AutomaticTransfer Switch

Our automatic transfer switches are engineered and built to provide a dependable and safe transfer from one energy source to another.

We start by providing time delays between transfers from one energy source to another. We do this to eliminate voltage transients that can be generated when two sources are out of phase.

In the diagram below the top figure is a schematic representation of some transfer switches that are being used in the RV industry today. It is a double throw switch that can only be closed to one source or the other, ie. there is no resting place in between the two positions. So when the switch transfers from the generator to utility the only delay between the two sources is only a few milliseconds.

Now one would think that as long as the generator is removed prior to the application of the utility source there is no problem, this however is not true. Energy is stored in distribution system and it takes this stored energy time to decay. The energy is stored in reactive loads such as motors ie. air conditioner compressors, fan motors, capacitors in inverters and other electronics. When the stored energy is switched into an out of phase utility source voltage transients will be introduced to the system. There is not a lot of energy present in this stored energy because the reactive loads are relatively small but there can be enough to produce voltage spikes that can damage electronics.

Our transfer switch use microprocessor control from the MCP-500 to control two independent contactors. The control algorithm includes time delays for generator warm up to prevent loading a cold engine, transfers between between utility source and generator, and generator back to utility.

When the MCP-500 is set to automatic for loss of AC power, the utility becomes the preferred source otherwise the generator is the preferred source.

The manual bypass switch can be used if there is no control power, which should never happen with the MCP-500 because of its ability to start the generator automatically when the battery voltage is low, but just in case it's there.

The above, top wave form diagram shows two out of phase sources before a transfer from one source to another. In reality they could be in phase but only for a moment.

The middle wave form is what might be seen right after the single throw transfer switch transfers. It does not show the chaos of the resultant wave form which would be a function of the system.

The bottom wave form shows how the stored energy eventually decays to a point where it is safe to transfer. This is the way we prefer to transfer between two energy sources in all RV and most Marine applications.