# Pairing up two power supplies

Hi Guys,

I've done a nice job of fitting a 500W inverter in my car's boot which gives me mains voltage in my car the likes of which I'd normally only have coming out of the wall sockets in a house 230V 50Hz AC.

The only problem is I want more power. 500W at 230VAC is not enough to boil even a travel kettle without overloading the power supply and triggering the warning alarm on it. Sure I could get a 2kW inverter but they cost over £1000!! Naturally it wasn't long before I thought of using two power supplies in tandem. This does of course come with some rather big problems though. Firstly the power supplies in question are nowhere near of high quality enough to be producing exactly the same voltage so they cannot simply be connected in parallel. They only cost around less than a \$100 each.

What I was initially thinking of was connecting them in series to make roughly 450VAC and then pass this through a good voltage regulator to get the voltage back down to 230VAC whilst still making use of the fact that two power supplies would give enough power to boil a kettle without using enough current to operate the thermal shutdown and overload alarm on either unit.

I then realises that this analogy is false however due to the fact that when connected in series the current through each will actually increase and thus almost certainly trigger the thermal shutdown and overload alarm on both units. So this is a no go.

So:

The only thing I can think of now would be to connect each power supply to it's own precise voltage regulator to give a very accurate output and then connect the output from the two voltage regulators in parallel thus providing 230VAC and plenty of power to the appliance (e.g. a kettle).

However, it then further occured to me that there is still a problem when it comes to frequency. Just because they are switched on at the same time it doesn't necessarily mean that the two power supplies will be in phase. The worst case scenario I can imagine is that they may be perfectly out of phase where no voltage would be generated at the appliance terminals at all, but a huge current would circulate and cause catastrophic problems.

So:

Is it economically viable and practical to acquire two decent voltage regulators accurate enough to keep circulation currents through supply devices down to a minimum, and also to purchase a device to keep the output of both regulators in phase with each other to prevent nasty problems such as differences in potential between both positive output terminals?

Sorry to be so long-winded but I wanted to show you that I've done alot of thinking about this, instead of just throwing out a half-assed idea and allowing other people to think it through to completion for me. Thanks for any help you can offer!

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berkeman
Mentor
Voltage regulators are for DC, not AC.

Also, you are limited in your 230VAC output power by what your car's electrical system can stand to put out. You'd be better off getting a dedicated generator for making higher 230VAC output powers. Car electrical systems are not designed to support large external loads.

Thanks for the reply berkemeister. Yeah I know the car isn't designed to run high power drains consistently, I just want it to be able to boil say a 600W kettle when the engine is idling which it should be able to handle. I've run seven stranded 10mm cable to the existing power supply through the car so there's plenty of cable there to handle the current too so that's not an issue. Don't really want to have to get a generator.

To be honest I'm just looking for an interesting project to keep me occupied. Is it possible to get a device which can keep two power sources at 50Hz synchronised in phase with each other?