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Forum Index : Solar : Simplified Solar Hot Water
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| Jacob89 Newbie  Joined: 10/09/2017 Location: AustraliaPosts: 39 |
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. |
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| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
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. |
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| MrNorm Newbie Joined: 09/05/2020 Location: CanadaPosts: 2 |
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 |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
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. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
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. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
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? |
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| Jacob89 Newbie Joined: 10/09/2017 Location: AustraliaPosts: 39 |
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. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
That sounds pretty logical, and its easy to do. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
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. |
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| MrNorm Newbie Joined: 09/05/2020 Location: CanadaPosts: 2 |
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 |
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| bob.steel Senior Member  Joined: 27/02/2020 Location: AustraliaPosts: 188 |
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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| Jacob89 Newbie Joined: 10/09/2017 Location: AustraliaPosts: 39 |
I finally got enough bits today to put together a couple of units but no luck getting them to run properly. I was just using a 2kw kettle for a test element and a string of 8 250w panels. 14 470uf capacitors salvaged from an old grid tie inverter. I didn't have any 1 w carbon film resistors anywhere near the right rating so I put some 1/4 watt metal film in series to get the values for setting the high and low voltage trip points. I used FDA50N50 mosfets, and also tried some salvaged APT50GN60BG IGBTs. The IGBTs seemed to just be hard on. A few strange things happened: 1. Does the TVS diode need to be bi directional, unidirectional, or does it matter either way? I seem to have ended up with unidirectional ones. They don't have any polarity markings on them. On one of my units I burnt up two of them, they seemed to just start conducting and the element was powered through them until they let the smoke out. I ended up taking them out of the circuit to continue testing. 2. Couldn't seem to get either unit to do any switching, except by accident. The capacitor bank would charge up to the maximum array voltage (270v) and stay there. Measuring voltages at different points on the board, I accidentally found that when I put my multimeter between the Solar + terminal and the midpoint of the high voltage trip point voltage divider it would start switching the mosfets and powering the elements. I don't think it was switching as intended though, although it was difficult to tell exactly what was going on. Has anyone else gotten one of these working? I'm a bit out of my depth with fault finding on this sort of thing. Edit: You'll notice I'm using two different 3182 driver chips. The black ones came from aliexpress and the white ones are more expensive ones from Mouser. I had better luck with the black ones though so far.  Edited 2020-08-03 16:42 by Jacob89 |
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| Jacob89 Newbie Joined: 10/09/2017 Location: AustraliaPosts: 39 |
Did you ever have any luck with yours Davo? |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I sort of gave up on mine through Frustration of being too ignorant to trouble shoot it. I'm a bit OCD when I can't get things to work and when I was dreaming of it every night, I had to take a step back! :0( I did have similar experience to you though with not being able to get it to switch. Maybe mine burnt out something as well but I didn't see any smoke but then again I built it into an old solar inverter cabinet before I powered it up. I made a couple of mistakes with the limiting resistor set up Tony put me straight on and In doing that I think I may have cocked something else up as well. Tried my hardest to check and double check everything but..... done that before to discover what I was sure was right was arse about completely. I am sure I have done something wrong at some stage and Tony Kindly offered to have a look at it for me if I send it back to him which I am going to do soon as I line someone up to take it to him with some other things. All a bit hard with the China flu Biz atm. I ordered some components back in about March and some came last week! The little caps. TBH I don't know what the hell I have and don't atm because some never arrived like the driver chips which I'm thinking I might have Lunched. At first I was getting things quick but now things are so all over the place and have shot up in price so much I have given all my electronic endeavours away for the time being because by the time stuff arrives, I can't remember what I wanted them for anyway. :0( I'm convinced the problem is something basic and stupid I have done and Tony will figure it out in a bout 2 sec flat. I'm sure he will be able to run someone more knowledgeable like yourself through the trouble shooting and you should be able to get it going. