DIY Backup Power Supply Build


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1gkar

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Joined
Feb 5, 2022
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29
DIY ~1.6kWh
Lithium-Ion Portable
Backup Power Supply

As I live in the hills, in the West, of New Zealand's largest city (Auckland) I tend to experience significant power outages, which leaves me without access to the internet -as I have a flaky (at best) mobile signal -so much for living in a 1st World country; so, no wifi, & only 1G mobile connection.
I also am left with no water, as I am on a water tank/pump system. So I decided to design & build a portable backup power supply (PS), to improve my knowledge, as a fledgling hobbyist electronics enthusiast.
Below are the basic design specs, divided into sections.

Battery:

Using repurposed lithium-ion 18650 batteries, sourced from discarded laptop batteries. Here is the repackr cell configuration:

1655099319683.png



As you can see it is a 3S72P battery (not the ideal 12V config; I know. But it is what it is, at present. I will probably rebuild it, when I have more, & better cells. Have just found a better supplier).
When I have completed further testing, & have better knowledge, I may even decide to upgrade to 24V, if it will still be portable; which means, it has to be able to be manually carried. The battery strings are wrapped in Kapton tape. The positive & negative terminals are connected to the PS with stainless steel nuts, bolts, & spring washers.
The BMS is a cheap Aliexpress 3S100A one, with balancing ability, and a circuit breaker cut-off current of 60A. I will upgrade to a better quality, bluetooth one, when the battery is upgraded.
I used DIY busbars, from electrical cable, & connected the battery strings using XT90 connectors. I used the Tesla fuse method, on both positive & negative, as I like the idea of individual fusing, for safety.
The battery is monitored, & manually balanced, with a Cellmeter 7 -see image in the charging section.
At present, the cell variance is around 0.050VDC.

1655099454510.png


The Case:

I built my project using an AEG toolbox. Rather than have a significant number of penetrations, for mounting screws, I decided to mount acrylic panels, which the electronic's components -& the battery- were affixed to.

1655099537030.png
1655099608254.png


Temperature Control:

You can see, from the above & below images, I am using a W1209 temperature controller to set 2x 12VDC 80mm fans, to turn on, at around 33°C. They are so configured that one is an input fan, the other is set to output, from right to left, to coincide with the inverter's fans, to expel any hot air, once the device fans switch on. I am yet to set the controller fans accurately, based on the inverters fans' activation.
The W1209 is regulated with a buck converter, set to 10.6VDC.


1655099852176.jpeg



Charging:

The PS is designed to be charged by both AC & DC, either via solar, or a CVCC power supply (I am in the process of repurposing an old PC PSU. At present, I am using a Chinese D3806 module), on the DC side.
The AC charging is completed using an old laptop power supply (~19VDC/3.4A), which is then voltage-reduced, to 12.4VDC, with a 150W CVCC buck/boost converter.

1655100312955.png



Connections:

I decided to charge my various devices, using multiple connectors. Below, are listed the types, & reasons, for their inclusion:

LHS Connectors:
-1x 12V cigarette light socket. For various options.
-2x 2.1mm DC jacks. Mainly for charging electric shavers.
-1x GX-16. For direct charging, of my lithium-ion golf trundler battery.

RHS Connectors:
-2x USB charge sockets. One includes a type-C PID socket. For any 5V device charging.
-2x XT60. For the ability to connect my D3806 CVCC power supply.
-Positive & negative binding posts.

The connections are all individually switched. The left hand side connectors are regulated through the ZK-4KX boost/buck converter, so I can set the voltage, as desired, for the various applications.

nb. there is an issue with aforementioned ZK-4KX CVCC boost/buck converter. It is not performing as stated in the product description, on the Aliexpress auction page. The temperature increases constantly, until the over-temperature protection, kicks in, shutting down the module, in quick time, when operating near full current. I will try fitting a fan, to mitigate the converter's heat generation, otherwise I will replace it, with a different type.

Nnb. As I live in New Zealand, I am limited by access to quality products (& NZ does not have decent part options, held on-shore), so am relegated to procuring Chinese parts. Purchasing decent components from USA, is often not an option, as the shipping charges are ridiculously high.

