Build A Contactor/relay

[AussieGuy]

hmmm, well clamp meters generally are only sensitive to larger currents in big cables, for tiny currents such as conatactor coils you want an inline ammeter for most accurate results (think multimeter, thing is you have to break into the circuit and have it in series, with a contactor you would remove the wire to a1 and wire the meter in series) you can get clamp meters that can read low currents, but they're expensive as they have to be really sensitive

ok just found the meter you have online, the minimum range is the 400A range!! so this is no good for sub 1A readings, may have just been a dodgy readout, or if it was true then there's some kind of wiring fault, the only other reason a contactor would get hot is if the contacts are worn, then a resistance is created across the contacts, and if a current passes through a resistance then power is gievn off as heat. so this could be why it got hot and the dodgy readout was due to the meter range

I agree, it's not the most accurate item in the world for low currents - my air pumps, pedestal fans, recirc pumps etc all used 0.1A, and I doubt that they were all using the same amount of power.

It still looks brand new, there's no worn contacts from what I can see. Maybe it was just a dodgy unit.

Thanks for all the info mate.

AG.

[Guest herbhead]

been away a while ,sorry about the delay

on my own site i state that the design is adapted to supplies i could readily find ,unfortunalty there is no maplin where i stay so i had to use a store most people could find

i did not adapt it to three core because i am not an electrician like yourself and i followed skunkaroos instructions with my parts ,although my cousin is an electrician and he inspected it and said as long as all my contacts and wires were screwed in tight it would not present any problems to me

although i will present your quandry to my cousin and see if he thinks i need to adapt further still

thank you for drawing this to my attention Mr B

the d.o.c

or you c ould just get a higher rated timer on a 1000w inductive load the rating would be....7.8amps therefore i would use a immersion heater timer , most are rated at 16 amps more than sufficient for the job , but in most cases i would just double the load to get a safe inductive load the calculation, to workout your inductive load is as follows:-

on a 1000w lamp it would 1000 by voltage 230 in this case = 4.3 amps then times this by 1.8 =7.8 amps this is my full inductive load factor hope this is usefull to anyone.

[scraglor]

you need to do more than double it, most 13A timers are rated at about 2-3A inductive, and even then they still weld on, the inductive load ratings are generally for light inductive loads, whereas ballasts and inductive loads designed specifically to create high power high voltage pulses are much heavier inductive loads, an immersion heater timer will be ok as they're designed for the huge load of the heater, but even these have soft copper contacts designed for resistive loads and the contacts dont survive long under arcing, best just to get a contactor, you can pick one up for £5 on ebay

Edited March 4, 2008 by scraglor

[Guest herbhead]

yeah actually ill go with what u say,thinking about it whats the point of having the risk, ill just buy a contactor and stop bvein a tight arse not worth the repercussions hey niceone fellas keep up the good work

[scraglor]

the contacts can generally handle the high current levels from the cap though, as the contacts actually have to be closed to feel the effects of the capacitor, and the current never lasts long enough to heat the contacts to melting point. it's the arcing caused on opening that welds them on. i have never ever seen a true double break contactor stuck on from hid lighting when loaded up to it's ac3 rating.

not saying that there aren't different catergorys etc for hid lighting, just that if you buy pretty much any contactor and run it within the stated ac3 current you will highly unlikely have a problem, you have to really overload them to fuck them up

if you look at merlin gerin data sheets, they list all the different lighting types and numbers for there contactors, the rating of the contactor is UPGRADED with capacitor compensated lights, not downgraded

Edited March 23, 2008 by scraglor

[Davey Jones]

the rating of the contactor is UPGRADED with capacitor compensated lights, not downgraded

Yeah which is pretty logical seeing how the resultant of a capacitor's waveform and an inductors waveform will always have cancelled each other, hence the supply current is more resistive.

Over size a contactor and be happy.

