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DIY Tesla UPS
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DIY Tesla UPS

randvegetarandvegeta Member, Provider

Hello all.

Some months back, I mentioned I was going to build a UPS out of old Tesla battery modules.

There's been some significant delays but it looks like my DIY UPS will be ready within the next few days. It's working well under testing on my bench, so it just needs to get packaged into a nice box.

Specs are as follows:

6KW Inverter (Output)
21.2KwH Capacity (17KwH usable)
2KW Charger

I'm using 4 Tesla modules for this first version. Should be enough for almost 3 hours run time under FULL load.

I have a BMS monitoring the voltage of each cell. It balances the cell voltages if the delta is too high. There is a contactor which is disengaged if the overall voltage, current or temperature exceeds spec. This is for safety.

In order to reduce risk further, and increase battery longevity, the charger will only charge upto 24.2v (85%). And it cuts off at 18v (5%), hense the 17KwH usable capacity of the nominal 24v.

The inverter is for 24v, so we're using some chunky cables! 70mm2.

This thing is going to replace our ageing lead acid based UPS, where batteries need to replaced every 3 years. And even when replacing them, they still have shit capacity (45 mins when new, and seemingly halving every year). Hopefully this Li-Ion setup will last a decade or longer.

Thanked by 2kkrajk SinSiXX
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Comments

  • Hostsolutions will continue to be such an inspiration for all of us.

  • yoursunnyyoursunny Member, IPv6 Advocate
    edited July 31

    Failsafe fails, UPS halt and catch fire, the Nigh Sect is waiting.

    At least you have a balance circuit.
    A script electronic kiddie simply connects multiple LiPo batteries in parallel (don't).

  • randvegetarandvegeta Member, Provider

    @yoursunny said:
    Failsafe fails, UPS halt and catch fire, the Nigh Sect is waiting.

    I love how everyone thinks that batteries will catch fire willy nilly.

  • Falco33Falco33 Member

    Do you have any pictures of the setup? :smile:

    Thanked by 1randvegeta
  • bdlbdl Member

    photos please :)

  • @Neoon said:

    I didn't know that a borden cheese wedge is 16A. I will be installing these as fuses from now on.

    Thanked by 1randvegeta
  • LTnigerLTniger Member

    @CheepCluck said:

    @Neoon said:

    I didn't know that a borden cheese wedge is 16A. I will be installing these as fuses from now on.

    Why not audiovisual auto-alert?

  • randvegetarandvegeta Member, Provider

    @CheepCluck said:

    @Neoon said:

    I didn't know that a borden cheese wedge is 16A. I will be installing these as fuses from now on.

    Make sure to keep the cheese inside the foil.

  • randvegetarandvegeta Member, Provider

    @Falco33 said:
    Do you have any pictures of the setup? :smile:

    Yes but I'd prefer to make a tidier setup before displaying it.

    I originally used extremely thick, low thread count 70mm2 copper cable. It's incredibly hard to bend by hand. It's more like a solid rod of metal than a cable. As such, the cabling is not tidy.

    Im replacing as much cable as i can with high thread count cables I pulled from the Tesla. But I only have a couple meters of the stuff.

    Thanked by 1Falco33
  • randvegetarandvegeta Member, Provider
    edited July 31

    Ok some photos after I got rid of all the crap and swapped some unsightly cabled for better length ones.

    As you can see, it cannot really be left out like this. It needs to go in a nice box of some sort. I will re-purpose my existing UPS cases. So it will look the same as always and occupy the same space. (I'm using the kettle as load).

    Inverter comes with a basic display but does not really say much other than show the input and output voltage as well as the battery voltage. The SoC indicator is incorrect.

    This is my BMS. I can measure the voltage of the modules as well as the total current going in/out. It has a much more accurate SoC gauge. It is calibrated by voltage and the AH capacity is given.

    Here you can see all the individual cell voltages. 4.2v is the actual 100% charge level, but for my purposes, 4v is considered 100%. The BMS will automatically discharge cells with voltages over 4v. The BMS controls a contactor inside the box. So if anything goes out of spec, which includes cell voltage delta, total voltage, battery temperature or current, it will disconnect the whole thing.