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The transient voltage suppressors come in two different styles, and both will work in this circuit. I just went out to the shed and grabbed one of each type.  The first is a 1.5KE 300, and its a 300 volt ac type that works exactly the same in both directions. Yours appear to be like this, so it can go onto the board either way around. The second example is a 1.5KE 150A. This has both the A suffix, and a clearly marked polarity band indicating its the dc type. This type MUST be installed the right way around with the band as shown on the circuit board. It would clamp at anything above 150 volts in the forward direction, and act as an ordinary diode in the reverse direction. If the dc type is connected the wrong way around, its like placing a conducting diode right across your solar panels, and the several amps of short circuit current that would flow, would quickly burn it up. Quarter watt resistors will work perfectly well for initial testing, but if they get wet or dirty over time, may cause long term reliability problems simply because they are so small and can suffer from electrical leakage, or even break down over time fairly readily. Now the mosfets should turn on at the upper voltage threshold, and cause the load to pull the voltage across the electrolytic down to the low voltage threshold, where the mosfets are supposed to then turn off. Several things can go wrong with this if the voltage thresholds are inappropriate, or if the load is insufficient, or solar is excessive compared to the load (same thing really). The solar panels must be able to charge the capacitor right up to the upper voltage threshold. That may not happen if either the threshold is set way too high, or its a grey day and there is just insufficient solar, as in twilight conditions. Once the mosfet turns on, the load should pull the capacitor voltage down in voltage to the low voltage threshold. That can go wrong too. If the voltage threshold is set way too low, or there is insufficient load, the voltage may not fall low enough to switch the mosfet off. So the load just locks on continuously. If it goes up to 270v and stays there, set the upper trip point lower. Try a 220K or 180k resistor for the upper trip point. Anything higher than about 270k is just not going to turn on the mosfet. Cheers, Tony. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Dave, pack it up and mail it back to me. Chances are pretty good something has died on the board. There is not that much there to fix, so its going to be pretty easy to locate the problem. I don't have any spare boards here, I ordered only five and sent you the lot. Cheers, Tony. |
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| Jacob89 Newbie Joined: 10/09/2017 Location: AustraliaPosts: 39 |
The TVS I have is a 1.5KE400CA. I don't know what the C indicates but the A would still indicate its the DC type? Odd though, considering there is no polarity band. I've put together a third unit tonight and will test it tomorrow. I've set the upper threshold at 220k (first two were 260k and 270k) and dropped the lower one to 170k (from 200k). I'll try a higher wattage element as well. Is it an issue if it there is too much solar/not enough load when there is full sun? As long as it switches on in the first place I don't mind if it stays hard on, as long as the lower threshold is high enough that its still producing useful heating. There was some other weird stuff happening as well that I forgot to mention earlier. At one point I was measuring about 30amps going into the element, but at very low voltage, about 14v. And switching at some ridiculously high rate, 400khz or something like that. It must have been my cheap clamp meter giving erroneous readings, there's no way a 28 ohm element could draw that much current at only 14v. |
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| Jacob89 Newbie Joined: 10/09/2017 Location: AustraliaPosts: 39 |
I can relate to that. I get all enthusiastic about a project but by the time all the bits turn up my enthusiasm has found something else to latch onto. |
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| BenandAmber Guru Joined: 16/02/2019 Location: United StatesPosts: 961 |
I am thinking about trying this circuit I also have enough Square transfomers to build a warpspeed inverter Can I use both Square and toroid on the same inverter I will most likely want it to be 120 volt only I also am trying to get a external 48 volt voltage regulator designed It need to work just like a regular car truck van alternator work just higher I need a cad file so I can order pcbs I think bigmik might do it I apritiate you warpspeed you are amazing!!! be warned i am good parrot but Dumber than a box of rocks |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I Googled "1.5KE400CA data sheet" https://www.alldatasheet.com/datasheet-pdf/pdf/222963/HY/1.5KE400CA.html At the top left of the data sheet, under "mechanical" it says: There are two versions, 1.5KE400C which is the bi directional ac type, and 1.5KE400CA which is the unidirectional dc type (and should? have the band). Try a 220K for the upper set point resistor. Try 100K for the lower set point resistor. That should get it to switch on and off. Once you have that, experiment with the set points so they are either side of the actual maximum power voltage. Cheers, Tony. |
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