Author Topic: EEVblog #811 - How The Varta 15 Minute Battery Charger Works  (Read 43876 times)

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Offline apis

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #50 on: October 30, 2015, 02:55:11 am »
Whenever reading about quick charging NiMHs they recommend dT/dt termination and using max-voltage, max-temperature and max-duration for backup since detecting dV/dt is going to be difficult.

Charging them in series shouldn't be a problem as long as you can detect when individual cells are fully charged and disconnect them, but I suppose you could pulse charge them one by one as well.

For detecting discharge current, could they somehow be grounding the positive battery terminals one by one and thereby measure current via the shunt resistor?

Don't really understand how it detects if it's an AA or AAA battery though, there must be more to it and all the 1 ohm resistors must have some purpose, but the only reason I can think of is current sensing? :-//

This thing needs more probing.
 

Offline drussell

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #51 on: October 30, 2015, 03:48:39 am »
I would love to see Dave get in there with a four trace scope and and see what sequence those MOSFETs are being switched in.

Oh, I forgot to mention....

I'd love to see a four trace scope of the four + battery terminals during a charge cycle.  Even just looking at the voltages there relative to each other would tell us pretty much exactly what it's doing with the charge profiles.  Current to each cell and investigating how the mosfets are being switched would be interesting also but even just seeing those voltage curves would be very revealing.
 

Offline AF6LJ

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #52 on: October 30, 2015, 03:50:46 am »
I would love to see Dave get in there with a four trace scope and and see what sequence those MOSFETs are being switched in.

Oh, I forgot to mention....

I'd love to see a four trace scope of the four + battery terminals during a charge cycle.  Even just looking at the voltages there relative to each other would tell us pretty much exactly what it's doing with the charge profiles.  Current to each cell and investigating how the mosfets are being switched would be interesting also but even just seeing those voltage curves would be very revealing.
Agreed.  :-+
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Online HKJ

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #53 on: October 30, 2015, 03:52:55 am »
Whenever reading about quick charging NiMHs they recommend dT/dt termination and using max-voltage, max-temperature and max-duration for backup since detecting dV/dt is going to be difficult.

That charger probably uses all the methods. -dv/dt is easy at 8 amps.

Don't really understand how it detects if it's an AA or AAA battery though, there must be more to it and all the 1 ohm resistors must have some purpose, but the only reason I can think of is current sensing? :-//

My guess is that they measures the voltage on both sides of the resistors (Maybe measuring the switcher output voltage). To do that they may use the mosfets to switch connections around, but with only a few mOhm in each they will not affect the result significantly.
 

Online NANDBlog

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #54 on: October 30, 2015, 05:39:32 am »
Actually it would be fairly simple to test any battery lifetime with 4C charging. All you need is a good battery tester, set up 4C charging, dv/dt or even cc/cv to fixed voltage which would take about 20-30 minutes and discharge with 1C/2C rate. Measure the coulumbic efficiency, and in an hour you get the expected lifetime.
Or even 200 cycles would be finished in a week and a half. I would do it myself and post results if there wouldnt be that bloody NDA.
 

Offline IanB

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #55 on: October 30, 2015, 05:56:04 am »
Actually it would be fairly simple to test any battery lifetime with 4C charging. All you need is a good battery tester, set up 4C charging, dv/dt or even cc/cv to fixed voltage which would take about 20-30 minutes and discharge with 1C/2C rate. Measure the coulumbic efficiency, and in an hour you get the expected lifetime.
Or even 200 cycles would be finished in a week and a half. I would do it myself and post results if there wouldnt be that bloody NDA.

I recall that user SilverFox on CandlePowerForums tested some Eneloops on a 15 minute charger. He put them through continuous charge discharge cycles. They were still holding up quite well after 100 cycles, but they lost some capacity and also lost some of their low self discharge properties.

I can't seem to find the thread right now to link to it.
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Offline drussell

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #56 on: October 30, 2015, 06:23:10 am »
They were still holding up quite well after 100 cycles, but they lost some capacity and also lost some of their low self discharge properties.

