Info on charging NIMH battery packs

[daz]

I am in the process of building a 50 watt umbilical dive torch.  The head unit is complete and I am looking at my options for the battery pack.

Currently I have 40 AA NIMH 1800mha batteries and am looking at the best option for putting them together as a 12v battery pack.  So far I am considering either using all 40 to give me approximatly 12v at 7.2ah or 2 packs of 20 to give me 12v at 3.6ah in each pack.

This raises the question of charging !!  I already have a charger for a 7.2v NIMH pack that indicates an output of 12v at 600mha.  Would this work for charging the pack(s).

Any ideas or advice appreciated.

Daz

[Pierre Farrugia]

Hello,
I have a pack of 10 Nimh cells of 1.2V, 4100mAh. I use a Maha 777smart charger. One of it's good points is that has a temp. sensor so that cells do not over heat.Can you give more details of your charger, does it has a temp sensor, time limit or deltaV termination?

Regards

Pierre

[Pierre Farrugia]

Hello again Daz,
With my pack 12V 4100mAh with a 35w gives me 65min. So I think that for a 50W you need a 7000mAh pack. Sorry if I am telling you the basics but if you run a 7.2Ah with a 50w halogen bulb you wil get the following.
Power W = Voltage V * Current I
50W     = 12V * Current ?
50W/12V = Current
4.17A
So if you divide power pack current by your current needed you get burn time but to get a more realistic value you have to multyply by 80%
So 7.2A divide by 4.17 = 1.73hours = 103min * 80% = 83min burn time, which is very good for a 50w halogen bulb.

[Lawrence Debono]

Pierre, can you give us a link to some pictures of your canister light, please. I'm sure you would make a few heads turn. It looks neat, well constructed and effective. Did you ever use those SS D ring holders on the canister? From what I already seen it is worth every minute that you put into it. Well done.

Lawrence

[daz]

Hi Pierre,

Thanks for the info on times.  I had roughly worked out that it would pull about 4ah and I thought that with this sort of current draw it would make sense to have the maximum capacity in the canister.  So I will probably put the pack together as 4 packs of 10 cells.  I can then connect the packs together to give me approx 7.2ah total capacity.

The time to charge is not to critical and I will look at the charger tonight to see if I can work out what type it is.  It does not do any temperature sensing, but I know it switches to a trickle charge.  It is definately a NIMH charger as it came with my 20watt torch which has the 7.2v nimh pack.  I do not believe it uses a timer as the time to switch from full charge to trickle charge varies depending on how much use the battery has had.  

I will see what info I can find and post.  Thanks again.

I am also quite interested in canister construction,  I have not got that far yet but any ideas are greatly appreciated.

Daz

[Duncan]

Daz
im working (slowly) on an umbilical torch. im hoping to make mine HID and have sourced the lamps/gear, i also have some lamps which are 50W halogen but give the same type of light as HID (4200, 5400 & 6500K) andy2tanx has tried one in his green force & seemed to like it.
i wouldnt mind having a look at your head unit & or canister as ive got all the internals pretty much sorted but havent made much ground on the head/canister

[daz]

Duncan,

Ok not very innovative I know, but I used a old maglight as has been used before (http://www.oneandoneis2.demon.co.uk/...b/diytorch.htm )  I already have a 20w umbilical but just fancied having a go at making one myself.

So far it has worked out exactly as said.  I am using a 50watt low voltage bulb.  I will take a picture of it and send it when I get chance.

I would be interested in a bulb with a temperature around 6000,  What type of fitting are they ?  

The nice thing about the low voltage 12v unit is that it really does fit straight in the maglight head.

Tomorrow I am making my switch assembly out of a relay and reed switch.

Daz

[daz]

Oh almost forgot,  I did cut the maglight down and using fimo plastic and araldite fixed the head unit to the stumpy end as recommended.

Daz

[daz]

And another question.  

I am considering some sort of wet connector on the cannister.  I was thinking of having a couple of connectors through the lid and equivilent plugs on the lead so I can disconnect the head of the torch easily.  Does anyone have any ideas on how to achieve this,  I believe by using a diode I can avoid the battery discharging in the water.

Daz

[Pierre Farrugia]

Here is a link to my dive light <a href="http://groups.yahoo.com/group/hiddivelights/files/Pierre%20Malta%20Dive%20light%20Ver.%202/

The" target="_blank">http://groups.yahoo.com/group....e</a> canister is 40cm long * 50mm diameter with 2mm walls.