# How do I run a regular electric device on batteries?

I need to run an electric merry-go-round which plugs into the wall on batteries because it's going to be used in a play, and there will not be any power available to the location. How can I rig up a battery pack to plug the merry-go-round into it so it can be run anywhere on stage?

### 4 Answers

- EckoLv 76 years agoFavorite Answer
I am assuming the motor is a single phase induction motor. The merry go round uses power according to:

Motor nameplate Volts * Amps plus lights etc., or maybe a figure for the merry go round is provided. You can instead measure the current, which is better, because the motor may not be using its full power except during starting.

Lets say the motor was 120V * 10A, so 1200 watts.This is actually KVA not watts, but for an inverter that you will need, the KVA and Watts rating are usually the same.

If the motor is rated in watts and a power factor (PF) instead of voltage and current, divide watts by PF to get KVA (a higher figure). Now you have the motor power rating (continuous maximum power).

The motor needs additional power while starting, typically 3 times for induction motors. This affects the inverter rating, if it will not supply more than its rating. Some allow for a short term surge like this, some do not. Multiply the KVA rating by 3 to get closer to the motor starting surge. This is the inverter rating (output watts or KVA). Add any lights to this figure. Lets say 300W extra.

If the merry go round has lights too you will need to add the watts they use to the motor power for the battery rating. A rating for the merry go round itself (instead of the motor alone) may include these already. If you use motor nameplate ratings the lights are additional. The battery supplies the motor rating + the lights. The surge during starting is probably infrequent so we can ignore it unless it takes a long time or is started often.

The inverter input power (watts at the battery voltage) is greater than its output, according to the inverter efficiency. This is the motor + lights divided by 0.8 efficiency to get input power. Thus the 1500W of the example becomes 1875W.

The batteries need to be sufficiently large in ampere hour capacity as well as ampere capacity to deliver this power for the time involved. If the power is what I am expecting, it might mean a 24V battery (2 x 12V) for better efficiency. This is used with a 24V inverter of course.

The power from the battery is the same as the power rating for the motor, after allowing for inverter efficiency as above, thus 1875W. Divide the power by battery voltage to get the current in amperes (78 amps. This is a lot). From this comes ampere hours, the battery capacity. Multiply amperes by the time in hours, and allow a reserve. Test it all before you go. Thus in the example, 78A for 3 hours would mean 234Ah battery. There needs to be a reserve.

As you can see this probably needs a large battery and a large inverter (sine wave inverter recommended), with some expert help. It is probably not the best way to go. Best to get a suitable electrician to work out the requirements too. It makes sense to get a quiet generator instead, in this example probably a 3KVA generator will suit, considering it also needs a surge rating for the motor starting. These can be hired. Do not run a generator indoors for any reason (carbon monoxide). Try it out before the night.

- Dollar BillLv 76 years ago
House hold electric is alternating current (AC) and batteries produce direct current (DC). So you will need to change the DC to AC what you will need is an inverter. You will need to find out much power the merry-go-round uses, there should be a data plate somewhere that will tell the amperage or wattage that it uses then with this information find an inverter with a high enough ratting to carry it. Auto parts stores carry inverters and they can help you.

- biire2uLv 76 years ago
Is it a small merry go round , just for looks, or is it one that little kids can actually ride on?

If it is small, like easy enough to carry small, it probably uses very little power and would be easy to power with a car battery which is 12V and big capacity and lots of inverters are made for it.

Look for the input vs output nameplate and look for something like... input 120V , 1 amp and output 12V

250 milliamp or something close.

Here is a link to inverters: http://www.amazon.com/s/ref=nb_ss_gw?url=search-al...

You are looking for an inverter that has enough wattage to run your merry-go-round

watts = volts * amps

So look on the nameplate for the input volts and the output amps and multiply them for the wattage required

- 異域秦後人Lv 76 years ago
Buy one 12V DC into 120V AC converter 2000W power and must be in sine wave.

Buy one 12V car battery 85AH rate and fully charge it.

Set it up, it can support 1500W at 120V ac drain by your Merry-go-round at least 30 minutes at full load.