Questions About LED Lighting and Direct Current Water Pumping

This thread was originally called --- Questions for Brian Knight --- I've changed it to make it clear that it is open to all and to be more specific as to the questions. --- Hi Brian. Rather than asking you things in a PM, I figure it makes sense to do it here so that many will benefit. I'm soon going to add some electricity to my cottage. Until now, a 12v deep cycle lead acid battery has been the only power used. Two 20w incandecent bulbs were attached. That's it. It worked very well. Many days of lighting on a charge. The battery is heavy.

The New Plan --- I'm going all out. I want LED lighting in about 5 spots and I want 5 plugs that will mostly be used for lamps. I want a little RV water pump to power a shower. I want everything to run off of batteries that I charge elsewhere. When I'm in the cottage at night, I expect to use an average of 20 watts for say 5 hours a night. This adds up to 100 watt hours or 1 tenth of a kilowatt hour. About one penny worth at grid prices. This will afford a degree of luxury that this building has never seen. I'm thinking 7 to 15 watt units with a little 3 watt night light.

I have seen 40 volt LEDs(unless the posters confused volts and watts) and would like to use them in conjunction with batteries from some yard tools, if you think that this will be an economical choice.--- I need some yard tools that use a 40 volt battery --- --- The beauty of buying my batteries this way is that I'm not the one who ultimately pays for them. Whenever I've bought a power tool, my customers pay for them. I'm tired of fiddle pissing with extension cords and I'm tired of breathing fumes when I get up close and personal with thick hedges. I'm going to get a hedge trimmer and a leaf blower for now. I may grab a chainsaw later. Both will be useful at the farm as well. The road often needs little branches trimmed with the hedge tool. Gravel from the side of the road needs to have the organics blown clear before it is used. These batteries power a lawnmower for 25 minutes. That's more power than I would ever use in a day for lighting. I expect to have at least 3 batteries.

When I search the net for 40 volt lights, I get some results, but I think some or all of them are confusing volts and watts. In your experience,(if they exist) will 40 volt lights work as well and last as long as the ones that are made for regular grid powered homes. I see a lot of stuff for 12 volt as well. The problem is that none of the good tools come with 12 volt batteries. How complicated and expensive would it be to transform the power to one of the common voltages ? What would my power losses amount to ? Do these lights care what type of battery they are on ?

There are several other small buildings planned for the property which is long and skinny. It's 1.2 km or 5/8 of a mile long, so I will never run wires everywhere. I'd like to wire all of the little camping structures, spa, and pond side terrace for light only. One or two bulbs. These 40 volt batteries weigh about 2 or 3 pounds, so are something that can be carried in a jacket pocket. I'd like to be able to simply slip a battery into a saddle in each building.

Thanks Brian. I leave this in your capable hands.

I also welcome input from others. I'm only seeking ways to do this with batteries. I may one day get a wind mill, solar collectors, a generator or a nuclear power plant. Right now, all of those things would be targets for theft or vandalism. None of them will help me trim a hedge.

Charging --- My work and leisure time both take me to places with grid power. I commonly charge cordless tools at customer's houses and at Starbucks. When I move into a Starbucks my arms are full. I charge my phone, computer and cordless tool batteries. I bring my own power bar. The penny worth of power is part of the deal. They have never questioned what I'm up to. I think it's obvious. I may set up the van for charging.

Hi Dale! Honored you directed a question towards me but Ive always had a distaste for asking specific people for answers on forums. Ive sometimes not left my thoughts on those threads as the poster seems uninterested in other's ideas. I know thats not the case here but this question in particular is well outside my area of expertise. There are many more here who are better qualified for this question, hopefully Len, Marcos, Armedean, R Scott and others will have better answers than me.

Kind of curious if you call the cottage and land in question your primary residence. If so thats an impressive lifestyle of conservation and efficiency. Its tough to discount the battery access and charging options but have to wonder if a PV setup might be a wise investment although I guess Victoria island can get some crummy insolation levels. I suppose the special inverter would be the toughest cost to justify huh.

