Circuit limitations

[RPh_Guy]

Just so I don't find this out the hard way...
I'm going to be using a 1650W element for RIMS on a 15A 120V circuit. My pump is only 0.1A. I assume the Inkbird isn't taking much power.

Do I have to worry about using the garage door motor or the fridge compressor kicking on if they're on the same circuit?

 

[processhead]

Just so I don't find this out the hard way...
I'm going to be using a 1650W element for RIMS on a 15A 120V circuit. My pump is only 0.1A. I assume the Inkbird isn't taking much power.

Do I have to worry about using the garage door motor or the fridge compressor kicking on if they're on the same circuit?

Yes, in all likelihood you will experience breaker trips when almost anything else switches on in the circuit. Your heater by itself is right at 13.75 amps.
Further, as circuit breakers age, their trip point can drift above or below the rated trip point.

 

[day_trippr]

Agreed. Indeed if the breaker doesn't trip with both devices powered up it's suspect...

Cheers!

 

[RPh_Guy]

All righty. I will unplug the fridge when I'm brewing.

Thanks guys

 

[Smellyglove]

All righty. I will unplug the fridge when I'm brewing.

Thanks guys

Does the fridge pull enough that that's what you need to unplug?

But, I don't know. But might the characteristic of the breaker help you? Some units pull some start-up amperes to charge the capacitors. C/B breakers? How much does a garage door motor pull?

 

[day_trippr]

I had to take one of my 3/4 hp openers apart to replace a stripped gear and that motor is quite small, I'd be surprised if it pulls more than a couple of amps peak startup and about a quarter of that steady running.

It's all about the gearing...

Cheers!

 

[RPh_Guy]

Does the fridge pull enough that that's what you need to unplug?

Finally had time to look.

The fridge says 7 amps.
The garage door opener says 4 amps.
I assume those are at peak usage.

The RIMS heating element would only pull the 13+ amps when it's heating at full strength (i.e. ramping), right? And not when it's just maintaining the mash temp?

 

[Gnomebrewer]

You should generally (assuming it's the same in the US as it is in Aus) only have a continuous load up to 80% of the rated capacity of the breaker, so the element alone is already overloading it (which is a bit pathetic for a small element - I'm glad we use 240V). But, they can also handle bursts of nominally 20% over the rated capacity of the breaker, so you're probably OK with the garage door on top of the element (except that the element is already causing it to heat up more than normal, so the burst might be too much) but not the fridge.

 

[golfindia]

Finally had time to look.

The fridge says 7 amps.
The garage door opener says 4 amps.
I assume those are at peak usage.

Refrigerator probably draws at least double that during compressor start inrush.

 

[processhead]

The RIMS element draws full load rated current while it is heating at 100% or 25%. The only difference is the duty cycle time (time on vs time off).

Any motor load, like the garage door opener and the frig will have a momentary in-rush current surge when the compressor cycles on or the door is opened. That surge current will exceed the name-plate amp rating on the device

 

[RPh_Guy]

The RIMS element draws full load rated current while it is heating at 100% or 25%. The only difference is the duty cycle time (time on vs time off).

Ok, so I don't understand how it works.

How does the PID reduce the wattage of the heating element?

 

[day_trippr]

Pulse Width Modulation. 100% duty cycle ("on time") would be the maximum rated element output, but as you increase the "off" time the element output (vs time) is reduced...

Cheers!

 

[Gnomebrewer]

The RIMS element draws full load rated current while it is heating at 100% or 25%. The only difference is the duty cycle time (time on vs time off).

While that is technically correct, the breaker will effectively register it as 25% of the full load if the duty cycle is 25% (assuming the cycling is very short in duration) because it works on a temperature increase to produce a current between contacts (through air or oil) within the breaker - the temperature increase doesn't happen in an instant unless the load is massive (i.e. short circuit) - it takes time. That's why short bursts that overload the breaker can be tolerated, but long periods at or a bit below the rated load may not.

 

[RPh_Guy]

The PID cycles the element on and off really fast? That's makes sense.

 

[Gnomebrewer]

The PID cycles the element on and off really fast? That's makes sense.

The minimum cycle length can be adjusted. If a PID is running a fridge (for example) you don't want it cycling on for a second or two at a time (that's bad for the compressor) but with a heating element the cycle can be short. Mine (a different brand PID) tends to run in about half-second bursts (you can tell when it's cycling because a light comes on).

 

[processhead]

The cycle rate is the key to whether this would be an overload condition for the breaker.

For a RIMS application, you need to accept that there will be times when the element is on long enough for it to be an issue with the total circuit load. The only time the duty cycle is short enough to not be an issue is when you have reached the temperature set point and are just maintaining mash temp.