EEVblog #812 - Varta 15min NiMH Charger Part 2

Dave further investigates the Varta 15 minute NiMH batter charger.
Mixed signal analysis with the new Keysight 3000T oscilloscope, and current tracing with the TTI i-Prober 520 positional current probe
And some more reverse engineering.

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[ericgee]

This is what the EEVblog is about. Nice one Dave,

[Tangobaldy]

When Dave says a quick follow up you know your in for a mini movie. Yay

[joyange]

HI Dave. @30:32 in your video. You talked about a major discrepancy in the voltage on your meter and what was showing up on the charger. That's not because the charger is off cal. It's because the charger is measuring the voltage when the charge circuit is off. The charger is measuring the voltage of the battery in-between those short off pulses on your oscilloscope, Your meter is measuring the voltage while the charger is on and that 200mV discrepancy is cause by the battery internal resistance.

[inthenameofjustice]

Nice one. Discovering that return path has put my brain back into equilibrium. Thanks.

[MrZhilvinas]

I think Dave gave the poor charger too much hate on the voltage measurement. Remember the weird short pattern that the channels were displaying during charge (14:15)? I think this is where it actually measures the cell voltage. It first disconnects all the batteries to get the out-of-circuit voltage for each cell that is actually displayed on the screen. Then it gives full charge current to or each, one by one, to test if charge voltage is still within safety I guess. I think Dave should've used the scope to measure battery voltage and trigger on the drop to get the cell voltage. I'm not an experienced engineer by any means, but just gave my 2cents.

[TheSkytherMod]

It's nice to see that you genuinely enjoy talking about this stuff.

[ChrisKoch]

Ha! I was shouting at the screen like a sports fan at one point, "you're schematic isn't complete!!!"
Great video, Dave – with lithium charging getting so much attention, the lowly NiMH is at risk of being totally ignored.
As someone working on a project that incorporates multi-cell charging, I found it quite entertaining and informative. BIG thumbs up!

[jameslamb]

Glad you found the discharge path eventually, would have suggested using the FLIR to find the hotspots had you not.

[alextrofimov]

I love it when you say, "It's just a quick follow up video...", and it lasts for 40 min )))

[gavinandrews]

Glad you nailed that ladder! Well worth the re-visit.

[xtal]

I love how complicated a simple battery charger is.

[MrJeffschefke]

For some reason my fucking brain blew when he wiped the ink off...

[rymannphilippe]

Absolut fantastic how Dave take all out and share this with us. I have learned a lot of this video. Thanks Dave.

[CH_Pechiar]

I guess battery voltage during charge is measured during the cuttoff time, which would be reasonable.

[glonch]

Yet again, another awesome video... BTW - Dave, you could get the LAN/VGA add on unit for your scope - DSOXLAN. That way you can do split screen and the scope screen would be nice and clear with still being able to have the test device in view

[TheRealSasquatch]

More like this please. Finally understanding the circuit. Hate you make it look so easy ;)

[nd_Channel]

"Hi, just a quick follow up" and 37:48 min later we're done

Btw: the quick follow up is longer than the main video :)

[gertk]

Even if a bit late: reverse engineering at its best! Kudos Dave!

[ElmerFuddGun]

+EEVblog - Well I still think my idea of discharging exactly reverse of charging is more elegant! (posted in part 1) Less parts required and variable discharge rates with ease. Also, the higher than expected charging voltage is required to push the higher than standard charge current. Disconnected voltage would still be under max battery charged voltage. Great video!

[jsleeio]

Grouse work chief, really enjoyed this one. Bonza!

On a more serious note, it was great to see the gadgets come out and using more of that Agilent scope's feature set. I love how responsive it appears to be in all scenarios... Unlike the Tek MDO