Using a Capacitor to cancle pulse load.
Using a Capacitor to cancle pulse load.
(OP)
Hello all,
I have a residential unit that currently has a single phase 100A power supply.
In this unit there is a on demand water heater that uses 46A @240V which switches on and off as the thermostat demands.
The result is a flickering of all the lights in the building when the heater is running.
Can I size a capacitor that I can put in parallel with the load?
Thanks for your time.
I have a residential unit that currently has a single phase 100A power supply.
In this unit there is a on demand water heater that uses 46A @240V which switches on and off as the thermostat demands.
The result is a flickering of all the lights in the building when the heater is running.
Can I size a capacitor that I can put in parallel with the load?
Thanks for your time.





RE: Using a Capacitor to cancle pulse load.
Do you actually mean 'flicker' as in alternating light-dark-light-dark-... or a dimming of the lights when the heater is on and a recovery when the heater switches off? 'Flicker' is a defined term and the loads which cause it aren't typically found in a domestic environment.
Assuming that it is a dimming of the lights when the heater is on, it sounds like your load is a large proportion of the feeder and / or source capacity, or you have a feeder which is long for its size, all of which are capable of causing excessive volt-drop. That said, tungsten lighting is very sensitive to small fluctuations in voltage and human eyes do a great job of picking up on it so you might find that you are within accepted tolerances for volt-drop yet still see a noticeable dimming when the heater kicks in.
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If we learn from our mistakes I'm getting a great education!
RE: Using a Capacitor to cancle pulse load.
A small diesel generator for hot water would be another option.
Or, get rid of that 11kW monster and put in a 300kW or 4000 kW conventional water heater.
I have had experience with a number of "On Demand" water heaters, none of it good.
If I want a little bit of hot water I just open the tap a little bit. I then pay for the hot water I need. With On Demand I have to open the tap wide enough to trigger the flow switch. Then all 11 KW kicks in. I probably have more flow than I want so I have to waste more cold water to cool the "Energy saving, On Demand" water to a usable temperature.
The proponents of energy savings with "On Demand" don't mention and probably don't know that in some installations, heating the piping between the On Demand unit and the point of use loses more energy than heat loss through the tank insulation of a conventional hot water tank.
Furthermore during the heating season, heat loss through the tank insulation is not really a loss, and it is not that much anyway. If the outside of your hot water tank is hot, replace it, the insulation is shot.
Any one who intentionally installs an "On Demand" system deserves all the grief he gets.
Any one who gets an "On Demand" system through no fault of his own has my sympathy.
Bill
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"Why not the best?"
Jimmy Carter
RE: Using a Capacitor to cancle pulse load.
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If we learn from our mistakes I'm getting a great education!
RE: Using a Capacitor to cancle pulse load.
Wow Bill, some real anger in there over just On-Demand water heaters!
My opinion? EXACTLY the same. They're horrible and you left out that they have about a 20 year payback. Unfortunately they only last 8 years.
idratherbefishing; There really is nothing you can do about it short of some serious rewiring and possibly a new service drop.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Using a Capacitor to cancle pulse load.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Using a Capacitor to cancle pulse load.
Should have read 3000 Watts or 4000 Watts.
And I worked in a facility in the Yukon territory where the diesel engine coolant from the generators was run through heat exchangers to provide much of the energy to heat the domestic water.
On demand, I've suffered poor showering experiences from Canada to Chile with a lot in the tropics in between. Gas or electric.
I like to wash my hands under a running tap. With on demand, I use two or three times as much water and energy as I would with a conventional tank. I doubt that this is figured in to the payback schedule Keith.
My worst experience was/is with a small cabin I own. I had a contractor in to do a little work while I was out of the country. He was supposed to be re-installing a couple of thermostats. He took it upon himself to throw out my water tank and install an on demand unit. Then he died before I could tell him what I thought of his judgment. I think of him every morning when I am enduring my cool shower. I was going to re-install a tank, but I find that I am only using the cabin for a few days a year and it's just not worth the time or money to change now. But I've put that behind me now. I never think of it anymore, UNLESS someone mentions On Demand or I have to take another cool shower. LOL
Bill
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"Why not the best?"
Jimmy Carter
RE: Using a Capacitor to cancle pulse load.
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RE: Using a Capacitor to cancle pulse load.
Despite all recent achievements in chemical energy storage, storing hot water is still the cheapest way to store energy, at least if the form of energy you intend to use is hot water.