DC Voltage Relay

[Arranman]

Helllllllp

New to this, but hope there is someone out there that can help me find a voltage / current sensitive relay for 24 volt operation, an adjustable DC Voltage Relay with
0 to 255 second time delay. These things are available in the US, but cannot find them in UK.
I want to use the spare juce from the wind generator to heat the water tank and then pump it round piping under the floor to keep her nice and warm through the winter months.

[sahona]

must be one hell of a wind generator!!
If you know of a device available in the U.S., I would just order it from there (probably cheaper anyway)
Otherwise use the "dump" function of the regulator to pick the relay and start an electronic timer if necessary.
Really need more info - do you actually have the ability to heat a calorifier from a windmill?

[Arranman]

Hi Bill
Thanks for the reply.
This idea is still in the theory stage. I have a Rutland 913 24volt wind generator feeding two 12volt 120 Amp hour batteries. when the batteries are fully charged the regulator is dumping between 4 to 5 amps, have amp meter monitoring turbine current. My calorifier only holds about 8 litres, and the plan is to tap into the coil and pump water through 8mm dia. pipes which will be bedded into channels cut into polystyrene insulation under the cabin floor. I would need a relay with an upper voltage setting, say 27volts, to switch in a 24volt 200watt immersion ellement, ( 8 amps /hour )and a lower voltage setting to switch it back off when the battery voltage drops to arround 25volts, there would also have to be a time delay to stop the relay chattering in and out. I have found exactly what is needed but only from 2 companies in the states, neither of them have answered my emails.
Hope this is not too long winded, Long dark nights out here on the island and the imagination runs riot.
Please let me have your thaughts on above

All the best

Jim

[sahona]

I would identify and tap into the "dump" signal, ie sense the voltage across the dump load resistor, or find the digital signal that causes the relay or transistor to 'pick'.
Use that signal to pick your new relay ( A 12volt one will be OK as it will be in a circuit of it's own) via a single transistor which has a significant capacitor in it's base circuit. This will pick when the dump starts and remain picked until the voltage drops (dump stops) plus the decay time of the capacitor (that will stop chatter)
The relay points can then be used to redirect the power from the dump resistor to your project circuit.
The voltage for the relay and it's transistor would be fed via a 7812, giving a stable 12v from the varying 24v supply.
The actual pick and trip voltages could be set by a potentiometer and possibly even a zener diode in the base circuit of the tranny.
Sounds like a fun project, which could be 'done and run' in the shed before the boat is ripped apart...
If you need a proper delay relay, you can get one for the interior lights of a car from most auto part stores. That's what I use in the bilge pump circuit to stop cycling.
Best of luck,

[Arranman]

Hi Bill
I undestand your theory and agree with your idea, but it would take me a month of Sundays to work out the circuit and build it. Still trying to source one from the states, hoping some good person out there might get me one.
If you are interested search VRDC on Yahoo and look for Inteccontrolls.com/pdfs/VRDC.pdf
In todays wind the turbine is dumping 2-3 Amps, not shure quite how much hot water that would supply on its own, need to what BTUs equal in Watts.
Hope all is well with you and yours
Jim

[DaveS]

If you don't want to build your own, then a manufactured voltage sensitive relay (VSR) should do the job. I have used a 12V model for a similar application: when the batteries are being charged and at a high enough voltage mine switches on the fridge and a dehumidifier. Obviously you'll need one designed for 24V. I think BEP make a 48V model, and I'm sure there's others. ASAP or Marinepower Superstore might be a good starting point.

Say 2.5A at 24V = 60W of power. In an hour that would provide 216 kJ of energy. This could raise the temperature of 1 litre of water by 51.6 degC, or 2 litres of water by 25.8 degC, etc. (neglecting losses). So, as others have hinted at, not much good if you want a bath, but useful for a few cups of coffee.

[Rowana]

Rather than using the "Spare" power to heat water, how about using it to drive a heat pump to extract the heat from the water round the boat?

Would this be a option?

Would it work?

Would it be more efficient to do it this way?

I'm no expert, but I suspect the initial cost would be quite considerable, and how long would it take to pay for itself?


Just a thought !

[Arranman]

Hi DaveS
Have had a phone call from the US Company RE the VRDC. Oh God, another senior moment, I gave them the wrong email address, should have ended .com not .co.uk.
Hope these moments don’t get any more regular, walked out of work an hour early a couple of weeks ago thinking it was stopping time, and I am not quite 60 yet.
Thanks for the watts v temperature equation, 100 watts is the smallest immersion heating that I have found for 24 volts, so that should give 60 deg.C per hour roughly, at 4 amps/hour.

Hi Rowana
Well here’s another slant, Air Conditioning. There are units that are made for 12/24 volt systems; I would presume that they would work in both directions, heating or cooling.
A 24 volt system draws 6.5 amps at 50% duty cycle but costs around £3000.00, don’t think the summers are really hot enough in Scotland to warrant that amount of outlay.
Maybe a fridge compressor using an air dumped heat exchanger would provide a bit of heat in the winter, kill two birds with one wind generator!


Life is all about the 3 Ls, Living, Learning, and Loving

[DaveS]

Thanks for the watts v temperature equation, 100 watts is the smallest immersion heating that I have found for 24 volts, so that should give 60 deg.C per hour roughly, at 4 amps/hour.

I'm not sure you've quite got this. The rating of your 100W heater is the power that it will dissipate when rated voltage, in this case 24V, is applied to it - provided that the power source is capable of supplying the necessary current, in this case 4.17A (A, note, not A/hr). A 24V 100W heater is a passive device with an (almost) constant resistance of 5.76 ohms. You have a variable power source , with a potential output dependent on wind strength. If you connect a fixed resistance of 5.76 ohms to it at a time when it is unable to generate 100W then the voltage will be dragged down accordingly, and your heater will deliver less than 100W.

Maybe your 60 degC per hour is just shorthand, but I thought I had explained (perhaps badly) that a given amount of energy can provide a given PRODUCT of temperature rise and water mass.

[Arranman]

Hi and thanks for all the useful comments.
Have had a change of plan and bought a second hand 24 volt Eberspacher heater on ebay for £170.00.
So far I am pleased with the system, it is timed to run for an hour a day and the wind generator is still keeping the batteries charged. Not quite heating for nothing, but for the small amount of diesel the heater uses it keeps the cabin dry and in the long run will be cheaper than the mains electric heating. It also switches it’s self off if the battery voltage drops to low.
So I have at least achieved part of my goal in using wind power to keep the boat warm and dry in the winter months. There are still enough winter months left before sailing starts again for me to dream up some other mad ideas.

All the best
Arranman

[Silkie]

So I have at least achieved part of my goal in using wind power to keep the boat warm and dry in the winter months.

You forgot the smiley.