Can you Run a Power Inverter off an Alternator? Here’s How

If you’ve got appliances in your RV, boat, or car that use AC power, rather than connect and run a generator, you may want to consider hooking up an inverter to the alternator -battery setup to supply the AC you need to run the fridge, heater and other electrical appliances instead.

Should you do it through? Is it safe?

Read on to learn if and how you can use an inverter to safely off your alternator- battery setup and how else you may be able to supply power to the appliances that use AC.

Can you Run a Power Inverter Directly Off an Alternator?

You could but the power from the alternator can vary depending on the load, and engine speed, and therefore it is recommended that you have a battery in between as a buffer.

Rather than hooking the inverter directly to an alternator, connecting it to the battery bank instead has the advantage that, it does not have to keep up to supply the maximum power demanded by the inverter.

Assuming you’ve connected an appliance such as a heater with a heavy draw current that maxes out the alternator capacity, the alternator will have run at full capacity for the duration of use of the appliances.

This is generally not good for the alternator as several manufacturers tend not to design and build them to run at maximum power for extended periods.

In short, you risk damaging the alternator.

Is it Safe?

Honest answer – you should do a proper system design starting with the appliances you plan to power – their consumption and duration of running and based on that size batteries and the alternator.

Off, hand, the alternator needs to be able to recharge the batteries and it can only do so fast.

So the alternator and battery need to be sized appropriately so that the alternator can keep the batteries charged so that there’s no severe discharge or else the batteries will be damaged.

Alternatives to Power AC Appliances

Instead of using an inverter to supply AC power for your appliances, you could use a portable solar generator (with an inbuilt inverter) instead to supply 115-120V.

The generator has a lightweight lithium battery that makes it light to carry around for the capacity of power it supplies.

A portable solar generator can support 3 charging options – 12V DC, so you can charge off the charging port in your RV, or Car, solar panels and lastly you can charge it from a wall outlet.

How Much Power from an Alternator?

How much power an alternator supplies depends on a number of factors, especially its capacity and current output.

There’re alternators with varying capacities – 80, 90, 120, 200 amps, and others.

A car alternator rated 90 amps at 12V has a power output of about 90 amps x 12V = 1,080 watts at full power.

The charging current from an alternator is not constant and depends on the battery charge level. When a battery is deeply discharged or connected electrical appliances require significant power to run the alternator current will increase.

All in all, the output power depends on the capacity of the inverter and the current it is supplying. Consult your alternator’s manual or specifications on its nameplate for its rated current.

Tips to Safely Connect a Power Inverter to an Alternator

To safely connect a power inverter to an alternator:

1. Let the alternator charge the house batteries and then connect the inverter to the batteries. You’ll need to size the battery bank, inverter, and wiring to match the power draw of the appliances you plan to power off the inverter!

2. Connect the alternator to house batteries instead of the starter battery to avoid the risk of the inverter running the starter battery flat.

3. Keep the car engine running to prevent the car batteries from draining flat.

4. The alternator to battery and battery to inverter cables should be appropriately sized to handle the expected current draws so that there is no risk of fire from overheating and loss of power from voltage drops.

Related Questions

1. What Size of Alternator to Use for an Inverter?

Unfortunately, there is no one answer as there are several variables at play. You’d need to do a proper system design and ensure that the alternator can supply enough power to charge the battery, and power the car’s electrical accessories as well as the power draw by the inverter.

So, how large an alternator you need depends on:

  • Power consumption of the inverter
  • Battery size (Ah)
  • Power drawn by the onboard accessories. Have you for instance installed an after-market amplifier? Additional high draw lights?

All these have to be taken into consideration when sizing the alternator to use.

2. Can a Car Alternator Power a 2,000-watt Inverter?

Yes, you could but make sure the alternator supplies enough power at idle to both charge the starter or house batteries and meet the demands of the inverter at the maximum power expected.

With a 2,000-watt/12V inverter, the DC power input for it to meet the demands of the connected accessories is over 2000/12v 166 amps.

The alternator should be able to deliver that much current at idle running the alternator at maximum power risks shortening its lifespan.

Closing Thoughts

While you can wire an inverter to a car alternator, it’s recommended that you connect to a battery instead that’s then charged by the alternator.

The complete inverter, battery, and alternator should be sized appropriately so that you do not drain and damage the batteries or damage the alternator too.

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