Relay to protect timer from 120v converted chromega D

[3e8]

I recently converted the halogen lamp in my chromega to 120V with a 300W 120V halogen bulb. It works fine when plugged directly into a wall outlet, but when I attempt to use it with a timer, it blows the fuse of the timer. I'm guessing the inrush current is just too much, so I'm looking to wire in a SSR and just have the timer provide the switching current and the power current from a wall outlet. I'm just not up enough on electronics to calculate which SSR I would need. Could someone help me figure out what specs I would need for the SSR?

Thanks,
Bryan

[Jody_S]

300W / 120V = 2.5A. You would typically use a 250V 5A SSR. There is no 'surge' with a halogen lamp, it's not like an electric motor that may draw several times it's rated current on start-up, depending on load.

[BetterSense]

What is the fuse of the timer? As stated previously, a lamp is a resistive load with no appreciable inrush.

You may have trouble finding an SSR that is switched by 120vac. Most are DC.

[Leigh]

As stated previously, a lamp is a resistive load with no appreciable inrush.
Not true.

All lamps have a positive temperature coefficient of resistance. This means the resistance increases as the temperature goes up.

From a cold start, the resistance must be considerably lower than the operating resistance for it to come on rapidly. This is normal, and necessary for proper lamp operation.

If the AC line voltage is at or near its peak (happens 120 times a second), the current can be quite large.

My first suggestion would be to install a slo-blo fuse in the timer.

- Leigh

[BetterSense]

Good point. Maybe the fuse can be replaced with a "slow blow" fuse of the same rating.

[gleaf]

Not sure this is a match for your model.. Limited internet search data says those are low voltage high watt bulbs.
105295

[ic-racer]

What kind of timer? A little unusual to have a fuse on the timed circuit with such low specifications. I have 3 timers rated 500w and 700w and neither of them is fused. You are not trying to use a Chromegatrol for timing a 120v lamp are you?

[3e8]

I'm using a RH Designs Stopclock timer, which can handle 500w at 120v. My rewiring of the head consisted of simply connecting the lamp socket directly to a two prong plug and replacing the 24v bulb with an EWG (120v, 300W) bulb. It lights up fine when plugged into the wall outlet, but when used with a timer (both my stopclock and an old gralab 300) it blows the timer's fuse.

[gleaf]

http://www.littelfuse.com/products/tvs-diodes/~/media/Electronics/Datasheets/TVS_Diodes/Littelfuse_TVS_Diode_AK6_Datasheet.pdf.pdf

If it is a transient generated during switching. The a Tranbsorb across the AC line will handle the spike. Your local electrical supply house should have them, or be able to order them.
I am puzzled over the behavior. Does it blow on turn on or when it turns off?

May be a neutral/hot/ground issue. "Black to Brass.. Bet your A**" rule. Neutral side of house power is grounded to earth at the breaker box. The Chromega should have a 3 wire plug, earth ground (green), Neutral (White) and AC hot (Black). If the bulb socket is such that neutral is connected to the mount/shell and the white/black are reversed you may have a direct short of hot to chassis ground at the socket.
Switch the wires and see if the problem disappears. or ohm out the bulb pins to the Chromega plug pins and see if there is a short to ground.

[Jody_S]

I am also thinking you may have a wiring issue somewhere. A 300W halogen bulb should not blow a fuse in a 500W timer. In any case, if you want to run it through a relay, simply use an electromechanical relay instead of an SSR and you'll be fine. If you're blowing fuses on the timer, you will blow an SSR also (unless you get a 30 or 50A one). It's very easy to find an electromechanical relay with a 120V coil, and it's probably cheaper than the equivalent SSR.

Question: if you plug in a lamp with a 60W or 100W bulb into your timer, does it work properly?

[Leigh]

This is not a transient or "spike" issue.
The load is resistive. Resistive loads don't generate spikes.

It appears to be an inrush current problem.

I had considered reversed hot/neutral as a possibility. It's a common problem.
But I can't come up with a good scenario to explain why that would blow a fuse, unless...

Perhaps the existing lamp socket will not handle 120 volts, given that the original part
was low-voltage (probably 24 volts).

If the socket is breaking down or has significant leakage to ground, it could blow
the fuse without leaving any visible indication of the fault.

- Leigh

[Len Middleton]

Given the price and availability of the RH Design unit, you might want a electro-mechanical relay for switching the lamps anyways just to keep it safe, unless of course its current configuration has its switching through a relay.

Leigh's comment regarding the voltage rating of the socket is reasonable, but then what is the voltage rating of the original wiring as well? You could be having a phase to ground or phase to phase fault blowing the fuse, if the voltage rating and condition (e.g. deterioration due to age) in the circuit is not up to your revised requirements.

Looks like you have more work ahead...