The charging ports are:

DC -XT60
AC -IEC fused socket

The sockets are switched with a 20A-rated toggle switch.
The AC inverter output sockets are extended to the case exterior, using 3-pin flush-mounted panel sockets.

1655100688100.png
1655100717594.png


Volt/Amp Display:


I have installed a 4in1 meter, running through a 100A shunt.

1655100891688.png


Wiring:

Battery cabling is 8AWG, connecting to the battery terminals, & the distribution posts, with non-insulated crimp connectors. Also, the main positive runs to a 60A circuit breaker, which then runs to a 6-way fusebox. And the main negative runs straight to a busbar.
All the other wiring is conservatively sized, 1-2 sizes above the recommended current requirements.
Below, is the full wiring schematic. It is hand-drawn, as that is what I am comfortable with. As I'm not in any of the relevant industries, & am a bit old-school, I prefer that method.
All distribution posts are stainless steel.

1655101190952.png



nb. don't look too closely, there could be mistakes :oops:; but it is mainly accurate.

Inverter:

I bought a cheaper type 12VDC/1000W (2000W surge) inverter, locally.
It is mounted on an acrylic shelf, separating it from the the battery. At present, it is wired individually of the rest of the circuitry, except the display meter. The two output power points are extended, via cut-down extension leads/plugs, to the panel AC sockets.

1655101664525.png


Testing:

To follow...

Accessories:


I 3D printed up the following:

-fan grilles
-AC charging boost/buck converter housing.
-accessory box, fit into the inside, of the lid. Yeah, I know; a little bit of ego ;)

1655106488759.jpeg
 

1gkar

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Feb 5, 2022
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29
One thing I meant to mention, the AC charging is only charging at very low current -~0.6A. Need to do some troubleshooting.
 

1gkar

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Feb 5, 2022
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Here's some photos, of the complete project:
-Coming soon-
 
Last edited:

Redpacket

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Feb 28, 2018
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1,457
Nice project :)
Re the low charging current, the CVCC module its likely overloading the laptop supply (~70W max?)
You might have to set the CVCC module output current lower so the laptop PSU can startup & run properly.
Also claimed specs are famously not actually usable.... maybe expect to derate a bit.
 

harrisonpatm

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Jan 5, 2022
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168
Keep us posted on the longevity of the temperature controller; i was hoping to use one in the future to keep LiFePO4's warm in the winter.
 

1gkar

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Feb 5, 2022
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Keep us posted on the longevity of the temperature controller; i was hoping to use one in the future to keep LiFePO4's warm in the winter.
Might take a while, given we are heading into winter, & the weather has only just turned south 🤧
 

1gkar

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Feb 5, 2022
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Nice project :)
Re the low charging current, the CVCC module its likely overloading the laptop supply (~70W max?)
You might have to set the CVCC module output current lower so the laptop PSU can startup & run properly.
Also claimed specs are famously not actually usable.... maybe expect to derate a bit.
Thanks. Will try your suggestion. Tell me about the Chinese components specs' disappointment; already finding that out 😧.
 

Mazlem

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Aug 8, 2017
Messages
100
Nice work! Over here in the US that case is sold as a Ridgid brand. I bought one and fully intended to make a portable power box like this... 3yrs ago. :p
 

1gkar

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Feb 5, 2022
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Nice work! Over here in the US that case is sold as a Ridgid brand. I bought one and fully intended to make a portable power box like this... 3yrs ago. :p
Thanks. No time like the present.
I also had mine sitting around for a while;)
 

ajw22

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Nov 16, 2018
Messages
733
Very very nice!
For a portable solution, the AC/Solar toggle switch sticking out will get bent or broken sooner or later. A different switch, or perhaps 3D print a recess?
The exhaust fan is located quite low, so heat from the inverter will likely accumulate in the upper part of the box. If it indeed is an issue, you could remove the lid gasket, insert 1mm thick spacers so there is always a gap, and make both fans intake fans? Maybe there's not enough play for a gap.

For internet connectivity: have you tried hanging a Pocket Wifi on a pole or chimney, wherever the best (least worst) reception is?
 

