Which batteries should I choose

Hi

My first post ever and already I ask for help!
I've just bought this torch

and I want to use rechargeable batteries in it. I can't find anything about the discharge rate - I only know that it's a 20w torch that takes 5 d-cells.
I've been looking at these two:


I want long burntime, so could they do the job and will they be much worser then e.g duracell batteries?



Danish regards, Lodberg

Welcome to CPF!

The light will be drawing 3.33 A. Duracell D cells will give you less than 1.5 Ah with this current so you would get less than 30 minutes runtime.

In this thread you can see the discharge curve for the Duracells at 3 A:
http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Number=744320&page=&view=&sb=5&o=&fpart=1&vc=1

NiMH cells on the other hand will handle this current quite well (depending on brand). The CTA C cells performs very well so I think the CTA D cells you can buy here will be what you want:
http://www.thomas-distributing.com/cta-d-rechargeable-batteries.php

I currently have Silverfox testing these batteries, so if you can wait a week or two (it takes a long time to test D cells), then I can PM you the results. If these performs as well as the C cells did, then you should get 200 minutes of runtime with these.

Sigbjoern

Hi Sigbjoern

Thanks for the advice. I would love to get the result form Silverfox's test and have no problem waiting.

Can someone advice me in which charger I should choose to such high capacity cells?

/Lodberg

Hello Lodberg,

I think the AccuManager 20 by AccuPower is well suited to the high capacity C and D cells. It is also available from Thomas Distributing.

I have a Vanson BC-1HU that also works well, but you have to reset the timer if you run the cells way down. It can charge a 8000 mAh cell, but for higher capacity cells you have to reset the cell to start the timer over. The timer switches the charger to trickle mode after 11.5 hours.

I believe Sigbjoern was able to determine that the AccuManager 20's timer is around 35 hours which allows charging higher capacity cells.

Tom

Lodberg, your light (20w Vega 2 Rechargeable) already comes with a rechargeable internal NiCad battery pack with a 90-minute runtime.

http://www.technisub.com/ing/vega.htm

It may be possible to replace the NiCad pack with a custom NiMH pack that you would build out of the cells you show, for somewhat longer runtime. This will take some work, I think.

If you're actually intending to use this as a dive light then keep in mind it will change the buoyancy characteristics.

Hi Nubo

I bought the NON-rechargeable version - because I didn't wan't to have nicad batteries.

I'm going to use the torch for spearfishing during the night but haven't given the buoyancy a thought, do you think it will change much?

Lodberg, I see. So, you planning on replacing the bulb also? According to that site, the non-rechargeable version does not come with the 20W bulb; it has a much less powerful bulb that claims 16 Hours on alkaline D cells.

I think the buoyancy is only an issue if you're underwater. That is, it is not designed to float, but be fairly close to neutral buoyancy so that it is easily manueverable underwater. On the other hand, if you DO want it to float, I'm sure you can find someting to attach.

Some interesting lights on that site. The Vega100 (3600 lumen!) and Alulight 50 (1600 lumen for 50 min) might even get the interest of the Superbulb folks! Though, being immersed in water probably does help with heat dissipation /ubbthreads/images/graemlins/smile.gif

Hi Nubo

You're right it's not a 20W bulb as I thought, I thought it was because the rechargeable version of the torch is 20W - but mine is the non-rechargeable version.

I've checked the bulb - it's a 6407370-OSRAM which is 6.5V, 0.849A which gives 5.53W.
With my 5 rechargeable cells I get 6V and NOT 7.5V as I get with alkalines. So do I have to few volts and will that effect the torch's performance?
Can anyone give a estimate on the burntime with 5 CTA D 12.000mAH in the torch?

Danish regards, Lodberg

You should get 13 1/2 hour runtime with that bulb by using the CTA batteries. If you look at the rechargeable version of the light you can see that it has both a high and a low bulb. From the specs it appears the low bulb is the same as the bulb used in the non-rechargeable version. I would check out if it was possible to use the 20 W bulb from the rechargeable version in your light.

Sigbjoern

Hi Sigbjoern

13,5 hours sounds like much are you sure about that, and can you show me how you did the calculation?

I've read a post on a spearfishing forum, that you get 4 hours of runtime using Duracell Ultras and only 2 of them are with optimal light! Can that be true?

Lodberg

If we again look at Silverfox' test, now at 1 A discharge:
http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Number=744320&page=&view=&sb=5&o=&fpart=1&vc=1
You will see that the Duracells only gives you 5.3 Ah (and it reaches 1.0 V already after 200 minutes), while I estimates the CTA to give 11.5 Ah. If you set the cutoff to 1 V instead of 0.8 V as Silverfox did, then the Duracells only give you 3.4 Ah.

