How to tell if its Ac or DC... And why would I need to know?

[Floody]

Ok guys, I'm gonna now start asking questions that I think even some other forums members will want to know, but not want to ask (although they should). I really want more students signing up here to ask these sort of questions as this is a safe haven for us students here.

so ill start off with this thread and get more up as I think of them (which will be daily, and good practice for our tutors)


question: How am I able to tell apart, AC from DC? And why is it important that I know the difference between the 2?


Cheers

 

[Happy Jack]

Ok guys, I'm gonna now start asking questions that I think even some other forums members will want to know, but not want to ask (although they should).

Don't you think that is a little presumptuous? How could you reason what others will want to know, but will not want to ask?

 

[Marvo]

Hmm, I'm not sure about this testing the tutors mumble mumble.


AC and DC isn't as clear cut as it sounds, you get varying DC which is halfwave or rectified AC and you get modulated DC which complicates things as well. You'll need to make your question better defined.

If you're talking about telling the difference between a system powered by a battery or main supply you would tell the difference by either identifying the supply or by identifying the load ie read the info on the manufacturers sticker if it's a motor for example.

It's important to know the difference because you need to know what you're testing in order to prove isolation if you're working on it. You can't prove a 100v DC system is isolated using the ACscale on your tester. It would also be important to know the difference because a DC load isn't usually compatible with an AC supply and vice versa so failure to identify could result in damage to the load. Also many components such as isolator switches can be used on both AC and DC but you need to apply a derating factor to them when used on DC. Example, if an isolator can be used on 120A AC supply it might only be suitable for an 80A DC supply.

 

[Floody]

Don't you think that is a little presumptuous? How could you reason what others will want to know, but will not want to ask?

You know yourself that this forum takes an approval stage to get into. Why would students go though the trouble only to have this forum 90% dead all the time?

Im just ring to help get this forum flowing as I will be glued here for the next 3 years of my life.

 

[not_today]

there's a chap in the main forum who was asking about hooking up a generator to his house. he got shot down pretty quickly.

it would be an idea to invite him in here and answer his question as best you can. i'm very interested in how you would do such a thing also.

just a thought

sam

 

[northstar]

You know yourself that this forum takes an approval stage to get into. Why would students go though the trouble only to have this forum 90% dead all the time?

Im just ring to help get this forum flowing as I will be glued here for the next 3 years of my life.

where are you doing your course at ?

 

[Floody]

Afan College, Port Talbot.

 

[Marvo]

there's a chap in the main forum who was asking about hooking up a generator to his house. he got shot down pretty quickly.

it would be an idea to invite him in here and answer his question as best you can. i'm very interested in how you would do such a thing also.

just a thought

sam

Start a new thread Sam and ask the question about backup generators, you'll be doing trainees a favour for years to come.
Problem with them is they're a minefield with regard to earthing/isolation from main supply and they're extremely dangerous if they're not installed correctly....not just to the users of the installation but also to the DNO employees out on the streets working on their LV and MV network cabling and transformers.

Some generators simply can't ever be used as backup power because of the configuration of the windings and the chassis earthing bond. Some generators can be used as back-up power if there's alterations made to their internal wiring and some generators are specifically designed for back-up power applications and will work safely off the bat without alterations.

Earthing and N-E/chassis bonding are critical. Like I said they're a minefield and certainly not in the realms of a DIY'er to be connecting them to his house. Many of the guys who understand how dangerous they can be will get very shirty when there's someone trying to connect one up using a pair of crock clips and some old copper wire to connect it to the MET. I on the other hand have got to the point where I just cringe and avoid the thread like the plague.

 

[Happy Jack]

Im just ring to help get this forum flowing as I will be glued here for the next 3 years of my life.

No, I appreciate that and can see that is what motivated you to post. I'm glad you took my response in the right way.

I try to be proactive and relatively self-serving, and least attempt to answer whatever question I might have via the literature I own, via Google or by using the search tools via the forum. If my attempt doesn't yield the results I require, then it tends to inspire another cycle of research / Q+A's in an attempt to better acquaint myself with the subject matter, and so to inform and improve the nature of my questioning.

This is why my thread concerning AC / DC motor theory is dormant, as the subject is relatively new and question was, as Marvo rightly alludes to, poorly defined. I cannot expect a certain output without the necessary input.

Put it this way, if this particular sub-forum were my outlet for every single question I had, my presence here would be ubiquitous and, frankly, irritating.

 

[Floody]

Put it this way, if this particular sub-forum were my outlet for every single question I had, my presence here would be ubiquitous and, frankly, irritating.

Mine too, I really try and stick to posting threads that I think will be useful to us all, and not only benefit myself. Otherwise im just becoming a pain in the arse, and like you said...irritating. More students are likely to join the the thread if a question has already been asked... I think!

 

[not_today]

i really want to start learning about generators now.

 

[Floody]

I don't

 

[Baker1988]

i really want to start learning about generators now.

haha you should do mate they are rather intresting how they generate electric and that haha

 

[trev]

if this particular sub-forum were my outlet for every single question I had, my presence here would be ubiquitous and, frankly, irritating.

While the intention wasn't to make this place a substitute for the graft you need to put in, the reason a lot of people pushed long and hard for this bit to be set up was just so you could have a place where you can loiter and be a PITA. I think I can speak for all the guys who volunteered that you lads aren't an irritation, it's good to be passing on a bit of knowledge, there's no way just now that I could take on an apprentice so I'm looking at this as a bit of a payback for me for all I had given to (and slapped and punched into) me

 

[Marvo]

Yeah I agree, if you have any questions whatsoever you should be posting them even if you think it will be a pain in the --- for the mentors, it doesn't matter. The thing with basic question threads is they often get a lot more complex and contentious than you migh imagine they would and every body will learn something.