looking for supplies of electric water heaters - Page 1
Forum section: electronics / general

author: Simon
author_rank: Unknown
timestamp: March 29, 2013, 11:07:22 am
content: I'm after sourcing inline water heaters. The power can be as low as 500W and the capacity should be 2.5ish litres. These need to run off the mains. any ideas anyone ? everywhere I look they make the whole on the wall unit whereas i need just the gubbins to put into my product.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 30, 2013, 02:11:25 am
content: What about a heating element and some galvanized pipe?

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: March 30, 2013, 03:30:13 am
content: How does a coffee maker do it? Stove-like element attached to the water reservoir?

author: Simon
author_rank: Unknown
timestamp: March 30, 2013, 08:47:29 am
content: Well we are looking at instant water heaters now so around 3KW, we don't particularly need to store much.Coffee machine flow rate is far too slow, this is for hand washing

author: G7PSK
author_rank: Super Contributor
timestamp: March 30, 2013, 10:26:05 am
content: Have you tried these people.http://www.redring.co.uk/

author: Things
author_rank: Regular Contributor
timestamp: March 30, 2013, 11:54:09 am
content: Have a look for a spa heater, usually designed to go inline with a pipe, and usually quite a large range of powers too.

author: SeanB
author_rank: Super Contributor
timestamp: March 30, 2013, 02:16:33 pm
content: If you use a spa heater make sure you buy the right elements for it. A standard water heater unit does fit, and will work for a very short time before failing. You need a special spa element that is designed for spa use, it is a lower energy density unit with a stainless steel or nickel element housing that is thicker and more resistant to corrosion from the flowing water, and is a little more expensive. As well when using it mae sure you firmly bond all metal pipework and fittings to a ground point, and make sure that you bond the tap as well. Use a 4mm cable minimum for all earth wiring, thicker than the supply cable at least.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 30, 2013, 02:48:23 pm
content: One trick I have heard about is to run a 240V element at 120V. It would last almost forever at that voltage. There's even a gadget out there that uses a relay to switch between 120V and 240V operation.

author: SeanB
author_rank: Super Contributor
timestamp: March 30, 2013, 02:54:41 pm
content: I pulled an element out of a water heater a year or two ago, and it had corroded through so that the water was acting as the element, and eventually arced down to nothing but a ceramic tube. The killer of them is not normally the resistive wire dying but the actual housing corroding away.

author: SeanB
author_rank: Super Contributor
timestamp: March 30, 2013, 03:23:58 pm
content: Try these.... Google for kd12dw45k kelvinator dishwasher water heater inline.

author: IanB
author_rank: Super Contributor
timestamp: March 30, 2013, 05:47:55 pm
content: Quote from: Simon on March 29, 2013, 11:07:22 amQuote from: Simon on March 30, 2013, 08:47:29 amYeah, 500 W won't do it for you.For hand washing a flow of 2.5 l/min is about right. Any lower and it will seem like a trickle.For instant in-line water heating you can estimate the power requirement from the heat capacity of water and the desired temperature.A comfortable hand washing experience requires a water temperature of about 40°C. For the sake of argument, let's suppose the incoming cold water is at indoor temperature, say about 15°C. Therefore it needs to be heated through 25 degrees.The heat capacity of water is 4.18 kJ/kg-C.With this information we can determine the power required:(Power) = (flow) * (heat capacity) * (temperature rise)Power = 2.5 l/min * 1 kg/l * 1/60 (min/s) * 4.18 (kJ/kg-C) * 25 degC = 4.35 kJ/sPower = 4.35 kWSo from this information, 3 kW is about the minimum you could get away with. You either would have to sacrifice water flow and go for a dribble, or sacrifice temperature and have only lukewarm water. A 5 kW heater would work out better.

author: Simon
author_rank: Unknown
timestamp: March 31, 2013, 08:58:23 am
content: I think our limit is 3KW. This is for use on a train so low flow rates to save the water 25ml/second I think. We were going to use a small 2.5L storage heater hopefully at 500W as we need power for a hand drier motor too but now we are looking at the issues of legionairs infection so need to either store the water at over 60C and mix on use or get it to over 60C to kill anything and then mix with cold again.We don't want complete units, just the guts as we need warranty cover on the paerts.

