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]
