Why Do My On-Demand 12V Pumps With Pressure Switches Keep Blowing 20A Fuses?

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#1 21663742 16 Sep 2012 21:02

Ed Thompson Ed Thompson

Anonymous

Post #1
21663742 16 Sep 2012 21:02

We've been burning out a lot of pumps. I suppose my first question is how does a pump that is rated to operate at 16 amps max wind up drawing enough amps to blow a 20 amps fuse. Ive burned up a lot of these pumps but can't figure out why. These are on-demand pumps with pressure switches. Hopefully someone can ask me the right questions to help solve the riddle. Thank you in advance.
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#2 21663743 16 Sep 2012 22:52

Timothy Shuck Timothy Shuck

Anonymous

Post #2
21663743 16 Sep 2012 22:52

Well, the motor in the pump will draw its maximum current when stalled: starting or otherwise prevented from moving physically. If you are trying to cycle the pump on and off too quickly, you'll be drawing a lot of current.

That said, is the 16A rating for continuous current draw or current spikes? If it's continuous, then you have your answer: the motors are creating a huge current spike, blowing the fuses.
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#3 21663744 17 Sep 2012 02:20

Peter Evenhuis Peter Evenhuis

Anonymous

Post #3
21663744 17 Sep 2012 02:20

I pump needs to come on speed to reduce its current.
So if you have a series of burn outs, then check the following.
1. liquid is to thick as a result its speed is to low.
2. input is to small or blocked filter.
3. output is to high or blocked, yes i know that you have a pressure switch still you can be on the border in that case install a lower pressure switch.

Also keep in mind that a lot of pumps have specifications that are tested in a laboratory and in real live it does not work.

As a last step what is your power supply and is it stable a under rated battery can drop voltage and again give problems, a switched power supply not made for this current draw will give extreme high start up current in PWM.

I hoop this helps
#4 21663745 17 Sep 2012 04:23

Ian Brown Ian Brown

Anonymous

Post #4
21663745 17 Sep 2012 04:23

Can you post up link to pump spec sheet and or email it?
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#5 21663746 17 Sep 2012 04:54

Ed Thompson Ed Thompson

Anonymous

Post #5
21663746 17 Sep 2012 04:54

The best I could find was this here http://www.delavanagpumps.com/powerflo/5800.htm.
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#6 21663747 17 Sep 2012 05:07

Ed Thompson Ed Thompson

Anonymous

Post #6
21663747 17 Sep 2012 05:07

Here's a pdf of some specs http://www.delavanagpumps.com/powerflo/5800.htm. I believe 16 amps is the start-up draw. My retailer swears they're great pumps but need specific installation. He suggested 12-3 wire because the wire strands are fine making better connection, crimped connections- no wire nuts, short wire runs to the battery, biggest marine battery possible fully charged.

The spraying nozzles cannot be too small or it will cycle like you stated. The pumps will always run smooth at ground level. But I believe once the hoses reach the 2nd or 3rd floor of a roof, the fluid in the hose is creating a head pressure which pushes back to the pump and cause cycling. So it a fine line of using a hose big enough as to not create restrictions and cause cycling, but also not to large as to hold more fluid and create more head pressure.
My batteries are 600 ca or higher and are new to 2years old. They hold good charges from 12.2 to 12.8 volts. The only thing I havent check is the voltage drop when there's a load on.
#7 21663748 17 Sep 2012 05:12

Ed Thompson Ed Thompson

Anonymous

Post #7
21663748 17 Sep 2012 05:12

Thanks for the reply. My reply to Peter is also for you. I am no electrician by any means, but my pump retailer has me feeling stupid. We run 4 trucks with these pumps. Sometimes the pumps last for months, others have crapped out rather quickly.

I understand these are marine pumps. We run chlorine through them for which its not intended, but that should not matter. Theyre not really designed to pump 2nd floor but allegedly Im the only one having these problems.
#8 21663749 17 Sep 2012 05:15

Ed Thompson Ed Thompson

Anonymous

Post #8
21663749 17 Sep 2012 05:15

P.s. If I do not solve my problem in this forum, I am grateful that you guys quickly responded to offer assistance. Really good stuff, much appreciated.
#9 21663750 17 Sep 2012 14:54

Chuck Sydlo Chuck Sydlo

Anonymous

Post #9
21663750 17 Sep 2012 14:54

I suspect that you are exceeding the duty cycle of the pumps. The responders here need to realize that some of these pumps are designed to pump water in recreational vehicles. The normal usage is a few minutes on and long periods of off time. The longest normal usage would be a shower and many RVs don't have a shower so many of these pumps have duty cycles that are quite short. Good news is that there are many of these type pumps that are higher durability and may have up to 100% duty cycle. I did notice you mentioned nozzles in your note so I suspect that when the pump is turned on there will never be enough pressure built up to turn it off so the pump is probably running continuously. The manufacturer recommends not letting the surface temp of the pump exceed 180 degrees. Check, carefully, the temp of the pumps in service and see if they are hot. If they are hot then I think you have found a smoking gun. Don't hesitate to use a larger, gpm, pump as well as one with a longer duty cycle. A higher flow pump will be more likely to build up enough pressure to shut off periodically and even if it's off only 10% of the time it will run cooler and be less likely to burn out.
#10 21663751 17 Sep 2012 18:08

Ed Thompson Ed Thompson

Anonymous

Post #10
21663751 17 Sep 2012 18:08

Fair enough Chuck. I suspected this model pump is not up to the task. I do have the option of running pumps with internal fans and thermal protection. These pumps were fairly cheap and others have claimed to have good success with them. I suspect we may be cleaning more roofs than the average.

