# Transformer problem



## RVMrs (Aug 24, 2013)

I have a problem I cannot figure out and I am hoping an electrical whizz can help me out. I have an RV with an onboard 110v generator and a two way 3KVA transformer. (flicked a switch for either gennie or hook up)

Recently my gennie passed away and I replaced it with a 220V version with the same power as my old one. For some reason when I run my aircon, after a while, it seems the thermal cut out kicks in and stops power coming through from the gennie. I have been told I need a more powerful transformer. What I do not understand is that the aircon used to worked fine when on hook up (220V) so why does my transformer overheat now that I have the same input of 220V from my gennie. I just want to understand what is going on before I splash out on a 4 or 5KVA one way 220 to 110 transformer. Any ideas????


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## 747 (Oct 2, 2009)

I would physically check the voltages with a test meter.

ie, the output voltage from the genny (it might be high or low). The output voltage from the transformer (to check it is operating correctly).

It could just be a dodgy thermal cutout. We have had some exceptionally hot weather lately, could that be a factor?


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## Glandwr (Jun 12, 2006)

As you double the voltage the current halves for the same number of watts (ohm's law). Here is a simple calculator that you can play about with that should tell you what size genny you need if you know the current the air con needs.

Dick


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## listerdiesel (Aug 3, 2012)

If your original genny was 110V and the new one is 220V ???

Is there some information missing?

Peter


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## rayrecrok (Nov 21, 2008)

listerdiesel said:


> If your original genny was 110V and the new one is 220V ???
> 
> Is there some information missing?
> 
> Peter


Hi.

+1 ?

Thats what jumped off the page when I read it 8O

ray.


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## Glandwr (Jun 12, 2006)

US voltage 110V a 3KV geny would provide 27plus amps of power. EU voltage 240 a 3KV genny would only provide 12plus amps.

You need to double the KV of your original genny to get the same power.

Dick


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## listerdiesel (Aug 3, 2012)

Glandwr said:


> US voltage 110V a *3KV *geny would provide 27plus amps of power. EU voltage 240 a 3KV genny would only provide 12plus amps.
> 
> You need to double the *KV* of your original genny to get the same power.
> 
> Dick


I Like these high voltage generators!

3kVA is 3kVA, whatever the output voltage.

Presumably the OP had a step-UP transformer to allow the 220V appliances to run from the 110V genny?

So the 220V genny doesn't need the transformer any more.

Need some input from the OP please.

Peter


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## Glandwr (Jun 12, 2006)

If it was a US appliance in a US RV the likely hood is that it would have been a 110v appliance wouldn't it Peter? I thought they operated on a 110 domestic system throughout N. America.

Dick


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## RVMrs (Aug 24, 2013)

Thanks for the input.
A few more details. My genny is 5.5KW a big beast. My aircon, fridge and battery charger are the only things that are 110v. Now that I have a 220 genny I only need to transform one way; 220 to 110 whereas before I needed two way; 110 genny to 220 and 220 hookup to 110 appliances. 
Mention of hot weather is a point - yes it was hot hence the need to use to the air con but I did not have the problem before in hot weather. 
Glandwr - it is my transformer that is 3KVA not my genny. 
Listerdiesel - still need the transformer to operate the 3 x 110 appliances from 22o genny or hook up.

Hope this gives you more info to help solve the problem.


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## listerdiesel (Aug 3, 2012)

OK, thanks for the clarification.

Have you looked into reconnection of the genny output to give 110V AND 220V?

Most of these 3000 and 1500rpm small alternators have twin 110V stators so you can have full power at 110V only, or a mixture of 110V and 220V by putting the two windings in series and running the 110V off the centre tap point.

It all depends on the power you need for the 110V, and what effect hanging a big low power factor transformer onto the generator.

A standard power tool transformer might be a good way forward if you need that facility.

Peter


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## Glandwr (Jun 12, 2006)

Is it a modified or pure sign wave output from the generator? A bad mismatch would lead to heat in the transformer maybe.

Dick


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## Glandwr (Jun 12, 2006)

Also is the wiring post transformer man enough. Remember it will be carrying twice the current as the input.

Dick


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## RVMrs (Aug 24, 2013)

> Most of these 3000 and 1500rpm small alternators have twin 110V stators so you can have full power at 110V only, or a mixture of 110V and 220V by putting the two windings in series and running the 110V off the centre tap point.
> 
> It all depends on the power you need for the 110V, and what effect hanging a big low power factor transformer onto the generator


.

OK - I need to look into this with some help. Too technical for me. The most powerful appliance in the RV is aircon (I think it is 20amps on 110) Did not know you could run a 220 genny at 110v. If I were able to do this would it make any difference to the problem of thermal cut out.

A power tool transformer is not ideal as it is intermittent and I need continuous.

Thanks for thinking this one through

Pauline


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## RVMrs (Aug 24, 2013)

Dick,

I have been told the wiring is man enough but if there is a way to get 110 output from the genny it could solve the problem?



> Is it a modified or pure sign wave output from the generator?


I am really not sure but you have given me another question to ask when I eventually take it somewhere to get sorted.

Thanks

Pauline


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## RVMrs (Aug 24, 2013)

By the way I live in Bedfordshire. Does anyone know of a good electrical guy that I could take the RV to who could look at all the scenarios and options you have given me and who will understand 110 and 220 compatibility?

Pauline


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## Glandwr (Jun 12, 2006)

Roadpro in Daventry has a good reputation for all things motorhome and electrical and shouldn't be too far away.

Let us know how you get on Pauline

Dick


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## 747 (Oct 2, 2009)

What might be an issue is that the US system is 60 cycles/sec and Europe is 50.


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## RVMrs (Aug 24, 2013)

Thought of Roadpro but they specialise in 12and 24v. I'll contact them anyway - they may know someone who can work around 110 & 220 problems. 

747 - I do not think the difference in hertz would throw a spanner in the works. The old 110 genny worked fine with 220 appliances including the microwave.

I'll definitely keep you guys informed of the solution (if there is one!!)

Thanks

Pauline


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## listerdiesel (Aug 3, 2012)

We are up the road from Bedford in Rushden, if you want to pop up and have a chat over it, let me know.

A 50Hz genny can normally be made to run at 60Hz by running the engine at 1800rpm instead of 1500rpm for a four-pole alternator, or 3600rpm instead of 3000rpm for a 2-pole alternator.

Transformers are more efficient at 60Hz, 60Hz gadgets generally don't like running at 50Hz, so that may well be where your problems are.

Peter


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