fluorescent lamps and relays

I have nearly completed a project but i have one final hurdle. I am trying to control 4 sets of 8x18W fluorescent lamps using a 4 channel relay module. Each relay is rated at 10A and after speaking to an electrician he said the entire lighting circuit will be fed from a 6A breaker, so my 10A should have been ample.

But every time i set this up it will work once then the relays will stick closed (luckily so the lights stay on). I am sure this is due to the striking current of the lamps/ballasts, however i can't find anything to tell me exactly what a single 18W fluorescent lamp and ballast will pull when striking.

Can anyone offer any suggestions? I'm currently looking at upping relays to 30A but if that doesn't cover it i'm stuck!

I'm in the uk so switching 230/240 VAC

Thanks in advance!

joshbailz:
I have nearly completed a project but i have one final hurdle. I am trying to control 4 sets of 8x18W fluorescent lamps using a 4 channel relay module. Each relay is rated at 10A and after speaking to an electrician he said the entire lighting circuit will be fed from a 6A breaker, so my 10A should have been ample.

But every time i set this up it will work once then the relays will stick closed (luckily so the lights stay on). I am sure this is due to the striking current of the lamps/ballasts, however i can't find anything to tell me exactly what a single 18W fluorescent lamp and ballast will pull when striking.

Can anyone offer any suggestions? I'm currently looking at upping relays to 30A but if that doesn't cover it i'm stuck!

I'm in the uk so switching 230/240 VAC

Thanks in advance!

We need much more information ...

  1. Post the Part Number and SPECS of the Relay.
  2. Post the Make, Model # and Specs of the fluorescent lamps
  3. Post your schematics

What does "8x18W" mean?
I am guessing the 18W portion means 18 Watts per bulb, right?
But what does the "8x" portion mean? T-8 bulbs or qty 8 bulbs per assembly?

Assuming, Qty 8 bulbs per assembly ...
4 x 8 x 18W = 576 Watts / 240 Volts = 2.4 Amps
Double that for starting amps.
So, 5 Amps +/- for starting ?
And your relay contacts are rated at 10 Amps.
Hmmmmm ...

What is the Voltage Rating of the CONTACTS of your Relay?
Are the Relay Contacts rated for AC or DC power?

Can the Arduino turn the Relay "On, Off, On, Off" many times with no lamps?
Can the relay properly control one "8 Lamp Assembly" without sticking ON?

How do you get the relays "unstuck"? Are they open frame so you can force the points apart? Surely, the contact points are not being welded together.

With no power to the lamps, do the relays still "stick" closed? If so, your program, sketch, is certainly the prime suspect.

Paul

I think you would be better off using Solid State Relays (SSRs). Ones like those in the link can be driven directly from an Arduino output.

8 x 18w means that i have 8 18w flourescent tubes per 10A relay running at 240V AC, the relays are rated at 10A for 250VAC.

With your calculation i would be pulling around 5A per relay apart from the striking current which if you say is double the running current would tip me close to my 10A and these are cheap relays so wouldn't surprise me if they have welded themselves shut.

I think the sketch is fine as this was all tested on my workbench under no load, as soon as the load was added it worked once then stopped, i can't get to the relays as they are encapsulated, to me it does sound like they have welded together.

I have heard solid state relays can't deal with the high inductive load that the ballast places on them?

Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Flouro type loads have very high inrush currents, that are capable of welding relay contacts together apon contact.
HighInrush Relays are made for this job.
See the attachment. This is a representative of what is available in industry installations, but explains the cause and principle of high inrush.

Thanks..Tom..... :slight_smile:

Relays_HighInrush_WoR15.pdf (879 KB)

joshbailz:
8 x 18w means that i have 8 18w flourescent tubes per 10A relay running at 240V AC, the relays are rated at 10A for 250VAC.

With your calculation i would be pulling around 5A per relay apart from the striking current which if you say is double the running current would tip me close to my 10A and these are cheap relays so wouldn't surprise me if they have welded themselves shut.

I think the sketch is fine as this was all tested on my workbench under no load, as soon as the load was added it worked once then stopped, i can't get to the relays as they are encapsulated, to me it does sound like they have welded together.

I have heard solid state relays can't deal with the high inductive load that the ballast places on them?

So, the relay turned on once and is now stuck on?
Welded contacts?
If you welded 20 Amp contacts then 30 Amp contacts won't last very long, either.

What is the Part Number and SPECS of the Relay ?

Also, is there any information on the Lamp Assembly "nameplate" that indicates:
a) Running Amps
b) Surge / Starting Amps

I have heard solid state relays can't deal with the high inductive load that the ballast places on them?

Highly Inductive?
If these are new fluorescent lamps then they should have electronic ballasts, not magnetic ballasts.
But now the inrush could be to charge the capacitor.

I would seriously consider a Zero Cross 30 amp SSR ( Solid State Relay )
and maybe a 30 Amp fuse to protect your investment.

How can you easily stagger start the 4 different Lamp Assemblies?

... control 4 sets of 8x18W fluorescent lamps ... 4 channel relay module ... Each relay is rated at 10A ...

I just re-read those statements, again.
Are you saying, just ONE of the "8 bulb lighting fixtures" was connected to one 10 Amp Relay and
that made the contacts fuse together?

I originally thought, all 4 lighting fixtures were connected to one relay.

... however i can't find anything to tell me exactly what a single 18W fluorescent lamp and ballast will pull when striking ...

I think, the only person who knows the striking amperage is the engineer that designed the circuit.
China?

4 Possible options for you:

  1. Call or email the manufacturer
  2. Setup a Test Jig and actually measure the in-rush amperage in the real world
  3. Use a smaller and smaller Fast Acting Fuse (30A, 25A, 20A, 15A) until it blows = Surge Approx
  4. Add an NTC device (can get hot!) to limit the In-Rush to a reasonable value

I do not see how anybody else can give you a valid answer.

Hello everybody, I have exactly the same problem, so could I ask you how has been it solved...? Should I buy Solid State Relay?

Btw when I get the relay after it has been "welded" and then tap on it a bit with a hammer then it starts again...

alliaalliaallia:
Hello everybody, I have exactly the same problem, so could I ask you how has been it solved...? Should I buy Solid State Relay?

Btw when I get the relay after it has been "welded" and then tap on it a bit with a hammer then it starts again...

Did you notice that this thread has been dead since 2015? I get caught that way, sometimes!

Paul

alliaalliaallia:
Should I buy Solid State Relay?

Yes.

Buy a relay with appropriate ratings for your load. If there is any doubt, go 4 times higher.
Or more if they are particularly cheap.