iRobot Roomba/Scooba 110V to 220V mod

If have bought or want to buy a iRobot Roomba Discovery series (second generation: Discovery, Scheduler, etc) or Scooba 5800/5900 in the US and want to use it in Europe, you need to modify the included power supply that works only with 110 Volts mains.

<Roomba Discovery Series>

<Scooba Series>

 Why do I need to make the mod?

It’s not possible to use an external 220V -> 110V converter since it is explicitly prohibited in the iRobot documentation, it wont work and it may destroy the power supply (and eventually the Roomba/Scooba internal recharging circuits).

 Let’s understand why it’s not possible to use external converters!

The first problem you encounter if you use an external 220V -> 110V converter to power the original Roomba/Scooba power supply is the output voltage quality (the 50/60 Hz rating is not critical).
If your converter outputs 110V RMS, this doesn’t mean that the peak voltage will be less than the maximum allowed (155 Volts) of the original power supply.
For example, with a Remington 220V -> 110V electronic converter, which outputs 110Volts RMS, the peak output voltage is more than 200V (without any load). In this case the converter would certainly blow the Roomba/Scooba power supply (please note that the peak voltage cannot be measured with a standard digital multimeter, but only with an oscilloscope).

The other problem is that if you fed the original Roomba fast charger with a voltage below 80V AC you can have an output voltage over the rated 22V DC.
For exapmle feeding the fast charger with 60Volts AC, it’s output would be at 40V DC and any connected Roomba/Scooba will be destroyed.
According to the TOP245 (TOP246 for Scooba) datasheet, the 1Mohm and 1.3Mohm resistors R1 and R2 (on the power supply board) at the Line Sense pin of the TOP245/TOP246 should shut it down if the input voltage falls below 100 VDC at the filter capacitor, but this does not happen. It seems there is a bug at the design of the power supply and at undervoltage conditions, the TOP245 can behave in a wrong way.
This condition (60Volts AC mains) would never happen in real life, but with an external 220V -> 110V converter it could be possible.

Maybe these are the reasons why it is expressely specified in the Roomba manual not to use external converters.

WARNING

Before continuing in reading the rest of the article, please read carefully the following notes:
1) The modification of the Roomba fast charger will certainly void your warranty
2) Once you open the fast charger casing, you are exposed to lethal high voltages
3) Any mistake in the modification can lead to components exploding & causing fire
4) If you are not an experienced electronics technician, don’t even try to open the charger case
5) Electrolytic capacitors have polarity, are mechanically sensitive and may easily blow
6) If you want to proceed with the mod you will take the responsibility for any problem that could arise
If you don’t want or if you feel that you don’t have enough experience & knowledge for this kind of modifications, it is better to use a good 220V AC to 22V DC 2Amp minimum power supply, rather than a 220V -> 110V converter. Usually you can find this kind of power supply as replacement parts for laptop, with prices ranging from 40 to over 100 Euros. If you find a power supply with more than 2Amp it would be perfectly fine, considering that the recharging circuits are inside the Roomba/Scooba, not in the power supply, nor in the Roomba base.

THE MOD
There are three kind of power supply
 that need to be modified in different ways:

1) Roomba power supply first revision (model number 10556)

2) Roomba power supply second revision: it differs from the previous because it has a Zinc Oxide Varistor named VR1 or RV1 (see pictures below)

3) Scooba power supply (model number 13143)

 <second revision with varistor>

<first revision without varistor>

1) Mod for Roomba power supply first revision (model number 10556)
The Roomba power supply is a standard switching power supply, based on the TopSwitch Top245Y chip. The whole power supply circuit it’s already designed for universal 110V-230V usage, except for the input capacitor after the rectifying diodes, which is a 47uF @ 200V electrolytic.
The 200V rating is fine for 110V mains, but will surely blow if used at 220V mains. So you need just to replaced it with a 47uF @ 400V (you need at least a 360Volts capacitor when rectifying 220V mains).

Why do we need a 400V capacitor?
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 continuously 311 Volts peak DC on the capacitor.
The original 200V capacitor will blow in a few seconds.
To dimension correctly the voltage of the capacitor we need to add an extra 15% (311 + 15% = 57 Volts). If you add some momentarily input over voltage spikes of the mains and the capacitor derating due to ageing, the result is 400V, which is the minimum acceptable Voltage rating of the capacitor in our case.

The cost of the 400V capacitor ranges from 50 Euro cents to 3 Euro.

Considering that the cost of the 400V capacitor over the 200V is only a couple of cents, it looks like that iRobot designed a proper universal power supply and then decided to lock the product for US usage only by using the 200V capacitor.

 

  

 

2) Mod for Roomba power supply second revision
In this revision of the power supply you need to follow instruction of the previous mod 1) and additionally you need to remove the varistor named RV1 or VR1.
This varistor, rated at 175 VAC, has been added by iRobots to the second revision of the power supply to protect the unit from power spikes and would blow if you connect the power supply to 220 V.
If you remove the varistor your power supply would revert to first revision and will work perfectly fine. Alternatively you can replace this varistor with another one rated at around 360 volts (like the VAR360V04W from Fuji Semiconductor).
 

3) Mod for Scooba power supply (model number 13143)
Step 1: The Scooba power supply is very similar to Roomba one, but more powerful. It is a standard switching power supply, based on the TopSwitch Top246Y chip. The whole power supply circuit it’s already designed for universal 110V-230V usage, except for the input capacitor after the rectifying diodes, which is a 100uF @ 200V electrolytic.
The 200V rating is fine for 110V mains, but will surely blow if used at 220V mains. So you need just to replaced it with a 100uF @ 400V (you need at least a 360Volts capacitor when rectifying 220V mains). In the picture the capacitor has been replaced with a 450V one (everything more than 400V is fine).

Step 2: In the Roomba power supply you need to remove the varistor named RV1 or VR1.
This varistor, rated at 175 VAC, has been added by iRobots to the second revision of the power supply to protect the unit from power spikes and would blow if you connect the power supply to 220 V.
Alternatively you can replace this varistor with another one rated at around 360 volts (like the VAR360V04W from Fuji Semiconductor).