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Old 03-19-16, 07:51 PM   #391
jeff5may
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Quote:
Originally Posted by Xringer View Post
Since I have a dry contact from the controller (closed with calling for heat, open when the tank is hot enough),
I could use it to switch +12V into the Rin..

When the contact opens, Rgs would pull the gate down to Zero volts...

I'll check out the specs on the FETs to see what resistors will be needed to
develop the gate voltage needed for full turn-on..

The PV panel array can't deliver any more than 8Amps. It impossible for
PV to exceed it's amperage rating, since it's limited by sun light.

Only when you get certain solar-cloud-effects, will you get more power..
And that will be on the order of 2 to 20% more..
It would take a supernova to get much more than 20%..

I can short out the PV inside the house and never blow the 10A fuse on the array..
Which is why it's a waste of time to put fuses on solar panels..



Not sure why those DC SSRs suck so bad. I think it might be the DC signal source I'm using. Spikes maybe..

I'll have to think about a way to pull down the DC signal level quickly in case of a grid failure.
Don't want the gate voltage to drift down slowly, after the power supply input dies.. Need to load it down..
I figure the (AC powered) controller contact will fall out fast enough to prevent much over-heating of the SSR, if the AC failed..
I ẃould definitely rig up some kind of gate driver circuit to the mosfet. Since you have experience with vacuum tubes, you know how sensitive the grids are to interference and oscillation if you don't tie them down. Mosfets are the same way. Where a tube will redplate or arc if it's not happy, a mosfet will just die. They are not forgiving at all. All it takes is a couple of milliseconds of something nasty to ruin a mosfet.

Relays will have some "bounce" in the contacts when they open or close, which could cause the mosfet to leave saturation. At 100VDC, driving a 13 ohm load, the mosfet would only survive a fraction of a second if it rose above a couple of ohms above its minimum resistance. Even on a big heat sink. A schmitt trigger or pulse stretcher are a few ideas that come to mind. Anything that makes sure the fet gets a nice discrete transition when changing states should make it last a long time.

You definitely have something strange going on there. The IRF250 transistors you are using are heavier than what I would have started out with. They are pretty tough as far as power mosfets go. The only circuits I have seen these die in, they have been driving big flyback transformers. They throw lightning for a while before the mosfet finally dies.

Another product I should mention for pipe joints is this stuff:

I originally used this stuff in the Navy on joints that had to be watertight but easily separated for maintenance. Naturally, they had jars and buckets of the stuff, and it wasn't blue, but gray. Since then, I have used it on more surfaces than I can remember. It is a lot like the nylog sealant used on flare joints, made specifically for sealing machined surfaces, and for holding o-rings and gaskets in place during assembly. On threaded fittings, it works in places where pipe dope or thread tape leaks. OEM's like Jaguar, Harley Davidson, NASCAR, and Rolls Royce use it all the time.

Like I have said before, I don't trust teflon thread tape. On pneumatic fittings, I will use it if nothing else is on hand. For anything hydraulic, I would rather run to the store.


Last edited by jeff5may; 03-20-16 at 11:07 AM.. Reason: spelling
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Old 03-20-16, 06:34 AM   #392
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From that picture it looks to me that too much teflon tape was used. That may have kept you from threading the fitting on far enough to get a good connection. you only need 2 to 3 wraps of tape.
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Old 03-20-16, 08:28 AM   #393
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Quote:
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From that picture it looks to me that too much teflon tape was used. That may have kept you from threading the fitting on far enough to get a good connection. you only need 2 to 3 wraps of tape.
That picture (above) showing the top of nipple does look like it has at least 3 turns.
But, it's the bottom of the nipple, where it screws into the tank, that's leaking badly now..

After drying it up, then re-pressurizing it, I could see nothing on the top,
but the cup around the bottom started to fill with water.. In less than an hour.
Looking at the bottom picture,(above) it seems like I may not have used enough tape.?

When I replace the nipple this time, I won't be using any tape..

What happened with the 2-piece Pex-to-iron adapter, seems like un-screwing.
I'm pretty sure vibration from the ASHP is being transmitted into that nipple.
The Hot side nipple isn't clamped with a U-bolt.. No problem there.

So, after the brass is installed, I'm going to try to isolate the brass from the clamp.
Rubber wrap around the brass and a loose U-bolt might do the trick.?.

Or, maybe not. I think there might be a design problem with the A7.
The over-hang might be pulling up (with the U-bolt) with considerable force.
The cantilever effect plus the vibration works on that cold water nipple. (bottom pic).
Those two rubber feet that sit on the tank-lid have very hard rubber. Like rock.
Note: Those little rubber buttons on the rails, help installation they aren't part of any shock absorbing scheme.

Maybe there is a way to take some of the up-loading off that nipple..
Like supporting the A7 in the front maybe?



