Fast Charger (includes 5XX & Scooba) mod for 220/230 Volts!

[vassilis_eco]

Hi everybody!
I received my Discovery last week, and faced the 110 Volts only problem of the included fast charger. I live in Athens, Greece, where we have 220Volts @ 50 Hz. I didnt want to use an external converter (not an elegant solution), since it is explicitly prohibited in the irobot documentation (!), so I did the next most prohibited thing, I dissambled the power supply!
The Discovery Fast Charger seems like a standard switching power supply, based on the TopSwitch Top245Y chip. The whole circuit should be OK for universal (110V-230V) usage, EXCEPT the input capacitor after the rectifying diodes, which is a 47uF @ 200V electrolytic. The 200V rating is OK for 110V mains, but will surely BLOW if used at 220V mains. So, I just replaced it with a 47uF @ 400V (you need at least a 360Volts capacitor when rectifying 220V mains).
The cost of the 400V capacitor over the 200V is only a couple of cents , so I guess that the irobot guys designed a proper universal power supply (the TOP245 chip is NOT the usual el cheapo chinese solution), and then the marketing guys decided to "lock" the product for US usage only by using the 200V capacitor.
The modified power supply is working fine for 80V to 240V mains input, without external converters. The whole modification costed less than a Euro, including the european power cord.
Some notes:
1) The modification will certaily void your warranty (and with good reason)!
2) Once you open the fast charger casing, you are exposed to LETHAL High Voltages. Any mistake can lead to components exploding & causing fire. This warning is not to be taken lightly, I MEAN IT. If you are not an experienced electronics technician (like I am), DONT EVEN TRY to open the casing.
3) Electrolytic capacitors have polarity, are mechanicaly sensitive and may blow anyway...
4) I cannot say for sure that there are no other components (namely the transformer), which will fail if the fast charger is used at other than the rated 110Volts. I will not be suprised if the charger blows on my face after a month, possibly ruining my roomba, but I am an adult and have taken my measures. I cannot be held responsible for you...
5) For those of you that use external converters with the fast charger, and if your charger is the same model as mine, the 50/60 Hz rating is not critical, but the output voltage quality is. If your converter outputs 110V RMS, this does NOT mean that the peak voltage will be less than the allowed 155 Volts. For example, I have a Remington 110 to 220V electronic converter, which outputs 110Volts RMS, but the peak (no load) output voltage is more than 200V. My converter would certainly blow the roomba charger! Please note that the peak voltage cannot be measured with a standard digital multimeter/voltmeter. You need an oscilloscope for that.
6) When I was testing my modified charger, I fed it with 60Volts AC, from a Variac. For a moment the charger output was at 40V DC! (had I connected the roomba, it would be destroyed...) It seems there is a bug at the design of the charger (at undervoltage conditions, the TOP245 can behave erratically and through feed the input voltage!). This condition (60Volts AC mains) would never happen in real life, but with a converter, how knows... Maybe this (and the [5] above) is the reason why irobot guys are so strict about not using external converters.
7) If in doubt, it is better to use a good 220v to 22Vdc 2Amp power supply, than a 220v to 110v converter.

BTW my wife loves our roomba. I am still waiting for the "roomba-clean-a-window" and "roomba-iron-a-shirt" models.

Cheers,
Vassilis

[Finch]

Wow, very impressive!!

Do you have any pictures?

[vassilis_eco]

I dont want to post any pictures, because I dont want to encourage anyone not familiar with electronics to try this mod. As I mentioned before, messing with a switching power supply can be dangerous.

[PHyde]

Thanks Vassili, excellent info for those of us in 220V+ regions. Thanks also for the clear warnings.

[astro]

I have modified the power supply of my discovery SE, and it works great with the 230v main. Neither switch heatsink nor the two transformers look like they're getting hotter than when fed with 120v and in my power suppply it also looks like all components are dimensioned for the full 110-240 range except for the filter capacitor. Thanks vassili!

There's a strange thing though: since I brought the roomba to europe, the power led blinks in a more reddish color than the usual amber. I would say that the red color of the led is totally lit while the green is only half way or less. Does that happen to anyone else? I've also noticed that the voltage while charging drops from 22V to about 18, and my theory is that the charging circuitry somehow complains about the "quality" of the input voltage by lighting the green less. Any idea?

