As I've recently learned from @bertus, Japan has a 100 VAC system. At this point I would not suggest trying to plug your supply into a 240 line. Not unless you don't mind chancing the possibility of blowing out your supply.

Back to your original proposal: Use of a Variac (variable transformer) - I don't see why it would be a problem. But then again, it's not my money and equipment on the line. At this point I can give you no further assistance. I hope you solve your problem. ME? I'd opt for buying a supply that can work from a 100 to 240 input.

You don't say where you're from. I'm in the US. When I want a 12 volt supply of around 2 to 4 amps I just go to the local cable company and ask them if I can have one of their returns. They don't reuse the old supplies, and I often can get two at a time. Xfinity and DirecTV are a few places I can go to get power supplies for free. If you have such in your area, perhaps you can give that a try. I also find a lot of old printers that have external power supplies. I've found one at 30 VDC, one at 18 VDC and one with two different voltages, I don't recall. I don't know if that will address your needs but it's worth a shot if you can get your hands on something like that. Last year I modified one of those freebee PS's from 12.1 volts to 13.8 volts by varying the resistors on the reference voltage. I use it to keep an old car battery in the garage topped off so that when I'm working on the car I can play an old car radio. Works sweet.

Bottom line, be creative. But also be careful.

Hi Tony,
Thanks for your feedback. I will be taking the risk and plug it into my Variac.
JL

 

100 volts has been the standard in Japan for a long time. Like zillions of others sold all over the world, the charger likely uses an iron core transformer and was designed for a specific location. Use your variac box and don't fuss about it. It will work just fine.

Yes, actually I bought this Variac sometime back mostly for the purpose of handling equipment with AC voltages from 100V (Japan), 110(US), 220, 230 and 240. The variac hasn't been used so far other than powering a light bulb just for fun from 100V to 240V. So I'll give it a go by this week.
Thanks.

 

Just make sure it does NOT have a rectifier on the output that would make it output DC. Check with the manual that the output is AC.

Les.

 

Post #20 is RIGHT!! So a series diode would destroy the device rapidly. the variac device will work quite well. An option not mentioned is to use a 24 volt transformer, wired as an auto-transformer, to step down the local 120 volts to 100 volts. But for use in the 200 volt world you will need to find a 24 volt transformer with the dual voltage primary option, and then connect the 24 volt winding to the center tap. A bit of voltmeter checking will reveal the correct phasing to provide you with the desired 100 volt output. BUT CAUTION, this circuit IS NOT isolated from the mains, so proper wiring and insulation FOR 220 VOLTS IS REQUIRED. Somebody else can draw out the circuit if you need it.

 

Just make sure it does NOT have a rectifier on the output that would make it output DC. Check with the manual that the output is AC.

Les.

Just make sure it does NOT have a rectifier on the output that would make it output DC. Check with the manual that the output is AC.

Les.

Yes the output is AC. I should have posted a picture of the box earlier. Those yellow stickers are from me to remind myself not to turn on immediately after turning off.

 

Post #20 is RIGHT!! So a series diode would destroy the device rapidly. the variac device will work quite well. An option not mentioned is to use a 24 volt transformer, wired as an auto-transformer, to step down the local 120 volts to 100 volts. But for use in the 200 volt world you will need to find a 24 volt transformer with the dual voltage primary option, and then connect the 24 volt winding to the center tap. A bit of voltmeter checking will reveal the correct phasing to provide you with the desired 100 volt output. BUT CAUTION, this circuit IS NOT isolated from the mains, so proper wiring and insulation FOR 220 VOLTS IS REQUIRED. Somebody else can draw out the circuit if you need it.

Thanks for this alternative. I may need it in case the variac fail one day.

 

Well, I plugged the charger into the variac set at 100VAC. There is some unexpected behavior but this could be due to my lack of knowledge.
I was observing the current draw from the variac on the front panel. At 100V, it settled at approx 0.4A after a while. I'm assuming this current is the output current from variac. Then I noticed the current climbed rapidly to as high as 2.6A for a short while and then back down to 0.4 A. I wasn't expecting such a high current draw from the charger, given the specs says the charger is rated 27 Watts. Is this the normal behavior of a charger? I posted a video to illustrate what I mean.

.
Luckily, nothing blew up. The charger and battery wasn't hot and the charger indicator lights behaved according to the charger specs. It took about 50 mins to reach full charge. Any feedback on the large current output from the variac and/or the rapid fluctuation on current is appreciated.

 

I can't see why there should be any problem. The only thing I can think of is that the 2.6 amp reading was due to the none sinusoidal current waveform that the charger may draw causing the current meter to give a false reading. I am assuming that your "variac box" uses the toroidal transformer as a 1:1ratio isolating transformer whose output is fed to the variac. The output socket is connected to one end of the variac winding and the slider on the variac. I expect the small transformer provides the power to the two digital meters. If it was me I would trace the wiring in the box to see if my assumption was correct. It is quite possible that the charging current is changed at different points of the charging cycle so the input current would also change.

