Powering a Dyson cordless vacuum cleaner

[asdex]

Hi, we have bought a Dyson vacuum cleaner which has a 230volt ac to 25.1volt dc charger.
i plan to buy a 24 volt variable DC output converter.
I can get constant voltage or constant current.
I'll use this to charge it from our 24 volt battery bank.
They have these on AliExpress: 1PC DC 300W 20A CC CV Constant Current Adjustable Step-Down Converter Voltage Buck Z09 .
Should I get constant volt or constant current?
Thanks

[PNPmacnab]

That is awful big to charge a vacuum. What does the wall wart specifications say as far as current. It probably doesn't need a buck converter costing more than $2. The charger itself should have the current limiting if it is supplied with an external wall wart DC source.

[Sunking]

I can get constant voltage or constant current.

Well you need to get both because every battery charger is CC/CV. Only a Chi-Com would sell half a battery charger.

[asdex]

Great, found one as mentioned: DC-DC CC CV Buck Boost Converter 9-35 to 1-35V 80W Buck Booster DC Step Down Step Up Adapter Module Adjustable Voltage Regulator
The existing wall adapter is one amp so I think these are just rated higher, they should just supply what I set it to.
If it's constant current, what limits overcharging?
Cheers,

[Sunking]

what limits overcharging?

Constant voltage.

[asdex]

Ok, so I'm guessing that if the voltage is set to maybe half a volt above battery voltage as the voltage comes up to near the charging voltage the current drops away even though it is a constant current charger?

[PNPmacnab]

No guessing. Internal to the vacuum is a 6S BMS board. It controls the charging current and balancing of the battery. Search that where you buy your converter for general idea and typical specifications It is analog and any excess voltage is turned to heat. 6S is 6 X 4.2V or 25.2V. Reducing that charge voltage slightly increases life of battery with a tiny reduction in capacity. The board will work wih a couple volts higher but go into thermal shutdown and reduce charge current. It is not unusual for a BMS board to go into a short period of shutdown when batteries are deeply discharged. Current is out of your control, but 25.1V is what you should shoot for.

[asdex]

Hi, thanks for that information. I have bought one of these:
DC-DC CC CV Buck Boost Converter 9-35 to 1-35V 80W Buck Booster DC Step Down Step Up Adapter Module Adjustable Voltage Regulator.
I'll set it to 25.1 volts output and by the sound of it maximum current output.
Cheers,

[asdex]

Thinking about this it seems the best board controls the current so I will be controlling the current twice
One with the constant current voltage reducer and the also with the bms board.
My battery bank voltage varies between 24 volts and 31 volts. The Dyson power adaptor says 26.1 volts DC.
Could I plug the vacuum cleaner straight onto the battery bank and allow the bms board to control everything or is 31 volts on occasions be too high?
If so, I could just use a variable voltage 5-35 volt power supply I already have which is Max 10 amps. The Dyson adaptor is 750mA.
Thanks,

[PNPmacnab]

All your numbers keep changing, I don't know what to think. There are plenty of boards that will work for less than $2 with no limit current feature. As I said before, board generally can only take a couple volts above charge voltage. Having no idea what the chip set I can not say further. Regardless, this would be abusive and lead to shorter life. There is nothing more I can say on the subject.

[Sunking]

Thinking about this it seems the best board controls the current so I will be controlling the current twice
One with the constant current voltage reducer and the also with the bms board.,

No the BMS does not control current. There are only two things that control the battery Charge Current.

1. Is the battery state of charge and Ohm's Law which you have no control over.
2. The charger current capacity and is the only thing you can control. Your job is to provide a charge source of the right voltage and current required for the battery and BMS. To low of a current and it will take way too long. To high of a current and you can burn up the batteries and BMS Thermal Over Loads. To low of a voltage and you will never get to full charge. To high of a voltage and you will let the smoke out and have a brand new boat anchor if there is anything left after the fire.

So your job is to find a CC/CV charger of the right voltage and current. The correct charger is the one that came with the vacuum.

Short story here is you have idea what you are doing and are playing with fire.

MODS I suggest you close the thread. OP is playing with fire.

[asdex]

Well looks like we should put this one in the too hard basket. I'll let you know if I get it sorted.
thanks,

[Sunking]

It came with a charger. Why replace it?

[asdex]

It came with a ac charger (adapter). If I run it on my inverter the charger uses about 20 watts but the inverter also uses 20 watts just to run. I normally have the inverter on pulse so it's running power consumed is only 8 watts. ( Outback FX2420).
If I can run straight from the battery bank I save power by not having the inverter on 24/7. I run our TV, satellite box and laptops directly from battery using dc-dc reducers.
The only things on the inverter are fridge, freezer, and water pump.
Cheers,

[Mike90250]

Then just charge the vacuum from the inverter when the fridge is running. They only need a couple hours a day, not 24/7 to keep the vac cleaner charged, If the inverter is on anyway, you are set. But the battery BMS is only made to work with the charger it came with. With Li batteries, you have no "grace" it's either working, or burning. If the Mfg design burns your house down, their insurance company buys a new house for you. If your DIY charger burns the house, your insurance will say "What were you thinking", and cancel your policy.