Can you run a power inverter off an Alternator? Here’s How

Using the existing car electrical system to power additional AC appliances such as an AC, sound systemand others can be a smart option.

Not only does it help minimise investments in additional hardware, it also allows you more space in your van or RV.

For example, you may want to connect a power inverter directly to the car alternator so that you can use the inverter power for an AC, heater or any other power needs while you are out on the road.

You may be wondering if it is as straightforward as it appears or there are other considerations you need to take into account to do it safely?

So this post not only explores whether you can connect an inverter directly to an inverter, it also provides some information on how you can do it safely, what risks you need to be aware of so that you can make an informed decision whether you should do it or not.

Are you looking to power some additional electrical equipment that uses grid-like AC in your RV or boat?

If so then perhaps you are considering connecting the power inverter directly to the alternator.

Can You Run a Power Inverter Directly Off an Inverter?

Yes you can run an inverter off an alternator but be mindful of how much power you can draw from the alternator considering that it is likely to be powering the car’s electrical systems and charging the battery.

This is particularly relevant if you are using the existing car alternator.

For example, a 1000-watt inverter draws about 83 amps from a 12V battery using the calculation 1000 watts/12V = 83 amps.

To power the 1000-watt inverter at full load, you’d want the inverter to be able to supply at least 100 amps when idling.

This is best done if you use a dedicated alternator rated about 250 amp or higher.

Alternatively, you should consider upgrading your existing alternator to one that can meet the additional power requirements of the inverter.

Therefore, check your alternator’s specifications to confirm if can meet the necessary power demand.

You may also be interested in this post: How much power does an inverter draw on load?

Should You Run a Power Inverter Off an Alternator Directly?

While you may be able to do so, its probably better to connect to a battery bank that is charged by the alternator.

The battery acts as a buffer in the event that the alternator is not running or running but is not able to supply enough power to the inverter, the batteries step in and meet the deficit.

How to Connect a Power Inverter to An Alternator

A typical setup will require:

  • an alternator with a large enough current supply at idle to power the inverter, ;
  • battery bank to buffer the alternator power supply,
  • DC cables of a gauge large enough to handle the current from the alternator with a minimal voltage drop,
  • a current meter to monitor the current flow between the alternator the battery (optional),
  • fuse between the alternator and the inverter.

Connect the appropriately sized positive cable from the alternator to the positive cable of the inverter and the negative (ground) cable to the inverter ground.

The cable gauges and fuse rating depend on the inverter and the alternator power rating.

For example, with a 1000 watt inverter, you could use a 150 A rated alternator, 100 A fuse and 2 AWG cabling from the alternator to the inverter.

Is Bad to Connect a Power Inverter Bad Directly to an Alternator?

You can connect a power inverter to an alternator directly in most cases without any harm befalling to the inverter or alternator provided the alternator can meet the required current (amps) draw by the inverter on load without overheating.

Alternators can fail prematurely from overheating when they have to supply their rated current continuously.

You may also be interested in this post: Why your car alternator may be burning out

How to Safely Run a Power Inverter Off an Alternator

#1. Do not overload the alternator

As a general guide, If you are to connect an inverter to an alternator, make sure it is able to match the power requirements of the inverter at idle.

This way it does not have to run at maximum speed or drain the battery when the inverter is fully loaded.

For example, for an 1000-watt rated inverter, the current draw is about 83amp at 12V. For an alternator dedicated to supplying power to the inverter, you’d want the alternator to be able to supply 100 amps at idle.

Therefore check the alternator specifications.

#2. Consider connecting the inverter to the batteries instead

You can also connect the inverter to the car starter battery or to house batteries that are charged by the alternator.

This battery acts as a buffer and helps supply the inverter with more stable voltage output and power especially when the alternator is powering other electrical systems in addition to the inverter.

Connecting to house batteries instead of the starter battery guards against the risk of draining the battery flat and not being able to start the car or van.

#3. Keep the car engine running

To prevent the car batteries from draining flat, keep the car engine running.

#4. Make sure the wires extending from the alternator and batteries have been appropriately sized according to the current that will be handled and the length of cables. Undersized cables can overheat causing damage or fire.

Additionally, there can be a voltage drop if the cables are too long resulting in less power available to the inverter.

How Big of An Alternator You Need for an Inverter

What size of alternator for 1500 watt inverter?

A 1,500 watt inverter draws approximately 125 amps at full power. This is from the calculation, current = inverter watts/ battery voltage, i.e. 1,500 watts/12v = 125 amps.

As a general guide, i’d use a 250 ampl alternator or any other alternator that can supply 125 amps at idle to minimize the livelihood of the alternator overheating when the inverter is fully loaded.

What size of alternator for 3000 watt inverter ?

A 3000 watt inverter draws approximately 250 amps at full power from the calculation, current = inverter watts/ battery voltage = 3000/12.

You’ll need to invest in a high amp alternator and/or large battery bank, very thick cables to handle this large current draw.

This assumes that the appliances connected to the inverter are drawing up to 3kW.

Alternatives to connecting an Alternator to an Inverter

Considering the necessary investment in a high amp alternator, battery bank, large cabling plus the space requirements for the battery bank, its probably cheaper and more convenient to use a 10kVA genset or larger to supply the 3,000 watts of power.

Final Word

You can connect an inverter directly to an alternator. Make sure though that the cable gauges from the inverter to the alternator are appropriately sized to handle the current without heating.

Additionally, you’d want to keep the voltage drop to a minimum when the inverter is fully loaded.

It is advantegeous to connect the inverter to the battery instead of directly to the alternator.

The battery acts a buffer and continues supplying current to the inverter should the car engine stop running.

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