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Backup power for your lights?


Dimi

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Who thinks that this is a good idea? 

I have built a battery backup for my lights. It is connected to my regular light switch via an extension box. When the mains are on it charges 6 x 18650 cells, storing about 50wh of power. When the power is out it switches to battery and a mini inverter. This will power a single 5w light bulb for 10 hours, a 10w for 5 hours etc. This is at full brightness, no dimming as with the rechargeable bulbs. 

The cost for the entire system is about R600 using off the shelf parts, making it really affordable, even for multiple units around the house. 

This is a solution for those who can't afford a full on lithium battery / inverter setup but want to keep the lights on. 

Thoughts? 

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For lights only.

I like the idea of a 12V250VA Victron paired with a 12V 50Ah battery and a Victron Blue Charger connected to the light circuit at the DB level.

Small system and keeps all your lights on ( within reason provided they are LED ), a whole house solution with just a little bit of upfront work.

 

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1 hour ago, Chris.P.Bacon said:

For lights only.

I like the idea of a 12V250VA Victron paired with a 12V 50Ah battery and a Victron Blue Charger connected to the light circuit at the DB level.

Small system and keeps all your lights on ( within reason provided they are LED ), a whole house solution with just a little bit of upfront work.

 

So the idea here as at an individual light switch level. Your lights switch is removed, and an extension box with all the necessary circuitry is placed in it's place, and the light switch screwed back on to the extension box. Underneath this extension box is another connected box which houses your batteries. Batteries can be easily swapped out or upgraded if needed. I do however like the idea of connecting at the db level. What would the cost be for such a solution? I'm trying to find innovative ways the less fortunate can at least have lights during loadshedding. 

I'll have the prototype mounted with the new battery pack I'm waiting for delivery on, and will post pictures for comments. 

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22 minutes ago, Dimi said:

So the idea here as at an individual light switch level. Your lights switch is removed, and an extension box with all the necessary circuitry is placed in it's place, and the light switch screwed back on to the extension box. Underneath this extension box is another connected box which houses your batteries. Batteries can be easily swapped out or upgraded if needed. I do however like the idea of connecting at the db level. What would the cost be for such a solution? I'm trying to find innovative ways the less fortunate can at least have lights during loadshedding. 

I'll have the prototype mounted with the new battery pack I'm waiting for delivery on, and will post pictures for comments. 

There is nothing wrong with your solution and for only some key lights it is a good approach. No disagreement from my side.

Cost at DB level is around R8 to 10k if you work on a 12V 50Ah Lithium battery. 
So agreed, substantially more than if you only need to keep some key lights on.

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@GMAC yes, that's the whole idea. I want to build a solution that is accessible to anyone. The solution works, and is cheap.

This is what it looks like on my desk, I'm waiting on a 3s2p battery will and put it up on the wall and take better pics. 

Another extension box with a blank plate would house 18650's. 

IMG_20230521_155811.jpg

IMG_20230521_155843.jpg

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You are talking about lights.  Only lights.  LEDs are not good from a health perspective (too much blue light radiation) but they are the only lights with a decent efficiency.  So LEDs it is.  Well, LEDs are by definition low voltage devices, each LED having a forward voltage of typically 3V.  So if you are only catering for lights, going the 230VAC inverter routed is a bad idea.  There are many reasons for this:

1. An inverter costs money which you could save by staying with low voltage DC.
2. If you are extremely lucky, your inverter will waste 10% of your battery power.  For tiny inverters (as in your picture), the losses might be close to 25%.  By comparison, a low voltage DC system will have no losses.
3. You would need to remember to switch your inverter off to prevent battery drainage.  A low voltage DC system could remain "on" 24/7 without drainage.  
4. 230VAC can be dangerous.  Especially on small inverters and even inverter trolleys where nobody fits earth leakage protection due to cost considerations.
5. The safety aspect here is even more important.  Your system will not be integrated with the building.  You will likely have loose wires across floors, etc. Wires over which people could trip, tearing wires out of their connection blocks and exposing the user to potentially dangerous high voltages.
6. Even the best pure sinewave inverters produce HF switching noise.  Small modified sinewave inverters will really be noisy as the manufacturer will not use any filter components due to cost considerations.  Such noise could cause interference in RF (radio frequency), audio and video systems.

