EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: subhajit on April 19, 2021, 06:19:04 pm
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Hi,
I bought an LG Sound Bar (SJ7) with sub-woofer in US. The speakers have power adaptors and run both in India (230v) and US (120v). However the sub-woofer takes raw power and there's a sticker pasted which says 120v. Looking at the PCB can anyone share some knowledge on whether this will run in 230v? I googled with EBJ63030301 (written on the transformer) and it says Switching Transformer. Thanks in advance.
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no one to help here? So I try...
240VAC tolerant switching power supplies normally (!) have no problems with 100 VAC. Vice versa is a lot more difficult: Board layout and all primary components have to stand much more voltage, i.e. rectifiers, primary capacitors, isolation, air gaps ... This is not only a question if the components can handle 350 VDC, but also a question of safety. I remember SONOS-like components sold from China in Europa, which I NEVER would use due to unsufficient gaps between conductors.
All this I cannot verify on your picture. For a first idea, look at the values printed on the big capacitor. It should accept at least 350, better 400V. If not so, forget any affords and look for another power supply...
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You really need to reverse engineer the whole mains side of the supply to be sure. That it wasn't marked universal voltage isn't a good sign.
Might also see if those board numbers cross ref to a 240V product.
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Look at voltage rating on the largest electrolytic capacitor (top left corner). If it's less than 350V, then this PSU certainly is not suitable for 230V.
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Picture I found says it's rated for 110-240V
(https://i1.wp.com/musicphotolife.com/wp-content/uploads/2017/08/LG_Soundbar_Flex_SJ7_4.jpg?w=1067&ssl=1)
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Another says 120V
(https://cdn.shopify.com/s/files/1/1886/0165/products/IMG_6612_530x@2x.JPG?v=1571439834)
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So there is a chance they use the same PSU for different markets but use different rating on the label.
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Check voltage rating on main round capacitor as well as grey and yellow parts (see image).
Fuse is 350V rated, no voltage selector is on the board. It could be rated 1110-230V overall.
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So there is a chance they use the same PSU for different markets but use different rating on the label.
A chance. But it makes sense to modify/optimize PSU for lower voltages. A wide range PSU is convenient, but the primary capacitor has to be big enough to cover low voltage mains at high loads. Manufacturer can save $$$ if you use components for less voltages. Over voltage protection must be adapted, too.
A voltage selector on a switching PSU? what for?
Check the marked items, as we all said. And yes, it's a kind of reverse engineering ...
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A voltage selector on a switching PSU? what for?
Common in higher power switchers, e.g. PC supplies, there will be two mains smoothing caps and a switch. In the "240" position the mains input circuitry is configured as normal. Switched to "120" the mains input circuit is reconfigured to a voltage doubler.
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A voltage selector on a switching PSU? what for?
Common in higher power switchers, e.g. PC supplies[/b], there will be two mains smoothing caps and a switch. In the "240" position the mains input circuitry is configured as normal. Switched to "120" the mains input circuit is reconfigured to a voltage doubler.
Not in the last 15 years. Only shittiest computer PSUs have them. And something like that is almost certainly illegal to sell in EU and many other places unless they put some huge passive PFC inside. But in low power PSU it makes very little sense to add such switch to get wide input voltage range.