Absolutely getting away from incandescents will be critical to your strategy. You must be one of the few off-gridders using that lighting technology and the minute you add a pump to your setup, the power will be too precious to be wasting on inefficient lighting when there are such better alternatives available. My quick search for 40V lights yielded many results for incandescent scooter lights with the automotive style bulb base. The biggest LED selection seems to be here with the candelabra bases probably being the easiest option to work with. 100K hour life! Incredible. Disappointing that no Lumens per Watt are given and wonder just how much these guys would put out. http://www.bulbtown.com/40_VOLT_LIGHT_BULBS_s/399.htm

I dont see why you couldnt wire some circuits to run these bulbs off of your 40V tool batteries. I must say weve had bad luck with large voltage battery tools (batteries dying, Rigid brand), but they were original version Li and this technology seems to be getting better and better. The reviews for the Ryobi were surprisingly good but its still a very small sample size and am skeptical of the longevity of these newer tools. One of my best purchases this year was a corded impact driver, sooo much better than cordless if power is available and cant help but think that many of the larger tasks intended for these tools would be better served with corded tools and a genny. I scolded my dad recently for buying a battery powered weed eater, as it was taking several charges to get the job done, although he was letting it get too far ahead of him, still my gas fired Stihl would have done the job on thicker grass 5x as fast. I dont think Ryobi has that great of a reputation among professionals either. Cordless tools are obviously a great thing to have in the arsenal but I think relying on them only, leads to disappointment for most pros. Getting batteries free and having a bunch of them certainly helps!

What exactly are your current transformer goals? I think you would be much better off separating the tool system from the house system. It just gets too tricky (for me anyway) to make everything compatible and work together. Better to have a standard 12 or 24 volt system when dealing with pumps, panels, and inverters. Figuring out how to make 40V mesh with 12 or 24 batteries, inverters and loads is way beyond my knowledge which isnt much in this area. I do understand your desire to make it work that way with your charging system (which I would love to witness by the way... Whos the wierdo with the green batteries next to his laptop!?) I bet that more than half of this exercise is to free yourself from lugging that 12V battery around? Arent there ways of rigging up a charging station off a running vehicle? I guess that's what you mean with the van for charging?

Thanks Brian. I read quite a bit of your stuff about LEDs as compared to CFLs. But then you weren't talking off grid. I hope I didn't put others off with the question addressed to you.

The cottage is not my primary residence, but it will be soon. I still will spend less than half of my time there. For most of the past 15 yrs. I've lived at job sites in buildings and vehicles. Often my only source of power is the van's 12 volt system. But I don't live in the van. It's my bedroom. The world is my living room and urinal. I have never heated any of the vehicles. Still, I roll out every morning looking like a GQ model. By comparison, most people are sissies, or they've made better choices.

So, I wasn't joking about the luxurious state of cottage life. A roof over my head, heat, a hot shower, a cell phone, and computer are all I desire for now. I seldom go to the land. Useless tenants will move out in 3 weeks and I will move in. Some of the neighbors have million dollar houses on lesser lots that don't follow the valley ridge for a kilometre. I gonna be strutting like George Jefferson. I'm movin on up.

Now, back to battery powered lighting. I wonder if the tool companies make a light for those batteries ? The other options are not an option until I or someone is there all of the time. The yokels will steal everything. My area is somewhat gentrified, but we're not there yet.

I had the pleasure of visiting VI last year and was wishing the whole trip was there instead of Vancouver and Seattle instead. That area is amazing. The closest thing Ive done to off-grid was hiking the AT which was a longer duration journey than most by far. Still, Iam obviously much more of a sissy than you. Ive gone soft Dale..

I think for 40v LED lamps that, considering you are using more than one anyway, you may do just fine with three 12v models in series. These are designed for about 10 to 16 volts so 40 volts across the three would be no problem (yes I mean automotive turn signals etc). They would have to all be the same power rating to ensure equal voltage across each one. I don't know how intelligent the tiny switchers in the smaller 120v AC LED lamps are, but they may just work on lower voltages too (I am thinking about the night lamp replacements)... the only thing is, they use so little power anyway they may just have a series resistor in them and be using some 10 to 50X the power really needed depending on how many LEDs they use. Or because the load is well known, the switcher may be a fixed duty cycle unit. I think that low voltage LEDs for automotive use will last better than the 120v ones, but I could be wrong. Another place to get LEDs is Christmas lights in a string... Just cut the cord 4/12ths of the way along for 40v. The motor... is in your drill or dremel style tool that comes with the battery.