The loss of low-self-discharge (increase in internal leakage current) is by far the worst result of any kind of fast charging of most types of rechargeables.  Even 1h chargers will severely increase the self-discharge compared to being trickle charged over the cycle lifetime.  I have lots of batteries here that still hold quite a good charge after 10+ years and hundreds and hundreds of cycles but they're totally dead after just a few days off the charger.  That might be a useable situation for a power tool but not so good if you have cells you want to use in a remote control or something.  :)

Best to keep some cells marked as trickle-charge only for low-drain, long term, low-cycle use and blast the crap out of your other ones, your older ones, etc., whatever, for your heavy repeated charge/discharge use and beat 'em until they just won't charge anymore...  lol
« Last Edit: October 30, 2015, 06:28:25 am by drussell »
 

Offline apis

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #57 on: October 30, 2015, 07:13:56 am »
Whenever reading about quick charging NiMHs they recommend dT/dt termination and using max-voltage, max-temperature and max-duration for backup since detecting dV/dt is going to be difficult.
That charger probably uses all the methods. -dv/dt is easy at 8 amps.
Yes you're right, the reson charging in the .1C to .5C region isn't recomended is because even dT/dt detection becomes unreliable, but at 4C it should be much easier.
 

Offline tombi

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #58 on: October 30, 2015, 02:52:38 pm »
This come up on Dangerous Prototypes recently - here is an appnote from Vishay on dT/dt sensing for fast charging.
http://www.vishay.com/docs/29089/fastappl.pdf

Not clear how much current they are pushing.
 

Offline Stonent

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #59 on: October 30, 2015, 03:04:26 pm »
I would think at some point, all this heat is breaking down the chemicals inside.  The external temperature may be quite different than what's going on in the center.
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Offline VK3DRB

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #60 on: October 30, 2015, 09:39:30 pm »
To measure each battery discharge current, the micro might be multiplexing the FETs to measure the current from each battery bay one at a time periodically, and using the single sense resistor. Same for charging. Most the duty cycle is not measuring but actual charging and discharging.

Comments about the board...

1. In general, 45 degree micro is also a good idea for hot air and vapour phase reflow. The reason is the paste screening is generally a lot more uniform. You get less chance of shadowing and therefore less chance of dry joints.

2. No pin one on the micro and the SOIC. Crap.

3. Could have done better in the component designators. Not what I would call artwork. Also some white ink labels going over vias. Sloppy work.

4. Breaks in the high current tracks were a good idea. I have not tried this myself but I assume this tends to prevent solder voids at one end of long tracks due to surface tension during a wave soldering.

5. They used a crappy sleeve fan (probably bronze bushes) that dries out and then wears out, creating a very annoying whirring sound and eventually seizing. So it is clearly not a quality product.
« Last Edit: October 30, 2015, 10:06:53 pm by VK3DRB »
 

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #61 on: October 30, 2015, 10:01:52 pm »
Another video uploading now.
 

Offline VK3DRB

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #62 on: October 30, 2015, 10:05:22 pm »
As I mentioned, the fan in the charger is crappy sleeve type.

Good products use sealed ball bearing fans. Expensive graphics cards for gamers and CAD gurus and cheapo power supplies often also have fans with cheap bushes. First thing that fails is the fan. You can oil the bearings with sewing machine oil, but that only delays the inevitable... finding a replacement fan.

I own an expensive Pioneer 7.1 channel audio amplifier. Pioneer used a cheapo fan rather than a ball bearing fan. I have replaced the fan twice in 5 years and it is a unique form factor in a tight spot so I have to get the same rubbishy fan each time at never-to-be-repeated prices. How was I supposed to know Pioneers would put a crappy fan in? The product was not old enough when I bought it so I guess there were no failures in the field yet. Sales people won't tell you the product has a crap fan in it. In some stores you have to buy the device sight unseen (cannot take it out of the box.) The only solution is "once bitten, twice shy". That is, never buy Pioneer again. Stores will not allow you to tear down a product to look at its fan. I would not have bought the amplifier if I have known the trouble I would have with its fan. You'd think Pioneer being a Japanese company would know better.

Manufacturers should use quality fans like Panasonic or NMB DC brushless ball bearing fans, and avoid Hu Flung Dung brand fans if they want to build trust in the market place.

It is false economy using cheap and nasty fans - you lose customers. 
 

Offline bktemp

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #63 on: October 30, 2015, 10:39:07 pm »
As I mentioned, the fan in the charger is crappy sleeve type.
But does it matter? The typical lifetime of a sleeve bearing type fan depends on its temperature. You can find values in the range of several 10000 hours.
Lets assume the fan fails after 10000 hours. With one charge cycle every 30 minutes you can charge 80000 batteries. Most likely something else will fail before the bearing of the fan. If you charge one set of batteries per day the fan will last 50 years. I doubt many people charge that many batteries in their life.

A pc or some other device running 24/7 is a different story, but in rarely used charger even the cheapest bearing will last long enough.
« Last Edit: October 30, 2015, 10:41:38 pm by bktemp »
 

Offline Groucho2005

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #64 on: October 30, 2015, 11:20:53 pm »
With one charge cycle every 30 minutes you can charge 80000 batteries. Most likely something else will fail before the bearing of the fan.
Yes, at 8 amps charge current probably all 80000 batteries.  :-DD
 

Offline AF6LJ

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #65 on: October 31, 2015, 12:13:05 am »
Another video uploading now.

