Author Topic: Off grid water heating project  (Read 25265 times)

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Offline dochubert

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Re: Off grid water heating project
« Reply #15 on: April 04, 2020, 10:33:06 pm »
Here's a pic of my dump control for my pre-heat tank;

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Now that I look at the pic it looks pretty sloppy.  A kludge.  I need to dress things up. 
The 2 white framed meters are actually voltmeters I'm using as power indicators.  The upper one lights when the upper element is on and the lower is for the lower element.  That way I know what's going on.
The breaker under that lets me shut off the ac feed to the tank elements.  Black box on lower left converts 48vdc to 12vdc to power the dc/ac relay to its right.  Bottom right is the actual 48vdc dump control.
Its all been working very well.  (unlike my previous setup)
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Offline dochubert

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Re: Off grid water heating project
« Reply #16 on: April 28, 2020, 01:18:42 pm »

A month or so since last report.  I don't think I switched to grid for water heating even once during April.  Only twice that I remember in March.  Early March.  Now both water heaters are up to temp by late morning (unless someone uses a bunch of hot water during that time).  It easily regenerates after one daytime shower.  We're not even in full summer yet!

I'm pleased with the results so far.
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Offline solarnewbee

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Re: Off grid water heating project
« Reply #17 on: May 03, 2020, 05:23:10 am »
Well, young man, that’s just Awesome!

Keep up the most excellent work!

Take care!
SN

Any day above ground is a day for potential mishaps

Offline eidolon

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Re: Off grid water heating project
« Reply #18 on: October 30, 2020, 11:31:35 am »
Been a long time. Almost forgot this place existed.  This summer I ran my large LG washer off panels with no battery.  Nice to just start a load, close the garage door and go shopping without having to watch the generator.  I'm all about hot water.  The house has two tanks powered by just excess solar not going to batteries. I had stored a 40 gallon water heater in the garage for a couple years and finally got that working to supply hot water to the washer only.  That heater only gets excess energy not going to the other water heaters and battery.   Hoped to get it up to 75 or 80F, but this often gets over 120F and is fed into the cold water hose of the washer.  All cycles are hot.   Chart is month long record of tank temp. This board keeps the panels at power point for heating water and can divert as little as 1W to a KW automatically sensing whatever excess is available. It can track power point and has arc interrupt so existing heater control can be used in current path.  Indecently, the whole house works on a car battery and even have a dishwasher with heated dry.

 

Offline dochubert

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Re: Off grid water heating project
« Reply #19 on: January 31, 2021, 12:21:29 pm »

Eidolon, I didn't see your post until I started to post myself.  I have to say you are accomplishing some amazing results there.  You are way beyond what I can do.  Hats off.

My system seems pretty common compared to that, but its what I've got.

I just got a new 24v 15kw Upower inverter.  This one is to replace my oldest and longest working inverter.  It's still going strong but I had nothing else in 24v to back it up if (when) it finally fails.  My experiences with trying to repair the older models prompted this purchase.  Also, the older 24v is just an 8k model and won't power the water heater at 230v.  Using it at 115v works fine but it takes much longer to heat up the tank.

With this new 15kw model I should be able to run it at 230v for a faster warmup.  And my new larger Lifepo4 battery bank should handle it just fine.

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So a stainless steel case is nice.  More importantly, it has the new much simplified v10.3 control board.

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This control board can be jumper-selected for 48, 24, or 12v inverters.  A big plus for keeping backup parts!
Regardless of what voltage is used/selected, the fan connection is only for 12v fans.  This inverter, in keeping with powerjack's record of being inconsistent, has a 24v fan controlled independently from the onboard fan connection.  Go figure.
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Offline dochubert

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Re: Off grid water heating project
« Reply #20 on: January 31, 2021, 12:42:16 pm »

As is my habit with powerjack inverters, after a quick visual inspection for shipping damage (none this time!) I run it for awhile on the bench.  After that, its time to start modifying!

First, unbolted the transformer.  Experience tells me the transformer will run too hot as shipped.  So.
Cut some rubber spacers from a rubber buffing wheel (about $8 on ebay) and raised it up the 3/4" or so that gave me.  This for better transformer heat dissipation.  Later will mount a small fan on top blowing down into the middle.

