Hi, I bought a Tube Amp kit which come with a power transformer which primary is 2 x 110V.
Normally, I would consider 220V is good enough to plug into the 240V GPO. However, I think this would affect the output due to winding ratio.
There are various opinion regarding this issue (such as hum, transformer degrading and cause component failure), there are also mention of Bucking Transformer to step down the 240V to around 220V.
My question is it worth while to create a step down based on Rod Elliott's Bucking Xfmrs
Anyone know how to calculate the VA rating for this bucking transformer?
I can only get 240V primary with the following secondary:
a) 2 x 9V 20VA
b) 12 - 18V 18VA (multitab - which I can use the 18V)
c) 24V 72VA
d) 9 - 24V 60VA (multitab - which I can use the 18V)
e) 6 - 15V 30VA
Thanks
Normally, I would consider 220V is good enough to plug into the 240V GPO. However, I think this would affect the output due to winding ratio.
There are various opinion regarding this issue (such as hum, transformer degrading and cause component failure), there are also mention of Bucking Transformer to step down the 240V to around 220V.
My question is it worth while to create a step down based on Rod Elliott's Bucking Xfmrs
Anyone know how to calculate the VA rating for this bucking transformer?
I can only get 240V primary with the following secondary:
a) 2 x 9V 20VA
b) 12 - 18V 18VA (multitab - which I can use the 18V)
c) 24V 72VA
d) 9 - 24V 60VA (multitab - which I can use the 18V)
e) 6 - 15V 30VA
Thanks
Are you quite certain that there's an issue? If it's a modern kit that you just bought, it might be OK as is. I would check the secondary voltages as a first step. Do you have the know how to put a power resistor across the heater winding to measure it's voltage? Just picking whatever power resistor you have on hand to put a 0.5A to 1.0A load (assuming we are talking tube power amp here) on the heater secondary and measure it's voltage.
If (c) 24V 72VA is used, I=72/24 or 3A, resulting voltage is 216 (240-24)V, VI=216* 3=576VA is total you can safety draw.
Normally you can connect 220V to 240V supply during the day when 240V can drop to below 220V but at midnight the voltage can rise to 265V or so, that is bad news.
Normally you can connect 220V to 240V supply during the day when 240V can drop to below 220V but at midnight the voltage can rise to 265V or so, that is bad news.
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Thanks everyone. I'll check out the secondary without step down to see the voltage difference first, if there's problem, then I'll use the buck transformer method to reduce the voltage. I can safely assume all I need is to make sure the secondary of the buck transformer must match (as a minimum) the current of the power transformer primary current.
Hi,
a rough calculation for bucking/increasing the mains voltage from 240 to 220 or vice versa is that your bucking trafo must capable to handle 10% of the rated power of the load.
I had the problem years ago before we turned to 230V. A live music pub here had loads of bands from Britain gigging. They got their own eqipment from England. So I installed a 24V/25A Trafo behind the stage and step the 220V up to 240V. To avoid issues with local equipment I put a original british 2.gang socket on the wall. It works perfect. The guys were amused!
73
Wolfgang
a rough calculation for bucking/increasing the mains voltage from 240 to 220 or vice versa is that your bucking trafo must capable to handle 10% of the rated power of the load.
I had the problem years ago before we turned to 230V. A live music pub here had loads of bands from Britain gigging. They got their own eqipment from England. So I installed a 24V/25A Trafo behind the stage and step the 220V up to 240V. To avoid issues with local equipment I put a original british 2.gang socket on the wall. It works perfect. The guys were amused!
73
Wolfgang
ESP autoformers/bucking transformers.
Do NOT copy fig3.
Go to fig4 and wire up the step down autoformer correctly as shown in the right hand half.
220:240 & 240:220 are roughly a 10% adjustment of the voltage.
The secondary current of a 230:10+10Vac or 230:12+12Vac will be roughly 10times the primary current.
It's the secondary current that determines the VA of the autoformer.
eg. a 230:10+10 230VA 7% regulation transformer will have a winding ratio of 230: (10*1.07) + (10*1.07) for the three windings.
