Ask MetaFilter questions tagged with electrical

UPS and battery reference on the large scale

thewalrus — Thu, 17 Dec 2009 05:04:11 -0800

I would like to learn more about large-scale UPS systems, particularly the battery strings used in traditional RBOC/Telco applications. These are the sort of beasts that use huge strings of 6V 220aH deep cycle batteries, or even large numbers of 2V 400aH batteries on very strong earthquake-resistant shelving wired up to create a 48V mega-battery. Can anyone point me to the most definitive reference materials on the subject?

The 40-Year-Old Electrical Engineer

lekvar — Fri, 13 Nov 2009 12:59:52 -0800

How are things looking for Electrical Engineers? I'm considering going back to school to get a degree in Electrical Engineering and I was hoping that The Hivemind could provide some perspective.

Firstly, what is the market like for someone with a BS in Electrical Engineering? What jobs are commonly available in the US? I've done some looking around and the school's website is a little vague about the particulars.

Secondly, and probably more importantly, what kinds of hurdles will I be facing as a 40 year old with a freshly-minted degree?

How do you fix a fried laptop?

Bobby Bittman — Sun, 08 Nov 2009 09:20:31 -0800

How badly have I fried my laptop? I went to a friend's house last night to watch a perfectly legally downloaded movie, and planned to hook my laptop up to his TV with an S-Video cable. Well, something wasn't grounded - when I touched the S-Video cable to the jack on his TV, there was a spark and my laptop shut off.

Now it's a brick. No power lights, no response at all.

I'm going to find all of this out on Monday when I take it in to the repair shop, but I'm anxious: how badly have I damaged it? Is this the kind of thing that can be repaired? How much does it cost? And most importantly - is all my data recoverable?

If it matters, it's a 4-year-old Gateway laptop. All educated guesses welcome. Thank you!

Why are my headlights blinking off while driving?

COD — Fri, 16 Oct 2009 09:20:17 -0800

The headlights on my 2004 Dodge Durango randomly blink out for a few seconds while I'm driving. As you can imagine, this is a bit unnerving, not to mention dangerous, on a dark road at night. It is not consistent. It may happen a few times one night, then not again for a week. I do not have the automatic headlight feature. It does not seem to be connected to using the brakes, or turn signals, or anything like that. It's not even connected to moving as it has happened while the truck is not in motion. The 2nd generation Durango's do not have a headlight relay, which was my first thought on a part to check. The lights are apparently digitally controlled. I took it into the dealer and of course, the damn lights wouldn't act up there and the on board computer is not reporting any error codes, so the dealer didn't do anything but overcharge me for an oil change and tire rotation. I'm worried the lights will go out for good at a very inopportune time, like on one of our two trips in the next month. Has anybody had this problem, or have a guess as to where I should be looking for the cause?

Can you swap one apple power adapter attachment for another older one?

ndicecco — Wed, 14 Oct 2009 16:13:47 -0800

Is it safe to swap the power adapter attachment between an iBook G4 and an intel MacBook? Please bear with me, because I'm not sure of the proper terminology: my girlfriend has an intel-based MacBook (2 or 3 years old - from just after the switch to intel). She was unplugging her power cord and the casing came off the power adapter attachment... I'm referring specifically to the piece that can be swapped out for a longer cable (if this is still unclear, let me know).

I have a seemingly identical piece from my old iBook G4 - both say "2.5A 12.5V-" on the bottom. The piece fits perfectly, but is it safe to use? Will it void her applecare? She's going to call them tomorrow to see if they will replace the piece, but I don't see why they would. She still has the long cable, but she would prefer not to carry around the extra weight.

Where to get a list of guitar pick-up electrical characteristics?

mhjb — Wed, 07 Oct 2009 20:25:22 -0800

Where can I find a reference chart of the electrical characteristics of common electric guitar pick-ups? Guitar pick-ups have an inherent resistance, capacitance, and inductance. For simulation purposes I need a reference chart listing these values for common pick-up types. Data for individual pick-ups is fairly easy to come by, but I'm looking for a single resource with many different types.

