Add a Diversion Load to a SkyStream

April 18, 2013 · 1 comment

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There are a few methods to add a diversion load to your Skystream.

Skystream Diversion Load OptionsThe best methods are shown below (option #1 or option #2) but it assumes you either have a charge controller/ inverter with a programmable relay driver/output or you will purchase a diversion controller.

Outback Power, Schneider Electric and Magnum Energy. Midnite Solar, Apollo Solar all include the relay driver in their high-end equipment such as inverters or charge controllers.

It is usually referred to as a “auxiliary relay driver”, or “aux output”.

For any of these systems you must have a dump load at least big enough to handle the amount of power that must be dumped. Over-sizing the element is good as it will not have to work as hard and will last longer. If you oversize the element you MUST have either a solid state relay or diversion controller large enough to handle the wattage of the element.

Forty eight volt (48 volt) battery systems are preferable as it keeps the current lower (1/2) than 24 volt systems.

At 48 volts you will need at least a 40 amp dump load if you only have a Skystream charging your batteries.

At 24 volts, it will need to be at least 80 amps. This presents a challenge as you will need a dump controller or solid state relay (SSR) that can handle 80 amps. You will likely have to have multiple units in parallel.

48 volts makes your system easier as you can use either one 60 amp dump controller or one 60 amp SSR.

SKYSTREAM DUMP LOAD OPTION #1

DC HEATING ELEMENT
AUX OUTPUT RELAY DRIVER (BUILT INTO YOUR INVERTER/CHARGE CONTROLLER)
DC SOLID STATE RELAY

Skystream Dump Load #1

In the above example the dump load (water heating element) is a DC low voltage element. We are using the AUX OUTPUT in an FM60 charge controller to control the solid state relay. We could have also used the AUX OUTPUT in either of the Outback inverters as well. The AUX OUTPUT is the most efficient and accurate for diverting power as it can perform pulse width modulation (PWM) to hold the bulk, absorption and float voltages as stable as possible.

If you do not have a programmable relay driver (AUX OUTPUT) you can use OPTION #2, OPTION 3 or OPTION #5.

A few tips…

  • Make sure you use a DC rated solid state relay (SSR)
  • Add a heat sink to the SSR. It will burn up if you don’t
  • Use the PWM option when programming the AUX OUTPUT
  • Make sure your dump load is big enough to handle all excess power
  • Use a breaker or fuse on the Skystream &  between the DC breaker panel and SSR
  • Consider a back up dump load. What if your element or SSR fails?

Another good idea is to program all charge controllers to disconnect the solar modules (or other wind turbines) at a volt or so above the dump load trigger voltage. That way if any component of the diversion load fails, the batteries will only be slightly over charged.

See how you can use an AC element as a DC dump load.

Diversion load intro.

SKYSTREAM DUMP LOAD OPTION #2

DC HEATING ELEMENT
DIVERSION CONTROLLER

Skystream Dump Load with Morningstar TS60.

Using a charge controller such as the Morningstar Tristar 60 as your dump load controller. This is very simple, efficient and reliable. This setup (and OPTION #1) is the best as it will hold the battery voltage stable using (PWM) pulse width modulation.

You will need only one TS60 and element in a 48 volt system. Each unit can dump 60 amps x 60 volts=3600 watts.

You will need two units at 24 volts. Each unit can dump 60 amps x 30 volts=1800 watts.

A few tips…

  • Always use a breaker (or fuse) between the TS60 and the DC panel, and another between the TS60 and the element.
  • You can use AC elements in a DC system. Learn more.
  • Xantrex/Schneider Electric makes a similar unit called a C60.

It is also a good idea is to program all solar/wind turbine charge controllers to disconnect the solar modules (or other wind turbines) at a volt or so above the dump load trigger voltage. That way if any component of the diversion load fails, the batteries will only be slightly over charged.

SKYSTREAM DUMP LOAD OPTION #3

DC HEATING ELEMENT
MORNINGSTAR RELAY DRIVER
DC SOLID STATE RELAY

Skystream Dump Load #3 using RD-1, SSR and DC element.

The above system uses a Morningstar RD-1 relay driver to turn the solid state relay (SSR) on and off as necessary. The SSR (solid state relay) is what opens and closes the DC element’s circuit. The RD-1 is simply on or off. It is not capable of pulse width modulation (PWM) making it less preferred than the AUX OUTPUT of the charge controller or inverter.

Even without PWM, this system will be very effective. There are also other units that work exactly like the RD-1. Solar Converters Inc. also makes a similar unit.

SKYSTREAM DUMP LOAD OPTION #4

AC HEATING ELEMENT
AUX OUTPUT RELAY DRIVER
AC SOLID STATE RELAY

Skystream Dump Load #3

This diversion setup uses the AC side of the system, an AC SSR and an AC element to dump any excess power.  The signal that operates the dump load comes from the AUX OUTPUT either from the charge controller or inverter. This setup can be common as it is much easier to locate AC elements and AC solid state relays. DC elements are quite rare and high amperage DC SSRs (solid state relays) are quite rare as well.

The disadvantage of this system is you CANNOT use the PWM option for turning the dump load on and off. The turbine and inverter could be damaged by the constant on/off cycling of the dump load many times per second. Make sure the relay driver is set to on/off instead of PWM.

It is usually not preferable to use AC dump loads as they do not work in the event the inverter shuts down or fails.

If the inverter was to shut down for what ever reason, the batteries could over charge.

However, if the only charging source is the Skystream, the system will be fine of the inverter shuts off or fails. The second the inverter fails, the turbine will think the “power grid” has failed. The Skystream will automatically apply a brake until the inverter is turned back on.

SKYSTREAM DUMP LOAD OPTION #5

AC HEATING ELEMENT
MORNINGSTAR RELAY DRIVER
AC SOLID STATE RELAY

SKYSTREAM DUMP LOAD OPTION #4

This option is much like OPTION #4 but uses a voltage controlled switch instead of AUX OUTPUT of an inverter or charge controller. The downside of this method (just like OPTION #4) is the lack of pulse width modulation.

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