Replacement D Cell options - Portable spotlight project.


I have been given one of these: as it has a buggered battery pack.

Taking it apart reveals a 10S D cell NiCad battery pack, beautifully made by the way, nestled behind what I have found out is a bona fide aircraft landing light bulb/reflector assembly! :smiley:

The pack refuses to hold charge, never managing to extinguish the red light on the charger and setting off the low voltage alarm within moments of turning on the beam.

The low voltage alarm is apparently set for 10.3 volts so for a freshly charged pack to be dropping to that level almost immediately means that at least one cell is dead, probably two of them.

The cells themselves are 4000mAh D sized NiCds, probably due to their toughness in a military context and although a new battery pack is available at £65 it would be the 4000 mAh NiCds ( again presumably due to their resilience) rather than one of the more modern and capacious options.

Whilst I have it apart and am going to be spending money, I am thinking that I may as well upgrade the NiCds to NiMH or maybe even Li-ion batteries.

The first question is which sort of NiMH batteries to use, looking around reveals a bizarrely wide range of capacities, ranging from AA battery capacity to 12,000 mAh or so. Can anyone recommend a good quality, ideally cheap as possible as I need ten of them, D cell NiMH battery for this purpose?

The lamp is rated for 100W at 13V so around 8-9 amps, would D cell NiMH cells be able to handle this sort of discharge rate comfortably?

The second question would be where can I get such batteries from most economically in the UK?

Using Lithium batteries is an interesting option, I have had good luck with D cell sized 36200 sized Li-ion batteries in my modded mag light but at £25 per pair, and I would be looking at a 4S3P configuration. I think there is space for the extra 2 cells but will check. A PWM voltge limiter could the bring the voltage down to the 12.5V for the bulb.

Comments, ideas and criticisms please chaps.

Search the forum here were some topics about d cells. I don’t use d cells personally I use AA LSD nimh only, eneloops are probably the best cells. and of course as a cheap and good alternative the ikea laddas which are around 1£ per cell so 20-30£ total costs.

Also consider how you want to charge them, do you have a hobbycharger?
How big is the pack, or how much space do you have for the new cells.

3s2p 18650 might work if you find a battery holder you can charge them in your standard charger. The 10.3V battery protection is good for 3cells.
But I am unsure how bright it will be, hard to estimate how the nicd compare in terms of voltage under load to the liion cells.
6 cells for 5-10$ plus holders…

Oooff… 100 Watts…
Halogen lamp…
20 years old? :wink:

The thing is, LiPo is attractive, but you’ll need to balance-charge them when used in series.
NiMH and NiCd is a lot easier to charge in series.

So you plan on keeping the halogen set-up?

Thank you for your post.

I’m not sure I understand what you mean when you say Ikea laddas Werner?

The pack is as the picture in the second link, basically three and two cells wide and two high. there looks to be space for 12 cells ie three and three wide and two tall.

As to charging I have the original charger for the torch which was designed for Nicads.

The Spotlight has some internal circuitry and I think it may have the charger circuitry built onto that rather than the charger enclosure but would need to check.

Will the charger work with NiMH or would it be NiCd specific?

The charging algorithm for nicd is different to nimh, my general experience with all nimh/nicd built in chargers is bad either it was in a flashlight, tool or toy.

But it might work if it only gets random use…

Ikea laddas are a cheap and rather good option for AAs all around the world(every country where ikea has its stores).

Another thing which came to my mind is the li battery packs for bikes, they have a balancing charger already build in… Forget it theses are 2s 8.4V only

Have you followed the threads about the laptop pulls of the American guys here? Check your local ebay, maybe you can source some cheap 18650.
With all that space even a 3s3p or 4p should be possible.

The battery pack is marked 2006, the trouble was that it has probably been on charge for most of the intervening 8 years… :smiley:

I was looking at my laptop and thinking “Hmmm, an 11.1V 5100mAh battery, I wonder if that’s a 3S2P lion pack with balancing wires built in?” J)

I do, it’s full one of these: Getalamp | Lamparadirecta

Never played with an aircraft landing lamp before and I would need to spend a lot more than 20 quid to find something with a much better luminous intensity.

In theory a 4S3P configuration of 36200 would fit. :beer:

I was a bit worried about making a large Li-ion pack as I don’t know quite what I’m doing with Lithium cells.