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Interesting to note that with this inverter, the transformer output voltage is back to 115/230v  input is 18v instead of the 16v of my older models.  Other previous powerjacks had 260v output voltages. I personally feel better with the 230v models as seems less likely to have damaging high voltage spikes.

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Offline dochubert

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Re: Off grid water heating project
« Reply #21 on: January 31, 2021, 04:20:50 pm »

A few notables on this 24v 15kw inverter. 
First, to be clear, there's no way this will ever do anything close to 15kw.  This one is even chincier than the last one I bought.  Of course I did not expect any better but thought it ought to be said.

Stainless steel case is a nice touch but unimportant to me.  I would have been fine with painted black like before.

There is only one pair of battery terminals instead of two sets.  All things considered, probably an improvement.

The L2 lead coming out of the transformer is very small. Appears to be just one strand of 12ga.  I haven't yet peeled back the sleeve to see for certain.  230v loading may be a problem.  The center tap is at least two strands.

Fuses in parallel.  Whose bright idea was that?  It doesn't "double the rating" if that's what they think.  Actually makes the fuses useless for anything but a dead short of the load.  I use external output breakers anyway, and usually just bypass the fuses.

A new mosfet used in this model I haven't seen before.  NCE60H15a  Rated to 150a.  No idea whether good or bad.
The mosfets used in the 48v models are rated to 180a.  Lower voltage for the same Kw means higher amps, right?  I would assume a 24v model should have higher amp rated mosfets.  Am I wrong?  Between that and small wire sizes it is apparent powerjack doesn't expect this inverter to handle too much load for any length of time.
When I start pulling 4kw from a water heater I guess I'll find out.

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The last Upower inverter I got had solid heatsinks on the mainboard.  No fins.  It takes a strong fan to keep it cool.  This unit does have fins so I expect better heat transfer there.  Guess they learned something.

They are still doing screwy wiring, but not as bad as the last time.  The L1 transformer output to the control board is connected to the neutral terminal.  The neutral/center tap transformer output to the control board is connected to the L1 terminal and has the hall sensor on it (It used to be on the L1 lead).  I changed it around on my previous unit but don't care enough to mess with it on this one.  The output voltages measured at the output terminal are correct so it doesn't really make much difference, but why would they do it that way?

Last point of interest;
There is a ten switch pack on the control board.

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What are they for?  Do they need to be changed if you change the voltage jumpers?  This is something we really need some info on.  We need a switch position chart!  Oztules could probably figure them out in 5 minutes.  Wish I was half as smart.
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USA = Communist former republic
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Offline dochubert

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Re: Off grid water heating project
« Reply #22 on: February 01, 2021, 03:54:04 pm »

This morning added the small fan on top of the transformer and removed the battery charge input connections.

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While doing that noticed this very small board wired in with 5 leads and tucked into some heatshrink.  Last minute revision?  Its just two transistors and 4 resistors.  Suspect something to do with the lcd screen.


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Added a couple refinements to my preheat water heater controls. 

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Bottom left white 24hr timer lets me designate window of operation (daylight hours).  Above that is the voltage control to limit operation to proper battery voltage range.  And added small fan to keep solid state relay cool.
The two whjte voltmeters at the top indicate which element is on (mainly so I know what's going on at a glance)

With this stuff done its all pretty much automatic and ready for summer 24hr use.
We're all going to DIE!  (eventually)

USA = Communist former republic
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Offline dochubert

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Re: Off grid water heating project
« Reply #23 on: February 03, 2021, 10:04:07 pm »

Well, I put the fan on the transformer, then the cover wouldn't fit because of the lcd screen.  Ok, the fan is more important than the screen, so I reversed the hardware and mounted the lcd on the outside of the case.  A little hokey but don't care much about the lcd anyway.  This unit is intended for my water heater setup, so I hardly ever look at the lcd anyway.

