Control voltage advice?

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Location
Seattle
I'm a Washington State 01 Master.
We brought in a temp company "certified journeyman", and he promptly wired a 208 1P commercial dishwasher to 480 3P.
Along with that, didn't bother to even energize correctly, and by the time him and the owner of the business heard the "pop", they had already let out all that most excellent magic smoke.
The unit is older, and some parts are not available.
Owner wants it fixed instead of replacement.

The transformer is one of the not available, it is 110 vac to 15 vac @ 45 va.

I took 2 doorbell transformers, 110 to 16@ 30 va.
Synchronized the windings and hooked up in parallel, then put an inline 3 amp fuse on the secondary so it wont overdrive the controls.
I'm getting 18v output. The control board is working, but not getting anything from the control pad.
I'm told the control pad was intermittent operation before.
I'm sure that difference is within the design tolerance to allow for the 10% utility fluctuation.
Just trying to get other opinions.
Thanks.



 

growler

Senior Member
Location
Atlanta,GA
Did you think of bringing in a professional ? Someone that's familiar with restaurant equipment repair. They may know better where to find replacement parts.

When a piece of equipment is smoked there may be more than the transformer that was damaged.

That's one of the risk we take when hooking up used equipment, we never know how well it worked before we touched it.


When dealing with transformers it's possible to get a transformer custom wound for the desired input and output.
 
Location
Seattle
150812-2003 EDT

You should be able to use a Stancor RT transformer. See http://www.stancor.com/pdfs/Catalog_2006/Pg_008_10.pdf

Also look at Signal Transformer. See http://www.signaltransformer.com/sites/all/pdf/241.pdf 241-7-16

.

Awesome links, thanks.

That's one of the risk we take when hooking up used equipment, we never know how well it worked before we touched it.

Thought about it, but would have added several hundred plus parts markups.
Am already out over $700, plus my time.
The job shop is refusing to take responsibility for their workers actions, so I'm thinking of with holding the costs of repairs, but for now I am eating the full expense.
Didn't mention I replaced the processor control board and relay board.
There's the pressure control board and display panel left, but I going to try to bypass those to get operation before ordering.
Troubleshooting appliances is for the most part straight forward.
I do have a tendency to toss factory junk and use over the counter components when possible.

I'm just rusty on my power formulas and want to be sure I avoid a reactive flow loop with the parallel transformers.
Think I'll just go to one, and see if it can hold the current.

Thanks to both for your replies.
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
I'm a Washington State 01 Master.
We brought in a temp company "certified journeyman", and he promptly wired a 208 1P commercial dishwasher to 480 3P.
Along with that, didn't bother to even energize correctly, and by the time him and the owner of the business heard the "pop", they had already let out all that most excellent magic smoke.
The unit is older, and some parts are not available.
Owner wants it fixed instead of replacement.

The transformer is one of the not available, it is 110 vac to 15 vac @ 45 va.

I took 2 doorbell transformers, 110 to 16@ 30 va.
Synchronized the windings and hooked up in parallel, then put an inline 3 amp fuse on the secondary so it wont overdrive the controls.
I'm getting 18v output. The control board is working, but not getting anything from the control pad.
I'm told the control pad was intermittent operation before.
I'm sure that difference is within the design tolerance to allow for the 10% utility fluctuation.
Just trying to get other opinions.
Thanks.




Here's a link to a voltage-compatible and VA-compatible transformer:

http://www.mouser.com/ProductDetail...GAEpiMZZMvwUzoUXIIvyTw34uqMHR%2buCiui5ut8JZU=

For a 120V supply, wire the primary windings in parallel, and wire the secondary windings in parallel. This will give you 120V in, and 15V out.

Something to check:
Are you sure your transformer is fed L-N? For example, if you were to wire the above transformer's primary windings for 240V and feed it with 208V L-L, it would only give you ~13V; probably too low for proper operation. You'd need a transformer with an 18V secondary and a 240V primary to give you ~15V when operating at 208V L-L.


If the owner wants to try and use this dishwasher, and replacement control parts are impossible to get/too expensive, perhaps replacing the control with a small PLC is an option. I assume it's mostly on/off control of valves, pumps, heaters, etc... with possibly some analog inputs to monitor temp? Pretty easy to refit controls for a machine like this. Just a thought.



