Wants inverter / charger - battery priority

[Dave B]

 I own a Trace DR3624 inverter / charger and will soon be installing this and my 16' axial and 24 V battery bank. After reading all the manuals and specs. as well as e-mailig tech. support I now realize that this inverter runs basically as grid priority. In other words, as long as there is grid power this inverter will act as a charger keeping the batteries topped off (3 stage charging) and will run the select (inverter) circuits from the grid as well until .... the grid drops out. This then automatically kicks the 3624 into inverter mode to run the select AC circuits at the sub panel off the batteries.

 OK, I got it but I want priority to be inverter mode running off the batteries and then only when the batteries drop to a low setpoint do I want the inverter to kick into charger mode from the grid to charge the batteries. Then of course back to inverter priority when the bank is fully charged.

 Trace tech. support basically said that to do this would require a few other "things" but did not offer their solution. Is anyone out there running their inverter / charger as a battery priority set up with auto charging when the batteries reach a set low point ? I hope this makes sense as to what I'd like to do. Thank you for any ideas or suggestions.  Dave B.

[SparWeb]

Hmmm.  I have a SW4024 so this advice may be relevant, or maybe not.  The 4024 has a "LBX" mode, meaning "Low Battery Transfer" and a couple of utility-connected modes, to boot.  Even so, the number of options on these Trace inverters may be limited and even the SW4024 manual admits that you have to do weird things if you want the LBX mode to optimally use the wind/solar.  For example, choosing a voltage for the low-battery cut-in (where the inverter will switch over to the grid) that is lower than the typical at-rest battery voltage, then you'll find the inverter switching from grid to wind to grid and back too often.

If your DR model doesn't offer this, then maybe the tech support guys were right.

[Dave B]

Steven,

  Thank you for your thoughts on this. I will read over the manual again and possibly again.(the full manual for the DR3624 is online as a PDF also)

  I have thought of different ideas and I keep thinking of maybe a timer to "fool" the inverter/charger into thinking it's off grid. Have the AC in of the unit on a timer set for maybe 1 day a week to be on for "on-grid" for a certain anount of time then off. This will then be inverter priority until the grid power (timer) kicks it back on AC bypass and charger mode.

  This sounds reasonable and depending on the wind available could be adjusted to keep the batteries topped off and yet still use them as priority. Figure the wind to fill in the gaps for charging. Any thoughts on this idea ?  Dave B.

[dlenox]

Dave,

Are you saying that the inverter does not monitor the battery voltage and go into sell mode once the battery bank has hit some limit?

Dan Lenox

[jimjjnn]

Aren't the DR series Invertors Mod Sine Wave?

I think if it goes into Sell mode, magic smoke may be released

[bob golding]

the dr series is a msw inverter. what it does is run as a UPS with battery backup with a transfer switch so as long as the batteries are fully charged it will take power from the mains, not work as a grid tie inverter. the only way to get it to run off the batteries is to disconnect it from the mains. you could have a switch that turns on the  charging side of it when you dont have any wind, maybe trigger it from the battery voltage separatey. cant think of any other way to do it simply. you would need a hefty relay to handle the inrush current. i have a dead dr2424 that was very unhappy about trying to run of a generator which i think is very simular. i must add this is only an idea,i havent tried it.

bob

[SparWeb]

The DR series looks like it's discontinued, but I eventually found the manual after 20 minutes of looking.  The DR manual definitely is different from the old SW manual, which features such things as complete sentences, practical examples, and easy readability.  Anyway, you have it, but there isn't a lot of choices of operating mode, you just seem to have features to connect or not connect.  It doesn't look programmable like the SW's.  In fact it looks downright clunky with all those potentiometers.

So it does sound like bang-bang AC timers may be one way to control it.  Not elegant, but make sure you get ones rated for heater loads.  They should be okay, but you have to mind the up to 30 amps of you switch on+off.  You're also getting away from the "hard-wired" distribution panel configuration, and it would be easy to just get a cheap plug-in timer and splice it in.  Now you're going down the road to spaghetti nightmare, and it would be a shame to mess up that really tidy installation you have there.

It would require some monitoring so you'd have to consider what to do when you're away from home, etc.  

[TomW]

Dave B;

I think I have some 3 phase motor start contactors that might fit your AC side switching needs. At least one was over 100 amps rated. If interested I will dig thru my stuff and see what sizes there are. You are welcome to one if you wish to try that route. I got these from Drives Dean awhile back and my projects list has been shortened to where I doubt I will use them all anyway.

Let me know here if interested and I will contact you off board.

Much rather pass them on to someone who will use it that rot in my pile.

Tom

[Dave B]

Tom,

  I am interested in a contactor if something like this could maybe be controlled with a Ghurd controller or the like ? Nothing is ever easy, I just figure if I'm going to invest in batteries then I'm going to use them and I've got the wind to do so. I figured I'd keep this thread open for any other ideas out there for now and I sure appreciate the offer of the hardware for a possible solution. E-mail me here at :  bruggelog at netsync dot net  Thank you Tom and all out there for your replies.  Dave B.

[OuttaSight]

The big risk with the timer approach would be that you'd have to monitor the battery bank manually to watch for it getting over-discharged.  If you leave it to the inverter it will run the pack down to something like 21V before LVD kicks in and the inverter shuts down.  Do that too much and you'll rot the batteries as they will have been discharged to more than 80% DoD whereas you shouldn't discharge them by more than 50%.

Also, if you rely on just the timer you may run heavier than expected loads on the inverter and it will shut down before the next "grid window" and then any critical loads (like a fridge) will suffer from the outage (if you're not around to override the timer).

I've got a SmartGauge that does what you want. It can measure the battery SoC directly and can be programmed to output a relay alarm at a particular low SoC.  So when the battery bank hits 50% it alarms and the relay closes/opens (it's a change-over type) and you can use this to operate an external buzzer, light or even start up a genset to charge the bank.  The alarm will continue for a set time (programmable) so you are meant to set it to a time that would allow a genset to fully recharge the bank and then it will time-out and stop.

In your case, you set the alarm relay to drive a big grid change-over relay so that while the battery stays above 50%, the grid is disconnected and the inverter runs but if the wind power isn't enough to keep the SoC above your chosen set-point, the SmartGauge will alarm and connect the grid and charge the bank for some programmed number of hours (avoiding any weird cyclic behaviour).

Hopefully the wind charge controller would take care of things like topping off the battery once in a while and equalising the bank (if you've got floodies), as the SmartGauge will not connect the grid unless the bank gets critically low.

You can see more on the SmartGauge at www.smartgauge.co.uk

Maybe to avoid the bank sitting for a long time at a partial charge you could also trigger the grid relay once a week for a few hours just to make sure that the bank gets topped off at least once a week to keep the sulphate at bay.

The SmartGauge isn't cheap though (about £145 / $230).  You could rig something with voltage comparators & some logic but then you'd maybe suffer from false alarms as a large load can easily drag a bank down to under 24V temporarily but as soon as you remove the load (boiling a kettle) the bank voltage rebounds and it hasn't actually discharged that much (just maybe 3-4% in reality).

IMHO it's worth having the SmartGauge anyway, as it takes a lot of guess-work out of monitoring my batteries.  You don't have to resync it ever and it reads SoC % rather than Volts or Ah.