Backup Power Supply
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.
Using repurposed lithium-ion 18650 batteries, sourced from discarded laptop batteries. Here is the repackr cell configuration:
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.
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.
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.
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.
I decided to charge my various devices, using multiple connectors. Below, are listed the types, & reasons, for their inclusion:
-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.
-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:
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.
I have installed a 4in1 meter, running through a 100A shunt.
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.
nb. don't look too closely, there could be mistakes ; but it is mainly accurate.
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.
I 3D printed up the following:
-AC charging boost/buck converter housing.
-accessory box, fit into the inside, of the lid. Yeah, I know; a little bit of ego