3.4/0.849 = 4 h
11.5/0.849 = 13.5 h

Sigbjoern

To set things in perspective:
You will get the same runtime with the CTA with the 20 W bulb as you get with the Duracells with the 5W bulb.

Sigbjoern

Hi again Sigbjoern

I'm really grateful that you take the time to help me. Thank you.

I must admit that the results is VERY surprising for me - that rechargeable batteries beats alkalines big time! Maybe it is because I grew up using extremly bad nicads in my remote-controlled car /ubbthreads/images/graemlins/grin.gif

I can see from Silverfox's test that the alkaline Ah depends a lot on the dicharge current, they perform worser the higher current. But is it correct to say that Nihm's Ah not in the same way depends on the current?


Lodberg

I also grew up with those bad nicads in RC cars, but remember, those were rated 500 mAh cells, so Alkalines performed better. NiMH on the other hand is a hole different story...

Yes, Alkalines doesn't like high current, the higher the current the worse they perform. NiMH's performance are also affected by high current, but not at all so bad as Alkalines. With good NiMHs you actually doesn't loose much capacity at all at higher currents, the thing that will happen though is that the voltage will sag a little bit, the higher the current the more the sag. This is because of internal resistance in the batteries.
The discharge curve of NiMHs are very flat compared to the Alkalines. PM your email address and I can mail you the discharge curve for the CTA C cells.

Sigbjoern

[ QUOTE ]
Lodberg said:
I've checked the bulb - it's a 6407370-OSRAM which is 6.5V, 0.849A which gives 5.53W.
With my 5 rechargeable cells I get 6V and NOT 7.5V as I get with alkalines. So do I have to few volts and will that effect the torch's performance?


[/ QUOTE ]

Lodberg, probably a noticeable difference in output. Incandescent bulbs are influenced heavily by voltage. The chart below shows a rule-of-thumb relationship between voltage, output and bulb-life.

The difference you'd notice will depend on just how much voltage the bulb is actually getting from the alkalines. At nearly 1 amp, probably less than 7.5 volts but I don't know how much of a drop. I suspect the design somewhat overvolts the bulb. At 6 volts, you'd be significantly under-volting. As a hypothetical example compare the "luminous flux" line at 90% vs. 110% of nominal voltage. That represents 70% vs 140% of the "normal" output of the bulb. So, if the alkalines supplied, say 7.2 volts to the bulb they would put out twice the light of the 5 x NiMH pack at 6 volts. And the light would be significantly whiter.

If this doesn't work for you, you might find success by using 6 of the rechargeables. That might present a space problem and then you'd need to think about maybe using smaller cells or modifying to gain space for an additional D cell.


On the other hand the 20W bulb seems to be designed for 5-cell NiCad pack (probably a 5 or 5.5V bulb) so if you were to use that bulb, 5 NiMH cells would provide the intended voltage. The only question then is if the non-rechargeable version can handle the heat/amperage of the 20W bulb. They both have metal reflectors so probably ok as far as the reflector goes.

Hello Sigbjoern,

You may have to rework your calculations. The CTA D cells are only coming in at around 10.3 Ah (tested at 1 amp)... They may improve over time, but that is with 3 cycles on them.

Tom

Thanks Tom,
it appears D cells doesn't live up to their rating as good as C cells does /ubbthreads/images/graemlins/frown.gif

10.3/0.849 = 12h

This must still be considered very good.

Sigbjoern

[ QUOTE ]
Nubo said:
So, if the alkalines supplied, say 7.2 volts to the bulb they would put out twice the light of the 5 x NiMH pack at 6 volts. And the light would be significantly whiter.


[/ QUOTE ]

If you compare the discharge curve between an Alkaline battery and a NiMH battery, then you will see that the NiMH actually has a higher voltage for almost all of its runtime. So my guess is therefore that they are using the same bulb in both versions (and the specs on their site indicates this as well), and that this is a 6V bulb.

Sigbjoern

Thanks to all who have given their contribution to build up this thread and help me.
But I still need help to one more thing: Choosing a good charger. The AccuManager20 has been mentioned as a charger that maybe up for the job. Can it charge the CTA 12.000mAh battery in one go?
Or maybe there is a better alternative?

Best regards, Lodberg

Yes it can charge the CTA D cells in one go. I don't know of any other charger that can do that.
Take a look at Silverfox's charger comparision here:
http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Number=818782&page=&view=&sb=5&o=&fpart=1&vc=1

I don't see that you can go wrong by choosing the AccuManager. I bought two of them since it takes so long time to charge D cells (nice to have if you need to charge more than 4 cells).

Sigbjoern