Rebuilding a Roomba Battery for Less

Inside the Roomba and Scooba and more, Cool mods, Repair and Upgrades - including the all new iRobot Create Kit. Let's void that warranty baby!

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Postby gimgim » December 16th, 2005, 5:01 pm

http://www.cs.brandeis.edu/~gim/RoombaLi-ion/

I've recently re-opened the battery, removed the glue and the chopsticks, added NTC and thermal protection and wrapped the cells with PVC shrink wrap (also from Batteryspace).
I have more pictures, but no time to comment them, so I have posted them here:
http://www.cs.brandeis.edu/~gim/Roomba/RoombaLi-ion%20II/

And this is a rebuild of a standard NiMH battery pack:
http://www.cs.brandeis.edu/~gim/Roomba/RoombaNiMh/

The second set of pictures shows the PVC shrink wrap better. And the home made screwdriver...
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Postby joel » December 19th, 2005, 11:06 pm

Was the battaries 2- 7.2A 3000 mAh or 3300mAh?

Joel
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Postby gimgim » December 20th, 2005, 1:07 am

The original APS had a pencil correction on the sticker that says 3000mA/h
It was rebuilt as a 3300mA/h
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Postby bholio » December 27th, 2005, 11:50 am

If you really want to upgrade the roomba, try out some of higher end RC car batteries. The last time I looked (ove the summer), the top of the line nimh were either GP 3700, or IB 3800. They will cost a bunch more than the batteryspace cells, but will have better performance and runtime. Not sure how much that matters in a roomba, but hey.

The true state of the art in RC batteries is lithium polymer, but they would need a special charger and discharge logic which the Roomba (most likely) does not have. They come in up to 8000mah and are very lightweight. Maybe next generation.
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12V versus 14.4V battery packs?

Postby CB » December 28th, 2005, 5:45 pm

BradMurray wrote:Why not try the following:

http://www.batteryspace.com/index.asp?P ... ProdID=217

Plus two single batteries (http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1158) would give you 5000 mAh for the same price as the pre-packed option batteryspace offers for the same price. That should give a serious run-time. I just bought a replacement battery for my Discovery and will probably do this to rebuild my dead one.


The battery on my Roomba Discovery does not seem to be holding the charge it once did and I am considering replacing the battery myself according to the examples posted here.

My question about BradMurray's post above is this. Most of the other posters appear to be using the "two 7.2V 3300mAh NiMH Side by Side Battery Packs for RC Traxxas and Losi RC Car" from Batteryspace for a total of 14.4V. The configuration suggested by BradMurray above comes in at 9.6V according to Batteryspace's details. I know that it is a 10 piece battery pack and he suggests adding two additional single batteries to the pack. But at only 1.2V apiece, this only adds an additional 2.4V for a total of 12V when added to the 10 piece battery pack. Is 12V enough for the Roomba Discovery?

My apologies if my question appears ignorant. I am very handy with tools and understand the basics of electron theory. However, I am the first to admit I am no electrician. But I can follow directions and examples and am confident I can do this project myself with a little help (as provided by this forum). Just wondering about the voltage discrepancies noted above. Thank you for any assistance you can offer.
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Postby rj5555 » December 28th, 2005, 6:18 pm

You need 12 cells to make a Roomba battery, the two 7.2V (6 cell each) RC battery packs are your best/easiest option.
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Re: 12V versus 14.4V battery packs?

Postby bholio » December 28th, 2005, 10:06 pm

CB wrote:
BradMurray wrote:Why not try the following:

http://www.batteryspace.com/index.asp?P ... ProdID=217

Plus two single batteries (http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1158) would give you 5000 mAh for the same price as the pre-packed option batteryspace offers for the same price. That should give a serious run-time. I just bought a replacement battery for my Discovery and will probably do this to rebuild my dead one.


The battery on my Roomba Discovery does not seem to be holding the charge it once did and I am considering replacing the battery myself according to the examples posted here.

