# AA Eneloop voltage ever above 1.2?



## novice (Apr 11, 2010)

Hi,
I have done some thread searching, but have not found out much about voltage issues with Sanyo eneloops (except the fact that the voltage doesn't 'sag under load', whatever that means. If someone writes 'The Idiot's guide to EE', I will buy it).
I'm just starting out with Nimh rechargeables, and am not diving into lithium rechargeable chemistry yet. I just bought a dozen Eneloops, and am trying to find creative ways to utilize them besides my AA and 2xAA lights.
I would eventually like to try running a Malkoff M30 or M30w off of eneloops, but its hard to find them right now.
All of the eneloops that I now have, I first 'slow-charged' on a Maha MH-C401SF, that has separate charging bays. Although they are supposed to be 'pre-charged', the Maha indicated that all of them needed to be charged, and 3 charges (4 X AA) took several hours each.
I have bought a number of SureFire incan lights, either new or used, and immediately swapped out the lamp assembly for some sort of led unit. I did not keep track of which P60s were from used lights (silly, I know), and which were new. Last night I put a P60 assy. in a 6P + A19 + A14 + A14 + A14, which makes it about the right length for 5 eneloop AAs. I was thinking (caution: newb thinking ahead) that 5 X 1.2 volts = 6 volts, and since the P60 is rated for 6 volts, I'm going to get the maximum performance possible, at quite possibly a comparable runtime. I turned it on very briefly a few times, and headed out with it, to take the dog for a walk. Used it for maybe 30 seconds crossing a street, then again for about 60 seconds testing the throw in a field. About a block later, I started to use it again, fumbled with the momentary (thumb slipped off of the end of this 'baton', and then tried to use it on momentary again, and nothing happened. When I got home, I tried the same lamp assembly in a Z2 with CR123a primaries, and it didn't work in that either, so the lamp is definitely dead now.

There are 2 possibilities that I can think of:
1) The P60 was at the end of its life and finally just died.
- or -
2) I am unaware that AA Eneloops can actually be charged above 1.2 volts, and that the small amount of 'overvoltage' (my term), multiplied times 5, fried the lamp assembly. 

I then took off one of the A14 extension tubes so that I only had 4 Eneloops in a row, and the next spare P60 I put in seems to work fine, so far.

My question is, can Sanyo Eneloops be charged above 1.2 volts? One of the threads mentioned, in passing, a terminal cut-off charge of 1.47 volts for the Maha C-9000. Does that mean that my Eneloops might have approached that level in my MH-C401FS? I don't mind blowing a spare P60 so much, but I was thinking of hooking up 4 eneloops to a Malkoff M30 (4 x 1.2 = 4.8), and I sure don't want to fry a Malkoff.

Thank you!


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## Mr Happy (Apr 11, 2010)

Some things to know are that the voltages quoted on lamps or batteries are not always what they seem, that Surefire lamp assemblies are matched and intended specifically for CR123A batteries, and that when matched to the right batteries those lamp assemblies are driven to within an inch of their life (that's why they are quite bright).

So a CR123A battery might have 3 V written on it, but as soon as you try to load it up with a bright lamp assembly the voltage will drop down to 2.5 V or maybe less. When Surefire sells a "6 V" lamp assembly they know this, so the lamp is really rated for about 5 V, not 6 V.

Now Eneloops are nominally quoted as "1.2 V", but this does not mean 1.2 V either. A fully charged Eneloop will come off the charger at about 1.45 V, and when first used will comfortably deliver 1.3 V or more at a significant current. This means 5 cells equals 5 x 1.3 V = 6.5 V or so. Therefore you are driving a lamp intended to see 5 V with 6.5 V, a 30% over voltage. On a lamp assembly driven to within an inch of its life, 30% over voltage is too much for it and it will die rather sooner than normal, as you discovered.

Four Eneloops rather than five should be OK though.


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## novice (Apr 11, 2010)

Thank you for a very clear explanation, Mr. Happy!


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## TorchBoy (Apr 11, 2010)

curious_character wrote an excellent PDF explaining how an alkaline cell is rated 1.5 V but will actually give an average of 1.2 V or less, and how a NiMH cell is rated 1.2 V and will actually give that.


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## Burgess (Apr 11, 2010)

Hello Novice --

I'd welcome you to CPF, 
but you've been a Member here as long as I have.




May i suggest that you purchase a *Digital Multi-Meter*.

You will find *All Sorts* of uses for such an instrument.

:thumbsup:
_


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## march.brown (Apr 12, 2010)

novice said:


> I am unaware that AA Eneloops can actually be charged above 1.2 voltts.


 
I have just bought a pack of AA Eneloops from Amazon ... They are dated January 2009 ... I checked the open circuit voltages and all four cells are 1.313 Volts ... That is after sitting on a shelf for 15 months ... I have them on charge at the moment , but after charging I would expect them to settle to about 1.4 volts after a rest period ... My other AAs (Hybrios and Recyko) that were charged within the last few months or so are sitting at 1.37 Volts ... Can't actually remember when they were charged last , but that's the advantage of the low self-discharge cells ... Straight off the charger these (slightly warm at 93.5F) Eneloops now measure 1.45 Volts give or take a couple of millivolts ... Back at room temperature now and they read 1.442 volts.

So these cells do measure above the 1.2 Volts that you were expecting.
.


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## novice (Apr 12, 2010)

Thank you all for the information that you have provided!


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## Alex K. (Apr 12, 2010)

I don't know much about battery chemistries and whatnot, but all the rechargeables I have (Eneloop, Chicago Power) are rated at 1.2, and according to a friend's voltage meter, actually give that or a little higher.


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## march.brown (Apr 12, 2010)

march.brown said:


> I have just bought a pack of AA Eneloops from Amazon ... They are dated January 2009 ... I checked the open circuit voltages and all four cells are 1.313 Volts ... That is after sitting on a shelf for 15 months ... I have them on charge at the moment , but after charging I would expect them to settle to about 1.4 volts after a rest period ... My other AAs (Hybrios and Recyko) that were charged within the last few months or so are sitting at 1.37 Volts ... Can't actually remember when they were charged last , but that's the advantage of the low self-discharge cells ... Straight off the charger these (slightly warm at 93.5F) Eneloops now measure 1.45 Volts give or take a couple of millivolts ... Back at room temperature now and they read 1.442 volts.
> 
> So these cells do measure above the 1.2 Volts that you were expecting.
> .


 
They have rested a few hours now and two cells are 1.426 Volts and two are 1.427 Volts ... About what I expected.
.


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## Mr Happy (Apr 12, 2010)

A typical Eneloop discharge curve can be seen in this thread. For the first part of the discharge the voltage comfortably exceeds 1.3 V. This is with an old Eneloop in poor condition. A fresh new Eneloop in good condition may do even better.

Even though NiMH cells are described as having a "flat" discharge curve there is a significant peak at the beginning, and one needs to take note of this when running incandescent lamps in high stress situations like hot wire mods.


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