655 won't charge

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655 won't charge

Postby uoficowboy » December 10th, 2017, 5:45 pm

Hi - I just received a Roomba 655 from my mom, who no longer uses it. Unfortunately, it seems to be dead.

If I set it on the charging dock - the power light on the dock briefly flashes on (for a few seconds), then goes off again. In the meantime, the battery icon on the roomba flashes angrily at me. I let it sit like this overnight and there was no change.

I measured the dock voltage with no roomba sitting on it and it measured at about 3.2V.

I pulled the NiMH battery from the Roomba and it has 4 contacts. Going from one of the big ones to the other three, I see about 1.2V from one big contact to the other big contact, and 0 volts between that big contact and the two small contacts.

I'm guessing this battery is just over discharged and the charger is refusing to charge it? I can force some charge in via a power supply - but perhaps the battery is just dead and needs to be replaced?
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Re: 655 won't charge

Postby vic7767 » December 10th, 2017, 6:24 pm

Most Roomba owners don't realize that whenever a battery is installed inside their Roomba, it is being continuously discharged due to some circuits that never turn off, like the circuit used to receive signals from a remote control. If the Roomba is not on a charger then the battery is being discharged. If the battery remains inside the Roomba without being charged it will completely discharge in about 4 days. If left installed for more than a week or two then the internal charging system of the Roomba may not be able to recover the battery at all. If would be best to replace that pack.
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Re: 655 won't charge

Postby uoficowboy » August 29th, 2018, 11:54 pm

vic7767 wrote:Most Roomba owners don't realize that whenever a battery is installed inside their Roomba, it is being continuously discharged due to some circuits that never turn off, like the circuit used to receive signals from a remote control. If the Roomba is not on a charger then the battery is being discharged. If the battery remains inside the Roomba without being charged it will completely discharge in about 4 days. If left installed for more than a week or two then the internal charging system of the Roomba may not be able to recover the battery at all. If would be best to replace that pack.

So I finally got a new battery pack. Ordered from Bed Bath and Beyond to try to avoid counterfeits (don't trust Amazon).

Old one measured ~0.5V. New one measured ~15.5V.

Installed new pack. Behavior of Roomba has not changed much. Now it just sits there permanently angrily flashing the battery symbol at me, regardless of if it is on charger or not.

Any idea what gives? I've pulled the new pack for now so it doesn't kill it.
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Re: 655 won't charge

Postby vic7767 » August 30th, 2018, 12:58 am

Another issue that sometimes will occur is that when attempting to charge a deeply discharged battery, the charging MOSFETs can be damaged and must be replaced. Presently I don't have an image of the MOSFET location on the 600 model board.
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Re: 655 won't charge

Postby uoficowboy » September 6th, 2018, 2:31 pm

vic7767 wrote:Another issue that sometimes will occur is that when attempting to charge a deeply discharged battery, the charging MOSFETs can be damaged and must be replaced. Presently I don't have an image of the MOSFET location on the 600 model board.

Hi - I pulled out the motherboard. I don't see anything that is obviously blown - but can probe whatever you think is worthwhile?
IMG_20180906_095132.jpg

IMG_20180906_095101.jpg
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