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Davo
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« Reply #75 on: January 18, 2012, 09:32:07 PM » |
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Using PV while sun shines....
Decided on a mechanical timer, switching on my 3 kW immersion heater, at reduced volts, from say 10 am till 2 pm.
I've bought a hefty transformer today, (1.5 kVA) to give 110 volts. (Screwfix for £60)
Gives roughly half the volts; therefore half the amps; therefore about 3000/4 = 750 watts.
(when required, would be easy to plug into 240 volts for full 3kW)
Was pondering using 1 kW immersion heater, or even choice of 1 kW and 3kW in same tank.
But went for the transformer option... avoiding the tedious changing of immersion htrs.
Eventually will have a more sophisticated controlling system.
Ben - just posted this: http://www.navitron.org.uk/forum/index.php/topic,16274.0.htmlIt maybe of some interest if you are handy with a soldering iron |
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20 x BP 190W Mono (3.8kWp), SMA Sunny Boy SB4000. SE facing.
Grantham, Lincs, UK
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Ben55
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« Reply #76 on: January 19, 2012, 08:57:16 PM » |
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Hi Davo. I've been reading your solution with amazement ! No doubt we'll all be wanting something like that.
But at the mo, I've found my immersion heater at 110 volts defies Ohm's law !!
Seriously, giving 110 volts to a 240volt immersion heater should reduce the power to about 1/4, but reduces far more.
At 240 volts it uses 3000 watts...... and at 110 volts it uses only 220 watts!! Consistently.
(no probs with transformer or wattmeter, cos a 2kw fire comes down to 500 watts.)
How does your own imm. htr. behave ?
Mine's a strange kind of resistance ! or do we re-write the whole of physics ? LOL
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« Last Edit: January 19, 2012, 09:02:41 PM by Ben55 »
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supremetwo
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« Reply #77 on: January 19, 2012, 09:25:01 PM » |
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But at the mo, I've found my immersion heater at 110 volts defies Ohm's law !! ----Mine's a strange kind of resistance ! or do we re-write the whole of physics ? LOL Temperature coefficient of resistance - http://www.allaboutcircuits.com/vol_1/chpt_12/6.htmlWork it out for Nichrome. |
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Ben55
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« Reply #78 on: January 19, 2012, 09:40:29 PM » |
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Supreme2 - I dont think it can be temperature coefficient, which is smallish;
and the measurements were taken very soon (few secs) and didn't change much after that.
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Davo
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« Reply #79 on: January 19, 2012, 11:35:03 PM » |
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Hi Davo. I've been reading your solution with amazement ! No doubt we'll all be wanting something like that.
But at the mo, I've found my immersion heater at 110 volts defies Ohm's law !!
Seriously, giving 110 volts to a 240volt immersion heater should reduce the power to about 1/4, but reduces far more.
At 240 volts it uses 3000 watts...... and at 110 volts it uses only 220 watts!! Consistently.
(no probs with transformer or wattmeter, cos a 2kw fire comes down to 500 watts.)
How does your own imm. htr. behave ?
Mine's a strange kind of resistance ! or do we re-write the whole of physics ? LOL
Very strange  Where are you measuring the power for the 110v reading ? How big is your transformer ? Mine is a 3.3kVA and consumes 1.5 amps just on the transformer losses (without a load connected). Are you sure the immersion stat is calling for heat - baffled As Scotty (of Star Trek fame) would say "Ye cannae change the laws of physics!"  |
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20 x BP 190W Mono (3.8kWp), SMA Sunny Boy SB4000. SE facing.
Grantham, Lincs, UK
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Ben55
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« Reply #80 on: January 20, 2012, 12:01:49 AM » |
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Hi Davro - Ive been checking the wiring....
and hey presto, the problem was caused by the centre-tap on transformer !! (1.5 kVA)
It was only using 55 volts, from one side to neutral.
(modification about 4 yrs ago, I diverted the immersion live wire to a timer, but not the neutral...
but now both wires need diverting to transformer, two live wires each doing 55 volts AC, opposite phase)
So physics is OK but CARE with centre-tap transformers.
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« Last Edit: January 20, 2012, 12:05:44 AM by Ben55 »
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Ben55
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« Reply #81 on: January 20, 2012, 09:01:10 AM » |
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Sorry guys !!! Rewired and now working fine. 110 volts now gives 700 watts approx. |
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« Last Edit: January 20, 2012, 09:09:00 AM by Ben55 »
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Davo
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« Reply #82 on: January 20, 2012, 09:43:59 AM » |
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Hi Davro - Ive been checking the wiring....
and hey presto, the problem was caused by the centre-tap on transformer !! (1.5 kVA)
It was only using 55 volts, from one side to neutral.
(modification about 4 yrs ago, I diverted the immersion live wire to a timer, but not the neutral...
but now both wires need diverting to transformer, two live wires each doing 55 volts AC, opposite phase)
So physics is OK but CARE with centre-tap transformers.
That's a shame - I was just off to buy one of those clever transformers that runs on BOGOF electricity. Be careful not to scold yourself when you use the hot tap now |
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20 x BP 190W Mono (3.8kWp), SMA Sunny Boy SB4000. SE facing.
Grantham, Lincs, UK
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Ben55
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« Reply #83 on: January 20, 2012, 10:05:56 AM » |
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LOL well now I have the option of 220 watts or 750 watts.
No scalding danger, the thermostat is not set high.
Anybody else getting these transformers should be aware, some have the centre-tap earthed, this got me muddled.
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Davo
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« Reply #84 on: January 20, 2012, 10:32:52 AM » |
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I thought earthing the centre tapping was standard. Limiting the risk of electric shock on building sites by keeping the voltage down to 55v (to earth).
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20 x BP 190W Mono (3.8kWp), SMA Sunny Boy SB4000. SE facing.
Grantham, Lincs, UK
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