Battery pack for remote controlled blinds

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Old 05-16-17, 05:42 PM
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Battery pack for remote controlled blinds

OK so bear with me because I'm sure I will leave out some bit of important information. I have a Bali blinds system that has a battery pack. Each blind comes with 8 AA lithium ion batteries, 1.5V each to (as I understand it) make 12V which is what the blinds need. They say you absolutely can't use rechargeable batteries, and from what I understand, that's because rechargeable batteries operate at 1.2V, and thus 8 of them would only get me to 9.6V total.

So I'm now realizing that I've bought blinds that are going to apparently require an investment of about $60 every 6 months just to operate. Now, I don't really want to hard wire the blinds unless that's the only option. So I'm looking around trying to figure out how to power these things in a rechargeable way. I see some NiCD batteries that purport to operate at 1.5V (jugee 8 aa | eBay) but I don't know how likely that is to work. I've also thought about a powerbank type thing, but finding one that does 12V seems to be hard to find, and very expensive.

So... any suggestions? I've contacted the company and they are totally unhelpful. I'm no electrician but I'm pretty handy and good with a screwdriver.
Appreciate any help!
 
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Old 05-16-17, 07:26 PM
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Welcome to the forums.

So what would your plan be..... take the 8 cells out and charge them every couple of months?
 
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Old 05-16-17, 09:28 PM
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I checked out that link for chargeable cells.
They look like they may be a worthwhile investment.

You could use lead acid technology at a much lower cost but the size of the battery would probably be too big for the area where you need it.
 
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Old 05-17-17, 06:39 AM
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Do you only get 6 months use out of a set of disposable lithium batteries? I could see a life that short if you are operating them a couple times each day but if you're using them less the batteries should last longer. And, I'm pretty certain you could use regular alkaline batteries but would just have to replace them more often.

You said you can't use rechargeable batteries but didn't say what type. There's NiCd, MiMh and then several different lithium's. Each has it's own specific voltage. The NiCd you linked are not NiCd but are lithium and have been out for a couple years. The ones I tested/tried would output up to 2amps before their internal regulator would shut down which is quite a lot. I wasn't seeing anywhere near the rated capacity though and was getting around 1'800 mAh per cell.

The actual cell inside the AA package operates around 4.2-3.7 volts and there is a circuit to drop it's output to 1.5. They do work but the biggest issue is you get no warning before they go "dead". They keep going and then stop without warning. There is no warning like the device operating slowly and a battery tester doesn't work on them. It just stops and the battery needs charging.

Charging is the Achilles heal in my mind. There are no good chargers out there for them. Most, like in your link, are inexpensive units that plug into a USB for power and can only charge up to four cells at a time. All that I've seen don't have any brains in the charger and instead rely on the batteries internal circuity to cut off when they reach a set point. It works but it's a crude and slow by lithium standards but that very slow charge rate also helps makes it safer.

If you want to try a NiMh to avoid safety concerns with rechargeable lithiums I would try Eneloop cells. They are a high quality NiMh with a very low self discharge rate so they would remain useful for many months. Yes, their initial voltage is less than a alkaline or regulated lithium but quite stable over the life of the battery but will not compare to the almost horizontal line of a regulated lithium.

 
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Old 05-17-17, 09:06 AM
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Yes, the goal would be to take out the cells every 6 months and charge them. It will be annoying but I can't fathom paying $60 for 4 sets of lithium batteries every 6 months.

Yes, only 6 months of use. I was aghast as well - the manual says 12-18 months, which is still not great, but a hell of a lot better than 6. I reached out to the company and they basically said that's not abnormal. And yes, the death of the first set of batteries that came with the blinds just died one day, all at once amazingly. 3 blinds (4 sets of batteries), and all hit the wall the same day, late last week. We basically put them up in the morning and down at night, and that's it most days.

The company didn't get highly technical in their advice, they just say you can't use rechargeable batteries. I'm sure the assumption is that most consumers will just buy the NiCD ones that are too low voltage, while the nerdy consumer will do what I'm doing here to find the real answer.

Slow charging would not be a problem - I would expect to stagger them by a day each, at least, so that every 6 months, each day I would pull down one set, charge it for 24 hours (if that's not a bad idea?) and replace them. Have one extra set on hand ready to install so there was no downtime, although frankly downtime of one blind in a bedroom isn't a problem either.

Thanks for the tips!
 
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Old 05-17-17, 02:47 PM
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There is a lithium technology that would work perfectly for this. It's called Lithium Iron Phosphate (LiFePO4). They come in an AA size but they are 3.2volts per cell. The usual method of AA replacement is to install one LiFePO4 and one "dummy cell" (basically just a plastic AA size slug with the + and - wired together) per pair. So you would use four LiFePO4 and four dummy cells per battery pack. It would be almost a volt high for the whole pack, but that is very unlikely to be a problem since alkalines can be a couple tenths high anyway.

Nitecore makes a great 4-bay multi-chemistry charger (Digicharger D-4), it sells for about $28. It is not a fast charger, it takes about 5 hours to do my vape batteries (which are much higher power than these too), but slow charging is better for the cells anyway. You are actually only charging half the cells anyway so you can charge one whole blind unit at a time. It also does not require you to charge in pairs - each bay charges independently, and it will detect and charge all the popular battery chemistries that come in AAAA, AAA, AA, C, and 18mm sizes (Lithium-Cobalt, Lithium-Manganese, Lithium-Iron, Ni-MH, and Ni-Cd).
 
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Old 05-17-17, 05:00 PM
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Cool! I did not know anyone was making lithium iron in AA size. I use LiFe batteries in my RC planes and love them. You are right. They don't take a charge as fast as other lithium batteries and I limit my charging to 1c but that is still much faster than what the USB charger linked in the original post could do.
 
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Old 05-17-17, 05:56 PM
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They come in an AA size but they are 3.2volts per cell.
Very interesting. I hadn't seen them before either.
 
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Old 05-17-17, 06:33 PM
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Thanks! What is it that makes LiFe better for this purpose? Just the fact that I'd only need 4 per blind instead of 8?
 
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Old 05-17-17, 06:55 PM
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I see a few on Amazon, but they seem to be much lower capacity (like 700 mah instead of 3000+ in the Lithium Ion). Is this something to be concerned about? Or does something about the physics mean the capacity is actually similar?
 

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Old 05-18-17, 06:46 AM
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LiFe is a different chemistry. The down side is that it does not hold near as much energy as LiIon or LiPo. The plus side is that it's voltage can more closely match alkalines and NiMh and it's much safer. LiIon and especially LiPo can create some very spectacular fires that cannot be extinguished. LiFe is inherently safer and extremely resistant to runaway fire even when severely abused.

LiPo batteries are absolutely incredible. They hold a tremendous amount of energy in a very small, light package. With something very powerful in a small package there are dangers. Everyone has seen news stories of laptops, cell phones, hover boards and Boeing 787s catching fire. Abuse them, especially when charging, and they can catch fire. That fire cannot be extinguished. All you can do is get it somewhere safe and watch it burn. But, we all have LiPo's in our cell phones which get dropped, baked in the sun and charged every day so they can be safe when handled properly.
 
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Old 05-18-17, 07:00 AM
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Gotcha. One must then consider the actuarial risks in front of me. Which am I more likely to die from - climbing up a ladder 4x more often, once ever 6 weeks instead of every 6 months, vs a fire. Then factor in the annoyance of getting out the ladder 4x as often. I think the LiPo batteries are the better and less risky choice, all things considered. Thanks for the thorough explanation!
 
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