Is there a good primer on pack design on the web?

I’m fairly handy with a soldering iron and did A level electronics but this stuff is beyond me at the moment.

You have to decide how to charge, if you just randomly use this light battery holders and a standard charger you already have are the cheapest option. You could also use the batteries in other devices(maybe not the best idea because the cells would get a different usage level…)

With a battery pack either self built or bought a hobbycharger is needed.

A easy and probably brightest solution might also be a lipo RC pack and a hobbycharger for charging.
I have some packs from hobbyking and these packs hold voltage even under high discharge current well.

Thank you Werner, you have been very helpful. :slight_smile:

So if I want to keep the existing circuitry I have to replace the battery pack with an identical one of NiCd cells? Seems reasonable.

If I want to replace the battery pack with NiMH cells I would need to junk the existing internals, build a new split charging circuit and get a hobby charger?

If I am doing that I may as well use Li-ion or LiPO cells as the amount of work and the rough cost seem to be the same and in that case may as well buy a RC battery pack rather than make up a pack myself?

The light is sealed after assembly so I don’t think a solution that involves taking it apart to charge the batteries will work. :frowning:

Thanks again.

I understood that the charging algorithms were different for NiCd and NiMH, if I simply swapped the old pack out for a new one made up of NiMH cells, would the old charger and internals still work? Would it be a question of charging it twice or something?

A 3S Li pack will produce an average of 11.1V, will this be underdriving a 13 volt spotlight?

Hard to tell how this all behaves because the internal resistance of these lipo packs is super low and I guess the original pack couldn’t hold more than 11V for a long time.

Check this eneloop discharge graph to get a feeling for the voltage under discharge conditions

Of course a bigger D cell will be better, maybe a D cell will behave like three parallel AA so we check the 3A discharge graph of the AA eneloops….
This would give around 1.2V and eneloops are well known for the high voltage under load.

I have an ongoing projekt of a light which had 6V Leadacid battery in it, I already bought a 12V 55W bulb and I have a 3S lipo which I want to use in it. I will check how far I am with it later, maybe I can measure the difference between 12V and 11V….

Ah, of course. :slight_smile:

How far would a decent Li pack sag under the same load though? I mean if the D cells sag to around 11 volts from 12, would the Li pack sag even further?

Now I know why I stopped working on that light, it’s total crap. It consumes 55W at 12V but only gives dim light…maybe 900lumen…crappy beam inclusive…
I used a new Philips vision H3 bulb 12V 55W.

I have a turnigy nanotech 2650mAh RC pack just wired up with some monitoring electronic from hobbyking which measures voltage, current and Calculates the power.
Voltage sags to 12V in short time under load and had about 55W(58W at 12.4V), half empty the pack had 11.3V and gave around 50W, still more than the 3.7V each cell should have, 11V 48W, 10.3 43W after that I have no further measuring point because my low voltage beeper started because one cell was below 3.3V and I switched off.

Lux measurement is difficult, maybe 100lm less after voltage sag and around 600lm at 44W. Which would give around 15lumen per Watt… :frowning:

Compared to a King this old style lamps are crap, bulky, heavy and dim even throw is not better than a king…
If yours would be the same just twice as bright and maybe would have a better reflector I would still toss it. Do you know how bright the bulb in your lamp could theoretical be?
I have seen some posts here about guys which built in such searchlights a xenon bulb, maybe that is an option

Tenergy NiMH D cells are well-known for their low cost and ability to deliver BIG amps (the Premiums are rated at 50A maximum). But as others have said, there could potentially be issues when it comes to charging them.

Tenergy also sells 5000mAH Nicad D cells. They go for about $4 apiece, or $30 for 8. So they are fairly budget friendly. Capacity is lower than NiMH. But there would be no worries when it comes to charging.

I know that there are chargers that can charge both NiCad and NiMH batteries without needing to be told via a switch which battery type is installed. How do they do this and determine when each is fully charged?

Could the charging circuitry in the light be replaced with a appropriate NiMH charger or with a smart charger that can handle both NiCad and NiMH cell packs?

I think that I would rebuild the battery pack using These:

That would technically be the easiest solution if those batteries are available in the UK or the EU. Note that they even have the solder tabs for pack building.