Author Topic: Running on eneloop AA batteries  (Read 4400 times)

ssmall

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Running on eneloop AA batteries
« on: January 13, 2015, 09:26:15 AM »
I have had good luck using eneloop batteries.  -14*F last night and they are still going strong.

Felix

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Re: Running on eneloop AA batteries
« Reply #1 on: January 13, 2015, 09:33:12 AM »
Are you using rechargeable eneloops?

ssmall

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Re: Running on eneloop AA batteries
« Reply #2 on: January 13, 2015, 10:12:28 AM »
Yes, I am using rechargeable AA eneloops.  They are the older version so I think they are 1600mAh.  I use 3 of them in series to power the weather station.  Looks like the latest eneloops are 2000mAh.

Felix

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Re: Running on eneloop AA batteries
« Reply #3 on: January 13, 2015, 10:54:45 AM »
Do you see a drop in voltage relative to the drop in temperature?
I would totally expect so, although not as dramatic as other cells.

ssmall

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Re: Running on eneloop AA batteries
« Reply #4 on: January 13, 2015, 12:01:30 PM »
I do see a drop in voltage during really cold weather but it isn't much.  To be honest I am measuring the voltage using the moteinos built in voltmeter that others have referenced, so I don't think method truly reflects the actual voltage drop.  I have not tried to set up a proper voltage divider circuit to measure the actual battery voltage yet.

TomWS

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Re: Running on eneloop AA batteries
« Reply #5 on: January 13, 2015, 12:47:25 PM »
I do see a drop in voltage during really cold weather but it isn't much.  To be honest I am measuring the voltage using the moteinos built in voltmeter that others have referenced, so I don't think method truly reflects the actual voltage drop.  I have not tried to set up a proper voltage divider circuit to measure the actual battery voltage yet.
Do you mean that you are using measuring the 1.1V reference voltage and extrapolating the VCC from that?  If so, that's fairly accurate, even over temperature.

Tom

ssmall

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Re: Running on eneloop AA batteries
« Reply #6 on: January 13, 2015, 12:53:47 PM »
Tom, that is what I am doing.  If that is correct, I am seeing voltage drops on the order of 100ths of volts on days where the temp is below zero F.

TomWS

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Re: Running on eneloop AA batteries
« Reply #7 on: January 13, 2015, 04:44:31 PM »
Tom, that is what I am doing.  If that is correct, I am seeing voltage drops on the order of 100ths of volts on days where the temp is below zero F.
WOW, that's pretty outstanding!  Makes me want to switch to these!  But wait... they don't spec these to work below 0 degrees C!  What's up?  I sure wish they'd spec what these are 'supposed' to do in 'normal' outdoor cold conditions.  -15F spec would be very useful.

1.2V is a problem unless I make a cylindrical battery holder that would hold three of them...
Wikipedia page states that early versions of their C and D cells were just that, three of the A type batteries in parallel.

Anybody seen a cylindrical 3xAAA holder???Nevermind, I just designed one to cut out on my CNC router!  8)  Unless, of course, you HAVE seen a holder like this (in which case I'll buy instead of build)!

Thanks for the info.
Tom

ssmall

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Re: Running on eneloop AA batteries
« Reply #8 on: January 13, 2015, 10:05:55 PM »
I looked on the eneloop site about year ago and as I recall it said they were good down to -20*C.  I could be mistaken.  I have not seen any holders like you describe.  I do have the plastic C and D battery holders that you can insert a AA battery.  Not that useful.  Wish I had a CNC router!  ;D

TomWS

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Re: Running on eneloop AA batteries
« Reply #9 on: January 13, 2015, 11:15:23 PM »
<...snip>Wish I had a CNC router!  ;D
Build one!  That's what I did.  Check out http://www.solsylva.com/

Tom
BTW, which battery website had the -20C info?

ssmall

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TomWS

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Re: Running on eneloop AA batteries
« Reply #11 on: January 14, 2015, 03:31:21 PM »
http://www.panasonic-eneloop.eu/home/whats-eneloop.html
Thanks. ::)
I can visualize that marketing guy giving the 'specs' to the webpage developer and it slipped his mind to tell the engineer who wrote the datasheet...   Probably too busy thinking about his next golf outing with a customer.

Sigh...

kiwisincebirth

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Re: Running on eneloop AA batteries
« Reply #12 on: January 16, 2015, 11:13:44 PM »
Here is my last year (sort of) on 3xAA envelop batteries. I say sort of because I have composed it from six months of data from four different nodes that started at different voltages.

All nodes have a simple voltage divider (few meg ohms) to measure the input battery voltage. All nodes also power a DS18B20 temp sensor, except node 12 which has a Lux meter. All nodes wake up every minute and transmit a reading. I am Sydney, Australia so ambient temps are good.

I am hoping to get about 1.5 - 2 years from a single charge, but will see.

The graph shows number of days on the bottom axis, and volts on the side.

TomWS

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Re: Running on eneloop AA batteries
« Reply #13 on: January 17, 2015, 08:35:50 AM »
Kiwi,
thanks for sharing!  This is GREAT and perfect timing for me.  I've been considering switching to these (from LiPos) as battery backup for my Gateways but was concerned at how fast they'd drain to 1.2 volts.  It seems from your data that, with minimal discharge, their voltage stays on the high side for a long time.  I think you'll get far more than two years because they are only now reaching their plateau level (nominal 1.2V). 

I just need to look into charging circuits before I make my 'leap'.

Thanks again!
Tom

kiwisincebirth

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Re: Running on eneloop AA batteries
« Reply #14 on: February 19, 2015, 03:29:57 PM »
Hi There. Here is my first eneloop crash. Was fairly liner down to 3.6v (mid jan) then fall sharply to 3.3v Interesting is what happened when it reach 3.3v Node is still running fine. Thoughts ?
« Last Edit: February 19, 2015, 04:10:57 PM by kiwisincebirth »