I need the cheapest option to go from 208V to 240V

[crankbait09]

I have a friend that recently installed a 400A, 208V/3PH/4W service into his shop.
We have a 20A/3P breaker within his 400A panel, feeding a dryer unit. Turns out, the dryer needed 240V, not 208V.
When he runs the dryer, obviously it works, but it doesn't get hot enough.
This dryer has a cord/plug, and is not hard wired.

What is the cheapest option to convert 208V to 240V for that 20A circuit (I believe the dryer has an FLA of 15A)?
It would also need to have the plug in order for him to plug into.

I am not an electrician, but I would like to go back to him with options (before we contact an electrician to do the work)

I have seen the step up transformers, as well as the Buck and Boost. With me not being experienced in this type of conversion, I am not sure if there are better options out there.

 

[ptonsparky]

Buck boost. Cant get much cheaper.

 

[hillbilly1]

Be careful if there is any 120 volt loads on that equipment. If there is, you must use an open delta buck boost (two transformers) and make sure the third leg (unboosted) feeds the 120 volt leg on the dryer.

 

[MD Automation]

What kind of dryer? Like clothes - or parts? Just curious.

And when you say it does not get hot enough, how are you sure of that?

Do you have access to some kind of clamp on ammeter - and can you tell if the heating elements cycle on and off at some point - or are always on?

The reason I ask is it's quite normal for a dryer (various types) to run on either 208 or 240 (single or 3 phase). Supplied w/ 208, they might take a little longer to reach some operating temperature, but once they get there they will cycle on and off to maintain that temp.

Just thinking out loud - the do nothing option should always be considered first. Especially since you mentioned the cheapest option

1000 pardons if you are 100% sure it needs 240VAC and does not cycle heating elements to regulate temperature.

 

[LarryFine]

Start with one or three phase? Neutral?

 

[Knightryder12]

Are there heating elements in this equipment? Can you change the elements to 208v rated ones?

 

[Barbqranch]

Are you sure that one of the heaters hasn't failed?

 

[Jraef]

What kind of dryer? Like clothes - or parts? Just curious.

And when you say it does not get hot enough, how are you sure of that?

Do you have access to some kind of clamp on ammeter - and can you tell if the heating elements cycle on and off at some point - or are always on?

The reason I ask is it's quite normal for a dryer (various types) to run on either 208 or 240 (single or 3 phase). Supplied w/ 208, they might take a little longer to reach some operating temperature, but once they get there they will cycle on and off to maintain that temp.

Just thinking out loud - the do nothing option should always be considered first. Especially since you mentioned the cheapest option

1000 pardons if you are 100% sure it needs 240VAC and does not cycle heating elements to regulate temperature.

In a dryer application, the SURFACE temperature of the heating elements themselves may be lower, but the AIR temperature resulting from contact with it will eventually be the same. For example the designed surface temperature of the NiCh element at 240V might be 1500 deg. F, then at 208V it is only 1125 deg F, but unless you are actually USING the air temp at 1500F, what you are after is the EFFECT that the heating elements have on the air going over them. So the only difference, as MD Automation said, is the time it takes to get the air to that temperature and unless that time frame has a dramatic effect on the process taking place, what you are proposing is basically an issue of assuaging someone's impatience.

But assuming that this was all known and understood, and there IS a valid need to attain that shorter time frame, then also as mentioned, a boost transformer is the least expensive option.

Assuming single phase, here is what your transformer connection would look like (Buck-boost transformers come in specific ratios, this is as close as you will get off the shelf):

As to size, you look at the load amps you need and the voltage difference, in this case 28V. Then using basic Ohm's law for Power (Watts);

P= I x E / 1000

So I = 15A (according to you), E = 28V, ergo P = 15 x 28 = 420/1000 = .42kVA, so all you need is a 500VA buck-boost transformer for this. If you want the full 20A capacity, it's .56 kVA, so typically the next size up will be 750VA.

 

[winnie]

Very good information has been presented so far. I'm going to try to summarize:

1) lower voltage means less wattage from the heating elements and lower maximum temperature. But quite often the lower voltage simply means the system takes a bit longer to get to operating temperature and then the thermostat takes over and the system runs just fine.
1a) It may be cheaper to modify the machine for 208V operation than to provide 240V

2) A buck/boost arrangement is the cheapest way to get from 208V to 240V.

3) Be absolutely certain you understand the machine requirements. 240V means 240V 'line to line'. But the machine may have 'line to neutral' or 'line to ground' requirements as well. Addressing these other requirements might mean a more complicated buck/boost arrangement or might force the use of a step-up 'isolating' transformer.

Can you post a picture of the machine data plate or a link?

Jonathan

 

[Jraef]

But the machine may have 'line to neutral' or 'line to ground' requirements as well.

Line to neutral, yes, for example if there is a motor, the motor may run on 120V.

But line to ground wouldn’t be a thing…

 

[jim dungar]

Line to neutral, yes, for example if there is a motor, the motor may run on 120V.

But line to ground wouldn’t be a thing…

It could be with some filter circuits.

 

[winnie]

I agree, line to ground should never be a load current path.

But IMHO the issues of VFDs on other than wye systems are line-to-ground voltage issues.

 

[Besoeker3]

I usually have to stick my nose in............we just use 230V. That's it.Just simple. Why, Jrjef, do you need 208, 103, 236, 240V ?

 

[Jraef]

But for that, there is no need for a special BB transformer config, you just need an EGC…

 

[tthh]

May also be that the dryer manufacturer has a different heating element option.

 

[Jraef]

I usually have to stick my nose in............we just use 230V. That's it.Just simple. Why, Jrjef, do you need 208, 103, 236, 240V ?

Need?

We are not one small island with non-autonomous regions, we are a large spread out nation of different states with distances between population areas that can exceed the longest distance on your entire island! So when electric utilities started forming in the beginning of the last century, there were no standards or even consensus. Everyone did their own thing with regard to voltages, phases and even frequencies. We didn’t try to standardize until the 1930s, so by then there were a lot of difference already entrenched.

103 and 236 are not among our standards though. 120/240 for single phase, for 3 phase it’s 208Y120, 240 delta, 240/120 delta 4 wire and 480 delta or 480Y277, with some pockets of 600V here and there.

 

[Besoeker3]

Need?

We are not one small island with non-autonomous regions, we are a large spread out nation of different states with distances between population areas that can exceed the longest distance on your entire island!

Incorrect, old fellow. You have roughly 300 millio in various differences across your nation. We have 300 mil across EU spread equally.

The euro is the official currency of 20 European Union countries which collectively make up the euro area, also known as the eurozone.

 

[Besoeker3]

Incorrect, old fellow. You have roughly 300 millio in various differences across your nation. We have 300 mil across EU spread equally.

The euro is the official currency of 20 European Union countries which collectively make up the euro area, also known as the eurozone.

That includes UK.

 

[Hv&Lv]

just my ridiculous 2 cents…
pull the coil and remove some of the coil to get the resistance lower.
calculate and measure the resistance needed for the voltages. Solder it back on.

i know this works. Mine was like that while i was apartment living until I moved.
had to buy a new coil though when I got in a 240V house…

 

[LarryFine]

Solder it back on.

Solder a heating coil??? Braze it, maybe.