For anyone interested, this question was inspired by the first schematic on this excellent webpage: Rangemaster.de

Unpolarized cord used in a device that expected polarized cord; is it doomed?

medpt — Wed, 30 Sep 2009 20:59:16 -0800

Unpolarized cord used in a device that expects a polarized cord. Device no longer works. Doomed? My girlfriend inadvertently plugged an unpolarized (either C7 or C8) cord into our Tivoli Model Two stereo. It worked for a day and then stopped. I love this stereo so I am pretty sad. A few questions:

What kind of damage have we likely done to the stereo? Would it make sense to try to have it repaired or should we give up and replace it?

Why won't my car start?

nadawi — Sun, 27 Sep 2009 21:39:47 -0800

Why won't my 99 chevy malibu start? open the door, the dome light comes on. put the key in the ignition and turn it past acc and all the lights die. it doesn't even attempt to crank or turn over. take the key out of the ignition all the lights come back on, dim at first and then they brighten up. with the key in or out of the ignition, pressing the brake pedal also makes the lights die (and taking my foot off the brake has them all come back dim and then brighter).

the other day i had a theft system/pass lock problem described here and leaving the car alone for 10 minutes fixed it.

today, no blinking theft light and leaving it be didn't fix it.

Wiring a dimmer for outlet use

davidriley — Wed, 16 Sep 2009 09:57:33 -0800

Basic wiring: can I put a clamp light on a dimmer? I want a cheap means of fading in and out lights for my makeshift light kit. The dimmer I bought only has one pair of wires, plus an extra red wire and a green ground. I want to send power in and out of the dimmer. Is this possible? Photos inside. http://img441.imageshack.us/img441/1069/dimmer1.jpg
http://img441.imageshack.us/img441/1016/dimmer2.jpg

Estranged pieces of metal in an Organ from the 1960s are the topic of the day

tmcw — Mon, 07 Sep 2009 11:33:36 -0800

Fixing an old transistor organ: how do I fix these switches that seem to rely on the springiness of metal in order to make contact? So, I'm working on fixing this big ol' Doric organ (previously), and I stumbled upon a big break: it appears that the voices, as well as the vibrato, may not be broken, but just the switch activating them. However, this switch seems to rely on the exact same principle as the key contacts, and that principle is failing hard fourty-something years after this thing was built.

See this picture for a quick hint.

Basically, two wires, one which is the contact and stays at a certain place, and the second which is supposed to spring onto that contact when the key is depressed. Unfortunately, the second one is no longer very springy and I believe that these contacts are a bit rusty/bad.

So, contact cleaner is obvious solution #1, but the other problem is that with a few of these buttons, the piece of metal which is supposed to move onto the other just doesn't, and I don't have much of a way of bending it, since the furthest it can travel right now is the other contact. Also, just rebending this wire is a temporary fix, I'd guess, since, after all, it'll bend back like it has over all these years, leaving the next aspiring electrician thinking that the vibrato circuit is broken.

So, please let me know your thoughts! I am not even sure what the term for this 'keying system' is called, so my google-powers are weak. And any help would be so, so appreciated!

Thanks!

Wiring up an old radiogram

carter — Fri, 14 Aug 2009 10:25:59 -0800

I found a radiogram on the street. There are two short wires out the back, both stripped about 1/4" bare, and no plug. With regard to polarity, does it matter how I attach a new lead and plug? I'm in the US and will be plugging it in to 110V. I did search through previous AskMe posts, but such is the parlous state of my electrical knowledge, I could not come to any firm conclusion.

It's probably a Magnavox Astrosonic, and it's solid state. Here's a couple of photos: 1 2

Recommend a Car Power Inverter

tocts — Thu, 13 Aug 2009 08:26:14 -0800

I'm looking for recommendations for a power inverter for use in a car on a road trip. The wife and I will be going on a lengthy road trip, and we'd like to be able to keep various gadgets powered en route. The biggest use will be for a laptop, but we may also need to charge some small electronic devices (a camera, a Nintendo DS, etc).

