Hello,

I am thinking of building an UPS that uses a few banks of 18650, 3.7 Li-Ion batteries.

Mainly i need 12v so, wiring them in sets of 4 (4x3.7v= 14.8v), should give me a lot of juice, and considering the price is somewhat lower than the old lead boxy ones, it should be a viable option.

The only concern is the charging circuit that must have good protections and at least 350W at about 2.5 Amps to run sensitive electronics.

This is the first step.

If any details, please ask. I have limited knowledge in electronics.

Thank you!

 

Other concerns include: spending more money on parts than you can get the finished product for, spending hundreds of hours designing something that won't have the kind of safety certifications that make your insurance pay off if it catches the house on fire, and working from, "limited knowledge of electronics" to try to equal people with dozens of years of education and experience.

Just one persons opinion, but I refuse to spend dozens or hundreds of hours trying to design things you can already get cheaper at a retail store than what you'd spend for parts.

Those who disagree with me will be answering you soon.

 

I don't see a single gain in using a Li Po battery bank system for such a device.

The control systems are designed to work with LA based batteries and their voltage drop curve and as far as sensitive electronics go running a modified UPS off of a non stock plus slightly higher voltage source is certainly not going to make things better.

If you need extra backup time just modify the UPS to run off an external deep cycle battery. I have done that to several and it works well.

 

Just one persons opinion, but I refuse to spend dozens or hundreds of hours trying to design things you can already get cheaper at a retail store than what you'd spend for parts.

Then why are you here? We "waste" time and money because we want to make it ourselves and hopefully improve the world someday. Bill Gates and Dell started in garages Excuse me, but you seem to be a bit harsh on people. Could you try to lighten up or just don't answer?

I am presently trying to do something similar, but to replace 12 volt NiMH tool battery packs. From what I've seen, 3 of the 3.7 volt batteries is good enough for Rockwell's Lifetime Guaranteed Batteries so all that's left is to charge them safely.

That's where #12 meant to be leading you... and if you don't know much about it perhaps we can all learn something here.

 

It's obvious that I have helped hundreds of people repair machines, find their assembly mistakes, interpret a datasheet, clarify an educational point, etc. but designing a machine from scratch, when they are easily available, cheaper and better than I can make them, is one of my personal limits.

One person asked me if I could design and build a VCR from scratch. Sure. It would take me most of a year, cost probably more than ten thousand dollars if I did not charge anything for my time, and they are already obsolete. Seriously, the record head alone would require some excellent machine tools and a magnetics laboratory, but it can be done. A UPS is a lot easier to do, and I can't imagine when they will become obsolete.

If that's how you want to spend your time, the AAC forums are at your service. At least a dozen people will contribute helpful circuit ideas, appropriate math formulas, and proven experience. I will probably be one of them, but I'm not willing to take the lead position on designing a UPS from the power cord to the THD of the output.

 

I don't see a single gain in using a Li Po battery bank system for such a device.

+1

First step of every design project is to understand the advantages/disadvantages of the choices. Li-Po main advantages are light weight... which is great for portable electronics but does not really matter in a UPS that sits around waiting for a power failure. Li also gives lots of recharge cycles... again does not matter in UPS. Main advantages of lead acid batteries: very cheap for power delivered, delivers high peak currents, long shelf life with proper maintenance. Guess what is ideally suited for UPS service?

 

3 of the 3.7 volt batteries is good enough for Rockwell's Lifetime Guaranteed Batteries so all that's left is to charge them safely.

Another disadvantage of Li: much more sensitive to overcharge, requires precision charging hardware. LA is very tolerant of overcharge and loose tolerance on charging voltage.

 

Thank you all for the fast replies.

My thought was at first:

I use an UPS to convert and store 220V electricity into batteries of 12V.

then, when i need it, i use another circuit to power my computer no I take the 12v, pass it trough an inverter to recreate 220V and that only to send it all to my LCDs and PSU which have the job of taking the 220v and regulating it to 12v (and a few smaller) again.

I took a look at what google did with their data centers:

http://www.upsonnet.com/Articles/Learning-From-Google-UPS-Design.html

The +90% efficiency stuck to my head, not to mention that later i could add a Solar Pannel to the battery input and go off grid with this built.

