Shureflo Aqua King II pump tripping circuit when engine running

[Mike G.]

Just installed a Shurllfo Aqua King II (model 4158-153-E75) fresh water pump. We were told that it is best replacement for the old and tired Shureflo Smart Sensor. The Aqua King works great although much louder.

Weird problem. Runs fine without engine running, but when using pump with Perkins 4-108 running it trips the water pump breaker on panel.

Thoughts?

 

[Ralph Johnstone]

but when using pump with Perkins 4-108 running it trips the water pump breaker on panel.

I'll take a wild guess and say the breaker is on its last legs and on the verge (but not quite) of tripping on battery alone. Your alternator on the engine will increase the voltage slightly to the point where the slightly increased amperage will trip the breaker. You are likely no where near the rating of the pump breaker. It would also be of interest to see what the the output voltage of your alternator is when running. Test at the battery terminals.

Good theory but maybe not worth the powder to blow it too hell. The only way to prove it is to :

- shut OFF the main DC breaker at the top of your DC panel
- disconnect the output wire from the pump breaker
- insert a voltmeter between the pump breaker terminal and the disconnected wire AFTER setting the volt meter selector to amperage

- turn on the DC main breaker
- ensure the pump breaker is in the ON position
- open a faucet to cause the pump to come on
- record the amperage draw.
- see if the draw is anywhere near the breaker tripping amperage.

If you're not comfortable using a voltmeter, replace the pump breaker with a new breaker of the same amperage.

 

[Stu Jackson]

The only way to prove it is to

Good analysis.
Only thing to add is make sure your DVM (Digital Voltmeter) amperage range is OK for the proposed load. Some DVMs have a very, very LOW amp rating. RTFM for the DVM.
Good luck.

 

[Ralph Johnstone]

Some DVMs have a very, very LOW amp rating.

That's why I only use high quality instruments.

 

[capta]

With increased voltage amperage is reduced, not increased. However, it was also my first thought that the breaker could be weak. But because of the above, it all seems backwards. The breaker should trip when the alternator is not raising the voltage and lowering the amperage.
What are the specs of the two pumps?
It just occurred to me that your voltage on that pump and/or the 12vdc panel may be 24 vdc, instead of 12 vdc, once the alternator is running.
Therefore, I believe it is probably more a wiring problem. Have you tried to duplicate this with other systems on your boat?

 

[jviss]

With increased voltage amperage is reduced, not increased.

Not necessarily so.

"Overvoltage can drive up amperage and temperature even on lightly loaded motors. Thus, high voltage can shorten motor life even on lightly loaded motors. Efficiency drops with either high or low voltage. Power factor improves with lower voltage and drops sharply with higher voltage."

The Highs and Lows of Motor Voltage

(By the way, out of respect for our great inventors and engineers of the past, we should always capitalize units named after them - Volts, Amps, Ohms, etc. )

 

[Ralph Johnstone]

on lightly loaded motors.

There's the catch I neglected to mention.

 

[Mike G.]

With increased voltage amperage is reduced, not increased. However, it was also my first thought that the breaker could be weak. But because of the above, it all seems backwards. The breaker should trip when the alternator is not raising the voltage and lowering the amperage.
What are the specs of the two pumps?
It just occurred to me that your voltage on that pump and/or the 12vdc panel may be 24 vdc, instead of 12 vdc, once the alternator is running.
Therefore, I believe it is probably more a wiring problem. Have you tried to duplicate this with other systems on your boat?

Good thought, but I Checked the pump specs. It is the 12 vdc version. -- The amp draw listed on the new pump is slightly lower than the old pump.

 

[Mike G.]

Thanks all for the thoughtful replies. It was suggested by a friend as well that the breaker may be on its last legs.
I'll be working on it this weekend and let you know.

 

[DaveJ]

Switch the wires at the breaker, with a different circuit, this may tell you the state of the breaker.
cheers

 

[Ralph Johnstone]

Switch the wires at the breaker,

That's just way too simple. Waaaaaaaaay too simple .

 

[Davidasailor26]

Good thought on switching the wires.

I have two guesses - the breaker is weak and the engine vibration is enough to push it over the edge. Or, the alternator doesn’t hold the voltage as high as the shore charger, and the problem is really being off the shore charger, not that the engine is running.

 

[Mike G.]

Life got in the way. -- Finally got to work on the breaker issue. It ended up being an old and tired breaker. Many thanks for all of the replies.