Hi all,

I have two ballasts, both rated at 250W, both claiming to be able to run Metal Halide lamps. However if you look more closely, one says MV/MH and is rated at 2.13A whereas the other is 3A and is for MH and HPS. So is there a mistake somewhere or are there MH lamps that run at 2.13A and/or 3A..?

Halides will run on both, it all started with Thorns MBIF, they were designed to run on both existing SON and Mercury gear, with slightly differing light output, however as you get below 250watt, this doesn’t work.
For instance, a 70 watt halide lamp doesn’t do very well on an 80 watt mercury ballast, (I’ve tried this and they under run, burning green), but higher 250/400 watt halides are more or less interchangeable.

The ones with an auxiliary staring electrode are more designed for mercury gear though, but the ones without  are pretty much universal for both sets.

Osram HQI-BT 400W/D runs only on SON gear. On mercury gear it burns green.
Philips HPI-T Plus 400W can run on SON gear, but the life is reduced compared to on mercury gear.
Tungsram MH lamps are to be used on mercury gear only.

Halides will run on both, it all started with Thorns MBIF, they were designed to run on both existing SON and Mercury gear, with slightly differing light output, however as you get below 250watt, this doesn’t work.
For instance, a 70 watt halide lamp doesn’t do very well on an 80 watt mercury ballast, (I’ve tried this and they under run, burning green), but higher 250/400 watt halides are more or less interchangeable.

The ones with an auxiliary staring electrode are more designed for mercury gear though, but the ones without  are pretty much universal for both sets.

But what about the current ratings..? The lamps will be rated for a particular current, the ballast should match that. For example, a 100W US (H38) mercury lamp works on a UK 70W HPS ballast as the current rating is close enough. I want to know how to find out what current a particular lamp is rated for, and unless it's specified somewhere it makes life difficult.

Makes me wish we had the ballast numbering system over here, it makes life a lot easier, as lamps are often marked with the ballast code they require.

Osram HQI-BT 400W/D runs only on SON gear. On mercury gear it burns green.
Philips HPI-T Plus 400W can run on SON gear, but the life is reduced compared to on mercury gear.
Tungsram MH lamps are to be used on mercury gear only.

It's all very well saying "SON gear" or "mercury gear" but what are the current ratings of this gear..? As I said I have 250W ballasts which both claim to be able to run MH lamps but they are different current ratings. How do I know which ballast to use for a particular lamp if I cannot find the lamp data..?

It really doesn’t matter, unless you’re going to take the time trawling through each individual lamps manufacturing data, matching lamps to the EXACT gear isn’t as important as most people on all these lighting forums seem to think,  I read on here too many times people obsessing about how lamps will be damaged on the wrong set of gear and so on, it’s all a myth, unless you’re going to extremes, (i.e, like running a 70 watt SON on 250 watt gear), most lamps won’t even notice minor fluctuations in current and voltage!
Even street lighting engineers make mistakes, Davy once pulled 250 watt SON lamps from out of 400 watt geared lanterns, and they had been in full night time service!! 

Maybe so, but I'd still like to get as close as possible. It's likely part of my condition; autism, OCD, call it what you will, but it is important to me that things are correct. It's why I insist on using PFC capacitors even though they may not strictly speaking be necessary. They are specified by the manufacturers, therefore they should be used. If you don't want to, fine, but when people tell me I am wrong for insisting on them, as they sometimes do, then I get upset.

Why we can't have the US ballast numbering system or its equivalent here is a mystery to me.

You have the best of both worlds with those ballasts though, you can build two display boards one to run 250 HPS, and another to run 250 MH, the one I built up in the loft as a test bed was using SON gear, and I’ve had both SON and halide lamps running on it without problem.
Another example, my brother in law has a BETA 5 on his shed, when he ran out of 35 watt spares, I put an 18 watt SOX in it, this was on the 11/5/18, it’s still in there today 20 months later, running without issue, and it’s going to be interesting to see what hours an 18 on 35 watt gear will go to!, thanks to Danny I now have some spare 35s for it, but this is just an example of how lamp and gear specs don’t have to be perfectly matched.

Maybe so, but I'd still like to get as close as possible. It's likely part of my condition; autism, OCD, call it what you will, but it is important to me that things are correct. It's why I insist on using PFC capacitors even though they may not strictly speaking be necessary. They are specified by the manufacturers, therefore they should be used. If you don't want to, fine, but when people tell me I am wrong for insisting on them, as they sometimes do, then I get upset.

