Directly replacing NiMh cells with Li-Ion cells - bad idea ?

[eccerr0r]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

No, it could not have been a cheap cell. The internal impedance of this cell necessarily is low because of the heavy load it needs to drive. Remember this thing needs to discharge at 8C. Surely if it's discharged at 8C, it can be charged at 1C at least?
Does that cheap battery you buy get hot at 2C load? Probably does if it gets hot at 2C charge.

--
Oh BTW:

I charged it with a CC-CV charger when I first got it as a test, and it did not get warm at all!

[sam_sam_sam]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

No, it could not have been a cheap cell. The internal impedance of this cell necessarily is low because of the heavy load it needs to drive. Remember this thing needs to discharge at 8C. Surely if it's discharged at 8C, it can be charged at 1C at least?
Does that cheap battery you buy get hot at 2C load? Probably does if it gets hot at 2C charge.

If this is case then I am confused about why charge the battery at such a low rate

I curse what brand name is this battery that is in this unit

[eccerr0r]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

Yeah the battery was covered in paperboard (which was around the heatshrink), so I couldn't get a brand or model number without ripping it apart. I figure let sleeping dogs lie, it works, don't fsck with it or fsck with it minimally. I guess I have to stick with my conclusion even if it's unfounded, at least until it stops working... mainly had to make assumptions because I needed to charge it and didn't want to buy/integrate a fast charge system for it.

Besides, if I needed to run this vacuum more than even 5 minutes at a time, I might well try to use an AC powered vacuum. Or even the 12VDC vacuum I have...

[sam_sam_sam]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

Besides, if I needed to run this vacuum more than even 5 minutes at a time, I might well try to use an AC powered vacuum. Or even the 12VDC vacuum I have...

You have a good point

[sam_sam_sam]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

Yeah the battery was covered in paperboard (which was around the heatshrink), so I couldn't get a brand or model number without ripping it apart. I figure let sleeping dogs lie, it works, don't fsck with it or fsck with it minimally. I guess I have to stick with my conclusion even if it's unfounded, at least until it stops working... mainly had to make assumptions because I needed to charge it and didn't want to buy/integrate a fast charge system for it.

You’re assumptions might be correct in that if only used for a few minutes at a time then you do not necessarily need to have a fast charging rate if used in this manner because most of the time people would have the unit on charge all the time anyway

[stj]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

it's probably just lazy designers,
charge controllers cost peanuts now.
that said, larger psu's dont.
so it may be slow to reduce the cost of the transformer.

btw, all the solar lights i'v opened have been NiMH
it would be a bit risky putting a lithium or lipo in the hot sun!!
there are other exotic chemistry's about, but they arent cheap or superior to NiMH

[Dannyx]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

Well guys he did it again: my super skilled old man here replaced some cordless DRILL batteries with Li-Ions now and added a Wii-U charger in parallel to charge/power the thing, so if you thought the vac deal was questionable, this is downright dangerous IMO I'm afraid we might see the shop up in flames one day

[stj]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

still in the shop??
i would love to know the stall current of the device.

[Dannyx]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

still in the shop??
i would love to know the stall current of the device.

Yeah, I'm still here amazingly, if that's what you were getting at

The stall current is precisely what I was thinking of too, because we know high-torque motors can draw quite some amps - they put BMSs in there for a reason ! I don't know for sure since I haven't measured it and probably never will, but the 3.5a adapter would occasionally give up and the drill would stop when you start putting significant pressure on it. He doesn't seem to get it, so he keeps believing there's some sort of thermal trip in the drill itself or something...I doubt the cells were new to begin with, so couple that with the insufficient current of the adapter and you've got the reason: when the load suddenly increases, the current draw first causes the adapter to shut off and the batteries to drain instantly (provided they held some charge in them to begin with !) and it takes a few seconds for the adapter to restart and allow the drill to at least turn again...
It's guys like these who are treated like gods around here sadly....age is just a number I say Louis Rossmann drove this point home a couple of times when he showed some very competent youngsters on his channel. Same here: I don't claim to know sh!t, but COME ON !

[stj]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

looking forward to the smoke & flame.

[Dannyx]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

looking forward to the smoke & flame.

Yeaaaah...don't really think that's going to happen that easily, but who knows how much abuse those things can take and what their failure mode is

[redwire]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

I would plan my escape route, so when the fire starts, grab your tools and RUN AWAY. Or stay away from the charging station.

But these idiots are like a cat and have 9-lives.

[budm]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

It sounds like the owner of the business does not care either.

[eccerr0r]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

Technically I'm also playing the dice with that HT with unprotected li-ion cells... been "manually" balancing them... eek (can't protect them from overdischarge!)

I really should get a bms board for them...

(oh btw, this was acquired second hand, though I didn't design it, I suffer the consequences if I accidentally abuse it...)

[Dannyx]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

It sounds like the owner of the business does not care either.

No, not at all...as long as the joint runs, that's good enough. He doesn't know half this stuff either - i.e. he's not tech-minded. Just your average-Joe running a business....which somehow happens to be the biggest in town

[Dannyx]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

But these idiots are like a cat and have 9-lives.

PFFTTT....geez, you have no idea how right you are how often I think the same thing >_>

[stj]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

your co-worker is following the old saying, "if at first you dont succeed, try try again"
(at starting a fire!)

[Dannyx]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

Yes, to his merit, he's persistent and he often pursues some avenues which seem completely ridiculous and sometimes ends up with total success and praise from tech-illiterate people around him who don't know better. Sad, considering "nice" guys like me who try to do everything nice and perfect are shoved to the side...all well....

[Dannyx]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

Sorry for digging up such an old thread. Hopefully people are still following Today I came across something which comes oddly close to what my dear old dinosaur friend was doing to that vacuum way back in the first post - remember him ? Of course you do

So: someone bought a(n overpriced) flashlight from an online shop, one of those things with overblown specs, which of course came without batteries. It's rechargeable by USB. The small instruction sheet that came with it claim it accepts an 18650 cell OR 3 AAA NiMhs, which I find a bit concerning in the long run...what do you think of this ? A flashlight capable of charging BOTH NiMhs and 18650 with no user interaction ? Not only they're completely different capacities, but also different chemistries, so is this the recipe for disaster and trashing some good cells ? :|

[eccerr0r]

Re: Directly replacing NiMh cells with Li-Ion cells - bad idea ?

A 18650 with protection you can charge fairly easily. And NiMH cells usually are tolerant with charging (at least they won't burst into flames.) But if you optimize for one, the other won't work to their potential, so choose one.

However if you design it such that it can detect chemistry and choose proper charging algorithm.

Now if you stuck Alkaline AAA's in there, all bets are off...