Converting a cordless drill charger (Hitachi UC18YKSL) from 110V to 220V

[John_doe]

Greetings, electronics gurus.
Prior to buying a cordless drill from Amazon US, I came across several people saying that sometimes the battery pack charger can be converted to work natively off 220V (which is the mains voltage here in Israel) thus saving the clumsiness of a bulky and heavy mains transformer. I read up very briefly on the process and decided to give it a try once the drill arrives (because I didn't know the exact charger model). When it did arrive, I started looking for specific instructions for my charger and received some good and bad news:
The good news: If you speak Russian, you can find instructions on how to convert every single battery charger ever created (or so it seems...).
The bad news: I don't speak Russian

Anyway, if I understand correctly, all recent Li-Ion battery chargers start the circuit with a Switched-Mode PS, but not all SMPS's are created equal - Some 110V models have a voltage doubler (E.G. some Milwaukee and Ryobi chargers), they use 2 smoothing capacitors in series and create around 310V DC for the PWM controller chip and the chopping MOSFET to work from. These chargers are very easy to convert with absolutely no downsides.

The other 110V chargers create around 155V for the chopper, and unfortunately, the Hitachi UC18YKSL (also sold under the names "Metabo HPT UC18YKSL" and "Hikoki UC18YKSL")  is of the latter kind.

Now here is the weird part, some people claim they have converted such chargers by simply replacing the main smoothing capacitor from 250V to 400V (and if applicable, some other non tolerant components such as the MOV and other capacitors) and the charger works with no side effects on double the DC voltage.

Here is a schematic of the first stage of my charger (Please forgive the sloppiness, there is a good reason this is posted in the beginner forum ):



Note: The block named "Control circuit" is a lot of small components and includes the PWM control IC which has "787205" written on it (not sure about the package but maybe SOT-23-6 ?).

The thing is, I don't really want to spend too much time and effort on this conversion. Things like removing the transformer, rewinding it, or even monitoring the temperatures of parts are things I just can't spare the time for right now.
On the other hand, replacing capacitors, resistors and even the MOSFET are things I don't mind doing.

I guess my question is, is there an easy way to convert this charger?
Will just replacing C2 be enough (won't it stress the transformer)? And if not, is there a simple way to drop the voltage to rectified+smoothed 110V levels?

Here are some photos:




I'd love to hear some opinions because I found very little information on the topic online.
Thanks.

[george.b]

The MOSFET might withstand the 220V mains. Assuming a turns ratio of about 1:10 (155 V -> 15V-ish), and assuming it's a flyback converter, the maximum V_DS the MOSFET will see will be in the vicinity of 475V, plus the voltage spike during switching. The MOSFET is rated for 600V.
What amplitude will the spike be? Will the original snubber be sufficient to suppress the spike? No idea.

Will just replacing C2 be enough (won't it stress the transformer)?

Good question. We don't know the transformer parameters. Maybe it works, maybe it'll saturate. Maybe it'll output a higher voltage than the controller can take and it will go poof. It's hard to tell without knowing how the transformer was designed and/or at what point it originally operates... or without experimenting. Dunno how attached you are to this charger (i.e. how willing you are to risk setting it on fire).

[james_s]

Do they offer a 220/240V version of that charger? If you can find a picture of the inside of one that might give you some clues. If it looks identical then there are probably only minor differences.


Google Translate supports Russian, although I have no idea how well.

[rstofer]

Step down transformers are pretty cheap:

https://voltage-converter-transformers.com/collections/step-down-voltage-transformer-converter

[John_doe]

Will the original snubber be sufficient to suppress the spike? No idea.

I think the snubber diode is FR107 but I'm not sure. Will it help if I desolder it and give you the exact model?

Dunno how attached you are to this charger (i.e. how willing you are to risk setting it on fire).

Not attached at all (to quote Jimmy Pop: "Let the mother****** burn!"), but the question is, will fully discharging the battery and then fully charging it once while keeping an eye on the temperature be enough to determine it will always be stable? Because the drill (actually drills, plural, because I bought 4 of them) will not be used by me.

Do they offer a 220/240V version of that charger?

Seems like they do:
https://www.amazon.co.uk/Hitachi-93199708-uc18yksl-Charger/dp/B01GVTZGV6
But I couldn't find any photos of the circuitry

Google Translate supports Russian, although I have no idea how well.

