Converters for 24VDC to 12VDC/120 VAC ??

[papakb]

I picked up one of the 100 amp Vanner battery equalizers at a flea market here for $20 that works just fine. They were used in city busses all over the country so if you know anyone who scraps out old busses there's a good chance they'll have the vanner units. The nicest thing about them is they're a straight forward connection to the batteries and they work without any problems. As for the alternators, Leece-Neville has been making dual voltage alternators for years for the HMMWVs and they're available surplus but we all know what surplus means. They could be brand new or 10 minutes away from turning into a Toyota. They're good units too and they are supported by Southern Automotive in the marketplace. Personally I would stay away from inverters. The majority of what's on the market are what they call "modified sine wave" which means they are square wave inverters that they trick into something other than a square wave. While they're OK for lighting and most low end electronics they aren't well liked by computers and anything with transformers in power supplies. The semi-sine wave gets converted to heat in transformers and motors and will eventually break them down not to mention harmonic noise in the circuits they power. True sine wave inverters are the way to go if you go that way at all. Remember too that all of this electrical stuff needs to operate within it's power requirements. When doing power conversion you always have to keep the power factor in mind. A unit that draws 10 amps on 24 will end up drawing 20 amps running on 12 volts. This is for DC. When you go to AC taking 24 volts to 120VAC requires not only voltage inversion but also adds some loss in the power conversion circuitry. For instance, a unit drawing 1 amp of AC (about 100 watts) will be drawing about 5 amps of DC from your batteries. Doing the math a 1KW inverter will be drawing about 50 amps from your batteries. Most batteries won't handle loads like this for very long without the engine running.

 

[papakb]

Some tips on terminology:

Voltage conversion is a term used when voltages are changed from one level to another whether it's AC or DC. AC voltage conversion is done with transformers that either step up or step down the voltage. DC voltages are changes using either regulators or voltage droppers to lower the DC voltage or boost converters or voltage doublers to raise the DC voltage.

Voltage inversion is a term used when changing DC voltages to AC. The output of the inverter can be either higher or lower depending on the circuit design. There are several types of inverters available. Square wave invertors are really only much good for use with non-inductive loads like lighting. Modified square wave inverters will run motors and less sensitive electronics without much trouble but for radios or computers you really want a true sine-wave inverter. This electronically mimicks the power waveform of your normal household outlets.

The basic formula for power is P = I E

P=I x E or power (P) is equal to Current (I) times voltage (E).

Something drawing 2A (I) at 24 VDC (E) is using about 48 watts of power. Something drawing 2A at 120 VAC is using about 240 watts of power.