[vassilis_eco]

Hi Astro,
I'm very happy that my mod worked for you.
One word of caution: I retested my charger at 60-80 VAC input, and it still outputs 40+ Volts! (see point [6] of my original post). This may be a problem of my charger, or it may be a general design fault.
I had already placed a 24V zener & 2A fuse at the output for overvoltage (crowbar) protection, and last night, after a serious mains power glitch at my neiborhood, the fuse & the zener blew! That means that during this power glitch the charger output was more than 24V for a considerable amount of time.
According to the TOP245 datasheet, the approx 2 Mohm resistor at the Line Sense pin of the TOP245 should shut it down at voltages below 100 VDC at the filter capacitor, but this does not happen on my charger.
To fix things, I replaced the 2 resistors (in series, totaling approx 2 Mohm) feeding the Line Sense pin, with a 5 Mohm resistor. The charger now starts up at 170 VAC input (not a problem really), and shuts down completely (without freaking) at 70VAC.
I'm keeping the zener & fuse protection, but now I'm confident that I wont be replacing them at the next power glitch.
I repeat that I cannot explain the charger failure (it happens at the 60-80VAC range, even when I shortcircuit the collector-emitter of the feedback optoisolator!!!), as the irobot circuit is quite straightforward and similar to the Power Intergration application example circuits. It may well be a problem with my charger only (I'm too lazy to replace the TOP245Y with a new one).

I cannot understand your remark about the blinking red light. The power button on my roomba slowly blinks red (not amber) when charging.

The output of my charger stays constant at 22.4 Volts, even when charging. In fact, it stays constant (with only 200mV drop) for up to 2 Amps of load.

Greetings,
Vassilis

[fraserinmelbourne]

Hello vassilis_eco, Have you experienced any problems with your charger since replacing the capacitor?

Ta,
Fraser

[Fred]

By approx 2M I assume you mean the 1M and 1.3M Ohm resistors R1 and R2?

-B

[vassilis_eco]

Re: fraserinmelbourne
Sorry for the delayed answer, it's been a while since I last checked the forum...
The answer is no, I had no problems. The charger is working OK several months now.


Re: Fred
Yes, I do mean R1-R2. The point is that the existing 2 MOhm totaling resistors SHOULD BE OK for proper undervoltage cutoff (according to the TOPSWITCH datasheet), but my charger has this curious behavor. I do believe this is a problem with my charger only. It would be interesting if somebody else could try the charger on a Variac...

[fraserinmelbourne]

vassilis_eco when mine arrives in Australia from the States, I'll give it a test on a variac, I think I have one lying around from an old power supply somewhere, I'll let you know the results.

[fred]

I did the mod last night, and it worked. However it does get warm / hot, is that normal? It does not seem to be make any noises etc, and seems to be holding at 21.8V steady....

I did encounter 1 problem however, probably not related....

The unit charged past 3 hours infact I suspect it would have kept charging for ever had I not stopped it. the battery pack was getting warm, so I know the batts were full at about 3 hours. when pressing the power button the unit showed green (full batt), so I thought maybe it's almost full, and leave it a bit..... nothing, still kept charging.... so I removed it from the dock and pressed the power again, this time it was orange, wierd..... so I removed the batt and restarted... green. at that point I just assumed that the units input processor has issues, it was full, and it needed to be reset. The unit worked fine until the batts ran out a few hours later (normal), it is now recharging again, I will see if it stops charging this time....

-B

[Fred]

Well I'm not sure whats ment to happen, but aftyer about 4ish hours the light finally went green, so I assume it charged correctly this time.... wierd, anyhow I think long term I may buy a better power supply, from what I have been reading etc, this one does not seem to be up to the job. I guess we will have to see how it goes.

-B

[vassilis_eco]

Hi Fred,

The roomba battery pack is made of 12 cells, 3Ah, NiMH. Charging a fully discharged pack at 0.3C (approx 1 Amp) would normally take more than 3 hours (the charger must provide 120% - 130% of the nominal 3Ah), so approx 4 hours is not alarming if the pack was discharged.
The voltage of each cell should rise to 1.47V - 1.5V for 100% - 110% of charge, so that amounts to 17.3V - 18V for a fully charged pack. Measure the cutoff voltage of the pack (the voltage of the pack when the light goes green). If it is around 17.4V, then you are OK.
The pack temperature can reach 45 degrees C easily. Remember that the motherboard PCB is located just next to the battery, and the charger circuit on it must dissipate some heat also.
Check http://www.gpina.com/industrial/batteri ... H_perf.htm for info on NiMH batteries (the roomba batteries are not GP though).

