This is kind of a random question, but is it possible to ballast small fluorescent tubes like this with resistors instead of chokes? I need to run a lot of these for a project and I don't really have the money to buy a whole bunch of ballasts. This would work almost how the GE bright stik worked with the resistive wire.

If it is possible, what resistors would you use for:
F4T5, F6T5, F8T5, and F13T5 lamps? All these lamps can be driven with a standard 120v choke.

I'm not sure about the values of the resistors, but you can also use incandescent lamps as ballasts. Also, the F13T5 will NOT work on a simple choke. It requires an autotransformer ballast on 120V mains.

Oh yes, I forgot about that lol, I might play around with the values

If it is possible, what resistors would you use for:
F4T5, F6T5, F8T5, and F13T5 lamps? All these lamps can be driven with a standard 120v choke.

The 13W has too high arc voltage (nearly 90V) to work on just 120V OCV, so it won't work with just a resistor (it won't work in just an inductor either, there it will need an extra series capacitor as well plus an electronic starter; "classic" with a glowbottle starter ballasts for this were step up autotransformers).

For the 6 and 8W lamps I think the 25W incandescent would be quite closest to the rated current.
The 4W lamps have arc voltages about 27V, so these may work two in series on a single 8W ballast, but for that you most likely won't find any suitable glowbottle starters (it would need trigger voltage around 50..60V).

But there will be yet another problem: The resistive ballast does not provide enough OCV to reignite the lamp after current zero cross, so then the lamps exhibit quite high overshoot on reignition and that may cause starters to false trigger.
So that problem may reduce the resistive ballast to work only on the lower power lamp, so the F6T5 and just a single F4T5 (then the ballasting lamp should be just 20W). But that will make the lamp installation quite inefficient.

And for the inductive ballasts: Don't forget the PL-S 5..9W ballasts are the same spec as the F4..8T5...

Hi looking at your scope pictures of the capacitor ballast am I right in thinking the initial current spike just around zero crossing is the rapid discharge of the capacitor thr9ugh the lamp and then the rest of the current is the recharge and lamp current?

The capacitor ballast is very similar with the resistive in one aspect: There is quite long period of time around the zero cross, when there is really no current through the arc. That means afterwards the voltage has to go higher, above the normal arc voltage, to reestablish the plasma. But once this happens, the plasma forces the voltage back down. With resistor ballast this isn't that big problem, as it just means the current appears with some delay and directly to a higher level. But with the capacitor that means the capacitor has to discharge/charge very quickly for this difference, leading to very high peak current. And that spike is then practically killing the lamp.
After that spike the current corresponds to about the level desired for the arc.

So the main problem is there only the discharge current spike just at the reignition, so that should be eliminated.
The easiest method for that is to connect a resistor in series with the capacitor, so that resistance will limit the current. On the measurements there I was already using some 100W incandescent for that purpose, so the shown spike is already limited by that. The problem is, to get the spikes under control, the resistance has to be so high, the losses will  be not that far from just a resistive ballast.

However I've seen another method (in the "F8T5 worklight sticks"): There was a bridge rectifier inserted between the capacitive ballast and lamp, with one extra diode on the output. Two diodes in the rectifier (the two connected to the Neutral) have each connected a series combination of some ~2.2uF capacitors combined with a 100Ohm resistor, then from the Line input goes about 10nF capacitor behind the additional series diode.
This combination serves three purposes:
First when the lamp is not lit yet, the structure becomes a mains voltage multiplier, generating up to 1200V pulses (it forms a sinewave of 300V amplitude stuck between the ~600 and ~1200V). This voltage then ignites the lamp.
Second the two 2.2uF capacitors with the resistors form a voltage doubler, capable to deliver some significant current (up to 50..100mA or so) through the discharge with still cold cathode mode discharge, so providing enough ion bombardment heat to warm up the cathode.
And the 3'rd the capacitors always get charged to about the arc voltage in one halfwave. When the zero cross region changes the polarity, that voltage is added on top of the capacitive ballast output. That means the discharge is reignited way sooner, than the voltage in front of the rectifier reaches the arc voltage. That means the reignition spike gets limited by the (for this purpose) high ohmic resistor connected in series with the capacitor. Then when the voltage in front of the rectifier reaches the arc voltage, the discharge is already present, so the main current may flow and that time not heating the resistor anymore. By that the resistors could be made so high they work well to reignite the arc after current zero cross, yet do not pose that ,uch extra power dissipation, as the main current flows directly into the arc.
The only drawback is, that circuit rectifies the current into the lamp, so the lamp is in fact operated at DC, with all consequences (so not usable for longer lamps, the cathode has to be connected on the top side in case of vertical position, all the heating components should be close to the cathode as well, both of these to counteract the electrical field pushing the positively charged mercury ions towards the cathode...).

