Electric oil filled radiator

[blackrose]

I just bought an oil filled mains electric 2.5kw radiator. (£44 from B&Q)

 

I calculate this will draw 10.4 amps at full load (is this correct?)

 

I am also running a 30amp and a 20amp battery charger plus a TV/freeview box, and 3 x 60watt lamps.

 

I thought this would put me over the 16amp supply limit but nothing has tripped?

 

 

Also a separate question: The heater instructions advise not to use it with an extension lead, but if necessary then the lead must have cables of 1.5mm dia and minimum of 15amp rated.

 

Do they mean 1.5mm2 and how do I find the rating of the extension lead as it's not embossed on the outer cable?

Edited December 21, 2006 by blackrose

[chris w]

Worse case you will be drawing:

 

1. 10.4 amps from the radiator

2. 50 amps @ 12v @ say 90% efficiency from the chargers = 3 amps @ 240v

3. Tv/Freeview say 80W total = 0.3 amps

4. 3 x 60W lamps = 180W = 0.75 amps @240v

 

So total current drawn = 14.5 amps, hence no trip.

 

Also the chargers won't be pumping in their full amperage most of the time (in fact rarely) so you have some headroom.

 

Chris

 

PS: re cable: YES they mean 1.5mm^2 cross-sectional area - that's about 15-16 amps rating @ 240v

 

If you have a vernier or micrometer measure the diameter of one strand of the multi-strand cable, calculate its area (pi.r^2) and multiply by the number of strands to get the overall area. Otherwise try to measure the overall diameter of the copper cable, square the result and divide this by 1.3 to get the area.

Edited December 21, 2006 by chris w

[blackrose]

PS: re cable: YES they mean 1.5mm^2 cross-sectional area - that's about 15-16 amps rating @ 240v

 

Thanks, the cross sectional area of the extension lead is labelled and now you've told me that's at least 15 amps I should be fine.

 

Quite honestly I don't know why they recommend this cross section cable - the supplied 2m length mains lead is only 3 x 1.0mm2 cross section!

Edited December 21, 2006 by blackrose

[ChrisPy]

Do they mean 1.5mm2

don't you just love these technical inaccuracies that always creep in when the copywriter and the checker take over from engineers who are obviously all illiterate? tonight on TV there was an item about battery capacity - 85 amps an hour !

[Guest]

i have seen those coiled up extension leads melt to a big blob when used at approaching full load. It is important to roll the cable out as it will stay cooler. The old boys in my game used to say it was due to induction, but I do not believe that theory.

[chris w]

Catweasel

 

Yep - a coiled mains lead becomes an inductor

 

Chris

[Keeping Up]

No, it just gets hot because it's coiled into a small space

 

Allan

[Gibbo]

Catweasel

 

Yep - a coiled mains lead becomes an inductor

 

Chris

 

It does indeed. But that's not what causes the heating (well it contributes a few percent in reality).

 

The overheating extension lead is mainly because the cable current rating is specified in free air. Without the free air it cannot cool anywhere near as efficiently. And why waste 2 pence in manufacturing costs to use the correctly sized cable? Or at least rate it correctly?

 

Gibbo

[Gibbo]

don't you just love these technical inaccuracies that always creep in when the copywriter and the checker take over from engineers who are obviously all illiterate? tonight on TV there was an item about battery capacity - 85 amps an hour !

 

85 amps an hour?

 

I can't even get my head round that. It's as nonsensical to me as 17 eggs per foot. But then again I'm an engineer so I must be illegitimate, or something.

 

Gibbo

[DHutch]

The overheating extension lead is mainly because the cable current rating is specified in free air. Without the free air it cannot cool anywhere near as efficiently. And why waste 2 pence in manufacturing costs to use the correctly sized cable? Or at least rate it correctly?

To be fair, all the ones i have seen say on them somthing like "Coiled: 4amps max Fully Extended:13amps"

 

Also, rightly or wrongly, at the union whenever we have to coil up some excess cable, we coil it in a figure of eight.

 

 

 

Daniel

[blackrose]

Since the supplied 2m mains lead is only 1.0mm2 (x 3) cross section why do they insist on me using a 1.5mm2 (x 3) extension lead?

 

Is this in case you left it coiled up? Just checking as my lead is 1.25mm2 (x 3) and I don't want it to turn into melted blob.

[Gibbo]

To be fair, all the ones i have seen say on them somthing like "Coiled: 4amps max Fully Extended:13amps"

 

You must buy them from proper places. Mine say something like L*dl and "millions of amps"

 

Also, rightly or wrongly, at the union whenever we have to coil up some excess cable, we coil it in a figure of eight.

Daniel

 

That's an extension of the the wives' tale about inductive heating. Though it would help reduce interference to sound equipment. Which is probably more important for students

 

Gibbo

[DHutch]

You must buy them from proper places. Mine say something like L*dl and "millions of amps"

Haha! No, i dont actaully own any, all our extensions are just a lenght of flex with plug/socket, i was just going on what ive seen around.

 

That's an extension of the the wives' tale about inductive heating. Though it would help reduce interference to sound equipment. Which is probably more important for students

Yeah, i thought as much.

- Powercables are rairly near any sound equip. And although i guess theriticaly you might get some inteference onto the DMX cabling, i doubt thats any more relivent.

 

 

Daniel

[greyowl]

Since the supplied 2m mains lead is only 1.0mm2 (x 3) cross section why do they insist on me using a 1.5mm2 (x 3) extension lead?

