Hz on a on-demand water heater

Status
Not open for further replies.
McLintock

McLintock

Senior Member
Location
USA
Occupation
Electrician
Customer has a 24kw on-demand water heater, her lights(some) flicker when the hot water is on.
The unit is 240v, has 3-40 amp two pole breakers. Voltage is fine on each of the three elements, amps of the same on each leg, 90 amps at the feeders coming in to the panel, so since all that was good I took a Hz reading, all at the conductors before the main breaker, on both legs with the heater off, I have 60, with the heater on I have 60 on I leg and around 200 on the other leg.

Is the best solution here is to replace the whole unit, or replacing the elements be a better idea? Have not dealt with any thing like this so any advice would be greatly appreciated.


Sent from my iPhone using Tapatalk
 
Sounds like the water heater is modulating, which is causing electrical noise on the whole system. Your meter is reading this as 200Hz, and the lights are responding to this.

I doubt changing the heater will help, because it is supposed to be modulating.

Unless there is some sort of filtering that has failed, which I doubt. The electrical noise is being introduced by the modulating current interacting with the electrical service impedance.

Jon
 
I agree with Jon that the water heater is probably operating as desired, but it's modulating its current and creating electrical noise on the phases. Is there any common factor between the lights that flicker and those that don't? For example, are they on a dimmer, are LED bulbs or LED wafer lights, are circuits on the same phase, etc.?
 
synchro said:
I agree with Jon that the water heater is probably operating as desired, but it's modulating its current and creating electrical noise on the phases. Is there any common factor between the lights that flicker and those that don't? For example, are they on a dimmer, are LED bulbs or LED wafer lights, are circuits on the same phase, etc.?
Click to expand...

She as new LED bulbs in the bathroom that flicker, and the light in the range hood flicker, not sure if LED or not. They are not on a dimmer, and they are on the same phase

Should I change those bulbs out to a better LED bulb?, I’m guessing she got the bulbs at Walmart


Sent from my iPhone using Tapatalk
 
It's possible that non-dimmable bulbs would be less likely to flicker than dimmable ones, but it's still a crapshoot.

If only circuits on one phase are affected, perhaps that phase has a higher impedance than the other. You could try moving one of the problem lights over to the other phase to see if it helps.
 
Customer sent me a video last night, and her lamp was strobing while the water heater was on


Sent from my iPhone using Tapatalk
 
hillbilly1 said:
Could be voltage drop from the high current pulses too. Long distance to the transformer? Service maxed out?
Click to expand...

Agree. A plug-in incandescent lamp could be tried on a 120V circuit off of one phase, and then compared with powering it off the other phase to check flickering and see if there's any significant difference. Also, a plug-in heater could be used to quantify the amount of voltage drop for it's current level to check whether it is reasonable.
 
Status
Not open for further replies.
Top