    Here you can see I'm using the original BMBs that was used on the Tesla. Most people replace this with a simpler one. But Teslas BMBs have integrated resistors for balancing. Most other setups have additional components in the BMS to handle this same job.

    And just in case, a 3000 amp fuse. Thats a lot of amps!

    Thanked by 2vimalware fragpic
  • SirFoxySirFoxy Member

    @randvegeta said:
    Ok some photos after I got rid of all the crap and swapped some unsightly cabled for better length ones.

    As you can see, it cannot really be left out like this. It needs to go in a nice box of some sort. I will re-purpose my existing UPS cases. So it will look the same as always and occupy the same space. (I'm using the kettle as load).

    Inverter comes with a basic display but does not really say much other than show the input and output voltage as well as the battery voltage. The SoC indicator is incorrect.

    This is my BMS. I can measure the voltage of the modules as well as the total current going in/out. It has a much more accurate SoC gauge. It is calibrated by voltage and the AH capacity is given.

    Here you can see all the individual cell voltages. 4.2v is the actual 100% charge level, but for my purposes, 4v is considered 100%. The BMS will automatically discharge cells with voltages over 4v. The BMS controls a contactor inside the box. So if anything goes out of spec, which includes cell voltage delta, total voltage, battery temperature or current, it will disconnect the whole thing.

    Here you can see I'm using the original BMBs that was used on the Tesla. Most people replace this with a simpler one. But Teslas BMBs have integrated resistors for balancing. Most other setups have additional components in the BMS to handle this same job.

    And just in case, a 3000 amp fuse. Thats a lot of amps!

    TIL my work blocks hosthongkong.net, had to use my phone to get the imgs to load.

  • servarica_haniservarica_hani Member, Provider

    why not changing the setup so that the batteries can run much more Kwh for less time
    usually 15m of battery backup is enough as you only need it till the diesel generator kicks in

    I dont know how much tesla batteries cost but usually batteries and UPS are much more expensive that a diesel generator

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  • randvegetarandvegeta Member, Provider

    @servarica_hani said:
    why not changing the setup so that the batteries can run much more Kwh for less time
    usually 15m of battery backup is enough as you only need it till the diesel generator kicks in

    I dont know how much tesla batteries cost but usually batteries and UPS are much more expensive that a diesel generator

    The idea is to eventually get rid of the diesel generator. The generator is indeed much cheaper. But maintenance anand running costs is an order of magnitude higher.

    Over the long run, batteries will be cheaper.

  • randvegetarandvegeta Member, Provider
    edited August 1

    Sadly no advertised prices.

    I bet it's significantly more than my cost. Also my DIY setup has 5x more capacity.

    If their 4.8KwH solution cost ~US$1K, that would be very interesting. But my 21kWH setup only cost me ~$3K. Less if I factor in all the offsets I managed by selling excess parts. But the conveninece of placing in a rack in a convenient size and form factor is interesting.

    Edit: Although, the next time I do this, I'll be using Model 3 modules instead of Model S/X. The fact that they are not very desirable makes them vastly cheaper per KWH. I could pick up a whole pack (75KWH) for less than $2K USD. The higher voltage of the modules will mean much easier handling of cables. Cheaper too. I just need a bigger inverter/charger. But overall, it will have a cost of around 1/3 my current setup both in terms of storage capacity AND output capacity.

  • dedicatserver_rodedicatserver_ro Member, Provider
    edited August 1

    we have buy from them for our DC
    2 x CMS-900/75 ( Max. power: 900kW , Power module: 75kW ) + 2 x 10 x Lithium Battery Module 80AH,48VDC- 2 Racks ;)

  • DrvDrv Member
    edited August 2

    You want to use "used tesla batteries"?
    I think you want to die/set your assets on fire.

  • randvegetarandvegeta Member, Provider

    @Drv said:
    You want to use "used tesla batteries"?
    I think you want to die/set your assets on fire.

    Just because you don't know how to deal with batteries safely, doesn't mean I don't.

    @dedicatserver_ro said: we have buy from them for our DC

    How much did they cost? Nice rack mounted solutions are certainly attractive. But most solutions I've seen cost in excess of $300/kwh.

  • MrRadicMrRadic Member, Provider

    Will you be running 1 of these per cab?