Computers... I haven't tried this, but a lot of the xt or older power supplies may run on 40 volts and give you 12 and 5 volts out... The laptop PS may even just work. Switchers can (in theory) handle anything from 5 or 10 v higher to whatever the primary caps can deal with. I have seen 120v power supplies run by mistake on 220v for months before they blew (bad wiring had 220v on a 120 outlet).

The PV panel doesn't sound wrong either. Victoria has enough sun most of the time if it can be mounted so it isn't visible by thieves. Harder to claim you need it for the job though

Thanks Len. I understood some of what you're telling me. So the voltage used by Christmas lights is determined by the number of little bulbs. They are so cheap right after Christmas. I could see mounting a long skinny mirror near the ceiling, so that light is all projected where needed. Any idea on whether it would be more efficient to use fewer more powerful bulbs rather than dozens of little ones ?

So, am I correct in assuming that these lights could be tailored to be used with any voltage of battery, just by finding out the voltage of each bulb and using the right number to add up to that voltage ? I can add and count ! This could be really easy if the answer is yes. Also, is it better to slightly under power or slightly over power. I've heard that they don't dim well. I found strings that use only 6 watts. This should mean that when cut into thirds, each string would draw 2 watts. Cut one into six and the battery from my 18 volt drill could work to power a little camping structure.

I've seen some quite large clear bulbs that have some sort of Christmas theme frosted onto the lens. I'll bet that stuff will scratch off. Get the off season discount, then scrape the ice. I saw one on e-bay that has a Santa Claus that could be pulled off.
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The 40 volt Ryobi batteries are rated at 4 amp hours. If I'm drawing 20 watts continuously, how long will it be good for ? I could easily do it from KWH but am not familiar with amp hours. I want to know how much energy is stored when fully charged.

Dale Hodgins wrote:Thanks Len. I understood some of what you're telling me. So the voltage used by Christmas lights is determined by the number of little bulbs. They are so cheap right after Christmas. I could see mounting a long skinny mirror near the ceiling, so that light is all projected where needed. Any idea on whether it would be more efficient to use fewer more powerful bulbs rather than dozens of little ones ?

Without knowing the internal details I can't say. AC power is specified at +- 10% so 110vcan be as low as 100v and as high as 120v (if I have it wrong and nominal voltage is 115, then the highest voltage would be more than 120). LEDs have a set diode drop and so can't deal with +- 10%. So I expect each Christmas lamp in the string has some series resistance so they can be slightly over volted even at the lowest likely voltage. A common voltage drop for small LEDs is 3v. This means if you put 2.9v across the LED it will not light but if you put 3.1v across with no current limit, it will burn out. The higher power LEDs have a bit more range, but basically all LEDs have to be fed by a current source rather than a voltage source. So for a 3v LED with +-10% you would assume 3.3v in and ad a series resistance that at .3v will give the LED it's working current (30ma or so for those little ones). So i x r = e then 0.03 x r = 0.3 or 0.3/0.03=10ohms resistor. But wait! most light strings are designed to still work even if one of the lamps is bad... more circuitry. There is probably another diode with a diode drop slightly higher than the LED in parallel with the led.

But wait! thats still not all. 110 volts AC is RMS... not peak voltage.... but the LEDs will see that peak voltage, so you have to remember that 110 is only .707 of peak... so more fun with math 110/0.707=156v peak. Your LEDs will only see one side of the peak which is why they look like they flicker on AC, you won't see that on DC. So then the next question is if the designer is running the LED at a higher current than normal because of the low duty cycle and therefore on DC should you derate them It will take some experimenting (and maybe some blown LEDs) to figure it out exactly. Start with using the rms voltage and see how bright they are compared to AC use... then remove a bulb at a time till it is the same (cut the socket out of the circuit ... a sharp probe poked through the wire instead of cutting it off will work) or for fun keep going till it burns out and use one more on the next string

Also, remember that the diodes are polarized. they will only work one way on your battery, but it is not marked, try it both ways. So you will have a maximum number of lamps that will work at your voltage and a minimum number before they start to blow. one more than the minimum will be most efficient.