If redesigning all, i could simply break the circuit and buy:

This picoUPS board:
http://www.mini-box.com/picoUPS-100-12V-DC-micro-UPS-system-battery-backup-system

Then their PicoPSU:
http://www.mini-box.com/picoPSU-160-XT

although i am concerned by the fact that it has a 160W /200 W peak, from my math i have a cpu that takes 70W, adding another 30W to my motherboard (this is estimate, i could not find specific data online)

and the next variable is the graphic card, which is a whale of a consumer and a big question mark if I wish to upgrade plus other circuits + fans that i plan to add to my rig.


so, I get probably should get 2xPico PSUs... or I could make my own regulated 12V circuit (i buid one of these with an full documentation on it when i finished high-school - hence my knowledge in electronics) to power fans, LED strips, LCDs plus the Graphic card since it takes in a 6-pin connector (that is a 3x +12v and 3x negative wire)

http://pcsupport.about.com/od/insidethepc/a/atx-pinout-6-pin-12v-psu.htm


The reason i choose 18650s is that i recently stumbled again across them while watching a documentary on the new Tesla Motor car, that uses exclusively laptop power cells to have an autonomy of 500km, it made me think that i could shape it to my needs, and add more.

I do not know if I can simply repair (if it is possible, my old UPS) or should I buy a new one for 70Euros and simply add a second battery, for the low end ones i have not seen this option and i do not know if the warranty still stands if I add 10 sets of 4x18650s attached to it

thank you all for your replies!


@#12: I have a broken UPS at home, i had a hard time trying to figure it out, if my memory serves me, the input circuit was ok the battery was very low (5 or 7V), the output gave on the ground wire 110V . - I live in EU so our standard is 220V so that made no sense. Is there a workaround?

 

Another disadvantage of Li: much more sensitive to overcharge, requires precision charging hardware. LA is very tolerant of overcharge and loose tolerance on charging voltage.

I seen on ebay 18650 with protection circuits incorporated (a pcb on one of the ends that resolves this problem)

I also have a few worries regarding LA batteries, the maintenance or the fact it could leak, they are bulky, etc.

As to li-ion, true: they need a protection circuit, and if 1 cell has 3000mah, using 40 of these should cover my needs. if not i could always buy more, plus i can arrange them to fit into my case flat on the bottom.

 

I was thinking more like 12 volts of battery with a 12 volt DC to AC inverter. How could you charge 40 LI batteries in series safely? I'm worried about charging 3 because all of the chargers I have found charge only 2 in parallel. Besides even on Ebay that would cost more than a brand new UPS.

I do have an extra Rockwell LI charger that charges 3 in their 12 volt battery packs which look a lot like 3 18650 batteries taped together in a triangular case.

 

The +90% efficiency stuck to my head,

@#12: I have a broken UPS at home, i had a hard time trying to figure it out, if my memory serves me, the input circuit was ok the battery was very low (5 or 7V), the output gave on the ground wire 110V . - I live in EU so our standard is 220V so that made no sense. Is there a workaround?

First, I'd like to mention that the 90% efficiency number is only talking about one stage of the process. Every conversion from one voltage to another has a waste factor, and they add up.

Second, a 12 volt lead-acid battery that measures less than 10 volts has something very wrong inside it, like a single shorted/dead cell. When you get to 7 volts, that battery has gone into sulphation and might not survive even the best efforts to resurrect it. It would be no surprise that a battery that is months past "discharged" would only put out 110 volts from an inverter that is designed to make 220 volts out of 12 volts. Try a known good battery and see if your output voltage suddenly gets right. (Borrow one from a car or truck to do this test. It only takes a few minutes.)

The method to add more batteries is to simply connect them in parallel with each other. First, make sure they are healthy and properly charged, like 12.6 volts at rest. Then use fairly large wire to connect positive to positive and negative to negative. If the world was perfect, the 2 batteries would match voltage exactly, but you'll be OK if they are a tenth of a volt different from each other. Once you have them connected to each other and the UPS, they will be charged by the UPS and become good friends for a long time.

I have never bought a computer or a UPS, but I have 2 computers that work and they are connected to a UPS. People give me these things and I fix them. The UPS only needed a new battery. It's called, "sealed lead acid" or, "SLA". They don't leak.

What's a, "large wire"? If you want 200 watts from a 12 volt DC source, that would require 16&2/3 amp. A 12 gauge wire would handle that, but you need a bit more current to cover the 90% efficiency, so the current is more like 18.5 amps. Try size 10 AWG wire or learn the math I just did and adapt to your situation.

That's all I have right now.

 

I also have a few worries regarding LA batteries, the maintenance or the fact it could leak, they are bulky, etc.