I'm having a real hard time weeding through all the marketing and specs for what is out there. Wattage ratings seem to vary from as low as 50 to as high as 2500, with prices similarly all over the place.

So, I'm looking for advice -- hopefully to answer the following questions:

1. What wattage do you really need for a laptop and a few small battery charging devices? How realistic are the ratings?

2. Is there a significant difference in performance in more expensive models?

3. Is overheating a concern? Are some models better at preventing this than others?

4. Any specific models that are notably good? Notably bad?

Size is a bit of an issue as well, so I'd really like to find the smallest and most reliable inverter I can to meet my needs.

How is incoming charge distributed amongst multiple batteries wired in parallel?

gribbly — Mon, 27 Jul 2009 16:03:53 -0800

Say I have a three batteries (all 12V SLA of the same Ah capacity) wired in parallel to form a bank. I connect a dumb charging source (let's say 12V, 5A). How will the incoming charge be distributed amongst the three batteries, and what does it depend on? I'm keen to understand the principlesat work here. I've built several battery banks (largest was eight deep cycle marine batts), so I've done a fair bit of just plain trying it out. I'm not trying to enhance my theoretical understanding, so I can figure out what will happen in a simple situation like:

Battery 1: 100% charged
Battery 2: 50% charged

...Battery 2 will receive more of the incoming current. But how much more? Will it receive 100% of the current, with Battery 1 receiving 0%? That's my guess - and in fact I'm guessing that Battery 1 will be charging Battery2 in this situation, and they'll end up equalizing then charging in parallel.

If I'm right about that, how do I generalize to:

B1: 100% charged
B2: 75%
B3: 50%

...I'm guessing B1 and B2 will charge B3 until B2 and B3 equalize, then B1 will charge B2and B3 until all three equalize?

What are the key factors at play here? State of charge of the batteries has to be the main one, but... well any help appreciated. I've googled for info, and read the basic battery faqs, but none have helped me understand this.

2001 Corolla, Fog Lights Always On

churl — Fri, 24 Jul 2009 21:53:36 -0800

My 2001 Toyota Corolla has spontaneously developed a problem: the front and rear fog lights never turn off, even when the key is out of the ignition. A good mechanic was recommended to me, but he won't be able to see me for several weeks. He warned me to expect to spend $200 minimum. Is there anything I can do in the meantime to try to solve this myself? This is, naturally, a totally awful time for this to happen. This all began yesterday, with no precipitating incident.

My car simultaneously began exhibiting the following symptoms, which I'd never seen before:

1) Although my car normally has daytime running lights, my headlights stopped turning on automatically, both day and night. They do turn on normally when I engage them manually. My high beams also engage and disengage normally.
2) While the car is on, while the lights are off, the high beam indicator on my dashboard is blinking constantly, at roughly one second intervals.
3) When the door is open, the car's warning sound / idiot noise is emitted constantly (as if I'd left the lights manually turned on or the key in the ignition, but neither is the case)

Google gave me this, but in my case pulling the high beam switch does not temporarily solve the problem. I don't have a security system or anything unusual installed. I've tried pulling each of the smaller fuses in each of the obvious fuseboxes under the hood, and none extinguished the lights.

When making the appointment with the mechanic, I asked if there were a way to keep this from running down my battery. He said I could disconnect the battery lead while the car was off, but warned this would "wreak havoc" with my car's onboard computer.

The guy at the shop also told me to be prepared to spend at least $200 to resolve this. What little I can glean from Google seems to imply as high as $750 for similar problems.

Is there anything I can do to mitigate the problem myself? The solution doesn't have to be elegant or flawless, just get the car back to a state where I can drive it at night and it doesn't murder my battery. Any, any insight is appreciated.

Thanks in advance

How to fix an outlet who's ground voltage is incorrect?

jmg967 — Tue, 14 Jul 2009 17:20:19 -0800

Replaced a 2-prong ungrounded electricl outlet with a 3-prong grounded one, but when testing the voltage, the hot-ground only shows 50v, while the hot-neutral shows 120v. Any advice to fix this? I am not an electician, but consulted two before doing this and after I got this problem, and they are stumped.