From experience: Not too well... If all you have to translate are a few lines it's OK most of the time, but a lengthy research takes forever.
Also, YouTube's speech recognition is far from perfect which makes it hard to watch videos showing the conversion (Because I'm not looking for what they do, I'm looking for why they do it).

Step down transformers are pretty cheap

Well... Cheap compared to what? A transformer for this charger will cost about half the price of the complete drill package (drill+charger+battery+bag).
But as I said in the OP, it's more an issue of these transformers' size and weight.

[james_s]

Hikoki? That looks like a cheap knockoff of a Hitachi charger? I wouldn't trust that to have any internal similarity to the real deal. If you can find a genuine 240V charger for a not too unreasonable price it might be worth buying one of the real deal so you can compare.

[John_doe]

James, I was told by a professional that when it comes to power tools, "Hitachi", "Hikoki" and "Metabo HPT" are the same manufacturer but have different names in different countries. I actually never tried to verify this... I'll look now.

[james_s]

I have no idea, that may be true. I know there are tons of Chinese brands deliberately made to resemble popular western brands. I don't know what gets marketed to the rest of the world.

[BravoV]

Hikoki? That looks like a cheap knockoff of a Hitachi charger? I wouldn't trust that to have any internal similarity to the real deal. If you can find a genuine 240V charger for a not too unreasonable price it might be worth buying one of the real deal so you can compare.

Hitachi power tools company is officially now named Hikoki.

[Marck]

Here are some pictures from the inside of the Australian 230v - 240v  50Hz version of the charger.  If you need more detail let me know. 

[John_doe]

Thank you, Marck!
Unfortunately, it looks like your charger is a UC18YFSL:
https://www.amazon.com/Hitachi-UC18YFSL-14-4V-Lithium-Battery/dp/B07F93BFWQ

Which is different from my UC18YKSL:
https://www.amazon.com/HITACHI-UC18YKSL-18-Volt-Universal-Charger/dp/B01M8PVTBW

But I really appreciate the effort! 

[george.b]

I think the snubber diode is FR107 but I'm not sure. Will it help if I desolder it and give you the exact model?

Not really, no. The diode is just part of the snubber circuit (R? and C3, as well as R7 and C5, being the rest of it). It's not exactly trivial. http://www.ridleyengineering.com/images/phocadownload/12_%20flyback_snubber_design.pdf

Not attached at all (to quote Jimmy Pop: "Let the mother****** burn!")

Then the issue of whether the snubber is sufficient or not isn't that important, I mean, if the 600V MOSFET can't take it, an 800V one probably will at the expense of some added EMI. Just replace the primary filter cap and see what happens?

but the question is, will fully discharging the battery and then fully charging it once while keeping an eye on the temperature be enough to determine it will always be stable? Because the drill (actually drills, plural, because I bought 4 of them) will not be used by me.

That depends on how marginal (or not) it becomes. How warm the transformer gets is a good indication - if the core saturates, losses will be higher, possibly to the point of self-destruction, so that's the main thing to look out for, I think. I would test it a couple times - maybe recharge all 4 batteries in succession? Not the same as factory reliability testing, but...

[james_s]

Hitachi power tools company is officially now named Hikoki.

Interesting, I wonder why they would do that? Hitachi is a very well recognized and respected brand. When I saw Hikoki I just assumed it was one of those Chinese knockoff brands like Solny or Panashiba.

[george.b]

I just found some comments in a Russian site saying it works by just replacing the primary capacitor for a 400V one.

Здравствуйте, есть зарядка Hitachi UC18YKSL, подскажите пожалуйста, как ее переделать в 220В

"Hello, I have a Hitachi UC18YKSL charger, please tell me how to convert it to 220V"

Скорей всего только заменив основной выпрямительный конденсатор со 100мкФ 250В на 100мкФ 400В.

"Probably just by replacing the main rectifier capacitor, from 100µF 250V to 100µF 400V".

Все работает, заменил только конденсатор на 400v.

"Everything is working, I just replaced the capacitor for a 400V one".

So it should work

[magic]

No one mentioned R2 yet? This will now be running at 4x its former power dissipation, but it's still 0.12W if I got my math right so probably OK. I can't see where this resistor is and its power rating.

[Nerull]

Hitachi power tools company is officially now named Hikoki.

Interesting, I wonder why they would do that? Hitachi is a very well recognized and respected brand. When I saw Hikoki I just assumed it was one of those Chinese knockoff brands like Solny or Panashiba.

