# Solar Rock Address Sign Battery Replacement Problems?



## adirondackdestroyer (May 2, 2010)

I have a Solar Address sign that is no longer working anymore. I'm pretty sure the batteries have kicked the bucket. It uses two AA 1.2v 800mah Ni-cd batteries. 
I was wondering if I could just drop in a couple AA Duraloops, since they are the same size/voltage, or would I have to use the exact same kind of batteries in this item?


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## adirondackdestroyer (May 2, 2010)

anyone know?


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## cimino (May 2, 2010)

I don't know for sure, but the "charger" in that kind of thing is usually pretty simple. Often just a resistor and/or diode.

So I would say, go ahead and replace them with any sort of NiMH cells.


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## Light Sabre (May 2, 2010)

I have noticed that most of the LED solar night lights use NiCad, but a few use NMH. I bought some of them just to get a hold of the solar cells. A lot cheaper than buying the solar cells individually. I would recommend a few break-in cycles on your NMH battery charger before installing them in your outdoor lights or address sign. That way they have a good start right off the bat. Match batteries with the same mAh on your chargers readout. Not sure if using a higher mAh battery than what was installed originally is a good or bad idea. Since a higher mAh battery would run longer on the first few nights, I was wondering how well the battery charge circuit could keep up with the higher mAh battery.


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## adirondackdestroyer (May 2, 2010)

Light Sabre said:


> I have noticed that most of the LED solar night lights use NiCad, but a few use NMH. I bought some of them just to get a hold of the solar cells. A lot cheaper than buying the solar cells individually. I would recommend a few break-in cycles on your NMH battery charger before installing them in your outdoor lights or address sign. That way they have a good start right off the bat. Match batteries with the same mAh on your chargers readout. Not sure if using a higher mAh battery than what was installed originally is a good or bad idea. Since a higher mAh battery would run longer on the first few nights, I was wondering how well the battery charge circuit could keep up with the higher mAh battery.



Thanks for the reply. 
I'm charging the AA Duracell rechargeables as we speak. I figure they should last a little longer being 2000mah compared to the 800 of the original cells. I'll post back with my results.


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## Lynx_Arc (May 2, 2010)

adirondackdestroyer said:


> Thanks for the reply.
> I'm charging the AA Duracell rechargeables as we speak. I figure they should last a little longer being 2000mah compared to the 800 of the original cells. I'll post back with my results.



just because the cells have higher capacity doesn't mean they will give out light longer. I would guess the solar cell probably won't even charge up the 800mah nicad completely which means when the duracell finally is discharged down low enough the solar cell will probably only be able to half charge it daily. I would recommend using a cheap generic 1200-1600mah nimh instead.


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## Dave_H (May 4, 2010)

Lynx_Arc said:


> just because the cells have higher capacity doesn't mean they will give out light longer. I would guess the solar cell probably won't even charge up the 800mah nicad completely which means when the duracell finally is discharged down low enough the solar cell will probably only be able to half charge it daily. I would recommend using a cheap generic 1200-1600mah nimh instead.


 
I agree, cells could be replaced with cheap generic NiCds, even 600-
700mAh might be OK. The low self-discharge of Duraloops is being wasted
on a device that gets charged/discharged every day.

As an aside, I have a small solar rock, about the size of a potato, which
uses one 1/3AAA NiMH, 200mAh driving a single 5mm white LED. Everything
seems to be sized right to stay lit most of the night given a good sunny
day. I'd like to replace with a bigger cell only because it's readily available, 
but due to sizing would need to be external.

Dave


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## Lynx_Arc (May 4, 2010)

Dave_H said:


> I agree, cells could be replaced with cheap generic NiCds, even 600-
> 700mAh might be OK. The low self-discharge of Duraloops is being wasted
> on a device that gets charged/discharged every day.
> 
> ...


I haven't had one of these solar lights apart.... I just shake my head at using a single nimh/nicd cell to power solar lights. They must do this just to save money (profit) making the lights as the efficiency lost through a boost circuit wastes perhaps 1/3 to 1/2 the power collected to the battery. 3 cells would be more ideal but then they would have to have a higher solar voltage output to charge them I guess.


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## Dave_H (May 5, 2010)

Lynx_Arc said:


> I haven't had one of these solar lights apart.... I just shake my head at using a single nimh/nicd cell to power solar lights. They must do this just to save money (profit) making the lights as the efficiency lost through a boost circuit wastes perhaps 1/3 to 1/2 the power collected to the battery. 3 cells would be more ideal but then they would have to have a higher solar voltage output to charge them I guess.


 
Not sure where the 1/3 to 1/2 came from, was that just made up?
Can't say I've checked efficiency of some of these boost circuits but
the electronics are cheap. I am guessing 75% or better is being
achieved. Some cheap solar lights use an IC for power control.

A single cell has advantages over 3-cell. The number of cells plus
contacts are reduced. In some cases the energy storage is more
right-sized for one cell, as 3AA is overkill. Since NiCd are still used
and not always disposed of properly, keeping cell count and volume
down helps.

The number of solar cells is minimized to 4. For 3-cell it is 10-12.
The assembly is less complex (reduced cost) and connections
between cells fewer , which helps reliability.

Series cells, especially cheap ones that are not matched for
capacity (graded) have the problem that eventually the weakest
cell will fail (short). That usually results in the other two getting
tossed even though they are still good; even worse, the whole
device thrown out if it is cheap.

So yes, some of it is lower cost, but that can be passed on to
the buyer in a competitive market.