I'm describing a 230V version, 120V one may require more multiplier stages with the small capacitor to reach the required ignition voltage.
In any case this type of ballast is rather crude, not that small and quite hard on the lamps (really cold starting)


Generally for your use I would rather use ballasts salvaged from 7..11W CFL's (to be sure they are working, you may even just buy new ones for that). These are cheap, the ballasts small and lightweight, so you may buy and then install even the higher quantity you need.
When installing these, remember the wires from the ballast to the lamp should be as short as possible, without forming any large loops or large wiring capacitances (to make sure the inverter really stays off and so does not blow off when e.g. the lamp is removed or so...).
And because in your application they won't be exposed to the heat from the lamp, there is rather high chance they will last quite long time.
Even the "instant starting" ones heat up the electrodes during the ignition and mainly during the cold cathode mode, so stress the cathodes way less than the previously described "light stick" ballast. And are quite readily available...

Medved I never realised there were so many different circuits for flourescent lamps I can see that a DC current driving a lamp is very bad I've seen lamps like that suffer very bad blackening also I never like circuits that start a lamp too quickly it seems unnecessary cruel to the cathodes

180 ohms 10w resistor in this nice strip. Has 2 capacitors & 2 diodes in the circuit & even has a fuse.

Doubler/Rectifier, resistor and starter - Indeed nothing more.. Atleast if the capacitro values are high enough, it will light continuously without extinguishing on half cycles (only fluctate)

Alright, thanks for everyone's help! I don't want to use incandescent lamps, I would like to use resistors to keep it small. Could anyone provide me with a circuit diagram or parts list for a ballast for a 4 6 and 8 watt lamp? Remember this will run on 120v

I guess you can clone what you see in the picture above.. Capacitors mus be same type, not just same value. Diodes are probably 1N4007

What i dont like here is, the thing may go charmander when the starter gets stuck

I guess you can clone what you see in the picture above.. Capacitors mus be same type, not just same value. Diodes are probably 1N4007

What i dont like here is, the thing may go charmander when the starter gets stuck

So will that ballast work with 4 6 and 8 watt lamps? Also what's the parts list and schematic?

I have no marks on this (except for a UL approved sticker on bottom). Because it's a fixed length with T5 sockets, I would assume it's only for F6T5 lamps, but it might work for 1W or 2W above or below that. I can open it up again and take better pics to see the exact circuit if you still want. You'll have to let me know. The parts "seem" commonplace.

The resistor + 2diodes + two capacitors is practically the same as the "light stick" - it drives the lamp DC as well...
The difference there is the rather low OCV, so the lamp won't cold start, for the starting the starter then preheats the cathode (I don't know how it is connected, but it is sufficient to heat up only the cathode side).
The DC drive is not that much what is killing the lamps there. The "killers" are the current spikes and cold starts, without any heating assistance.

F8T5 from 120v 600 Ohm 10 W

F20T12 from 120V  212 Ohm 20 W


GE Bright Stik may have more going on than a simple resistive ballast.  Lamps seem to start very easily without inductive kick. I believe the proximity of the resistive wirewound wire to the lamp aids in starting..