Roomba 880 melting charging contacts

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Re: Roomba 880 melting charging contacts

Postby GermanRoombaUser » May 4th, 2015, 2:27 pm

Can anyone here connect thermal sensors to DC+ and DC- to measure normal charging temperatures? Or can install small current clamps/transformers? Would be interesting. :)
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Re: Roomba 880 melting charging contacts

Postby vic7767 » May 4th, 2015, 3:08 pm

You can monitor the charging reports from the Roomba by placing the Roomba on the charging base and connecting a comm cable from the SCI port to a USB port on your computer. The charging report is generated once per second and will contain charging current, voltage level, battery temp, amount of charging time, and capacity.
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Re: Roomba 880 melting charging contacts

Postby Conker » May 23rd, 2015, 4:46 am

A recent inspection of the charging contacts revealed evidence of pitting on one of the electrical contacts (the one closest to the spinning brush). I'm uncertain whether this would be a symptom of overheating contacts, though.
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Re: Roomba 880 melting charging contacts

Postby Brett » July 30th, 2015, 12:10 am

Brett wrote:Things still to be proven (or disproven):
1. Seems to be prevalent in 220V/ 240V areas. <<<Updated
2. It seems to affect the left hand tab.
3. Seems to be prevalent in later models ie 7xx on.


Just got another 880 in with this problem.

1 - CHECK
2 - CHECK
3 - CHECK

Bizzarre!

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Re: Roomba 880 melting charging contacts

Postby DJWillis » October 24th, 2015, 12:14 pm

Add a UK spec 760 to the list :D.

Brett wrote:Things still to be proven (or disproven):
1. It seems to be only in the 220V/240V areas.
2. It seems to affect the left hand tab.
3. Seems to be prevalent in later models ie 7xx on.


In my case right on all counts.

The dock left hand area plastic around the contact has softened up badly enough to 'pop out' the contact due to the spring tension. The core plastic under the contact has sagged. I may have a look at repairing it all with some putty. but right now I am thoroughly distrusting of the dock.

There is also evidence of a little arcing but I did not pick up on the sound of the arcing before it happened.

It looks like it happened over a fairly short period, or rather the physical symptoms showed up (no more than 72hrs?) as I tend to check the unit any move it to get into the cupboard it sits in front of and would have noticed. It could have course been arcing and warming up the plastic for much longer.

As for the 760 itself. The contact has also slumped into the frame somewhat but not badly enough to warrant much attention I hope.

I did raise it with iRobot in the UK but they just sent me away with my tail between my legs. As the unit is not under warranty any more they don't want to know, not a shock really but it was worth a try ;).

For now we have just gone back to running the DC direct into the unit and looking after it that way.
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Re: Roomba 880 melting charging contacts

Postby glukriek » November 11th, 2015, 6:36 pm

Hello Everyone,

Just got this same issue on a 880 and I am in the US so on 110V.

Has anyone successfully (and safely) fixed the problem?

Thanks
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Re: Roomba 880 melting charging contacts

Postby Brett » November 11th, 2015, 8:02 pm

I have had a few in since I last posted in this. I have successfully "fixed" them (mechanically anyway) by plastic welding and reshaping the plastic and repositioning the tab where it needs to be. This gets the unit working again and a happy customer, but I have no idea (nor the ability to change this) what is causing this.

Is it a bad positioning on the dock - then why is it only the left tab?
Is it something in the electronics - then why is it intermittent (none of the units I have "fixed" have re-offended)?

I think we can discount the 220/240V as there have now been a few in 110/120V areas.

So the things still to be proven (or disproven):
1.
Not a 220V/240V issue.
2. It affects only the left hand tab.
3. Seems to be prevalent in later models ie 7xx on.


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Re: Roomba 880 melting charging contacts

Postby robocleaner » November 12th, 2015, 6:52 am

Forgive me if I’m being too simple and missing the obvious here; I’ve skimmed through the comments thus far and it seems to me to be a fairly straightforward problem.

Coming at it from a (retired but once qualified) electricians point of view, high current being drawn through any inadequate connection (of under-rated capacity or unintentional/loose/poor fittings/contact) will generate heat.

