Problem with Light Cannon and NiMh batteries?

[Genesis]

HID lamp arcs are actually fairly low voltage once they are ignited.

The ignitor must generate very high voltages to strike the arc, but maintaining the arc is the responsibility of the ballast.

The ballast produces a high-frequency output at relatively low voltage with a controlled current. It is a constant-current source; that's how it works, since the resistance of an arc is almost zero. It is easier to maintain a stable arc with a high-frequency AC current than with a DC one, thus, the use of a high-frequency oscillator in the ballast for a HID lamp. (This is the same reason, by the way, that high frequency power supplies are used in inert-gas-welding systems; with a DC welder you must touch the work to initiate the arc - this is not necesasry with a high-frequency energy source.)

Basic electrical laws (Ohm's Law) says that E = IR. Since "R" is very low, if you apply a lot of voltage then I (current) will be extremely high!

This will cause the bulb to burn up or even (in an extreme) to explode due to vaporization of the electrodes.

So with an arc lamp what you do is use a charge-train device (a series of diodes and capacitors) on a constant-current power supply to "pump" an output capacitor for striking. With each "half-cycle" into the capacitors the current is "pumped" into the final HV capacitor by a series of diodes that allow flow into the capacitor but deny the reverse-flow back out. Since the supply is a constant-current device, and voltage is allowed to "float", the voltage will build until it is sufficient to strike the arc. This is how the lamp "ignites." (It is also why, if you ever turn on a ballast without a lamp inserted in the socket, or with a defecitve lamp, you can burn up the ballast - the voltage will rise until the insulation in the ballast fails and it arcs internally!)

Once it has struck the arc provides a VERY low resistance path for energy to flow. Since the striking circuit can provide almost no current (but a very high voltage), it does not contribute to the operation once the lamp strikes and the direct connection to the ballast's circuitry takes over. The ballast's job is to provide a high-frequency controlled-current electricity feed to the arc. The voltage across an operating HID lamp is actually quite low; the current is regulated to prevent the lamp (and power supply) from melting down.

If the current control circuitry in the ballast fails, it can fail "wide open" and will lead to a runaway. The fuse is there to prevent this failure, which could lead to the lamp exploding, as it will open before current can rise to dangerous levels.

One potential problem with any electronic circuit of this kind is that as supply voltage falls the current required to maintain the total wattage rises. This causes the circuit to run hotter, since heat losses depend on current flow, not voltage. With a sufficiently low supply voltage that can deliver lots of current (and NiMH batteries fall into this category) you could conceivably get a thermal failure of some part of the regulating circuit in the ballast.

This MAY be what is happening, but without tearing the ballast apart I can't say with any kind of certainty.

It is interesting to note though that Welch-Allen, who makes nearly ALL of the HID lamp/ballast combinations used in various "small" applications (including dive lights), has TWO separate ballasts for their 10w lights. One is designed for NiMH batteries, the other for Alkalines.

 

[grouchyturtle]

Have any of you used the Light Canon with the rechargeable battery pack, made by UK.

I was thinking about getting it, to save $$$ on batteries, but someone told me that when it runs out of juice it dies very quickly. As in one minute there's light, next minute it's dark.
As oppossed to batteries, where when they start to die the light will start to dim.

Is this true?

 

[Genesis]

HID lamps work DIFFERENTLY than Halogens, and NiMHs work differently than dry (or Lead/acid) cells.

With Halogens, you will notice a dimming on alkaline batteries before it goes dead. Quite a bit, in fact.

HOWEVER, batteries are different too.

Alkalines will give you plenty of warning, as the voltage drops slowly over their life.

NiMHs DO NOT do this. They have very little voltage drop until they are essentially dead, then the voltage collapses!

So with EITHER Halogen or HID lamps, on NiMHs, you will get very little (but not zero) warning.

Now HID lamps conspire in a different way to cause this.

With a HID lamp, you have an electronic ballast that takes the current from the batteries and converts it into a higher-voltage, high-frequency electrical current. There is also an "ignitor" circuit (which I think I described earlier in this thread) that is basically a charge-pump to "light" the lamp when it is first turned on.

Because of this circuitry, the brightness of the lamp is more-or-less independant of the battery voltage! As the voltage falls, the current drawn increases - the total wattage remains a constant, up until you reach the low-voltage cutoff and the lamp shuts down.

The Light Cannon is somewhat unique in that your first warning of low batteries on Alkalines is USUALLY that the lamp will not reliably strike. You get in the water, turn it on, and NOTHING! Turn it off and back on a couple of times, and it strikes - and all is well. Be warned - your batteries are going dead!

So, in general, don't count on a low battery "warning" with HID lamps at all. Instead, you pretty much have to keep track of the burn time you've put on the cells, and charge NiMH batteries before each dive day, lest you get a "surprise" underwater.

 

[grouchyturtle]

So, in general, don't count on a low battery "warning" with HID lamps at all. Instead, you pretty much have to keep track of the burn time you've put on the cells, and charge NiMH batteries before each dive day, lest you get a "surprise" underwater.

So that's why I got that SL4!

