DIY UPS

[Joe2016]

Hi all,

I'm currently in the process of building a ups to back up a cctv system. I have been using this as a guide http://www.instructables.com/id/Super-Simple-Super-Cheap-DIY-UPSCCTV-system-fro/
I've got as far as the relay and I'm now stuck as this guide does not explain it very well (not at a dummies level any how!) This is the relay I have (please see photo attached) I would like to know how to wire this to the mains as well as the inverter, as I'm a little lost of which pins to attach the wiring to. Any tips or advice would be greatly appreciated. Thanks Joe

 

[bernardgreen]

PLease treat those "instructions" with extreme caution.

The first error they made is to suggest connecting second hand batteries in parallel. Even with new batteries parallel connection requires they all be the same type and "age" and should have a fuse in series with each battery. If a cell in a battery fails then the other batteries will discharge through that battery without any effective current limiting. This could result in that battery boiling over, boiling batteries can explode and hot sulphuric acid causes a lot of damage and injury to anyone nearby.

At that point I stopped reading......

 

[Joe2016]

Hi Bernard,

Thanks for your advice. I've slightly adapted my ups as I thought the same. I've gone with a deep cycle leisure battery instead...much safer and will last a lot longer. Do you have any advice regarding the relay? Thanks. Joe

 

[bernardgreen]

Against my better judgement this is the terminal numbering on that 3C-U relay. Ensure that the contacts are break well before make otherwise with that simple circuit when the mains restores and the relay energises there is a risk of mains being applied to the ouput of the invertor. That could destroy the invertor.

If the CCTV will work properly on the simulated sine wave from the invertor then it would be more sensible to run the CCTV from the battery and invertor at all times and use a float charger to supply the UPS with 12 volts and keep the battery charged.

 

[PBC_1966]

The first error they made is to suggest connecting second hand batteries in parallel. .

Not to mention not querying why the alarm companies from which they suggest you obtain the batteries are disposing of them so cheaply in the first place.

 

[Joe2016]

Hi Guys, Thank you for your reply and advice. Apologies for the basic questions but this is a bit like learning a foreign language to me! If I do not use the relay I would just have the inverter connected to my deep cycle leisure battery with the battery charger on constant maintenance mode, is that correct? Would the battery not eventually drain out/be ruined? Regarding the relay (if I were to do it this way) I think I'm understanding you, just to be sure I have quickly sketched out a diagram of the relay, inverter and sockets if you wouldn't mind labelling this that would be greatly appreciated, as I really don't fancy potentially blowing the place up. Also regarding the inverter would a modified 300w sine wave be ok? The total load is just under 300w. Thanks again for your advice. Joe

 

[Europlex]

The first error they made is to suggest connecting second hand batteries in parallel. .

Not to mention not querying why the alarm companies from which they suggest you obtain the batteries are disposing of them so cheaply in the first place.

Where are you getting that from then, cheaply, you have to be joking.

By the way, I'm not going to tell you what a few Cos. here sell them for, and they are not cheap

 

[PBC_1966]

As I read it, he was obtaining used batteries which the alarm companies were otherwise just going to sell off cheaply for recycling.

 

[Joe2016]

Morning guys, thanks for all your advice. I think I'm going to go scrap the mains and relay and go with the following - a inverter and deep cycle battery with a battery charger connected on maintain to keep it topped up. Regarding the inverter how do I work out what size is needed? Also would a modified sine wave do the job? Thanks, Joe

 

[bernardgreen]

Morning Joe

I'm going to go scrap the mains and relay

That is the best option to be honest.

Will the modified sine wave be OK for the CCTV ? That will depend on the CCTV and its power supply modules. Modified sine waves can have a lot of harmonics ( generated by the sharp edges of the switching that creates the modified sine wave ) and these harmonics can affect the picture quality. If the unit has a fan that runs on 230 volts direct from the input connector then expect some problems as some fans will not run properly on a modified square wave.

I would add at least 25% to the CCTV's rated power requirement and then be prepared to fit a good quality harmonic filter between invertor and CCTV if picture quality is reduced when running on the invertor

If you haven't yet purchased the CCTV then consider a system that runs directly on 12 volts

 

[SimonH2]

Not to mention not querying why the alarm companies from which they suggest you obtain the batteries are disposing of them so cheaply in the first place.

I suspect some alarm companies "just change the battery" as a routine task - after all, the customer is paying for it They can't be sold as new, and there probably isn't all that much market* for used ones other than someone knocking on your door and asking if you have any.

* For most of the larger businesses, it's not worth the man hours trying to flog them.

But back to the DIY UPS ...
If you are going to run the load permanently off the charger/UPS then you need one that's designed for the job - they basically just sit there pushing out whatever is needed to keep the output at between 13.2 and 13.8V. A normal intelligent charger will not do it - the load will confuse it and lead to it (probably) overcharging and cooking the batteries. Such PSU/chargers tend to be rather expensive - I bought one at work and IIRC there wasn't much change from £100 for something like 11A.
Many modern caravans also have them - much is run off "12V" all the time, either off the battery if mains isn't there, or off the charger/PSU if mains is available. I know it failed in Dad's caravan and he didn't want to pay for a new one !