It's essentially a repeat of HP/Agilent/Keysight. Hitachi sold off their tool division to a separate company who can no longer use the Hitachi trademark.

It's also not Hikoki everywhere. In north america the new name is Metabo HPT, not to be confused with Metabo, the existing German company owned by the same parent company that bought Hitachi Tools. Metabo and Metabo HPT tools, chargers, and batteries are not interchangeable. 

[Electro Detective]

Who's going to remember 'Hikoki' ?   

if they were too cheap to pay for the 'Hitachi Tools' brand name,
they should have at least hired Bruce Banner to do some live infomercials

and plant some jeering trolls in the audience   

[John_doe]

Then the issue of whether the snubber is sufficient or not isn't that important, I mean, if the 600V MOSFET can't take it, an 800V one probably will at the expense of some added EMI. Just replace the primary filter cap and see what happens?

Thanks George, I'll do that when my caps arrive from China (bought them almost 3 weeks ago).

That depends on how marginal (or not) it becomes. How warm the transformer gets is a good indication - if the core saturates, losses will be higher, possibly to the point of self-destruction, so that's the main thing to look out for, I think. I would test it a couple times - maybe recharge all 4 batteries in succession? Not the same as factory reliability testing, but...

Not all batteries have arrived yet, but what I could do right now is check the temperatures for one discharged battery at 110V. Unfortunately, I've had two setbacks: 1) Both of my 220V -> 110V transformers seems to be defective (Odd, because I don't remember them breaking down...), but fortunately I already ordered a new one beforehand which is scheduled to arrive in a few days. 2) I had problems discharging the battery. I first tried with my Turnigy B6 PRO (an Imax B6 clone), but it refused to discharge claiming low voltage (My guess is that it needs to use a balance connector), so I just connected some power resistors directly to the positive and negative terminals thinking it will discharge until the protection circuit kicks in. About half an hour later I checked and the DMM showed 0.6V - I thought "great, overdischarge protection working as it should", but when I disconnected the resistors it didn't immediately jump to 15V as I expected, instead it very slowly creeped up (E.G. after 5 minutes it was at 6V). So I opened the pack and measured the voltage directly on the 5x18650 terminals:


It was the same as the positive and negative terminals on the pack socket.

So, I overdischarged the battery pack... That's great
I still don't understand, how can a cordless drill battery pack not have overdischarge protection? Maybe I used the wrong terminals? These are the ones I connected the resistors to:


Sorry for going off-topic, I was just curious.

I just found some comments in a Russian site saying it works by just replacing the primary capacitor for a 400V one.

Yes, to be honest, I also found similar posts but I was wondering about the longevity and stability of a post-conversion charger. I reckon it's just like you suggested before - there's no other way to be sure until I replace the cap and monitor the temperatures of the usual suspects (transformer, snubber , etc).
I'll post an update when the stuff I need arrives.
Thanks again for all the help.

No one mentioned R2 yet? This will now be running at 4x its former power dissipation, but it's still 0.12W if I got my math right so probably OK. I can't see where this resistor is and its power rating.

R2 is hiding behind the MOSFET heatsink. Judging by the size (roughly 9mmx3mm) it's a 0.5W resistor. So, IMHO, should be a little hot but still within spec. I think if I'll measure 40°C over ambient (so around 65°C in my house) I'll replace it with a bigger sized one.

[james_s]

What's wrong with your step-down transformers? There is not much to go wrong with a transformer, look closely for a bad connection.

The over-discharge protection may be in the drill itself instead of the battery. If you are working with the battery directly that would bypass that.

[John_doe]

What's wrong with your step-down transformers? There is not much to go wrong with a transformer, look closely for a bad connection.

One of them Is just dead - no continuity on the primary.
The other is... It's just acting weird. Maybe it's just too small for the charger or maybe the charger itself is faulty, maybe I damaged it while taking it apart. I'll be much more informed when the new heavy duty transformer arrives.

The over-discharge protection may be in the drill itself instead of the battery. If you are working with the battery directly that would bypass that.

I considered it, but that just seems like very poor design! I mean, think about it, a brushed electric motor can consume dozens of amps when strained (E.G. when held in a vice) and even with thick wires there's still going to be a voltage difference between the cells and the drill. Not to mention that like most cordless power tools, these batteries are used in multiple devices and are interchangeable. The tool has no way of knowing the cells specification but the battery pack does. Again, IMHO it's just poor design, so I don't think that's what they did.

