Powering and charging a netbook from Roomba's on board power

[Cerin]

I'm trying to connect a Dell Mini netbook to and completely power and charge it from a Roomba Create.

What's the consensus opinion on powering and charging a netbook (19V @ 1.5A) from a Roomba?

I read http://www.robotreviews.com/chat/viewtopic.php?f=4&t=12118&start=60, but it seemed to trail off without any clear conclusions.

I've seen a few posts like http://www.instructables.com/id/MAYA-Telepresence-Rover/step5/Charging/ which power a netbook by tearing apart both the Roomba and docking station and modifying them to expose the 22V or AC lines directly to the Roomba so the netbook's adapter can take the higher power input. However, this is way more damage than I want to do to my Roomba, and I'm uncomfortable with the possible safety implications.

I found this post http://www.instructables.com/id/OLPC-Telepresence/step3/Attach-the-OLPC-and-Cables/ describing how to power an OLPC directly from the Roomba's parallel power. Would this work for normal netbooks, or is this an OLPC-only option since the OLPC's power requirements are much more flexible?

If I had to quess the answer to my question, it would be "it's possible, but quite hacky". Are there better options?

Regards,
Chris

[Jozer99]

Aren't Roomba batteries only 14.4V? I wouldn't think there would be any higher voltage signal on the mainboard, and if there was, it would probably be to drive some sensor, and be very low amperage. I think your best bet is to use a 12V car charger for your netbook. This will have all the necessary circuitry to step up the voltage to an appropriate level, as well as being able to handle the full power load easily. Car system voltages vary quite a bit, so I bet a 12V charger should handle 14V just fine. If you are nervous, you can get a 12V regulator (just make sure it is appropriately beefy, as it will be dissipating several watts).

[mfortuna]

You may be able to charge the netbook from the roomba's charging source although the extra current may be too much for it. If you have a dock it is pretty easy to access the contacts. Just remove the front bumper and splice in.

[Gordon]

I must say, several of us may not have recognized this thread's OP-date, which is almost six months old and has grown whiskers without ever receiving a reply! I failed to notice that until the second day after the very tardy, and uninformed reply by Jozer99 brought Cerin's old post into view!

Quite likely, Cerin was sufficiently miffed about lack of interest, that he never even bumped his thread to see if anyone was tending the store.

Although I wrote no immediate replies to posts #2 & #3 -- which, if I had, would have been more for Jozer99's and Mike's benefit -- I did get triggered into reviewing bhylak's MAYA/Instructable page, a page I had read when it was new, and I can recall not understanding what he said regarding powering and charging MAYA Rover's Roomba & battery. But, this time around I succeeded in greatly decoding what bhylak wrote on that page, plus what he wrote in a series of question & answer interactions with a correspondent (whose handle is:) "MovieMaker".

Thanks to MovieMaker (and a more recent Q&A exchange in a rr-thread (TBD link)) it is almost possible to explain what bhylak did to his Home Base to accomplish simultaneous Roomba charging and netbook charging while docked to his Home Base, (HB).

More about those details below -- inserted in a copy of Cerin's post.

===== Powering and charging a netbook from Roomba's on board power =====

OPENING Post by Cerin » December 11th, 2011, 1:25 pm

I'm trying to connect a Dell Mini netbook to and completely power and charge it from a Roomba Create. ...What's the consensus opinion on powering and charging a netbook (19V @ 1.5A) from a Roomba?

I would have answered that by saying: I doubt that a "consensus" has been established in these fora, so what you read here is my opinion, or sometimes its my guess.

There are old threads that correspond to this thread's subject, but to hunt them down could be fruitless because less was known about Roomba design and I/we posted some incorrect data. I will list a few Roomba characteristics that must be known to exist before one tries to make Roomba share its power source (its battery) with additional equipment:

DISCHARGE PHASE:

1) A healthy and freshly charged NiXX battery will finish slightly over-charged in the 17V to 18V range.

2) When a Roomba carrying that battery is switched into Clean Mode, the small amount of charge causing the relatively high voltage will fall within a few minutes to around 15V, after which voltage reduction will follow a shallow slope ramp to the mean level of 14V, and then to 13V at which point in time, say two hours later, practically all useable charge has been consumed.

3) Roomba continues cleaning for a short interval as battery voltage rolls over a knee, and starts falling below 12 volts, but Roomba's operating system senses that level and ends Clean Mode by stopping all motors.

4) Roomba, then, indicates (via a red illuminated Power button) that it requires a re-charge.

I've prepared some graphic aids for this pitch, and I think it is appropriate to flash one now showing an elemental Roomba + Home_Base + PSU in a normal charging mode setup. It is important for a DIY'er intent on messing with these H/W items to have a notion of how they play together before trying to tap power out of such a system:

CHARGING PHASE:

1) Roomba is designed to be charged with regulated voltage/current power supply units, (PSU).

