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Fixing the AEG CX8-50EB, battery powered vacuum cleaner
#1
Technically it isn't broken, so fixing means actually modifying. Enhancing the unit and getting rid of some stupid issues (from my point of view) that AEG has built into this model.
Oh, and when I say AEG I mean Electrolux. AEG used to be a german company but has been bought by swedish company Electrolux and is now one of their brands. You will see some part numbers below, maybe you'll find that this particular model is available under different trade names:


I bought one of these some time ago because I'm lazy and didn't want to get out the corded vacuum cleaner all the time. It does its job very well. I have no carpets and no pets so I don't need a super high power vacuum cleaner to get the job done. And the battery powered one can be charged from my solar setup so that's a win-win.
Researching about vacuum cleaners leaves you with the usual results: Lot of cheap and nasty stuff, small handheld ones and low power units 10.8V/12V (3S), 14.4V (4S), non lithium 9.6V and weird stuff like 13.5V lithium, whatever that is. Then there is the 18V (5S) and 21.6V (6S) in the middle and 25.2V (7S) and more at the top. And the "high end" stuff like Dysons which are overpriced at all sizes and voltages. The AEG CX8-50EB is a midrange 21.6V model, based on reviews it's a decent machine so I got that one. There are also 25.2V models in the CX8 range which is important later on.

AEG screwed up the battery a bit, I knew that from other reviews and AEG actually acknowledged battery issues. Usually DOA batteries (the ones that come with the unit as well as spare ones) or batteries that just die after a few cycles. I wasn't overly bothered with that, replacing cells and building/rebuilding batteries is what we do anyways. AEG used probably old stock of Samsung INR18650-15L cells or had the assembled batteries lying around for a long time, the issues are likely caused by long term storage.

But I knew that I had to fiddle with the battery at some point anyway, so to make easier I've chosen the CX8 series. I bought a second CX8-50EB with a dead battery for cheap on eBay so I didn't have to play around with my fully functional vacuum cleaner on the first try. All units from this series have a removeable battery as you can see:


Unfortunately AEG didn't think this through. The battery can only be charged inside the unit. There is no external charger bundled with the vacuum cleaner. It's not even available as an option. So what is the point? The battery is easily user-replaceable, sure, but spare parts are overpriced and low quality so I'm not sure what the idea behind this was. On the chassis there are two metal contact pads on the back. When putting the machine on it's charging station it makes a connection with the power supply which then puts 35V across the pads, 500mA max. Charging takes quite a while, even though it is just a 1500mAh battery.


The power supply is, according to its label, the same for the 21.6V and 25.2V models. When I saw this the first time I thought about whether they share more parts. Turns out they do, here is the 21.6V / 6S battery I have:



It's a 7S BMS, two wires are joined together on the same cell. On the 7S models there is just one more cell in there. The cells are hold in place by cell holders (not pictured) and there is actually an empty slot for the seventh cell.

And this is what the inside of the vacuum cleaner looks like after you've removed its chassis:


It's really not much. The white cable that runs down the side of the table has a PCB with two buttons on the end, power on/off and the speed selector. When starting it it automatically runs on full power and you can turn it down to save energy and increase the runtime but I never found this to be very useful. On the right there is the battery connector together with my remaining original battery. The small PCB with the white wires attached to the main PCB has the charging and error LEDs on it. The motor is wired directly to the main PCB. The other red/black wires with the big connector in the middle is the connection for the powered brush. Not sure why there is a connector on these wires. There is also the blue and green wires going down to the brush, have yet to work out what they are for. The red connctor on the PCB is the input, I've unplugged the wires, you can seem them on the top between the screwdrivers.

