Switch 120 volt dc to 220 volt dc

[(unknown)]

New guy at this so bear with me , built a windmill out of old waterpump mill and chevy truck axle .Installed a PMA and produce dc power to run direct to hot water heater element.It works with my solar hot water direct pumped into floor. no tank no batteries. At about 20-30 mph runs 120 volt element perfect but at 35+ mph burns them up because of volts in excess of 150. I want to simply turn on a 220 volt element when I have enough volts. Won't run a 220 element from the start and 90 % of my wind is below 40 mph. any Ideas ?

[dnix71]

I don't think the real problem is voltage. It's that the element is not large enough to handle the power from shorting your mill, and therefore the voltage rises until something breaks, in this case, the element.

Two 120 elements in parallel will double the power dissipation capacity, while lowering resistance of the circuit as far as the mill is concerned, so it should start and run just fine.

[GWatPE]

You can connect 4 of the same elements, in a series and parallel arrangement.  This will present the same resistance, but with 4X the power dissipation capacity.  Running just 2 in parallel with half the effective resistance will probably just stall the windmill.  The load needs to be the same resistance, but a higher power dissipation capacity, hence add an additional 3 same ratings heaters to the existing heater in a series-parallel arrangement.

Gordon.

[Hobo]

What is the wattage of your 220/240v element? Is it different than the 120v element?

Are using one element only, or one and turning on a second?

Hobo

[ghurd]

The problem with switching a relay depending on the voltage of the system is that when the 220V comes online, the voltage changes, so it switches back.  Repeat...

Gordon's idea sounds pretty good to me, depending on how the system is assembled and how easy it is to add 3 more elements.

"solar hot water direct pumped into floor. no tank"

Curious about the element assembly, and how the plumbing physically goes together.

Sounds interesting.

G-

[(unknown)]

The smallest element in 220 i could find was 1500w but was not very effective in low wind so choose 120 v 1500w worked much better in low wind just a problem in high winds above 40 mph.

[(unknown)]

G I am using the mass of the floor as the tank so hooked up the same way and when i resolve the element issue it will become an extension of the water in the floor i plan to use a old pressure tank from a well system or an old air tank and weld in my own bungs. I can try to get you photos if you would like thru e-mail. steve.

[(unknown)]

Gordon Talked to my electrical friend says great idea i will get more elements hook it up and give it a try spring is on the way should be windy soon.steve

[Flux]

If you run a 220v heater on 110v it will take 1/4 the wattage so your 220v 1500W would have taken 375W compared with the 1500W 120v one.

The same result could have been got with a 220v 6kW heater.

Gordon's series parallel method will work fine and comes much to the same thing.

Flux