Thanks everyone for the help. Look me up for any questions regarding exterior cleaning of every nature.

Ed from New Jersey
Thompson Roof Cleaning and Powerwashing
#11 21663752 18 Sep 2012 00:55

Peter Evenhuis Peter Evenhuis

Anonymous

Post #11
21663752 18 Sep 2012 00:55

Chlorine is a bad chemical for pumps. It eats iron even stainless steel.
As soon as that one off the valves stops working correct you start over loading the pump a second one and your pump will start over heating and it does not have protection.
Next to that Chlorine is thickening under heavy motion, like a pump.
These pumps are also not designed to pump to height As stated they are for RV and Boot use.

Seeing on your email you use them for your work.
Go to a farmers store they have pumps for spraying chemicals.
It will give the easy the pump height that you need and if you take care for the oil in the gear box it will live longer than your truck.
#12 21663753 18 Sep 2012 04:00

Frank Bushnell Frank Bushnell

Anonymous

Post #12
21663753 18 Sep 2012 04:00

Hi Ed,
You could determine the current drawn by the pump at any particular time by connecting (preferably by someone electrically qualified) an ammeter in series with the pump, then have someone watch it and note the values while the job is being carried out (or simulated).

Then see how the results compare with the maker's heat rise graph, which (if I read it correctly) shows that a constant current of 13 Amps (or an equivalent duty cycle) should be indefinitely sustainable.

The pump's maximum pressure is rated 100 psi, so you could calculate its suitability for the pressure required for your purpose, from the density of the fluid being pumped and the height it has to go to.

Is it possible to fit an output pressure gauge on the pump ? Or even a flowmeter ?

Apart from that, may I suggest you use the "Contact Us" button on the maker's webpage ?

Give them full details of your usage, duty cycle (time on to time off)(as the pump will cool when its off).
(As this pump is non-ventilated, its duty cycle at higher currents will be limited.)
Tell them the substances you use and the height pumped to.

I would expect their technical department would give you all the information you need to determine whether this is a suitable pump for the purpose, or if you need a more powerful or special purpose unit.
#13 21663754 18 Sep 2012 07:45

Ed Thompson Ed Thompson

Anonymous

Post #13
21663754 18 Sep 2012 07:45

Thanks Frank. Hooking an ampmeter should not be a big deal, and technically there should be a gauge in-line to make sure the pump is not exceeding recommended pressure. We pump a mixture of chlorine, water, and a surfactant which technically voids the warranty of the pump, but would also destroy such objects such as gauges, etc. I'm going with a bit larger pump to see how I fair.
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Topic summary

✨ On-demand 12V pumps with pressure switches rated for 16A max are blowing 20A fuses due to current spikes caused by motor stall conditions, rapid cycling, or excessive load. The pumps draw maximum current at startup or when physically stalled, such as when fluid viscosity is high, input or output lines are restricted, or pressure settings are borderline. Using chlorine mixtures, which are corrosive and thickening under motion, further stresses pumps not designed for chemical spraying or vertical lift beyond typical RV applications. Inadequate wiring (undersized gauge, poor connections, long runs), unstable or undersized power supplies, and lack of thermal protection contribute to premature pump failure. Duty cycle limitations of these pumps, often designed for intermittent use in recreational vehicles, mean continuous operation or cycling can cause overheating and fuse blowouts. Solutions include verifying current draw with an ammeter, ensuring proper wiring (e.g., 12-3 wire, crimped connections), using larger marine batteries, selecting appropriate hose sizes to minimize head pressure and cycling, installing pressure gauges, and considering pumps with higher duty cycles, internal fans, and thermal protection. Switching to pumps designed for chemical spraying with suitable gearboxes and oil lubrication is recommended for applications involving chlorine and elevated pumping heights. The Delavan PowerFlo 5800 series was referenced as a typical model with a 16A startup current and 100 psi max pressure rating.

FAQ

TL;DR: Your 12V on‑demand pumps are blowing 20A fuses because heat and stall/start spikes overwhelm RV‑style units; “The manufacturer recommends not letting the surface temp of the pump exceed 180 degrees.” [Elektroda, Chuck Sydlo, post #21663750] Why it matters: This FAQ helps roof cleaners, RV users, and sprayer techs quickly diagnose fuse blows, cycling, and premature pump failures.