Easy peasy

EM2

[Davey Jones]

not saying that there aren't different catergorys etc for hid lighting, just that if you buy pretty much any contactor and run it within the stated ac3 current you will highly unlikely have a problem, you have to really overload them to fuck them up

Agreed they are tested to destruction and I have seldom encountered an electrician who cares TBH, they are rated to switch many times a minute (For machinery) which growers don't do its once every 12 hours this drastically reduces the contacts workload.

[scraglor]

well we agree on some things ey

[scraglor]

i too install 100's of contactors a year, as well as having to replace them and fault find when they go wrong, yeah that tables all good and everything, i have actually seen that chart loooong before this thread. the thing is most contactors don't actually have an ac5a/b rating on them or in the data sheet (unless they're specific lighting contactors which generally cost more, same as most things with a specific use in industry) also some materials i.e. the first one in that chart have a higher rating for ac3 than they do ac5a? now what welds contacts on is heat, caused either by overcurrent or from arcing, the ac5a rating is irrelevant, it's not a correction factor, you have a whole load of different lighting configurations all with different ratings, yet all in the ac5a category, who the hell buys a contactor then searches through which material and type of discharge lighting it's for? no-one

what they do is what em2 said, just ignore the ac5a rating if it even has one, look at the ac3 rating, the difference between ac5 and ac3 is never very much and motor ratings are designed for many many more switching operations per day than what we use them for, overate your contactor a kilowatt or so and be happy

Edited March 25, 2008 by scraglor

[scraglor]

oh well, if you do as suggested and just overrate your contactor it becomes irrelevant anyway, 99% of installations wont be anywhere near the limit

[dikki]

right then

i've read through pages & pages of tech talk & tbh if i were a newbie, i wouldn't be any the wiser!

I realise that the correct industrial levels of usage would need high rated contactors, but in a small growroom environment...?

So far there's been a couple of very good DIY kits drawn up

if you can do better, let's see the designs!

call it a challenge, if you will

maybe we need more than 1 design for differing styles of growroom

after all, there's a hell of alot of difference between 1x400 & ??x600's that some peeps grow with

if the confusion continues.....

the only ones who win, are the firemen!

[scraglor]

it's simple, buy a contactor that's rated much higher than the load you plan to put on it, the cost difference will be next to nothing, a 5.5kw contactor suitable for lighting can be had for 15quid

DO NOT USE RELAYS as was first posted in this thread

Edited April 19, 2008 by scraglor

[minter]

I know this an old thread & I have read through it from beginning to end (think I was wiser before reading it to be honest) anyway, I checked on fleabay & have found 22amp contactor timers on there for less than 15 quid including postage, at this price, surely its better than trying to source the bits & then building your own? :wink:

[scraglor]

if it's for sale on ebay it is likely of very poor quality, most likely made or designed by someone totally unqualified and you could be just as at risk as if you use only your timer.

i've seen some labelled up wrong with the plug, so the load goes through the timer anyway, other where both plugs are connected to draw the full load, both making the use of the thing totally pointless, others made with relays that simply aren't anything like up to the job....... it may be cheap, but there may also be a reason for that.

on the other hand you may get a bargain, and i've had many from ebay, just make sure you check it out before you use it

[minter]

if it's for sale on ebay it is likely of very poor quality, most likely made or designed by someone totally unqualified and you could be just as at risk as if you use only your timer.

i've seen some labelled up wrong with the plug, so the load goes through the timer anyway, other where both plugs are connected to draw the full load, both making the use of the thing totally pointless, others made with relays that simply aren't anything like up to the job....... it may be cheap, but there may also be a reason for that.

on the other hand you may get a bargain, and i've had many from ebay, just make sure you check it out before you use it

Thanks for the advice scraglor, have to say tho that the unit is made by a company that specialise in grow lights an stuff & they have 100% feedback for over two years now. They state the unit is capable of handling 6 x 200w envirolite lamps or 1 x 600w HPS mechanical ballast. As I only want it for a 400w ballast I think it should be ok