andy Street

Nov 23, 2015
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I'm struggling to find a 1.5v supply online, is there a safe ( and cheap) way to drop down the voltage from a standard 5V / 9V / 12V transformer, as I have a box full of those.

Its a long time since I did O Level physics, but would a resister in series to the load do it ? and if so, what sort of value ? )

Or would the voltage even matter as long as the current was reasonable.

On another note, what sort of current would the curcuit usually pull from a AA NiCad battery ?

Andy
 

Martaine2005

May 12, 2015
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Hi Andy,
Based on the advice given by two highly experienced engineers, I can deduce that there is an easy method or a complicated method!
I like easy because I am not experienced.
It would be very simple to pull the boards completely and wire all lights in series with an adapter indoors. Turn it on when you want the lights on! And/or PIR for when you go outside.
I really don't see the point of trickle charging 24/7 when you can power them when needed.
Just my 2 cents worth..

Martin
 

swagguy8

Dec 10, 2014
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I'm struggling to find a 1.5v supply online, is there a safe ( and cheap) way to drop down the voltage from a standard 5V / 9V / 12V transformer, as I have a box full of those.

Its a long time since I did O Level physics, but would a resister in series to the load do it ? and if so, what sort of value ? )

Or would the voltage even matter as long as the current was reasonable.

On another note, what sort of current would the curcuit usually pull from a AA NiCad battery ?

Andy
you could use a regulator, although that would be highly inefficient since you are trying to get rid of like 8 volts. you could use a voltage divider, then regulate that. that should work.
good luck!
 

Andy Street

Nov 23, 2015
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Great advice, but I'm afraid I don't know what a regulator or voltage divider actually are. My knowledge of electronics is limited to a O level in physics 30 odd years ago.
I can manage to put a resister on parallel to drop the current, or series to drop the voltage, but that is about the limit of my skills.
 

Andy Street

Nov 23, 2015
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Pictures as requested, no code numbers on the component i'm afraid
 

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Arouse1973

Adam
Dec 18, 2013
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Ok so I think we need to recap on what you actually need to do. And what the solution is going to be and get everyone to buy in to it I guess.

Questions to answer.

1) 5 sets of lights, how many LEDs per set? I guess one LED per light also?
2) Is a timer an option for switching on the light? or does it need to be light operated.
3) Do you want one power supply to run all 5 sets? Or split into 2-3 sets?

Adam
 

Andy Street

Nov 23, 2015
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1) 5 sets of lights, 100 LEDs per set, single LEDs
2) to be light opperated using existing solar panel sensors to reduce cost
3) one power supply to run all 5 sets.

Power supplies available - 5V, 6V, 9V & 12V standard plug in DC power supplies. various currents from 350mA to 2,000mA
Current batteries - AA size, one per set, 1.2V Ni-MH 600mAh
 

BobK

Jan 5, 2010
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100 lights per set and run off a single 600mAH battery? Impossible.

Bob
 
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