Voltage levels, how low is dangerous for electronics?


Old 06-07-05, 08:11 PM
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Voltage levels, how low is dangerous for electronics?

Well today two air conditioners (in window units) were put in my house. I have my computer on a UPS (uninterruptible power supply) which monitors voltages and I also have all my home theater equipment (except my subwoofer) plugged into a component style Panamax surge protector which has a voltage meter. I frequently check out my voltages, usually though the UPS since it seems to be more accurate and before today I was seeing around 119-120 on off hours when there were little appliances running in the house, and usually around 116-118 on average when some other appliances were running, esp. big ones like the washer/dyer. The lowest I ever saw it drop before today was about 115 and that was very rare, now today with the air conditioners running I did except a voltage drop, but it is a little worse than I thought it would be. My new average voltage is around 115, and when someone ran the washer a little while ago I was seeing it drop as low as 110-112 volts.

Now the good news is both my UPS and Panamax surge protector have under/over voltage protection, for the UPS if the voltage drops below 95 it switches to battery backup, although I think it switches at more around 105 because I have heard it (it clicks when it goes to battery) kick in a quite a bit today, usually when the air conditioners motor kicks in. My Panamax on the other hand just cuts the power to all plugged in components if the voltage drops below 95, I have not seen it do this today. So my important equipment (except my subwoofer) is protected from severe drops but I am wondering if this constant 110-115 volts they are getting is bad for them. I would assume and have heard that power supply manufactures take into account voltages fluctuations such as these and build their units to withstand it. That plus the fact that this is the first summer my equipment will be on the UPS/Panamax, last summer the same ac's were running and my computer was not on a UPS and a year later is still doing fine. And likewise for my HT gear, for the past three summers it has just been plugged into a strip surge protector and everything still works fine. Still I have some money in my computer/HT and still I worry. Just looking for some advice here, I cant really correct the problem, but I would like to know just how bad voltages in the 110-115 range are, they are not always that low though, as I type this I am at 117, but no other major appliances (besides the acís) are running. Sorry for the longwinded post, thanks.
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Old 06-07-05, 09:43 PM
Join Date: Nov 2004
Location: CA
Posts: 2,041
Any voltage between 110 and 120 is condidered " normal ". Today, most utility companies deliver 120, but in the past 115 of even 110 was not unusual. Any equipment should be rated to run on any voltage in that range. When you see a drop as the A/C kicks on, your entire service could be a little marginal size-wise, or you have too many loads on one circuit.

Now, a large motor such as in an A/C draws huge momentary starting surge current. This can probably cause a trip on your UPS.

Realize that surge protectors are to protect against HIGH voltage spikes ( in the thousands of volts) caused primarily by lightning, or sometimes switching transients on the street. They have absolutely no impact on any type of low voltage situation.

If you and all your neighbors crank up all those sub-woofers all at once, the utility company may experience brown-out, which is caused by overloaded
lines and gererators. The UPS should protect the computer, but the woofer will just have to sweat it out.

You mentioned 2 air conditioners. If they are on the same circuit, that circuit is probably overloaded.
Old 06-08-05, 09:32 AM
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Join Date: Feb 2005
Location: Near Lansing, Michigan
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110 to 127 volts is considered "normal" based on your area and distance from the utility transformer.

However, the voltage probably drops significantly lower than the 115 you're measuring when the compressor motor first kicks on. This is what causes your UPS to trip. The UPS will protect the computer equipment from damage due to the voltage drops, but UPS units are not designed to trip 100 times a day. You will shorten the life and protection of your UPS if you keep this up.

Moreover, there are complex issues of "dirty power" other than voltage. Motors introduce noise and current leakage where "regular" loads don't. I would highly recommend you put in a new circuit for either the AC units or for the computer, or both if you're feeling ambitious.
Old 06-11-05, 11:35 AM
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Thanks for the replies, good to know that 110 is considered normal. But the problem is actually worse than I thought. This weekend must have been the one that everyone in my area decided to install their ACís. Right now the only high draw device on in the house is my brotherís air conditioner, and I am seeing voltages in the 110-112 range. If I turn my AC on (which is on the same circuit as my brothers BTW), the AVR on my UPS kicks in but now it stays on. The weird thing is that when it is on it is saying the input voltage is 110, I thought it did not kick in until much lower than that. So right now I have my AC off and I guess I am just going to put my computer back on a strip surge protector for the summer and forget about it, which sucks because I love the protection my UPS provides, but I cant have my computer running off AVR all the time and there is nothing else I can do about it, its my parents house and they will not get another circuit installed for my AC. Besides even if they did I doubt it would correct the low voltages, because if I am seeing 112 with just my brothers AC on right now, I cant wait to see what it drops to when someone runs the Stove, Washer and my parents put in a third AC, which will be on a separate circuit, but still. It will probably return to somewhat normal during the weekdays when everyone is at work and most donít leave the AC running all day to conserve power, but the weekends are bad. Why did I have to get this damned UPS, I went along the last two summers with the same AC setup in the house (three total, two on the same circuit as my computer) not knowing/caring about voltage levels and my computer did just fine.

EDIT: I forgot to add that when the UPSís AVR does kick in and stay on, it increases the voltage to around 130 volts, because what it does it take whatever the input voltage is and increases it by 20%, this would be perfect if the voltage was around 100, 130 seems a bit high though, but I suppose it is better getting a steady 130 than 110 with drops. Also I just turned my AC on and AVR does shut off after around five minutes. I honestly might just say screw it and continue to us the UPS, I mean it was $50 (I got a great deal on it), if I need to replace it at the end of the summer o well, I would much rather replace that then my hard drive. I bought the thing to protect my computer and AVR was one of the main reasons I bought it, up until now it rarely ever used it, now it is putting it to use.

Last edited by Smithdogg1; 06-11-05 at 12:44 PM.
Old 06-11-05, 12:54 PM
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I thought I would post up a picture of my voltage levels. In this pic the red line is the input voltage and the blue line is the output voltage, so you can see that here it was on AVR, then went off, then back on again then off again. Thinking about it, I donít know what is worse, my computer getting a low voltage, or it being at a low voltage and then ramping up to 130 and back down when AVR goes on and off. What do you think? Or am I just thinking too much about this and varying voltages are not that big of a deal?


EDIT: The third AC went in; it is on a 20 amp circuit with pretty much nothing else on it. My AVR is now always on ha-ha, with my input voltage at about 107-109, and output at around 128-131. I really donít think it is bad for the UPS, all it is doing is providing a bit of battery power in addition to the incoming AC power, and it has been running on AVR for a long time now at the battery level is still at 94%. Now I am just wondering what the less of two evils is, under voltage or over voltage? In other words whatís worse, to be running at 108 (with drops to the 90's) or 130 all day? I am thinking that 130 is better because it is constant and when the ACís motor kicks in (which rarely happens now because it is so hot out), it does not have to deal with the very low drop. I am hoping that during the nights and weekdays things will be normal again and my UPS wont have to run AVR constantly.

Last edited by Smithdogg1; 06-11-05 at 01:52 PM.

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