Specifying a Buck Boost Transformer
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MTW
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That all depends on what your trying to accomplish?
hillbilly1
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What’s your input voltage? What’s the output (boost or buck) voltage needed? If the input is 480, the second one could clearly not be used.
For the sake of this example I am trying to get 220V single phase from a 200V single phase input.
I see that at the top of each table there are different primary and secondary voltages (I guess this is what I am not clear about) but is the table saying that both QC05DTCB and QC05ERCB can give 220V single phase from a 200V single phase input?
LarryFine
Master Electrician Electric Contractor Richmond VA
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The first one has two 24v secondaries, while the second one has two 12v secondaries.
With the first one's secondaries in parallel, or the second one's secondaries in series, they're funtionally identical.
For the configuration you have used, either would suffice. Do you need a center tap?
With the first one's secondaries in parallel, or the second one's secondaries in series, they're funtionally identical.
For the configuration you have used, either would suffice. Do you need a center tap?
As Larry said, the difference is in how the secondary windings are arranged to give you your desired output, but both would be sufficient for what you are trying to accomplish. The only difference is the winding arrangement, and what other configurations you can achieve with each model.
If you scroll down on the Hammond catalog you took this snip from, at the bottom of the column there is a connection diagram number, which will correspond to a connection diagram a few pages down. This will show the winding arrangement graphically so you can see the difference between the two.
wwhitney
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I think that the two transformers have identical winding ratios, and so if you have <= 240V on the primary, you can use either transformer, and you'd wire it the same either way. So the only difference would be that the first transformer has higher voltage ratings on its windings.
Cheers, Wayne
Thanks for your reply.
Technically yes, both transformers have a 10:1 ratio, but there are two sets of windings. You have to wire them differently based on your desired primary and secondary voltage. Looking at the second model (120X240 to 12X24) you can see that for a 100, 110, 115, or 120V low voltage, there are two different available voltages to boost to, depending on if you arrange the secondary windings in series or parallel. If there were simply two windings (one primary, one secondary) and the transformer is always wired the same way to boost, there would be no ability to have two different voltages to boost to.
Here are the aforementioned connection diagrams. For 200 to 220, the 240X480 to 24X48 is diagram #1 and the 120X240 to 12X24 is diagram #4.
View attachment HPS-Universal-Buck-Boost-Brochure_Page_12.png
winnie
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For the specific combination of voltage you describe (and circled in red in the tables) the two are equivalent. You would wire them using the 240V primary voltage configuration and the 24V secondary configuration.
Where they are different:
1) The lower voltage version gives you options around the 100-120V supply voltage range, the higher voltage version gives you options around the 400-480V range.
2) I think for the 200V input range the higher voltage version will give you options for up to a 20% boost, and the lower voltage version will give you options for a 5% boost. Both give you the desired 10% boost. So you might pick one or the other if you are not quite certain of the required voltage boost and need options.
3) To get the necessary 240V and 24V connections they would be wired differently.
-Jonathan
Where they are different:
1) The lower voltage version gives you options around the 100-120V supply voltage range, the higher voltage version gives you options around the 400-480V range.
2) I think for the 200V input range the higher voltage version will give you options for up to a 20% boost, and the lower voltage version will give you options for a 5% boost. Both give you the desired 10% boost. So you might pick one or the other if you are not quite certain of the required voltage boost and need options.
3) To get the necessary 240V and 24V connections they would be wired differently.
-Jonathan
wwhitney
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I'm not seeing that you'd have to wire them differently, just that you'd have the option to wire the 240Vx480V unit differently. In the following I'll use a voltage of 240V, but you could use 200V and just multiply all the voltages by 5/6.
If you have 240V two-wire, with the second transformer you'd have to wire the two primary coils in series, as each coil is only rated for 120V. So each secondary coil would give you 12 V, and you could wire the secondaries in parallel to buck/boost 12V or in series to buck/boost 24V.
For the first transformer, you could hook it up exactly the same, and it would behave the same. Or since each primary coil is now rated for 240V, you could wire the primary coils in parallel, so each secondary coil would give you a voltage of 24V. That means you could wire the secondaries in parallel to buck/boost 24V or in series to buck/boost 48V.
So I think that each transformer can give you a 5% or 10% boost for the 200V input range, and only the 240Vx480V can give you a 20% boost.
Cheers, Wayne
winnie
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@wwhitney you are correct that you could wire the 240x480 : 24x48 volt transformer in the same fashion as the 120x240 : 12x24 transformer and get the same voltages because the turns ratio would be the same.
I was only considering the 120x240 transformer with the primaries in series, and the 240x480 transformer with the primaries in parallel for the OP's 200V to 220V scenario. My reasoning was that using the 240x480 transformer with the primaries in series for the 200V application 'throws away' half the kVA capability, and would be a bad choice if you were selecting a transformer for purchase. But if you happen to have a transformer sitting on the shelf it is good to consider this as a possible use case.
-Jonathan
I was only considering the 120x240 transformer with the primaries in series, and the 240x480 transformer with the primaries in parallel for the OP's 200V to 220V scenario. My reasoning was that using the 240x480 transformer with the primaries in series for the 200V application 'throws away' half the kVA capability, and would be a bad choice if you were selecting a transformer for purchase. But if you happen to have a transformer sitting on the shelf it is good to consider this as a possible use case.
-Jonathan
The voltage output would be the same, but you would hit the design current through the windings at only 50% of the rated kVA.
Probably also a 110.3(B) issue.
winnie
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- Springfield, MA, USA
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- Electric motor research
AFAIK there is no prohibition or manufacturer instructions that prevent using the transformer below its rated voltage. In fact many intentional buck/boost configurations use the transformer coils at lower than their 'rated' voltage.
But as we both noted doing so reduces the kVA capacity of the transformer.
Agreed that there are many configurations that are not at the 'rated' voltage, such as the 200 to 220V example above, where it is only 83% of the rated voltage (and hence the boost is only 20V, 83% of 24V). However, these configurations are approved for use by the manufacturer. Under each of these voltage configurations the manufacturer specifies how the transformer is to be wired - in this case it is connection diagram #1. If the manufacturer's instructions say to use connection diagram #1, and you use connection diagram #4, I think someone could make a case that you are not using the equipment "in accordance with any instructions included in the listing, labeling, or identification."
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I would not be surprised that there is actually a low voltage limit where enough magnetizing current cannot be created, but it would have to be extremely low.
After all, look at the definition of an impedance test on a transformer, % rated voltage that causes 100% rated current in secondary.
Joethemechanic
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These 2 different transformers that are both have the same Primary voltage as connected but one being series and the other parallel, how much difference in impedance do you think there would be if any? It'll probably be too small to matter, but I'm just wondering
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wwhitney
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