BaFuxa
Hazard to Self
Posts: 61
Registered: 18-9-2017
Location: Mars
Member Is Offline
Mood: Buzzing
|
|
Variac Heating Up
Hi,
My variac is heating very quickly when I use it. I set it up to about 1KW and the control panels goes up to 100°C in about 5 minutes. What could be
the cause of this ?
I assumed it was a difference in current, the variac outputs 8A from 0 to 250V but the current in AC systems is " infinite" so I ruled that out.
Any idea ?
Potential counts for nothing until realized.
|
|
|
G-Coupled
Hazard to Others
Posts: 287
Registered: 9-3-2017
Member Is Offline
Mood: Slightly triturated
|
|
AC current is what now? o_0
What is the Variac rated at, and what are you powering with it?
|
|
|
BaFuxa
Hazard to Self
Posts: 61
Registered: 18-9-2017
Location: Mars
Member Is Offline
Mood: Buzzing
|
|
Ha. Yes I have read that on an electronics forum. I could not find any info as to how many amps flow from the mains.
Here the mains are 230V at 50 Hz. The variac output is 8A from 0 to 250V.
I am suspecting a resistance somewhere on the load.
Potential counts for nothing until realized.
|
|
|
RedDwarf
Hazard to Others
Posts: 166
Registered: 16-2-2019
Location: UK (North West)
Member Is Offline
Mood: Variable
|
|
I would stop using your variac or any non-standard use of mains power until you have a better understanding of what you are doing. Very little of what
you have said made any sense and you are likely to damage yourself, others or property if you continue.
Variacs control only voltage NOT current or power.
8A is the maximum current that your variac can safely handle.
The current is determined by the load (the device that you are powering).
I'm not trying to be rude, but you are high risk of serious injury or death if you continue without a better understanding of what you are doing.
|
|
|
G-Coupled
Hazard to Others
Posts: 287
Registered: 9-3-2017
Member Is Offline
Mood: Slightly triturated
|
|
RedDwarf speaks sense - I would listen.
What is the load you're running with the Variac?
|
|
|
BaFuxa
Hazard to Self
Posts: 61
Registered: 18-9-2017
Location: Mars
Member Is Offline
Mood: Buzzing
|
|
@ RedDwarf : Thanks I appreciate the concern.
Variac used
I have used this variac for over a year to power small lab furnaces and I always had this heating problem but I lowered the output to keep it to a
reasonable level.
I never had any accidents or problems with it because I am very concerned with safety. In fact I stopped immediately when I noticed the overheating.
The load is about 7 meters of 1mm thick nichrome wire. It glows yellow at around 1 Kw.
Potential counts for nothing until realized.
|
|
|
G-Coupled
Hazard to Others
Posts: 287
Registered: 9-3-2017
Member Is Offline
Mood: Slightly triturated
|
|
So, how many volts are you hitting the NiChrome wire with to get it to glow yellow?
|
|
|
B(a)P
International Hazard
Posts: 1139
Registered: 29-9-2019
Member Is Offline
Mood: Festive
|
|
What voltage do you have it set at when using the 7 m of 1 mm nichrome wire?
|
|
|
BaFuxa
Hazard to Self
Posts: 61
Registered: 18-9-2017
Location: Mars
Member Is Offline
Mood: Buzzing
|
|
125V
[Edited on 2-12-2019 by BaFuxa]
Potential counts for nothing until realized.
|
|
|
Twospoons
International Hazard
Posts: 1324
Registered: 26-7-2004
Location: Middle Earth
Member Is Offline
Mood: A trace of hope...
|
|
I would put an ammeter in line and check the current. You may be pulling more than 8A.
Given the Chinese origins, its probably only barely capable of 8A, and it will get hot. In order to get the price down it is usual to use the least
iron and copper possible, which means zero margin on the ratings.
[Edited on 2-12-2019 by Twospoons]
Helicopter: "helico" -> spiral, "pter" -> with wings
|
|
|
wg48temp9
National Hazard
Posts: 784
Registered: 30-12-2018
Location: not so United Kingdom
Member Is Offline
|
|
The VA scale on the variac indicates the maximum VA rating at that voltage. Its is not necessarily the power dissipated in the load connected to the
variac.
As has already been said the variac principaly controls the voltage to what you connect it to, not the VA/power.
A quick look at a table of resistances of nichrome wire suggests your wire is about 10ohm in which case the current would be 12.5A which would about
double the dissipation in the 8A variac and eventually over heat it.
You need to measure the current to the wire and keep it below the 8A maximum current of the variac. Yes it does look like you need to swot up on
electrical theory.
You can buy a clamp on ammeter at ebay for about £7. Be careful using it too close to the variac as the magnetic field from the variac can make the
reading very inaccurate.
[Edited on 12/2/2019 by wg48temp9]
I am wg48 but not on my usual pc hence the temp handle.
Thank goodness for Fleming and the fungi.
Old codger' lives matters, wear a mask and help save them.
Be aware of demagoguery, keep your frontal lobes fully engaged.
I don't know who invented mRNA vaccines but they should get a fancy medal and I hope they made a shed load of money from it.
|
|
|
BaFuxa
Hazard to Self
Posts: 61
Registered: 18-9-2017
Location: Mars
Member Is Offline
Mood: Buzzing
|
|
[Edited on 3-12-2019 by BaFuxa]
Potential counts for nothing until realized.
|
|
|
G-Coupled
Hazard to Others
Posts: 287
Registered: 9-3-2017
Member Is Offline
Mood: Slightly triturated
|
|
My (admittedly haphazard) calculations indicate that you'll be hitting the (optimistic) 8A rating of your Chineseum Variac when you dial it to around
75V.
It looks like you need a more powerful, higher rated Variac for the heater you're using at the moment to get the temperatures you want, and you should
also brush up on Electronics 101 - Current, voltage, resistance, Ohm's Law, what is power etc. as well IMO. It's not that hard (easier than chemistry
IME!), and it's well worth it.
|
|
|
Twospoons
International Hazard
Posts: 1324
Registered: 26-7-2004
Location: Middle Earth
Member Is Offline
Mood: A trace of hope...
|
|
Or you could use thinner nichrome in your heater. This would increase the resistance, raising the voltage and lowering the current needed to get the
same 1kW. With lower current the losses in the variac will be considerably lower.
Going from 1mm wire to 0.9mm wire will raise the resistance by ~23%, drop the current by 10%, and should drop the variac losses by about 20% (possibly
more as the wiper will be in a different position).
[Edited on 4-12-2019 by Twospoons]
Helicopter: "helico" -> spiral, "pter" -> with wings
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