Basically, all the outlets in my living room are 2-pronged without a ground. Needing to plug in electrical things (TV, Computer, etc), I would like a ground, so I shut off power to the outlets at the breaker, and took them out to have a look. Behind each one there are 2 bare copper wires wrapped togethor not connected to anything, the ground wires. I hooked everything up to the new outlets, turned the power back on, and went to test the voltage of the new outlets to make sure they are working properly. When testing hot to nuetral, it reads 120V like it should. But when testing the hot to ground, it reads 50V. Does anyone know what could be causing this, and how I can fix it?

How to provide power to a dozen (or more!) home computers?

skyscraper — Sat, 11 Jul 2009 10:21:48 -0800

My sister and brother-in-law have a large (12) and growing number of desktop boxes at home. They're rightly concerned that they're putting a strain on the electrical circuits they're using. What should they be asking an electrician to do to set them up correctly? No problems with networking or internet service here, just power. It sounds from her description (note that I'm in Seattle and they're in Chicago) that the main electrical panel is relatively new and sized appropriately. The computers are in a finished basement room.

They're not sure what to ask for & would like to be somewhat informed before talking to an electrician. With this level of power demand (with some room for growth) would they be okay with new dedicated circuits run form the main panel, a new subpanel in the basement with dedicated circuits, might they need a new main panel, or what?

Cost is not a primary issue - this will be a business expense.

Secondary question: any recommendations for an electrician to handle this type of thing in suburban Chicago (Glen Ellyn)?

Tertiary question: They're using their computers for raw computational power, nothing internet-related. If I was hip & in the know, what would I call the individual computer? I suspect "server box" is not appropriate.

Light switch making popping noise.

feathermeat — Wed, 01 Jul 2009 06:33:45 -0800

Calling all MeFi electricians: why does my light switch make a popping noise, and will it kill me? I have a light switch in my kitchen that intermittently makes a small popping noise when turned on or off. Usually it'll happen a few times in a row, and then not happen again for several weeks. I have not experienced any flickering/dimming of the light in questions and I have not seen any sparks. There have been a few times when it's happened and I have smelled a little bit of ozone (at least I think it's ozone). I have tried to google this, and it seems like the answers range from "this is going to start a fire, call an electrician immediately" to "the switch is going to stop working eventually, but it's not a safety hazard, so replace it whenever." I don't mind replacing the switch if that is what's needed, but money is tight enough so that I really, REALLY don't want to call an electrician if this is not a big deal.

Where to buy travel adapters in NYC

cookie googleman — Thu, 25 Jun 2009 07:56:18 -0800

Where to find a three-pronged British style electrical adapter plug in New York City? Hello,

I'm leaving for Tanzania tomorrow and am looking for a travel store that sells adapters in New York City. It's too late to order online. Thank you in advance!

An oven element's silent protest...?

Decimask — Sun, 31 May 2009 08:23:56 -0800

My electric oven's bottom element looks fine, but... ...it won't heat up. The broiler works just fine. My first job was in the hardware section of a store we lovingly refer to up here as Crappy Tire, so I've seen a few fried elements, and they tend to fail pretty catastrophically. But this is weird: not only is the oven's element immaculate, the backing plate it is still shiny and clean.

Note:

I've tried switching the 30amp fuses for the elements, and it made no difference

There's no evidence under the wiring plate on the back of anything smoking, shorting, etc.

Has anyone ever had an element fail without any sign like this?

Click on, Click off!

frwagon — Thu, 28 May 2009 07:39:12 -0800

Most lamp switches require two clicks to turn on or off... why do they need 4 positions for only two states (on and off)? Every lamp switch (of the turning variety) that I've run into, you have to twist it two clicks to turn it on, and two clicks to turn it off... is there a design reason for this, is it electrically necessary?

I'm in the dark, Charlie. Again.

GuffProof — Sat, 23 May 2009 11:06:55 -0800

Light bulbs with short life spans + older house = scary wiring problem? For years I've rented a small, old house. There are two rooms (bathroom and kitchen) with ceiling light fixtures. Very basic set up- two light bulbs screw into exposed sockets under a glass cover.

