Convert 220v/50Hz illuminator to 120v/60 Hz. Safe to plug in?

[mcfudge]

Last week Amazon shipped me a "great deal" of an item (1/3 price) but with the wrong specs -- European power instead of North American.  Is it safe to plug in to 60 Hz, or can this be converted to 120V 60Hz?  I've done a lot of reading but haven't found a clear enough answer.

It's an AmScope microscope illuminator (fiber optic dual gooseneck light) model HL150-AY.  Instead I think it should read HL150-AY-220V.  They make both models.  It has a European plug, is marked AC-220V 50Hz on the back, and the documentation indicates it requires 220V +/- 22V 50Hz +/- 1Hz.  I have a step up transformer to get 220V but the output is still 60 Hz.  I'm tempted to plug it in but for $200 I don't want to fry it.

GoHz has a 500 VA frequency converter for $1,100 USD, nice to have perhaps but buying that for this item defeats the "great deal".  I'll post some pics and hopefully I can get some advice including modifying the single mainboard as needed.  Thanks in advance.

Myles

[Zero999]

60Hz shouldn't be a problem. It's operating a 60Hz device at 50Hz which would be more of an issue.

[Gyro]

I'm not sure what lamp it uses, I'm assuming Halogen.

The PSU is a non-isolated forward converter, not a problem as long as all wiring is inside the grounded enclosure. Unfortunately I can't see any evidence of links or jumpers on the board to convert it to 120V, they must use a different PCB.


P.S. That's a really lousy choice of a mains input connector, I'm not even sure it's legal!  The mating socket has very little clearance between the contacts and the outside world (or the metal shell). Why on earth didn't they use an IEC?

[Yansi]

P.S. That's a really lousy choice of a mains input connector, I'm not even sure it's legal!  The mating socket has very little clearance between the contacts and the outside world (or the metal shell). Why on earth didn't they use an IEC?

It most then likely isn't,  but it is convenient that (school) laboratory equipment manufacturers are complete jerks that like to sell overpriced crap - I have seen more examples of this "obfuscatory" designs in school lab eq., to force customers buy only from them - the specific manufacturer, that makes the purest BS of all.

The PSU is of one of the worst junks I have seen. Not even sure why they have opted for this overly complex nonsense, they could have just used a 230V halogen bulb on a triac dimmer. Much cheaper, same result.

I do not see anything complicated to convert it to 120V.  Just rewire the full bridge rectifier into a half wave doubler circuit. (You will also need to replace the small mains transformer  though).

[Richard Crowley]

Is there no nameplate on the frame of the power supply module?
That looks very much like a modern switch-mode power supply (SMPS).
Virtually all SMPS are "universal voltage" and are designed to operate properly from 100V to 240V AC
Or in some cases, there is a switch or jumper, etc to switch between 100-120V and 220-240V

The power mains FREQUENCY is of no importance at all.
Because the SMPS is converting the power to very high frequency AC, and then to DC, so it makes no difference what is coming in.

Traditional "linear" power supplies used a "heavy iron" transformer that operated directly at the mains frequency. Many products that were designed for use at 60Hz will overheat at 50Hz because of the marginal (cost-cutting). But SMPS do not suffer from this phenomenon.

I agree that is a particularly poor choice for the mains input connector.  If you don't modify the unit to use an IEC connector, I would certainly avoid handling it especially when plugged into the mains outlet. Connect it and tighten the ring and never remove it when plugged in.  I would remove it and substitute a proper IEC connector.

[Gyro]

...
I do not see anything complicated to convert it to 120V.  Just rewire the full bridge rectifier into a half wave doubler circuit. (You will also need to replace the small mains transformer  though).

I think that's a choke, PFC? I can only see two wires.

