My second burned out pump

[mas985]

I stated to them that in my water industry the pumps run cooler under added load and they had never heard that.

Perhaps the confusion is from the way you worded this statement. It is factually incorrect and should have been stated as:

"pumps run cooler under added head"

Higher head results in lower GPM and lower load which is why the motor runs cooler.

 

[jongig]

Pretty much dead-on.
These are double-make/double-break, which basically means that when the switch opens, it opens at two points instead of one. It helps prevent/extinguish arcing.
The relay on the left is essentially a pair of N.O. contacts operating together. The relay on the right appears to be a pair of N.O. contacts and a pair of N.C. contacts. Pairs are doubled up to provide twice the current capacity. NC contacts feed one speed, NO contacts feed the other. It all adds up to a DPST feeding into a SPDT. This is actually a common arrangement in industrial controls.

You mention double but only one contact from one throw being welded could provide current to the motor at both legs? I would understand if I saw the actual mechanics of the relay but in 4 post relays the posts are usually assigned to a lug and not the same lug. I would rather see a SPDT relay with the common contact being the hot and the two contacts being high/low speed to the motor. In this setup you can not have both speeds energized. We're not talking about Large Power here.

I've seen relays weld for only moments and then release, not a problem if it's doing one thing at a time.

 

[Ohm_Boy]

See: http://www.carlingtech.com/products/swi ... s_contacts
Scroll down just a bit and you'll find line drawings of single-make/break and double-make/break designs

In your case, the same mechanism which moves one set of contacts also moves the others. In most industrial control relays I've dealt with, welded contacts will seize the relay movement - it is a positive engagement device which is pretty solidly fixed to the contacts themselves. I should mention that most are also of the 'wiping' contact design, where the contact patches actually slide a bit when engaging and disengaging to help prevent sticking.

 

[JamesW]

No way is the shaft stainless, it would not look like that.

A.O Smith claims that the shaft is 303 Stainless. 303 Stainless contains some sulfur to improve machinability. 303 is slightly less corrosion resistant than 304, and less resistant than 316. However, it is good enough that the shaft should not look like that.

In the early part of this I got an idea that they would try to deny my warranty based on the results of the technician from the pool company when he measured voltage on the off leg to the pool pump.

I think that the technician measured voltage between the unpowered leg and the powered common. This will produce a voltage reading and is not indicative of a problem. The voltage should have been measured between the unpowered leg and the ground.

The solar exchanger is pool water in the shell so the shell would not be warmer than the pool water. Based on the max that I ever see in BTUs, 30,000, exchanged in the pool exchanger and a minimum of 25 gallons per minute of pool water flow the highest temperature in/out and shell would not exceed 2.4 f degrees difference.

At 15:20, the inlet temperature is 139.5 F and the outlet is at 137.1 F. Since there is only a small temperature difference, that means that there must not have been any pool water flow and the entire apparatus must have been at at least 137.1 F. The solar heat exchanger is right next to the pump motor. That would have radiated out a lot of heat to the motor.

At 14:00 there is a delta-T in the log and at 14:40 on there was no delta-T, which would mean there is no exchange meaning no pump. The automation switched off the pool exchanger at 16:00 when the temp went above 140 on the LWT side.

Why did the solar exchanger continue to operate for an hour and 20 minutes with no heat exchange? It was during this time that the pump failed. Maybe the pump lost prime and continued to run. Heat from the exchanger would slowly be transferred to the non moving water. With no water flow to help cool the impeller, the shaft would have heated up. Perhaps the fan melted due to all of the heat. The combination of factors probably contributed to the pump's failure.

According to your posts, the closed loop solar system was also responsible for overheating your system before.