# Is there an equivalent of wattage to amps?

I own a power inverter for my pickup truck. It's a 1000 Watt Bestek. I own a circular saw that is 13 amps. I do not know if 1000 watt inverter is enough. I was visiting:

and understand I need the engine on. BUT, what else should I be concerned with? I do know of any equivalent. Please help.

• Volts x amps = watts, or divide the rated wattage by the voltage supplied, which in you case is 12-14v. – Moab Apr 4 '18 at 22:14

Power is Current * Voltage.

Your saw needs 13 Amps at either 110V or 230V,

This means the power (using 110V) is 13 * 110 = 1430W

The supply to the inverter has to supply the same power, plus the losses - assume 10% just for illustration, so now:

1430 *1.1 = 1573W input, at 12V this means

1573 / 12 = 131A

So,

1) The inverter is too small, especially as the starting current is usually higher

2) A single battery will do this, but it has to be a large battery

3) I would not advise having the engine running - a large load like this could damage the alternator

I would suggest a second battery or batteries... Or, a genset... Edit: What you describe is a manual split charge version with a switch. There are automatic systems that will connect to charge the second battery once the engine has started - which means you don’t forget.

The split charge systems can be found on the bay of fleas or places that do caravans are also likely to have the parts, so do places that suppy and fit winches. A competant vehicle electrician can fit this easily.

Also see this answer and question : https://mechanics.stackexchange.com/a/53030/10976

• Thank you very much. I do not know how to install a second battery in a Ford Ranger (little 1/4 ton), but I remember my dad's motor home had a 2nd battery, but there was a switch to separate the 2nd battery's current from the main battery's current to "start" the motor home. While driving, the switch was turned the other way, to charge both batteries. Any ideas? – Doug Benoit Apr 1 '18 at 13:57
• @DougBenoit, if you find this answer useful, please upvote and select as an answer; by upvoting you show your appreciation for the response, and selecting it as an answer removes it from the unanswered queue. – BillDOe Apr 1 '18 at 20:24