So you figure a lithium based battery bank made of many small cells is going to be less maintenance, safer and easier to charge/keep charged than a common sealed LA type battery?

What books/websites are you reading?

 

So you figure a lithium based battery bank made of many small cells is going to be less maintenance, safer and easier to charge/keep charged than a common sealed LA type battery?

What books/websites are you reading?

You bring the marshmallows, I'll bring the hot dogs..... singing round the campfire.

 

@#12:

- I know about stacking the batteries on an UPS, you just have to make sure that it can recharge them.
- Regarding efficiency taking AC220v transforming it to DC12V then, making it again to AC220v that powers appliances that really need DC12v seems to be a waste.
_________

To leave behind my choice for Li-Ion cells and not LA:

The LA batteries available to me, are at most 7.2A at 6v, and this one costs 16Euros delivery included.

The 18650s are rated at min 3000mAh = so 3Ah and they cost 1,5 eur shipping included. I might even get a discount and buy 10 packs of 4 or 8.

Lead are heavier to mail and cost more, i will have to buy them locally.
I have an Yuasa LA 12v, 12.0Ah at 75euros.

if you take in account that i can get 10 pack of 3.7v 18650 5000mAh at 14.99$ shipping included. i buy a 40 for 60$ that gives me a total of 20Ah... way cheaper. With a double live, lighter and less bulkier in my build.

Costs tend to be lower on the Li-ion, given that they last at least twice as long.

The only setback is: i need a charger with protection for them. And here i have some concerns. I know that i cannot simply connect 3.7v*4=14.8v of output to the battery sets. It's not that simple.

Regarding the UPS i have:

The protected plug in which you are supposed to plug your PC:

it has 3 contacts:
A phase, neutral and Ground.

I check Phase + neutral => i get 220V (eu Standard) - OK
I checked phase + ground => i get 220v - again, OK
But when i check Neutral + Ground => i got 100V - ?????? is this normal?
________________________

Concerning the PicoUPS and PicoPSU anyone?

thank you all for your thoughts!

 

I would consider any homemade battery pack with lithium-ion batteries a ticking time bomb. Do not be a dingbat. Even Boeing could not get it right in 787 Dreamliner. The latter plane was grounded due to system problems caused from its lithium-ion batteries.

 

I stumbled across that article, i thaught they had an error... errors tend to be fixed... anyways.... if I can't get apples... i will settle with oranges...

I will get 1 or 2 12v 12Ahm Lead batteries...

What is next?

 

I'm sorry Boeing screwed up, but I just recalled that i got this idea from the Tesla Motor Model S sedan car... so... someone got it right...

 

I'm sorry Boeing screwed up, but I just recalled that i got this idea from the Tesla Motor Model S sedan car... so... someone got it right...

Ok if you spend as much money as Tesla did, developing their battery system. Be my guest by all means. What you do not understand. Is that every rechargeable battery pack sold. Has gone through a approval and testing process according to the adequate standard. The link will give some insight http://www.ul.com/global/documents/...ty Issues for Lithium-Ion Batteries_10-12.pdf
This to reduce as much as possible hazards like thermal runaway. You will be surprised how much energy it is even in a small battery. More than enough to start a fire. Your DIY self battery pack will most probably be missing most of the safety mechanism/measures that you find in say your laptop battery. And it will for sure not have been subjected to any testing. A worst case scenario would be that your DIY battery pack go up in flames then you are asleep. And you never wake up. A less more scary scenario is that your apartment burn down while you are not at home. It will for sure be an investigation. And they will most sure be able to find the cause, your DIY battery pack. The insurance company will of course refuse to pay you anything. I hope you get my drift now

 

The LA batteries available to me, are at most 7.2A at 6v, and this one costs 16Euros delivery included.

You could just stop by the local auto parts store and buy a real deep cycle battery that is designed for heavy discharge use.

They call them marine deep cycle batteries around here and a sealed 12 volt 100 Ah one sets you back about $150 (~110 euro). A small 30 - 40 Ah one is half that.

Since we don't know where you live no one here can do a online search in your area to find the best local prices.

 

I would consider any homemade battery pack with lithium-ion batteries a ticking time bomb. Do not be a dingbat.

So, the weenie roast is off?

Seriously, using Li cells in series/parallel battery packs requires individual cell monitoring and balancing and it still goes wrong sometimes. Just ask boeing about the battery fires on their dreamliners.