Adapters vs. Intended Cell size - tell me

[rhwestfall]

I see many folks commenting that they are using AA to C (or others) adapters to power their lights off smaller cells. What are the benefits/disadvantages of this?

 

[herman]

The main reason I swapped over to AAs with adapters is I got tired of having a drawer full of partly used Cs that were accumulating from dive trips. I hate to throw a slightly used battery away but I did not want to chance taking them on another dive trip 6 months or more away. Since I use rechargeable AAs in all my other dive related battery devices - camera/strobe/marker lights/small lights it only made sense to convert my C lights to AAs as well. The down side is the capacity (burn time) of the AAs may be slightly less than that of a C but unless you are using the battery up fully on each dive who cares, you just recharge it between dives. NimH batteries do have one more characteristic that can be considered a benefit or a disadvantage depending on your point of view. The power curve of NimH batteries is a good bit different than standard non rechargeable batteries. In a light application, standard batteries start out slightly brighter than NimHs but a few minutes into their burn time, they dim to match a fully charge niMh but then continue to get dimmer and dimmer until they are dead. NimHs on the other hand, start out slightly less bright but remain at an almost constant output until they get nearly discharged at which point they drop off rapidly. Some divers don't like the rapid drop-off so they see it as a disadvantage, they prefer the lower light but much more predictable output of standard batteries. I on the other hand, prefer the longer, more constant output of the rechargeable and if my light goes out, I just grab the backup.

 

[rhwestfall]

Thanks Herman. Taking this further, is there any "rule of thumb" for the difference in life (not cycles, but "burn time" power supply) between, for example, an AA and a C sized cells?

Like, is a C going to last 2.5x (just throwing numbers out there.....) longer than an AA (same chemical make-up)?

 

[flots am]

Thanks Herman. Taking this further, is there any "rule of thumb" for the difference in life (not cycles, but "burn time" power supply) between, for example, an AA and a C sized cells?

Like, is a C going to last 2.5x (just throwing numbers out there.....) longer than an AA (same chemical make-up)?

You would need to look up the specific cell on the manufacturer's website. They're rated in ma/hour., so you can compare various manufacturers and cell sizes.

A 1200 ma/hour cell (any size) will have about twice the burn time of a 600ma/hour cell (any size).

flots.

 

[herman]

A quick google search indicates that alkaline Cs are around 6000 to 8000 mHr as opposed to around 2500 mHr for rechargable AAs or roughly 2 or 3 to 1. I am not sure where the cutoff point is but there is a point where the battery is still putting out power but the light is so low that it is not at an acceptable level, the discharge curve I was talking about in the last post comes into play here. In other words, is the last say 1/4 or so of the battery capacity of the standard C really useful, plus would you actually take a known half or more discharged light on a dive, remenber you will have to guess what the actual charge level is. For sake of argument, lets say it's 2 to 1. Which would you rather do, take a fully charge battery that will last 2 hrs or take a hopefully half discharged battery that will last 2 hrs? I have been using AAs in 4C lights for years and so far I have not had one go dim, much less out. If I were depending on it for cave diving, I would likely go with the biggest standard battery light I could get but for OW, non critical dives, I just don't see the issue....so what your light goes out, you grab your backup or just hang with your buddy. I would rather gamble on the chance my light goes dim/out than have the drawer full of half used but useless batteries. All that aside, there is also a cost issue. Rechargable AA are expensive but will last for hundreds of charges so the overall cost is considerbly lower not to mention waste production.

 

[rhwestfall]

thanks again Herman.

 

[YankBoffin]

I've just purchased a UK C4 ELED light and was looking into using rechargeable AAs as described in this thread. My only remaining question is if using AAs with spacers could have an undesireable effect on the bouyancy of the lamp. Will it be too positively bouyant with all that new air space in the housing (to the point being annoying to handle) or will it be negligible?

 

[dfx]

You would need to look up the specific cell on the manufacturer's website. They're rated in ma/hour., so you can compare various manufacturers and cell sizes.

A 1200 ma/hour cell (any size) will have about twice the burn time of a 600ma/hour cell (any size).

Just to do some nitpicking...

Capacity is given in mAh, that's milliampere-hours, which is very different from mA/h, which would be milliamperes per hour.

As for NiMH batteries, there's two types. The regular ones, and the LSD (low self discharge) ones. The difference is that the regular ones quickly lose their charge without being used, up to 20% after 24 hours and 50% or more after a month. LSD NiMH batteries retain most of their charge for years. They're usualled marketed as "pre-charged". Their downside is that they generally have lower capacity than non-LSD batteries, but their benefits generally outweigh that disadvantage.

Another thing to watch out for is fake larger-sized (i.e. C or D size) NiMH cells. There's quite a few on the market that are just AA cells in an empty larger capsule, while costing twice as much.

To get the most out of NiMH cells, I recommend getting a good "smart" charger, like an MH-C9000 or a BC1000.

 

[lucca brassi]

I see many folks commenting that they are using AA to C (or others) adapters to power their lights off smaller cells. What are the benefits/disadvantages of this?

Main idea behind this is switching between Li-ons bateries and NiMh ( or alkaline ) , with most simple led drive (linear ) that usualy meean resistor and in advanced form low drop voltage regulator in current mode ( or FET as current source -GRS ) . Usually these lights are used as BACKUPS ( Hesser , Halcyon scout , Agir ......SOLARIS....)
Led needs tension cca 3,5V -3,8V +/-1 V to take right current through. 3,7 V is nominal voltage behind SINGLE Lion cell or 3x NiMH (3x1,2V (1,5V)) =3,6 V so there is ratio .

Battery cells have standard size and that mean

1D size = 3 x AA
1C size = 3 x AAA

if is build some maybe 4x cell adapter there is also posibility to be built in some'' drop regulator-buck '' ( normaly have some modes ) in other case - lover voltage if light have some modes must be built in some ''step up -boost regulator ''.

in a short words

 

[herman]

I've just purchased a UK C4 ELED light and was looking into using rechargeable AAs as described in this thread. My only remaining question is if using AAs with spacers could have an undesireable effect on the bouyancy of the lamp. Will it be too positively bouyant with all that new air space in the housing (to the point being annoying to handle) or will it be negligible?

There will be a slight change in buoyancy but it's going to be fairly small, I do not recall any of my lights shifting to the positive side. Most of these lights are still negative with the AAs but if it does shift to positive (I really dislike anything positive attached to me when I dive), you could always add a small rod of lead beside the adapters to compensate for the buoyancy increase. In most lights, there is enough space between the adapters that an 1/8 inch /3mm diameter rod of brass or lead can be inserted to restore the negative buoyany. I would cover it in a layer of tape or heat shrink tubing as a safety precaution.