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Dyson v8 battery upgrade
Recently i bought a Dyson vacuum cleaner.
One word: perfect, BUT the battery capacity is low, really to low.
After some searching on You Tube some guy give me an idea: use powertool batteries for it.
So as fond Hilti user i have some broken stuff in the shed.
I use Hilti in the construction a lot, no brand can handle it!!! especially the frequency of use.
I had a broken Hilti charger(went for a ~"swim" Blush )
I ordered from aliexpress a "dummy" battery holder.
Cut both up to fit inside each other.
So i can use my power tool batteries and swap when empty.

Perfect so far: his own bms is in the battery pack, i can charge fast with my normal chargers, triple the amount of capacity per charge and (~free) batteries enough.
However the cut off is in the tools switch.
If you don't use the cut off and if you don't pay attention, the battery will drain to a lower voltage than it is healthy for the cells.

What is this piece of magic that disconnects the engine and battery when it is getting to low?
Disconnect voltage is around 16v (nominal is 21.6v) 22v tools.
I don't think it would be anything like a 7815 or such, but i would not be surprised if it was one of his bigger brothers.

Other surprises with Dyson(clever against diy!) is the mechanical switch, there will be an electrical switch in the side of the new "battery converter/holder".
Dont get the cells disconnected from the bms or the bms will go in protection mode, also dont enlarge the existing cells, apparently the bms will also go into protection mode.
Or buy one with bms:


If someone is interested I can post photos of the full build/transformation.

But with what electronic gizmo I can achieve that disered cut off?

Thanks in advance
Could that electric gizmo be a zener diode or a connecting resistor.
Both have a minimum voltage to operate on?
Or could there be an integrated circuit around a LM or such?
Sinds the zener diodes can not take more than 50w at 18v, i thought of the following for the cut off.
The dyson needs 4.5a in "low" mode and 22a in "max" mode at 22v nominal.
If i going to solder a led board with resistors, so all the leds will light up when the bat is full, and one volt drop means one led out.
I will put a relais at the desired cut off voltage = 18v, if that led does not glow aka does not receive power anymore the relais wil also no longer receive power and thus close and the engine will not receive power.
Does this make any sense? will or can this work?

Thanks in advance.

btw that electric gizmo is a 18v 50w zener diode.
The lines from the bms from the battery are connected to this.
One v cut off and one temp cut off(to high drain also)
Have you found anyone that makes a case for 2P, 3P, or 4P for the 6S Dyson packs? I have several Vanon replacement batteries and I'm in the process of making a 6S4P pack so that my wife can stop complaining about Dyson's battery life (even though she never remembers to charge it when she's done using it). I thought that having several battery packs would work, but if you don't use at least 1 screw, the battery pack will slip out and fall mid-vacuuming, so that didn't work.

For you, instead of toying around with the Dyson BMS, which seems very self-protective, just get the aliexpress kit you linked to and call it a day. Make it 2P or more. The hardest part will be finding a bigger case that "fits with the aesthetics of the Dyson."
Check out my long-term capacity test of 18650s:

I glued the stuff together and put it in the cleaner. first couple of runs where perfect.
To look for a gizmo that can handle those currants, i give up on that one.
In Low it draps 4 amp, on max it draws 24 amp.
But i can do the whole living with one battery pack, upstairs with one pack, in the back with one pack.
Instead of every day one room on Low.

I thought about the bms and make a bigger pack on it, but i wont suit my needs, to low on capacity.
(dog owner, no chiwafwafs)
I will try to find a relais that could solve the problem for the cut off, but one for a 24a draw...
Just keep a eye on the leds indicator, red is stop. Blush

I misread your whole first post. You are trying to use a swapable Hilti battery pack with the Dyson, not make your own custom battery pack. I guess it was late, I read too fast. I got excited because I have a similar side-project. And you obviously don't have to care about aesthetics, that thing is a total Frankenstein haha!
Check out my long-term capacity test of 18650s:
A decent MOSFET will easily do 24A, many are rated 50A?
Maybe a low voltage alarm or cut off which controls the MOSFET?
Starting to sound like a BMS....
Any reason you're not going with a basic BMS?

For display, maybe a voltmeter this:
or this:
Running off solar, DIY & electronics fan :-)
My V8 battery look like this.
Original BMS , so far works very well.

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