Why Does My Letterpress Machine Keep Blowing Fuses?

[wudingbin]

Please help -- machine blowing fuses!

Recently i just bought a letterpress machine from USA.
The electrical requirement of the machine is as follow:
1) 115V
2) 2.6A
As i am living in singapore which has a different voltage, i bought a transformer to step down Singapore's 240V to 110V, which close to the US voltage.

The tansformer model i bought is ST 500. Which is able to give 2 output voltage, 110V and 220
V.

when i on the letterpress machine, the transformer fuse burnt instantly. i had alrdy tried with 3A and 4A ampere fuse, but it all burnt instantly after on the machine.

Please advise on the value of ampere fuse i should use.
Million thank!

 

[dlgoff]

I suspect that your machine has an http://en.wikipedia.org/wiki/Surge_current" fuse.

Fuses have different characteristics of operating time compared to current, characterized as fast-blow, slow-blow, or time-delay, according to time required to respond to an overcurrent condition.

 

[Simon Bridge]

Singapore has the same power delivery as Australia - see these notes on running US appliances from Aussie mains:
http://www.armory.com/~stacey/aus-us-power.html

The transformer fuse is supposed to protect the transformer - so upping the fuse is a bad idea.

Check the peak power rating of the transformer against the peak consumption of the press. But I'm thinking you are suffering from a high inrush current.
http://www.armory.com/~stacey/inrush-current.html
... in this case you need an inrush current protector (or get an electrician to install an 115V outlet :) )

also see:
http://en.wikipedia.org/wiki/Inrush_current

I wouldn't have normally considered a slow-blow for this application - the fuse is between the transformer and the rectifier (from context - maybe it is on the supply side?) - well, between the transformers. But that could have been a bias - so I decided to check: eg. http://www.marcspages.co.uk/pq/2511.htm
Although many designers opt for "slow blow" types, these too can easily fail under such inrush conditions. It must be remembered the current curve of a rectifier system is short but intense during the conduction phase. Slow-blow fuses have two ratings, the lower long term average current (the slow-blow rating) and the higher instantaneous rating - a rating that can easily be exceeded by the current curve of the rectifier. Such fuses are only suitable on the input to a mains transformer (where the impedances are much higher) rather than between the secondary and rectifier.
... meh.

 

[wudingbin]

Sir please take a look at the spec of the machine.

 

[Simon Bridge]

115V 2.6A @60Hz
That would be for the press? What about your transformer you are driving it from?

This is just to make sure you are using a grunty enough transformer (likely - but it pays not to assume.) I still think that inrush current is your problem.
Have you read the references?

 

[AlephZero]

I'm going to ask a dumb question: do you know if the machine was working before you bought it? It may be blowing fuses because it has a fault.

 

[Averagesupernova]

I am going to ask another dumb question. Are you sure you are not reversing the input and output windings on your transformer? Are you actually doubling the voltage mistakenly while trying to halve it?

 

[phinds]

I think dlgoff's suggestion of a slow-blow fuse is what you should try next. Get a 3amp slow blow. You'll note that the OPERATING current is 2.6 amps (full load) but that does NOT mean that the startup current is going to be so small.

 

[wudingbin]

i went to US to check out the machine before shipping, its working perfectly ok

 

[wudingbin]

i am currently using ST500 transformer which is able to produce 500Watt of power more than enough for the machine. However, the frequency needed by the machine is 60Hertz but Singapore's frequency is 50 Hertz so...?

 

[AlephZero]

However, the frequency needed by the machine is 60Hertz but Singapore's frequency is 50 Hertz so...?

It's not possible to answer that without knowing a lot more about the machine.

It might not make any difference. It might work OK but run 20% slower. It mght mean it draws a higher current (possibly 20% higher) at the same supply voltage. Or it might not work at all.

If the operating manual doesn't tell you what rating of fuse to use, you could email whoever you bought it from and ask them what they used.

