Botvac with LiFePo4 mod

News and information about the Neato XV-11 Robotic Vacuum. All discussion and troubleshooting questions go here.

Re: Botvac with LiFePo4 mod

Postby glnc222 » December 31st, 2016, 1:54 pm

Great news. According to the battery literature, those cells could last several times the life of other lithium chemistries, besides being inherently fireproof, and might last the lifetime of the robot. Too bad there is no commercial supplier for that type of pack for the Botvac. It takes too many cells (15 in a 5 series compared to 4 in regular lithium, 3 parallel) for the XV series vacuum, where only 12 fit in the compartments (from the lower energy density, lower cell capacities).
[edit] Note this battery is for the original Botvac supplied with NiMh battery, not the Connected supplied with lithium battery at higher voltage (I think; needs checking).
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Re: Botvac with LiFePo4 mod

Postby shirgal » January 1st, 2017, 5:37 pm

Happy new year and Great job for the modding :clap: i really need to make a few sets soon.


glnc222 wrote:[edit] Note this battery is for the original Botvac supplied with NiMh battery, not the Connected supplied with lithium battery at higher voltage (I think; needs checking).


As for this mod i think it might work well in the newer model.
Base charger that came with D series and connected model is compatible with Nimh battery,
The pcb inside is 2nd generation and has been modified from the 1st model,
Works with Neato p/n:205-0012,and LI-ION p/n 205-0011,
Check out the print from the base label here.
Attachments
botvac d base .jpg
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Re: Botvac with LiFePo4 mod

Postby Clark » October 8th, 2018, 7:03 pm

Hi there! This thread is gold and I intend to build my own set of two batteries today.
How's it holding up?
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Re: Botvac with LiFePo4 mod

Postby carrierlost » October 9th, 2018, 5:42 am

Clark wrote:Hi there! This thread is gold and I intend to build my own set of two batteries today.
How's it holding up?


Battery is still going strong. Will probably outlast the other components. I have already replaced two of the bump-switches and lately lidar has been acting up sometimes refusing to start - probably the motor or belt.
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Re: Botvac with LiFePo4 mod

Postby Ben_Affleck » July 1st, 2019, 10:12 am

LiFePo4 conversion with circuit that simulates end of charge - part 1

This is a very cheap to do conversion from the original NiMh Battery to a brand new LiFePo4 pack with balancing and full charge cut-off.

What you will need:
* From the original NiMh battery:
    - the original black plug with the thermistor (black thingy at the end of the yellow wires of the plug)
    - the bimetallic thermal switch (white thingy connected in series with the 2 rows of NiMh cells)

* From the internet (ebay, amazon, aliexpress) / local electronics shop:
Resistors are dirt cheap. If you cannot find them locally, you can buy an assortment pack on ebay with multiple values (just make sure the kit you buy includes the above values..)

*Required tools:
    - soldering tools, etc
    - glue gun (optional)
    - hot air gun (optional)
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Re: Botvac with LiFePo4 mod

Postby Ben_Affleck » July 1st, 2019, 11:26 am

LiFePo4 conversion with circuit that simulates end of charge - part 2

Step 1:
Build this circuit:
Untitled1.jpg


Step 2:
Build the battery pack:
Untitled.jpg
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Re: Botvac with LiFePo4 mod

Postby Ben_Affleck » July 1st, 2019, 2:02 pm

LiFePo4 conversion with circuit that simulates end of charge - part 3

The finished pack must look something like this:
IMG_20190620_143847.jpg


In order for the pack to fit properly in the Botvac battery compartment, you must take care when you shape the cells. The cells must be adjusted to form something like a right triangle:
IMG_20190620_144005.jpg


For keeping the electronics in place, keeping the thermistor and the bimetallic switch in place, and keeping the pack in the desired right triangle shape, I used a glue gun and some kapton tape:
IMG_20190620_143942.jpg

IMG_20190620_143907.jpg


Although not necessary, I capped the ends with cardboard and wrapped everything up in shrink tube (80mm type, which I bought together with the cells for just 1 EUR / meter):
IMG_20190701_162039.jpg
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Re: Botvac with LiFePo4 mod

Postby Ben_Affleck » July 1st, 2019, 2:47 pm

LiFePo4 conversion with circuit that simulates end of charge - part 4 (THE END)

The pack fits perfectly in the compartment:
IMG_20190701_162157.jpg


The compartment lid closes perfectly over the pack (but only if you kept the right triangle form for the cells):
IMG_20190701_161941.jpg


================================

How does it work:
    - The balancing circuit readily available from the internet does exactly that, it balances the pack when charging occurs, ensuring that every pair of cells gets charged to a maximum of 3.65V. Anything above that gets bled through a bleeding resistor in the circuit.

