As the title suggests. 4.4uf 650v capacitor wanted for used with Philips BSX180H96 180w SOX gear.

 hace u thought of getting caps from microwave ovens
U may jave to put  a few in parallel  to add up the uF value

That's something to think about.

I'd get just a couple of good quality film capacitors from electronics supply house like RS. 2x2.2uF will give you 4.4uF needed. 650V rating is a bit vague - if it means AC, 630VAC/1000VDC or more capacitors will be OK.


 

Be careful here. The voltage rating is important. If you do what you are suggesting and wire the caps in parallel you will indeed double the capacitance but will half the maximum operating voltage. Far better to find two 8.8uf caps and wire them in series. That way you will get the 4.4uf and the voltage will be doubled. I had the same problem for a 131W sox e lamp. Two 6.8uf caps at 450vac gives 3.4uf at 900vac, more than the 650vac required and much safer to use.

half the maximum operating voltage

As far as I am aware this is completely false. Insulation thickness does not depend on any external factor including parallel capacitance.

Indeed, voltage rating stays the same for one and for few of them in parallel

Series is a problem, especially in DC circuits or circuits with significant DC offsets. Any tiny leakage in the capacitors or in the external assembly (like contamination on the PCB) will lead to the DC voltage (or DC component of thevoltage) being divided between the capacitors according to the leakage, and not to the main (and well controlled) parameters. This essentially means that any tiny leakage in one capacitor will charge the other one into overvoltage

(This can be overcome with equalizing resistors or Zener diodes, but is only effective as long as the current draw of the resistors is higher than the expected worst case leakage, which might be a noticable waste of power)

I would take two motor run capacitors in parallel. One 3uF + 1.5uF. mine ones have both 475V ratings. We also recently ordered a couple proper capacitors at an online lamp supply store in the Netherlands. They still listed them for sale. I need to ask a colleague which site it was exactly…

If you run two dissimilar size caps with different uF you will need to balance them with a resistor so they take the same voltage. It will work no problem without, but one of the caps will be working harder than other and run the risk of early failure. In my case I had a 131W SOX E lamp which I rescued from Watford in 2015. I had the SX131 ignitor and the BSX131 H96 Ballast, but the cap was bust. I go two 6.8uF caps at 450VAC from RS, and at £44, not cheap. With that I had 3.42uF at 900Vac, more than enough to run the lamp. It started and warmed up perfectly with not issues after 30 min. I might create an account on Made-in-china and get a supplier to make the caps up. I know the type you mean, meant for a motor, they do a perfect job. its just 4.4uF and 3.4uF at 650Vac are not readily available.       

To be fair I was using googles AI Gemini app to find a way of achieving 3.4uF when no caps were available. The answer I got is below Quote!

Yes, you can use two 6.8µF 450Vac capacitors connected in series to replace a single 3.4µF 650Vac capacitor for a 131W SOX lamp, provided they are non-polarized motor-run type capacitors suitable for AC use. The series connection will result in the correct capacitance and a sufficient voltage rating.
Technical Details Connecting capacitors in series is a standard method to achieve a lower total capacitance and a higher combined voltage rating.

Capacitance Calculation (Series): For two identical capacitors in series, the total capacitance is half the value of a single capacitor

(C_total = C / N, where N=2).
6.8µF / 2 = 3.4µF

This precisely matches the required 3.4µF capacitance for the SOX lamp circuit.
Voltage Rating Calculation (Series): When capacitors are connected in series, "the voltage rating increases." The total voltage rating is the sum of the individual ratings (assuming identical capacitors and proper voltage balancing).

450Vac + 450Vac = 900Vac

This 900Vac combined rating is significantly higher than the original 650Vac requirement, providing a good safety margin for the lamp's inductive circuit.

Important Considerations

Capacitor Type: Ensure the 6.8µF capacitors are AC-rated (e.g., motor-run or power factor correction capacitors, likely made of film) and not general-purpose electrolytic DC capacitors. The circuit uses AC power, and DC capacitors used in AC circuits can fail catastrophically.

Voltage Balancing: In practice, using a high-value balancing resistor in parallel with each capacitor is recommended to ensure the voltage divides equally between the two, compensating for slight manufacturing tolerances or leakage current differences.

Physical Fit: Verify that the two capacitors will physically fit within the ballast enclosure or mounting area of the existing single capacitor.

end quote.

I always try to be as helpful as I can and I think the ultimate solution to our conundrum might be here:

https://capacitorfilm.en.made-in-china.com/product/LmPYuRgObCVy/China-Cbb65-80UF-Motor-Running-Capacitor-Start-Capacitor-for-Air-Conditioner-AC-660V-540V-450V-440V-370V-250V-50-60Hz-5-.html?pv_id=1jfo65loa13c&faw_id=1jfo65qv59a2&bv_id=1jfo6g4vne51&pbv_id=1jfo65g4p738

This seller offers caps in low volumes and there appears to be a range of voltages up to 660v and a range of capacitance. All we need do is pop the question and see what happens.