6 hours ago, CallumWK said:

What UPS would I need to keep ~400W active for about 30 minutes to an hour?

I get a bit contradicting results when I google for it. AI tells me I need a 1500VA 800W system, and even give suggestions about brands and model numbers.

When I next look up those particular suggestions on their website, or ask AI for it again, I get result of less than 15 minutes at best.

So anyone can tell me what I would need?

My setup is 8 cameras with night vision, 1 DVR 12V2A, a wireless alarm system, which would use about 20W when active alarm, and a 24V18A siren.

UPS are made for that time, 15 minutes ,sort of standard.

If you want to do longer, you need to put more batteries in it.

You should double SAME batteries in UPS for 30 minutes, add on.

The batteries hold the energy. Of course batteries need to be charged, so need of bigger charger or it will take more time to charge all batteries.

Then you come to a modified UPS, built to your specifications, longer time in supporting.

Or UPS with external battery feed.

Recommended UPS Size: 800 VA

This VA rating accounts for your current load plus 20% future expansion.

Real Power Capacity: 640 Watts

Based on a power factor of 0.8.

Estimated Battery Requirement: 45 Ah @ 12V

For 45 minutes runtime at 500W load (70% efficiency).

Recommended UPS Type:

Standby or Line Interactive

A calculation on this site: https://upssize.com/ups-size-calculator/

Took a time of 45 minutes and 500 W.

Are you sure your siren is 18 A ?! That is quit heavy.

43 minutes ago, xtrnuno41 said:

Are you sure your siren is 18 A ?! That is quit heavy.

Thanks for the reply and explanation.

This is my siren, I don't like half work LOL, and I'm considering putting one inside the house as well

https://shopee.co.th/product/1314687584/28706851241

Do you have some dead that require awakening with that horn?

Anyway, as others have intimated it sounds like power supply interference.

Have you tried turning the power supply down slightly from maximum?

You could try placing a 2000-3000uF electrolytic capacitor in parallel with a 0.1uF ceramic across the power supply output (talk to your local TV repair chap to get them), that should slug any remaining noise. Well, With luck anyway.

50 minutes ago, Crossy said:

Do you have some dead that require awakening with that horn?

Not really, but with a default siren not even the closest neighbour will wake up. With the horn everyone within a range of 300 meter will be awake, and also notice the floodlights on the roof that are connected to it.
I think the burglars will also take note, and not gonna take chances for somebody to show up.

54 minutes ago, Crossy said:

Have you tried turning the power supply down slightly from maximum?

You could try placing a 2000-3000uF electrolytic capacitor in parallel with a 0.1uF ceramic across the power supply output (talk to your local TV repair chap to get them), that should slug any remaining noise. Well, With luck anyway.

The power supply was set to minimum when it arrived, and had the interference. I turned it up to the maximum 12.75V in the hope that would sort it, but to no avail.

The ceramics I have tried already, first at the output, and when that didn't work near the camera, but also no change.
The electrolytic capacitor is the first I hear about. Are you sure there isn't on in the supply already?

Anyway, I have spend so much time under the hot roof that I think it will be easier to just individual adapters and a real UPS.

On that note, I use the DVE DSA-26PEA-15 FUS adapters which are excellent. I want to purchase a few spares. Good luck to find a genuine one on Shopee these days.

All those I have received were copy, and have been returned, as it is easy to compare if you have the genuine ones in hand.

Oh, and of course Shopee makes it impossible to report counterfeit these days. You can report through the app, but can not upload evidence.

If you call them they will pretend to be concerned and send you an email where you can upload evidence, It says reply to this email. Only that the email never arrives at their end.
In fact 10 seconds after you press send, you receive a reply that you only can report through the app.

Great customer protection. NOT

The supply should have a big electrolytic, but adding more never hurts (and it's possible that they used carp), do use the ceramic as well.

Without a 'scope I doubt there's really much more we can suggest.

Incorrect.

Bad technical writer.

If it's a physical fuse it can't be both 2A and 1.1A.

Solution: take out the fuse. It should say how many amps it can handle on the fuse.

2A is a lot for a digital camera. It won't pull that much current.

That's the maximum safe output < 2A.

5 minutes ago, Crossy said:

The supply should have a big electrolytic, but adding more never hurts (and it's possible that they used carp), do use the ceramic as well.

Without a 'scope I doubt there's really much more we can suggest.

Thanks for the advice, but I really have given up on it. I lose 1kg a day under that roof LOL

I have used the ceramic in the past without result. How do I check carp?

On a side note, you know where to find genuine DVE adapters? I already emailed the manufacturer in Taiwan, but no response so far.

2 minutes ago, SiSePuede419 said:

Incorrect.

Bad technical writer.

If it's a physical fuse it can't be both 2A and 1.1A.

Solution: take out the fuse. It should say how many amps it can handle on the fuse.

2A is a lot for a digital camera. It won't pull that much current.

That's the maximum safe output < 2A.

If the fuse couldn't handle it, it would blow, right?

If it gets less A than what it is specified for, it wouldn't create interference. Correct?

On 7/18/2026 at 10:03 PM, CallumWK said:

OK Guys, thanks for your advice and suggestions. I have spent another hour in the loft sweating my arse off, and the power supply will go to the rubbish dump, as that is where it belongs.

The decision to stop chasing this issue may be best for your sanity.

You have been dealing with a noise problem that really requires proper diagnosis with the right test equipment. The fact that the power supply is involved does not automatically mean the power supply itself is defective.

Using individual adapters stabilises the system, and that is useful evidence, but it does not provide a definitive diagnosis by itself.

When the noise is present it should be possible to observe it with suitable test equipment and use that information to identify the source and the path it is taking. If the source is not the power supply itself investigation can become much more complex because the cause may involve grounding common mode currents cabling video shields or even interactions between different parts of the system.

Your conclusion that the power supply is junk is understandable given the level of diagnosis available. The supply is clearly implicated because changing to individual adapters removes the problem.

PS

Take care when adding large capacitors to power supplies because you can quite easily exceed acceptable inrush currents.