The main downside to low voltage DC is that the available form-factors of the LED lamps is limited and that these bulbs are not freely available in your Game, Checkers, etc.

Use MR16 12V spot lights that are available in 3, 5 & 6W ratings.  Although being DC, these lights will work with any polarity and at a constant brightness with any battery voltage between 11-15V.

If you use LED strip lights you need to be careful.  These are unregulated and thus require the correct DC polarity and an exact 12V.  Voltage fluctuations will cause brightness fluctuations and over-voltage would kill them.  For these, a buck/boost regulator would be the best option.

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@Modina thank you so much for taking the time to highlight the potential issues with the solution. These are issues I have thought of beforehand, and hope my answers provide some clarity.


1. An inverter costs money :

The inverter module costs R70, not an issue. 


2. If you are extremely lucky, your inverter will waste 10% of your battery power :

It turns out to be very efficient. Ran a test yesterday with minimal loss, under 10%, I was surprised as well. 


3. You would need to remember to switch your inverter off :

The inverter is switched on by the relay, only used when there is no ac power. No battery drain, no standby mode. Lights go off for a second during switch over. 

4. 230VAC can be dangerous :

Not if enclosed in the plastic enclosure and not at such low current. Had myself a tiny tingly shock, wasn't bad. 


5. The safety aspect here is even more important :

Safety was first priority in the design. No external wires, everything enclosed safely.

 
6. Even the best pure sinewave inverters produce HF switching noise :

Not an issue given it's on a single circuit, powering only lights. 

 

I hope I have addressed the concerns here. Let me know if I should expand on any of these points. 

 

Note:

Why am I doing this? 

They say that necessity is the mother of inventions, and it's true in this case. Loadshedding is a huge problem, and there are really good solutions for all needs, except for lightning, which is the most important, especially to the poor. The idea is to build a low cost solution for those who don't have 10s of thousands to invest in a full inverter/battery system tied to the db board. 

I intend to complete this project and adhere to all safety regulations. If this is materializes with the off the shelf components, I intend to design a single board pcb with the complete circuit, no individual components. I'm a Software engineer by trade, so final designs will be done by qualified electronics engineers. This will bring costs down even further. 

I don't believe that the government will solve the problem, it's up to us to come up with solutions. 

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So, a quick update. I've decided to move to a 5v circuit instead of the 12v. There are 2 reasons for this, cost reduction and size reduction. The power supply will be 5v/3a, enough to charge the battery pack in about 3.5 hours, so you are fully charged for the next round of loadshedding. 

I have also sourced a more effecient, smaller and cheaper inverter, capable of powering up to 20 watts. 

I'm missing a single part, a 5v relay, so I have placed an order and waiting for the part to arrive. 

With the size reduced, I will be able to mount all modules on a prototype pcb with no additional wires needed to connect the modules. 

Will update you once again in a few days. 

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  • 3 weeks later...
On 2023/05/20 at 6:37 PM, Dimi said:

Who thinks that this is a good idea? 

I have built a battery backup for my lights. It is connected to my regular light switch via an extension box. When the mains are on it charges 6 x 18650 cells, storing about 50wh of power. When the power is out it switches to battery and a mini inverter. This will power a single 5w light bulb for 10 hours, a 10w for 5 hours etc. This is at full brightness, no dimming as with the rechargeable bulbs. 

The cost for the entire system is about R600 using off the shelf parts, making it really affordable, even for multiple units around the house. 

This is a solution for those who can't afford a full on lithium battery / inverter setup but want to keep the lights on. 

Thoughts? 

Great idea from a cost saving perspective. Worth looking into.

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