Weird problem with LED tubes in fluorescent fitments

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1

Now solved, but I thought I’d share.

I’ve moved my business and the new address still had fluorescent lights. Options were to replace them all with LED panels or swap the tubes with LED ones. As its rented, I though the panels to big of an outlay and replaced the tubes. With the type of LED tubes and fluorescent fitments, all I needed to do was replace the tube and starter.

After replacing the tubes the fuse kept blowing. First I thought I’d messed something up. Then I suspected a leak in the roof might be getting to a junction box in a hidden cavity. Some of the terminal blocks in the light fitments had degraded, so swapped them. What I thought was suppression capacitors had their casings degraded and I thought they might be shorting, so heat shrunk all of them. I even tried bypassing the ballast, but the tubes used more current. The more lights that were on, the quicker the fuse blew, so gave in called an electrician.

He determined there was to many lights on 1 fuse. The electrician that had fitted the new fuse board joined 2 lights circuits into 1. One circuit alone was taking 7.5A and the fuse was 6A. So we split them to 2 fuses and all was well.

However, there were 28 24W tubes that drew 7.5A (240VAC). This didn’t add up. Some measuring with a clamp meter and I found the additional current was going through the suppression capacitors. Quick Google found these are actually power factor correction capacitors. I found a video showing fluorescent lights current measured less when these capacitors are added. All I can assume is that the drivers in the tubes have some funny affect on the capacitors, or they duff. So ripped them all out.

Anyway, if you have replaced fluorescent tubes with LED ones, check if you have power factor correction capacitors and remove them.

2

This reminds me of a similar (but opposite) event in the late 1970’s.
Philips introduced the SL*13, rated 13W at 240V AC, 50Hz. The unit is basically a magnetic “choke” ballast, starter and specially formed tube shoehorned into an enclosure with a prismatic glass diffuser. It has an E27 socket, so it can replace existing (60W) incandescent lights. It starts up just like old linear fluorescent fixtures.
A Rotterdam hotel wanted to replace all the incandescent lights in its endless hallways. From 60W to 13W per fixture was a promising incentive, but all the fuses blew. Turned out the power factor of the SL*13 was about 20%. Solution: installing capacitor banks.

3

I believe the ballasts in the light fittings are magnetic type, so probably why they had the capacitors. I just thought it was weird how it had the opposite affect on the LED tubes.

4

In an AC circuit, a capacitor acts like a variable resistor; depending upon the frequency and capacitance it could be low enough to blow the fuse.

e.g. 100uF at 50 Hz could be your culprit