[Richard Crowley]

The 110V version of this gadget also claims "Power Frequency: 50±1Hz"
And: "Supply voltage: AC 110 ± 20V"

I don't know of anywhere on the planet (except perhaps parts of Japan?) that have 110V, 50 Hz mains power.
And the "±1Hz" seems particularly silly and ignorant. There is nothing in that gadget that is frequency-sensitive in the least.  Even the cooling fan is an industry-standard low-voltage DC (likely 12V) fan.

[Yansi]

And the "±1Hz" seems particularly silly and ignorant. There is nothing in that gadget that is frequency-sensitive in the least. 

The input capacitors are what is the frequency dependent component. Too low frequency and it will not filter enough. Too high frequency and you will smoke the diode bridge.

Is there no nameplate on the frame of the power supply module?
That looks very much like a modern switch-mode power supply (SMPS).
Virtually all SMPS are "universal voltage" and are designed to operate properly from 100V to 240V AC
Or in some cases, there is a switch or jumper, etc to switch between 100-120V and 220-240V

Very wrong assumption I would not expect from you Richard. Not even close to all power supplies are wide input range.  This one certainly ain't and NEVER do assume such thing!

This is a clearly half-bridge power supply with a pair of bipolar transistors (no modern power supply at all! Ultra cheap one at best), with likely a passive PFC (using the choke I mislabeled as a small transformer). This power supply is NOT wide range input.

To switch it to 110V, you would need to modify the bridge rectifier to doubler and replace the PFC choke.

//EDIT: It indeed is a small transformer - to power the fan.

[Zero999]

I don't know about other countries, but 110VAC 50Hz is a common voltage in factories and building sites in the UK, but I agree, the frequency isn't important.

Changing it to a voltage doubler would require the capacitors to be replaced with much larger ones. There's also a small mains transformer fixed to the chassis, which would have to be replaced with a 120V one or be reconfigured, assuming it has two 110V or a centre tapped primary.

There's a valid reason for using a lower voltage halogen lamp, over one designed to run straight from the mains: it will have a thicker filament which means it can be run at a higher temperature, giving a longer life and better quality light.

[tooki]

I don't know of anywhere on the planet (except perhaps parts of Japan?) that have 110V, 50 Hz mains power.

According to Wiki, there are the following 120-ish volt systems at 50Hz:
- Jamaica is 110V/50Hz
- Barbados and parts of Bolivia are 115V/50Hz
- Curaçao, Libya and parts of Madagascar and Morocco are 127V/50Hz.

Japan is unique: it's 100V. And for historical reasons, it's 100V/50Hz in east Japan, and 100V/60Hz in west Japan. I expressly don't consider the Japanese 100V to be a "120-ish volt" system, because 100V–tolerance is too low for many non-SMPS devices to work, and conversely, 120V+tolerance can be enough to fry some 100V devices.

[james_s]

The input capacitors are what is the frequency dependent component. Too low frequency and it will not filter enough. Too high frequency and you will smoke the diode bridge.

Not to any degree that matters. Anything from about 40Hz to 400Hz or more ought to be just fine with a capacitor and rectifier intended for 50 or 60Hz. Sure if you feed it 20kHz you will probably have issues but that's way outside of the frequency of any mains system.

[mcfudge]

Yes, the lamp is 24V 150W halogen.

[StillTrying]

I'd have plugged the 220V 50Hz device into the 120V 60Hz by now, I'd be surprised if it actually blows up.

[mcfudge]

Hey Richard,

Uh no nameplate, it's so basic and cheaply manufactured.  And the only identifying marking on the board is underneath the S20LC20U rectifier just above the PFC choke ("BC-150 1407 126531"), image attached.  The obscured components are TL494 PWM control chip, two Toshiba C3306 NPN (left side) and two bridge rectifiers KBPC110 and KBU810.  They weren't captured well in my original photo.  AmScope makes several claims in their brief 3+ page operating instructions pamphlet.  I'll include a couple screenshots of it.

In the case of this board, there doesn't appear to be any intended method to easily switch between 120 V and 220 V.  There are only a few unpopulated locations - CE5, C2, C3, and the rear of the chassis only has a fuse, mains power switch, and that epic mains input connector.