The problem can’t really have anything directly to do with the 240v or 120v input of the dock/charger... it has to do with the charger's DC output... specifically the amount of DC charging current (amps) being passed/drawn by the robot through these contacts.

When you pass high(ish) current through a pair of metal contacts which are not making good contact with each other, they will generate heat. The arcing shown in some pictures is more extreme evidence that this is happening... that there is poor contact between the robot and dock charging plates.

Maybe the dock isn’t level, or maybe crud has accumulated on the riding roller raising the robot, maybe the sprung nature of the dock contact(s) is/are sticking preventing good contact between the plates, maybe the contacts are just plain dirty increasing resistance... maybe the contacts are just plain inadequate to carry the current being passed. Maybe the output current is higher from this dock charger than previous models, or the contact method has been cheapened/made less robust in some way on these newer models? Or maybe it's just poor alignment of the robot when docking. Any could cause heat and melt the plastic.

From the photos, it seems as if it’s the Docks positive DC contact that’s suffering, which would seem right to me. Either way, too much current (amps) is being drawn through a contact that - for whatever reason - it can't handle due to poor connection.
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Re: Roomba 880 melting charging contacts

Postby glukriek » November 12th, 2015, 3:57 pm

Thanks Brett,

Talked to Irobot this morning and it looks like they'll exchange it no questions asked...

That is great news for me!
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Re: Roomba 880 melting charging contacts

Postby Brett » November 12th, 2015, 8:35 pm

Good outcome!

But it still does not change the fact that it happens more often than it should and there seems to be no explanation yet.

robocleaner wrote:... What he said ...

Yeah, all that you say is true and fairly logical (even to a nuts-and-bolts type engineer such as myself), but taking it further, surely the current flowing through the two contacts is the same? IE in and out? So if it was simply arcing / poor contact, why:

> is there a 100% hit rate on it being the left tab that is damaged?!
> are there such a high numbers of 7xx/8xx machines getting this compared to the very low numbers of 5xx/6xx machines? (I might be wrong but I'm guessing there are many more 5xx/6xx units "out there"?)
> similarly if I had to guess about the numbers of 120V to 240V machines out there (yes, the older units, pre universal adapters) there might also be a scewing of occurrences to the 240V units, but it seems less apparent.

Dunno?

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Re: Roomba 880 melting charging contacts

Postby Brett » November 12th, 2015, 8:48 pm

Brett wrote:... IE in and out? So if it was simply arcing / poor contact, why:

> is there a 100% hit rate on it being the left tab that is damaged?!
...

Actually, maybe that is a clue?!

Is it feasible that an alternate path is being found and a short term or intemittent current is flowing in the one tab and out somewhere else to earth?
> Does the Dock sense imbalance in the current in/out?
> I would have thought that there isn't nearly enough potential difference in these to be finding 'other' routes to earth but who knows? (< not me!)

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Re: Roomba 880 melting charging contacts

Postby GermanRoombaUser » November 13th, 2015, 2:02 am

A current unbalance could be a point. But how? I will think about it.
Brett, what do you think about electrostatic effects (carpet) causing a problem when docking?

Would be nice to know if iRobot solved the problem with 886 and 960. Has anyone a chance to compare at least the docking stations of these?
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Re: Roomba 880 melting charging contacts

Postby robocleaner » November 13th, 2015, 10:42 am

Brett wrote:...surely the current flowing through the two contacts is the same? IE in and out?'

No. It doesn’t work like that. The energy is flowing through the (poor/left) positive contact and being absorbed by the batteries.

Even in an alternating/AC circuit, the phase/positive supplying the load is the one that gets hot/burns/melts... at mains voltage, at high current draw, with poor contact(s), your house catching fire and burning down to the ground is quite possible such is the heat being generated (usually the contact wire simply melts with the heat and self-disconnects the circuit. I have witnessed burnt insulation/melted wires/contacts on (only) phase/supply wires many many times in my career, and in the extreme, two houses did burn down which subsequent investigation proved was due to poor positive/phase electrical contacts).

With a low voltage DC supply and poor contact, if the current is higher than the contacts can cope with, a bit of melting plastic is quite possible/normal.

