Author Topic: 10 second recharge of cold NiMH batteries  (Read 2856 times)

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Offline MrMobodies

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Re: 10 second recharge of cold NiMH batteries
« Reply #25 on: December 11, 2018, 09:45:45 pm »
They might appear charged.

He should have used a proper charger, like a SkyRC MC 3000 and apply the same charging parameters as that Energizer 15 minute charger, that would have displayed the current going into them and discharge them and then do the comparison between hot and cold. That would have been interesting.

On a charger like that in the video you can't just make assumptions because they reach a certain voltage in a shorter amount of time or if the lights change that is fully charged.

It sounds misleading.
 

Offline Kilrah

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Re: 10 second recharge of cold NiMH batteries
« Reply #26 on: December 11, 2018, 09:46:36 pm »
You missed the whole point didn't you?
 

Offline ogden

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Re: 10 second recharge of cold NiMH batteries
« Reply #27 on: December 12, 2018, 12:54:16 am »
Temperature has very little effect on battery capacity.

I would not consider 50% capacity loss at -20oC as "little effect" (consumer grade NIMH AA). Usually NIMH are not even specified for operating temperatures below 0oC, that's why number is not widely known.

Here's an experiment for you:

Fully charge a consumer grade NiMH at room temperature. Now place it in a freezer and freeze it down to -20°C for a while. After that, bring it back up to room temperature and discharge it. What do you think will be the remaining charge in the battery as measured by the discharge? Will it be 50% less than nominal, or will it be more or less the expected full charge?

Pretty close to nominal obviously. Most likely meaning was lost in translation - I am not native speaker. I did mean -50% capacity loss AT -20oC - when you discharge frozen battery you get only 50% of the nominal "room temperature energy"  out of it. After all we are talking about battery charging at frozen state right? :)
 

Offline IanB

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Re: 10 second recharge of cold NiMH batteries
« Reply #28 on: December 12, 2018, 01:12:22 am »
Pretty close to nominal obviously. Most likely meaning was lost in translation - I am not native speaker. I did mean -50% capacity loss AT -20oC - when you discharge frozen battery you get only 50% of the nominal "room temperature energy"  out of it. After all we are talking about battery charging at frozen state right? :)

Yes, sure, but I do not have evidence or sources to accept your statement about capacity loss. If we stipulate that none of the internal chemicals are permitted to freeze or solidify (for example, by crystallization), then I assert that the capacity of the battery during charging and discharging will not be strongly affected by temperature. This includes when charging or discharging at low temperatures. The limitation will mainly be on the rate at which charging or discharging can proceed, and the time that must be allowed for this.

My thought experiment was designed to convince you that this is the case. If it wasn't the case the frozen battery would lose some of its charge during the freezing/thawing process.

I'm not an EE--what am I doing here?
 

Offline ogden

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Re: 10 second recharge of cold NiMH batteries
« Reply #29 on: December 12, 2018, 02:14:40 am »
Yes, sure, but I do not have evidence or sources to accept your statement about capacity loss.

Can't find original source I was referring to, but this is close. 3C rate: 50% @0oC, 1C rate: 60% @-20oC.
Page #9:

https://www.mouser.com/pdfdocs/PanasonicBatteries_NI-MH_Handbook.pdf


 

Offline beanflying

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Re: 10 second recharge of cold NiMH batteries
« Reply #30 on: December 12, 2018, 02:35:22 am »
Discharging at lower temperatures is an issue with the effective battery impedance increasing and as a result the output voltage dropping. This drop off in output voltage tends to be the issue long before you run out of stored charge.

In my case on a sub zero morning the batteries (5 x Sanyo AA Enerloops so nominal 6V) were pulling so low under load the receiver in my glider on launch was being pulled so low it went into it's failsafe mode (3.6V) and was peeling off and heading for the ground  :scared: When released from the towline the plane flew perfectly normally until landed. I did this again and got within 5m at speed before recovery :phew: Same result after and on the ground everything was fine.

Much head scratching later and some bench testing with ice and containers we reached the conclusion the failure was temperature related as our better chargers give a read out of impedance while charging.

So the conclusion to this is Enerloops NiMh are crap at delivering high currents (circa 2-3A) when cold (-3-4C) but are fine at lower loads (2-300mA). I switched them out for high discharge Panasonics with a way lower impedance but at the cost of self discharge increases.
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Offline IanB

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Re: 10 second recharge of cold NiMH batteries
« Reply #31 on: December 12, 2018, 02:43:51 am »
Can't find original source I was referring to, but this is close. 3C rate: 50% @0oC, 1C rate: 60% @-20oC.

Page #9:


Yes, and this clearly shows how the limitation is on rate of charge and discharge.

The graph particularly shows the effect of temperature on discharge at 1C and 3C rates. What happens is that at lower temperatures ion mobility is reduced and the internal resistance goes up. This means that the discharge reaches the 1.0 V cut-off voltage sooner as the temperature goes down. Essentially the discharge is stopped due to voltage droop before all the stored charge is extracted.

It can be seen how the 1C curve is higher than the 3C curve. At 0°C we have 50% at 3C and 95% at 1C. It's not shown, but if we had the discharge curve at 0.1C it would be higher still, and would probably approach 95% at -20°C.