Also you will probably note that these strings have three wires running through them not two. That is so the string can also act as an extension cord.

LED lamps in general are all multi LED units. That is the only way to get enough light even out of high power LEDs. I assume they are wired in series and that the 9w (60w equiv) lamps use some sort of switching power supply for efficiency. That is they take short spikes of power from the ac and use them to charge a capacitor (all 120v LED lamps turn off slowly, so they have caps, LED turn signals are very fast) at the running voltage. Because the high power LEDs have a drop voltage that changes somewhat with current, no series resistor is needed.... This is all guessing from what I know and how I might design it, not from inside knowledge or having dismantled one.

So, am I correct in assuming that these lights could be tailored to be used with any voltage of battery, just by finding out the voltage of each bulb and using the right number to add up to that voltage ? I can add and count ! This could be really easy if the answer is yes. Also, is it better to slightly under power or slightly over power. I've heard that they don't dim well. I found strings that use only 6 watts. This should mean that when cut into thirds, each string would draw 2 watts. Cut one into six and the battery from my 18 volt drill could work to power a little camping structure.

Something like that. They dim fine with the right dimmer. They do not work with the dutycycle dimmers that are most common. This is because they already use a short duty cycle and because the dimmer drops even higher peaks on the line so that the LED may get brighter rather than dimmer (same with many CFLs... plug your drill in close by and watch the lamps get brighter when you run it).

The 40 volt Ryobi batteries are rated at 4 amp hours. If I'm drawing 20 watts continuously, how long will it be good for ? I could easily do it from KWH but am not familiar with amp hours. I want to know how much energy is stored when fully charged.

20watts at 40volts is (i x e = p) i x 40 = 20 or 20/40 = 0.5 amps... so I am guessing about 8 hours. Amp hours are rated at a particular draw rate and normally last shorter at higher draw and longer at lower draw. So maybe longer than that. The shortest day (Dec 21) gets dark about 5pm (445pm or so in Courtenay) so till 1 am you would have light or go to bed earlier and you have some light to get up with in the morning.

Let us know how it goes.

Thanks Len. I regularly see free lights and then there's the sales.

Am I correct in assuming that it would do no harm to under power a string ? I could start with a few too many and then prune it back one at a time until optimum performance is achieved.

I contacted a marine supply. They carry 24 volt LEDs. Many cordless tools come in that voltage. I may get some and some extra batteries. Some kits come with a flood light.

Dead lap tops --- I often see free computers that are given away when non battery issues kill them. These are a nice sized battery for the camping structures that might use 50 watt hours in an evening. Those little batteries that power kid's ride on toys are nice as well.

I don't expect any power shortages in the winter. From November through May, a seasonal stream with over 100 ft. of head pours into the valley on its way to the Nanaino river. It runs under my road. Long after flow stops, I'm able to suck irrigation water from a pit in the dry bottom. A 12 volt pump will move water up 8 feet to the truck tank.

I just bought this DVD player. $70 down from $130. The box says it draws 2 watts, which seems low.

The TV is the central component of many single male abodes. This will be mounted by the bathtub. The screen turns and tilts.

Dale Hodgins wrote:

Am I correct in assuming that it would do no harm to under power a string ? I could start with a few too many and then prune it back one at a time until optimum performance is achieved.

Ya, like I say, use a sharp nail or something for one of your connections. It can poke right through the wire insulation without having to cut it.

Dead lap tops --- I often see free computers that are given away when non battery issues kill them. These are a nice sized battery for the camping structures that might use 50 watt hours in an evening. Those little batteries that power kid's ride on toys are nice as well.

I have always found that the laptop battery is the weak point. Their lasting ability goes down pretty much linearly with the number of times they are cycled. Lion batteries need proper charging to even do that well. Maybe it's just me.

--- 12 VOLT WATER PUMPING---

There seems to be plenty of inexpensive 12 volt water pumps available. The only thing needed currently for the cottage, is a little pump that can move 2 or three gallons per minute for a shower. All other water will flow from the elevated tank outside to the sink or the wood fired water heater. From the heater the water can gravity feed to the kitchen or bathroom sinks or to the bathtub. The only issue here is that the pump must be able to withstand 140 F.