 

Is this in case you left it coiled up? Just checking as my lead is 1.25mm2 (x 3) and I don't want it to turn into melted blob.

 

Blackrose,

Usually, although not always, heaters and such like come with a heat resistant mains lead, although it may look like standard flex it can take the added induced heat.

[Gibbo]

Blackrose,

Usually, although not always, heaters and such like come with a heat resistant mains lead, although it may look like standard flex it can take the added induced heat.

 

That's a bloody good point. I'd never even thought of that.

 

Gibbo

[greyowl]

Gibbo,

Most people don`t even think of that, unless they`re looking at an iron with a braided flex.

 

As for coiled extension leads !!!!! as an electrician i despair at them

[Guest]

It does indeed. But that's not what causes the heating (well it contributes a few percent in reality).

 

The overheating extension lead is mainly because the cable current rating is specified in free air. Without the free air it cannot cool anywhere near as efficiently. And why waste 2 pence in manufacturing costs to use the correctly sized cable? Or at least rate it correctly?

 

Gibbo

Glad someone agrees with me. The inductive effect must be minimal because we have a phase and netral cable to balance each other. This is a similar senario to the dangerous practice of putting just a phase conductor down a metal conduit/trunking without the corresponding neutral (or of couse the other phases for a TP/TP&N supply).

[Theo]

85 amps an hour?

 

I can't even get my head round that. It's as nonsensical to me as 17 eggs per foot. But then again I'm an engineer so I must be illegitimate, or something.

 

Gibbo

 

 

It is perfectly sensible if you want to talk about the rate of change of current! I bet the maximum rate of change of current in an AC electric fire is quite big!

 

Nick

 

It is perfectly sensible if you want to talk about the rate of change of current! I bet the maximum rate of change of current in an AC electric fire is quite big!

 

Nick

 

Just a bit of nostalgia. A few years ago there was someone regulalry advertising solar panels and the associated gear in the WW. The advertisements were such a load of electrical nonsense that I felt I could use them in my Physics A level classes for the kiddywinks to rewrite. I decided not to because I couldn't word out what they were trying to say! They used the term A/hr IIRC.

 

Nick

[carlt]

Of course you could just do away with the heater, plug your big, wound up extension lead into something doing something useful and warm the boat from the heat given off by the coil.

[Theo]

I just bought an oil filled mains electric 2.5kw radiator. (£44 from B&Q)

 

I calculate this will draw 10.4 amps at full load (is this correct?)

 

I am also running a 30amp and a 20amp battery charger plus a TV/freeview box, and 3 x 60watt lamps.

 

I thought this would put me over the 16amp supply limit but nothing has tripped?

Also a separate question: The heater instructions advise not to use it with an extension lead, but if necessary then the lead must have cables of 1.5mm dia and minimum of 15amp rated.

 

Do they mean 1.5mm2 and how do I find the rating of the extension lead as it's not embossed on the outer cable?

 

I fear that the calculation is amiss.

 

Power = volts x amps

Amps = power/volts

In your case 2.5kW = 2500W

 

Amps = 2500/12 = rather more than 200A

 

Nick

[chris w]

I fear that the calculation is amiss.

 

Power = volts x amps

Amps = power/volts

In your case 2.5kW = 2500W

 

Amps = 2500/12 = rather more than 200A

 

Nick

Nick

 

It's a 240V heater that Blackrose is using from an inverter hence 2500/240 = 10.4 amps

 

Chris

[Theo]

Nick

 

It's a 240V heater that Blackrose is using from an inverter hence 2500/240 = 10.4 amps

 

Chris

 

 

I assumed that he was intending to run it from his batteries via an inverter! This cannot be the case! He must be running it from his shore line or 230V generator. Duh!

 

N

[DHutch]

Of course you could just do away with the heater, plug your big, wound up extension lead into something doing something useful and warm the boat from the heat given off by the coil.

Well, just wire it back into the mains really...

- Somone calulate the resistance of 40meters of 1.5mm of extension lead, couple of kilowatts? Lovly jubbly!!! (please dont try this at home...)

 

I assumed that he was intending to run it from his batteries via an inverter!...

Well ofcause he still could be...

- In which case the heater would still be drawing 10.4amps (from the inveter)

- But the inverter would be then be drawing about 200amps from the batterys, plus efficiency losses.

 

 

 

Daniel

[blackrose]

Well, just wire it back into the mains really...

- Somone calulate the resistance of 40meters of 1.5mm of extension lead, couple of kilowatts? Lovly jubbly!!! (please dont try this at home...)

Well ofcause he still could be...

- In which case the heater would still be drawing 10.4amps (from the inveter)

- But the inverter would be then be drawing about 200amps from the batterys, plus efficiency losses.

Daniel

 

No I would never dream of running this heater from my inverter. According to Daniels figures, at full heater power my batteries (405 A/h) would last less than an hour before they were damaged.

 

I bought a load of electricity cards just before BW doubled the prices, so when it's not too cold outside I can heat the boat much more cheaply than burning coal.

Edited January 8, 2007 by blackrose

[chris w]

No I would never dream of running this heater from my inverter. According to Daniels figures, at full heater power my batteries (405 A/h) would last less than an hour before they were damaged.

About 27 minutes to half charge (ie: the point below which the batteries shouldn't fall).

 

Chris