220V Step Up with 110V PSW - Voltage on ground post transformer?

Dizastrous
Dizastrous Registered Users Posts: 12
I have read several threads in here about folks using a 220v step up transformer with a 110V inverter. I learned to not use MSW - check. Have a simple 1000w PSW. Have a simple 1500w step up to 220v transformer.

This is a small system for family in the Philippines and they want 220V for items over there. When connecting the 220V step up, I read voltage from the neutral to the ground on the 110v and the 220v lines out of the transformer. Is that normal and can anyone tell me if this is expected behavior? Certainly don't want to send a dud overseas.

Thanks for any insight!

Comments

  • Dizastrous
    Dizastrous Registered Users Posts: 12
    Additional question...the inverter also shows voltage from neutral to ground....again, is this normal and expected? Is it harmful?
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    voltage from neutral to ground sounds like a bad thing. Sure it's a pure sine inverter ? What voltage do you read ? Can it light a 7watt night light bulb ? A 25 or 40W bulb ?
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  • Dizastrous
    Dizastrous Registered Users Posts: 12
    I have several smaller inverters and they seem to all do this. As for the configuration I am referencing with the 220V step up transformer, when I plug things into both the 110 and 220, everything works...Used a bench grinder, dremel and many other small items on the 110 that use cords with a ground. Found a couple power packs and chargers that will accept 240v and they all work on the 220V side, but do not use a ground (2 prong plugs). Having family send me a mixer from Philippines so I can test it here first.

    The voltage seems to hover around 60v between the neutral and ground on the 110v and about 85 volts on the 220v side after the transformer.

    I did read a thread in here about the hot and neutral "splitting" the 120v between them in smaller inverters...just never considered it or thought about this until I tested voltages and saw this. If it is normal, then no biggie.

    Thanks for the reply and any insight!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Many smaller PSW AC inverters (and some larger ones too) "float" the AC output (isolated pure transformer output). DMM (digital multi meters) have very high input resistance (very little current draw) and measuring the voltage between AC output and ground could be all over the place.

    As Mike says, use a small filament lamps (120 Volr, 7-40 watts or so) clipped between AC 1 and ground, measure voltage across light; and clipped between AC 2 and ground, measure voltage again.

    If they output is floating, you should see close to zero volts across the light in both cases. If the output is not floating, you will measure >> few volts across the light.

    Transofmers--There are two major types. Isolated with full Primary Winding and a full Secondary winding.

    And there are Auto Transformers. These are a "single winding" with voltage taps. These types will bring the "DC ground" or other other voltages from the input to the output.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dizastrous
    Dizastrous Registered Users Posts: 12
    Thank you both for the test steps:

    From the inverter outlet directly-
    AC1 and AC2 - 120V and 40w bulb lights up
    AC1 and GRND - 0V and no light
    AC2 and GRND - 0V and no light

    From the 120v side of the step up transformer-
    AC1 and AC2 - 120V and 40w bulb lights up
    AC1 and GRND - 0V and no light
    AC2 and GRND - 0V and no light

    This indicates a floating voltage inverter, right?

    The transformer is a $68 Great Electric from Amazon - not sure of the windings or how to read that from the wiring of the coil.

    Judging by the voltage tests, the fact the the DMM reads the voltages across GRND and AC2(Neutral) with no load, but no voltage when a load is present seems to indicate this is expected and normal and once a load is placed, the inverter responds accordingly.

    Am I close here?

    Thanks for the replies and continued insight!
  • Dizastrous
    Dizastrous Registered Users Posts: 12
    Also, the step up transformer has BOTH a 110 outlet and 220 outlet. Each voltage has its own circuit breaker. Both work at the same time. The only adjustment the user makes is selecting the input voltage. Unsure if that helps discern the windings type.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Yes, it sounds like isolated AC outputs.

    You can make a "truth table" with an Ohm meter... Connect T1 to T2, T1 to T3, T2 to T3 and write down the resistance for each connection. Should be able to figure out the wiring (primary/secondary, or non-isolated transformer).

    Beware--When you measure the resistance with an Ohm meter, there can be enough current flow to give a good inductive kick when disconnecting the meter. Try not to do the hold one lead in the left and and another lead in the right hand with your fingers holding the bare wire against the leads--You may get a nice little shock when the connection to the meter is broken.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dizastrous
    Dizastrous Registered Users Posts: 12
    Thank you BB! In summary, the step up transformer and inverter should work fine together for overseas small appliance power <1000w? The voltages I see across the grounds and neutrals expected and once a load is present, power is provided where it needs to be?

    I will "truth-out" the transformer. Is there a benefit to any particular type (primary/secondary or non-isolated)?

    Thank you again for the insight and assistance!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Isolation transformers can be "safer" (lightning surge, etc.). And if you are working outdoors (wet) area, you cannot get a Hot to Ground shock (of course, you can use a GFI outlet too).

    Auto Transformers are generally smaller/lighter for similar power levels. But, do not have primary to secondary output--Ground loop isolation, etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dizastrous
    Dizastrous Registered Users Posts: 12
    Thank you very much BB!