dump load

Cariboocoot wrote: »

This is what we call an opportunity load: batteries charged and panels capable of more output than is being used to you take the opportunity to run something and make use of power that would otherwise be lost.

There are several ways to do it, depending on what equipment you have now. Some of the higher-end charge controllers for example have programmable AUX ports which can be used to activate a specific load under certain conditions such as the charge stage being Absorb or Float. The top of the line here is MidNite's Classic with its "waste not" function.

Another way to do it is with a Voltage controlled switch which monitors the battery Voltage and turns the load on solely dependent on Voltage. A third way is to use another charge controller as a diversion controller which monitors battery Voltage and (hopefully) follows charge stage to send power to the load via PWM.

Voltage controlled switch: http://www.solar-electric.com/volconswit.html
Voltage controlled relay: http://www.solar-electric.com/moredr.html
PWM controller on diversion load (bootm of page 2): http://lib.store.yahoo.net/lib/wind-sun/TSdatasheet.pdf

vtmaps wrote: »

It may not cost as much as you think... it depends on what components you already have in your system. Perhaps you should put your system components in your signature line.

If you use a voltage controlled relay to do the switching, you need to have some way to prevent relay chatter. When the relay switches the load on, the battery voltage drops and the load is turned off, and then the battery voltage rebounds and the load is switched on, and then off and then on and then off...

--vtMaps

Cariboocoot wrote: »

Depending on what the load is in comparison to the battery bank the addition of the load can pull the Voltage down below the point when the relay turned it on cause it to shut off which lets the Voltage come up again to where the relay clicks on, reengages the load, Voltage drops ... repeats rapidly.






If you could add the system Voltage and battery Amp hour capacity we'd have a better idea what you've got to work with.

Cariboocoot wrote: »

Absorb starts out at high current and tapers off. At the end the Amps should be down around 2%, or in this case about 10 Amps. That's 240 Watts from the 1.4kW (about 1kW derated) array leaves 800 or so available for your 400 Watt load (not including other loads). But again that's at the end of Absorb. What's the current like at the beginning? About 45 maximum yes but when you enter Absorb stage what kind of current do you usually see?

400 Watts on 24 Volts (28 actually) will be around 14 Amps. If the current to the batteries and other loads is <30 it should handle it.

Cariboocoot wrote: »

If the current draw is that high when the opportunity load kicks on you will definitely have trouble: there's no doubt that the added load will cause Voltage sag and the resulting relay chatter.

This is one of those instances where you want to rethink the design. I'm not sure you have any surplus power available to use under the circumstances.