Les.

 

I can't see why there should be any problem. The only thing I can think of is that the 2.6 amp reading was due to the none sinusoidal current waveform that the charger may draw causing the current meter to give a false reading. I am assuming that your "variac box" uses the toroidal transformer as a 1:1ratio isolating transformer whose output is fed to the variac. The output socket is connected to one end of the variac winding and the slider on the variac. I expect the small transformer provides the power to the two digital meters. If it was me I would trace the wiring in the box to see if my assumption was correct. It is quite possible that the charging current is changed at different points of the charging cycle so the input current would also change.

Les.

Thanks. Glad to know there should be no issue. Not sure when I might be opening the box again. Weighs 34 lbs. The reason why I opened it the last time was to install a NTC thermistor but I found out later there was already one installed.
Anyway, If I do open it again, I'll post some pics.
jl

 

It is easier for you to trace out the schematic as it is often not possible to trace wires that are part hidden in pictures.

Les.

 

(Some text removed for clarity) The reason why I opened it the last time was to install a NTC thermistor but I found out later there was already one installed.

If it turns out to be a PTC thermistor, that could explain the current surge at turn-on. Such mistakes happen in stock rooms, purchasing offices, and sadly enough in sustaining engineer offices.

 

Yep, 100V is normal in some parts of Japan. We had two SEM's (Scanning Electron Microscopes) from Japan in the US, One, an ISI had an external transformer as part of the decor (Painted to match) and likely came with unit. The other one was Jeol. With that one, we put a non-isolated variac on the wall and took the knob off so it works on 120 V.

 

It is easier for you to trace out the schematic as it is often not possible to trace wires that are part hidden in pictures.

Les.

Oh, I thought you were referring to the physical trace. Unfortunately, there's no schematic. The documentation, if I can call it as such, has minimal information.

 

If it turns out to be a PTC thermistor, that could explain the current surge at turn-on. Such mistakes happen in stock rooms, purchasing offices, and sadly enough in sustaining engineer offices.

Initially, I thought there was no thermistor because it tripped the circuit breaker. But when I opened the unit, I saw a thermistor with NTC printed on it. I then realised that the last time it tripped was because I turned it on immediately after turning it off. It seems to behave well now that I realised I should not have turned it on immediately after switching off. There was no mentioned of this nor the thermistor in the documentation.

 

Battery charging runs through a number of stages and so the current draw will certainly vary as the battery charges and as it heats up from charging.

 

The power rating of 27

Battery charging runs through a number of stages and so the current draw will certainly vary as the battery charges and as it heats up from charging.

I was not expecting such a huge variation. Anyway, the specs for the charger says 27 Watts so this time round, I took a clamp meter to compare the reading on the variac. What I got was the reading from the variac and the clamp meter vary widely.

almost full charge

full charge 11mA trickle

The clamp meter stayed fairly constant during charging except when nearing full charge. Just to be sure, I use another
clamp meter and both showed approx same readings.
Now I'm wondering whether the panel ammeter is highly sensitive, inaccurate or both. Or maybe it's showing the input current into the box? Unlikely. Maybe next charge I'll measure the input.

 

Yep, 100V is normal in some parts of Japan. We had twp SEM's (Scanning Electron Microscopes) from Japan in the US, One, an ISI had an external transformer as part of the decor (Painted to match) and likely came with unit. The other one was Jeol. With that one, we put a non-isolated variac on the wall and took the knob off so it works on 120 V.

Jeol. That's a name I hadn't heard in a while. I worked on a Jeol cross-section TD SEM and a few other 100VAC analytical Jeol tools that Fujitsu Microelectronics had in the states during the 90's.

 

It certainly is interesting that there is so much variation. I wonder if the issue is harmonic content, or maybe temperature. It may even be a loose wire inside your supply.

 

Yours sounds like a good question for the manufacturer. Maybe the best way to ask would be to ask how to recharge with a 240 volt supply, a question they may be prepared to answer.

Panasonic Japan came back with a reply that I'll like to share.

"The reason why we don't recommend to use step down transformer is because we didn't test our product and therefore can't guarantee its quality in the usage condition. If you will use transformer under your own responsibility, technically it's possible to use."
Well, I guess the answer is yes, you can use a transformer to step down from 230 to 100V to power the battery charger but at your own risk.

 

If the device that you are using is really an adequate transformer then it will not have any problem. Some groups call their modules transformers even if they are something else, because most folks have no idea what an actual transformer is. The variac package in the pictures is certainly a real transformer device and will be fine, even if it is inconvenient to carry around.