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Forum Index : Solar : Simplified Solar Hot Water

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Jacob89
Newbie

Joined: 10/09/2017
Location: Australia
Posts: 7
Posted: 05:43am 09 May 2020
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Big thanks to Tony for sending me the gerber files. Got them ordered today. First time ordering PCBs and building a circuit like this, should be a good learning experience.

Couple of questions about the circuit:
a.  I might have missed it, but I don't see any provision a thermostat? I thought I could just use the original 240v thermostat to switch the 12v output from the postage stamp powersupply? Obviously the contacts aren't up to switching the full load of the element with a DC supply, but surely they can handle the tiny current supplying the controller at 12v?

b. Is there reason an IGBT couldn't be used instead of MOSFETs? From my ( very limited)understanding, an IGBT is less than ideal as it would be more lossy (ie dissipate more heat, require more heating). But I have some scavenged from old GTIs and it would be good to use them even if just for testing.
 
Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 3273
Posted: 07:04am 09 May 2020
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You are quite right about the original thermostat contacts in a hot water heater not surviving very well when switching continuous high voltage dc directly. Continuous arcing can be absolutely devastating.

Several possible ways around that, and as this is an experimental circuit, I leave that up to the user to decide on their own method of choice.

One way might be to use a commercial dc solid state relay between the solar panels and energy storage electrolytic.
Another as you suggest would be to interrupt dc power to just the control electronics.
Or power could be interrupted going to the heating element itself.

If the circuit is set up to cycle at a relatively high frequency, say 50Hz or more, arcing is not likely to be so much of an issue. The switching device will be turning alternately on and off and not be on for more than 20mS at a time anyway. Any arc that develops will be extinguished within less than 20mS, so it should be no worse than switching with normal mains ac power.

A system where the discharge part of the cycle is less than maybe 20mS should not suffer arcing, unless its overpowered with excess solar. If that is the case, there will be so much solar that the system voltage cannot fall to the low voltage threshold.
It will remain on with continuous dc power to the heating element. If the thermostat then tries to interrupt the power, instant arc welder, and catastrophe. So a great deal of caution is required. Extra panels may need to be switched out in summer for example.  Many schemes are possible.....

So I leave the arcing problem for the user to decide on the most convenient and safest approach to the problem.  

An IGBT would be the better choice for higher voltage systems, say over 100 to 150 volts, high voltage mosfets are expensive and may still have higher conduction losses.

At lower operating voltages, mosfetets with very low rdson are more readily available and would be a better choice.  
There is provision for two devices, so it should be fairly easy to find something suitable, and its not all that critical.

If the IGBTs/mosfets are getting too hot, either a larger heat sink, or better devices.
Edited 2020-05-09 17:14 by Warpspeed
Cheers, Tony.
 
MrNorm
Newbie

Joined: 09/05/2020
Location: Canada
Posts: 2
Posted: 03:47am 25 May 2020
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This is my first post.

Bin flowing this for some time. Anyone have anymore updates?

I would like to thank Warpspeed for the files to get the board printed.

Anyone seen this http://techluck.com/ ?

Norm
 
Davo99
Guru

Joined: 03/06/2019
Location: Australia
Posts: 502
Posted: 10:23am 25 May 2020
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I have had some problems getting it going.  Made a few errors in the setup myself but can't figure what is happening with it now.  I have not got back to warp to help me trouble shoot it as I was getting a bit too OCD about it and decided to give it a break. I spent days on it tearing my hair out and I know I'm going to be completely annoyed when I find the Dumb arse mistake I am making  with it.

I was looking at it again yesterday but still can't find what I am missing. I ordered a bunch of parts to build another one and a heap of them haven't turned up for the second time.

I think some got lost and I also firmly believe that some were never sent in the first place. When a Chinese fleabay seller refunds you without question, I get sus wheter the stuff was actually sent.
I'll get the opto chip and try again with what I have and see how I go from there.

I have been upgrading my Grid tie solar setup so have also been wanting to get that organised so I can set up something permanent, practical and not an eyesore with these boards.

I have just about maxxed out what the main fuseboard will take with solar so being able to power the heater direct would be a  big advantage this time of the year not the cold has set in.
 
Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 3273
Posted: 11:06pm 25 May 2020
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Sorry to hear that you are still having problems there Dave.

If you would like to mail me your circuit board, I can fix it easily enough, and if you include one of your blank boards I can assemble a spare for you as well.
Cheers, Tony.
 
Davo99
Guru

Joined: 03/06/2019
Location: Australia
Posts: 502
Posted: 03:23am 26 May 2020
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That would be great Tony.
It's hard being Dumb I tell you. I have been over everything as methodically as I can so many times and pulled all my wiring apart and started again a number of times as well. I got some new connector/ bus bars last week to use to see if that made my stuff up obvious.

Checked and rechecked my voltages and stuffed if I know where I'm missing the problem.

I'll try one more time later this week and see if I can crack it.

Has anyone else put one of these together yet?
 
Jacob89
Newbie

Joined: 10/09/2017
Location: Australia
Posts: 7
Posted: 10:41am 08 Jun 2020
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My boards have arrived from China, they look good. Just waiting on other bits and pieces now. I'm working away from home for the next month or so, hopefully when I get back everything will have arrived and I'll have a go at putting one together.

I think I will use the 240v thermostat to switch the 12v output of the postage stamp power supply for temperature control. It seems to me that if we've already set up solid state switching we might as well use it for temperature control as well.
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 3273
Posted: 11:42am 08 Jun 2020
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That sounds pretty logical, and its easy to do.
Cheers, Tony.
 
Davo99
Guru

Joined: 03/06/2019
Location: Australia
Posts: 502
Posted: 03:33am 09 Jun 2020
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  Jacob89 said  

I think I will use the 240v thermostat to switch the 12v output of the postage stamp power supply for temperature control. It seems to me that if we've already set up solid state switching we might as well use it for temperature control as well.


I'm very interested to see if the Cycling of the controller will allow things like AC thermos to switch The DC through them. If It will, this opens up a lot of other possibilities. One could use these controllers direct for things like Kettles or Heaters with thermos and other things.
 
MrNorm
Newbie

Joined: 09/05/2020
Location: Canada
Posts: 2
Posted: 04:19am 15 Jun 2020
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Got my boards, look great. Have the parts on order, could be some time before I get them.

MrNorm
Edited 2020-06-15 14:20 by MrNorm
 
bob.steel
Newbie

Joined: 27/02/2020
Location: United Kingdom
Posts: 29
Posted: 02:08am 18 Jun 2020
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Been watching this for some time . Has anybody actually got this circuit running? I am about to order the boards . Thanks Tony
Edited 2020-06-18 12:09 by bob.steel
 
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