The idea is now to remove the main PCB. Apart from low voltage cutoff it provides no feature that I want or need. The motor will be powered directly from the battery, controlled by an old fashioned switch. Still have to measure the current the motor draws to properly size the switch. Low voltage warning will be done by a standard LiPo beeper from the RC world and charging will be done using a balance charger, I'll add balance wires to the battery. Not using the crappy battery BMS board anymore obviously.
Also I want to find out if this is actually the same motor as in the 25.2V models. If it is then I'll make a 7S battery for free extra power, otherwise I'll stay at 6S.
hbpowerwall likes this post
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#2
Ok, so the motor is specced for 24Vdc, so probably not the same as in the bigger model. I guess I could push it a bit but that's not really necessary as it has enough power for my use. Together with the powered brush the system draws just under 8A from the battery. The cells are specced for 18A and 11A after 250 cycles, so while their capacity is lacking a bit it isn't the worst design decision, on paper, to use these cells. But it wasn't the best either. Still they are a bit troublesome for some customers but maybe this is also down to the BMS.

I will now get a switch that can handle the current and then build a new battery.
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#3
I've put it back together which was a pain in the butt. The body is pretty bad quality, cheap plastic, and it doesn't fit properly anymore after disassembly. But it still works and next thing to do is finally making a new battery!
Korishan, tuncd, wim like this post
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#4
(03-25-2018, 09:36 AM)DarkRaven Wrote: I've put it back together which was a pain in the butt. The body is pretty bad quality, cheap plastic, and it doesn't fit properly anymore after disassembly. But it still works and next thing to do is finally making a new battery!

Hello DarkRaven, why didnt you try to rebuild the battery with the new cells? is the mainboard in the vacuum broken?
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#5
I've been pretty busy lately and only now I'm coming back to revisit some things I've started ages ago, including this.

To answer the question, even though it might be a bit late, no, it's not broken. I just went for a minimalist approach. Like this any 6s battery can be used without any further modifications. That said I still have two of these devices and on of them is in its original condition, I might build a new battery for that one as well.
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#6
(01-05-2019, 01:21 AM)DarkRaven Wrote: I've been pretty busy lately and only now I'm coming back to revisit some things I've started ages ago, including this.

To answer the question, even though it might be a bit late, no, it's not broken. I just went for a minimalist approach. Like this any 6s battery can be used without any further modifications. That said I still have two of these devices and on of them is in its original condition, I might build a new battery for that one as well.

I tried to replace the batteries in the pack, but result is not good. I was realy very careful, isolated each cable when disconnected from the pcb, but when I connect them pcb is getting hot. I found an other dead battery, tried the same thing, on this one pcb started to getting hot at first cable, when connected the 3 one it got fried.
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#7
Maybe you have to connect the new cells before disconnecting the old ones. Sometimes on newer PCB's this is the case, some sort of "safety" feature.
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#8
I haven't found the time to do this yet, but I will investigate when I finally get back to this. Thanks for the warning though!
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#9
(02-09-2019, 12:06 PM)LEDSchlucker Wrote: Maybe you have to connect the new cells before disconnecting the old ones. Sometimes on newer PCB's this is the case, some sort of "safety" feature.

+1 

While not a vacuum cleaner, I did try to repair a relative's Dell laptop battery with new cells and encountered the same "safety" feature. Apparently, the BMS shuts down permanently if a proper voltage is not present in the pack. If the cells don't hold a charge, but still have a voltage, you need to somehow keep the BMS alive while changing out the cells.
Formerly known as Dallski
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#10
(02-09-2019, 08:15 PM)Dallski Wrote:
(02-09-2019, 12:06 PM)LEDSchlucker Wrote: Maybe you have to connect the new cells before disconnecting the old ones. Sometimes on newer PCB's this is the case, some sort of "safety" feature.

+1 

While not a vacuum cleaner, I did try to repair a relative's Dell laptop battery with new cells and encountered the same "safety" feature. Apparently, the BMS shuts down permanently if a proper voltage is not present in the pack. If the cells don't hold a charge, but still have a voltage, you need to somehow keep the BMS alive while changing out the cells.

I did also recognize this by trying to change the cells of a laptop battery (HP ProBook). That's also the reason why I do not have a battery in my Laptop now Big Grin
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