 

[jim hardy]

try a google on volts per hertz

there's a long shot thought here,

basically a 50 hz transformer (or motor) needs 20% more iron in it than one made for 60 hz and same voltage.
reason is in concept of 'Volts per hertz"

some manufacturers just overbuild for 60hz, that is put in the extra iron, and label the machine 50/60 hz
others do not.
the symptom of too many volts/hertz is sharp current peaks that almost immediately blow the fuse .


the sure test would be to borrow an adjustable transformer
they're called "Variac" (a popular brand)
"Sliders" - a colloquial name for the sliding tap they have
"Staco" another brand name

borrow one and try powering your device a 5/6 of 120 volts -- 100 VAC and see if that eliminates the fuse blowing problem.
if it does contact manufacturer and tell him of your trouble.
He is best equipped to design a proper fix.

Myself - if it runs at 100 volts and doesn't get hot, i might declare victory

 

[cmb]

If the other options don't work, try;


1) This is a random suggestion and its success will depend on how adventurous you are, and if you would understand how to determine if the bulb is correctly acting as a current limiter/voltage divider (given we don't know exactly what current the device will pull in operation): Stick a ~200W 240V bulb in series with this device, and run them serially off your 240V supply. (If you don't get why I am suggesting that, then best not do it.)

2) If that sounds too risky to you, I suspect if you ask someone with electrical knowledge to open this device up they'd find a transformer with enough connections to rewire it for direct 240V operation. There may even be a simple internal switch to do this, but might not be so straight forward if it feeds a motor directly.

3) If you do want to stick with your transformer set up, you could always try a NTC thermistor between the transformer and the device. This has a high resistance when cold, preventing high current flowing, and decreases resistance as it gets hot

 

[dlgoff]

If the other options don't work, try;


1) This is a random suggestion and its success will depend on how adventurous you are, and if you would understand how to determine if the bulb is correctly acting as a current limiter/voltage divider (given we don't know exactly what current the device will pull in operation): Stick a ~200W 240V bulb in series with this device, and run them serially off your 240V supply. (If you don't get why I am suggesting that, then best not do it.)

Nice troubling shooting.

 

[wudingbin]

Hi guys, i had just bought a few 3A slow blow fuse. The motor inside the letterpress machine start to run for about 5 mins before i saw some smokes coming out from the transformer. And now my transformer is burnt.

Why is that so?
I tried to find technician but none of them know how to fix this problem. I had even asked a few of my electrical engineer friend to come down to take a look but none of them know the reason behind.

Help needed urgently, cos i am going to have an Expo soon, need to rush out my product.

Million thanks.

 

[dlgoff]

Hi guys, i had just bought a few 3A slow blow fuse. The motor inside the letterpress machine start to run for about 5 mins before i saw some smokes coming out from the transformer. And now my transformer is burnt.

Why is that so?
I tried to find technician but none of them know how to fix this problem. I had even asked a few of my electrical engineer friend to come down to take a look but none of them know the reason behind.

Help needed urgently, cos i am going to have an Expo soon, need to rush out my product.

Million thanks.

Did you read post 5? See the bold print by me.

115V 2.6A @60Hz
That would be for the press? What about your transformer you are driving it from?

This is just to make sure you are using a grunty enough transformer (likely - but it pays not to assume.) ...

Sorry the transformer burned out.

 

[cmb]

Looks like the transformer was 500VA, and you used a half of the winding, 250VA, to run a 115V x 2.6A device. Your calculator is your friend here!

That's why the fuse blew. The secondary windings were only rated to 2A.

But this should not have been a problem, per se; any decent transformer should have a thermal switch. So even the 250VA rating [on one winding] might be expected to be optimistic.

What you needed to do was to parallel up the outputs (which'd not have been possible if it were centre-tap, though).

So, at that power, I suspect what you have looks like just an inductive 'dumb' motor load (difficult to tell from this distance!). In which case, a thyristor switcher for limiting the average voltage should be perfect. There are ebay vendors that sell them with heat sinks on little boards to 3800W, adjustable with a pot, for $10. That should be what you need.