Regards,
Vassilis

[Fred]

Allthough I havn't checked my pack, it's wired that there 3Ah, as people have been replacing them with new 3Ah batts and getting longer run times.... I suspect there just "cheap" batteries...

-B

[Eric]

Thanks for all the wonderful information in enabling the charger to be modded for 220V. I do learn a great deal from this site... However, on searching for the 400V capacitor, I noticed that it is only available at a much larger size which the current board cannot take in unless it is extended to a daughter board. Do you guys happen to get them at the same size as to the original 200V? Also, if a 400V is not available, what is my chances to get by with a 250V on a 220V environment?

[vassilis_eco]

Greetings Eric,

Ask for a super-miniature capacitor, at 400V. The 400V rating is critical, anything less will blow! If you cannot find one, then use whatever size is available at 400V & 47uF or more. Extend the connecting wires, insulate them and put the capacitor over the PCB. Watch the polarity also!

Electric companies are allowed by EU laws to provide anything between -10% to +15% of the rated voltage, that means that they can provide up to 255V easily and lawfully. But this is only AC RMS voltage. The capacitor inside your power supply is loaded with fully rectified current not AC, with peak DC voltage equal to (AC RMS Voltage) * (sqr root of 2) = AC RMS Voltage * 1,414. That means that for normal 220V AC, you get at least 310 Volts peak DC on the capacitor, every day, every second. A 250V capacitor will blow in a few seconds. For 220V * 115% * (sqr root 2) you get some 360 Volts peak on the capacitor every other week. If you add up some momentarily overvoltage spikes and the capacitor derating due to ageing, the result is 400V, which is the MINIMUM ACCEPTABLE Voltage rating of the capacitor.

One last, polite, notice: If you feel that you dont have enough experience & knowledge for this kind of modifications, then dont try them. I'm sure you can find a proper 22V 1,5A power supply and replace the roomba charger alltogether.

Vassilis

[Eric]

Whew... that's a lot of info man! Thanks. Anyway, I was trying to do the mod as I thought the original charger might be better as the TOP245Y might be providing better charge than normal 22V adapters. Will try to mod for the 400V as you mentioned. BTW, I have used another switched supply at 22V, 2.9A. Just charge it once (as mine Roomba is still new) but it finished charging just after 2 hours. Running time for my red after that is only 15 minutes. Not yet charge the second time to confirm on the second running time. That's why I wanted to try on the mod on the original charger. Wish me luck!

[Eric]

It's confirmed... charged my RR again today using the 22V, 2.9A supply and the charging time now reduce to 1 hours then the power led turned green. Running time is down to around 10 mins. What a dissapointment... Is the charger running to much of a current to charge? Also, will it be better and ok if I use another charger of 19V, 1.6A? Meanwhile, I would still be doing the mod on the capacitor for the original charger; guess just have to search patiently for the capacitor though.

[Foxtrot]

Just received a 110V Discovery, and need to operate it off 220V/50Hz.

I understand from this thread that any 220V/50Hz to 22VDC 1.5A power supply will do. Is there limit to the current, or is any current higher that 1.5A ok?
Another question: is the original 110V charger just a DC power supply, or is it a smart charger that receives feedback from the battery pack and perhaps adapt itself accordingly.

Thanks,
Fox

[vassilis_eco]

The discovery charger seems to be just a 22V, 1.25A power supply, not a charger. All the charging circuits are inside the roomba, not even the docking station. Using a higher rated amperage PSU is OK, the Amp rating is just the maximum current that can safely be drawn from the PSU. Roomba will actually draw from nearly zero amps (when not charging...), up to approx 1 amp. The only difference when using a high amperage PSU is that, in case of a short circuit, the PSU can output greater power and cause greater damage... (take it as a joke)
The output voltage rating is the important factor. Switching PSU are preferable, because even the cheap ones have rather stable output. But cannot be sure until you measure it under load.

Eric,
does your roomba stop after 10 minutes due to empty batteries? Are you sure that there is no other cause? Have you measured the voltage of the power supply while charging? Your description does not make sense, even if you had a faulty battery.

Also, in my previous posts, I was referring to the fast charger of my roomba discovery. You are referring to a roomba RED. From what I understand, the roomba RED charger is NOT the same as mine. I have no idea what your charger looks like, let alone how to mod it for 220Volts. Please, try to get an experienced person to look at your roomba & charger. Maybe something is wrong, and irobot will not replace roombas used in Europe.