All drinking water will continue to be picked up in town for now.

My primary source for washing water is a clean stream that flows under my road. The water must be lifted 10 feet into a truck mounted tank. Sometimes this water may be needed up to 3000 ft from the stream. The truck will be driven to within 100 ft of the spot and in most cases the water will flow by gravity to where it is needed.

The cottage is about 150 ft from the stream. The tank is about 22 ft. above stream level. I may run a hose to the tank and pump directly, using a good quality bilge pump. The current plan is to power all outdoor water pumping with my vehicle. I won't idle the vehicle during pump operation. An auxiliary battery that does not run the starter will be used for pumping.

There are some other areas of the property where I may wish to move water but I don't want to remove the primary pump in the stream to do this. The vehicle can't get to all of these spots. I have a few battery powered drills. I may use these to run inexpensive pumps that are made to fit a drill. The drill could be left running until the battery dies. I would probably leave these hoses and pumps in place. The drills would be taken away until they're needed again.

It's very important that I leave nothing behind that is desirable to thieves. They don't bother with hoses, but would surely steal easy pickings like the bilge pump, drills or a generator. So far, none of the neighbors has had any losses from inside buildings. These are mostly crimes of opportunity. Break and enter is a whole different crime that attracts well armed owners. I have no intention of leaving a dog at a place that I may leave for a month on short notice. Jobs.

This plan is open to tweaking.

Have you considered a small pressurized holding tank? That way the pump doesn't have to withstand high temps. Not sure exactly how you're heating the hot water (boom squish?)

I also recommend a holding tank as high up as possible. This will preheat your water to room temp.

LED's to a great job at lighting but I think you could power lots of them with AA batteries. Keeps a charger going in the car or solar if you have enough batteries for rotating. Use the Eneloop brand. Headlamps work great though some take AAA. Some LED's stay in place magnetically and turn on automatically - like this one.

Most of the battery operated tool lines seem to sell a flashlight.
Good thing both on and off the job.
Your lucky if thieves avoid b n e, where I live they will steal the copper out of occupied homes while the occupant is at work
Then again I dug a grave sized hugle bed in my front yard, after midnight, with no comments or calls to the police ffrom passers by...

Copper theft has been an issue in vacant buildings. My issue is that I leave for extended periods. The demographic problem is improving. Most thieves do their scouting on motorcycles and ATVs. I intend to do more in road mulching of tree waste. It doesn't hurt trucks but makes a tangly mess for unwanted visitors.

Drill-powered pumps are cr@p. HIGHLY INEFFICIENT.

Solar/battery pumping is a place you can spend a LOT of money in a hurry. 2 gpm is easy with an RV or sprayer pump. I lived for 6 months on one of these: http://www.tractorsupply.com/en/store/high-flo-12-volt-ag-sprayer-pump-60-psi I seem to remember it being much cheaper back then. That one has a built in pressure switch, so it is automatic--open the valve it kicks on, shut the valve it shuts off. You can get cheaper like this if you only want to pump to a tank: http://www.harborfreight.com/12-volt-marine-utility-water-pump-94639.html

If you want to go bigger, you can get the class A RV pump: http://www.amazon.com/dp/B00B1UMPRE/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=U8Z6BPC2IP24&coliid=I7OGSOJ0PM1K That thing outperforms most 220v shallow well pumps. That is for the family with teenagers and multiple bathrooms, not the bachelor pad. It is the one I am considering for a whole house off-grid pump for a family of 11.

The low-end solar well pump is: http://www.amazon.com/dp/B000NCEBDW/ref=wl_it_dp_o_pC_S_ttl?_encoding=UTF8&colid=U8Z6BPC2IP24&coliid=I2XY64KY1ACVIY You could hide that in the stream and pump to the top of the hill. But it is expensive. I will buy that one at some point to pump out of my pond for rotational grazing, but I do the totes in the truck for now, too.

You want the pump to put out enough volume to be a good shower but not over supply and short cycle all the time. So don't use a 2 gallon pump with a low-flow head.

Biggest issue for most pumps is getting grit in them, so put a filter on the intake side--just a simple screen on the intake can save a lot of grief: http://www.tractorsupply.com/en/store/hyproreg%3B-3-4-in-polypropylene-line-strainer-with-80-mesh-stainless-steel-screen

All those links are just links to easy places with pictures, not endorsements of products or sites, yada yada.

