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#28785 - 08/30/03 11:33 AM OT: Light flickers when powered off a UPS?  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
Yesterday evening I replaced the two 6-volt storage batteries in a small Trip-lite UPS. The originals swelled up and got damaged after they were drained completely and then were attempted to be recharged (under load) the day power was restored.

Anyway, this morning I plug my trusty Tensor lamp with its 40 watt high intensity incandesent lamp into the device and simulate a power outage (by pulling the plug on the UPS [Linked Image] ). The thing switches to battery mode and after a second of it winking out, the light starts getting juice from the inverter.

The bulb was flickering a bit when it was running off the inverted AC. It doesn't do that on standard AC.

Is this normal? I don't have any experience with UPS devices or inverters (the ones you plug into a car battery to get 110 volts).

Thanks guys.

[This message has been edited by SvenNYC (edited 08-30-2003).]

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#28786 - 08/31/03 09:48 PM Re: OT: Light flickers when powered off a UPS?  
Big Jim  Offline
Joined: Jul 2003
Posts: 394
Denver, CO USA
I would not expect it with an incadesent lamp but possibly it is so small of a load that the UPS is not stable. Most small UPSs don't make pretty A C. They put out square wave rather than sine wave. It's usually not a problem but some devices are sensitive to it. As I'm writing this, it just occured to me that a Tensor is a transformer powered device and transformers and square wave do not work together very well. Try a pure load like a simnple 100 watt light bulb and see if there is still a problem.

#28787 - 09/01/03 12:13 PM Re: OT: Light flickers when powered off a UPS?  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
Thanks Jim.

Later yesterday I took the UPS back out and connected it to a computer and monitor. I started everything up as usual and then turned power off to the UPS.

There was no blinking, no noticeable interruption (like there was when the power to the light bulb switched from AC to battery) and most important, no flickering.

I let the thing run for a minute or so (don't want to damage the new batteries), did a little websurfing and there was no problem. Your comment about whether there was not enough load on it got me thinking that that's possibly it. [Linked Image]

My particular Tensor lamps are not transformer operated. They use these 40 watt intermediate-base (like Xmas tree bulbs) bulbs called "high intensity" on the blisterpack -- they look like a ping-pong ball and work straight off the AC line.

These lamps are probably a good 30 years old or something... judging by the shape of the molded plug -- no strain relief and flat tiny thing with no flange to keep your fingers from slipping over onto the pins when shoving it into a socket.

Haven't seen them for sale anymore though...they make good workbench lamps. Better take good care of them.

[This message has been edited by SvenNYC (edited 09-01-2003).]

#28788 - 09/02/03 02:59 AM Re: OT: Light flickers when powered off a UPS?  
Big Jim  Offline
Joined: Jul 2003
Posts: 394
Denver, CO USA
Don't think I've seen that style of Tensor. All my experience has been with the ones that have a transformer in the base and use an automotive style 12 volt bulb. I always liked them because, with the transformer in the base, they were pretty stable and good for task lighting. I discovered another use for low voltage lighting a while back. Those 12 volt halogen under-the-counter hockey pucks do wonders on 12 VDC in a motorhome. Probably do well as dome lights in the back of a service truck, too.

#28789 - 09/02/03 05:13 AM Re: OT: Light flickers when powered off a UPS?  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Big Jim I was surprised too, I went to the Tensor web site and they have expanded the product line, it took a while to find the type you and I think of.

Bob Badger
Construction & Maintenance Electrician

#28790 - 09/02/03 03:48 PM Re: OT: Light flickers when powered off a UPS?  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
Guys, you're thinking of this one - the one they call "the classic"?

[Linked Image]

It's like US$40 [Linked Image]

Yeah, I've seen these in junk stores occasionally for a few bucks but always pass up on them because there's never a bulb to test them to check out the condition of the transformer.

Mine are older, more sedate versions of this much cheaper thing also from Tensor (picture the above version with a gooseneck and a flat metal base with a slide switch):

[Linked Image]

This is the one that uses the 120 volt 40 watt appliance bulb.

The other one is probably more expensive because of the transformer lodged in the base of the lamp.

That's probably the most expensive part of the whole thing I guess. And it's "retro" [Linked Image]

#28791 - 09/02/03 04:07 PM Re: OT: Light flickers when powered off a UPS?  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
The absolute cheapest inverters put out a squarewave, but in between those and true sinewave units are a murky class which go by the name of modified sinewave or quasi-sinewave. The output of these viewed on a 'scope looks like a sinewave made up out of small steps (imagine a sinewave plotted on a very low-resolution display).

They're much better than pure squarewave, but are still rather rich in high-frequency components which can cause problems to some equipment.

The low-load problem may be cause by the inverter section of the UPS sensing an almost-no-load condition and trying to drop into standby. You might find it works if you disable this feature.

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