What graphs like this show is the difference between actual capacity and usable capacity. If you try to have a high discharge rate at low temperatures you get a much lower usable capacity. But the actual capacity of the battery has not changed, it just becomes harder to access.
« Last Edit: December 12, 2018, 02:49:14 am by IanB »
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Offline IanB

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Re: 10 second recharge of cold NiMH batteries
« Reply #32 on: December 12, 2018, 02:47:53 am »
In my case on a sub zero morning the batteries (5 x Sanyo AA Enerloops so nominal 6V) were pulling so low under load the receiver in my glider on launch was being pulled so low it went into it's failsafe mode (3.6V) and was peeling off and heading for the ground  :scared: When released from the towline the plane flew perfectly normally until landed. I did this again and got within 5m at speed before recovery :phew: Same result after and on the ground everything was fine.

Much head scratching later and some bench testing with ice and containers we reached the conclusion the failure was temperature related as our better chargers give a read out of impedance while charging.

So the conclusion to this is Enerloops NiMh are crap at delivering high currents (circa 2-3A) when cold (-3-4C) but are fine at lower loads (2-300mA). I switched them out for high discharge Panasonics with a way lower impedance but at the cost of self discharge increases.

A much cheaper solution is to keep your eneloops in your pocket on the way to the airfield and only put them in the glider just before use. Also wrap the battery pack in insulation like expanded polystyrene inside the glider.

A good trick where the batteries are actually powering a propeller is to warm them up in a hand warmer before use to make them nice and toasty. That will dramatically increase their power output.
I'm not an EE--what am I doing here?
 

Offline beanflying

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Re: 10 second recharge of cold NiMH batteries
« Reply #33 on: December 12, 2018, 03:00:24 am »
Removing batteries in the nose of my competition gliders that is easier said than done it goes nose weight, battery, receiver, servos with nothing extra between ;) The reason for this is to minimize nose weight and hence overall weight.

There is also about zero room to wrap batteries in anything due to being minmal cross sectional area for low drag and they tend to sit close to the ground for an hour plus between rounds with little time between your team mates last flight and yours.

So dumping the enerloops was the best alternate in this case. The Panasonics cells btw we have used elsewhere at 15-20A so plenty up their sleeve.
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Offline BrianHG

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Re: 10 second recharge of cold NiMH batteries
« Reply #34 on: December 12, 2018, 07:42:05 am »
If I was in my younger days, I would comment on his videos 'Great Success' stories for each one.  Thanking him...
Just to see the responses...
__________
BrianHG.
 
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Offline beanflying

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Re: 10 second recharge of cold NiMH batteries
« Reply #35 on: December 12, 2018, 09:04:49 am »
Agreed to much bother to watch and troll, he has what he wanted 2 million subs but it is interesting to see how few views he gets as a percentage seems to average 30-60k so even his subs don't watch him ::)

This is how you load test a NiMh battery btw. 100-120kg monofiliment line pushed to breaking point, 6-8 seconds for 300m traveled on tow to the release point glider transition to vertical at about 120-180 km/hr. Not your average balsa and dope glider.  ;)

https://youtu.be/2WPfNt1AdBc
« Last Edit: December 12, 2018, 09:07:43 am by beanflying »
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Offline ogden

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Re: 10 second recharge of cold NiMH batteries
« Reply #36 on: December 12, 2018, 10:42:39 am »
Can't find original source I was referring to, but this is close. 3C rate: 50% @0oC, 1C rate: 60% @-20oC.

Yes, and this clearly shows how the limitation is on rate of charge and discharge.

This graph is for Panasonic industrial batteries, very good NIMH's specified for freezing temperatures. Most consumer grade batteries are much worse, some hilariously pathetic. [edit] Modern Panasonic Eneloops have good low-temp performance as well, other "low self discharge" batteries may be good as well. I know at least one another brand (can't say, sorry) that is as good as Eneloop.

Quote
The graph particularly shows the effect of temperature on discharge at 1C and 3C rates.
What happens is that at lower temperatures ion mobility is reduced and the internal resistance goes up.

Yes. This is how you see frozen electrolyte and slow chem reactions at work. Mentioned Panasonic was showing ~80% at average 0.2C or so.

So dumping the enerloops was the best alternate in this case.

What did you change to? Li-Po?
« Last Edit: December 12, 2018, 11:21:15 am by ogden »
 

Offline In Vacuo Veritas

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Re: 10 second recharge of cold NiMH batteries
« Reply #37 on: December 12, 2018, 03:18:01 pm »
I can't stand the narcissism of these young YouTube hacks who put pictures of themselves in the thumbnail. Utter narcissistic trash.

Yes, good thing we can all come here



to discuss these things....  ::)
 

Offline MrMobodies

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Re: 10 second recharge of cold NiMH batteries
« Reply #38 on: December 12, 2018, 03:26:56 pm »
I like that
I can't stand the narcissism of these young YouTube hacks who put pictures of themselves in the thumbnail. Utter narcissistic trash.

Yes, good thing we can all come here



to discuss these things....  ::)

Here's a joke:

I like that hand.
It puts a stop to all the nonsense.

The hand says stop!
The face says no!
 

Offline Buriedcode

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Re: 10 second recharge of cold NiMH batteries
« Reply #39 on: December 28, 2018, 07:48:59 pm »
I think this thread goes to show, we're all prone to being fooled - regardless of how intelligent/educated someone is, if you think you' can't be fooled, then you're more prone to it.   This guy has been going a while and has some great videos - and used to fool many-a-tech-journalist (who aren't exactly the smartest of the bunch).  Good to see data on batteries, but.. really? I wonder how many of you lot "ate the onion" too ?

It is clearly a joke, with no malicious trolling - although I did read that several people have microwaved their iphones, wrapped routers in foil, and broken DVD's to get faster internet because of this chap. The world is full of, what many would consider stupid/laughable ideas about tech/science, but this guy is the least of our problems. 
 


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