how to build your own (cheap) light canister...

[DavidG]

NiMH's - HELP!
I have a lathe and drill press so I have the capability to build the can and head but I'd like to make a smaller can that would contain enough power to last for three dives when using a 10watt HID bulb. Given those requirements, I thought going to NiMH batteries would be the ticket.

I've got a UW light cannon and thought of gutting the ballast and bulb and creating a light head using it, but...

I've got a pack of 20, 2000 mAh AA's in a 2 x 3-4-3 configuration that generates about 13.5 volts with a total of (therotecally) 4 Ah's. My amp meter only goes so far and the thing with NiMH's is that their design permits high amperage discharge. So, when I hook them up to the ballast, they blow the 2amp fuse EVERY time. The ballast creates the initial arc with 6000 volts and then once lit drops to 12 volts in order to sustain the arc. At just under 10 volts the light dies. So the inital draw seems to be what is killing the fuse.

What am I doing wrong? If I use a higher rated fuse, won't I kill the bulb? Should I try a slow burn fuse? The manufacturer says the ballast and bulb can operate using NiMH's.

Have any of you been able to successfully get something like this to work. Obviously, I KNOW NEXT TO NOTHING ABOUT ELECTRICITY OR BALLAST ELECTRONICS.

 

[Padipro]

It sounds as though your fuse is to small for the amount of current the light is drawing at start up. What size fuse did the light you robbed the parts from have installed? How many amps does the ballast draw from the battery when you flip the switch?
We need to figure out how many amps are being drawn at start up and install the appropiate sized fuse.

This is Watt's Law. Just plug in the voltage of your battery and the number of watts the ballast draws at start up, do the math and it will tell you how many amps the curcuit is drawing, which is more the 2 amps, and install the correct size fuse or curcuit braker.

P = I x E
I = P / E
or E = P / I

Where
P = Power (Watts DC)
I = Current (Amps DC)
E = Voltage (Volts DC)

For instance, my light is a 12 volt, 50 watt halogen light. To figure out the correct size fuse I need to figure out what "I" (Amps) is.
P=50 (50 watt bulb)
E=12 (12 volt battery)
50 / 12 = 4.16
I=4.16 Amps
So I installed a 5 amp fuse.

Scott

 

[DavidG]

Padipro once bubbled...
...What size fuse did the light you robbed the parts from have installed? 2 amp.
How many amps does the ballast draw from the battery when you flip the switch? I don't know
We need to figure out how many amps are being drawn at start up and install the appropiate sized fuse.

This is Watt's Law. Just plug in the voltage of your battery and the number of watts the ballast draws at start up, do the math and it will tell you how many amps the curcuit is drawing, which is more the 2 amps, and install the correct size fuse or curcuit braker.

P = I x E
I = P / E
or E = P / I

Where
P = Power (Watts DC)
I = Current (Amps DC)
E = Voltage (Volts DC)

For instance, my light is a 12 volt, 50 watt halogen light. To figure out the correct size fuse I need to figure out what "I" (Amps) is.
P=50 (50 watt bulb)
E=12 (12 volt battery)
50 / 12 = 4.16
I=4.16 Amps
So I installed a 5 amp fuse.

Scott [/B]

OK,
startup: 10watt HID BULB / 6000volts = WAY under the two amp fuse.
sustained: 10watt HID BULB / 13.5 VOLTS = Under 2 amps, so either way the two amp fuse should work.

No, I think it has something to do with the Ballast circuitry or the characteristics of the NiHM's. I think there is something with the ballast that when it strikes the arc it's pulling WAY more than the 10 watts because yes, it has to be total current that causes the fuses to blow.

Another thing I have to worry about is the ohms resistance of the bulb - I think???

 

[DeepScuba]

DavidG:

You're obviously blowing the fuse for "current" reasons The "I" in the equation.

Assuming the ballast/bulb/batteries are all OK, then you wouldn't hurt a thing by installing a 3 amp, or 4 amp fuse. That's what's wrong anyways.

A higher amperage fuse won't "hurt" anything, it just won't protect quite as quickly if something does go wrong...but even that is in theory only, since if something goes wrong a 2 amp or 4 amp fuse difference, probably won't be "the difference" whether a part lives or dies.

Put a higher amperage fuse in!

I'm assuming 13.2V Power source is OK for this thing?

Don't worry about any Ohm reading on a bulb, First of all it's HID (No resistance spec since it's an arc), secondly, even a normal halogen bulb Ohm reading is irrelevant since it heats up dramatically when running, thusly raising the resistance level, thusly reducing current flow. Thusly any resistance reading of a bulb will yield no useable data. Try it on your 60Watt bulb in the house, and then do the math!!!

(Please allow to cool before touching.......)

 

[PhotoTJ]

As far as quantity of light goes, how much does the halogen put out vs. the HID (Light Cannon)?

 

[jonnythan]

PhotoTJ once bubbled...
As far as quantity of light goes, how much does the halogen put out vs. the HID (Light Cannon)?

BWAHAHAHAHAHA

 

[Padipro]

Sorry about that David, I wasn't being clear enough in my first post. DeepScuba was on to the same point as I was trying to make. It's a problem with the curcuit drawing more current then the fuse can handle. Just a Deep said as long as the battery, wiring, ballast and bulb are in working order there is no reason to worry about burining anything up. Install a bigger fuse and try it out.

You might want to ask the manufacture what size fuse you need for this type of set up. It sounds like you've talked to them before. I'm not real familiar with HID systems but I would venture to guess it's not the 10 watt bulb that's drawing to much current. I think it's the 6000 volts the ballast is producing that's blowing the fuse. You need to figure out how much current the ballast is drawing from the battery when you flip the switch and use that figure as the "P" in the equation. If I understand the way these HID systems work the ballast draws power from the battery and steps it up from the 13.5 volts of your battery to the 6000 volts you need to start the arc. This would mean that it's not the 10 watt rating of the bulb you should be using to figure out the amperage draw.

I found this on the internet and it kind of explains what I'm thinking.

"...a ballast should act as a current source allowing the lamp to determine its voltage."

Again, if this is true it would seem you should be using the current draw of the ballast as the "P" variable instead of that of the bulb.

Hope this makes sense.

Scott

 

[PhotoTJ]

jonnythan once bubbled...


BWAHAHAHAHAHA

OK, wise a$$, a simple more or less would do nicely. Or do you know?

Padipro, can you answer this for me?

 

[Atticus]

I'll make a quick stab at this one:

For the same wattage, an HID will create a much perceptively brighter light. This has to do with color temperature as much as anything.

The rule of thumb that I have heard is that a 10w HID should be considered to be on par with a35w halogen.

When applied to the size of battery pack you need for a given amount of illumination this means that you will either get a longer burn or be able to carry smaller batteries with HID.

Hope this helps at least a little bit.

- Atticus

 

[PhotoTJ]

...thanks.