 

[Greg_Manko]

Just to add my 2 Cents worth. When my LC100 runs my rechargables down the light does give me some warning - the light gets dimmer and the light colour changes and flickers. 10 Min or so later the light goes out.
I beleive that the ballast the LC uses supports the range of voltages produced by both Alkalines and NiCD/NiMH batteries.
As with most blown fuses in electronic devices, when the fuse blows, something else is wrong - don't just replace the fuse. The fuse isn't there to protect the circuits, it's there to protect you from a total meltdown when the circuits fail.
I had a problem with my LC100 ballast not striking the light. It happened intermittantly and with both Alkaline and NiMH cells.
I sent it back to UK Canada for servicing and was pissed off when UK returned the light as "no fault found" and basically blamed me for not knowing how to use the light (I was using it properly). Thankfully, UK replaced the ballast and bulb as a "good will gesture" and the light has worked perfectly ever since!

 

[deepdiverbc]

ifukuda

I have been using 4200 NiMH with my light cannon and I think they are the best way to go. I have had it blink out on me a couple of times with both NiMh and alkeline but it restarts after a minute and I always carry a back up. I recommend using NiMH as long as you know how to use them. You always have a fresh light for a day of diving and your burn time is a reliable 2 hours and up to 3 hours.


ScubaAaron

"The charger have a timed cycle of 8 hours. It shows that this is good for 2800 mah C batteries and that 5000 mah D batteries require two 8 hour cycles. "

I would replace your charger with a better model. Not only will your timed charger not properly charge your batteries and risk overheating them which shortens their life span but it must take you forever to charge all eight batteries. Check out the Accupower and AllTech chargers at this link.
http://www.thomas-distributing.com/nimh_battery_chargers.htm


Wetman

"I got some Nimh batteries for mine and did a burn test on it. It lasted for under two hours and at some point some large "pop" sound came out of it. I opened it up and a burning smell was present. I put some alkalines in and it seemed to work ok after a while"

I get almost 3 hours from my 4200 NiMH but you need to cycle them a few times to get full performance. Also it is not a good idea to run them down until they die as they will off gass hydrogen and pop the porcelin absorbtion pellets in your light. Not good for the light. This is also the reason you souldn't put freshly charged batteries in your light until they have had time to cool and should not store NiMH in your light allowing them to discharge fully.


grunzster

"Have any of you used the Light Canon with the rechargeable battery pack, made by UK."

The UK rechargeable pack is a NiCad battery that required discharging after each use and has a memory but the biggest reason not to get it other than the price is that it only has about 2200 mAh of capacity compared to NiMh batteries with 4200 mAh and no memory. I would get the NiMh. Check this link.
http://www.batterymart.com/battery.mv?c=rechargeable_batteries

 

[grouchyturtle]

I assume that means the batteries would have a longer burn time right?

What do you mean by memory?

 

[ifukuda]

I've had no problems with the LC100 (and NiMh batteries) after the LDS replaced my old light with a new one.

After using up the alkalines that came with the light, and speaking with a rep at UK, I decided to put the 4.5Ah NiMh batteries back in the LC100. Since switching back to the rechargable batteries, I've had 8 dives between 45~62 minutes without any problems. Also, even after using the light on a multi-dive day (almost 2 hours of total burn time), there was plently of charge left in the batteries...took forever to discharge.

So far so good. So, I think I'll keep using the rechargables. If the light goes bad again, I suppose I'll just ask UK to replace it again.

 

[padiscubapro]

Genesis once bubbled...
Here's the mechanism.

The LC uses an electronic ballast. The draw of the lamp is 10w, and is electronically regulated.

A fuse is a CURRENT (not wattage) limiting device.

With alkaline batteries in it, each cell produces about 1.5V. In reality the voltage can drop to close to 1.2V before the cell is totally dead and cannot support significant current output. I've found that at ~1.3-1.4V I start having problems with the LC striking - the HV strike circuitry apparently requires more current than the batteries can deliver when discharged to that level.

So 1.5 * 8 = 12V, roughly.

NiMH batteries (and NiCDs) work differently. They have a nearly constant voltage output of 1.2-1.3V from full to almost completely discharged, and will support very strong current drain all the way down to nearly zero remaining capacity without much "sag" in their output voltage.

So 1.2 * 8 = 9.6V (!)

If we have a 10w lamp, we require 0.833A from the 12V pack.

But at 9.6V, we require 1.04A - or 24% more AMPERAGE.

Now is the fuse set THAT close to the "line"? I hope not. But it could be, or some other component could be unable to tolerate a 24% increase in current flow though it, leading to a meltdown.

It is interesting to note that WA, the maker of the ballasts, has two separate versions of their 10w HID ballast. One is designed for a 12V nominal voltage and dry cells. The other is designed for a 9.6v nominal voltage - NiCDs or NiMH cells.

I have no idea what UK is using for a ballast, or its specs.....

genesis.. normal alkaline batteries are rated for 1.5v down to .8 volts! not 1.2 v
look at most manufacturer's websites when they give you an Ah rating its almost always down to .8v

there are not 2 ballasts.. Welch Allan makes FOUR ballasts.. the one designed for alkaline cells has the lowest allowed voltage..

NIHM batters charge life is rated from 1.2v down to 1.0v as its useful life.

 

[TechnoMage]

I'm looking to get some NiMH C batteries and charger for my Light Cannon. I've had good luck with All Batteries on eBay before. Any comments on this package?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2575788180&category=4660

Thanks,
-Ron