Deltec PRA1000 Buzz

[elgato]

This is an older Deltec with new batteries. Everything seems to work fine.

At idle with AC power and switched on it has a buzz. The buzz is not present when running on batteries and does not appear to be caused by the charging cycle. The buzz would be acceptable in a server room or network closet but is just a bit too loud for HT.
I have read a lost of posts about people throwing a lot of parts at UPS's trying to quiet them down without much success.

Has anyone actually reduced or eliminated the buzzing in an older UPS?

Thanks

[Elysarian]

Re: Deltec PRA1000 Buzz

Best cure we found back in the days of CRT TV's for annoying bussing noises was almost always nail polish - common cause was either a choke (inductor) with loose turns or a transformer with loose laminations, a brush of nail poish on either would usually quiet them down.

The other main source of buzzing was chassis-mounted transformers vibrating the case of the item, fixable in some cases by putting rubber washers between the Tx and the case (be careful with grounding if you go this route though - you may need to install a seperate earth wire between the Tx body and the chassis to maintain bonding)

Used to get the latter a lot with stereo equipment.

The fact that your issue only appears when running on mains indicates that it's the mains input side that's the issue here rather than the invertor side.

[elgato]

Re: Deltec PRA1000 Buzz

I used a flex tube to try to isolate the sound. It was loudest near these components. The Caps and Transformers seem to be reasonably quiet.

[Khron]

Re: Deltec PRA1000 Buzz

As Adam Savage (of Mythbusters) would say, "THERE's your problem!.."

Since that FET "shouldn't" really be making any sort of sound, your prime suspect is that cylindrical inductor.

[elgato]

Re: Deltec PRA1000 Buzz

Thanks for the responses.

Should that be replaced or is it a candidate for nail polish?

It has
65100011-A
ONUBA9715
on it.

[Khron]

Re: Deltec PRA1000 Buzz

I'm not entirely sure if just smearing it in nail polish on the outside would fix much. Ideally, you'd wanna unwrap the yellow mylar tape, and dip it into transformer varnish or something similar.

Although, in a pinch (or a slightly "ghetto" version), i wonder if some suitably-sized heatshrink tubing would help...

[elgato]

Re: Deltec PRA1000 Buzz

Are these numbers significant to ordering a new one?

65100011-A
ONUBA9715

[Khron]

Re: Deltec PRA1000 Buzz

Nope, those are just some manufacturer codes

[elgato]

Re: Deltec PRA1000 Buzz

Any tips on how to find a replacement?

Thanks

[Khron]

Re: Deltec PRA1000 Buzz

Is the inverter/UPS otherwise working ok?

Is it just the buzzing that's bothering you?

And why are you insisting on replacing it, before having tried "just" quieting it?

[elgato]

Re: Deltec PRA1000 Buzz

Yes, I replaced the batteries and tested it with a dual halogen work lite for a load. It ran about 10 minutes and the battery only dropped one notch. I was going to use it for HT but at times the buzz is just too loud. It would not even be a concern in a server room or wiring closet. Sometimes the buzz is just the normal low hum. I have too much into the batteries to just replace it. Wouldn't replacing the component make as much sense as buying electronic varnish?

[Khron]

Re: Deltec PRA1000 Buzz

Well... Unless you have / can borrow an LCR-meter so you can measure the inductance value, and then unwrap it to count the turns (so you can figure out "entirely") the proper replacement for it... I'd say replacing it is the trickier choice

But hey, it's your gear, do what you want - i just thought i'd give my two cents as to what would be the easier way out of this...

EDIT: And in the previous message ("And why are you insisting on replacing it, before having tried "just" quieting it?"), by "it" i meant that noisy inductor, not the whole UPS

[elgato]

Re: Deltec PRA1000 Buzz

I do appreciate your help.

I removed it, removed the mylar tape and dipped it in "Red Insulating Varnish" for about 30 minutes. After it dried I added a couple more coats.

It helped to quiet it down some but it still seems to be the loudest component on the board. I know UPS's have a certain amount of hum and several components make what I consider normal noise. Funny, the transformers seem quiet.

Thanks again.