DIY off-grid energy experiments
Solar charging is mostly simple: when the battery is full, the controller limits charge. Wind and hydro experiments can be different. A turbine can keep pushing power when the battery is already full — and if that energy has nowhere to go, voltage can rise and things can fail. A dump load (also called diversion control) gives your system a safe place to send excess energy. This guide explains what diversion does, how to size it realistically, and how to wire it safely.
A dump load is intentionally wasteful. That’s the point. When your generator produces more power than the battery can safely accept, the system diverts the extra power into a load that converts it to heat.
Think of it like a pressure relief valve in plumbing: you don’t want to “use” that water — you want to avoid bursting pipes.
If you’re new to watts vs watt-hours, read solar basics. Diversion control is about managing watts in real time to keep voltage stable and components safe.
Batteries are not bottomless. When a battery is full, it should not keep absorbing charging power at the same rate. In a well-designed system, charging current tapers or is stopped.
If a turbine keeps producing energy but the electrical system can’t absorb it, one of three things tends to happen:
Diversion is a controlled way to prevent the “nowhere to go” condition.
Solar panels can be “turned down” by a controller because they are current-limited sources that respond predictably. Turbines can behave differently: changes in electrical load can change RPM and can create unstable behavior if not managed.
A diversion controller monitors battery (or DC bus) voltage. When voltage rises above a threshold (indicating “battery full” or “charging should be limited”), the controller routes current to a dump load.
In many wind/hydro situations, keeping the generator loaded is desirable because it helps prevent overspeed.
Many diversion systems pulse current to the dump load (PWM) to control average power smoothly. The dump load still gets hot — but now it’s controllably hot.
A dump load is simply a device that can safely convert electrical power into heat continuously. For DIY builds, that often means resistors or heating elements.
The “best” choice depends on power level and how you want to handle heat.
A dump load must handle the maximum power your turbine could plausibly produce in your conditions (or at least the portion you want to divert), plus a safety margin.
Use measured reality, not optimistic ratings. If your wind turbine has produced 120W peaks on a meter, assume the dump load should handle at least that, and preferably more. For hydro, you can estimate water power from head and flow (then apply a conservative efficiency).
If you want a measurement-first method, use a generator test bench approach.
Dump load sizing depends strongly on voltage because for resistive loads:
At higher voltage, the same resistance dissipates more power. At lower voltage, current rises for the same power, which increases wiring demands.
Suppose you want to dump about 200W on a 12V system. The effective resistance needed is roughly:
That’s a low resistance, which means high current (about 16–17A at 12V). That current must be handled by wiring, switches, and connectors.
Also, resistors must be rated for the heat. A “200W dump load” is literally a 200W heater. If you build a 200W resistor bank with no airflow or heat sinking, it will overheat.
A good DIY rule is to oversize thermal handling. If you think you need 200W, aim for a dump load that can safely dissipate more under your mounting conditions.
Diversion systems involve high current, and they are often installed in environments where wind/hydro is already stressing hardware. Build for safety and serviceability.
Use: fuse/breaker sizing, wire size guidance, and wiring decisions.
The conceptual model is:
A clean multi-source layout is described in the hybrid charge controller guide.
A dump load is a heater. Treat it like one. You need:
If your dump load is undersized or enclosed without airflow, it will overheat. If it fails open-circuit, the system may lose its safety valve at the worst time (high wind, full battery). That’s why oversizing and conservative mounting matter.
In a hybrid system, solar usually charges the battery through a solar charge controller. Wind/hydro sources can also charge the same battery system, but they may need diversion control as their “safety path.”
Dump loads can reach high temperatures. Treat them like a space heater: keep them away from combustible materials and plan airflow.
Low-voltage systems can still produce dangerous current. Use proper fusing, wire sizing, and quality connections.
Diversion helps keep a turbine loaded, but you should still design a mechanical safety strategy appropriate to your turbine type. Don’t rely on any one component to prevent all failures.
Often, yes — especially if you plan to charge a battery and the turbine can continue producing power when the battery is full. The need depends on your turbine type, controller behavior, and how your system handles “excess power” scenarios.
Sometimes. Heating elements can handle heat by design, but you must choose an element appropriate for your system voltage and mounting. Wire and protect it as a high-power device, not as an accessory.
Estimate maximum plausible watts to dump, then use P = V² / R to select an effective resistance and wattage rating. Oversize thermal handling and pay attention to current (especially at 12V).
Diversion loads the generator electrically, which can slow the turbine and reduce overspeed risk. It is not always a full mechanical brake, and it’s not a substitute for safe turbine design and mounting.
Start with measurement-first experiments and conservative power levels. Confirm your dump load can dissipate heat safely before relying on it as a protection device.