Roomba 880 melting charging contacts

[AMS63]

We need to have a closer look

[Brett]

I have seen this twice.

Once on a 780 - the plastic had melted/deformed enough that it broke away (probably got a bit of a knock as well) leaving only a hole. I repaired this with plastic welding. Once on a 577, the contact was still serviceable, but definitely at a bit of an angle. In both cases the block of plastic inside the tab on the dock was also melted making the spring (up) action of the tab not enough to pop up.

Unfortunately I do not know what might have started the rot? In both cases I was able to repair dock and Roomba to get good contact during docking and happy customers.

I wondered if owners persisting with trying to charge a bad battery might result in sustained overcurrent / heat? But I don't know enough to do anything more then wonder.

(-8

[vic7767]

No one has reported this type of failure on the 880. I'm also surprised by your statement

We have contacted iRobot, with no real response.

How did you contact them and what was their response ?

[Gordon]

... issue with the 800 series melting the Left charging contacts. ...

There is no evidence shown in this image revealing that anything has melted:

If you had removed that contact plate from 880's chassis and directly connected battery terminals across its length, there would have been a failure in the battery, such as its fuse opening, or a melted wire.

OR, if you had connected 880's charging (PSU) adapter's dc output across that metal plate, a functioning adapter would limit applied current and nothing, not even warming of the plate, would have happened.

OR, if the 880's charging (PSU) adapter suffered a failure that resulted in applying your home's mains voltage across that contact plate, the plate would have warmed slightly as your home's circuit breaker reacted to the overload before going open circuit.

Please derive some feasible reason for the break that we see in that plate. I'm guessing that a cold-chisel driven by a strong whack with a hammer head is what parted the piece of sheet metal. Yes?

[Brett]

I cannot see enough in the OPs pictures to support evidence of melting, and unfortunately, (as I said up front) I have no ability to derive any further theories about what might have caused any melting. But Gordon, you seem to have drawn the conclusion that anybody that is unable to diagnose electronic circuitry is by extension unable to recognise melted plastic - this makes you come across as arrogant? I'm sure this is not your intention.

Unfortunately I cannot take this unit apart again because I promised it back to the customer today, but here is some evidence of melting:






This tab is not loose, but firm against the chassis. My phone will not focus closer but at the front outer corner, some plastic has even oozed out the side of the tab.

Unfortunately I did not keep the piece of plastic from the 780 that I repaired before, but the piece of plastic (that eventually did "break" off) was shrunk and curled up like a rasher of bacon after a few minutes in the pan. So much so I was not able to re-use it for the plastic weld repair.

If another occurrence comes in I will attempt to document it better, with better pictures etc.

(-8

[Gordon]

I cannot see enough in the OPs pictures to support evidence of melting, and unfortunately, (as I said up front) I have no ability to derive any further theories about what might have caused any melting. But Gordon, you seem to have drawn the conclusion that anybody that is unable to diagnose electronic circuitry is by extension unable to recognise melted plastic - this makes you come across as arrogant? I'm sure this is not your intention. ...

Not at all. I am just seeking truth!
Brett, you are misreading the OP's introductory statement. Take another look:

...We are tiring to get some information about an issue with the 800 series melting the Left charging contacts. ...

Notice that he says "charging contacts." Contacts are metal. AMS63 said nothing about "plastic", so I concentrated on melting metal.

His contact is split into two parts. I assumed AMS63 to be saying the contact melted into two sections.

BTW, my argument dealt only with basic electric power--enough to melt a metal-contact into two pieces (as shown in the OP's photo). My argument has nothing to do with "electronic circuitry". Well "nothing", except it is handy to know that Roomba PSUs roll off output voltage when current draw exceeds the PSU's rating.

[Brett]

Okay - I'll pull my head in then!
*Chases high-horse out the room...*

Certainly 'melting' the metal is inconceivable without an ensuing fire...

