diy solar

diy solar

UPS/Powerwall

bigjme

New Member
Joined
Jul 3, 2020
Messages
4
Hi All,

First off, incredibly sorry if this is very off topic post or not the type of system to talk about here.
I recently started watching Will and he has now given me an itch that wont stop.

I live in the UK and where i currently live, solar is not really a viable option and power costs are not horribly high.
I am a bit of a tech head and for work i run a full server cabinet at home for various bits and pieces

My servers currently runs off a very expensive APC SMX1500RMI2U, it is a great little unit for battery backup and power cuts are few and far between
The longest power cut in the last 2 years was 2 hours so nothing over the top
I work from home so server downtime is money lost which is the reason for me wanting something a little bigger and i am always worried about warranty on units

The downside of the APC is that for the fairly high cost, i get roughly 40 minutes of runtime out of it when the server is idle and when using it, id be lucky to get 30
I can expand it to roughly 2 hours for a reasonable cost with a battery module but the unit is around 5 years old now, out of warranty, and its time to see if a viable alternative is available should it fail besides just looking for another generic computer grade UPS

So, now the back story is done, i got the idea from Will to look at build a DIY Powerwall that is primarily just a large glorified UPS for my server but that could move with me in the future where Solar may be more viable. For now, I have no need to do anything else besides to store power for in the event of power failure
My primary objectives are:
  1. Last at least 2 hours with a 400w load
  2. A roughly similar price to the APC unit and a battery expansion
  3. Provide a better warranty period if possible
  4. Not take up a huge amount of space as the existing units sits in a server cab at the bottom
  5. Have a fast enough switch over time to keep everything on (the part i am struggling with most)
Being as APC is realistically one of the few brands i knew and solar was not something i'd ever looked at before this, I have researched what i can but user feedback is always best. I did look at an online design to prevent any switch over time but the cost of them was just too high for a decent wattage from what i could find, not to mention the permanent noise and lower efficiency loss of the system due to the charger and inverter

My initial system idea was to run something like the following:
  • VICTRON MULTIPLUS 48/3000-35-50
  • Pylon Tech US2000 (expandable in the future)

The above setup covers everything i need really except the switchover time.
The apc is listed at 6ms, with the victron being up to 20ms (presumably at 50Hz), some other units offer 10ms listed times but their ones i have never heard of
Some other more reputable companies such as SMA or Growatt seem to offer similar systems but of course are primarily designed around solar only so i'm unsure what they offer similar

So in short, is this a viable solution at all (has anyone done anything similar?) or should i stick to running normal computer grade UPS systems and ignore this entirely?

I'm in need of a new hobby so this has given me something to look at for a while and its not something i am looking to purchase anytime soon, but i am also happy to take the hint if i am over my head and coming up with solutions that are far too convoluted or over the top for my use case (a generator is not an option for example)

Regards,
Jamie
 
Hi Jamie, this is my small mobile set up. I have 70 20ah 3.65v cells arranged in a 5p 14s config which at full charge is around 5kwh. The cell chemistry is nmc. I've just bought another 70 cells to double capacity. Obviously you know all about the apc. My apc has never let me down.
 

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Thanks for such a fast reply Silentpower, i was really unsure if i would get anything in response or not.

So with 5kwh at (presumably) ~48v with lithium, did you find you needed to do anything besides connect the terminals together as i know the apc already has its own inbuilt fuses etc.? I would assume it would be as simple as connecting the pack to the apc pack terminals inside?

Also, have you ever done a full runtime check on it to see how long it lasts? UPS's are still a little mysterious for me if i'm honest as they range so heavily between their rated va and their actual power output at loads, it makes it hard to follow.

For example, my main APC unit runs off of a single APCRBC115 pack which states each cell (4 total) have a 432VAH capacity which i would assume to roughly be correct when you consider the loss due to amps pulled and a 400w load getting roughly 40 minutes (~25% loss in capacity for current an DOD)

Mainly its just trying to understand in my head that if 3 432VAH packs (apc plus expansion) would give me 2 hours and cost roughly £1,800 then a 48V LI-ION pack rated at 2.4kwh with a victron (roughly £1900) should be giving me roughly double the run length if my assumptions are correct?

I do love my apc and if i can get a battery pack working that i could otherwise use on say a Victron, that i could use on the APC whilst its still working, it would be a huge win and not something i had actually considered if i'm honest. The main bonus with this is whilst the batteries are more expensive, i get triple the capacity from a single Pyltontech (£790) vs a single apc battery expansion (£660) although i'm unsure if something like a pylontech would work due to the BMS connection etc.
 
Hello there,

I was trying to check the battery pack arrangement but I couldn't find it.

I bought an used emerson gtx2 2kva for home that uses 48V sealed lead acid bank (4x 12V 7A). I removed the internal pack that was dead and I'm using it with an external "bank" of 86A gel batteries.

The bigger the UPS the higher the DC voltage it uses (for instance we got some GXT3 and GXT4 6kva at work that use 240V DC ). Since mine uses 4x 12V batteries, it was easier to replace them with bigger ones.

IF you had to comply with data center norms and such I'm sure you should not even try what I did, but if it's for home use and you read a lot and be careful, you could buy way bigger batteries on your own for the same price that the brand battery pack.

regards!
 
It looks like its 4 12v lead acid batteries at 9A with them all in series to make the 48v pack and they seem to be pushing them to a DOD of around 70% or so

As my unit has a rear anderson connector on it for external packs, i guess if needed i could remove the internal battery, get a pylon 48v 50A pack, and wire on an anderson connector and plug directly in with no unit modification required as the pylons have an inbuilt BMS anyway (it would also keep it rack mountable) so the ups would just see a large 48v battery connected and i think the charge/discharge profiles are fairly similar besides the higher DOD

This is entirely for home use so its just personal equipment being covered, basic things like CCTV recording which i'd prefer to have running during a power failure etc.
 