2) Roomba R2 (4XXX)'s nominal PSU output voltage is 22.0Vdc, and 22.5Vdc for Roomba R3 (5XX) and those nominal voltages are regulated to w/in +/-0.5V for load current ranging from 0A to 1.25A.

3) Both R2 & R3 PSUs utilize current overload roll-off protection when charging current exceeds 1.25 amperes. "Roll-off" means that when charging current exceeds 1.25A, NOM, the PSU automatically begins to lower the PSU's output voltage, as both a safety measure for the PSU, but to protect components of Roomba's charging control circuit (a circuit on Roomba's main_PCA). Here is a picture of that roll-off:

(More)

The PSU's output voltage will be taken to zero volts before current reaches 1.5A! During normal high-rate charging, voltage applied to the battery terminals is not much greater than the battery voltage. As the battery accepts charge, terminal voltage rises to follow the increase in battery voltage.

4) That same plot (keep in mind it is for an R2 Fast Charger PSU, not a more recent R3 PSU, not that we know there is a difference in roll-off) can reveal why Roomba's charging control circuit depends on voltage reduction. For example, suppose battery voltage stabilizes near 14V at beginning of the high-rate charging phase. We can look at the curve and see that current will be ~1.38A. If we then deduct 14V from the incoming 22V (before roll-off), we get a difference of eight volts to be 'absorbed' by a string of series resistances between the charging source and battery. With the nominal 1.3A passing through that resistance string, only about two volts drops across it, leaving six volts to ponder -- how may they be accommodated? Those six excess volts are accommodated by the Roomba charging system, with PSU's elex rolling off current to cause fewer input volts to enter Roomba and be impressed across the battery terminals.

====== Moving on to Cerin's research on this power-tapping matter: =======

I read viewtopic.php?f=4&t=12118&start=60,

but it seemed to trail off without any clear conclusions.

I've seen a few posts like http://www.instructables.com/id/MAYA-Te ... /Charging/

which power a netbook by tearing apart both the Roomba and docking station and modifying them to expose the 22V or AC lines directly to the Roomba so the netbook's adapter can take the higher power input. However, this is way more damage than I want to do to my Roomba, and I'm uncomfortable with the possible safety implications.

I found this post http://www.instructables.com/id/OLPC-Te ... nd-Cables/

{by damonkohler} describing how to power an OLPC {One Laptop Per Child} directly from the Roomba {Create}'s parallel {battery} power. Would this work for normal netbooks, or is this an OLPC-only option since the OLPC's power requirements are much more flexible?

If I had to guess the answer to my question, it would be "it's possible, but quite hacky". Are there better options? ...Regards,...Chris

My intent here is to address the mods that bhylak espoused in his own Instructable. But, in passing, I can say that I did review damonkohler's OLPC Instructable, and found it very well presented. He identified a DB25 connector in his Create's cargo bay that had switched battery power he could tap for his add on Laptop. Create has some reserve power (since its only motors, consuming battery charge, are its wheel-motors), and may have been able to power an OLPC device long enough to be useful.

In opposition to that well written 'instructable', bhylak's words about his Rover's power & charging system(s) were, to say the least, incomplete and mystifying. As I said at the top, it was MovieMaker's incessant questioning (via Instructables' comments section) that forced bhylak to reveal more about Rover's "power system".

Further "clarification" came forth from two rr posts that I came across: ADD to the "information" gleaned from the Instructable entry and comments these two rr posts by bhylak, in JAN 2011:

viewtopic.php?p=88378#p88378
"Get a 12v 7Ah Hobby battery on the Roomba. Hooked up to that batttery is a netbook and a monitor. (Or whatever else) There are leads going from the battery to the docking pads. On the Dock, the battery charger is clipped on to the contacts (Alligator Clips) underneath. If you take apart the dock, there is about 3 inches of metal, which come up to form those small little contacts."

viewtopic.php?p=89905#p89905
"Ok here's an original idea, proven to work. (Running a monitor off of it atm)

I have a 12v 7ah battery hooked up to the Roomba battery parallel. (Opened it up, and soldered them directly to the contacts inside) I bought one of these {cigar-lighter socket to clip-leads}: ...
and cut off the ends with the clips. {the "clips" are small size 'battery-clips' with red & black leads} I ran the wires from the Roomba battery through 2 resistors so it'll only give the battery 500ma, which is needed for charging. (Added a fuse for safety) The wires for charging are soldered together with the item I bought above, and connected to the battery. So when everything is off it charges."

The words between the curly braces "{...}" are mine.

