Yard Light Batteries

Flying Turtle

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I have a couple different solar rechargeable yard lights that use NiCd AA's. Could NiMH batts be substituted with any success? Thanks.

Geoff
 

Lynx_Arc

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nimh could be used but either they could be overcharged if possible or the extra capacity would go to waste after the first night or two because the solar panel may not ever be able to catch up. Most solar powered yard lights I have seen around here tend to be dimmer than a lethargic firefly after about 2am which probably means the nicads didn't get fully charged during the day hours.
 

WildRice

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OK, can Ni-MH's be fully discharged safely? most of the newer lawn lights have boosters in them to suck all the juice from the cells. FWIR Ni-Cad's can be fully 'dumped' but I am not sure of Ni-MH.
Jeff
 

Lynx_Arc

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My guess is full discharge would probably hurt nimh, but from what I have heard fully discharging nicad hurts them also.
I would recommend hooking an ammeter inline with the cells in use and see what is happening as I said earlier it may not be worth the trouble if the solar cells cannot even charge up the nicads included with them.
 

Flying Turtle

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Thanks for the responses. I should have mentioned that the lights are only used as night/accent lamps inside and don't normally get left on, but it has happened. I'd forgotten about not fully discharging NiMHs. I guess my main question was about whether I could get some usable charge into the NiMHs without damaging them?

Geoff
 

Lynx_Arc

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I would check and see how low the lights actually drain a battery down, it may be they don't drain them that low as many yard lights use non white/blue LEDs and drive them direct or resistored with 2 batteries thus draining the batteries down too low may not be an issue.
As for nimh if they are not overdischarged another problem may be if they are ever fully charged the solar cells may have them continuously trickle charging which is also bad for them, something nicads don't mind too much.
 

SilverFox

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Hello Geoff,

I have several solar yard lights that came with NiCd cells. I spent some time evaluating the conditions of use and decided that NiCd replacement cells would work best. In the winter they get completley discharged, and in the summer they get overcharged. NiCd chemistry handles that type of abuse better than NiMh chemistry.

NiMh cells will probably work for a while, but won't last as long as NiCd cells.

Tom
 

Genes

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I have been using 2200 Mah NiMh batteries that I get from WalMart in all of my solar yard lights for the past two years and they work great. I have yet to replace a single cell and even during the winter months, they frequently make it through the entire night without going completely dark.
 

eluminator

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I've used 1500 mah NiMH in yard lights for 4 years. Most are still working although they don't seem to last as long through the night as they once did.
 

Doug Owen

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Perhaps I'm not following, but if they're only used for indoor accent lamps, how are they getting charged? Normal indoor light levels can't be enough IMO.

If you're charging them with an external charger, this makes some sense. The key is discharge, if they aren't protected from discharge by design or (careful) use, NiCd seems the call. Without protection, complete discharge (even reverse charging) will kill NiMH fer sure.

Doug Owen
 

Flying Turtle

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When they go dim I just take them outside or stick them in a sunny window. They probably never get more than 4 hrs. of good sunlight when get charged. Anyhow, apparently I might get away with changing to NiMH, but I won't try that until the others die. Thanks.

Geoff
 

Doug Owen

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Geoff,

Thanks, got it now.

Back to the original question, 'should I try NiMH?', my money's on no. Overdischarge, while not a good idea with NiCds, is fatal on NiMH. Just a matter of time. Reverse charging (a very real prospect) will just hasten the end all the faster.

I suggest replacement (when it's needed, the original sets are still OK, right?) with 'what the factory used', NiCd. There are solid reasons.

Doug Owen
 

TrueBlue

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This is an interesting thread for me since I'm currently pairing up, matching, capacities of Ni-Cad cells for my solar LED yard lights.

When I installed a set of Malibu LED solar spot lights I was pleasantly surprised at how bright they were. The lights come in a box of three flood light units housing three Nichia type LED emitter per flood light for a total of 9 LED emitters for three lights. The spot lights are powered with a central solar panel. The lights will not replace incandescent spot lights for output but I didn't want them to. I wanted the lights as accent lights for my front yard at night. Happily the lights are brighter then I expected. What really surprised me was the rechargeable cells; the light came packaged with three 1500mAh Malibu labeled Ni-MH cells. Could the extra current that NiMH cells can send to the emitters be the reason the lights are brighter than I'm used to seeing? Another surprise is that the spot lights last all night...at least in the summertime they do.

So Ni-MH cells might be OK to use in some yard lights.

On another thought…with my other solar yard lights in my mind I went and tested the capacity of NiCad cells using the La Crosse BC900 charger. I bought extra cells from both Ebay and BatteryStation as back up cells and I've come to find capacities of NiCad cells are 'all over the road.' The mAh capacity of NiCad cells, both ones that come with the yard lights and aftermarket cells vary considerably. I might have 40 NiCad cells and only 30% of the cells come even close to their proclaimed 1000mAh capacity. I've only had one of the cells exceed capacity. That is a very disappointing revelation.

Test and match the capacity of the cells and your yard lights will run longer and because the cells, with less of a chance of cell reversal, will last longer.
 

Lynx_Arc

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Most likely the lights are brighter because of design not because of nimh vs nicad cells as both are about the same voltage and if anything nicads tend to have higher current capability while nimh has more capacity. There is a possibility there is some *smarts* in there so nimh wont be overtrickle charged.
 
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