iRobot 650/Create 2: Connect second battery for electronics

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iRobot 650/Create 2: Connect second battery for electronics

Postby MaxWeb » November 18th, 2017, 11:02 am

Hi,

as the iRobot Create 2 isn't available here in Europe, I would like to use a Roomba 650 as the base for my new robot.
I'd like to attach an Up Board, a LIDAR and an Intel R200 camera to the bot and control it via the Open Interface protocol using ROS. I did a bit of research and this shouldn't be too hard, except one thing: The Roomba 650 only offers drawing power via the serial port (100mA, which is not enough) or via the motor drivers. But as the 650's batters is not that large, I'd like to add a 2nd battery to my robot, as I'm doing now by using a 5000mAh 3S LiPo in my current robot.
But because the 650 also includes a charging station, I'd like to use this one to charge a second battery together with the 650's battery. Of course, I won't use the LiPo here :wink:.
As I found out, the 650's charge station offers about 22VDC at it's charging pads, but expects a certain resistance, so I can't connect the 2nd battery's charging circuitry directlty to the 650's charging pads because the charging station would simply turn off it's power if it doesn't see this resistance.

So, where is the charging circuitry of the Roomba 650? Is it inside of the robot or inside the charging station? If it's inside the robot, it should be possible to connect the 22V to the charging pads directly (using a fuse for security), shouldn't it? Then, it should be possible to attach the 2nd battery to the robot's charging pads so the 650's battery and the 2nd battery can load in parallel. If one of them is full, it would simply stop loading.

Is this correct or are there better ways to load 2 batteries? Does anybody of you have experience with this?

Best regards,

Max Web
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Re: iRobot 650/Create 2: Connect second battery for electron

Postby a1robotrepair » November 18th, 2017, 12:23 pm

The smart charging circuit is in the bot. The circuit is set up to charge NiMH/NiCad batteries using a dt/dT algorithm. Bots from mid 2014 and later also have a charging algorithm for Li-Ion using the battery sensors as a means of communication to the fuel gage in the OEM battery pack.
You should try to power your devices with one battery. Robbing current from the charging circuit could cause charging errors. The power supply is giving up all of its power on full charge.
Battery sensors pre 2014 http://www.robotreviews.com/chat/viewtopic.php?t=17151&p=139276#p139276
Charging circuit pre 2014: http://www.robotreviews.com/chat/viewtopic.php?t=15704&p=137432#p137432
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Re: iRobot 650/Create 2: Connect second battery for electron

Postby MaxWeb » November 19th, 2017, 2:39 pm

Hi,

thanks for your reply!

As the 650's battery is only 3000mAh, the calculated runtime would be a bit short if I connect all of my devices to the built-in battery. That's why I'd like to attach a 2nd battery without charging it through the robot's charging circuit, so both batteries are loaded independent of each other but still through the robot's charging pads.

As far as I understood the linked topics, the built-in charger detects whether the battery is full and signals this to the dock by providing a certain resistance, so the dock can turn off the charging power. Is this correct so far?

If it is correct, it should be possible to circumvent the mechanism in the dock so it always provides 22V, no matter which resistance it sees. The build-in charger then would simply stop charging, even if 22V are applied from the dock, shouldn't it?

Then, I could attach my 2nd battery's charging circuit directly to the pads at the bottom of the robot so it also receives 22V for charging the 2nd battery.

I found something similar here: http://www.instructables.com/id/MAYA-Te ... nce-Rover/ , but that's for an older model and I'm not sure if they changed anything in the meantime.

Is this possible? Am I missing something?
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Re: iRobot 650/Create 2: Connect second battery for electron

Postby a1robotrepair » November 19th, 2017, 7:08 pm

An extra battery pack will need to be wired in parallel with the battery or have its own charging circuit. The charger and battery are in parallel during charging making the chargers voltage equal to the battery and components and impedance voltage.
Charger, 22.5V open circuit, 1.25A max output.
Battery typical, 16.8V max, impediance typical 0.8V, components typical 2V.
2 packs in parallel néed to be matched.
Tenergy makes a decent 4.5AH pack, $45.
Lithium power inc makes a great 4.4AH pack, $70.
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Re: iRobot 650/Create 2: Connect second battery for electron

Postby vic7767 » November 19th, 2017, 9:44 pm

Simplify your battery needs by getting one of these packs:
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Re: iRobot 650/Create 2: Connect second battery for electron

Postby MaxWeb » November 26th, 2017, 12:19 pm

Hi,

thanks for the tip with the large battery - I bought that one and finally get good runtimes without carrying a 2nd battery around :D

Best regards,

Max Web
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