SceneryDriver
 

Tony S

Senior Member
I'm a Washington State 01 Master.
We brought in a temp company "certified journeyman", and he promptly wired a 208 1P commercial dishwasher to 480 3P.
Along with that, didn't bother to even energize correctly, and by the time him and the owner of the business heard the "pop", they had already let out all that most excellent magic smoke.
The unit is older, and some parts are not available.
Owner wants it fixed instead of replacement.

The transformer is one of the not available, it is 110 vac to 15 vac @ 45 va.

I took 2 doorbell transformers, 110 to 16@ 30 va.
Synchronized the windings and hooked up in parallel, then put an inline 3 amp fuse on the secondary so it wont overdrive the controls.
I'm getting 18v output. The control board is working, but not getting anything from the control pad.
I'm told the control pad was intermittent operation before.
I'm sure that difference is within the design tolerance to allow for the 10% utility fluctuation.
Just trying to get other opinions.
Thanks.




Is this actually about effecting a repair or apportioning blame?

You’re the one the customer employed, you passed it on to someone else that it would seem you have no previous knowledge of.

Is my nasty suspicious mind reading this wrong?
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150813-2015 EDT

iceworm:

I have no idea either what he is talking about. My conjecture is as follows as illustrated by a DC circuit:

Consider two batteries connected in parallel.

If both batteries have identical internal voltage sources, then whether the batteries are connected in parallel or just separate there is no current flow from one battery to the other.

Alternatively if one battery has a slightly higher internal voltage source than the other, then positive current will flow from the higher voltage battery to the other. For example: the equivalent internal voltage of battery 1 is 12.1 V, and battery 2 is 12.0 V. Assume an internal resistance (impedance) of 1 ohm in each battery. The current flow between the batteries is 0.1/2 = 0.05 A. If these are rechargable batteries, then the higher voltage battery is charging the lower voltage battery.

Put a 0.1 A load on the batteries and the higher voltage battery will supply all of the 0.1 A.

Put a load of 1 A on the parallel batteries, then the higher voltage battery current is 11/20 A (0.55 A), and the lower voltage battery is 9/20 A (0.45 A).

In a transformer circuit the series internal impedances are a combinaztion of reactive and resistive, thus some reactive current does flow between them.

.
 

kwired

Electron manager
Location
NE Nebraska
May want to figure out who is liable for what next time you deal with a temp. Without a contract of any sort chances are you are considered to be in similar position as you would be if they are your own employees from a liability perspective. Your insurance may also want to know whether such subs have their own coverage or not, both from liability and workers compensation perspectives.
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
Here's a link to a voltage-compatible and VA-compatible transformer:

http://www.mouser.com/ProductDetail...GAEpiMZZMvwUzoUXIIvyTw34uqMHR%2buCiui5ut8JZU=

For a 120V supply, wire the primary windings in parallel, and wire the secondary windings in parallel. This will give you 120V in, and 15V out.

Something to check:
Are you sure your transformer is fed L-N? For example, if you were to wire the above transformer's primary windings for 240V and feed it with 208V L-L, it would only give you ~13V; probably too low for proper operation. You'd need a transformer with an 18V secondary and a 240V primary to give you ~15V when operating at 208V L-L.


If the owner wants to try and use this dishwasher, and replacement control parts are impossible to get/too expensive, perhaps replacing the control with a small PLC is an option. I assume it's mostly on/off control of valves, pumps, heaters, etc... with possibly some analog inputs to monitor temp? Pretty easy to refit controls for a machine like this. Just a thought.



SceneryDriver

An excellent idea. I use Schneider Electric Zelio Smart Relays quite frequently. They are amazingly simple and versatile. http://www.schneider-electric.com/en/product-range/531-zelio-logic/

You also could use an Arduino with a relay board, which uses a simplified version of JAVA, but still infinitely more complex to program than the Zelio, which is all done with visual-based ladder logic.

You'll definitely want to know the number of discrete and analog I/O's you'll need so you don't overspend.
 
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