Thanks for the advice re IEC.  I do plan to make that modification.  It probably goes without saying that this device bears no electrical safety certification for NA or elsewhere.

[Richard Crowley]

Despite anyone's protestations otherwise, I don't see any way that could possibly be a linear power supply.  That is clearly a SMPS with the added feature of a variable output via the front-panel control.  Neither of the visible inductors are anything but ferrite-core high-frequency design.  You could confirm by looking at the value of those large capacitors.  If they are low voltage (30-60V) then that is a linear supply.  But if they are high voltage (200-300-400V) then that is clearly a SMPS.

And IME, there is absolutely nothing about it that cares about the power mains frequency, 50Hz, 60Hz or anything around that range.

My only question would be whether it would operate with 120V AC mains power input.  IMHO, there is little risk of simply trying it.  I would plug it in with the cover removed for observation and temperature monitoring.  I would turn it on for a few seconds and see if the lamp lights to full brightness and if the control works as expected. 

Best case would be that it will simple work properly and we are done here.  Worst case would be that it won't work and may even overheat one or more of the power supply components.  That is why I would try it for only a few seconds to start with in case the SMPS misbehaves.

Beware of the hazards of mains-powered SMPS. Those large capacitors are probably high-voltage (hundreds of volts) and will retain a good amount of energy even after power-down.  It is always good practice to discharge all of the larger capacitors before poking around inside.

[Yansi]

Jeesus crist, if you have one.

Do NOT plug this thing to 110V. It will NOT work without any mod! Done deal! It is only a single range (220V+-10% or such) designed half-bridge power supply.

The output in such condition will NOT light to full brightness. Rewire at least the diode bridge to a voltage doubler!

Even if it tries to work at the low voltage, it will end up with a damage of some key components, due to higher currents required by continued low voltage operation.  There are NONE undervoltage protections in such SMPS and likely even NONE overcurrent protection on the primary side.  (FUSE is not an overcurrent protection for the semiconductors, FUSE is protecting against the risk of possible fire, it does not protect semiconductors!).

Or just give to someone who can mod it safely for you.   

[mcfudge]

Those large caps are 250V 470uF, pic attached.  Since I already have a 220V step up transformer, I can give it a try @220.  I won't plug it into the local 120VAC without modification, as recommended.

[Jwillis]

Lets look at a SMPS that has a mains input switch. Here's one I have and note what the switch does. So lets do the same to yours using a jumper wire. The frequency of the mains input makes no difference because of the primary rectification to DC.The PWM converts that DC back into a very high frequency (around 30KHz)AC square wave into the transformer.

[james_s]

Trace out a schematic of the input rectifier and filter capacitors. Quite a few SMPS designs use a 330VDC bus regardless of whether they're made for 120 or 240V. The difference is that 120V models wire the rectifier and capacitors as a doubler while 240V models will full wave rectify the input. I have converted a couple of 120V devices to 240V by rewiring the input section and adding a second capacitor, the reverse is easily done too.

[mcfudge]

As expected, working fine at 220v 60Hz.  No noticeable heat after an hour or two.  Thanks so much.  Really great help here from you guys!  Especially helpful watching the back and forth dialogue from the more experienced guys.  I'll start on the other mods soon.  Now to show someone why their nasty micro hdmi and micro usb connectors aren't working...

Myles

[Jwillis]

Eew!

[Yansi]

Trace out a schematic of the input rectifier and filter capacitors. Quite a few SMPS designs use a 330VDC bus regardless of whether they're made for 120 or 240V. The difference is that 120V models wire the rectifier and capacitors as a doubler while 240V models will full wave rectify the input. I have converted a couple of 120V devices to 240V by rewiring the input section and adding a second capacitor, the reverse is easily done too.

I have said that far back in the fourth post. 

[james_s]

Good for you, I didn't see the 4th post, nor does it appear that this has been done.