Imaginative Regulator Dump load? 240v immersion?

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gregcope

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HI all,

Any imaginative bump loads from anyone?

From the manufactures tech support;

"Resistant load like a bulb. Do not connect motors or loads with high inrush currents."

So this excludes fridge compressors, unless I get the LOAD to activate a relay to power up the fridge compressor off the battery.

I doubt the dump load will come on when we are on board as the fridge is usually on! But it may during sunny weeks when the panels might have caught up with the weekend usage. Boat is used at weekends, and lives on a Swinging mooring.

Question: Can a 240V Immersion heater run on 12V? As it would be good to get some heat as a dump LOAD.

Any other imaginative ideas? A bulb, although simple, cheap and a good sign it is working, is quite boring.
 
I don't know if it's relevant, but light bulbs draw the largest current (many, many times greater than normal operating current) when the filament is cold, ie at switch on.
 
gregcope said:
Question: Can a 240V Immersion heater run on 12V? As it would be good to get some heat as a dump LOAD.

.
Click to expand...

The power dissipated in watts is = V2/R, where V=volts and R = resistance in ohms

So if the element is run on 12 volts instead of 240 volts because 12 is 1/20 th of 240 the power produced will be {1/20)2 ie 1/400 th of the power at 240 volts

So a 1000watt element will produce 1000/400 = 2.5 watts ! Not a lot of heat!
 
elton said:
I don't know if it's relevant, but light bulbs draw the largest current (many, many times greater than normal operating current) when the filament is cold, ie at switch on.
Click to expand...

VicS said:
The power dissipated in watts is = V2/R, where V=volts and R = resistance in ohms

So if the element is run on 12 volts instead of 240 volts because 12 is 1/20 th of 240 the power produced will be {1/20)2 ie 1/400 th of the power at 240 volts

So a 1000watt element will produce 1000/400 = 2.5 watts ! Not a lot of heat!
Click to expand...

Combining these points, the heating element will also be non-linear for thermal reasons, so with 12V across it may well have half the resistance it shows at 240V and soak up a whole mighty 5W.
 
JumbleDuck said:
Combining these points, the heating element will also be non-linear for thermal reasons, so with 12V across it may well have half the resistance it shows at 240V and soak up a whole mighty 5W.
Click to expand...


It might but since you raised the issue perhaps you would like to investigate and give us a more precise figure.

I was wondering who would be the first to nit pick.
 
Not nit-picking. 24V immersion elements are available as are wire-wound resistors to act as dump-loads.
Check wind-generator suppliers.
 
VicS said:
It might but since you raised the issue perhaps you would like to investigate and give us a more precise figure.

I was wondering who would be the first to nit pick.
Click to expand...

Sorry - I wasn't meaning to nit pick, just combine two good points. I would expect 5V to be about rightish, on the basis that (a) your calculation was spot on and (b) the element probably runs at about 250C, which is twice the absolute temperature (ish) and therefore twice the resistance (ish).
 
gregcope said:
Thanks AntarcticPilot. One issuette is that my clarifier already has an immersion fitted - the 240v one!
Click to expand...

Can you fit a second one? Other contributions make me suspect that putting 12v through a 240V immersion heater a) isn't going to generate much heat and b) would make for interesting problems isolating the 12v and 240v wiring! On the former point, my own calculation (not taking into account heat related resistance changes) is that the heat generated is proportional to the square of the voltage, so a 1kW 240V element driven at 12V will absorb about 2.5 watts.
 
JumbleDuck said:
I would expect 5V to be about rightish, on the basis that (a) your calculation was spot on and (b) the element probably runs at about 250C, which is twice the absolute temperature (ish) and therefore twice the resistance (ish).
Click to expand...

I am surprised the difference is that great. is the logic correct?

I am looking at figures for the resistivity of Nichrome, what I though was likely alloy for a heating element, of 107.3 at 273.2K and 110.0 at 573.2K, an increase of only 2.7 ( or 2.45%) in 300°

( data from Kaye and Laby, 14th edition)
 
VicS said:
I am surprised the difference is that great. is the logic correct?

I am looking at figures for the resistivity of Nichrome, what I though was likely alloy for a heating element, of 107.3 at 273.2K and 110.0 at 573.2K, an increase of only 2.7 ( or 2.45%) in 300°

( data from Kaye and Laby, 14th edition)
Click to expand...

Ooh, you could well be right. I was thinking of pure metals, which are pretty linear. Alloys are different. Also my research was in a world where 77K was hot ...

2.5W or maybe a shade more it is.
 
Late 60's british bikes with permanent magnet alternators used big zeners as dump regulators.
AFAIK these are quite expensive but can be emulated with a few parts and a big transistor on a heat sink.
Modern bikes with permanent magent alts tend to have series regulators. These regulate the output volts, but the volts on the coils are allowed to rise signifcantly. Available at reasonable cost though.

One thought is to use an inverter to drive the immersion heater, if the inverter was the sort that shuts down when the battery volts drop too far, you might have the beginning of a system?
Probably a 'cruel and unusual' use of the inverter which would swiftly destroy it. the whole thing would have a tendency to short-cycle or oscillate.
 
VicS said:
It might but since you raised the issue perhaps you would like to investigate and give us a more precise figure.

I was wondering who would be the first to nit pick.
Click to expand...
Did I see Jim Full Circle say JD was Ubergeekian in disguise? If so that would explain it!
St
 
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VicS said:
I am surprised the difference is that great. is the logic correct?

I am looking at figures for the resistivity of Nichrome, what I though was likely alloy for a heating element, of 107.3 at 273.2K and 110.0 at 573.2K, an increase of only 2.7 ( or 2.45%) in 300°

( data from Kaye and Laby, 14th edition)
Click to expand...
Given that the ambient temp out here in Portugal is still 22 deg and that my solar panels at anchor keep the batteries topped up and at midday are dumping, what are the thoughts on constructing a "day" water tank of say 10 ltrs, with an element, home made? in to give a nice warm shower at the end if the day? Those useless black pvc bags are exactly that!
S
Thinking on as I sit here, 500 watt element, Ive got 4 by 110 amp hr batteries, 40 amps for 1 hr, ambient mid 20s, how much heat would half a battery give me?
 
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skipper_stu said:
Given that the ambient temp out here in Portugal is still 22 deg and that my solar panels at anchor keep the batteries topped up and at midday are dumping, what are the thoughts on constructing a "day" water tank of say 10 ltrs, with an element, home made? in to give a nice warm shower at the end if the day? Those useless black pvc bags are exactly that!
S
Thinking on as I sit here, 500 watt element, Ive got 4 by 110 amp hr batteries, 40 amps for 1 hr, ambient mid 20s, how much heat would half a battery give me?
Click to expand...

It takes 4200 Joules of energy to raise the temperature of 1 litre of water by 1 degree C.

Half a battery would give you 55 Amps for an hour, or 3600 seconds

55 A for 3600 seconds is 198000 joules

198000/4200 gives you a temperature rise of 47 degrees Centigrade for 1 litre of water.

So if you took 10 litres of water at 20C and heated it with 55A for an hour, it would be heated to 24.7C.

Heating water is expensive!
 
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