# 400 watts @110volts = ? amps @240 Volts.

Discussion in 'Motorhome Chat' started by zaskar, Dec 10, 2008.

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Title says it all (hopefully!)

Basically, there is a HOTROD available for the Atwood/Suburban water heaters which uses 400 watts at 110Volts.
What I'd like to know is, when I'm on a 240Volt hook up, how many of my precious 10amps is that gonna use?

p.s Being sad (and bored at work!) I'd appreciate seeing the relevant formulae.
I tried Google and confused the hell out of myself!

Ta:thumb:

2. ### scotjimlandFunsterLife Member

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Hi

400 watt is the power, dived by the voltage for the amps..

ie watts = Volts x Amps

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Ah! Thanks Jim. I thought it would be more complicated than that.oh:

4. ### scotjimlandFunsterLife Member

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Hi
Don't worry, someone will be along soon to complicate it

how many motorhomers to change a light bulb ?
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5. ### American DreamRead Only Funster

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Last edited: Dec 10, 2008

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8. ### stagmanDeleted User

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You probabally will need a 240v to 110v transformer that can handle at least 6amp on the secondary side i.e the 110v side :thumb:

9. ### PeteHFunster

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Pedantry

Hi

400w @ 110v = 3.6?????? amps 400w @ 220V = 1.81???amps

400w @ 240V = 1.66??amps

A 2:1 step transformer with primary pd 240vAC will produce 120vAC (ignoring losses) Good quality transformers will have several "tappings" allowing selection of an output voltage nearest to your requirement.

The "hot-rod" will cope with just about anything from 100 to 130v.

Don`t forget to specify the Frequency rating, its not particularly critical BUT a transformer is designed for use on a certain frequency and "Off Frequency" can sometimes produce an anoying "humm" or "buzz". "overspec" can be expensive and a 5 to 6 amp rating on the secondary side, as suggested, will be more than adequate, you MAY even have one on board IF you are still using the American spec; Microwave etc? If so check its rating as it may be capable of taking the hot-rod as well?

Pete

Last edited: Dec 10, 2008