I have tried, but don't own any Roomba models. I would suspect something has been compromised in these later models which are now suffering this problem - a charge current/rate/draw rate which is higher than the contacts can cope with, or poor mechanical contact/higher than expected resistance... which generates the heat.
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Re: Roomba 880 melting charging contacts

Postby AMS63 » November 18th, 2015, 4:05 am

Hi,

This is caused by a build up of film, dirt and debris on the charging pads, this in turn creates resistance which causes heat when charging.

If you read the maintenance schedule in the manual it specifies to clean the charging pads and base station once a week.
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Re: Roomba 880 melting charging contacts

Postby GermanRoombaUser » November 18th, 2015, 4:30 am

But there is normally only dust on the other contact. Is this plausible?
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Re: Roomba 880 melting charging contacts

Postby robocleaner » November 18th, 2015, 5:31 am

AMS63 wrote:...a build up of film... this in turn creates resistance which causes heat when charging.

The metal contacts oxidising with exposure to air over time will increase resistance and add to the problem, but pitting on the contacts suggests the current is jumping...
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Re: Roomba 880 melting charging contacts

Postby Brett » November 18th, 2015, 6:32 am

robocleaner wrote:
Brett wrote:...surely the current flowing through the two contacts is the same? IE in and out?'

No. It doesn’t work like that. The energy is flowing through the (poor/left) positive contact and being absorbed by the batteries ...

Go figure! I'd always thought that seeing the process of discharging the batteries was the passage of electrons from the negative terminal through the "load" to the positive terminal and kind of assumed the charging process to be the reverse - IE removal of electrons from the positive side of the battery chemistry and "pushing" them back into the negative!

I'm out of my league here, but I'm still thinking there is more to this story than that.

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Re: Roomba 880 melting charging contacts

Postby robocleaner » November 18th, 2015, 8:37 am

Yes Brett... but you're not DISCHARGING the batteries... you're CHARGING.

Trust me... the problem lies with a bad electrical positive contact between the robot contact and the charger contact. I'll put good money on that bet!

The evidence is in the posted photos - burn marks/pitting. During CHARGING, the contact between the charger plate and the robot is not firm/good/adequate. The current is jumping from one contact to the other, generating heat, melting the plastic.

WHY is the question you should be asking.
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Re: Roomba 880 melting charging contacts

Postby Dargo » January 7th, 2016, 6:55 pm

As many others have experienced, I too had my Roomba melt at the charging contact points. What is extremely frightening about this issue is the fact that I noticed the problem when I smelled something burning and saw smoke coming from my Roomba 880!

I immediately unplugged the device and, after about 15 minutes began to look for the source. What I discovered was that one contact point on the robot had melted the surrounding plastic and had been displaced due to the plastic holding the metal contact tab being melted. I then noticed that the corresponding contact on the charger unit had also heated to the point that it too had melted and rendered any 'spring action' of the charger's contact point inoperable. Would this have started a fire if I had not been there to unplug it? I do not know, but with the smell and visible smoke, I am glad I did not find out.

I called Amazon, where I purchased the robot, and they referred me to call iRobot; which I did. After initially speaking to a lady and then waiting on hold for 23 minutes, I finally spoke to a very pleasant lady who informed me that they would exchange my robot and charger for new ones after I shipped my defective items back in a using a prepaid shipping label she said they would supply. She said that I should contact them again if I had not received the label within an hour. It has now been four hours and I have not received any email, other than one acknowledging our conversation, and I have checked any "spam" or "junk" folder and have made numerous attempts to again contact someone at iRobot.

I assume I will eventually receive a shipping label and ship my 'melted' Roomba 880 back for a replacement. My only real concern is that the representatives at iRobot informed me that, although they were aware of this problem, no recall has been issued nor has there been any changes to prevent this apparently frequent issue from happening again. At this point, I would certainly NEVER leave my home with a Roomba product plugged in to a power outlet. I am attaching a couple of pictures I've taken with my phone.
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image.jpeg
melted contact point on Roomba charger
image.jpeg
Melted contact point on Roomba 890
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Re: Roomba 880 melting charging contacts

Postby TechGuy » January 8th, 2016, 12:38 pm

iRobot will replace your melting 880 even if your warranty had expired. This was what my clients told me.

Check the charging contacts every time you clean your 880. Call iRobot if your 880 has slight heat damage. Don't wait until it is smoking before calling.
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