Why we can't have the US ballast numbering system or its equivalent here is a mystery to me.

I can see it from your point of view with autism, it must make it difficult when building displays, but I wasn’t saying you were wrong, I was just saying it doesn’t matter, also my own point of view doesn’t help here, I used to run discharge lighting outside at home, and each night as you do with your lamp of the day, but since I pulled them all out for LED, I personally couldn’t care less about HID lamps anymore, I know that sounds a bit harsh for someone with an interest in lighting, but after all these years of studying them, reading about them and running them, they become ‘same old, same old’ like every thing else, it’s hard to explain to people recently getting into a lightning interest, but you may eventually, ( like me), become board with it all?, but I hope this doesn’t put you off any? 

I can see it from your point of view with autism, it must make it difficult when building displays, but I wasn’t saying you were wrong, I was just saying it doesn’t matter, also my own point of view doesn’t help here, I used to run discharge lighting outside at home, and each night as you do with your lamp of the day, but since I pulled them all out for LED, I personally couldn’t care less about HID lamps anymore, I know that sounds a bit harsh for someone with an interest in lighting, but after all these years of studying them, reading about them and running them, they become ‘same old, same old’ like every thing else, it’s hard to explain to people recently getting into a lightning interest, but you may eventually, ( like me), become board with it all?, but I hope this doesn’t put you off any? 

Not a chance, we've spent far too much time, effort and last but not least money on all this, the last thing we're going to do is give it up..! Sammi has only really been interested for the last three or four years since I first joined LG, now she's got the bug more than I have, I think 

Re. capacitors, ballasts etc., it may well not matter to you, but it does to me, I can't explain it any more than I can explain why I don't like the colour green, it's simply the way it is. If I'm building a display, it has to be as correct as I can make it. I would use the old metal cased PFC capacitors as were originally installed if I could get them, but as it is as long as the rating is correct it has to do. Similarly, if a lamp is designed to run at 2.13A then running it at 3A is (a) not going to do it much good and (b) is just plain wrong to my mind..!

Yeah fair point, it will be an interesting experience for you to gather all the different manufacturers data then, and log it all down somewhere so you can know which of your lamps to run on which gear sets, this is where it helps to have an army of manufacturers catalogues, but this is no longer a problem with the wonders of the net!, happy hunting! 

If you use wrong parameter ballast vs lamp combination, you may shorten the life of both. If you use a lower voltage (so higher current) lamp on a ballast intended for the higher arc voltage lamp, the lamp will be underdriven (which means inferior color and output),  but mainly the ballast will operate at (seemingly just a bit) higher current than designed. The higher current then causes it to run hotter, so degrading faster. The current difference uses to be around 5..8% (between 70V HPS vs 115V MV), but the power dissipation is square of that, so 10..15% difference. Because of the usual thermal design, that can easily mean 10degC operating temperature difference, so halving the ballast life.

Normally only +/-5% long term voltage deviation is allowed on all HIDs (I'm speaking of Europe environment), there is a reason for that. So saying "the exact current does not matter" is quite a nonsense. It does not have to matter for short time when performance does not matter, but long time it makes a difference.

The MVs are using higher arc voltages, so lower arc currents for the same wattages than HPS.
So the 3A ballast is the HPS one, the 2.15A is the MV one. The reason is, the HPS needs larger voltage margin, because its arc voltage tends to rise as the lamp ages, so to keep room for long service life.

Now with the MH the story is quite a mess, mainly with the 250W and above.
Initially these were designed according to MV lines (so 2.15A for a 250W), to be used on MV fixtures.
But once the HPS became common, the HPS specs became more used (because the HPS fixture already had the ignitor, so no modification needed).
So both specification lines were used for MHs.
 The lower wattages (150W and below) came after that, so they are only designed along the HPS specs.

Back to the present (and near past):
Because of the mess around the 250W and 400W specs, many makers designed their lamps so they could be rated for both ballast types (so do not get overstressed, nor stress any of them). The only thing is, the performance differs whether the lamp is operated on one or other ballast (usually the HPS ballast yields a bit higher power, higher CRI and lower CCT), the details are in the lamp spec sheet (it lists two performance tables for the same lamp).

And with these lamps "in mind" came the labeling of these ballasts so both list the "MH". However they can operate only those MHs really designed for that current (specified as "MV" for the lower current one vs "HPS" for the higher current one), so you should always check the lamp specs (it is usually not listed as current values in amps, but as "HPS gear" or "MV gear", but it means the same).

Hi Medved, thanks for the very comprehensive reply