Off grid standalone electricity supply project

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Off grid standalone electricity supply project

Postby glenn0010 » Fri Mar 10, 2017 8:49 am

Hi all,

I have started work on a project to convert a room my dad has in a field to a fully convert it into a standalone electricity supply.

I have gathered a lot of 18650 cells and upon testing, roughly 130 of them have tested above 2Ah. I will solder these cells in a 14s8p pack (roughly 48V 16Ah). I know its not a lot but we only need a couple of lights and capacity can be added further on.

cells.JPG
Roughly 130 cells over 2Ah sorted by capacity from left to right in ascending order. Took one from each end to make the packs roughly equal in capcity
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I used adhesive to glue the cells together rather than hot glue.

glue.JPG
!4 packs like these glued together
glue.JPG (38.24 KiB) Viewed 249 times


I will buy my dad a 600W 48V inverter however currently funds are tight. SO in the mean time I planned to use a UPS as my inverter for a 12V system using SLA batteries. I have an old UPSthat I got working however when it is running off the battery, the voltage is not the required 230V that we use over here but it is at around 178V. What could be causing this problem? Even though the battery I used for the test is old I think that it is good since under no load, it holds at 13.1V and does not sag. Also I didn't find any trimmers on the PCB to adjust any voltages. What could be the issue?

Inverter output voltage.JPG
Low output voltage
Inverter output voltage.JPG (34.78 KiB) Viewed 249 times


Thanks all for your help.

Any suggestions are welcome!
Last edited by glenn0010 on Fri Mar 10, 2017 8:50 am, edited 1 time in total. View post history.
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Re: Off grid standalone electricity supply project

Postby Izits » Fri Mar 10, 2017 11:20 am

As to why the output voltage on your old UPS is low, if it's more than 20 years old I would look for aging and bad electrolytic capacitors. They tend to go bad with time just sitting on the shelf.
Last edited by Izits on Fri Mar 10, 2017 11:24 am, edited 1 time in total. View post history.
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Re: Off grid standalone electricity supply project

Postby Hillhater » Sat Mar 11, 2017 5:53 pm

If you are only going to power lights etc, why do you need inverter for 12v ?
Just run a 48v (or some other dc voltage) LED lighting system.
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Re: Off grid standalone electricity supply project

Postby glenn0010 » Sun Mar 12, 2017 1:35 am

Izits wrote:As to why the output voltage on your old UPS is low, if it's more than 20 years old I would look for aging and bad electrolytic capacitors. They tend to go bad with time just sitting on the shelf.


I will have to grab my meter and check the PCB, the UPS is only about 5 years old so it is not too old
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Re: Off grid standalone electricity supply project

Postby glenn0010 » Sun Mar 12, 2017 1:36 am

Hillhater wrote:If you are only going to power lights etc, why do you need inverter for 12v ?
Just run a 48v (or some other dc voltage) LED lighting system.


While that is the simplest and cheapest option using DC through a buck/boost converter, I want AC so if I bring a laptop or and small appliances we will be able to use them
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Re: Off grid standalone electricity supply project

Postby Hillhater » Sun Mar 12, 2017 2:45 am

Laptops have a dc charge port .
Most small appliances, tools, audio, heaters, fans, etc".. could be rechargeable , dc powered
Keep it simple.
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Re: Off grid standalone electricity supply project

Postby glenn0010 » Sun Mar 12, 2017 2:17 pm

Hillhater wrote:Laptops have a dc charge port .
Most small appliances, tools, audio, heaters, fans, etc".. could be rechargeable , dc powered
Keep it simple.


To be fair if I were smart that is what I would do however, I want really want to make it full AC haha.

Made some progress: Started soldering the parallel packs, first tiime soldering 18650's. Soldered 4 Packs so far 10 to go

Capture.JPG
4 Soldered \packs
Capture.JPG (59.67 KiB) Viewed 187 times

Capture1.JPG
Positive side
Capture1.JPG (50.27 KiB) Viewed 187 times

Capture2.JPG
Negative side
Capture2.JPG (42.8 KiB) Viewed 187 times

Capture3.JPG
10 packs still to go
Capture3.JPG (58.65 KiB) Viewed 187 times


I used a 3mm squared single strand wire, it should be enough correct for let's say 600W draws.
Also what do you think about solder the joints?
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Re: Off grid standalone electricity supply project

Postby vk4bxi » Sun Mar 12, 2017 5:55 pm

What are you measuring the output volts with ?
I would guess that the ups has a modified square wave output. So the peak volts will be dépendant on the battery volts and the time the volts are on will give the rms. And an ordinary DVM will be reading average and not a true reflection of what is going on. So increase the supply volts up to sla float volts and use a 100 W light load and see what you get then.

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Re: Off grid standalone electricity supply project

Postby Hillhater » Mon Mar 13, 2017 4:54 pm


Also what do you think about solder the joints

.....i assume you are aware of the issues/risks around soldering to those cells ?
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Re: Off grid standalone electricity supply project

Postby titooon2014 » Thu Apr 20, 2017 12:52 am

Hello,

vk4bxi is right, if you get 178V it is because you have a modified square wave inverter, and not a pure sinewave.
It is allright for most appliances, but some don' t really like it much (such as power tools).

Regarding the 18650 cells did you got through the 18650 post on ES ?

- The soldering on your cells is way too overkilll, such an amount of solder means that you need to heat up the cells quite a lot, which will degrade them, esp on the negative side. Explosion risk even.
- Do you plan to use a bms ? having many different brands and models of cells like you do, it is very very tricky to ensure all parallel blocks will stay within their limits, esp if you reach 0.5C discharge where some blocks may heat up.
- if you want to have a decent lifespan and efficiency , recommended discharge is 0.2C, so a 48V16Ah pack would be fine for around 200W discharge continuous.

Where are you living ? there are some super good deals on ups 48v on ebay in the UK.
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Re: Off grid standalone electricity supply project

Postby Hwy89 » Thu Apr 20, 2017 4:55 am

You need to get fiber washers for the positive ends of those cells. I'm actually surprised that you haven't already shorted some cells where the copper wire crosses the shoulder of the cell. That must be low temp solder for you to make such big globs without heating up the copper wire enough to melt through and short it out. Another point is that even a light impact to the ends of those packs will be enough to push the copper wire through.
Please be safe.
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