I invite all readers of this thread to critique my interpretation of what bhylak has said in these various sources. It is a great mystery. Review all the references, then, see if you can describe "exactly" what was done to merge third party power sourcing and battery charging equipment into Rover, the R2 Home Base, and the R2 Roomba transportation platform.

I was unable to come to that "exact" solution, however, I arrived at what I think is very close and what he must have done, because I can see that it sorta worked. My purpose in preparing this post is too ward off other DIY'ers -- who may pass this way -- from needlessly spending their own resources to replicate these mods. There is a simpler way to do it.

Here is a list of what bhylak did to create his Rover (not that I know the order of making these changes or purchases):

A) No changes were made to Roomba.

B) He set aside Roomba's 22.0Vdc, 1.25A Fast Charger and substituted a similar regulated PSU having higher output current: 22Vdc, 4A.

C) He opened the Home Base and disconnected / added wires from / to the HB_PCA pads:
i) RED & BLK Power-output wires were disconnected from solder pads J2(+) & J2(-), leaving those RED & BLK wires to the HB's external contact bumps temporarily OPEN.

ii) The RED wire, from (i) was connected to Power-input pad J1(+), and the BLK wire from (i) was connected to pad J1(-). Charging power (from element (B) PSU) enters the HB's Power Jack, goes to these J1 pads and on to Roomba, completely bypassing HB's PCA, but still powering the board.

iii) Additional RED & BLK wires, one each, were also connected to the two J1 pads, maintaining proper polarity, for the purpose of powering an add-on dc-to-dc converter module.

D) BH needed a 12Vdc power source to power Rover's netbook and a monitor, so he piled on a 12V, 7Ah, SLA (sealed lead acid) "Hobby" battery.

E) He then needed means to charge the battery in (D), and to do that job he selected a Mean Well DC-to-DC Power Converter that would run off the 22Vdc from the alternate PSU, of (B), and output 12Vdc to charge the SLA battery.

This next graphic aid shows those new purchases and HB-mods overlaid onto the Roomba and Home Base systems:

Following a brief familiarization study, to confirm that the graphic representation agrees with the above list, the next important group of elements to notice are the yellow, "squircled", note call-outs: [(1)], [(2)], & [(3)]. Rather that detail them on the face of the drawing I elected to write them here. Discussing each may take more than a few sentences. Basically, these notes are being used to call attention to PROBLEM areas, i.e., design oversights. Here we go:

NOTE [(1)]. This alternate PSU is is capable of delivering four amperes into the Roomba charging system! Roomba's Fast Charger exhibits voltage regulation, holding its 22-volt level out to about 1.25A, after which any additional current increase causes the PSU to lower its output voltage to a level dictated by the battery charge, and to a lesser extent by circuit component resistances that exist along the current path. The excess current delivery capacity of this alternate (4A) PSU is destined to overheat Roomba's charging FETs, via Joule heating, until they no longer perform as semiconductor devices. There is no threat to the HB, since its power-path is bypassed in the Rover application; but, a custom designed current-limiter module must be inserted between the PSU and HB to avoid damage to Roomba.

NOTE [(2)]. There is nothing to prevent SLA-battery charging current from exceeding the Converter's 4.2A output specification. When that occurs, the 22Vdc from the 4A, 22Vdc PSU will be pushing input current to the Converter above its maximum 3A rating; resulting in faulty operation of the converter.

NOTE [(3)]. There are several faults at this charging supply to SLA-battery interface:

i) The charging voltage is lower than required to charge a lead-acid battery (converter output can be cranked high enough, but may also depend on voltage dropped across the next item).

ii) A dedicated charging controller must be inserted between the charging power source and the battery. Refer to


Gel_Cell_Batteries.pdf

(109.51 KiB) Downloaded 68 times

, and other SLA charging references.

iii) The charging cable requires a disconnect connector from Rover (I saw no evidence of one being used in the BH material).

In summary, Rover is operating with an undercharged auxiliary (SLA) battery, and its Roomba tractor may no longer have operational U2 & U4 MOSFETs.

Although somewhat of a nit, its Home Base is unaware that a Roomba is docked to its contacts -- not critical -- except, that status permits the HB's IREDs to continue full-power radiant operation, when normally they would be set OFF to take rest.

The really IMPORTANT thing to understand about this Rover setup is:

There is no need to dock it for charging!

Sure, it can be (dangerously) charged while docked, but notice that the SLA-battery must be manually connected to its charger! There is not enough automation about this charging setup to make it worth hacking a Home Base, buying a dc-to-dc converter, buying a 12V-battery charge-controller (not done), or buying an alternate 22Vdc PSU.

What the hey: Just buy a stand-alone 12V-SLA battery charger, and plug it into the wall socket when needed to charge the Hobby Battery; and charge Roomba's battery through the side/rear Power Jack. Fuggedabout the Home Base! This is a manually charged robot.