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Outback FM 60 Controller dump load


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12V is half 24V so will only drive half the current through the element.

 

Power is voltage times current, so half times a half is a quarter. Simples!

 

(Actually, resistance goes up with temperature, so running at lower power you'll get slightly more current - but since an immersion heater is water-cooled anyway, the difference is likely to be very small wink.png )

 

Luv,

 

Roger

 

Thanks for that. I had wondered myself why half the voltage produced a quarter of the power, but it makes sense.

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Did you connect it direct from the panels, or via the MMPT controller (assuming you have one)? And what voltage and watts do your panels put out?

I had 3 spare 100 watts panels they were 12v panels which means they are really 17v ish and I tried it via a controller which didnt work so connected them direct

 

Peter

I had 3 spare 100 watts panels they were 12v panels which means they are really 17v ish and I tried it via a controller which didnt work so connected them direct

 

Peter

It was a 12v immersion which burnt out like I say its now connected direct to the 240v one which is surviving and produces warm water this time of year

 

Peter

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I had 3 spare 100 watts panels they were 12v panels which means they are really 17v ish and I tried it via a controller which didnt work so connected them direct

 

Peter

It was a 12v immersion which burnt out like I say its now connected direct to the 240v one which is surviving and produces warm water this time of year

 

Peter

 

Similar sums - assuming they were in parallel - 17+17 = 34V roughly 3 times the 12V at which the immersion was rated ...

so 3 times the current ... so 3 x 3 = 9 times the power, no wonder it burnt out...

 

Again: simples!

 

Luv,

 

Roger

 

PS The truth isn't quite so simple, but why invoke Eintein when Newton's Law is good enough?

 

R

Edited by MyLady
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Similar sums - assuming they were in parallel - 17+17 = 34V roughly 3 times the 12V at which the immersion was rated ...

so 3 times the current ... so 3 x 3 = 9 times the power, no wonder it burnt out...

 

Again: simples!

 

Luv,

 

Roger

 

PS The truth isn't quite so simple, but why invoke Eintein when Newton's Law is good enough?

 

R

Wrong, three in parallel is still only 17 volts

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Wrong, three in parallel is still only 17 volts

 

You're right, DC. (Pun intentional wink.png)

 

1. I'd forgotten the three panels.

2. I'd visualised: 'in series', but typed: 'in parallel'.

 

To correct the sums:

 

Three at 17V, in series, gives 51V, 4.25 x 12V ... 4.25 x 4.25 would give just over 18 times the design power.

Three in parallel, give 17V, 17/12 x 12V ... 17/12 x 17/12 = 289/144, still just over double the design power - and still enough to fry the element.

 

Still simples, but I've proved I'm old, going simples myself, and getting worserer...

 

blush.png To own up to my complete mental degeneration, when my panels arrived, I was daft enough to connect one of them to a 10W LED, but it couldn't drive the load properly - my meter read 35V open circuit but much less than 12V when connected directly - the LED only glowed faintly! For maximum power transfer, one must match internal and external impedance - and I didn't, fortunately! Amongst other things, that's what controllers are for.

 

Luv,

 

Roger

 

(After a couple of hours sleeping off the brandy...)

Edited by MyLady
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  • 3 weeks later...

Hi Robbo

 

Fortunately I didn't fancy the AC route, it just didn't sit right with me. I'm trying to source a 12v element from China, I think I've secured a free sample element from a manufacturer just £17 postage. It has a 2.25" BSP And I think you can wire different wattages depending on how many you connect together.

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  • 5 weeks later...

Did this ever get wired up and working was interested to see how it worked and which was the best route

 

The original poster is no longer a member of this forum, so we're unlikely to find out unfortunately!

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