Battery charger voltage tolerances - worth a shot or doomed to failure?

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mdf

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#315716 9-Aug-2024 10:28

I've got a vacuum cleaner with - I suspect - a faulty charger. I've just happened across a laptop charger with the exactly right barrel connector and +/- arrangement, but with the voltage a couple of volts off. I'm guessing that this would be enough of a difference that vacuum battery + laptop charger = magic smoke. But really have no idea about variances or tolerances with this type of thing so though I would see whether the GZgestalt thought this was worth a try?

All readings from the respective labels:

Battery: 14.8V

Original vacuum charger: 16.75V

Laptop charger: 19.5V

elpenguino

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#3269762 9-Aug-2024 10:43

A hack in this case is to use diodes to drop voltage. Each diode drops 0.6 V so use 5 diodes in series and bingo, you're pretty much at your voltage.

To do this, you'll need bog standard silicon diodes and to have the charger lead chopped open to expose the positive.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

richms

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#3269772 9-Aug-2024 11:01

14.8 is 4 3.7s in series - so possibly a li-ion pack.

16.75 is basically 4.2 * 4 - so standard max voltage for a 4S pack when on charge.

First option is that there is a full charger in the vacuum to limit the current and cut off when it is done. This would just get a bit hotter with slightly higher voltage, but be fine in most cases as they have thermal throttling in many charger chips to stop them overheating.

There is a chance that it will have a protected battery pack and just trigger the protection and do nothing when a too high voltage is attached.

There is also a chance that the battery terminals go straight to the input jack and rely on protection in the original power brick is actually a charger, so has the cutoff and monitoring in there instead. This would result in the cells just blowing up from being over voltaged.

I would not do it. I would get a 4S capable hobby charger and use that so it limits the current and has a cutoff when done. Still doesn't help if there is no balancing inside the vacuum to stop it going out of balance and having one cell give you some excitement.

Richard rich.ms

neb

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#3269959 9-Aug-2024 17:10

Was just going to post something similar to what @richms did, if it's a smart battery pack (in terms of power tools, Einhell / Ozito) then it'll control its own charging but may overheat due to excessive power dissipation in the pass transistor, if it's less smart then hopefully overvoltage protection will kick in and it won't charge, and if it's dumb (Dewalt) you'll get the SFX backing for this song. In neither case is it worth it.

tehgerbil

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#3269967 9-Aug-2024 17:29

mdf:

When I plug my charger in, I get a double flash with the old battery, and a blinking light with the new. Neither seems to be taking a charge, since the old battery will run the vacuum for ~5 seconds before stopping while the new battery will run it for maybe ~15 seconds before stopping. Since it is so old, there is limited info available online that I can find, but one youtube video seems to suggest it should be solid green.

Better yet, if you're in Wellington and willing to lend me a charging brick for a day or so to see if I can get the batteries to charge, could you let me know please!

To help all the troubleshooting/symptoms to one page. :)

When you say the vacuum is running for a few seconds - Is it pulsing on and off or is it staying constantly on for the few seconds?

mdf

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#3270730 12-Aug-2024 09:52

tehgerbil:

To help all the troubleshooting/symptoms to one page. :)

When you say the vacuum is running for a few seconds - Is it pulsing on and off or is it staying constantly on for the few seconds?

😃. Thanks!

Pull the trigger and it works fine for 5-10 seconds, no pulsing or anything. Then cuts out and the light on the top flashes. If I've found the right manual online, this indicates a flat battery.

T'internet almost unanimously puts this down to battery problems so I bought an aftermarket replacement battery. That however presents exactly the same issue.

Yesterday when I plugged in the original battery to charge, the light on the charger flashes. When I plugged in the aftermarket battery, the light on the charger more flickers than flashes. Which isn't exactly the same symptoms as when I made the original post.

My primary goal at this stage is not to throw further good money after bad so was hoping for some kind of cheap/free way to try and diagnose problem with (i) battery/batteries, (ii) vacuum itself, or (iii) charger before going off to buy (more) replacement parts and accessories.

tehgerbil

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#3270876 12-Aug-2024 16:40

mdf:

tehgerbil:

To help all the troubleshooting/symptoms to one page. :)

When you say the vacuum is running for a few seconds - Is it pulsing on and off or is it staying constantly on for the few seconds?

😃. Thanks!

Pull the trigger and it works fine for 5-10 seconds, no pulsing or anything. Then cuts out and the light on the top flashes. If I've found the right manual online, this indicates a flat battery.

T'internet almost unanimously puts this down to battery problems so I bought an aftermarket replacement battery. That however presents exactly the same issue.

Yesterday when I plugged in the original battery to charge, the light on the charger flashes. When I plugged in the aftermarket battery, the light on the charger more flickers than flashes. Which isn't exactly the same symptoms as when I made the original post.

My primary goal at this stage is not to throw further good money after bad so was hoping for some kind of cheap/free way to try and diagnose problem with (i) battery/batteries, (ii) vacuum itself, or (iii) charger before going off to buy (more) replacement parts and accessories.

Totally! I went down your same path with a Dyson V6 Animal recently, hence the pulsing query.

From looking at pics, can the battery be removed and charged outside of the vacuum itself? If so defo try that first.

For the new battery I've heard some BMS's need a charge for several hours before they'll 'kick in', so presume you have (but asking anyway..) charged the new one overnight?

With the charger light flickering and you've tried charging the battery unplugged from the unit and you've tried charging for 12hrs all with no change or success - Ask for a replacement.

Putting it another way - the likelihood of a faulty aftermarket battery is much higher than a faulty charger or faulty dyson vacuum causing the symptoms you're describing.