[MikeDobbs]

I have a Heat Siphon HP5.0 pool heat pump, about 12 years old. I recently changed the run capacitor and the unit was working well until the last couple of days. It's started tripping the breaker at some point in the day.

Today I went out and put a meter on it while it was starting up, running, and when it shut down. I set up a GoPro so I could monitor the amp draw for the entire run cycle. It registered a very high amp load for a fraction of a second at startup. My meter showed a spike of 138 amps for 1/3 of a second, then it settled down to 31 or 32 amps. This did NOT trip the breaker. The amp draw stayed right around there, floating up and down by a few tenths of an amp for a few hours, until the pool water reached the set temp. Then, when the unit shut down it tripped the breaker. When I played the video back I saw that it pulled 70 amps for just shy of a half second, when the breaker tripped.

The amp draw does not steadily increase as the unit runs. It holds steady. But when the water reaches temperature it jumped from 32.7 to 88.8 in 1 frame (1/24th of a second), then to 70 and stayed there until the breaker tripped. You can see all of this in the video below.

Thanks in advance for any suggestions.

Here's a 10 second video clip of the breaker tripping. If you listen with sound there's a bit of a strange sound just before the trip that I imagine would be a clue for a more knowledgable ear.

 

[user_12345a]

could be current leakage to ground which only shows up as it reaches temp.

if you have a second amp meter, maybe monitor current of both hots and make sure they match when it draws the 70 amps.

Post the model number and any other relevant info so someone more familiar with these units can help you.

 

[MikeDobbs]

When you say current leaking to ground only visible when reaching operating temperature, are you suggesting that there is a short in the thermostat switch? That's my current operating theory, and I'm looking into a replacement part.

I don't have a second meter, but I suppose I could pick another one up if that would be helpful. The model is a Heat Siphon HP5.0, with MCA 43.2, 50 amp breaker, LRA 176.

 

[user_12345a]

Short in the motor windings (or something else) to ground which only shows up when it shuts off.

It can show up if the contactor is a single pole switch, power from one hot can still flow.

I'm only speculating.

 

[beenthere]

Could be as simple as the thermostat not opening properly due to carbon on the contacts.

 

[MikeDobbs]

In an attempt to isolate the temperature control switch I turned the dial all the way to 10 and let the heater run yesterday with the intention of switching it off before the thermostat kicked in. After about 4 hours the heat pump tripped the breaker and shut down. The temperature was about 90 degrees, well below the set temperature of the thermostat, so unless the thermostat unit is completely malfunctioning something else caused the current surge.

Today I ran the pump with the amp meter on the neutral wire to see if any excess current ran through the neutral when the trip happens. The heat pump ran for about 4.5 hours, and then I shut it down because the pool was at the temperature I wanted. When I shut it down manually (by turning off the breaker), the heat pump shut down with no excess amperage draw as seen in the above video. I used a no-contact thermometer on the breaker today and did notice that it was running about 150 degrees F, which is about 65 or 70 degrees above the ambient temperature.

I'm planning to replace the breaker in case there's some internal resistance that's causing an issue. Can anyone think of anything else that may cause an intermittent current surge as I'm seeing here? Remember, since this is a pool heat pump, the unit is not cycling- it just runs until it shuts down, so it's not a hard start issue. Typically it runs for several hours before tripping the breaker.

 

[57TinkerMan]

Edit: Op addressed what is was going to say

 

[MikeDobbs]

After its been running for awhile, place the back side of your fingers (more sensitive) on the breaker and see how warm/hot it is. If it's very hot could be a bad breaker.

The breaker was running pretty hot- I measured it at about 150F this afternoon. Replaced the breaker, and the new one is only running about 90F (albeit later in the day so it was cooler out with no direct sun).

Fingers crossed, maybe it was just an old tired breaker. Will post with update tomorrow or Wednesday after I've had a chance to run it again.

 

[57TinkerMan]

Sounds like a good temp. difference, hope it works for you.

 

[MikeDobbs]

After two full days of trouble free operation I'm calling it.

Apparently the old breaker was wearing out and it was the breaker itself that was overheating and drawing too much current. After replacing the breaker everything is running as it should.

Thanks to everyone who offered suggestions.