Hello,

I've been reading these forums for ages and have learnt a lot
And  have managed to run some interesting lamps of off substitute ballasts.

I have some eye 50w HPS lamps and cannot get a suitable ballast, how do I calculate
The required choke sizing from my lamp data? I'll be running 230v supply, 50hz.

I can fire it up with a 58w t8 ballast or a pair of parallel 28w t-8 ballasts but
They definately over or under power the lamp. One combo runs it just over 100w and the other at 44w, but the single 58w fluro ballast gets quiet hot for 44w at the lamp..

Any thoughts ou there,

Have a good one

Tim

Prescribed ballast impedance for 50W HPS is 246 Ohm at 220V. Will be slightly higher at 230V. Some matching widespread substitute may be a pair of 30W fluorescent ballasts (480 Ohm @220V) in parallel.

58W ballast is right 240 Ohm @220V, so is a close match too. Will run at *slightly* higher than intended fluorescent tube current, nothing serious, but keep an eye on cooling, do not put in a tight box for example!

Hi,

Thanks for the reply

I'll get a thermometer onto the 58w ballast and see exactly how hot it gets,
The supply in my town varies a lot 220-240 is not uncommon.. I guess if I can get
the supply voltage lower (just under 220) it may not run too hot.
Where did you get the figure if 246 ohms at 220v?

I'll admit the 58w
Flourescent tube ballast appeared to perform well. It Just ran hot.
 I wonder how hot is too hot? id be thinking of keeping it well below 60c.

Tim

Usually there is a a ΔT or maximum temperature indication on the ballast.

It is not unusual for a ballast to get up to 100°C. "Modern" ballasts are very much cost optimized rather than life span optimized, though even so they will last for a decent number of years. I think a target temperature of 80°c is realistic. Too hot too touch, but won't boil off a droplet of spit.

Trying to keep it under 60°c is not realistic for anything made after the 1970s i think. The older ones were sometimes designed to run cooler.

Yes they are rated to 130deg C.  Your respone is reassuring there is an internal temp cut out so the ballast should never become a fire hazard. Electrically I thought I had it sorted with the 58w ballast. The heat threw me off, the current x voltage  was resulting in 44-50w (metering is tricky yo get spot on with a clamp meter)
 Once I get time next week to run it under supervision for a couple of hours I'll post the results.

Have a good weekend.

Tim

Where did you get the figure if 246 ohms at 220v?

The source is IEC 60662 for HPS and IEC 60081 for linear fluorescents.

Note that IEC specifies ballasts for 220V operation, but actual chokes designed with 230V network in the mind will have slightly higher impedances for both HPS and fluorescent. 

For example, IEC specifies 60 Ohms and 39 Ohms for 250 and 400W HPS, while actual datasheet from Tungsram on HPS compatble CMH lists 63 and 40,9 Ohms for 230V operation.

If you are playing with substitute ballasts a good idea is to use a well calibrated RMS ampermeter to verify the current you are getting. Remember however that especially for HPS lamps burning voltages are varying wildly so the result may be a bit off even with a perfect choke impedance.

Also you can verify actual choke impedance by hooking it on a slightly reduced line voltage, say 127V, and measuring the resulting current.

All of my fluorescent ballasts seem to run at around 85-90C all the time once warmed up, so I wouldn’t be worried about the ballast running too hot unless it’s hotter than 130C, then it’s time to worry! They’ve all survived from 2001, the paint is not even faded so 90C isn’t a problem at all

It is a good habit to mount them on heat sinking metal things. It makes a difference whether it's mounted to just a wooden board as an experimental setup, or whether you've mounted it to the sheet metal of a fluorescent fixture.

Lower temperatures also extend life. That 130 degrees can be the absolute maximum temperature it will reach, for instance when the starter fails closed. It won't get damaged right away, but life span can be shortened from 20 years at 80-90 degrees, to half a year at that 130 degrees.

If you are in an area where even standard fluorescent ballasts are hard to get, it's worth keeping the temperature in check. But 80-90 is fine.

In fact, using 58W choke on 50W HPS does not mean a huge overload, something 0.76A vs 0.67A nominal. Just be a little careful and not provoke overheating.


About temperature ratings: usually magnetic ballasts (European?) have two. Typically 130C is nominal and something like 160C is 'emergency'. Higher value is meant for temporary situations exactly like a stuck starter, and while the ballast should remain safe, insulation life is greatly reduced.

 

Insulation life…. That could explain why a fluorescent fixture I tried to relamp refuses to ignite new tubes. It had been ignored for years and years with two dead tubes just glowing at their ends, so I figured I’d relamp it since it bothers me extremely much if a fluorescent lamp has one or several dead tubes. I installed a pair of brand new starters and brand new tubes, and it just blinked. Blink blink blink for several minutes until I stopped because I didn’t want to ruin the new tubes.

My guess is that the ballasts had been damaged from the excessive heat from stuck starters aswell as the elevated mains voltage in my area (240-245V, when it’s meant to be 225-230.) excessive mains voltage made the ballasts overheat even more when the starters got stuck, maybe a few of the winding turns had shorted together and that’s why I couldn’t get the inductive kick needed to strike the tubes. It’s also possible that the insulation had been compromised to the point of not being able to insulate against an inductive kick causing it to leak to ground.

But yeah, a 58W fluorescent ballast shouldn’t overheat from running the HPS lamp. It will run a bit hotter but I don’t think you’ll be in the danger zone. Mounting it in a fixture base or something so it has thermal connection to the casing will cool it down quite a lot indeed, it makes a massive difference!

I have an update for the substitute 50w HPS ballast

On the weekend I ran the lamp with the 58w flourescent tube ballast.

Here's the info:

Burn time: 8 hours
Ballast was in free air (temp probe held onto laminations under a piece of  copper)
Room temp 20 deg. C
Ballast reached 70 deg C.

A cheap power Meter was attached.

Power factor .94
Input power 62-64w
Mains fluctuated 238v-243v (lots of grid tied solar on our street)

I think I'm on the money with this combo, I'll probably put the ballast on a good block of aluminium in the PSU enclosure and keep the ventilation up.

Thanks for the all advice with this project, any other thoughts would be appreciated.

 Now I can fit it into a fixture. 

Cheers,

Tim

Sweeeeet! I was certain it would work!

70C isn’t even hot, the ballasts in my big fluorescent fixtures run at 98C