On open circuit the output voltage will be 10.7Vac when the primary voltage is 230Vac. Note that esp shows a winding ratio that does not agree with my explanation.
The current rating of the secondary will be 230VA/(10+10) = 11.5Aac
Wire this up as fig4 right hand side and you can input 250Vac into the three series connected windings and the you have taps at 250 & 240 and 230Vac
If you use the two lower taps the output current must be less than the secondary rating i.e. <11.5Aac.
Using the top tap (250Vac input and 250Vac output), you can draw whatever current your mains wiring/fuses will allow.
The effective VA is 230* 11.5A = 2645VA
Yes, that small 230VA autoformer has an enormous effective VA
And you don't have to input exactly 250Vac to the input tapping. You can use 240Vac or 234Vac or 216Vac.
Using a lower input voltage just results in a lower output voltage. And using a dual secondary allows for three output taps, making it very flexible for a variety of uses.
The smaller the step up/down ratio, the higher the effective VA.
But beware a 115:230 or 230:115. The step up/down ratio is 2:1
The effective VA is only double the donor transformer.
i.e that 230:115Vac 230VA transformer has an effective 460VA when using the 2:1 or 1:2 ratio.
And use a Mains Bulb Tester to ensure no damage, while you try to get the taps in phase.
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EU harmonised supply voltage
The universal transformer that we see advertised as 230:secondary voltage, must be designed to be safe at upto 253Vac.
Indeed, the transformer and equipment manufacturers and retailers must ensure that their equipment works safely and properly with a Mains voltage from 216Vac to 253Vac.
The universal transformer that we see advertised as 230:secondary voltage, must be designed to be safe at upto 253Vac.
The transformer is form eBay (may in China) model KD 50-34 with 2 x 110V primary and 3.15V-0-3.15V, 5V and 2 x 6.3V. I can build it up and tested as per AJT suggestion.
The reason for asking is the provided case seems to be stainless steel and very hard to drill. If I need the step down, I wish to finish all drilling before I start mounting and soldering.
If someone has used similar transformer successfully on a 240V / 230V without step down please let me know.
Thanks for all suggestion and help, this forum rocks.
The reason for asking is the provided case seems to be stainless steel and very hard to drill. If I need the step down, I wish to finish all drilling before I start mounting and soldering.
If someone has used similar transformer successfully on a 240V / 230V without step down please let me know.
Thanks for all suggestion and help, this forum rocks.
Connect the 110+110 primary winding and leave it to cook with no load.
If it does not like your higher supply voltage it will get warm. Warm is OK. HOT is a fail.
Hot tells you to use an autoformer to step down the supply voltage.
If you have a Variac you can measure the change in Iprimary as you vary the Vprimary.
that will show you whether the transformer gets too close to saturation at your maximum supply voltage.
Have you asked your supplier what their maximum supply voltage is?
I have a sneaaky feeling (no evidence) that some Far East transformer sellers do not know what voltage exists in the markets they sell to.
As a result they do not know how to specify to their manufacturers what they need their product to survive with when in the field.
It is a complete lack of knowledge of their product. And they don't care !
If it does not like your higher supply voltage it will get warm. Warm is OK. HOT is a fail.
Hot tells you to use an autoformer to step down the supply voltage.
If you have a Variac you can measure the change in Iprimary as you vary the Vprimary.
that will show you whether the transformer gets too close to saturation at your maximum supply voltage.
Have you asked your supplier what their maximum supply voltage is?
I have a sneaaky feeling (no evidence) that some Far East transformer sellers do not know what voltage exists in the markets they sell to.
As a result they do not know how to specify to their manufacturers what they need their product to survive with when in the field.
It is a complete lack of knowledge of their product. And they don't care !
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Thanks Andrew, I'll give that a try.
The supplier (after asking) could not even give me the VA of the transformer nor the current of the secondary let alone the primary max supply voltage. The supplier only said that for AU, they always supply 220V transformer.
