programmable interrupter between batteries and grid tie

[makenzie71]

I'm wondering if one of these might work, only setting it up so that instead of using it for dump load using it to cut power from the batteries to the inverter.  I have my batteries setup in a 24v bank but my inverter tries to get power from them until they're down to 20v.  My inverter is not programmable.  My turbines don't have a problem keeping the batteries between 24 and 26 volts when the batteries are tied in, but as soon as the wind dies it sucks 'em dry pretty fast.

I'd be interested in other budget friendly solutions, as well.

Thanks!

[SparWeb]

Your inverter doesn't have a "low voltage disconnect" or perhaps one that runs them down too far before the cut-out.  20V is far too low if drawing only stand-by current from the batteries.  Unfortunately, when using the inverter at high load, the voltage can drop significantly.  In that case, a low-voltage disconnect shouldn't prevent the inverter from running at full power.  This "either-or" condition makes it difficult to include intelligent low-voltage disconnect in a cheap inverter.

The gadget you posted - good grief it's just a voltage-controlled switch isn't it?  From all the BS posted below the e-bay ad, it looks like they've cooked a few and posted the short-circuit inrush current as if that's a power rating.  It might have a decent relay that can handle 100 amps or so.  If you can get an independent source to confirm that the relay can handle switching the load your inverter can pull, then sure you can give it a try.

It's a fairly brutal way to control an inverter though.  As mentioned above, using this as a LVD can cause the relay to trip because you're pulling a high current, not just because your wind source has stopped or the sun has gone down.  Depends on the V setting you choose, and where it measures the system circuit voltage.

[makenzie71]

The inverter pulls down to 20v that's why I was thinking of using one of these cheap load diverters to disconnect the batteries before that happens...in use it actually errors out when the batteries get down to around 22v, but I don't like dropping them that low, either.  In the long run the plan is have an inverter that's programmable where I can set the low voltage cutoff a bit higher.  Looking for a "bandaid" for the time being.

[richhagen]

What is the maximum Amp draw of your inverter?  You can use a solar load controller as a voltage switch, something like a Schneider C40 can be used in this way if you want an off the shelf solution for example though I have found that if the voltage changes too rapidly they can get tripped up and cause a delay in turning the load off.  With electronics expertise I would bet the low voltage cutoff for the inverter could be adjusted for very little $. 

[makenzie71]

It's a cheap chinese inverter and I see them labeled at a lot of varying voltages so I would be there's probably a pot in there that can be adjusted...I want to take it apart and play with it when it gets to a point where it's not my only one.

I don't have a good way to measure what's going into the inverter but when the batteries are at 25.5v the output going into the wall is 122vac@6amps.