Calling electricians: How to make a MH ballast dimmable

[haninja]

I have 3 400w coralvue ballast non dimable and based on my early teen electronics hobby, and based on the fact the coralvue has a version of these ballast with a dim switch, I'm thinking it should not be hard to add a dim capability via a rheostat. Question which one and how where to add. I'm assuming it would be on the way to the bulb? Opinions?

 

[lilrobb]

I have a dimmable one if you wanna look inside of one...

 

[haninja]

Yes please.

 

[lilrobb]

Disclaimer: if you figure it out - you will also convert my two non-dimmable ones... haha, JK

I'll pm you to maybe come over next weekend...

 

[acroholic]

That would make a very interesting DIY thread, if you could take some pics if/when you do it.

 

[eric b]

Should not be that difficult because if you want we can open my Metrolight (Old IceCap) and it has the wires that extend out and all you have to do is connect the rheostat so we can see where the wires terminate inside to see if it is a similar build to a coralvue.

 

[lilrobb]

Party at Hanin's house...

 

[haninja]

LilRobb;550942 wrote: Party at Hanin's house...

:up:

 

[acroholic]

It would be really smooth if you were able to attach the rheo. thru the side of the ballast like the Coralvue instead of having it separate from the ballast.

 

[haninja]

Isn't it a selector? I think it has 3 positions dim, normal and overdrive? and yes, should be able to drill the side and add it in the same place the original one has it.

 

[lilrobb]

haninja;550958 wrote: Isn't it a selector? I think it has 3 positions dim, normal and overdrive? and yes, should be able to drill the side and add it in the same place the original one has it.

The newer ones, yes - the older ones are seamless...

 

[acroholic]

haninja;550958 wrote: Isn't it a selector? I think it has 3 positions dim, normal and overdrive? and yes, should be able to drill the side and add it in the same place the original one has it.

It is a selector: 50%, 75%, 100% +10% on the new ones they just came out with. Mine are the older model, with a turning rheostat that dims between -35% - 100% and clicks to +10%.

 

[haninja]

Ace of Spades;550959 wrote: My concern would be heat. If you control down the output, voltage will go up. If the rheostat also introduces a resistor of some sort, you could potentially take down the input voltage. But I'm still not sure the insulation factor of the wiring, etc can take the heat.

Isn't a rheostat just a variable resistor...

 

[lilrobb]

haninja;550969 wrote: Isn't a rheostat just a variable resistor...

However Coralvue did it - it works in their other models - so it can't be harmful to anything.

 

[darcurr]

ace of spades;551016 wrote: yes, i worded that wrong.

A rheostat is just that, a variable resistor. But with resistance comes heat.

+1

 

[acroholic]

Ace of Spades;551016 wrote: A rheostat is just that, a variable resistor. But with resistance comes heat.

The rheostat on the CV ballasts are connected to the ballast case, which are one big all-aluminum heat sink anyways. I'm sure they can handle it, because I had one continuously dimmed down 35% for several months without issue.

 

[acroholic]

At least with my model CV dimmable, the ballast is the same dimensions and appearance as the non dimmable. That is strictly looking at the case. The only visual difference is the knob sticking out of one end. they appear made of the same gauge aluminum. Inside, who knows, as I've never had one apart.

I had one go bad after about two years a couple weeks ago. Sent it back to CoralVue and they sent me a brand spankin' new one that is the clicker type.

I had just bought a new 250 watt dimmable to replace a 400 watt dimmable over my chalice tank, so I moved that 400 watter over to replace the burnt out one, so I have this brand new CV Ballast sitting around as backup.

 

[lilrobb]

I have both version of the CV ballasts and mine aren't in use - I'll coordinate a dissection of them for next weekend.
Hehe

 

[acroholic]

Ace of Spades;551122 wrote: Would, in your opinion, 2 years seem right in the amount of life one would expect from that model dimmable ballast? Have you had a non dimmable, of similar build, that you could compare life too? Are we seeing a substantial difference in life between the two?

If so, we could take that something is causing faster deterioration in these ballasts. From my view, the added wear could be caused by the substantial heat created when bottle necking output wattage.

And really my opinions are not based on the units themselves. Frankly, I've never owned a halide ballast that I've used on my tank. I have some experience with them elsewhere, but not in the setting we as hobbyists use them.

I think I just had a ballast that went bad and is in no way indicative of the expected lifespan of the equipment. They are warranted for three years. I expect the lifespan is longer, but something in this one stopped working. Happens in all product lines. No big deal if the manufacturer stands behind it.

 

[schwaggs]

I seriously doubt you will be able to convert a non-dimable ballast to dimable. There is little chance the dimable ones have a rheostat on the output, it isn't that simple and rheostats are rarly, if ever used any more. Most likely is a potentiometer that adjusts the drive current or voltage on the output. When you open the ballasts, be VERY careful of charged capacitors (the large cans), they can kill you. I know Icecap ballasts have some large capacitors in them so the Coralview ballasts may also.