Budget UPS Based Powerwall

Stingy49

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Nov 21, 2019
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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

 

hbpowerwall

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Love these types of projects - subbed
 

Stingy49

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Nov 21, 2019
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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.
 

hbpowerwall

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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.
 

Korishan

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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.
 

OffGridInTheCity

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Dec 15, 2018
Messages
1,265
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!
 

Stingy49

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Nov 21, 2019
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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.


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!

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

 

Stingy49

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Nov 21, 2019
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7
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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