Retail product that can supply 120V/30A from battery?

[primuspaul]

Are there any affordable products out there that can charge from a 120VAC source and then supply 120VAC (up to 30 amps) from a battery for around 2-3 minutes? The purpose is to use a device from a 15A mains source, but the device requires over 20A of power.

 

[Harald Kapp]

Look up UPS (Uninterruptible Power Supply).
For 120 V / 30 A you'll need a big battery! And "affordable" is a matter of what you are willing to invest to bridge that gap, keep a machine running, save you from loss of data or whatever.

 

[primuspaul]

Look up UPS (Uninterruptible Power Supply).
For 120 V / 30 A you'll need a big battery! And "affordable" is a matter of what you are willing to invest to bridge that gap, keep a machine running, save you from loss of data or whatever.

Most UPS's I've seen are for keeping a computer working for an hour or two, so it's a small amount of power (probably an amp or two) over 1-2 hours. Not really what I need and any UPS that can provide that kind of power would likely cost thousands of dollars.

 

[Kiwi]

120VAC/30A from a 12V battery source can be done with a suitable inverter.
Just Google "3600 watt inverter" to see what is available.

3600Watts from 12VDC is 300A?
As Harald said "you'll need a big battery". It will need to supply that current without the voltage dropping too much causing the inverter to drop out due to under-voltage.

Do you need pure sine wave, or will modified sine wave be ok?
Pure sine wave inverters usually cost at least twice the price of modified sine wave inverters.

https://www.aimscorp.net/4000-Watt-12-Volt-Pure-Sine-Inverter-Charger.html

 

[kellys_eye]

A 3600W inverter would 'just' do the job - with losses etc you'd be looking at a 5kW device(?) perhaps.

And at even 3600W they often use 24V or 48V - 300A cabling to an inverter is problematic.

Cheapest and easiest way is to get a gas generator.

 

[BobK]

The purpose is to use a device from a 15A mains source, but the device requires over 20A of power.

What is this 120V 15A mains source?

Typical residential wiring in the U.S., for newer houses is 200A with some 15A and some 20A outlets. Outlets for electric stoves are two-phase 50A.. Is is possible that all you need is new wiring to get the required current from your panel to where you want to use it? That could very well be cheaper than a 20A inverter.

Bob

 

[hevans1944]

any UPS that can provide that kind of power would likely cost thousands of dollars.

Yep. You have to pay to play in this arena. 3600 watts for two or three minutes may not sound like much, but a battery-powered inverter drawing perhaps 5000 watts (to allow for conversion losses and other inefficiencies), powered from a bank of ten series-connected 12 V DC lead-acid storage batteries, is going to consume about 42 amperes for those two or three minutes. That's "only" about two ampere-hours of electricity (42 A x 3 min / 60 min/hour), so a bank of ten small car or motorcycle batteries should work fine. Don't forget to make allowances in your budget for a suitable charger.

But, see @BobK's post #6 above. Maybe all you need is some upgraded convenience outlet wiring? Running a 10 AWG cable from a 20 A breaker to a new 20 A convenience outlet is probably going to be a lot less expensive solution than a battery-powered inverter.

The biggest problem I see is battery maintenance. Even with sealed lithium-ion batteries and charge-balancing chargers, this could turn into an expensive maintenance nightmare. But there are engineering companies that will design and build something for you, probably for a few thousand bux. If you want to DIY, plan on doing a lot of homework before purchasing anything. If it were my project, I would probably use sealed lead-acid (SLA) batteries, such as are commonly found in emergency lighting that comes on during a power failure. The installed life-time of an SLA battery is not great, especially if subjected to a deep discharge, but they are relatively inexpensive, and fairly simple to keep charged with a "float" charging system. Buy, don't try to build, the inverter that changes 120 V DC into 120 V AC, 60 Hz, sinusoidal waveform with up to 30 A current capability. You may be able to find less expensive inverters from Asian sources, such as are listed here, but caveat emptor with that.

 

[Externet]

As BobK says, you are aiming to a plain wall outlet; aim instead to a dedicated connection to a 30A circuit breaker from the mains circuit panel.

 

[primuspaul]

OK, I can see this is going to cost thousands of dollars and not worth it since even paying an electrician to put in a 30A outlet is likely to cost less and work better. I just thought there was a way to do it since starting batteries can typically put out hundreds of amps for a few seconds (to turn the engine), but I guess all of the power conversion equipment is going to make this too expensive.

 

[Hopup]

You could do H-bridge inventer quite cheaply having those specs I think. Capacitors, IGBT transistors and couple AGM car batteries, control circuits for IGBT's should be the most of the needed parts.

 

[hevans1944]

I just thought there was a way to do it since starting batteries can typically put out hundreds of amps for a few seconds (to turn the engine), but I guess all of the power conversion equipment is going to make this too expensive.

Your intuition about starting batteries is correct, just the scale is wrong. A few hundred amperes for ten or twenty seconds to start a car engine isn't a lot of ampere-hours, and 3600 watts at 12 V DC is only about 300 A... plus a little more to allow for inefficiencies... but, you said it needed to be sustained at that power level for two or three minutes, a far cry from the ten or twenty seconds it takes to crank an engine before it starts. I know from experience that no car battery can crank out three hundred amps continuously for two or three minutes. For that, and other reasons having to do with efficiency, I suggested a 120 V DC to 120 V AC inverter with a bank of ten smallish 12 V sealed lead-acid batteries providing about 30 to 40 amperes. If you were really good at building power electronics, this would not be beyond the realm of possibility for a DIY project. DIY is still pretty expensive, though, compared to hiring an electrician to add a 30 A circuit to your existing wiring.

As a home-owner since the early 1970s, I always did my own wiring and always followed the latest version of the National Electrical Code. I learned the electrical trade from my father and my grandfather, but never apprenticed or sat for any exams to become a licensed electrician. I would be interested in hearing here at EP what kind of quotes you will receive from a licensed electrician for this work. Please let us know what you decide to do.