1gkar

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Feb 5, 2022
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29
Very very nice!
For a portable solution, the AC/Solar toggle switch sticking out will get bent or broken sooner or later. A different switch, or perhaps 3D print a recess?
The exhaust fan is located quite low, so heat from the inverter will likely accumulate in the upper part of the box. If it indeed is an issue, you could remove the lid gasket, insert 1mm thick spacers so there is always a gap, and make both fans intake fans? Maybe there's not enough play for a gap.

For internet connectivity: have you tried hanging a Pocket Wifi on a pole or chimney, wherever the best (least worst) reception is?
Thanks. I realised as soon as I had cut the output fan's hole; basic convection :whistle: I had been thinking of 3D printing a duct, to suck out the hot air, from the upper case section.
Re. the switch: yeah, as I said, we are very restricted in parts' availability, where I live. About the only option. I might make a surround, at some point.
Was unfamiliar with pocket Wifi, until you mentioned it. Does it not still rely on a decent mobile signal, to generate the wifi, from the 3G-4G signal? Because that is also an issue, where I live.
Am restarting an old project; a basic router backup ups. Stopped it, as the cheap, crappy Chinese buck converter failed, & caused a voltage surge, in my old router, destroying it.
 

1gkar

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Feb 5, 2022
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Thought I would supply a sample of {what I perceive to be} the good quality batteries, I am now able to procure. I have gone away from the laptop packs, as they were too poor; with the last batch having about 30% under 1V.
These e-bike batteries have superior initial voltage (am only losing about 10 per 100 batteries. And I can swap those, when I procure more. Don't worry too much about the IR, it is recorded, using a Liitokala Lii-500. Gets me in the ballpark. Am thinking about getting a YR1030 tester.
As you can see, I am at ~300AH, with a number still to test. Then it's just the waiting, to see they self-discharge. Am pretty confident, they will be OK, given their initial voltage.

1655183379336.jpeg
 

ajw22

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Nov 16, 2018
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Was unfamiliar with pocket Wifi, until you mentioned it. Does it not still rely on a decent mobile signal, to generate the wifi, from the 3G-4G signal?
Had to look up what exactly 1G was - it's analog tech from the dinosaur age!! Quite possible that no modern Pocket Wifi is backwards compatible to that.
Yes, still needs a mobile signal, of course. The advantage is that you can duct tape it to a window, or even put it on a 10m tall pole on the roof in a waterproof housing... You should get better reception that way, perhaps even reach a 2G/3G station?

Some devices also have a LAN port, so you could place it about 100m away from the house. Need a separate Wifi access point for inside the house though.


I had been thinking of 3D printing a duct, to suck out the hot air, from the upper case section.
Such a "hot air snorkel" would work too, but only if the fans are on. It would kill any kind of "free" cooling through natural convection.
Since the box is no longer water tight anyway, I think the better approach is to make as many exhaust openings in the lid as possible. Maybe in these locations:
1655188228075.png
 

1gkar

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Feb 5, 2022
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@ajw22 Thanks for your input, it is appreciated (y).
My phone signal probably rolls back to 2G, not 1G; but same issue applies. Am looking into a mobile signal booster. Something I probably should have looked at a long time ago. With New Zealand's telcos looking to phase out landlines -most likely, next year- it is something I really should expedite.

I will probably wait until temperature testing is complete, before I look at putting more holes into the case. Always an option, at any future point. If I did, I would probably print up cowls, to cover them. I could always roll down the sensor's switch-on temperature.
 

1gkar

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Feb 5, 2022
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Just an update, on the way I went with improving my mobile signal. During research, of the various signal upgrade methods, I came across the fact that latest phones have the ability to send/receive calls, via WiFi (WiFi calling). Was totally unaware of this function (was looking towards a mobile signal booster).

Have since bought a new phone: Oppo A54 5G. The phone's reception, via WiFi, is brilliant. Just like using a landline. Beats my neighbour's iPhone WiFi calling reception, for stability.
Now I don't have to worry about losing my landline, when New Zealand's telcos cease voice functionality.

Haven't done anything further, on the box, as I am involved with other aspects, of life.
Stay safe, everyone.
 
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