Well pump drawing excessive current only when on portable generator...

Status
Not open for further replies.
S

sbrehler

Member
I have a customer who has a 5500W portable generator that he connects to a sub-panel in his garage (suicide plug to a receptacle that crosses about 20' to the sub-panel...NOT my work! I'm talking him into redoing it). The sub-panel is interlocked with a 30A DP coming off a main panel which separates the POCO from the generator.

The trouble is that when the well is sourced from the POCO it runs fine...momentary inrush, then settles at about 7-8 amps. But, when I switch to the generator it surges to about 27amps and stays there! The breaker hasn't tripped even though it is a 20A DP, but I believe that the well pump cuts out due to thermal overload after about a minute. It is a 1/2hp at about 400'. The well guy feels that it is undersized for that depth, but we can't figure out why it draws so much on generator power. When on POCO power I get about 123V on each leg to ground/neutral (sub-panel is not bonded to neutral). When on generator power I get about 130V.

I tried hooking up my own generator (same size/capacity) and get the same results with it.

From what I can tell, the other circuits (lighting/receptacles) that are fed from the sub-panel seem to operate fine using the generators.

An ideas as to why this might be happening?

Thanks...
 
If the pump motor, starting under load, cannot get enough current to accelerate to the point that the centrifugal switch opens, it will continue at high amps and trip the overload. That is for a single phase motor with capacitor start.
I will bet that the 130V from the generator does not hold up while starting.
You can reduce the starting load by throttling down or closing completely a valve on the pump output. Once the pump is up to speed you can open the valve.
 
ActionDave said:
Is the generator running at full speed when the pump kicks on?
Click to expand...
And does the engine lug down hard for a few seconds when the pump starts and does it stay distressed while the pump is drawing high current?
You really need to measure the generator output voltage as the pump is starting.
 
GoldDigger said:
If the pump motor, starting under load, cannot get enough current to accelerate to the point that the centrifugal switch opens, it will continue at high amps and trip the overload. That is for a single phase motor with capacitor start.
I will bet that the 130V from the generator does not hold up while starting.
You can reduce the starting load by throttling down or closing completely a valve on the pump output. Once the pump is up to speed you can open the valve.
Click to expand...

Thanks. We've had a garden hose on while watching all of this. So, like you say, maybe we need to close it off until pressure builds, then open it. I'll give it a try...
 
GoldDigger said:
And does the engine lug down hard for a few seconds when the pump starts and does it stay distressed while the pump is drawing high current?
You really need to measure the generator output voltage as the pump is starting.
Click to expand...

Exactly... I'll try measuring the voltage when it's trying to kick it.
 
Is there a capacitor in the pump box at the well head or nearby? I wonder if it has lost some of its value causing the pump to start harder.

What kind of a generator is this? Make and model and regulation scheme if you know it.
 
They do make soft start kits for 1ph home AC units but I have no idea how they work or if they would be appropriate. My gut feeling is they would be the same thing, though, and could work.

But first things first, just make sure that the existing starting system is up to snuff. A 5000 watt generator should be able to run a 1/2 hp pump with no problems, experience says. If it is a true 5000 watts and not some knockoff.
 
Birken Vogt said:
They do make soft start kits for 1ph home AC units but I have no idea how they work or if they would be appropriate. My gut feeling is they would be the same thing, though, and could work....
Click to expand...
I have no idea how they work, but the starting winding on a cap start motor, which is common for most well pumps, has to drop out pretty quick or it will suffer.
 
ActionDave said:
I have no idea how they work, but the starting winding on a cap start motor, which is common for most well pumps, has to drop out pretty quick or it will suffer.
Click to expand...

Yeah, I like Golddiggers theory, but the couple of times I've seen a single phase motor fail to get up to speed it blew up the starting caps because they never switched out. Maybe this has rugged caps anda sensitive OL, I'vejust never seen thisparticular mode of failure.
 
GoldDigger said:
If the pump motor, starting under load, cannot get enough current to accelerate to the point that the centrifugal switch opens, it will continue at high amps and trip the overload. That is for a single phase motor with capacitor start.
I will bet that the 130V from the generator does not hold up while starting.
You can reduce the starting load by throttling down or closing completely a valve on the pump output. Once the pump is up to speed you can open the valve.
Click to expand...
I thing GD is dead on as to the cause, but this sounds like a submersible well pump, so closing off the output may not have an effect, because a submersible still has to lift that water column. So it appears that the generator is just too weak.

With all the crazy suicide patch cords and all, are you SURE they are getting 240V out of that generator to the motor, and not parallel 130V lines off of the same hot leg? You only gave the Line to Ground voltage readings, what is the Line to Line reading? And as the others said, put your meter on WHILE the pump is starting and report back on what the voltage is then.
 
Birken Vogt said:
They do make soft start kits for 1ph home AC units but I have no idea how they work or if they would be appropriate. My gut feeling is they would be the same thing, though, and could work.

But first things first, just make sure that the existing starting system is up to snuff. A 5000 watt generator should be able to run a 1/2 hp pump with no problems, experience says. If it is a true 5000 watts and not some knockoff.
Click to expand...

Y access be current what did you measure to consider it as being excessive.? Also, what is the starting amps? It should be withing the generators peak output.
Did you actually measure the running voltage? If he voltage is lower the current will be greater in order to maintain the same HP output.
 
Probably wiring problems , maybe pump not right for the job , maybe pump on way out . The fact that 2 generators will not work lends more to a wiring problem , pump problem .





Don
 
big john said:
Yeah, I like Golddiggers theory, but the couple of times I've seen a single phase motor fail to get up to speed it blew up the starting caps because they never switched out. Maybe this has rugged caps and a sensitive OL, I've just never seen this particular mode of failure.
Click to expand...
I like GoldDigger's take to.

Yes, you can blow a cap instead of a winding but either way the motor needs to come up to speed.

I'll bet $20 on Gold.
 
My money's on a weak generator. We used to rent a place with an above ground pump, 120V. A 6500W generator would start the pump, but it wouldn't provide enough chooch to get the pressurestat to shut the pump off. I had to manually lower the setting until the pump would shut when we were on generator power.
 
PetrosA said:
My money's on a weak generator. We used to rent a place with an above ground pump, 120V. A 6500W generator would start the pump, but it wouldn't provide enough chooch to get the pressurestat to shut the pump off. I had to manually lower the setting until the pump would shut when we were on generator power.
Click to expand...
You would think that if the genset didn't have enough punch the actual genset voltage would drop.
Another issue is the age of the genset and how the genset actuaslly generates electricity.
 
PetrosA said:
My money's on a weak generator. We used to rent a place with an above ground pump, 120V. A 6500W generator would start the pump, but it wouldn't provide enough chooch to get the pressurestat to shut the pump off. I had to manually lower the setting until the pump would shut when we were on generator power.
Click to expand...

templdl said:
You would think that if the genset didn't have enough punch the actual genset voltage would drop.
Another issue is the age of the genset and how the genset actuaslly generates electricity.
Click to expand...

OP said he brought in another (his) generator to try with the same results.
 
Status
Not open for further replies.
Top