Quick Facts

Start/stall current spikes can exceed fuse ratings even if the label says 16A max. [Elektroda, Timothy Shuck, post #21663743]
Typical continuous draw guideline: ~13A sustained when within thermal limits, per maker heat‑rise graph. [Elektroda, Frank Bushnell, post #21663753]
Max pressure on the referenced model line: 100 psi; verify against your required head. [Elektroda, Frank Bushnell, post #21663753]
Many RV pumps have short duty cycles; some models are up to 100% duty. Keep surface temp under 180°F. [Elektroda, Chuck Sydlo, post #21663750]
Chlorine attacks pump internals and valves; use chemical‑rated sprayer pumps. [Elektroda, Peter Evenhuis, post #21663752]

Why does a 16A-rated 12V pump blow a 20A fuse?

DC motors draw maximum current at stall and at startup. Fast cycling or blockage raises current beyond fuse limits. “The motor in the pump will draw its maximum current when stalled.” Use correct nozzle sizing and avoid rapid on/off to reduce spikes. [Elektroda, Timothy Shuck, post #21663743]

What is stall current, in simple terms?

Stall current is the highest current a motor draws when it cannot turn. Starting and hard cycling mimic stall conditions and create big current spikes that blow fuses. Reduce restrictions and give the pump time to reach speed to cut peaks. [Elektroda, Timothy Shuck, post #21663743]

How do nozzle size and hose height cause pump cycling?

Too-small nozzles or high head from second/third-floor hoses increase backpressure. The pressure switch then toggles rapidly, creating heat and current spikes. Use adequate hose ID and flow so the pump runs steadily without chatter. [Elektroda, Ed Thompson, post #21663747]

What is duty cycle and why does it matter for these pumps?

Duty cycle is the percentage of time a pump can run without overheating. Many RV-style units are not 100% duty. If your sprayer runs continuously, choose a higher-flow, fan‑cooled, or 100% duty model to avoid burnout. [Elektroda, Chuck Sydlo, post #21663750]

Are my pumps overheating?

Check the pump surface temperature during use. The maker guidance cited is to keep it under 180°F. If it’s hot to the touch or cycling, upgrade to a model with better cooling or more flow to reduce runtime. [Elektroda, Chuck Sydlo, post #21663750]

Could thick fluids or blockages be the reason?

Yes. Thickened liquids, a clogged inlet filter, or a too‑high outlet restriction slow the pump, raising current. Consider a lower pressure switch setting and verify inlet/outlet paths are clear to restore speed and cut draw. [Elektroda, Peter Evenhuis, post #21663744]

How do I measure what the pump really draws under load?

Put an ammeter in series with the pump during real spraying. Log current while operating. Compare to the maker’s heat‑rise graph; ~13A continuous is indicated as sustainable when within thermal limits. Add a pressure gauge if chemicals allow. [Elektroda, Frank Bushnell, post #21663753]

Can chlorine mixes void warranties or damage parts?

Yes. Users report chlorine attacking valves and internals, leading to overload and overheating. Choose chemical-rated agricultural sprayer pumps and compatible plumbing to handle chlorine blends safely and reliably. [Elektroda, Peter Evenhuis, post #21663752]

Will a bigger pump help stop cycling and fuse blows?

Often yes. A higher‑GPM, longer‑duty pump can build pressure, then shut off periodically, running cooler. Even a 10% off-time reduces heat and stress on fuses and windings during long jobs. [Elektroda, Chuck Sydlo, post #21663750]

How high can this pump push fluid?

The referenced line lists 100 psi maximum. Convert your elevation head and flow needs accordingly. If you routinely spray to second or third floors, select a pump rated for that head with chemical compatibility. [Elektroda, Frank Bushnell, post #21663753]

Could wiring or power supply be part of the problem?

Yes. Long runs, poor crimps, or undersized wire increase voltage drop and current. Keep runs short, use fine‑strand cable and proper crimped terminals, and verify battery voltage under load, not just at rest. [Elektroda, Ed Thompson, post #21663747]

What’s a pressure switch and why does it chatter?

A pressure switch turns the pump off at a set pressure. If your nozzles are too small or head is high, pressure toggles around the setpoint, causing rapid cycling. A lower switch setting can stabilize flow. [Elektroda, Peter Evenhuis, post #21663744]

Do these marine/RV pumps suit commercial roof cleaning?

They can work, but frequent, long-duty spraying exceeds their design intent. For daily chemical use and height, choose ag‑rated chemical pumps with cooling, thermal protection, and the required head. [Elektroda, Peter Evenhuis, post #21663752]

Any tell‑tale edge cases I should check first?

Look for a partially stuck check/valve from chemical attack. One bad valve raises load; two can overheat the pump fast without protection. Replace damaged valves and flush lines after chlorine use. [Elektroda, Peter Evenhuis, post #21663752]

What battery numbers should I expect during operation?

Healthy systems showed 12.2–12.8V at rest in field reports. Measure voltage under load to catch drop issues that raise current and heat. Upgrade cabling or batteries if loaded voltage sags excessively. [Elektroda, Ed Thompson, post #21663747]

How do I do a quick 3‑step test to stop blowing fuses?

Measure current with an inline ammeter while spraying a typical job.
Swap to larger nozzles or lower the pressure switch to end rapid cycling.
Verify inlet filter, hose ID, and wiring gauge/length; retest current and temperature. [Elektroda, Frank Bushnell, post #21663753]