author: IanB
author_rank: Super Contributor
timestamp: March 31, 2013, 09:30:31 am
content: Trains won't necessarily have 240 V 50 Hz electricity so you will have to specify the required power supply before looking for heaters.The comment about "get it to over 60 C to kill anything and then mix with cold again" doesn't make sense. If the original water supply is infected before it gets to you, then the "cold water" that you mix the hot water with will simply undo any good you did by heating the hot part. In other words, if you have a sanitary cold water supply available and you heat it on demand to 40C for hand washing, you won't be introducing a legionnaires' problem. On the other hand, if you have a potentially infected water supply then you must heat all of it to the required temperature for the required time to sterilize it and then cool it down afterwards. You can't mix cold with hot to cool it down as the cold will just reintroduce the contamination.It is storing water at warm temperatures that introduces a risk. If you store the water in a tank above 60C you have your safety margin, but now you must size the tank for the expected demand. For example, a 2.5 l storage tank will last less than 2 minutes of use at 25 ml/s. If it has a 500 W heater it will take over 20 minutes to get above 60C. That gives you a 10:1 duty cycle (the tap can only be open for 10% of the time to keep up with demand). Would that be sufficient on a busy train?

author: Simon
author_rank: Unknown
timestamp: March 31, 2013, 09:34:17 am
content: the water needs to be heater to over 60C or cooled under 20C for legionares. Any mixing should be done as close to the point of use as possible to prevent the water "laying" in pipework at between 20 and 60C. Yes i guess heating on the spot to 40 is best. We have been told we have 240V available at least for the targets of this unit.

author: SeanB
author_rank: Super Contributor
timestamp: March 31, 2013, 11:39:39 am
content: If it is going on a train make it as close to unbreakable as possible. Look at the exterior and imagine it having to survive a guy with a hammer, or a set of size 14 Bovva Boots trying to kick it.As an aside, train trucks are at least 30 tons unloaded, the reason why is that they are 30 tons unloaded, and up to 300 tons loaded, and have to survive being fly shunted in a yard. Make them lighter and they bend. As well the electronics will have to survive being connected to 400VAC, probably blow a fuse or trip a breaker, and work afterwards. That, and be in a box rated to IP68, even indoors. Trains get washed inside and out with high pressure cleaners, and often with harsh detergents in them as well. Still have a drum of train seat rust remover, and it it is good at getting stains out, along with cleaning steel and derusting it. Place copper in it overnight and it goes green and corrodes. A PCB will turn into a blank board in a short time.

author: Simon
author_rank: Unknown
timestamp: March 31, 2013, 12:04:51 pm
content: We are not designing the outside, it will be mouded plastic by the customer, A mirror will be in from of our "box of tricks"

author: SeanB
author_rank: Super Contributor
timestamp: March 31, 2013, 12:32:48 pm
content: If you are going to sense water temperature get some airconditioning temperature sensing probes. They come in a small copper tube and can be clamped to a pipe with a small sleeve, along with some insulation so that you can read the pipe temperature accurately. They normally have a spec sheet giving the resistance at various temperatures, and as a bonus normally are a dual unit with an air temperature sensing probe on as well. you can also get a mounting kit for them from the suppliers as well. Simply a copper strap with holes punched in it and a nut and bolt, along with a small piece of insulating sleeve to cover it with afterwards.

author: Simon
author_rank: Unknown
timestamp: March 31, 2013, 01:39:14 pm
content: I would think we would buy a heater that had a built in thermostat that could be set.

author: marmad
author_rank: Super Contributor
timestamp: March 31, 2013, 04:42:01 pm
content: Hi Simon,I'm building a 2nd apartment in a large loft space so I was researching these relatively recently. I foundthis manufacturerthat makes a range between 2 - 9KW. I didn't use them so I can't attest to the quality, but where I live, almost all heaters are gas-powered so the pickings are slim for electric ones.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 31, 2013, 04:57:50 pm
content: Quote from: Simon on March 31, 2013, 09:34:17 amA heat exchanger is an easy solution to having to preheat above 60C. Have the circuit try to hold the heater temperature around 60C and use a bypass valve on the outlet side of the exchanger to adjust the temperature.

author: Simon
author_rank: Unknown
timestamp: April 04, 2013, 09:29:16 am
content: We are now looking at instant heating of the water. Clage in Germany seem to make some nice units.