Author Topic: F15/F20 preheat ballasts...F40 lamps?  (Read 6266 times)
nicksfans
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F15/F20 preheat ballasts...F40 lamps? « on: June 27, 2013, 01:01:33 AM » Author: nicksfans
This just came to my mind and I thought I'd seek answers. I've noticed that while F40 magnetic ballasts are long gone from store shelves, there are still small "choke" style ballasts available for F15 and F20 lamps. My question is, can these be used to run F40 lamps in a preheat fashion? I understand that just using one would likely overheat the ballast if it would even work at all, but what about two of them in series or parallel? I don't have any handy to test this, but I'm curious.
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Ash
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #1 on: June 27, 2013, 01:32:38 AM » Author: Ash
I think 2 of the 20w ones in series may be about right for a F40, but on 240v

Now, if my estimates are correct, the curent will be perfectfor the lamp but a bit higher than normal for the chokes so they may overheat. If this happens you can make a bigger array of chokes to spread the losses between all. But with 20w ones you'll need 8 (!) (4 series x 2 parallel) of them to make such "cool running" array. Instead it may be better to try to find a combination of chokes of different sizes (such as PL chokes) to try to hit the right current. But dont assume that you can just sum up the currents written on the chokes, since you are using 120v choke on 240v....

Or just import a couple 240v 50hz chokes. They will underdrive somewhat (i think about 0.8 of the output on 50hz) but it'll still work

I have also considered using the primaries of transformers (with the secondary unused) as chokes. but this will require measurements and possibly blow a few tubes and starters during experimenting
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marcopete87
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #2 on: June 27, 2013, 10:51:32 AM » Author: marcopete87
I think 2 of the 20w ones in series may be about right for a F40, but on 240v

series?  ???
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #3 on: June 27, 2013, 11:18:52 AM » Author: Medved
@macropete87: F20T12 and/or F18T8 are (when two or more are installed in a fixture) usually run as two lamps in series using one ballast choke. It mean double the useful power (two lamps) for the same ballast (on a single ballast) losses, as the current is the same. But this is possible only in 230..240V areas, on 120V the mains voltage would be insufficient for this.

@nickfans:
The F40 lamp need too high OCV (>180V for preheat), so for the 120V mains you need an autotransformer style ballast.
The "small chokes" are ballasts for lamps with arc voltages below 70V, what is a real limit for series choke on the 120V mains.
So an answer for you: On 120V they can't. On 240V you may try two of these chokes (of exactly the same make and model) in series, but the code does not allow the 240V to be used for lighting (to make it not yet code compliant, but at least reasonably safe, you would have to use two pole switch, disconnecting both phase wires)...
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #4 on: June 27, 2013, 01:26:23 PM » Author: Ash
Or use an autotransformer (the type used to supply 240v to appliances imported from Europe) and embed it inside the lantern. Now "from outside" it is a proper 120v device, which you can supply with 120v switched from 1 pole (still not code compliant, at the very least you are still using 120v rated chokes on 240v and with the wrong lamp, and maybe something else too)
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #5 on: June 27, 2013, 01:53:33 PM » Author: nicksfans
Makes sense that it would need 240v. I have an autotransformer so I could theoretically pull this off, but I won't worry about it for now. At least I've found the answer to my question.
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marcopete87
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #6 on: June 28, 2013, 08:40:02 AM » Author: marcopete87
@macropete87: F20T12 and/or F18T8 are (when two or more are installed in a fixture) usually run as two lamps in series using one ballast choke. It mean double the useful power (two lamps) for the same ballast (on a single ballast) losses, as the current is the same. But this is possible only in 230..240V areas, on 120V the mains voltage would be insufficient for this.

sorry, i misunderstood: i thought you was talking about 2 ballasts in series  :P
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Ash
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #7 on: June 28, 2013, 11:27:58 AM » Author: Ash
On 240v 50 Hz the 40w tube (which is the same 40wT12 as in USA) is used witha simple choke, The same choke can be used with 2x 20wT12 tubes in series

Now, imagine that you (in your mind) split the choke in half, and poke a multimeter across one half of the choke and one 20w tube, Since the choke i split equally, and the tubes are identical, the voltage must be exactly 1/2 of the input - ie 120v

But then it means that 1/2 of the 240v 50Hz 40w choke is exactly identical to what a 120v 50 Hz 20w choke would be ! Then the same must apply backwardds too, ie 2x 120v 50Hz 20w chokes in series would become 1x 40w 240v choke !

Now, you dont have 120v 50Hz chokes, but you have 60Hz ones. Applying the same line of thought as above, those will make a 240v 60Hz 40w choke. Since your 240v is 60Hz this is supposed to be perfectly what you need... (unless you consider tolerances like the 20 choke being made for 15w too etc so it may a bit underpower the 40w tube but i dont think too bad)



The only catch i can see is this :

The 40w tube is 430mA. The 20w tube is about 370mA (overdriven up to 400mA in some setups). The 40w choke, made to handle 430mA, will hav no issue powering 2 20w tubes in series on 370-400mA. But the 20w choke is made for 370mA only, so it may overheat at the 430mA of the 40wT12. You can try, it won;t get harmed immediately. If it is running to hot then consider changing the 2 chokes to a bigger array (with 2:1 proportions so that the ballast value will remain the same) to break up the amout of heat over more chokes, so each one heats less

Howver if the choks are meant to run 15w tubes they might be capable of handling higher current, and might be able to withstand the 430mA as they are (or with a bit extra cooling)
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #8 on: June 28, 2013, 12:09:35 PM » Author: Medved
@dor: I would rather guess the "15W" chokes would feed less current into the 40W tube as well, so it would likely run at about 30W or so...
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #9 on: June 28, 2013, 12:29:43 PM » Author: Ash
My name is ash....

When used with the correct lamp on 120v, i'd expect that if the 20w lamp take about 370ma, the 15w lamp will take more. As such, hte choke would be made capable o handl more, so less prone to ovrhat when "abused"
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #10 on: June 28, 2013, 10:55:18 PM » Author: Medved
My name is ash....

I'm sorry, when in hurry, I sometimes mix up people...



When used with the correct lamp on 120v, i'd expect that if the 20w lamp take about 370ma, the 15w lamp will take more. As such, hte choke would be made capable o handl more, so less prone to ovrhat when "abused"

Usually the current tend to be lower than higher - lower current yield cheaper ballast and less problems than the higher current used with lower current rated lamps...
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #11 on: June 29, 2013, 01:18:04 AM » Author: Ash
The 15w lamp is supposed to be the one with lower arc voltage, making higher curerent on a choke rated for "15-20w". So the choke then must be made capable to handle more than 370mA
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #12 on: June 29, 2013, 01:45:55 AM » Author: Medved
The choke maybe, but the 15W lamp won't...
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #13 on: July 09, 2013, 06:33:05 PM » Author: jrmcferren
With preheat ballasts for F40T12 lamps still readily available, why waste time converting a ballast? Advance has the L-140F-TP ballast and it is in stock on 1000bulbs.com and other places.
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Re: F15/F20 preheat ballasts...F40 lamps? « Reply #14 on: July 10, 2013, 01:40:10 AM » Author: Medved
@jrmcferren:
For the joy from experimenting with that stuff...
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