As to LEDs/power--EVERYTHING is centered around 12v DC. Even in telecom where they have 48 v dc as their power supply for critical equipment, the lights are 12v on a separate system. There are a few 12v LED lights that could be over-driven to 40v and survive, but they wouldn't last nearly as long and wouldn't be very efficient. Ever notice how HOT these new super-bright LED's get?

Here is an outdoor worklight that will handle 40v, notice the price http://www.superbrightleds.com/moreinfo/led-worklights/5-square-40w-heavy-duty-high-powered-led-work-light/1453/3408/

Thanks for the links Mr. Scott. I will most likely go for a pump that is under $200 as the main one from stream to cottage. It seems that every one I look at gives a flow rate without stating height of lift. There should be a table for each model. Nothing pressurized right now. I want to fill a tank and then use gravity. All of my water heating plans are for open systems that could not explode. The shower pump may be something as simple as a RV pump on a switch which pours into a perforated vessel overhead ( a stainless steel bowl). No blast pressure desired. Water will gravity feed onto the person in the shower. The required lift is about 40 inches.

40"?
My old Maytag has a belt driven pump, and it could do 40" all day long.
Rip a pump out of a washer, add a DC motor?
These pumps seem bulletproof, I have pulled nitril gloves and worse out of mine, put it back together and it just keeps going.
The washer came with the house ten years ago, and was old then...
I have been thinking that this type of pump has potential for being mechanically driven by wind, a good fit for your volcanic project.

Washing machine pumps move way too much water for the shower but might be perfect for irrigation water since they work like a trash pump. It might be useful for sucking crap from the bottom of a pond. Most of my wind arrives during the rainy season when water is abundant. A good time to suck the mud, since lots of water is lost.

I spent half an hour this morning talking to a guy who is in the sign supply business. Many of these signs are lighted. They use only LED. CFLs caused nothing but trouble in winter when the ballast doesn't reach working temperature. They had bad luck with no name LEDs from China. Light quality, poor service and durability issues along with never seeing prepaid orders have put him off of dealing directly with overseas suppliers. They now only use known brands and service issues with the lighting has become an insignificant slice of the business. Most problems have been because birds or insects built something that blocks the light. Customers are advised to do a quick visual, and most never require a service call.

He seconded much of Len's advice about putting bulbs in series to match battery voltage.

They aren't picky about the type of battery and nothing bad happens when batteries go dead.

Hi Folks - I came across this thread when searching for LEDs and 40v Batteries. Hope it's not bad form to resurrect an old thread.

Dale - I was curious if you ever came up with a use for your 40v batteries? I was given a set for a snowblower that I'll probably never use, at least during camp season, so I thought they'd be perfect to run lights. I was surprised to see they were 40v! I've tried running some LED strips from my 18v drill battery, which works well, but they seem hot so I suspect I could be running the risk of burning them out, and that would be much worse with the 40v. It seems one way mentioned to get over this would be to add extra strings to increase power demand. I'm lighting a schoolbus, so really any extra strings and i'm now trying to figure out a dimmer

Was there an easy way to step down the 40v to 12v? The idea of a computer PSU is interesting, I have lots of old ones about.

Also would love to hear if anyone has any other ideas for how to leverage power from 40v batteries. I'm off grid so there are lots of potential uses. Probably mostly in lighting though, not into water pumps just yet. I wonder if there is a way to wire a small solar panel into the 40v battery and run a shed light or something like that...

Anyhow appreciate any thoughts.

Thanks.

As Len mentioned, the individual LEDs are usually 3V. Don't buy AC bulbs as they contain regulators and rectifiers to get to 3V DC.
Don't buy bulbs of any voltage other than where the Voltage you are supplying is equal to 3V multiplied by the number of LEDs in the bulb.

So, simply buy 12V bulbs with 4 LEDs in them, and connect them up to your 12V supply. They will work at any reasonable voltage that a 12V battery could be expected to put out, as they have the resistors that Len mentioned need to go in series with LEDs in order to stop them blowing out.

These 12V 4-LED bulbs also happen to be the cheapest available.

