48v 1000 Watt Heating Element with Adjustable Thermostat

[TomW]

Tom, yes you're right, that's the main problem but I've never seen a safe switch for that specific use. I wonder if using Float on Aux1 (on/off switch) wouldn't be a better option for DC direct use fom batteries to supply a full steady 1500W on a voltage range. I'm not sure that Aux1 Float would worth the cost of an efficient WH/elements/SSR when only 2 or 3 hours on float are available.
Maybe waste not on Aux1 ? I'm afraid to overcharge battery with it.
Erik

Erik;

OK, maybe I am crazy here but perhaps there is a way to use the standard limit switch to drive a low voltage pilot relay that disconnects the element if the temp hits the limit?

Probably not the best way but a pilot relay can likely be had for most voltages and certainly for 12 or 24 volt?

I am just tossing ideas as they pop in to my feeble mind so take with a grain of salt.

Tom

[SolarMusher]

Tom, you're too fast to me.
I was still adding content to my previous post  .

[dgd]

Hi Erik,
SSRs or Solid State Relays like the Crydom we are considering don't have contacts that can arc and weld together like a mechanical relay. They use a FET for switching and I have not heard of one failing when used within its current and voltage specs.
Aux2 PWM signalling is ideal to use with a DC  SSR as it gradually introduces/removes the load
The classic manual has a nice explanation of how this works.
I used a Schottky diode I had in spares box, I remember it was rated about 300v so anything you find on ebay rated a few hundred volts should be ok. Jp's suggestion is good.

Dgd

[TomW]

Hi Erik,
SSRs or Solid State Relays like the Crydom we are considering don't have contacts that can arc and weld together like a mechanical relay. They use a FET for switching and I have not heard of one failing when used within its current and voltage specs.
Dgd

Dgd;

I think the main concern is for the limit switch[es] on the water heater?

That is what I was addressing WRT welded contacts and arcing.

Just FYI.

Tom

[SolarMusher]

Tom, are you talking about the thermostat? if so, there are cheap 48Vdc units that could be used.
Erik

[SolarMusher]

Hi Erik,
SSRs or Solid State Relays like the Crydom we are considering don't have contacts that can arc and weld together like a mechanical relay. They use a FET for switching and I have not heard of one failing when used within its current and voltage specs.
Aux2 PWM signalling is ideal to use with a DC  SSR as it gradually introduces/removes the load
The classic manual has a nice explanation of how this works.
I used a Schottky diode I had in spares box, I remember it was rated about 300v so anything you find on ebay rated a few hundred volts should be ok. Jp's suggestion is good.

Dgd

David,
Does this diode connect directly output 1 to 2 on the crydom relay?
Erik

[TomW]

Tom, are you talking about the thermostat? if so, there are cheap 48Vdc units that could be used.
Erik

Erik;

Yes. Or the high limit switch many water heaters used to have.

Personally, I wouldn't use DC for several reasons including the issues that can arise WRT cable sizing and proper switches.

There are usually many ways to accomplish the same ends. I use AC to dump power to a water heater with Aux1 as the switch to activate a relay on the AC OUT that feeds the heater. My hot water is pretty minimal with 2 10 gallon units plumbed in series and I dump power into the first one when I have excess production. It heats 10 gallons up in about 40 to 60 minutes with a 120 VAC 1600? watt element.  The second or main heater is connected to the grid to keep some hot water on hand all the time. I think of the #1 as a preheater. Just how I do it.

I know relays are old school but I have them on hand and these are 2 pole with NO and NC connections so act like a transfer switch for my water heater load.

Just rambling now and likely no help.

Tom

[SolarMusher]

Tom, what does your Classic look like when it hits absorb and then begins to divert a full steady 1600W?
Does it revert on bulk for a long time before reaching anew absorb and is overcharging a problem for you in this case?
Also does the Outback suffer from flickering on Aux1 or is it only a Aux2 PWM issue when triggering on Outback/Magnum?
Erik

[dgd]

For temperature control I used this device
http://www.jaycar.co.nz/productView.asp?ID=ST3821&form=CAT2&SUBCATID=969#1
I placed it near top of 180 litre hot water cyclinder  on copper at top outlet pipe.
Its wired into the cable that connects the AUX2 to the Crydom SSR.  When the temp gets high enough it open circuits, disables  the SSR
so no power to the heating element.  Works good and no high current switching involved.

dgd

[jp_le_gros]

But why  don't just control the SSR directly by the thermostat?
JP

[jp_le_gros]

What i realy mean is why not use a similar set-up that dgd use, but instaed of the thermostatic switch he use, take the WH thermostat ?
JP   

[dgd]

..because I use elements that do not have inbuilt thermostats.

Dgd

[jp_le_gros]

Hi dgd, i was talking about the Erik case, your set-up is perfect.
JP

[dgd]

Hi dgd, i was talking about the Erik case, your set-up is perfect.
JP

..sorry, I was too quick replying. Then realised what you referred to.
I think Erik has two 3kw elements that probably have inbuilt thermostats so just depending on those should be ok. My setup was built from scratch so I ordered plain $15 elements from eBay and added the temp control as an afterthought.  It also appealed to me to switch the control line to the SSR rather than trying to switch the full load current to the element.

Dgd

[jp_le_gros]

realy a good choice, it's a lot easier and cheaper to make the control of a circuit on the low power side.
JP