DIY Canister Light and Lighthead

[Web Monkey]

The formula is: Watts / Volts = Amps, so: 50 Watts / 12 volts = 4.17 amps.

2 hours of burn time would require 4.17 * 2 = 8.3 amp/hours, so in theory, and 12 volt 8.3 amp-hour battery would do the trick.

However. . . This isn't the whole story. The capacity of a battery is determined by the rate of discharge, the ambient temperature and the cutoff voltage (the greater of your minimum requirments or the battery's minumum usable voltage).

As you discharge a battery faster, the capacity (A/H) is reduced. For example, you might get 8 AH out of a battery if you discharge it at 1 Amp/hour, but only 6 AH if you discharge it at 8 Amp/hours.

You can get this information from the discharge curve sheets supplied by the manufacturer.

If I recall my calulations correctly for the light I built, a 12 V 7 AH Lead-Acid battery will run a 50W lamp for about 45 minutes, but will run a 35W lamp for about 1 1/2 hours

Terry

And something else.....

You guys have any formula's that I can use to get a rough idea of the battery capacity I need for a 2 hour burn time on the 50w bulb? I'm looking in to getting a custom made battery-pack for the PVC pipe (believe it or not there's an affordable shop just around the corner that will do this for me - it's like a cosmic hint) and I need to have an idea of the capacity beforehand.

R..

 

[Diver0001]

The formula is: Watts / Volts = Amps, so: 50 Watts / 12 volts = 4.17 amps.

2 hours of burn time would require 4.17 * 2 = 8.3 amp/hours, so in theory, and 12 volt 8.3 amp-hour battery would do the trick.

However. . . This isn't the whole story. The capacity of a battery is determined by the rate of discharge, the ambient temperature and the cutoff voltage (the greater of your minimum requirments or the battery's minumum usable voltage).

As you discharge a battery faster, the capacity (A/H) is reduced. For example, you might get 8 AH out of a battery if you discharge it at 1 Amp/hour, but only 6 AH if you discharge it at 8 Amp/hours.

You can get this information from the discharge curve sheets supplied by the manufacturer.

If I recall my calulations correctly for the light I built, a 12 V 7 AH Lead-Acid battery will run a 50W lamp for about 45 minutes, but will run a 35W lamp for about 1 1/2 hours

Terry

Terry,

Are you saying that an 8ah battery is only going to run my light for an hour or that it depends on the kind of battery?

I'm having a battery pack custom made. I told them the what and the why of it all and they're making me an 8ah pack. I still have time to change it if this isn't enough.

R..

 

[Padipro]

I realize the formula says that the bulb will only burn for about 45 minutes but I can tell you from actual experience that it burns much longer then that. I'm using a 50 watt bulb and only have one 12v 7Ah battery and I run my light the entire time on both dives of a two tank dive trip. My first dive is usually around 40 to 45 minutes and the second, shallower, dive is usually about 50 minutes. I've never run the light down so far that there is a noticable dimming.

I think that an 8Ah pack should be plenty.

 

[Web Monkey]

It depends on the type of battery, and it's discharge curve (the number of watt/hours at your particular discharge rate). Also, letting the battery discharge below it's rated minimum will damage it, so it's best to not always be running it dry.

The battery ratings are minimum ratings and the battery you actually get should give you the rated output or better.

You should talk to the place making your battery pack and tell them you need to run a 50W lamp for 2 hours (or whatever duration you need), and see what they recommend.

Since you're building it from scratch, you migh as well get the run-time you want.

Terry

Terry,

Are you saying that an 8ah battery is only going to run my light for an hour or that it depends on the kind of battery?

I'm having a battery pack custom made. I told them the what and the why of it all and they're making me an 8ah pack. I still have time to change it if this isn't enough.

R..

 

[j-valve]

I was speaking to an electrician a few years ago and the formula Watts / Volts = Amps is for A/C and and generally works for DC but not as exactly. Can anyone confirm if that is true? I think the discharge sheet is the best source for estimating your light output.

J

 

[ColdH2Odvr]

I was speaking to an electrician a few years ago and the formula Watts / Volts = Amps is for A/C and and generally works for DC but not as exactly.
J

J,

it’s just the opposite. DC circuits are simple Voltage (E) =IR, P=IE etc. With AC you get into the effects of the sinusoidal voltage. Kirchhoff and Ohms rules generally work for simple ac circuits but go out the window quickly with more complex circuits.

These guys have a great set of tutorials: http://www.faqs.org/docs/electric/index.htm

Enjoy,

Dave

 

[Diver0001]

Plastic maglite bits.....

Can't get a tempered glass maglite front in Holland. Best I can do is wait 6 weeks while one gets ordered from the States.

I have a couple of alternative ideas but I have a question. How hot do the 50w halogen bulbs get? Can I put the back of the reflector in direct contact with rubber?

R..

 

[Padipro]

Plastic maglite bits.....

Can't get a tempered glass maglite front in Holland. Best I can do is wait 6 weeks while one gets ordered from the States.

I have a couple of alternative ideas but I have a question. How hot do the 50w halogen bulbs get? Can I put the back of the reflector in direct contact with rubber?

R..

I've never mailed anything to Holland from the states before. Do you know of any restrictions, duties or problems with customs? If there aren't going to be any problems with me mailing a lens or two through the US Postal System to you PM me with your address and I could send one to you.

 

[j-valve]

Thanks Dave. I knew it was something like that.

J

 

[unfix8r]

Okay, I am getting close to finishing... The light isn't pretty to look at yet!! My biggest issue has been sealing of the lighthead... it really wants to leak through the lens cover/ threads.
Padipro, do you have to sink the bulb in deeper into the lighthead? I imagine that the bulb is sealed better than any other part of the flashlight, so getting water from going around it and into the lighthead tube seems like the biggest issue. Diver0001 asked the same question I have... can the rubber oring be in direct contact with the bulb?

Also... do you recommend Teflon taping all threaded surfaces, or will that be a waste underwater?