Dave


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## was.lost.but.now.found (May 5, 2010)

It's highly unlikely the charger uses any kind of complex charging algorithms (-dV) to terminate charging. To that affect, in all likelihood it just forces charge into the batteries for as long as there is sunlight. Therefore I would absolutely not use any NiMH batteries; you will most certainly kill your Duraloops. NiCad is the best battery for the application as it can accept a constant trickle charge even when completely full.

Just look here to find out what can happen when you put NiMH on a Ni-Cad charger: https://www.candlepowerforums.com/threads/264862


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## Lynx_Arc (May 5, 2010)

Dave_H said:


> Not sure where the 1/3 to 1/2 came from, was that just made up?
> Can't say I've checked efficiency of some of these boost circuits but
> the electronics are cheap. I am guessing 75% or better is being
> achieved. Some cheap solar lights use an IC for power control.


just from memory mostly, i may be wrong but I am guessing they are not putting their best design circuit in there. I recall a long thread about the dorcy 1AAA light they used to scavenge the boost circuit that had a 74% effficency after modding it by changing a few parts. This was however at 5ma output... just looked it up, after modding it a little they got about74% at 28ma. this however was a well designed circuit not typical of most boost circuits I have seen in flashlights so my bet it probably 66% is a guess of the efficiency of the solar lights as higher efficiency calls for higher quality components and a larger coil. if the runtime is lets say.... 8 hours unboosted then losing 25% would be 2 hours, 33% would be about 2.4 hours. I have no idea what these lights do as far as the numbers are but from what I have seen here most of the solar lights I have seen are dim to be unuseful well before the night it through (1am). I am guessing either the 5mm LED cannot cut it in max output or it is just not driven hard enough (underdriven). If I could get one of these for near nothing and take it apart it would be interesting but I wouldn't pay the $5-$7 for them they cost in the stores.
this is interesting Here


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## Dave_H (May 6, 2010)

I have a fair number of these mostly white but some amber,
and have had several apart for various reasons; either repair
or to see what's inside, change batteries etc. I typically have
not payed more than $3 each. One set was picked up 6/$10
and despite an intermittent problem with one (bad solder
joint) was a good deal.

Efficiency will be affected by type and quality of components,for
example, the radial wire-wound inductor. The ones they use tend
to have high series resistance, loss and therefore lower efficiency.
Also the diode used, whether any ordinary silicon, or schottky
with lower drop.

Not suggesting they go off the deep end with low-cost designs
but there are techiques to improve efficiency such as synchronous
rectification, which uses a FET as a diode but with much lower
drop (it is controlled to conduct like a diode). Not sure if any
designs use this but with higher integration it would not surprise
me.

I use solar lights as indoor nightlights by removing the diffuser,
flipping over and inserting a (usually partly run-down) alkaline.
The ones with on-off switches are best, as well as easy access
to the battery hatch (without having to take it all apart).

Dave


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## Lynx_Arc (May 6, 2010)

I think I perhaps figured out why they don't use more than 1 battery. The most common easy to get rechargeable batteries now are AA sized so in all respects they should be cheapest and the amount of total power (wattage) the solar cell can supply most likely won't even half charge 2AA cells so it may be that they are concerned more about capturing the energy than efficiently harnessing it. As for the higher quality components using better coils/inductors and diodes it can push the efficiency from ~50% to that 70%+ range for sure and better LEDs from what I have seen (5mm) can probably have more effect on light output than that extra 20% or so efficiency a cheap no name vs a nichia GS can be perhaps 50% more output but the problem with using them is they are not chinese made (that I know of) so instead of 3 cents each they would pay $1 or so each. 
I agree for simplicity of use that the 1 cell boost form factor makes for a good dim area light. I use a 1D energizer lantern made for lawn lighting indoors and in a pinch it can be run off AA/C/D easily enough with 1 cell factor not worrying about balancing cells when you accidentally overdischarge them (for nimh). 
I would say perhaps one day solar cells will put out enough to run a cree LED in yard lights without costing $40 each, when this happens a lot more people will consider using them. For now most solar LED lights here look more like decoration with their weird tints and dimming output half way through the night a nearsighted lightning bug wouldn't even mistake it for a buddy


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## deadrx7conv (May 9, 2010)

I have numerous lawn/driveway solar powered 'accent' lighting. 
I've replaced all the dead nicads with Energizer and Duracell NiMH batteries and they are working excellent for over a year now! The generic nicads they came with barely lasted 3 months. 

Even with a full day of sunlight, the little solar panel barely puts out enough power to fully charge the nicad so it'll never be able to overcharge the NiMH battery. 

When picking a AA or AAA cell for your solar light, don't pick one with maximum mAh rating, pick one that can be discharged and recharged more times, and hold a charge longer(like the precharged ones). 

My next set of batteries will be the Tenergy AA's which can supposedly be recharged 1000x. So, they should last 3 years in a solar lawn light. 

Many of the newer/better solar lawn lights at Walmart/Target.... are now coming with LiFePo4 batteries which are supposedly good for 1500-2000+ recharges in the solar lawn lamp.


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## Lynx_Arc (May 9, 2010)

deadrx7conv said:


> I have numerous lawn/driveway solar powered 'accent' lighting.
> 
> When picking a AA or AAA cell for your solar light, don't pick one with maximum mAh rating, pick one that can be discharged and recharged more times, and hold a charge longer(like the precharged ones).



I have found the lower capacity (below 2000mah) nimh retain charge longer than higher capacity so I don't think you need to go all out on LSD cells if they are being charged/discharged daily the percentage difference is probably negligable, but I agree the amount of cycles is probably tantamount.. sanyo makes some eneloops that are supposed to be something like 1000mah that does a lot more cycles than most nimh cells that would weigh in more cost/cycle than the LSD part.


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