UK storage heaters

[stag]

I have read in the past  that Hugh piggott has dumped power into storage heaters. But they are 240v. Are there some mods to make them suitable for 12v?

[dnix71]

You don't need any mods to use a lower voltage. But you are also not going to get a useful amount of heat from a 12v mill unless you just want to make coffee.

Talk to Damon here. Insulation will make you home more livable for a lot less money.

[DamonHD]

Ha, I was keeping my head down!

Potentially you could step up your 12V AC to something nearer 240VAC with a (big high-power) transformer operated in reverse, but in general note that resistance heating output is V^2/R, ie a 20-fold voltage reduction will give a 400-fold heat reduction, and you'd need huge fat power cables too.

Yes, insulation done right could reduce your demand for heat or even eliminate it.  I've knocked down our home heat demand about 2/3rds with insulation and haven't finished yet.

Pop over to another board I'm on if you'd like more info from the wise folks there: ebuild.co.uk

Rgds

Damon

[OperaHouse]

In theory a 1000-2000W 12V inverter could be used to boost up the voltage to 120V DC and you could PWM that depending on the power level with a small micro like a UNO.  I heat water with PV of about 50V DC using 2000W  120V heater elements.  These  are direct replacements, approximately 7.5 ohms and are only about $10.  Buying 12V elements seems like a good idea but it isn't, you will waste half your power just in wiring to the water heater.  A very simple problem if you have the knowledge.

[MattM]

I'm surprised with peltier plates going $20-$30 for up to 400W chips they aren't more popular for dumping some of the load.  They can push up to seventy degree temperature deltas and you could decide either heating or cooling.

[Mary B]

Peltier efficiency is horrible is why. Great if you have power to throw away on something that only uses 8% of the incoming energy for the end result.

[mab]

I do use storage heaters as dump loads - but either via the inverter or direct from the hydro (which is 120v and can run the elements at 1/4 power).

I have been thinking about making some 24v elements using some old toaster element wire - I haven't seen anyone selling 12/24v elements - to provide some high-reliability dump loads (I worry about having too many things to fail in the dump-load cct so always have a 28v dump in case the inverter shuts down for some reason).

But I was wondering how to hold it in the appropriate shape (storage heater elements are in a vaguely 'n' shaped loop and self supporting). the best thing I've thought of is to use the existing 230v element as a former and string '28v lengths' of wire across it to form a ladder, but I've still got to make some high-temp tolerant connections to all the short bits of wire... How do folks connect to resistance wire for dump loads?

[joestue]

Most water heater elements are a loop of nichrome wire encased in some kind of high temp sand.

Low voltage elements could be made in a similar way if you can cut the loop off the end, spot weld the nichrome to the inside of the tube and then cap the tube. this would divide the resistance in fourths, which gets you somewhere at least.

alternatively you can replace the coil of nichrome with a single straight rod of nichrome using the same topology.
alternatively, shake the sand out, and pull half the nichrome out, then refill with sand. yep, that's a lot of work and you'll need a pretty agressive vibrator to shake the sand back down the tube, while holding the nichrome under tension.

[Mary B]

DC water heater elements are common and not that expensive http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR2.TRC1.A0.H0.XDC+water+heater+elements&_nkw=DC+water+heater+elements&_sacat=0

[mab]

Aye, but not storage heater elements; and as storage heaters elements run dry and a lot hotter I doubt water heating ones could be substituted, alas.

[Bruce S]

Mab;
Here's a cute little diary of hat one person did back a few years ago.
http://www.fieldlines.com/index.php/topic,130307.msg848268.html#msg848268

Hope it helps!

[tanner0441]

Hi

I have taken several storage heaters apart for the heat resistance bricks. A lot of the elements are straight runs of nichrome wire running backwards and forwards, or from side to side in a small groove in the bricks. I found one that had three sealed boxes in, they had coiled elements in sand with asbestos (now a banned material) separators.

You could do the sums and cut them down for a lower voltage but you would have to crimp any connections to the ends.

As for Peltier they are designed to give a differential temperature across the junction, so if you want to get heat out you have to put heat in to the cold side, and as stated too inefficient to take seriously.

Brian

[mab]

I guess those are older storage heaters - mind are post-asbestos and the elements are enclosed tubes like grill/oven type elements.

That toaster link is interesting, thanks, and made me think about using the toaster 'cards'  whole in the storage heater though i'd like to use shorter lengths of wire for more amps at 28v - I guess I'll have to do some experiments with making nichrome connections would copper crimps work at high temp? probably not; so may have to improvise something in steel I guess...

[Mary B]

If it is a 120 volt toaster parallel 4 of them and you will have the right amperage and resistance for 28 volts

[stag]

Thanks Guys,been off line for a while. My small cottage is super insulated and heated for free, solely by a small wood burner. I use wind power to heat a  glass cabinet inside my greenhouse for winter salads and early seedlings. I thought a storage heater,painted matt black would warm it with wind and passive solar. Alternatively , I could just use the heater bricks and my existing 12v element . Thanks again.