Budget UPS Based Powerwall

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Stingy49

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Nov 21, 2019
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7
Hey all,

Already posted this on the FB group but figured I would post it here as well since this will be easier to follow for those finding it later.

I binged almost allof Peet's videos and got the idea in my head that taking my office off grid would be cool. I wanted to do so on a really tight budget and the inverter struck me as something that could be found for less if I got creative. I picked up a 1500VA (a bit over 1000 Watt)APC rack mount UPS from an electronics recycler for $109. It's a pure sine wave unit that runs on a 24V lead acid pack. I already had a stack of LiFePO4 cells from my brother's van solar build which play nice with lead acid voltages (that doesn't matter a ton though, see video).

The plan is to run the above unit on a ~1.3kwh lifepo4 bank charged via 2 panels on my roof that I'm going to loosely secure (set on my roof with some rope)for ease of removal if a neighbor or inspector complains. Monitoring will be done via adiyBMS v4which will be able to turn off a contactor to disconnect the battery bank if needed.

I'm trying to document the whole process on video too.

I would love to hear y'all's thoughts!

-Derek

 
Love these types of projects - subbed
 
The top dog himself! I do to, so I figured I should finally give back to the community :) and this way I can also remember what the hell I did or was thinking when I look back at it lol.

My 100ft 10ga solar cables came today! Hopefully I can snag my panels during Thanksgiving holidays next week and get them up shortly after.
 
Wouldn't say top dog at all round here. Kori, Daniel & Mike kick my ass around here along with many other valuable members. I learn and get ideas from you guys! So please I'm just a member that paid for a few domains.
 
Nice video. Also subbed.

Using a UPS to get started is a nice stepping stone. Some times you can get them almost dirt cheap from certain recyclers. I have a local store called Repurpose Project where people can donate old things, wide range of acceptable things, and they resell at huge discounts. I've picked up two 600VA UPS's for about $5 each. I just need to make the battery packs for them (or use some cheap equipment batteries; lawnmower, etc) as they are 12V. But good for things like routers and lights and light duty things.

I also have a 2000Watt (SUA2000NET) APC unit (not server rack mount, just stand alone) that I have, runs on 48V. I'll be upgrade the FETs and adding in the extra load capacitor. I got it for about $80 with shipping. I'd like to have the rack mount version of these like AveRageJoe has (he has the rack mount version of the one I have)

The biggest drawback of a UPS as the inverter is that the idle power draw is fairly high compared. However, if you have enough battery capacity & solar/wind to compensate, it's not an issue, really. If it saves you money off your electric bill, then even that wasted energy isn't costing you anything.
 
Sounds like a great project! I too started with 18650 lithium ion battery packs for my APC 1500 and found that the top voltage is 27.8 (which is 3.97v per 7s). If you put in a 'higher' voltage battery the APC complained. So its functionally OK to under-utilize the 18650(s) but it does leave some capacity unused. Later on (today) I don't charge above 4.0 on my bank to extend the life so my earlier concern was not that important as it turns out. :)

However, 27.8v/8 cells = and 3.47v/cell top. Also the my APC cuts off at about 21.6v. 21.6v/8 cells = 2.7v/cell bottom. Is this range - 2.7v to 3.47v OK for your cells/design?

@Korishan has pointed out that some APCs (server class) allow you to set the voltage range.

And... welcome to the site. Its really a first class site - my hats off to the founders/admins!
 
Korishan said:
Nice video. Also subbed.

Using a UPS to get started is a nice stepping stone. Some times you can get them almost dirt cheap from certain recyclers. I have a local store called Repurpose Project where people can donate old things, wide range of acceptable things, and they resell at huge discounts. I've picked up two 600VA UPS's for about $5 each. I just need to make the battery packs for them (or use some cheap equipment batteries; lawnmower, etc) as they are 12V. But good for things like routers and lights and light duty things.

I also have a 2000Watt (SUA2000NET) APC unit (not server rack mount, just stand alone) that I have, runs on 48V. I'll be upgrade the FETs and adding in the extra load capacitor. I got it for about $80 with shipping. I'd like to have the rack mount version of these like AveRageJoe has (he has the rack mount version of the one I have)

The biggest drawback of a UPS as the inverter is that the idle power draw is fairly high compared. However, if you have enough battery capacity & solar/wind to compensate, it's not an issue, really. If it saves you money off your electric bill, then even that wasted energy isn't costing you anything.
Click to expand...


Hey Korishan,

I did most of my replying on youtube but I thought I would say check out my first UPS modding video because I go into where the serial port is and how to adjust voltage/power limits on the newer ups (without a serial port in the back). If your unit still has the serial port in the back knurlgnar's stuff applies nicely.

-Derek

OffGridInTheCity said:
Sounds like a great project! I too started with 18650 lithium ion battery packs for my APC 1500 and found that the top voltage is 27.8 (which is 3.97v per 7s). If you put in a 'higher' voltage battery the APC complained. So its functionally OK to under-utilize the 18650(s) but it does leave some capacity unused. Later on (today) I don't charge above 4.0 on my bank to extend the life so my earlier concern was not that important as it turns out. :)

However, 27.8v/8 cells = and 3.47v/cell top. Also the my APC cuts off at about 21.6v. 21.6v/8 cells = 2.7v/cell bottom. Is this range - 2.7v to 3.47v OK for your cells/design?

@Korishan has pointed out that some APCs (server class) allow you to set the voltage range.

And... welcome to the site. Its really a first class site - my hats off to the founders/admins!
Click to expand...

Hey OffGridInTheCity,

My first and second (? maybe third) video's on UPS modding go into this. I have a newer UPS without serial on the back but between using Knurlgnar's videos and FFCosag I was able tofind and modify the voltage scaler (charge/discharge limits) and power scaler (max power output). My system right now willlow-volt cutoff appropriately and will slightly undercharge the batteries for LiFePO4. I'm not concerned because the solar charge controller will be able to get the cells up to what I want and the point is to be off-grid. :)

-Derek

Just posted part 2! Adding the BMS and a nice clip of my frying my active balancing board :( ohh well. I'll probably post a quickie later this week also

-Derek

 
Part 3 is up! Bottom balancing, some fun "features" of the diyBMSv4, and mounting the UPS unit in some Ikea furniture. I also posted 2 quickie videos covering my solar wire and the system components.

Enjoy!


Up next is the battery bus bars, mounting of the safety components, and making of the battery shelf :)
 
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