Diskussions about the batteries... ;)

Thanks for commenting my blogg... One person pointed out in the battery part ([ Homemade Divelamp ]: Batteries) that the capacity of the battery found in the the pdf about the battery is changed depending on the amount of Amperes used.

As I understand this graph shows how many hours/minutes the battery will last depending on the Ampere load on it... I am not very good at this electricity thing but I have read this graph like this:

1. First I calculated how much my lamp would use in Ampere during 2 dives:

Here the mathematics again:
P = U * I (P = Watt[W], U = Volt[V], I = Ampere [A, Ampere per hour])
'U' is simple, 12 V is standard for the bulbs and contacts to use. The 'P' is 35 W (from the bulb), so to get the 'I' = P / U = 35 W / 12 V = 2.92 A is this bulb using per hour.

So for using this bulb (35 W) for 1½ hour and have at least 1/3 left you need an battery of: 2.92 A * 1½ = 4.38 A is the bulb using for 1½ hour of diving.

Adding 1/3 to that gives us: 4.38 + (4.38/3) = 5.84 A which means that you need a battery with at least 6 Ampere Hours.

2. What batteries can I use that fits into an pipe with radius of 100 mm?

I found this cheap batteries from biltema that fullfilled my caclulation.

3. I had a look at the graph that I found in the specifikations of the batteries:


So when looking at this graph I looked how long the batteries would last with the 35W bulb using about 4.38 Amperes during 2 dives which for me looks like it will last for at least 1 hour (60 minutes) in the graph. Close enough for me... ;)

In the end of may I will go diving on the west coast of Sweden to finish of my Diveleader + 3 star (***) CMAS course and will probably use this lamp quite a lot. So we will see if the batteries last for 2 normal dives in Swedish water.... I will get back to you about this.. with photos and the story....