Transformer 240V to 110V how many watts do I need?

[EF]

Hi I'd appreciate some help.

I have a NiMh battery charger which has AC input of 100~120VAC
50~60HZ, 1.2A.

It outputs at 36VDC, 1.8A.

How many Watt transformer do I need to use this charger in the UK
where we have 240V? The output of the charger itseff is only 65W, but
the input is more, but I'm not sure how to take the phase into
account.

Cheers,
EF

 

[EF]

"Ken Taylor" <ken123@xtra.co.nz> wrote in message news:<7_D6e.17893$1S4.1789478@news.xtra.co.nz>...

"Charles Schuler" <charleschuler@comcast.net> wrote in message
news:RfydnbnW5IL7ncbfRVn-2Q@comcast.com...

"EF" <electronicfur@yahoo.co.uk> wrote in message
news:37e4eaf1.0504111419.3c1dbc1f@posting.google.com...
Hi I'd appreciate some help.

I have a NiMh battery charger which has AC input of 100~120VAC
50~60HZ, 1.2A.

It outputs at 36VDC, 1.8A.

How many Watt transformer do I need to use this charger in the UK
where we have 240V? The output of the charger itseff is only 65W, but
the input is more, but I'm not sure how to take the phase into
account.

Power = volts x amps so its about 65 watts. Given allowance for less than
100% efficiency, 100 to 150 watts would be my guess.

If the input spec's are correct then the input could be up to 144W so,
assuming inefficiencies as you suggest, I'd be looking to maybe 175-200W.
Seems ridiculous for the job but there you go.

Yeah, it seems over the top when the charger only outputs 65W.
Normally I wouldnt worry and just go for the larger transformer, but
in this instance weight is important as I need to carry the charger
and transformer daily.

Thanks,
Menno

 

[EF]

John Fields <jfields@austininstruments.com> wrote in message news:<bgam51l69n2ra64l4nm6r8fl8ilfgitikm@4ax.com>...

---
The input is 120VAC @ 1.2A, so that's 120V * 1.2A = 144VA, not 144W,
which pretty much takes the phase into account.

Assuming the transformer you get is 80% efficient anf you can get
144VA out of its secondary, you'll need at least a 180VA transformer.

Probably the closest thing to that is 200 to 250VA, something like a
Signal transformer DU-1/4. About 12 lb, about $120.

Many thanks for everyone's input.

How many watt is 144VA? I ask because some transformers here have
their rating listed in watts, not VA.

Thanks,
EF

 

[EF]

"CWatters" <colin.watters@pandoraBOX.be> wrote in message news:<UxS6e.63126$Xm2.4493350@phobos.telenet-ops.be>...

"EF" <electronicfur@yahoo.co.uk> wrote in message
news:37e4eaf1.0504111419.3c1dbc1f@posting.google.com...
Hi I'd appreciate some help.

I have a NiMh battery charger which has AC input of 100~120VAC
50~60HZ, 1.2A.

It outputs at 36VDC, 1.8A.

Can we ask what it's for?

It's to charge a 36V 8Ah battery pack for an electric motor. I'm using
the motor on a bicycle, so have to carry charger with me on the bike,
which is why I wanted to see if a 100VA transformer would be
sufficient, as they are a lot lighter. But from everyone's advice it
looks like it would have to be 200VA.

But I'll follow Jim's suggestion first and open it up to see if it is
switchable.

Thanks,
EF