As regards batteries in power tools, they are often, and increasingly so, made from 3.7V 18650 batteries. As are laptop batteries. As are Tesla batteries. As are some ebike batteries.
Three 18650 batteries give you a convenient, compact and surprisingly high capacity 12V battery (the batteries are rated 3.7V but when fully charged are at 4.2V each).
If you've got basic soldering ability and know how to use a multimeter then you can reuse 18650 batteries from "dead" laptop or power tool batteries, where in fact only one cell has a problem rather than the whole battery pack being "dead". Always take care with batteries containing lithium. They can and do ignite if damaged and occasionally during charging.

To convert AH to WH, multiple the AH by the voltage. So if you have a 100AH 12V battery, it has a capacity of 1200WH or 1.2KWH.

I'm a big fan of reusing 18650s from 'dead' multiple cell packs as Steve describes.

However, I do not use them in multiple cell configurations, and I only own SINGLE 18650 flashlights which have low voltage protection aka over-discharge protection built in.


High quality(and much more expensive than 'free') 18650s purchased new should be 'protected' cells; this means a small circuitboard has been added at one end of the battery cell that will break the circuit if the battery voltage gets too low, to prevent damaging the battery by over-discharging it. Importantly, damaging the battery by over-discharging increases the odds of the battery operating in new and exciting ways, like catching fire or blowing up. Not my favorite battery functions.

Why should you care if your battery blows up? After all, it was free! Well, first off, toxic badness. In the sense that the proper response is probably to call a hazmat team, if you blow one up in your house. Don't breathe the fumes.

Beyond that, an 18650 is around 4.2V at full charge, 3.6V (open circuit) when empty. A decent new cell might give you 3aH. If my math is right, 3aH at an averaged 3.8V is 11.4 watt-hours, aka 41,040 joules contained in a fully charged cell. It's no hand grenade, but to make a convenient though extremely apples/oranges comparison, it's about 73x the muzzle energy of a .45 round. If it doesn't sound scary, go watch a youtube video of a lithium ion explosion, I promise it will change your mind.


Anyhow, my original point was that the 18650s scavenged from larger packs will pretty well invariably lack this protection feature. They relied on the charger that went with the pack and/or other missing portions of the pack.

You can, to a certain degree, rely on the low voltage protection function in flashlights that have this. It's not universal, oddly enough; you need to check when buying a flashlight.

So why only use them in single-cell configs if you have a flashlight with low voltage protection? Multiple batteries will pretty much always be running in series inside your flashlight; the protection circuit doesn't know the voltage of each cell, only the total voltage. So, it can make mistakes. A freshly charged healthy cell and a nearly drained cell can average out and fool the protection circuit. Plus older and mismatched cells can have widely disparate capacities, and end up in the same mismatched state even if both were fully charged prior to loading the light.


Lots more reading for anyone interested:
http://www.candlepowerforums.com/vb/showthread.php?235164-Using-Li-ion-cells-in-LED-flashlights-safely
http://www.candlepowerforums.com/vb/showthread.php?285009-18650-s-Care-and-Maintenance
http://batteryuniversity.com/learn/article/safety_concerns_with_li_ion


Can you use these things safely in larger packs? Yes, but monitoring that would make me happy with such a setup isn't trivial... Your flaming toxic explosion risk tolerance may vary!


James, 40V is high enough that you might get away with 48V equipment; a quick glance at a couple nominal 48V inverters shows an input range starting around 38V... Depends how your battery was specced; all the '18V' tools I've seen (and Dewalts '20V Max') use 5x 18650s, assuming 3.6V per cell... 3.6V is an empty battery. If your '40V' is 11 cells, I'd expect you'd be alright for some LIGHT 48V loads; if it's only 10, not so much. Your packs are likely not very much in the way of amp-hours though, so don't expect much runtime on 48V stuff at all.

Lighting using appropriate # of LEDs in series should be no sweat, though.

my moms old camper was rigged with 2 car batteries and one 15w solar pannel. she used a suzuki car and booster cables to quick-charge on cloudy days. with a 12v camper TV/radio always running- and small (800w 120v) inverter at night to run normal household LEDs , the 3w full sized residential LEDs would last all night if need be.