Discussion in 'General Electronics Discussion' started by Duffy Moon, May 8, 2015.

1. ### Duffy Moon

2
0
May 8, 2015
Hi,

I'm working on a project and need to power a microcontroller that will be mounted inside of a washing machine. The washer has 3 phase power coming in and I was wondering if anyone had a suggestion as to how to pull 5VDC 2A from it. I've seen reasonably priced transformers but nothing for 3 phase. Any ideas?

2. ### Harald KappModeratorModerator

11,439
2,625
Nov 17, 2011
Welcome to electronicspoint.

A 3-phase transformer is overkill in this case and, as you observed, most dificult o buy anyway. You can use a simple single phase transformer. Connect it between one phase (it doesn't matter which one) and neutral - provided you have neutral available. if There is no neutral, you can connect the transformer's primary between any two phases, but watch out for the higher voltage [V(phase-phase) = V(phase-neutral)*sqrt(3)]. The transfomer needs to be rated accordingly.

As always when tinkering with mains: observe all applicable standards and use ever safety measure possible.

3. ### Tha fios agaibh

2,153
725
Aug 11, 2014
It certainly does matter in a delta connected configuration where a "wildleg" phase would be higher. Knowing the type of electrical system a utility is supplying is an important consideration.

4. ### Harald KappModeratorModerator

11,439
2,625
Nov 17, 2011
I don't know how the electrical system in the US is operated. As far as i know a true three-phase system should have a separate neutral, regardless of delta or wye connection. As the term "wildleg" was unknown to me, I googled and found this. How does that fit in here?

5. ### Tha fios agaibh

2,153
725
Aug 11, 2014
Both delta and wye configurations may or may not have a neutral. And both may or may not be grounded. There are many different ways to configure a system. The delta "wildleg" or "stinger" is usually the B (not always)phase opposite the mid tapped phase where the neutral (grounded) is landed. Other times, a delta is corner grounded. Just because one type of system is common in one area, one should never make assumptions, particularly in industrial or commercial settings. It is not uncommon to have a specialized transformer in order to run oddball foreign voltages.

Harald Kapp likes this.
6. ### Harald KappModeratorModerator

11,439
2,625
Nov 17, 2011
Thanks for the picture (worth more than 1000 words). The configuration shown is unfamiliar to me. I agree that in this case you have all these different voltages shown.
If this is the configuration in the op's washing machine, he will have to measure the voltage between the legs where he is going to attach his transformer and select the transformer accordingly.

7. ### signalman72

57
6
Jan 26, 2014
Yeah, delta systems are still common in some places, though most light commercial has went to 120/208 wye (at least in the US)

8. ### Tha fios agaibh

2,153
725
Aug 11, 2014
Yes, Delta is preferred in industrial settings with motors and machinery, because you can loose a winding or blow a fuse and still have full voltage on all 3 phases. (Reducing downtime)

Where as, Wye is more commonly used for lighting circuits.