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240VAC 1/2HP Water Pump - Contactor doing a double-take on start

ccpeabody

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Jun 12, 2022
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Looking for some practical advice on my water supply system at our off grid cabin.

Set-Up:

240 VAC, 1/2 HP Deep Well pump sitting on a saddle about 50' out from the cabin and sitting on the bottom of the lake. The pump has a contactor box mounted on the wall inside the cabin. When the pump cuts in, one can hear the contactor (Start Relay) click on. Pump intake screen is clean.

Power:

Cabin is powered by two LV6548 HF Inverters wired in parallel to provide 120/240VAC. Battery bank is comprised of 5, SOK 100ah (SK48V100) batteries.

Issue:

About 80% of the time, when the pump kicks in, the pump contactor snaps on, then off, then on again and remains on until the pump reaches the cut-out pressure. If you didn't hear the contactor doing a double click, one would never know there was a problem with the system.

My questions is this...

Has anyone else run into this problem? As each inverter is rated for 6500W and the pump is only 1/2HP, I can't imagine the inrush current at start being too large for the LV5648's. I realize that LF inverters are better at starting inductive than the HF LV6548 but I have to think that I've oversized the HF inverters enough to easily handle the load.

My thinking is that if no one else has experienced this issue, I may have a bad contactor and will need to replace it or clean it. Just trying to gather information on my way to diagnosing the problem and coming up with a solution.

Thank you in advance for all that take the time to reply.
 
Get a voltage reading at the contactor at startup.
It's possible that the surge is dropping the voltage enough to release the contactor for a split second.
 
Any reason why you have a pump way out in the lake? How far up are you pumping water? Less that 20-30f no?

A simple jet pump near the pressure tank will keep the run short so any voltage drop would be minimized. Least that’s how my parents camp is set up. Sure it takes a little to prime it each season but it’s darn reliable as you can service anything without getting wet.
 
Over 50 years of making mistakes have lead to our current set up with regards to the water. A deep well pump in the lake is far and away the very best method to get water to your cabin, especially in the winter.

Our cabin is used primarily on weekends and all year round. We spent many years using jet pumps before we realized we were doing it all wrong. With a deep well pump in the lake and lifted up well above the lake bottom, all one has to do is come down, turn on the pump breaker and you have water. No priming necessary... ever again! Even better in the winter. Because the cabin is not heated all winter, we drain and blow out all the lines before leaving each Sunday and dump RV Antifreeze down all sink traps etc. When folks arrive the next weekend, all one has to do is hit the switch for the heat trace in the supply line, wait about an hour and then turn on the pump breaker and you have water. This system has worked flawlessly for years.

It wasn't until I installed the solar system this summer that I've started to have trouble. I'm not convinced it's the LV6548's and suspect I may have a contactor issue or pump issue but wanted to hear from others that might have a similar set up before taking the deep dive into troubleshooting.

Here is a great link if anyone is interested in upgrading from the traditional Jet Pump System.

Cottage Water Supply System
 
The surge is dropping the voltage. You'll have a hard time seeing it with anything other than a lab scope.

The way to solve the issue would be to run a contacted who's control side (coil) is run on battery voltage.
 
I knew I could never measure the instantaneous voltage so I ignored that but do you really think 13KW of HF Inverters can't handle the surge? I just got here for the weekend. I'll go out and start the generator and see if I still have the issue. I may run into the same issue as the generator is running through the inverters?

I'll go try it now and report back.

Good puzzle for the weekend :)
 
I just cycled the pump 5 times on Solar only and it worked like a charm. LOL... Intermittent problems are a real problem. I'll work away at the problem this weekend.

@Checkthisout... really appreciate your input!
 
I knew I could never measure the instantaneous voltage so I ignored that but do you really think 13KW of HF Inverters can't handle the surge? I just got here for the weekend. I'll go out and start the generator and see if I still have the issue. I may run into the same issue as the generator is running through the inverters?

I'll go try it now and report back.

Good puzzle for the weekend :)

Well, it's not that they can't handle the surge. They are starting the pump fine without tripping.

They just take some order of milliseconds to ramp up and within that time frame, the contacted opens up for a split second.

You wouldn't know anything was wrong if the contacter wasn't within earshot.
 
A capacitor across the contactor coil wires might solve the issue. Not sure what size would be best for your situation. Might just have to try a few.
 
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