Discharging Capacitors

Carlow52

Neighbor has a 4 lamp bathroom heating unit which has stopped working.
On the cover it states that the capacitors need to be discharged before opening.

Any thoughts on how this might be achieved?
Thanks

fishdog

Im not sure to be honest. Is there any other information given? I am wondering why there would be capacitors in it in the first place. I would have thought it was only a resistive load. It sounds a bit starnge to me!

I would guess:

1) Disconnect the unit.

2) See if a voltage is present between the neutral and live supplying the unit. If so this may be due to a charged capacitor(s).

3) If there is a voltage present, use a large resistor to short live to neutral. A dead short may damage the capacitor.

Carlow52

Thanks FD
this is the unit
http://www.prismatics.ie/catalog//index.php?page=easyductsensationss

how big a resistor have you in mind?
Thanks

ps on reflection, the website says it comes with a plug already fitted which would seem to imply that there should be no residual voltage across the pins of the plug: the capacitors could still be charged.

fishdog

Thanks FD

To be honest I dont think my earlier advice was much good!

But this might be:

I dont think that you should install that unit in a bathroom. What you seem to have there are 4 exposed lamps at 230 volts. This fitting has no IP rating (is not sealed) from what I can see. It may not be safe anywhere near a bath or shower. I would be almost certain that it is against current ETCI regulations.

It is made in Australia where electrical regulations are quite different.


Back to your question:
I think most electricians like me have experience with working on live equipment. They would simply open the appliance and work on it carefully even if they knowing that the capacitors may be fully charged. If you are not 100% sure about what you are doing do not attempt this!

mark_d_spark

Carlow52 wrote: »

ps on reflection, the website says it comes with a plug already fitted which would seem to imply that there should be no residual voltage across the pins of the plug: the capacitors could still be charged.

If u havent plugged the unit in yet, there shouldnt be any charge on the capacitor. If u have already plugged it in there will be around 325volts of a charge. Just get a bit of cable and short out each leg of the capacitor (if u cant get at d capacitor just short out the live and neutral pin on d plug

fishdog

If u havent plugged the unit in yet, there shouldnt be any charge on the capacitor

Unless someone else plugged it in, such as in the factory or shop. The chances are this would have dissapated by the time the OP recieved it.

If u have already plugged it in there will be around 325volts

Mains voltage here is 230 volts rms.
Peak voltage is therfore 230/0.707 = 325.31

This is where you are getting 325 from I guess. This would be the maximum voltage across the capacitor possible.

Just get a bit of cable and short out each leg of the capacitor

This may cause a large current to flow that might damage the capacitor. That is why I was suggesting using a resistor. The problem is how to discharge them before opening.

if u cant get at d capacitor just short out the live and neutral pin on d plug

This is what I suggested, but then thought that the chances are they are not connected directly across the plug for safety reasons.

I think the more inportant thing to note is that the chances are it is against regulations to install such a unit in a bathroom for safety reasons.

RoundyMooney

I would agree, fishdog.

In relation to discharge on an appliance such as this (where any caps, if present, are so small as to present zero risk anyway), just shorting the phase and neutral are best.

However! This creates more hazards than it solves, as the well meaning DIYer may inadvertently try same with the yoke still hooked up and hanging out of the ceiling, thus inviting a nasty burn or a rattle depending on how they went about it. On larger apparatus, this cannot be attempted either, due to the possibility of surge damage when discharging larger capacities.

At the end of the day however, it's not an industrial PFC bank we're talking about here, it's some form of an IR lamp assembly with fan (which may/will have capacitive start, too small to be of concern).

It may have a shiny remote, and possibly be sold by some bloke in a shiny suit, but I would be more concerned about the exposed lamps, if/how they comply with irish regs, and if the company selling them is aware of the requirement, if applicable, and from a quality point of view the venting arrangement.

RoundyMooney

By the way, have you guys seen the price of this bad boy?

Board Walker

the good oul days in FAS charging up capacitors with the mehgger and fireing them across the room to an unsuspecting fellow student lol

Stoner

As part of safety standards capacitors need to discharge to a safe level before someone can work on the product.

In most cases this happens fairly quickly, however sometimes a cap may not have discharged quickly enough before someone has the cover off the case and are working on the device.

The health and safety way out of this at that time was to put a sticker on the product warning people to wait for a time before working on the unit after it has be powered off.

I remember measuring the charge and timing the opening of one particular programmable power supply, it was just outside the standard so a sticker stating to wait for 30 seconds before taking the unit apart had to be placed on the box before it could be sold into Canada.

the solution for many of these warnings is to wait for a bit, very important for people who like to run faulty units with the covers off when they are trying to fix them.

10-10-20

Or MAYBE, you just need to leave the unit in the on position when you pull the fuse.
That could deplete the capacitor.

But we're just guessing here, so best run it past the vendor/manufacturer for further advice!

fishdog

By the way, have you guys seen the price of this bad boy?

€435 :eek::eek:

It may have a shiny remote, and possibly be sold by some bloke in a shiny suit, but I would be more concerned about the exposed lamps, if/how they comply with irish regs, and if the company selling them is aware of the requirement, if applicable, and from a quality point of view the venting arrangement.

+1

My view is that technically there is nothing wrong with selling these items. This is because because these units would comply with the ETCI wiring regulations if installed in a suitable location, i.e. not in a bathroom. If this unit is not installed in a suitable location the electrician will ultimately be held responsible.

The criticism I would have is that the advertisement seems misleading in that it shows the appliance installed in a bathroom and it is clearly aimed at the Irish market.

Quote from website: "....... allows wireless operation of all functions from within the bathroom"

I am open to correction this, but it does not look like it would pass an ECSSA/RECI inspection if installed in a bathroom.

It does look nice and warm though:)