Rechargeable Batteries in UK Light Cannon HID 100

[TheAce]

A question for the technical pro's,

If the UK Light Cannon gives 3-4 hours on regular alkalines, how many mAh NiCad's or NiMh should I get to give me the same performance? In other words, how many mAh are regular alkalines?

It seems - because of budget limitations - I am going to buy NiCad's 2000 mAh with a recharger that discharges the batteries before it recharges them. Will I get 2 hours at least from this setting?

Thanks!

 

[ifukuda]

I do not know the capacity of the batteries that UK bases their burn time on. But, if UK is basing burn time on high-end alkaline batteries such as Energizer which claims that their C-cells have a capacity over 8Ah (1.5V), you have:

8Ah (at 12V) / draw_of_HID = 4 hours
------------------------------------------------

Therefore, if you use 2Ah NiCads (1.2V), you would end up with:

2Ah (at 9.6V) / draw_of_HID = 48 minutes;
------------------------------------------------------

Don't plan on staying underwater too long...

 

[Genesis]

First, the Light Cannon is a 10W bulb. Assume its 80% efficient; it therefore draws 12 watts.

With 8 "C" cells, it has 12V - or a draw of ONE amp.

If it burns for 4 hours on a set of Alkalines, those batteries have a REAL capacity (usable, not "to the last millivolt") of 4AH.

You can get 4500 mah Nicads and NiMH "C" cells now, and if you do they should have roughly equal burn time.

BTW, I've looked at the Energizer "C" cell and performance curves. The 8350 mah "claim" is with a final voltage of 0.8v, and at a continuous 25ma draw. Those are, uh, wildly optimistic conditions for things like dive lights!

In a more REALISTIC situation, with a 1.0v cut-off voltage, and discharge current at 1 amp, the threshold is reached at just over ONE HOUR of service life, which puts the REAL capacity in such an application at 1000mah - wildly inferior to to the claims. If you can tolerate a final voltage of 0.8v/cell, then you can get approximately two hours out of it at 1A, or a "real" capacity of 2000 mah. (Just realize that E = IR and W = EI, so as "E" drops to maintain the same wattage amperage draw must increase!)

A NiCAD or NiMH battery, on the other hand, will maintain its 1.2V terminal voltage until approximately 80% discharged, allowing you to use nearly ALL of its rated capacity.

In high-drain situations, such as a dive light, there is no contest as to which is the preferred chemistry.

 

[Aquamaniac]

Balderdash 8AH...

You have such a nice way of helping people

 

[Aquamaniac]

Genesis once bubbled...
(Just realize that E = IR and W = EI, so as "E" drops to maintain the same wattage amperage draw must increase!)

W=EI?

 

[Genesis]

to let people quote things like "8300 mah" when that's simply not true in the real world and real use.

The original poster would be better served to get some 3500 or 4500 mah cells. They are available. The 2000 mah cells will not be able to give the desired 2 hour burn time without risking damage; a 4500 mah cell certainly will, and is available in either NiMH or NiCAD chemsitry, depending on your wallet and willingness to cycle them in a charger (instead of just recharging them) when you are done for the day.

A 4500 mah pack would give you 3600mah of usable capacity (80% rule) which, at a terminal voltage of 9.6V, and a 12W draw (80% efficient lamp at 10W) would give you a burn time of just under three hours.

A 3500 mah pack would give you 2800 mah of usable capacity, which is just enough to reach the goal of 2 hours of burn time with a bit of slop. The problem with the 3500 mah pack is that as it ages its lost capacity will end up with you replacing it before you should, because you have no wiggle room in its capacity with a planned 2 hour burn time.

The 4500 mah pack is therefore the far better buy, since in the real world it will probably absorb at least twice as many cycles before its capacity gets below the threshold of usability for this application and its nowhere near twice the price of the 3500 mah pack.

A 2000 mah pack has a usable capacity of 1600 mah, which will result in your light going out in roughly 1 hour and 30 minutes.

W = Watts (Volts X Amps)

 

[Aquamaniac]

Ahhh you mean P=VxI and V=IxR

 

[Genesis]

Power is work over time, which Watts definitely aren't as there is no unit of time contained in their definition.

Now watt-hours is....

(Yeah, I know, pedantic.)

 

[Aquamaniac]

Long time arguement had by many people, when i did my degree P was the unit for power V for Volts I for current, other say its E for electomotive force, or EMF, which isnt a bad way to do it when your looking at reactance and reluctance circuits, because were talking "Back EMF".

But at the end of the day....you say tomatoe, I say Tomatoe.

http://ohmslaw.com/

 

[AquaGuy]

I justed purchased 8 C 4500 mha NiMH batteries for my new Light Cannon. I also purchased a high end Maha charger for them and a 6 Cell + 2 Cell battery holder to charge them. I am going to join the two battery holders together so I can charge all 8 batteries at once (Maha claims their charger can charge up to 12V at a time). My question is do I have to first run the NiMH batteries through the dischange cycle before charging them each time? I assume I dont.

Thanks for the help