As the kit is supplied with a 2A fuse (look like a quick blow) for the IEC socket, I would assume the max primary current is 2A. If step down is needed I may use the 2A secondary and depend on size to fit into the case I might use 15V instead of 24V.
The supplier (after asking) could not even give me the VA of the transformer nor the current of the secondary let alone the primary max supply voltage. The supplier only said that for AU, they always supply 220V transformer.
As the kit is supplied with a 2A fuse (look like a quick blow) for the IEC socket, I would assume the max primary current is 2A. If step down is needed I may use the 2A secondary and depend on size to fit into the case I might use 15V instead of 24V.
230:6+6Vac, or 7.5+7.5Vac, or 9+9Vac, or 10+10Vac, or 12+12Vac
The dual secondary does give you more options.
I meant your mains electricity supplier "have you asked what voltage"
We are on a nominal 230Vac supply where the maximum is 253Vac.
We used to be on a nominal 240Vac supply where the maximum was 254Vac.
Notice how small the change is before to after harmonisation.
The dual secondary does give you more options.
I meant your mains electricity supplier "have you asked what voltage"
We are on a nominal 230Vac supply where the maximum is 253Vac.
We used to be on a nominal 240Vac supply where the maximum was 254Vac.
Notice how small the change is before to after harmonisation.
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I would hope a mains voltage only 10% high wouldn't trouble the transformer itself, I'd expect its insulation to handle way more than that. In your case, I see the potential problems in the higher secondary voltages. But they too will only be the same 10% higher, assuming 240v applied to a 220v primary. SO 18vAC becomes 19.6v and the others similarly calculated. rectified and filtered, that becomes less than a 2v increase on DC.
SO if you plan to make 15v rails from those 18v secondaries, as an example, the input to the regulator will be a couple volts high, and most regulators are not spec'd so close as that would be a problem. In other words various gear rated 220 or 240 have been plugged into 220 or 240 mains for decades, and it usually works just fine.
SO if you plan to make 15v rails from those 18v secondaries, as an example, the input to the regulator will be a couple volts high, and most regulators are not spec'd so close as that would be a problem. In other words various gear rated 220 or 240 have been plugged into 220 or 240 mains for decades, and it usually works just fine.
Enzo,
the problem of using a 220Vac transformer on a supply that could be as high as 253Vac is that the primary may get too close to saturation and run HOT.
It may get so hot that the insulation fails, or that the in built thermal fuse ruptures, or that it just blows the mains fuse.
I see Iprimary on no load changing by over 100% going from 230Vac to 253Vac on some transformers.That equates to 220% of the heat in that transformer that needs to be dissipated.
One I posted about in another thread only increased by ~50% going from 230 to 253Vac, But even that one I modified to reduce the secondary voltage, since I regularly have 245Vac into a 230Vac rated primary.
If the transformer is not designed to survive the maximum mains voltage the increase in no load current could be very much worse than +100%.
the problem of using a 220Vac transformer on a supply that could be as high as 253Vac is that the primary may get too close to saturation and run HOT.
It may get so hot that the insulation fails, or that the in built thermal fuse ruptures, or that it just blows the mains fuse.
I see Iprimary on no load changing by over 100% going from 230Vac to 253Vac on some transformers.That equates to 220% of the heat in that transformer that needs to be dissipated.
One I posted about in another thread only increased by ~50% going from 230 to 253Vac, But even that one I modified to reduce the secondary voltage, since I regularly have 245Vac into a 230Vac rated primary.
If the transformer is not designed to survive the maximum mains voltage the increase in no load current could be very much worse than +100%.
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Test it first.. There is a small possibility that the transformer windings are something other than 110V.. Many people still consider U.S. mains voltage to be 110V and use that label out of convention, unfortunately that said many Chinese transformers with dual primaries are actually wound for 220V (110+110V). It's not wise to assume that they have built in sufficient margin for safe operation on harmonized 230V mains. (or even 120V U.S. mains - which in my house average 125V these days)
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