Electrical help needed--12V

[Pilot]

I have one of those cheapie 15 gallon sprayers. It has a Shurflo on-demand pump, so it comes on when there is a pressure drop. I haul it behind my riding mower in a little trailer and spray along my driveway, the road and my yard.

It decided to blow fuses. First time it ran just a few seconds to build up initial pressure, then the fuse blew. I replaced the fuse, it ran fine for about 20-30 minutes before blowing a fuse again. 5 amp fuse, 4.3 amp pump. I probably have 30-50 hours on this setup with no previous problems.

Checked the hoses, the wand, the entire flow system and found no obstructions that would put unusual load on the pump.

The wiring appears undamaged and with my ohm meter there are no obvious shorts.

So, where do I go from here? Suppose the pump motor is bad? How can I check it out? What else can I check and how can I check those things?

Thanks.

 

[Tapanti]

Hola Pilot,
I'm working in Solar Energy and i use a lot of this Shurflo pumps.
I think that the 5Amp fuse is very low with a 4,3Amp motor.
When the pump starts, the amps reach easely 4 time the rated motor amps so you must have a slow blow fuse, i don't know exactly the name but in France (i'm French) we call this fuse AM (motor acompagnment).
I sugest you to use a 8 Amps fuse and see what appens.
Saludos cordiales from Orosi, Costa Rica
Frank

 

[teg]

The sprayer motors I have need a 10 amp fuse (I don't think it's slow blow). Any chance you replaced the fuse with a different type?

 

[Pilot]

I replaced the fuses with the same type and rating.

Thanks for the fuse suggestions, but we have no explanation why the system worked well for several years and just decided to blow fuses the last 2 times I tried to use it.

Would it start blowing fuses if the motor was dying? Is this a typical failure mode?

Electrical stuff is a weak area for me, so I wouldn't know how to hook up my ohm meter to read the amperage draw. The meter cables are too small to run it in series.

 

[George2615]

I agree that a 5 amp fuse may be too small.
Check all your connections for rust or corrosion. rust or corrosion will increase the amp draw causing your 5A fuse to blow.

Go with a 7.5 to 10A fuse. The wiring should be at least 14Ga. If the upgraded fuse blows then its probably the motor getting ready to go.

 

[heehaw]

give shurflo a call: they are usually very helpful in solving problems with their pumps: the pump probably has a toll free number on it
heehaw

 

[EarPlug]

According to the Shurflo web site the fuse size should be on the pump label. Looking at the troubleshooting info an 8000 Series 12vdc pump would use a 15 amp fuse

 

[J_J]

Your pump probably has a pressure relief valve, and cuts off when the pressure is achieved. If the relief is sticking, and the pressure is building above the limits for the pump, then the motor will try and turn against the increased resistance caused by the higher pressure, and stalling, and drawing more current, until something happens. . Put a gage on it and determine if the motor is cutting off at the specified pressure. Read the ohms across the motor with no voltage applied, and figure what the current is with the resistance of the motor and the voltage.

 

[SPYDERLK]

Probably the motor brushes. May be sticking some or worn out. Easily replaced. Shaft bearings could have dried out a bit too - esp if motor ever gets wet.
larry

 

[SPYDERLK]

Could also be resistance in the fuse connections[oxidation] causing the fuse to run hot. Even at normal current/healthy motor this would cause the fuse to blow.
larry

 

[Pilot]

Ah, pressure relief or pressure switch may be it! I remember when I replaced the fuse the first time it seemed like the sprayer was putting out a little more volume and pressure than usual.

In taking things apart a little bit a couple days ago, I came across the switch. Since then I put it all back together, but I don't think I can access the inside of the switch to check the contacts. Don't know where the valve is, but we'll see if I can trace it down.

We'll see.

The label is faded; I don't know if I can find the fuse rating. The fuse is what I wired in with the battery connection on the mower; there isn't one on the pump that I know of.

Thanks for all the suggestions!

 

[honorbound]

Pilot first try a slow blow fuse. They are designed to handle the starting current from a motor. A typical starting current is 4x or more of the running current. Without knowing more on the design of the pump, being there are many styles. Positive displacement, centrifical, dosing, etc. If the pump is worn as in bearings, lobes, impellars, it will cause the pump to draw more and work harder therby blowing fuses. The manufacurers lable will should tell you what the current draw is at full load so you can match the fuses accordingly.
Hope this helps a bit.