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Technophiliac

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Joined: 18/12/2020
Location: New Zealand
Posts: 92

Posted: 02:04am 20 Dec 2020

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I am looking at using a oil heater (the one I have has standard 1 1/4 element thread (old mains 1.5KW element knackered.) with a 48V element - can get 3 phase 48V elements (!) so was thinking a 3 phase cable to the lounge heater (would be most efficient cable for size / weight) 3 phase rectifier installed, with dc to dc scr's to switch each element on and off, so can step a load of 500, 1000 and 1500 as dump load / heater in the winter. The first SCR can switch on with sufficient DC voltage, now contemplating how I turn on the 2nd and 3rd elements as needed by voltage criteria (e.g. volts > 49V - turn on 2nd element, volts above 50 turn on 3rd too....)
I am planning a 800W turbine (to start) and this seems a quick way to handle the power... before I arrange some sort of hybrid grid tie / buffer battery setup I figure this would be a good interim / monitoring load.
The OTT version would randomly select elements.... But a backup element is much cheaper....(!)
Posted to pass on the proposed approach, comments welcomed...

Davo, Wellington. You can have it perfect, on time, and at the best price. Choose any two.

Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 08:11pm 20 Dec 2020

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Just remember that a 1.5Kw element at 230v is only going to be a 60 watt element at 48 volts.

The voltage will only be x0.2 (48/230 = 0.2)
The current will also be x 0.2
Power falls to 0.04 (1500 x 0.04 = 60)

Cheers, �Tony.

Technophiliac

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Joined: 18/12/2020
Location: New Zealand
Posts: 92

Posted: 12:51am 21 Dec 2020

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Yes, thanks for that maths Tony, good to have my suspicions confirmed! Resistance would be 38.4 ohms, confirming your calculations and also showing at 12V the power drawn would be a mere 3.75W. We have shown a mains element can be used as a reasonably durable lowish load if needed!

I have bought a 3 phase 48V element - it has 3 x 500W elements (And jumpers to make its default format to be 1500W @ 48V) which is my planned load.

Davo, Wellington. You can have it perfect, on time, and at the best price. Choose any two.

Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 01:09am 21 Dec 2020

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Technophiliac said
I have bought a 3 phase 48V element - it has 3 x 500W elements (And jumpers to make its default format to be 1500W @ 48V) which is my planned load.

Splendid

Cheers, �Tony.

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