Choosing Car Inverters

Many of us spend a lot of time on the road – in our cars and most of us would like a little convenience along the way – the convenience provided by AC mains operated gadgets and equipments. We have quite a number of power hungry gadgets – Laptops, Mobile phones, Digital camera chargers, hair dryers and power tools to name a few.

“There are three kinds of people in this world:

The ones that make things happen,

The ones that watch things happen,

and the ones who look around and say what happened? “


This article is intended for those who make things happen – in style.


Before we start we must find out what is our requirement. Everything else is based on this critical decision. If you intend to use your laptop for extended periods and also cater to a few small appliances – you could manage to do this with a 300 W car inverter. The cost difference between a 75 W/100 W power inverter and a 150 W Power inverter is not much. A small 75 W inverter sells for about US $30 while a 150 W inverter retails for about US $40. A 300 W inverter sells for about $60 at the time of writing this blog.


The following table shows typical power requirements for most appliances we use at home – powered from the AC Mains.


Power requirement


45 – 90 W

Mobile Phone chargers

15 – 25 W

Digital Camera chargers

10 – 25 W

Hair Dryer – Cold /Hot

30 W / 300 W

Compact Fluorescent Bulb 20 W

30 W

15 inch CRT TV /Monitor

120 W

15 inch LCD TV/ Monitor

45 – 60 W

Table Fan with about 8 inch blade

60 W

Electric Drill

150 – 300 W

Electric Saw

1200 – 1800 W

Microwave Oven 17 L capacity

1200 W

Some appliances may need more or less than what has been mentioned in the table above. Refer to the manufacturer’s manual or read the small letters near the power cord.


Many types of equipment which use motors require a larger starting current than when they are running normally. That is why the inverters have dual rating – normal or continuous and Surge or peak power ratings. A typical 150 W inverter may have a continuous rating of 150 W with a peak or surge rating of 200 – 250 W.


Even here – the term continuous is only relative. Don’t expect the inverter to run for days on – located in the remote corner of the car unless you have a well designed product.


Anything above 150 W of usage requires forced air cooling to keep the electronics inside the inverter cool. The outer shell of the inverter often serves as the Heat sink. So placement of the Inverter is critical for its safety as well as yours. It is like the Cigarette warning – “don’t smoke from the bed – for the ashes falling may be your own!”. Don’t keep the inverter on top of anything which will melt or burn.

Choosing a Car Inverter

Safety Factor:

If your requirement is 100 W, add at least 20 % safety margin to this and get a 120 W inverter. Inverters of 300 W and above will need direct connection to the batteries. You will need heavy duty large core cables to connect them to the batteries. If you are planning to use them regularly, use rubber grommets wherever you require. Always add a correctly rated Fuse in between the inverter and the batteries. Inverters use power transistors which can short out when failed. Automotive batteries can supply hundreds of Amperes of current and you will see disastrous fireworks in your car if you don’t use fuses.

The cables must be adequately rated for the inverter. A 150 W modified sine wave inverter takes about 20 Amperes from your 12 V car battery assuming 80 % efficiency and adjusting for other losses. If your cable is not adequate to carry this current continuously, it will cause over heating and the inverter will malfunction as it sees low voltage at its end. You will need 24/48 V deep discharge batteries to run high powered inverters. Even with a 48 V bank of batteries, a 1500 W inverter will require about 33 Amperes. You will have to position the Inverter in close proximity to the batteries. Remember that non sealed lead acid batteries release hydrogen gas (explosive in nature) when they are active.


Types of Inverters: There are two categories – Pure Sine wave Inverters and Modified Sine Wave Inverters. Pure sine wave inverters deliver almost mains kind of supply – but they are inherently inefficient. They tend to be bulkier and heavier than the modified sine wave types and expend lot of heat. For most electronic appliances, modified sine wave is adequate. Some motors will buzz when run from these modified sine wave inverters and it is no reason for distress.


If you use high powered inverters, don’t drain your car battery. Automotive batteries are not designed for deep discharge cycles. You should not discharge them to less than 50 % of their capacity if you want any decent life out of them. You will have to use stand alone Deep cycle lead acid batteries for loads of anything more than 500 W. Run the engine for 15 minutes or more for every hour of usage – for lesser power inverters.


If you consider the points mentioned above, there is no reason why you can’t enjoy the services of your domestic appliances away from home.


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