Running 110v heatmat on 240v - can't get my head round the maths

[malc-c]

Hi,

I'm looking at running some heat strip in a reptile rack.

The product is not available in the UK, and whilst the manufacture and retailer can supply 240v version they only do so in 100' lengths.

Both the UK and US versions are rated at 8w per foot - I only need 20' max (maybe less) so that would be 160w total. However (and I can't remember if running things in parallel would affect it) I would be running around 8 x 2' lengths in parallel (8 x 16w).

Now to the main point of my post. I could run the US strip at 110v by using a transformer (I've seen several 240v primary to 2 x 55v ac secondary ) However I'm not sure how to ensure the VA rating of the transformer would be adequate to handle the load. This would be my ideal option, so if someone could inform me what current rating or VA rating transformer I would need that would be ideal.

The other option would be to run them at 240v, but I'm not sure if doubling the rated voltage would likely cause damage. The last thing I need is a fire, even though they will be controlled by a thermostat that I'm designing. Using online calculators, running an 8w item at 220v draws less current than at 110v. I presume that the resistance of the two products are different though ?

Looking forward to your comments and advice

Cheers

Malcolm

 

[gophert]

If 20' is what you need, cut a 10-foot section ("section A") and connect one end to 220vac cord. Then connect a short piece of wire to the other connector on "section A".

Connect the other end of short wire to a second 10-foot piece ("section B"). Then connect the second connector on Section B back to your AC cord.

Now you have two 110vac sections in series with a 220vac supply. Each section is getting half of the 220vac.

Everyone should be happy.

 

[JonSea]

Simple solution. Connect the two section in series. Each section will receive half of the 220v line voltage, therefore each will get 110v. Perfect.

Gophert beat me to it....

 

[malc-c]

Sorry each section has to be 2' as it will be independently controlled by its own thermostat. That solution is not workable.

 

[Nigel Goodwin]

Sorry each section has to be 2' as it will be independently controlled by its own thermostat. That solution is not workable.

Of course it is - if each 2 foot section needs to individually controlled simply cut the 2 foot section in to 2 x 1 foot sections and put them in series.

 

[malc-c]

Now that might work... sorry, it's early

 

[Diver300]

Using online calculators, running an 8w item at 220v draws less current than at 110v. I presume that the resistance of the two products are different though ?

A simple resistance will take about 4 times as much power at 220 V as it will at 110 V. A heating element designed for 110 V is likely to be damaged by running at 220 V because of that.

Running each part as two equal sized bits in series is fine, and is the simplest solution.

Appliances that can run at 220 V or 110 V have either complicated switching arrangements, or they have much reduced performance at low voltage. A laptop power supply has loads of clever switching devices, and runs fine at either voltage. A travel kettle runs fine at 220 V and is rather slow to boil at 110 V.

 

[Nigel Goodwin]

A travel kettle runs fine at 220 V and is rather slow to boil at 110 V.

 

[malc-c]

So basically where the strip is supplied by the foot (cut lines for guidance) and a 2 foot length would normally be wired as per A an the attached diagram when used with 110v, If I wired them as per diagram B and run them from 220v / 240c UK mains there would be no issues other than taking longer for the mat(s) to warm up to reach the set temperature of the thermostat

 

[JonSea]

No issues at all, and each section will be operating at the design power level and take exactly as long as it's supposed to to reach temperature.

Make the length of each piece as equal as possible.

 

[malc-c]

Thanks guys

 

[gophert]

If you start to smell a roast chicken odor from the reptile rack, immediately send me a PM before you look in the cages so I can delete all my posts before your discovery.

 

[audioguru]

I like to be cosy and warm. Maybe I am a reptile?

 

[gophert]

I like to be cosy and warm. Maybe I am a reptile?

Maybe Canada was the wrong place for you.

 

[audioguru]

This summer my part of Canada is very hot and humid. Global warming?

 

[ChrisP58]

So basically where the strip is supplied by the foot (cut lines for guidance) and a 2 foot length would normally be wired as per A an the attached diagram when used with 110v, If I wired them as per diagram B and run them from 220v / 240c UK mains there would be no issues other than taking longer for the mat(s) to warm up to reach the set temperature of the thermostat

If you're using it as a 2 foot section, this might be easier.

 

[Nigel Goodwin]

If you're using it as a 2 foot section, this might be easier.
View attachment 119652

Nice one!