My question about BradMurray's post above is this. Most of the other posters appear to be using the "two 7.2V 3300mAh NiMH Side by Side Battery Packs for RC Traxxas and Losi RC Car" from Batteryspace for a total of 14.4V. The configuration suggested by BradMurray above comes in at 9.6V according to Batteryspace's details. I know that it is a 10 piece battery pack and he suggests adding two additional single batteries to the pack. But at only 1.2V apiece, this only adds an additional 2.4V for a total of 12V when added to the 10 piece battery pack. Is 12V enough for the Roomba Discovery?

My apologies if my question appears ignorant. I am very handy with tools and understand the basics of electron theory. However, I am the first to admit I am no electrician. But I can follow directions and examples and am confident I can do this project myself with a little help (as provided by this forum). Just wondering about the voltage discrepancies noted above. Thank you for any assistance you can offer.


Someone else posted the following link from batteryspace.
http://www.batteryspace.com/index.asp?P ... rodID=2238
I don't think it gets any easier than that. 12 cells, presumably fits perfectly in the yellow battery case, all wired, ready to be attached to the battery case.

Some of the links you have mention 'C' battery cells, which are different then 'sub-c' cells. C cells probably will not fit. RC car cells are also sub-c sized, which is why people are recommending them too.

Note that I haven't changed my roomba battery or even had the case open yet.
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Postby far182 » December 29th, 2005, 8:30 pm

Wouldn't Lithium ION batteries be a better choice?
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Postby rj5555 » December 29th, 2005, 9:09 pm

Li-Ion would be great but the build in charger of the Roombas are not suitable for charging them.
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Re: 12V versus 14.4V battery packs?

Postby CB » January 1st, 2006, 3:03 pm

rj5555 wrote:You need 12 cells to make a Roomba battery, the two 7.2V (6 cell each) RC battery packs are your best/easiest option.


Yes, I understand that you need 12 batteries. Read where I wrote:

CB wrote:I know that it is a 10 piece battery pack and he suggests adding two additional single batteries to the pack.


The number of batteries needed was not my question.

The point I believe BradMurray was making in the post that I origanlly quoted was that the batteries he found at Batteryspace are 5000mAh as compared to the 3000 mAh or 3300 mAh batteries everyone else was suggesting to use in their posts. Presumably, the 5000 mAh would give the Roomba considerably more power/runtime.

However, the 10 piece battery pack suggested by BradMurray plus an additional 2 single batteries (for a total of 12) comes out at 12 Volts total. All the other battery packs suggested for use with the Roomba are 14.4 Volts total.

Ideally, if the 5000 mAh pack suggested by BradMurray will indeed give a Roomba more power/longer runtime, I would prefer to use those batteries instead of the 3000 mAh or 3300 mAh packs. But my question was:

CB wrote:Is 12V enough for the Roomba Discovery?
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Postby rj5555 » January 1st, 2006, 4:25 pm

The 5000maH cells will not fit inside the battery pack, the cells listed in Batteryspace are c size you'll need sub-c size for making the roomba pack.
The highest capacity would be if you use 3800maH from IB (see here and 4200maH is on its way) or 3700maH cells from GP but expect to pay a premium for these.

12V will NOT be enough to power the roomba for long, nominal 'empty' voltage of a typical nimh cells is 0.9 or 1.0 volts so battery empty level of the roomba battery pack would lie somewhere between 11 and 12volts
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Brushless Motors

Postby Anakin » January 24th, 2006, 9:44 pm

One thing that would give longer runtimes would be to replace the electric brushed motors with brushless motors. Of course, the motors would also need an electronic speed control as well as the need to instruct it to stay at a certain RPM.

I'm really into rc cars & trucks (see my website www.e-maxximumrc.com for an example) and converting to brushless motors is do-able, but very expensive. It would be the ultimate way to squeeze more power & run-time from your batteries though.

While on my website, check out my battery discussion ( http://www.e-maxximumrc.com/html/batteries.html ).
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Re: Brushless Motors

Postby DaveV » January 24th, 2006, 10:06 pm

Anakin wrote:One thing that would give longer runtimes would be to replace the electric brushed motors with brushless motors. Of course, the motors would also need an electronic speed control as well as the need to instruct it to stay at a certain RPM.

