Control transformer hookup question.

[ODCaveman]

I have a Hammond HPS Fortress 500va controls transformer in a control panel I built for a hydro-pneumatic pump control system. The incoming power is 3 phase 220V and I wanted 120V power for the controls circuitry. My secondary voltage is hovering around 129V under the minimal load of the controls and goes up slightly over 130V depending on line voltage. I put in a 500va transformer because I figured it would be better to have extra capacity but my load with just a few relays is very small. I think the high voltage burned out my Warrick level control relay so I am wanting to change the taps to lower the voltage to prevent any more damage.

I don't need the full 500va and the transformer had multiple taps, I'm just not 100% sure what connections to change to get a lower voltage because it's not a typical connection listed on the wire diagram. I'd be much happier at 110v than 130v. Any help would be appreciated. Right now it's wired up for 220v primary and 120v secondary. I was thinking I could change the taps to connect the line to H1 and H10 and interconnect H1-H6 and H5-H9 to get the lower voltage but just need some verification if that is correct before I try it.

Link

 

[itsmoked]

Stop using the 220V connection! You're in California! You have 240V or 208V you don't have 220V.

Wire the primary as 240V and use the 120V secondary configuration. Exactly like the diagram describes.

Measure the primary and see what it is.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jghrist]

If you get 130 V with the 220 V connection, changing to the 240 V connection will give you 119 V on the secondary.

 

[ODCaveman]

I'm in ME ,not in CA, its the VPN at my workplace if the IP came up in CA.

The primary is 220V. This is a panel being fed by its own 3 phase transformer in a factory.

In regards to the other suggestion, if you look at the schematic the 240V connections are the same as the 220V connections.

I did a search and found an older post on this forum from someone else with a similar issue and a couple folks suggested using the transformer wired differently to use one full 220 primary winding and a section of the second primary winding. Reducing power available but getting the desired voltage.

 

[waross]

Tape up all your primary wires (H1 to H10) and forget them.
Wire the transformer:
Lines to X1 and X4.
Connect X2 to X3.
220 or whatever applied to X1 and X4.
110 from X1 and X2-3, or half of whatever.
You will not be able to ground this supply.
You will have 50% capacity. (250 KVA)

The diagrams do not give the exact voltages, they give close enough voltages rounded to the nearest standard voltage.
If you wish to have a more creative solution, or one that allows grounding of the circuit you will have to supply us with the exact voltages.
To do that:
Connect 220 Volts or whatever across H1 and H5. Ignore the connections from H6 to H10.
Measure and report the voltages as follows:
H1 to H5
H1 to H2
H1 to H3
Hi to H4
From that information we may determine the almost exact ratios and the feasibility of an alternate connection.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Parchie]

Here's my take on your connection problem. Watch carefully the dots on the connection diagram, they mean a lot to know the magnetic polarity of your windings!
[ul]
[li]Tape/ isolate the transformer terminals H2, H3, H4, H7, H8, and H9. You don't need them when you use the 240V connection.[/li]
[li]Connect the primary line 1 on H1-H6 and the supply line 2 to terminals H5-H10. Another way of saying this is bring H1 and H6 to receive Line 1 and H5 and H10 with Line 2.[/li]
[li]On the secondaries, connect X1 and X3. This will be your secondary line 1.[/li]
[li]Connect X2 and X4.This will be your secondary line 2.[/li]
[/ul]
If you will supply the transformer primary with 220V, you will get a secondary voltage of 110V. In this connection, you can avail of the full 500 VA of your transformer.
Hope that helps.

 

[ODCaveman]

This was the other old thread I found that had basically the same issue I am having and the solution was what I am looking to do, I'm just not sure if my taps would be the same as the schematic drawing is slightly different. Essentially utilize the entire secondary side and only a section of the primary side.

[URL unfurl="true"]https://www.eng-tips.com/viewthread.cfm?qid=416004[/url]

It's currently connected as shown in the diagram for 220v primary and 120v secondary,(same as the 240v primary and same as the previous poster suggested) The root of the issue I guess is the regulation isn't that great on the transformer and I'm not loading it down enough because with 220v on the primary I'm getting 130v on the secondary. I should have just got a simple 240/120v transformer but I knew my available voltage to the panel was 220v and I figured this model would have any option I would need.

 

[waross]

ScottyUK (Electrical)
20 Oct 16 20:33
Ok, so you have two identical windings with taps at:

H1(H6) 0V
H2(H7) 190V
H3(H8) 200V
H4(H9) 208V
H5(H10) 220V

For 250V you need to connect one full 220V winding in series with the 30V tap of the second winding. To do this you should connect the supply line and neutral across H1 and H10 with a link between H5 and H7. The secondaries stay in the standard configuration for 120V.

Give it a try. You will not damage anything.
If the manufacturers voltages are off from the manufacturers diagram, you will not get the exact voltage that you expected but it will be close.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[ODCaveman]

I went ahead and hooked it up the way that was suggested in the older thread (Line on H1 and H10 and H5 and H7 connected together) and now I'm getting 113-114v on the secondary side. I realize I lost some capacity from the transformer but now I'm at a voltage I am happy with and should still have more than enough capacity.

Thank you for all the help!

 

[waross]

Be sure to check the voltage under load.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!