Neato XV charging base PCB

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Neato XV charging base PCB

Postby paddy » January 12th, 2019, 4:29 pm

Hi to all,

I recently get four defect Neato XV, all of them have board version 64 (binky). My first idea was to just grab the lidar out for other projects and put the rest to trash. After a few hours, two of them are cleaning my house so I try to get the others operating again.

One of them has a defect charging base. Diode D3 is burnd (for what ever reason). I tried to desolder it but the PCB traces are damaged too. I'm not skilled in SMD soldering so I may not be able to repair it, especially not without schematics.

I checked voltage of an other base station with robot attached and without. As I measure, the voltage on charging tabs is always 23,3V (NiMH battery). It doesn't depend if robot is attached or not. The power supply is rated to 24V output. This makes me wonder whar the PCB inside the charging station does. There seems to be not much, I found some SMD resistors, capacitor a vour channel voltage comparator and a few components I'm nut sure (marked as Q1, Q2 etc, maybe transistors, one is huge, I think it's a MOSFET)

May it be enough to replace the PCB with one of these cheap DC/DC step down converters to get 23,3V or will I burn my house? I wonder if it really is set to 23,3V or if just my multimeter is to slow to detect the right voltage (if it is generated by PWM)

Any suggestions?
Thanks Patrick
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Re: Neato XV charging base PCB

Postby glnc222 » January 12th, 2019, 8:43 pm

Just suggestion and partial info: note there was a change in the charger design in the course of delivering XV model revisions, with later models having a different charger (the old one rate 2.4amps), and incompatible with newer XV robots. The newer chargers are backwards compatible with older XV models. The newer bots, without the side charging jack on the original, communicate with the charger differently -- for safety charging is not turned on unless docked, and the bot also must detect connection with the dock to maneuver properly for charging (unfortunately the Neato docks do not have a bot-connected indicator light like the Samsung's). I think the newer docks have a lower voltage, which is how the bot detects and rejects the old chargers. The charger supply voltage etc. is displayed with the Neato Control program over USB or with terminal emulator text commands.

A former senior engineer member was interested in the dock circuits but never traced them out, but observed that in the newer docks an inductor was added and possibly moved from circuits in the bot. The charging circuit is a constant-current variable voltage regulator, step down buck voltage converter, which raises voltage on the battery as it gets filled; this circuit was originally inside the vacuum, supplied with an input only voltage from the dock. Inductors are part of such voltage converters, which use high frequency oscillating current to permit use of small transformer inductors. What exactly was being done was never determined, but note there is a power management IC on the dock board, which may do things like shut off in case of shorts to prevent shock hazard etc. with those open contacts used on Neato (other brands tend to have bottom contacts for chargers).

Note the power brick in the dock itself has its own short circuit cut off protection, and must be unplugged from the wall to reset if it shuts off.

It is possible to supply the internal charging circuit with a bench power supply instead of the dock, at least in old models, as this was done in Germany once I think to prevent an over-voltage situation (maybe when using lithium ion replacement batteries home made, I forget -- over-voltage protection more important there, with fire hazard -- none such with NiMh batteries though cell damage possible). The old XV's had a hot resistor across the charging contacts which would load the dock to switch it on, maybe with that power mgt IC, when connected. The newer XV's eliminated that resistor and use some other method.
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