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  • randvegetarandvegeta Member, Provider

    @MrRadic said: Will you be running 1 of these per cab?

    No. My racks are not super dense. I like to keep things reasonably low power to make cooling a bit easier. In any case, our DC is limited by power more than it is by space. A real luxury in HK actually. We could actually run twice as dense if we really wanted to but then we have no capacity for surges and we'd have to run ALL our AC units at full blast.

    It's easier for us to simply run light. We can gain density over time as equipment gets more and more efficient. We currently limit each rack to 3KW. But we're using 2U chassis and limit racks to 18x 2U machines. For dedicated servers, mostly running single socket CPUs and SSDs, the power consumption is only ~50watts. The whole rack may only ~1KW.

    TLDR; we will attach at least 2 racks, and upto 4 racks to 1 of these 'UPS'.

    Right now the UPSs sit at the end of the row of racks. But in the future, we will have a much BIGGER UPS in place of the generator. The generator occupies at least 4 racks worth of space (including the space required to walk around it). We can fit a good MwH of batteries and 100KW worth of UPS there. Should be plenty for our needs.

  • randvegetarandvegeta Member, Provider

    @dedicatserver_ro said: 74.950 USD per unit + 5000 USD shipping

    Cheap unit. Expensive shipping :D

  • dedicatserver_rodedicatserver_ro Member, Provider
    edited August 2

    @randvegeta said: Expensive shipping

    • in 2019 we have pay 4500 USD for a full 40" HQ container - 65mq , now 5000 USD for 12mq :'( and fast one month waiting time until they found a place in one

    • we build this DC now in Bucharest/Romania - 5 to 10 KW per Rack

  • randvegetarandvegeta Member, Provider

    @dedicatserver_ro said:

    @randvegeta said: Expensive shipping

    • in 2019 we have pay 4500 USD for a full 40" HQ container - 65mq , now 5000 USD for 12mq :'( and fast one month waiting time until they found a place in one

    • we build this DC now in Bucharest/Romania - 5 to 10 KW per Rack

    I used to ship containers from HK -> LT for $2K - $2.5K. 40ft ones. Now I can't get them for anything less than $15k. I have a container half full to the UK. I need to fill it with more shit to make it worth while. You want in? It's going to UK first though...

  • dedicatserver_rodedicatserver_ro Member, Provider

    Last week i have my last container here with the 4 x AC 129KW each, so thanks but for now we don´t need shipping ;)

  • raindog308raindog308 Administrator

    @randvegeta said: Over the long run, batteries will be cheaper.

    One advantage with diesel generators is that when the diesel runs low, you just pour more in. A good diesel generator can run continuously for months. I'm thinking with battery-only, you will always have a much shorter runtime.

    Granted, you usually hope that main power is back on shortly, but worst case...

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  • randvegetarandvegeta Member, Provider

    @raindog308 said:

    @randvegeta said: Over the long run, batteries will be cheaper.

    One advantage with diesel generators is that when the diesel runs low, you just pour more in. A good diesel generator can run continuously for months. I'm thinking with battery-only, you will always have a much shorter runtime.

    Granted, you usually hope that main power is back on shortly, but worst case...

    Very true. But it's just not worth it for me. As mentioned above, the cost of keeping the generator is relatively high. And power is very stable in HK. I think it would be easier for me to rent a generator in the event of long power outage.

    Pros and cons.

  • ApeWebApeWeb Member, Provider

    @randvegeta said: cost of keeping the generator is relatively high

    What maintenance are you actually doing on your generator? One of the older style ones shouldn't require much past oil + filters and using up the old fuel every 6 months or so. cheap if you can do it yourself. Tip is to not put much fuel in, 2-3 hours worth and if you do anticipate a longer downtime go and buy some on demand.

  • randvegetarandvegeta Member, Provider

    @ApeWeb said:

    @randvegeta said: cost of keeping the generator is relatively high

    What maintenance are you actually doing on your generator? One of the older style ones shouldn't require much past oil + filters and using up the old fuel every 6 months or so. cheap if you can do it yourself. Tip is to not put much fuel in, 2-3 hours worth and if you do anticipate a longer downtime go and buy some on demand.

    General services only. Costs about us$1.5k/yr. For the last 10yrs no outage has lasted more than 4 hours. All scheduled.

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