Using a Capacitor to cancle pulse load.

[idratherbefishing]

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.

 

[ScottyUK]

No, not unless your house runs on DC.

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!

 

[waross]

You could run the water heater on DC, it won't know the difference. Use a rectifier to charge the capacitors. Forget using the spare room. It will take at least that much space to house the amount capacitors needed to supply a useful fraction of 11kW for enough time to enjoy a shower.
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

 

[ScottyUK]

Bill! I know it's cold up there in Canada but do you crazy guys really have four megawatt heaters in your homes? We need photos!


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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

LOL He always has a few spare V16 diesel generators laying around.

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

 

[itsmoked]

Are you getting any of this jraef?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

The heat loss of the 4 MW water heater is just part of our gain. We tap the heat reduction of the two or three 16 cylinder diesel engines as well for heating. LOL
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
--------------------
"Why not the best?"
Jimmy Carter

 

[IRstuff]

Speaking of lights dimming, my cheap-a** color laser does that to my room lights. It apparently has a peak draw of something like 3 kW, but only for about a second.

TTFN

FAQ731-376

 

[electricuwe]

The suggestion to reduce power of the heater is simple and will work well as long as you can store the water to accomodate the high demand, e.g. for showering.

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.