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Oh, well
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Offline dochubert

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Re: Off grid water heating project
« Reply #24 on: February 12, 2021, 06:10:53 pm »

As I was setting this inverter up on its shelf, thinking I was done modifying, I remembered something.  These Upower units are all using 110v control boards. which is fine as far as it goes.  But.
If you are going to use the 220v or use the L2 leg for 110v you need to add shaping capacitors to that side.  Doesn't really matter for my water heater use, but if you look at the sine wave of the L2 leg to neutral/center tap, its very fuzzy.

Since I want to be able to use this inverter as a backup to run my house off of the 24v water heater batteries, I need to add a couple in.
A look at the control board shows the 2 large brown caps across the L1 and neutral lines.

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Powerjack used to use 475j 630v caps, 2 in parallel on their 110v boards.  All the newer 110v boards use 475j 400v caps (physically smaller). On the older 230v control boards, they used one cap across L1 and L2, which seemed to work fine. 
I have some of the 630v on hand so that's what I'll use.

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Since the L2 lead from the transformer goes directly to the output (no connection to the control board), I'll just solder a short piece of wire to the two caps in parallel and connect the wires to thr L2 and N output connector. (I thought about removing the two caps from the board and using one across L1 and L2, but that's too much work.)
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Offline dochubert

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Re: Off grid water heating project
« Reply #25 on: March 21, 2021, 01:18:54 pm »
The new inverter for the 24v bank is on the shelf next to the old one and ready to go, but...
Being lazy, and reluctant to change what's working well, I'm going to continue with the old inverter for now anyway.
If it fails I can hook up the new one in a few minutes.
I have used no grid power for water heating in more than a month.  With longer, sunnier days coming don't expect to use grid power unless we get bad weather.  Maybe we can make it all the way to next winter.
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USA = Communist former republic
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Offline dochubert

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Re: Off grid water heating project
« Reply #26 on: April 14, 2021, 11:35:50 am »
As we move into spring and summer, the 24v water heater bank is working so well I almost forget to check it.  With 6 of the byd modules, if they were new, I'd be calling it a 1200ah bank.  As is, maybe half that in reality.  Still way more than needed under normal conditions.  It's those wintertime 'normal conditions' that are at issue.  I'm hoping to add maybe 8 more solar panels to this bank's charging, all at high mounting angle for winter.  Problem is where to put them?  About every viable spot is already in use. That leaves my crappy garage roof.  I have to face removing the crappy existing sheet metal roof, sheet it with waferboard, then roof it properly.  Then I can mount some panels on it.

With my already lengthy project list, don't know if I can do it this year or not....

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Offline Pete

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Re: Off grid water heating project
« Reply #27 on: April 14, 2021, 05:41:40 pm »
Hi Doc well it sounds like you have it sorted.
Just a short note on waferboard. From what I have seen it does not stand up too well to condensation. Our carport roof was lined under the steel sheeting with MDF board, it has swelled and sagged quite a bit from moisture getting into it.
If your garage is closed in then it may be fine to use waferboard but watch the humidity and moisture.
Pete

Offline dochubert

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Re: Off grid water heating project
« Reply #28 on: April 14, 2021, 10:11:50 pm »
Thanks for the heads up, Pete.  I'm certainly no expert.  Just thought that's what everyone used.  My 'garage' is a converted carport, so not very tight and that's why it has a crappy sheetmetal roof (that leaks in heavy rain).
Any better roof will be an improvement, but don't want to waste my time and money putting in something that's going to fail soon.  What do you suggest?
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Offline Pete

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Re: Off grid water heating project
« Reply #29 on: April 15, 2021, 05:06:34 pm »
Hi Doc the most weatherproof lining for a carport or shed roof would be Cement Sheet. You could get away with tongue and groove timber boards but make sure you have a layer of foil or some other sarking over the boards. I think that the mistake the people who built the carport at my place was that they did not use foil over the top of the MDF. Then again Foil or Sarking can cause problems later down the track if rodents eat it, which they do.
So if I ever take the roof of my carport and fix it, I will be using cement sheeting with plenty of supporting battens so that it doesn't sag. Sometimes if it is just laid over the rafters and the gaps are too wide it sags a bit too so thin timber battens help prevent that.
Cheers
PEte