I'm really into rc cars & trucks (see my website www.e-maxximumrc.com for an example) and converting to brushless motors is do-able, but very expensive. It would be the ultimate way to squeeze more power & run-time from your batteries though.

While on my website, check out my battery discussion ( http://www.e-maxximumrc.com/html/batteries.html ).


Okay describe "very expensive". $50? $150 ? $1799?

Just give us a rough figure.
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Postby Anakin » January 24th, 2006, 10:38 pm

Depends on the size motors in the Roomba. I'm guessing the drive motors are 370 and the brush/beater bar motor is 540. You would be looking at $200 - $250 to replace the 540 and $150 or so to replace each of the 370's. Half of the cost would be for the speed control and half is for the motor.

Too expensive to be practical, but keep in mind your run time should about double (brushless motors are MUCH more efficient than brushed) and brushless motors have much more torque than brushed.

To give you an example, a small RC truck that I own (Team Associated's RC18T, look here http://www.e-maxximumrc.com/html/rc18t.html ) comes with a brushed 180 sized motor. Stock, the truck does about 20 MPH. I replaced it with a Mamba motor/speed control and the truck now does over 50 MPH with 2 1/2 times the runtime off of the same battery pack. You can see the motor here: http://www2.towerhobbies.com/cgi-bin/wt ... XJFY5&P=ML
This motor has a 8000kV (that means 8,000 RPM for each volt applied..yes, over 100,000 RMP @ 14.4 volts)

Here's a page to a place that sells a 14.4 volt 540 sized motor and electronic speed control http://www2.towerhobbies.com/cgi-bin/wt ... XBLB8&P=ML
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Re: 12V versus 14.4V battery packs?

Postby Guest » January 25th, 2006, 6:49 pm

]
However, the 10 piece battery pack suggested by BradMurray plus an additional 2 single batteries (for a total of 12) comes out at 12 Volts total. All the other battery packs suggested for use with the Roomba are 14.4 Volts total.


FWIW, I believe the confusion over number of cells probably arises from a typo on the 10-pack page. 9.6v is right for 8 normal cells, 10 cells should be 12V; add two (which appear to be identical and are certainly listed as 1.2V apiece) and you have your 14 regular 14.4v, just as for all the other 12-battery combos which have been discussed.

All of which is academic if full-C size doesn't fit in the pack.
[/quote]
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Li-ion battery pack

Postby gimgim » January 26th, 2006, 1:33 am

For the Li-ion pros and cons check this thread

http://www.robotreviews.com/chat/viewto ... ight=liion
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Postby twelfthplanet » January 26th, 2006, 11:59 am

This battery pack looks like it would work:

http://www.batteryspace.com/index.asp?P ... rodID=2041
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Postby Guest » January 26th, 2006, 12:25 pm

> This battery pack looks like it would work:

NO. C cells won't fit the original container and 12V is too low...
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Postby Guest » February 10th, 2006, 5:30 pm

If you are going to hack into your batteries, make sure that you re-use the solid-state fuse when you re-assemble it. iRobot has a fuse in there that prevents the battery from over-heating and exploding in a short-circuit condition. In some models this fuse is in the shape of a strap welded between two of the cells. It looks just like one of the strap conductors that connect the cells and is partially hidden under the shrink wrap. This part stands between you and a 50 amp short circuit if you goof. Might want to make sure you use a heat-resistant glue when you re-install the thermistor too (make sure to glue it to a cell or you will not measure the temperature properly) . Without heat resistant glue, the thermistor might sense over-heating too late.

Safety first!!
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roomba battery pictures

Postby sdj19 » February 11th, 2006, 1:39 pm

Is it my imagination or do the pictures and instructions at batteryspace.com for rebuilding a Roomba battery pack have the pos and neg positions reversed? I opened two Roomba packs and both have neg(black) closest to batteries.

Any ideas?
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