These lights are ALWAYS burning out. Maybe one bulb a month.

Other than being a huge annoyance (high ceilings, shaky step ladder, fear of falling and breaking my neck), every time another bulb goes POP, I wonder if there could be a scary wiring problem.

This doesn't happen with lamps that are plugged in. No problems with other appliances. Fuse has only blown once, years ago, while vacuuming when I had the AC unit running.

I'm using name-brand light bulbs. 60w or 75w max. As I mentioned, each light fixture has 2 bulbs- but they don't both go POP simultaneously, which eases my worry a little bit.

I should probably ask the landlord to inspect, but I hate to deal with him for any reason. He's a slightly creepy guy with absolutely NO home maintenance skills. Everything he's tried to fix around here has been a disaster. Also, he's very cheap and wouldn't spring for a qualified professional to do it. If anything, he'd poke around and make a mess and pronounce it 'fine'.

To prevent a fire, and the loss of everything I own, I'd happily pay a professional to inspect it myself. But I don't know if it's really necessary?

For those with electrical smarts: are short-lived light bulbs a sign of trouble?

Do I need a new roof?

amanda — Tue, 28 Apr 2009 13:51:44 -0800

In my second year of first-time home ownership and husband and I are thinking we need to do a little spring cleaning around the house. Other than a minor plumbing issue in the bathroom we have had (knock on wood) zero problems with the house. In an effort to keep up this track record, what trouble spots should we look for in the house? How do you know if the roof is in good shape? What are typical home maintenance needs? A little info.... Our house is a single-story 1950s cottage. The sewer line is only about 15 years old and was clean as a whistle when we scoped it two years ago. The roof looks pretty good from the ground but I don't really know what I'm looking at. We have a crawl space that is partially excavated to house the furnace and hot water heater. We have what we think is asbestos shingle siding. It has wood flooring throughout and still feels nicely solid. It's a pretty un-creaky house.

As we walk around, what should we look for? What are telltale signs that something must be done? I'm fairly handy so any advice on what can be done yourself verses calling the pros is welcome.

How do I convert impedance to this weird phasor-form?

DMan — Mon, 13 Apr 2009 15:16:30 -0800

ElectricalEngineeringFilter: How do I add electrical impedances together, and convert the result to what looks to be a phasor? So I'm in an electric circuits class, we have a test in three days and one simple concept is really confusing me.

I understand that electrical impedance (Z) can be in a complex format, like, for example, 90+j120. But then the book somehow converts that into what looks like a phasor. So 90+j120 turns into 150 /_ 53.13.

(If MeFi formatting messes up the above example, that's 90 + j120 turns into 150, angle sign, 53.13)

I have no idea where the 150 and 53.13 came from, nor do I understand how to calculate those values. I can't find a clear explanation of it in the book anywhere. Can anyone help me?

Too good a discount?

XMLicious — Mon, 16 Mar 2009 21:06:06 -0800

Construction electrical: why is this service panel on sale at more than an 80% discount? Elsewhere it indicates the original price to be around US$1500 but the current price is almost down to $200. There are several other panel boards marked as "clearance" on the Grainger Industrial web site that have similar massive discounts to their prices, yet there are also many non-sale ones that are near the original price - the original price being what several books have lead me to expect as standard pricing.

I'm not considering buying it, I simply came across this in the course of research while fantasizing about building a dream house. I'm curious as to whether this is really a clearance sale of the sort a retail outfit might have or if there's a more sinister caveat emptor reason for the price, like if the panel is useless in most jurisdictions now due to a recent code change or something.

My car's headlights have a problem!

longsleeves — Fri, 06 Feb 2009 15:12:27 -0800

What is going on with the headlights in my Dodge Neon? My 2003 Dodge Neon has a little problem. As of this evening, the headlights only work on the high beam setting. Low beams: both dark. High beams: both fine. A person who answered the phone at the dealer's service department said that 90% of the time when this happens it is a result of both of the low beam bulbs burning out at the same time. That seems weird. Could there be another explanation?