    - The custom made circuit is detecting the total pack voltage, compares is with a reference and when the voltage hits the reference it opens a circuit that includes a resistor that is in parallel with the original thermistor, thus lowering quickly the resistance over the thermistor, which is interpreted by the robot as a charge terminating signal.

    - The bimetallic thermal switch is a safety measure just in case everything fails and the pack overheats. In this case the whole battery pack and auxiliary circuitry is physically disconnected on the ground/negative side by the bimetallic switch.

Resistor values are very important:
    - The resistors are chosen of big values in order to have the smallest current consumption, as the circuit is always active, thus consuming current from the battery. I measured the total consumption at 600uA (in other words it would take about 2 years to completely empty a battery just on this consumption).

    - The combination of resistors for the voltage divider and reference circuit is tuned to trigger at 14.6 - 14.8V, just a bit over the total pack voltage when fully charged, in order to ensure full charge for the pack. Keep in mind that small variance of resistor values can move the trigger voltage by orders of times. I strongly suggest making and tuning the circuit on a breadboard first and measuring exactly at what voltage the circuit triggers.

================================

First use of the robot with the new battery:
It is recommended to NOT CHARGE THE PACK COMPLETELY BEFORE THE FIRST USE WITH THE BOT
If you do a full charge outside of the bot, when you will connect the battery to the bot, the bot will still want to charge it on its own. THIS IS NOT RECOMMENDED, because if you will put the bot to recharge it will not be possible because the signaling circuit will trigger from the start and the bot will believe that the battery is malfunctioning and/or overvolt the battery pack

If you DID charge the pack completely before joining it with the bot, you have two possibilities:
1. either consume SOME (not ALL) of the battery by external use
2. either connect it to the bot, use the Neato PC app to manually set the fuel gauge to full and run the bot a normal house cleaning sequence

If the battery is not fully charged (either by not charging it in the first place, or by depleting it through one of the above suggested methods), you are ready for your first charge on the dock. Connect the battery to the bot (if it's not already connected), place the bot on the dock and in the bot settings indicate that it is a new battery.

From now on the bot will function as you are used to.

The bot will completely recharge from empty to full in about 1h -1h15', a big step-up from the NiMh variant.

================================

FInal thoughts:

Keep in mind that YOU are completely responsible for this mod and neither I or Neato are responsible if you screw up and your house burns down or some other unfortunate event occurs.

I estimate that the pack will outlive the bot
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Re: Botvac with LiFePo4 mod

Postby glnc222 » July 1st, 2019, 7:39 pm

Thanks for extensive report.
What I found when trying to do this for the XV models was the LiFePo4 cell capacity available was too low for it to work and fit enough parallel cells in the space available. The original Botvac project reported here uses a different, newer model cell with higher capacity sufficient to work. The particular brand and model cell is important. I had also noticed that the Neato charger for NiMh tended to work better when the battery was charged from a mostly discharged condition, compared to dealing with an already charged battery -- its tricky dependence on temperature to terminate charging, used on NiMh chemistry which heats up. I had used a synthesized temp signal, however, compared to the thermal method with balancing circuits. (For newer XV models, the firmware can actually be switched over USB with a config command to a lithium charging method, since used by Vorwerk -- but not available in the Botvac firmware -- and would have the wrong voltage for LiFePo4 anyway.)
Notice the newer line of "connected" Botvac's with original lithium batteries moved to the higher 14.7v supply of the old XV's compared to the 12v NiMh Botvac (10 NIMh cell series vs 12 in XV). The higher voltage divides well into the regular lithium battery cell voltages, as used in the Vorwerk XV's, while the lower LiFePo4 voltage is needed to fit the lower 12v NiMh Botvac system).

[edit] Some of the Lawn Mower bots are supplied with longer lasting LiFePo4 batteries, being larger machines with room for the extra cells I suppose. The compactness needed in vacuum robots (similar to cell phones) and maybe higher cost of LiFePo4 compared to regular lithium ion, with higher energy density, may be driving the design choices made.

[edit] Note that with safe LiFePo4 compared to fire hazard lithium ion, it is actually possible to solder connections between the pack cells, when the preferred spot welded tabs on them are not available. Still should be soldered quickly to avoid damage, despite lack of fire hazard.
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