(-8

[harby]

The contacts would only themselves heat from ... poor contact. If there is any resistance or voltage drop across the contact, this will be converted into heat. Even a 0.5 ohm resistance from an oxidized connector that already barely makes contact would mean 0.75 watts of heat with a fast charger, three hours of that could certainly heat up the pads.

The broken contact metal in the first post though is likely due to the contacts being made out of foil-thin recycled tin cans, pre-bent to make a failure point, and someone stepping on the robot while it was charging in the dock.

[Jethro]

I'm experiencing the same thing on my Roomba 555. The right contact has moved inwards, now preventing roomba from docking on its own.
Does anybody know how to get the metal contact plate out to check what has happened behind it?

[vic7767]

Dis-assembly of the Roomba and dismounting of the main circuit board will reveal the two charging plates and the mounting assemblies. Removal of the two bumper sensor modules will aid in removal of the two power contact plates.

[Brett]

Take note that in both cases of plastic deformation that I've seen, the plastic block in the contact tab in the dock had deformed too. This resulted in it being too sticky for the spring action to work properly, making docking successfully harder still! I got away with shaving the plastic with a blade and a needle file to trim the little plastic tab that slides into / locates the tabs in the base of the dock.

(-8

[Jethro]

Thanks vic7767 & Brett, I've managed to get to the contacts. Its plastic base showed low temperature deformation, it was bent (in an arc) inwards without squeezing the plastic to the sides. Repositioning the contact has done the trick. Roomba is fully functional again. The dock seems to be in good order without deformation.

[bkmohs]

I have TWO 880s that have each begun to melt their charging contacts. Currently in discussion with iRobot on their replacement, but I hope it's not an ongoing problem. Here's a picture of one of them - this is after I tried to use a knife to pry it back out a bit.

[Brett]

Found some pics of plastic weld repair - before (cleaned up broken plastic bits):
http://imageshack.com/a/img913/7377/l10wNO.jpg

After (inside):
http://imageshack.com/a/img903/3554/l10MEI.jpg

After (outside):
http://imageshack.com/a/img537/4894/YiWeJh.jpg

(-8

EDIT: For some reason the images came up huge in the thread so just click on them if you want to see them.

[Gordon]

...EDIT: For some reason the images came up huge in the thread so just click on them if you want to see them.

Brett, your camera's default image size is 2560 px horizontal X 1440 px vert, but they could very well be 640X480 for insertion into posts.
You might like to try the service of free photo editor IrfanView. Download it from here: http://www.irfanview.com/ and play with it.
In just a few minutes I transformed your huge pix files into a single image of size only 640x1080px--with the set ordered as you next describe.

Found some pics of plastic weld repair -
before (cleaned up broken plastic bits):
After (inside):
After (outside):

Click image to enlarge.

[GermanRoombaUser]

Same here. It is melted. I think it started with Roomba making "tick tick tick" noises on the docking station but I am not sure if this was related. Roomba and docking station plus contacts melted. I got new robot and home base on warranty without sending robot to service. So seems to be a well known issue for service.
First robot run less than 6 months, I hope second robot will remain longer.
For me it is a problem by design. If resistance gets higher and higher voltage drop becomes bigger and bigger so current raises to a value to melt the plastic parts. If they would use metal it would be no issue I think.
Do you think this problem could end up in a more dangerous problem like a fire caused by the robot?

Regards

[Brett]

This is fast getting interesting! I have another one in with this problem, and I've just noticed that it always appears to be the left hand side tab?!!

|~:?'

[vic7767]

Is this only occurring where the mains are 220 ?

[GermanRoombaUser]

Some more detail pics of my above mentioned Roomba+home base.

I do not think the mains supply has anything to do with this as the problem is on the secondary/output part and this is 21 VDC.

[vic7767]

I understand that the Roomba is a dc device and uses 22.5 vdc with its built in charging base. The question is re-worded to ask, " are there any 110 vac Roomba showing this issue ?"