Good Something to watch while the test equipment warms up this afternoon...
Sue AF6LJ
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Offline VK3DRB

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #66 on: October 31, 2015, 12:20:32 am »
As I mentioned, the fan in the charger is crappy sleeve type.
But does it matter? The typical lifetime of a sleeve bearing type fan depends on its temperature. You can find values in the range of several 10000 hours.
Lets assume the fan fails after 10000 hours. With one charge cycle every 30 minutes you can charge 80000 batteries. Most likely something else will fail before the bearing of the fan. If you charge one set of batteries per day the fan will last 50 years. I doubt many people charge that many batteries in their life.

A pc or some other device running 24/7 is a different story, but in rarely used charger even the cheapest bearing will last long enough.

Your 50 years life from a cheap phosphor bronze bushing is far too optimistic. The lubricant would dry out way before then and start vibrating or seize. Maybe try 5 years, irrespective of the manufacturers' claims. I mostly use my Pioneer amp with Sennheiser wireless headphones, so the internal temperature is low, but the fans failed after only a few hundred hours of use over 2 or 3 years.

There are re-chargers too that get a heck of a lot of use, like in concert halls, churches etc where band mics have their batteries recharged and swapped out regularly. Whilst the 15 minute recharge time is impressive, the recharge life of the cells will be adversely affected compared to the recommended charge rates by reputable manufacturers.

I use a La Crosse BC-900 for recharging my genuine Sanyo Eneloops, all which I imported from a reputable dealer in the USA. The charger is excellent and no fan is required (slow recharging time). After 6 years and hundreds of recharges, the Eneloops are still going strong. Best batteries around in my opinion.

There are fake Sanyo Eneloops made where else but in "copywatch" China and sold on eBay. https://thecounterfeitreport.com/product/524/Eneloop-AA-Batteries.html
 

Offline rr100

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #67 on: October 31, 2015, 06:00:00 am »
Good Something to watch while the test equipment warms up this afternoon...

Not so fast, still traveling through the intertubes I guess...

I wonder how well it does different size (mix of AA and AAA). I ordered one myself for the heck of it, the old BC-900 was starting to have trouble with the LCD (tried to clean it up but seems to be a losing battle). Plus I've a feeling that it fails to terminate charging in time many times.
 

Offline AF6LJ

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #68 on: October 31, 2015, 06:16:55 am »
Good Something to watch while the test equipment warms up this afternoon...

Not so fast, still traveling through the intertubes I guess...

I wonder how well it does different size (mix of AA and AAA). I ordered one myself for the heck of it, the old BC-900 was starting to have trouble with the LCD (tried to clean it up but seems to be a losing battle). Plus I've a feeling that it fails to terminate charging in time many times.
This will be interesting to find out how well it works with mixed cells.

A search online reveals a hand full of 15minute wonders.
I'm not in a big hurry to charge batteries so something like this wouldn't appeal to me.
What does appeal to me is how they go about doing it.
Sue AF6LJ
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Offline felixd

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #69 on: October 31, 2015, 08:24:34 pm »
Dave I was wondering while watching 2nd part: Why not to use FLIR to track current flow for discharge and charge, test modes ? :)
Wouldn't that help to reverse engineer the process? BTW that would also look freaking GOOD to watch how this thing heats up! :)

I hold my fingers for that shot. Please make 3rd part with thermal images ! :D
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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #70 on: October 31, 2015, 09:24:02 pm »
Dave I was wondering while watching 2nd part: Why not to use FLIR to track current flow for discharge and charge, test modes ? :)
Wouldn't that help to reverse engineer the process? BTW that would also look freaking GOOD to watch how this thing heats up! :)

I would have done that, but the iProber is a more interesting tool I haven't shown much.
 

Offline oaliey

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #71 on: October 31, 2015, 09:52:57 pm »
When can we expect a teardown of that multimeter?
 

Offline blueskull

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #72 on: October 31, 2015, 10:11:00 pm »
When can we expect a teardown of that multimeter?

If you meant the current probe, Mike had done that.
 

Offline oaliey

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #73 on: October 31, 2015, 11:25:02 pm »
If you meant the current probe, Mike had done that.

I am referring to the Brymen BM235. The interwebs is suspiciously lacking any information on this meter.
 

Offline SeanB

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Re: EEVblog #811 - How The Varta 15 Minute Battery Charger Works
« Reply #74 on: November 01, 2015, 01:46:21 am »
Coming soon to an online store familiar to you........
 


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