Light question

[DiveBandit]

Ok, I have a older canister light. on a multimeter the batteries put out 12.5 volts. the battery says 7 amp hours. I have 50 watt Bi-pin halogen bulbs. I want to use this light with a video camera for filming cave dives. I know almost nothing about electronics

I'm wondering if -
1. I can get a 100 watt bulb?
2. will 12.5 volts, 7 amps be enough to power a 100 watt Halogen if one exists?
3. If they make such a bulb, and If the batteries can power it, how long do you think the batteries will last?

if you google the bulb part number ML50WH2CYS, you'll see exactly the bulb I have.

Thanks in advance for any advice.

 

[Web Monkey]

Ok, I have a older canister light. on a multimeter the batteries put out 12.5 volts. the battery says 7 amp hours. I have 50 watt Bi-pin halogen bulbs. I want to use this light with a video camera for filming cave dives. I know almost nothing about electronics

I'm wondering if -
1. I can get a 100 watt bulb?
2. will 12.5 volts, 7 amps be enough to power a 100 watt Halogen if one exists?
3. If they make such a bulb, and If the batteries can power it, how long do you think the batteries will last?

if you google the bulb part number ML50WH2CYS, you'll see exactly the bulb I have.

Thanks in advance for any advice.

The largest I've seen in the size you're using is a 50W bulb. You might be able to find bigger, but it's going to be a problem for battery life (and heat, unless you have a solid metal light head).

The 7ah battery is unfortunately not going to deliver 12.5v @ 7 amps for an hour. As the current draw increases the battery life decreases. A 50W bulb will get you about 45 minutes of good light and about 10 minutes of rapidly fading yellow/red light.

I don't have the discharge curves handy, but would expect that you could run a 100w bulb for maybe 10 or 15 mintues.

Terry

 

[DiveBandit]

I should also mention that there are 2 of these batteries wired together, Not sure how much of a difference that makes.
The canister is about 5" wide by 13.5" long

 

[Web Monkey]

I should also mention that there are 2 of these batteries wired together, Not sure how much of a difference hat makes.

If they're new and they're in parallel, you might get 45 minutes on a 100W bulb.

It also depends on the condition of the batteries. They're 7ah new. Capacity when used is an entirely different story. You'll have to try it and find out.

Just charge it up, toss the light head in a bucket of water, turn it on, let it run and see when the light starts to drop off.

Terry

 

[Meng_Tze]

Ok, I have a older canister light. on a multimeter the batteries put out 12.5 volts. the battery says 7 amp hours. I have 50 watt Bi-pin halogen bulbs. I want to use this light with a video camera for filming cave dives. I know almost nothing about electronics

I'm wondering if -
1. I can get a 100 watt bulb?
2. will 12.5 volts, 7 amps be enough to power a 100 watt Halogen if one exists?
3. If they make such a bulb, and If the batteries can power it, how long do you think the batteries will last?

if you google the bulb part number ML50WH2CYS, you'll see exactly the bulb I have.

Thanks in advance for any advice.

A halogen bulb is an incandescent bulb. I am assuming this one runs on DC so the calculations are as follows.

100W/12.5V= 8A. The battery can deliver 7Ah, therefore the burntime would be 7/8th of one hour = 52 min. and some change.

50W bulb would draw half the current and this burn twice as long. 52*2=104 min.
(50W/12.5V=4 A. => 7Ah/4A*60min=105 min. The difference is the rounding of 'some change' above)

The reality will be vastly different. I don't know how much real capacity the battery has, what/how the voltage under load is. But these calculations should give an indication.

Hope this helps.

 

[cool_hardware52]

Ok, I have a older canister light. on a multimeter the batteries put out 12.5 volts. the battery says 7 amp hours. I have 50 watt Bi-pin halogen bulbs. I want to use this light with a video camera for filming cave dives. I know almost nothing about electronics

I'm wondering if -
1. I can get a 100 watt bulb?
2. will 12.5 volts, 7 amps be enough to power a 100 watt Halogen if one exists?
3. If they make such a bulb, and If the batteries can power it, how long do you think the batteries will last?

if you google the bulb part number ML50WH2CYS, you'll see exactly the bulb I have.

Thanks in advance for any advice.

If you take the nominal voltage ~12 multiplied by the amp hour capacity you get watt hours. 12volts x 7 amp hours yields 84 watt hours.

Assuming your battery can deliver the 4 + amp necessary to power a 50 watt bulb you might expect about 84 watt hours / 50 watts = ~1.68 hours or about 100 minutes.

At 100 watts you might expect about 50 minutes.

Unfortunately you would be disappointed. Most batteries must be de-rated at high current discharge rates.

Much depends on the chemistry of the battery. If your original canister uses lead acid batteries then you have to derate these quite a lot. SLA batteries are usually rated at a 20 hour discharge rate. That means a 20 amp hour SLA cannot deliver 20 amps for an hour, or even 10 amps for 2 hours. It means it can deliver 1 amp for 20 hours.

If you increase the discharge rate (amp draw) to the point where the battery is discharged in less than an hour the battery will deliver maybe 50% or less of it's "20 hour rating.

That means the 100 minutes you expect from your 50 watt bulb will be maybe 50 minutes and the 50 minutes you expect from your 10 watt bulb will be less than 20 minutes.

In addition the internal resistance of the battery will be so large that your lamp will probably never see 12 volts, and reducing the voltage across the lamp will cause a great reduction in light output and a spectral shift to the infared end of the spectrum, not a good thing.

Other considerations is SLA's don't want to be fully discharged, and a 20 minute light is almost certainly going to be run down all the way every time it's used.

Chemistries other than SLA are often rated at 10 hour or 5 hour discharge rates, so these would perform a bit better, but at greater cost. Voltage depression is still a concern at when you need 8+ amps from a 7 amp hour battery.

Short answer, bad idea.

Tobin

Having read a little further it appears you have the potential for a 14 ah battery with two in parallel. 14 amp hour with a 50 watt load is starting to get reasonable, as you would have ~3 hours with fresh batteries. The 100 watt lamp is still a lot of load for a 14 amp hour battery.

These are no doubt SLA's and the good news is they will be inexpensive to replace.

 

[DiveBandit]

Thanks everyone for the advice, especially Cool_hardware52.

Now If I could just find a 100 watt bulb, I'd try this out in my pool.

 

[karstdvr]

Also remember going from 50watts to 100 watts doesn't mean double light output,you'd have to go to 200 watts. I came along diving halogen,and some people used to dive 100 watt bulbs,but the gains in output were minimal. If you want something that will provide good benefit for video consider 36v 200 watts.