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Old 03-20-16, 12:36 PM   #394
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Wow, this is the first time Amazon came by here on Sunday!
We were coming back from HF and we saw a big Ford van go by..
I asked my wife what kind of van that was, she said Amazon!
I started thinking.. 'humm, it was coming from our side of town, maybe?'...
Sure nuff, the package was between the doors..

The quality of the pipe looks excellent.. Might have to get on that job today.
I've been thinking about the 'cantilever' problem..

Testing the ($13.99) security thing that I got from HF now.. Seems to be working okay.
Wireless Driveway Alert & Driveway Alarm System

It's replacing an older unit inside the garage. The transmitter on the old one didn't have much range.. This cheap one works great.
I have the Rx on a 6vdc PSU and will put the Tx on a 9V PSU after the IM test is over.
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Old 03-21-16, 03:51 AM   #395
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Another thing to consider is water heaters usually have a sacrificial anode on the cold side supply line that needs to be changed every 2 to 5 years. Yours may be about used up.
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Old 03-21-16, 09:36 AM   #396
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Quote:
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Another thing to consider is water heaters usually have a sacrificial anode on the cold side supply line that needs to be changed every 2 to 5 years. Yours may be about used up.
I've been thinking about that anode. I had it out during install..
http://ecorenovator.org/forum/23071-post56.html

Since the top is flat, that means it's aluminum. (A bump on top = magnesium).

Because of the location of the A7, I'm not sure I have the clearance to unscrew it, or get it out, once I got it loose..
Maybe I'll wait until I get the leaking stopped. I do want to make sure it's good,
since I don't want my heating elements causing voltage in the water..

The one thing I do not like about this anode thing, is the idea of dissolving aluminum
into the water we are drinking and cooking with..
We got rid of those aluminum pots for a reason, right?
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Old 03-21-16, 01:53 PM   #397
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They got ride of the aluminum pots because they stuck like mad, or nowadays some get ride of them because they are coated in teflon

You can always get one of the Marathon water heaters
Because they are curved a bit, I support my A7 bracket from the rafters from above. The u bolts are on as just a back up in case I crash into the thing or something.

The marathon also has a inlet relief valve built into the coldwater nipple which makes a tight u bolt fitting difficult.

Here is the hylomar info
Hylomar Sealant
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Old 03-21-16, 06:03 PM   #398
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I've been meaning to buy a basement Jack to put under my deck.
The spot were I set up my telescope needs to be stiffened up.
Anyways, picked up the jack at HD, and stuck it under the A7, front and center.
Seems pretty good so far. Now the weight on the hard rubber feet isn't so much.
If I run into it, I'll just put it back in place. Just want to take the load off the brass nipple.

No leaks so far.. I'll keep watching it for a few weeks.. Maybe install some removable insulation.
I put the u-bolt forks on the grinder, to open them up.
Added some rubber to absorb vibration and protect the brass from abrasion.

That old nipple was loaded with brown gunk.. A reminder not to drink hot water!

The city must have been feeding Martian soil into the water supply this year.
Three times in the last few months, it was running reddish brown..

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Old 03-22-16, 08:48 AM   #399
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Yesterday, I removed the Dip Tube and cleaned it. I also cleaned the threads of the cold 3/4" input.
I noticed there weren't a lot of threads for the nipple to engage.
The coldwater input dead-ended with the plastic top of the Dip Tube..
Careful: You can't bottom out the nipple, without crushing the plastic flange of the Dip Tube.

There was leftover OEM sealant paste and very tiny bits of thin white Teflon tape in the threads.
The tape has been turned into paste.?.
It looked like the Teflon had been shredded into thin little 2-3 mm strips.
(Back when I installed this 6" Iron nipple, I used 3 turns (or more) of Teflon tape, because of the size of the threads).
I wonder if this destruction was caused by vibration? And because there is not much thread engagement?

This morning, I took a picture of the old iron nipple. (3/4x6 inch).
It seems like there was only 3 or 4 threads doing the sealing work.
Not much Teflon tape visible. Looking at all the rust or staining, Slow leaking had been going on for some time.
It just suddenly started leaking a lot faster the other day..

The design of the 3/4" ports, seems much too shallow. More threads are needed.
I would not recommend this model of hotwater tank for this type of application (ASHP on top).


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Old 05-10-19, 05:50 PM   #400
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The flood alarm went off this afternoon..
The tank top cover was wet. About 12oz in the catch pan set off the alarm..

I turned on the tank bypass (and the oil burner) and now I'm drying up the top,
and plan to turn it back on later to see if I can spot the leak..

The over-pressure valve port stayed dry, so It's either the hot, cold or anode.

I attempted to drain some water, but the drain valve isn't working very well.
It might be plugged up with sediment/dregs. When I turn the pressure back on, the drain will likely work a lot better..

I'm 73 years old now.. That might be too old to be dragging that tank up out of the basement, for the junkman..

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