[james_s]

I considered it, but that just seems like very poor design! I mean, think about it, a brushed electric motor can consume dozens of amps when strained (E.G. when held in a vice) and even with thick wires there's still going to be a voltage difference between the cells and the drill. Not to mention that like most cordless power tools, these batteries are used in multiple devices and are interchangeable. The tool has no way of knowing the cells specification but the battery pack does. Again, IMHO it's just poor design, so I don't think that's what they did.

I fly electric model airplanes and this is exactly how it's done in those. The LiPo battery packs have no onboard intelligence, doing so would require a switching device built into the battery that is capable of carrying tens of Amps, this would be expensive, add weight and produce heat right where you don't want it. An additional very importan aspect that won't apply to a drill is that in most cases the main battery also powers the radio gear so if the battery cut out the plane would glide out of control and crash. Instead the BLDC motor controller monitors the voltage and will first reduce power then cut out completely if the voltage goes too low. Normally we use a flight timer though to prevent ever hitting this situation.

[John_doe]

So it would seem that I am an idiot. The drill itself has 3 pins connected to the battery pack plug: '+', '-' and 'LD'.
Googling this easily found that the LD pin is the overdischarge signal, so the battery pack does monitor the voltage directly on the cells but when it detects low voltage it signals the drill (I assume by taking the LD pin to high but I haven't tested it), where there is already the control circuitry, probably no MOSFET is needed, it just needs to disable the drill trigger button.

Funny thing is, I have a circuit I made with an arduino which measures battery capacity. It monitors a battery voltage and cuts the discharge current via a relay (SLA-05VDC-SL-A). I was just too lazy to find it.

Sources:
https://www.reddit.com/r/AskEngineers/comments/1ib2jd/question_about_my_drill_battery/
https://www.quora.com/What-is-my-Hitachi-Drill-Battery-ld-issue
https://www.physicsforums.com/threads/pinout-of-a-lithium-battery.927486/

[james_s]

You'll want to charge them back up to a reasonable level soon, letting Li-ion cells sit at a low state of charge is not good for them. With some care you can use something as simple as a bench power supply with a constant current mode or any power supply and a resistor to limit the current. Don't attempt to fully charge them like that but you can put enough in to get them out of the over-discharged state.

[pcmad]

check out big clive video

[John_doe]

Back with an update, and apologies for the delayed response - I didn't want to bump the thread without a conclusion.

Everything eventually arrived, albeit extremely late. The new 220V -> 110V transformer fixed the problem I had with my old one. I assume the problem was that it was just too small to provide the necessary power.
I ran into difficulties measuring the temperature. I don't have a thermal imaging camera and trying to use my UNI-T UT139C's type K thermocouple proved unreliable. So I resorted to using a cheap GM320 infrared thermometer, used like so:  While the charger was charging a battery, closed, but with the screws removed, I quickly opened it (while still charging) and measured.
To get the charger to really strain for max heat, I charged one empty 3Ah battery (BSL1830) for 30 minutes and then a second BSL1830 for an additional 20 minutes. The reason for the switch being that I didn't want the CC-CV charger to reach the CV stage where it will undoubtedly start to cool. The user manual states a 90 minutes charge time to full so I figured 30+20 minutes are a safe bet:



After some measurement sessions I found around 10°C difference between charging at 220V to charging at 110V with a transformer, give or take 1-2°C (The 220V was the higher temperature one, obviously).
And since the temperature was high even at 110V, I didn't like this 10°C elevation. I thought about a simple way to keep it low as the original and, although untested, I think it would've worked (Spoiler: capacitive dropper).

Alas, during my testing I found an insurmountable issue:
While discharging the batteries for the temperature tests, I notice something odd. I checked, then double checked, then triple checked and unfortunately the results were consistent: When charged from 220V, the battery capacity is lower.

BSL1830 charged via 220V mains:

(Capacity: 2333mAh)





Same BSL1830 charged via 220V to 110v transformer:

(Capacity: 2722mAh)



So this is a deal breaker for two reasons, 1st because I'm not willing to settle for the lower capacity, and 2nd because it shows that not only the SMPS phase is affected by the conversion - the charging circuit is also affected, and that, IMHO, is possibly unsafe/dangerous.

Anyway I'm just going to tell the people I gift these to, that they need to get a 220V -> 110V transformer to use the charger.
I just wish I knew that before I bought an additional 3 drills (They're just so darn cheap! ).


Many thanks to george.b and all the helpers and participants! You guys make this forum great!