Instructables

Reducing 110v transformer output?

Hi all, as stated in the title I need to reduce the output of a 110VAC transformer. I'm using a US graco spray gun that is 60hz, and I understand that if I reduce the voltage to 90 this will compensate for the UK 50hz system.

Any help is greatly appreciated

verence6 months ago
A transformer can only ever transform voltages. It will not affect the frequency in any way.

What is your real problem? What is the spray gun rate for (voltage, frequency, power consumption)? Where do you live (i.e. how does your mains system work, again: voltage, frequency)?

Can you send a link to a description of said spray gun?  For most uses, it is important to match the voltage, while the frequency is not that important (if at all). For other applications (e.g. alarm clocks) the frequency is important.

For a good answer, we need more information.
dimmaz88 (author)  verence6 months ago
l'm in the UK where it's 50hz. I've found it hard to find an answer really. I read somewhere that if I reduce the voltage I won't damage the motor, I've no idea. Here's a link to the sprayer


http://www.graco.com/us/en/products/contractor/truecoat-pro-ii-electric-sprayer.htm

verence dimmaz886 months ago
Hard to say if the decreased frequency will affect the function. Lowering the voltage will not compensate for the difference in frequency.

Your best option will be to contact the manufacturer and ask them.

Or, you can just try it. The sprayer has an overheat protection.

> I have a 110v transformer
Is it rated for at least 5000W (6000W would be better)?
According to the data sheet, the sprayer uses 120V @ 4A.
The two converters mpilchfamily linked to are only rated 200W!
dimmaz88 (author)  verence6 months ago
Thanks for your detailed response. The transformer I have is rated at 3kW so is more than adequate. I contacted graco directly but they were no help, I just don't think they wanted to tell me it would be fine, just in case it's not.

Thanks
verence dimmaz886 months ago
Yep, 3kW should do fine. The numbers in my last post were too high by factor 10. It should have been "at least 500W (600W would be better)"
mpilchfamily6 months ago
dimmaz88 (author)  mpilchfamily6 months ago
Thanks for your response, I already have the transformer. Those ones you linked too aren't able to handle the power consumption. I was wondering how I could alter the output of my current one.

Thanks
Jack A Lopez6 months ago
I am guessing the thing you are calling a "110VAC transformer"  is in fact a transformer, and it is a transformer that takes input power the 220VAC mains, and outputs power at 110VAC.

I am also guessing that you have tried plugging in your "graco spray gun", into this transformer, which is plugged into the UK mains, but the spray gun seems to be running too fast, or gets too hot, or something like this, and this is the reason why you desire to reduce the amplitude of the voltage powering your spray gun.

Are any of these guesses correct?

Anyway, I am going to suggest two methods for lowering AC voltage.

One method is to use a variable autotransformer, also called "Variac", although technically that is a brand name.
http://en.wikipedia.org/wiki/Autotransformer#Variable_autotransformers
 Basically this is a transformer with a big knob on top of it that actually changes the turns ratio, thus changing the output voltage.   These devices tend to be heavy and expensive.

Another method that ?might? work, since you just want to change the voltage magnitude by a small amount, 20% or so, might be to use one of these triac-based lamp dimmers.  Basically what those do is slice-and-dice the AC waveform, turning it off briefly every cycle, so that the RMS voltage is in fact lower. 
http://en.wikipedia.org/wiki/Dimmer
The nice thing about lamp dimmers is that they're cheap and lightweight.  The not-nice thing about dimmers is that they change the AC waveform so it is no longer sinusoidal.  However, this distortion is worse at  "low" setting than it is at "high" setting, and for this reason I think the lamp dimmer ?might? do what you want it to do; i.e de-power your spray gun by just a little bit.

For either solution, autotransformer or dimmer, you have to pick one rated to actually handle the amount of power you're going to be putting through it.  Fortunately, lamp dimmers that can throughput large amounts of power, like 300, 500 watts, etc. are inexpensive and easy to find (at the time of this writing).  In contrast, a variable autotransformer capable of handling the same amount of power, would be much more expensive, and also much heavier.
dimmaz88 (author)  Jack A Lopez6 months ago
Thanks for your in-depth response. I indeed have a transformer that converts 240 to 110 volts, which is rated at 3kW. I've tested the sprayer, but as it's the first one I own I can't tell if it sounds or runs like it should.

I may find out more as I use it more, it certainly performs well enough though. I think I'll risk it, if it dies I'll buy a euro rated one. More expensive as usual!!
I just wanted to add a graphic to sort of illustrate what I was saying about the lamp dimmer and what it does to the AC waveform. There's a good chance you've seen this picture before.

Regarding my claim that the "lower" setting has more distortion than the "higher" setting, you can sort of see this from looking at the picture.  The higher powered waveform more closely resembles a sinusoid.  The low powered waveform looks like widely spaced little spikes.
lamp-dimmer-waveform.jpg
steveastrouk6 months ago
Don't bother, unless it gets hot in use.
dimmaz88 (author)  steveastrouk6 months ago
I think I'll try this idea, I can't see myself using it for prolonged periods to get overly hot.

Thanks
dimmaz88 (author) 6 months ago
I have a 110v transformer, I'd like to reduce the output to 90v.