Running a 24V vacuum cleaner from 19V only works sometimes - why?

[nuhega]

I have a battery powered (24V) vacuum cleaner. Now I'm kinda sick of replacing the batteries that no longer properly recharge, so I thought about replacing the battery pack with a "real" power supply.
I have an old laptop power supply that outputs 19V, 4A (Toshiba PA-1750-09) and fits perfectly inside the handle of the cleaner - very much in contrast to all other PSUs I found online for a somewhat affordable price that could output 24V and 2A (which is the current the vacuum needs when running off the battery).

Now the strange thing: When I first tried if 19V is even enough, it worked perfectly fine, but now I tested it again several times and most of the time it does not work and the motor just spins up for a fraction of a sedond and then repeats this pattern. But then again I had it working for whatever reason again one time.

Any idea what could cause this? Maybe the motor control on the vacuum does not like the "DC" frequency from the switched-mode power supply?
Do you have any suggestions?

[eccerr0r]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

Well need more details about the actual circuitry of the vacuum (is it just a switch to a motor?) alas the startup current of these motors are IMMENSE.

I have a 3.6V NiCd battery powered vacuum cleaner. The thing drains near 15 amperes on startup and sustains around 5 amps when running. I was thinking about using a Li-Ion cell since the NiCd pack is toast, but couldn't find a suitable protected Li-ion cell that could handle 15 amperes.

Since yours is 24V nominal, to get the same power, yours wouldn't need to supply 15 amps, but I suspect it still is fairly high on startup, probably near 6A. This may cause the PSU to sustain damage or get confused. Granted you're running a lower voltage and thus less power, I don't know.

[goontron]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

Well need more details about the actual circuitry of the vacuum (is it just a switch to a motor?) alas the startup current of these motors are IMMENSE.

I have a 3.6V NiCd battery powered vacuum cleaner. The thing drains near 15 amperes on startup and sustains around 5 amps when running. I was thinking about using a Li-Ion cell since the NiCd pack is toast, but couldn't find a suitable protected Li-ion cell that could handle 15 amperes.

Since yours is 24V nominal, to get the same power, yours wouldn't need to supply 15 amps, but I suspect it still is fairly high on startup, probably near 6A. This may cause the PSU to sustain damage or get confused. Granted you're running a lower voltage and thus less power, I don't know.

I think you are on the right track with this thought. It sounds like the PSU is 'Bootlooping" for lack of a better term. PSU starts, sees overload (motor startup current), shuts down on protect, repeat ad-nauseum.

If its anything like the Toshiba PSU i had the (mis)fortune of trying to use, it trips out under the slightest overload....

[budm]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

i think you are on the right track with this thought. It sounds like the psu is 'bootlooping" for lack of a better term. Psu starts, sees overload (motor startup current), shuts down on protect, repeat ad-nauseum.

If its anything like the toshiba psu i had the (mis)fortune of trying to use, it trips out under the slightest overload....

+1

[gabiz_ro]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

Except adding one bank of capacitors on PSU output, that may work or not, to supply a little more current during startup you may try adding some NTC in series with motor.
When are cold have some resistance and limit startup current but that warm up and decrease resistance.
You may buy or find on some PSU that kind of NTC.
Ex:


https://www.homemade-circuits.com/us...ge-suppressor/

[nuhega]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

I did some more testing, now I can 100% recreate it working or not working.

1: I connect the PSU cables to the vacuum cables. Result: Motor not working.

2: I connect the PSU to the vacuum with two crocodile cables I used earier when testing. Result: It works 100% of the time.

This is not about bad connections - I wiggled both connections quite good but only the second one works.
Both cables have ~1.5 Ohm together. I also tried another cable with ~3 Ohm and it works too. So the additional cable and thus the additional resistance seems to limit the current to the point where the PSU does not shutdown. With the multimeter I can see spikes up to ~3.8A with that configuraton, so without the additional resistance it's certainly over 4A and thus some protection shuts it down (I guess).
The whole circiut of the vacuum cleaner from the plus to minus battery cable has 2.5 Ohm by the way. Or 1.5 Ohm in the "power" setting.

How nice that a datasheet for a NTC I just pulled up literally says "Applications: Soft-start motors, e.g. in vacuum cleaners".

So I guess I need like a 2 Ohm NTC thermistor?

Thank you

[eccerr0r]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

Do you mean the charge port? A lot of devices will stop the motor from working no matter what you do if you have it plugged in to the charge port.

Need clarification/pictures of what you're actually connecting to ... to understand what's going on...

[nuhega]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

I just replace the battery pack with a laptop PSU. Directly connected to be former battery cables.
The charge port is separate, I don't touch it at all.

[eccerr0r]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

If you can power it 100% of the time with clips, then it's probably not an overcurrent situation, rather you still have too much resistance somewhere. When talking about amps, one ohm could be a lot of resistance when dealing with low voltages... Then again unsure how you're measuring resistance as a lot of meters aren't accurate that low, usually due to probe issues.

[momaka]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

I think you are on the right track with this thought. It sounds like the PSU is 'Bootlooping" for lack of a better term. PSU starts, sees overload (motor startup current), shuts down on protect, repeat ad-nauseum.

I third that notion.

Most laptop adapters tend to be quite sensitive to over-current. I tried using a 20V 3.5 Amp adapter to power a home-brew amplifier, and it kept shutting down on me the same way, mostly because I had a hard power switch going to the amp, so that when I turned On the amp, the uncharged capacitors in the amp would draw too much current and make the adapter turn Off. In contrast, I had no problems whatsoever with a SMPS adapter that was made for a CA subwoofer system, even though the adapter was rated only for 2.5 Amps (and 17V).

In the end, I found that I could trick the laptop adapters to work with my amp by using the secondary side of a large transformer as a large inductor - i.e. a "soft-start" / "peak current limiter". (But I switched back to the CA adapter, because it worked fine for my needs in the end).

This is not about bad connections - I wiggled both connections quite good but only the second one works.
Both cables have ~1.5 Ohm together. I also tried another cable with ~3 Ohm and it works too. So the additional cable and thus the additional resistance seems to limit the current to the point where the PSU does not shutdown. With the multimeter I can see spikes up to ~3.8A with that configuraton, so without the additional resistance it's certainly over 4A and thus some protection shuts it down (I guess).

There you go.
You just need more resistance or something else to limit the current spikes to prevent the laptop adapter from shutting down.'

Also, I bet you that if you connect the adapter to the vacuum cleaner but keep the adapter unplugged from the wall, then turn on the vacuum cleaner and then plug in the adapter in the wall, it would also likely work without the additional resistance from the cables (provided the vacuum uses a hard On-Off switch, and not some logic/relay/IC/transistor). Why? Because as the adapter voltage starts to climb, the motor will start to spin up slowly too. So that would avoid the big turn-On current spikes. At least that was another way I could use my laptop adapters with my home-brew amp. But it was impractical, of course.

By the way, another thing that came to my mind is if the original batteries were Li-Ion, the vacuum cleaner could have had an under-voltage circuit to cut power off from the batteries, in order to prevent them from over-discharge. But I don't think that's what we have here, since you were able to measure resistance directly from the (+) and (-) terminals of the vacuum's battery connector (which likely is the motor resistance + NTC, if there is one).

[nuhega]

Re: Running a 24V vacuum cleaner from 19V only works sometimes - why?

By the way, another thing that came to my mind is if the original batteries were Li-Ion,

No, SubC NiMH all in series, crap.

~2.2 Ohm NTC resistor is installed, starting the vacuum works fine, NTC gets to ~100°C after a minute or so, but I did not do any longer tests yet.