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Author Topic: DC immersion heater.  (Read 1620 times)
offthegridandy
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« on: November 20, 2017, 06:05:26 PM »

I am planning to use AC dump loads in the future as surplus's allow and when I've grown my wind farm a little more.  I propose to use surplus to heat DHW and the buffer tank which is part of the wet UFH system. The buffer tank has a 750w DC immersion element fitted but not wired in, mainly due to the cost of cabling at the time I fitted the tank.

So  please can I

A simply use the DC immersion on AC

B fit a rectifier adjacent to the  tank and go 220V AC to 24V dc for a spur connection to the existing heater element.

C simply replace the DC jobby with a new low wattage AC element.

Thoughts appreciated.

Andy
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knighty
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« Reply #1 on: November 20, 2017, 06:16:49 PM »

what voltage is the DC element made for ?

from that we can figure out the resistance of it, and then how much current it'll draw at 240v


but... I'm pretty sure it'll have too low resistance to run at mains voltage


yeah...

if it's 750watts at 24v, that's 31amps, 0.768ohms resistance.. at 240v it would be 312amps and 75kw of heat
if it's 48v, that's 15.6amps, 3ohms resistance, 240v would give you 48amps and 18.75kw
« Last Edit: November 20, 2017, 06:20:41 PM by knighty » Logged
billi
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« Reply #2 on: November 20, 2017, 06:36:29 PM »

Andy , whats the reason you do not  utilise the DC element controlled by your outback CC ?  I thought they have quite sophisticated control relais in their charge controller

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offthegridandy
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« Reply #3 on: November 20, 2017, 08:11:21 PM »

Hi Knighty, the existing element is 24VDC 750 watts.

billi I have 3 Outbacks with an auxiliary relay.  I plan to use them to switch on/off the 240VAC immersion elements sequencelly using appropriate relays.  The tanks which have elements in are a fair distance from the power house and DC bus.  I have in stock all the gear required for AC coupling the proposed larger WT.

The reason for the question at this time is that I'm about to add on a external heat exchanger to the heat store tank which will require a drain down.  So if I'm to change the element to AC now's the time.   A new 240V element being far cheaper and easier to wire up.

Any thoughts on plan B?

Cheers.

Andy
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4.6 Kw PV array ground mounted
Outback Flexmax 80
2 X Flexmax 30 PV CC
2.5 Kw WT H Piggot design 4.5 Mtr Dia AC coupled
12 Mtr free standing Tower.
u/floor heating from oil boiler cross linked to 12 K wood stove
billi
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« Reply #4 on: November 20, 2017, 08:56:12 PM »

Hi Andi

I went the AC route as well , after  investigating in the ideal setup via Aux relais of outback and DC immersion ( too much solid state relais etc things involved  , if you want to exactly take away any surplus from batt)

So whent the AC route and  controlled via my inverter  s aux relais and voltahe set points
Billi
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camillitech
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« Reply #5 on: November 21, 2017, 11:55:43 AM »


Any thoughts on plan B?

Cheers.

Andy

Is it not very inefficient rectifying single phase to DC ?
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offthegridandy
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« Reply #6 on: November 22, 2017, 04:47:46 PM »

I've put my hand in my pocket and ordered up a 240V 1Kw new immersion heater for the tank.  Seems like the easiest way to get where I wanna be.

Thanks for your input.

Andy
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8 KVA Lister TS2 Startamatic Genny
24 Volt 1000amp battery bank
Outback VFX3024
4.6 Kw PV array ground mounted
Outback Flexmax 80
2 X Flexmax 30 PV CC
2.5 Kw WT H Piggot design 4.5 Mtr Dia AC coupled
12 Mtr free standing Tower.
u/floor heating from oil boiler cross linked to 12 K wood stove
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