Thanks for such a fast reply Silentpower, i was really unsure if i would get anything in response or not.

So with 5kwh at (presumably) ~48v with lithium, did you find you needed to do anything besides connect the terminals together as i know the apc already has its own inbuilt fuses etc.? I would assume it would be as simple as connecting the pack to the apc pack terminals inside?

Also, have you ever done a full runtime check on it to see how long it lasts? UPS's are still a little mysterious for me if i'm honest as they range so heavily between their rated va and their actual power output at loads, it makes it hard to follow.

For example, my main APC unit runs off of a single APCRBC115 pack which states each cell (4 total) have a 432VAH capacity which i would assume to roughly be correct when you consider the loss due to amps pulled and a 400w load getting roughly 40 minutes (~25% loss in capacity for current an DOD)

Mainly its just trying to understand in my head that if 3 432VAH packs (apc plus expansion) would give me 2 hours and cost roughly £1,800 then a 48V LI-ION pack rated at 2.4kwh with a victron (roughly £1900) should be giving me roughly double the run length if my assumptions are correct?

I do love my apc and if i can get a battery pack working that i could otherwise use on say a Victron, that i could use on the APC whilst its still working, it would be a huge win and not something i had actually considered if i'm honest. The main bonus with this is whilst the batteries are more expensive, i get triple the capacity from a single Pyltontech (£790) vs a single apc battery expansion (£660) although i'm unsure if something like a pylontech would work due to the BMS connection etc.
Hi, I did a run time to get a basic capacity test for the bank. It was around 4 hours @20amp drain. I used a heat gun, like Will does. It was very simple and without a watt meter.
My batteries are charged with an EpEver nd series I tracer. This is custom programmable and has been rock solid so far.
With regards to choosing the battery bank, I just calculated the expected battery voltage the apc would expect with lead acid at full charge and came up with 14s lithium. Minimum voltage is higher with lithium than la, so I'm careful not to use the inverter lvc. The load the apc sees is fairly low, so overheating is not a concern, but these are supposed to be line active anyway, meaning they run the output from the inverter and power that from the mains (rather than powering the load from mains and switching to inverter if the mains drops off), the switch time being switching from mains to battery power. All in all, my system, being used the way I do, has been extremely reliable.
Hope this helps.
 
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That does help a lot yes, thank you. It's a very good example that at less then 10ah like mine sees on a daily basis that the 2.4kwh should indeed be seeing around 4 hours of runtime when compared to your 5kwh unit.

At least from a capacity foot print I now know that something more custom like this could have some real benefit.

For comparison, with the apc unit, I would need to buy at leave 3 battery packs to get near 4 hours, with a cost of over £2000 in packs alone and the use of over 8u in my server cabinet

And again, only 2 years on the warranty which is my biggest issue with the apc for the price
 
I see no reason to replace your existing UPS as its built well and rated for continuous operation. The typical consumer-grade UPSs are specified to overheat just after the internal battery pack goes dead. A new UPS rated for continuous operation will be very expensive.

I ran an ancient SUA3000XL for years, removing the internal battery pack and connected to my 48V golf cart. The AC output was back-fed to my breaker panel and would run my house for several hours.

golf cart.jpg

You can purchase any type of AGM or lithium battery providing the output is 48V. Considering the UPS is already setup to charge AGM, and your usage is minimal, I could not justify the high cost of lithium.

The challenge is finding space to store the batteries in your server rack. That will likely determine what batteries you purchase. If you have the equivalent of Harbor Freight a set of four 35AH batteries are relatively small, inexpensive and would give at least a 2 hour runtime.
 
I see no reason to replace your existing UPS as its built well and rated for continuous operation. The typical consumer-grade UPSs are specified to overheat just after the internal battery pack goes dead. A new UPS rated for continuous operation will be very expensive.

I ran an ancient SUA3000XL for years, removing the internal battery pack and connected to my 48V golf cart. The AC output was back-fed to my breaker panel and would run my house for several hours.

View attachment 18789

You can purchase any type of AGM or lithium battery providing the output is 48V. Considering the UPS is already setup to charge AGM, and your usage is minimal, I could not justify the high cost of lithium.

The challenge is finding space to store the batteries in your server rack. That will likely determine what batteries you purchase. If you have the equivalent of Harbor Freight a set of four 35AH batteries are relatively small, inexpensive and would give at least a 2 hour runtime.
I'm interested in the notion that consumer grade ups overheat. The apc range, which I've used are line interactive which I take to mean that the inverter side continually runs the load, and a brown out causes the external supply to switch to battery, rather than external supply failure causes the inverter to kick in. This means the inverter is rated to supply the expected load constantly without overheating issues. I run a 48v apc rated to 1.7kva. I cannot speak for any other type, but any line interactive should work on the same principle.
 
The apc range, which I've used are line interactive which I take to mean that the inverter side continually runs the load, and a brown out causes the external supply to switch to battery, rather than external supply failure causes the inverter to kick in.
No, on grid power the transformers only filter and buck/boost AC power while charging the batteries. Fans will run on low.

During grid-down the inverter will kick-in within a 1/4 cycle. The fans will then run on high. Reference the following video.


Edit: you are likely using continually 50% or less of the 1.7kva capacity which limits the heating of the transformers and mosfets.
 
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