Programming Conext 6848

WaterWheel · November 2015

Goal, Program inverter to not sell to grid but feed subpanel. Automatically recharge from grid only as last resort. Grid will always burn a bit of power (about 1.5 kwh/day which costs about 17 cents a day) so the inverter can track grid AC cycling and keep grid qualified. This is pretty much required if I want automatic grid backup during low battery conditions.

Context 6848 made June 2015 so up to date firmware with Context battery monitor feeding 395 amp/hr battery bank using 4500 watt solar array. Charge controller is a Magnum PT-100 that does not communicate with charge controller. I've read the manuals and learned some here and this is my current programming. Circuits wired to subpanel including well pump and clothes washer average 11 kw/hr draw per day. I intend to run dishwasher and clothes washer on sunny days further minimizing drain on this smaller battery bank. What do I need to do to optimize this setup?

Load Shave on with 0 Load Shave Amps, Sell is enabled with 0 Max Amps Sell, Grid Support is Enabled.

Grid Supply set at 49.2v so Grid will come on stopping almost all of the drain on my batteries below 65% to protect batteries; so far this is working well with the batteries draining less than 20% most nights. This hopefully will allow the next sunny day to recharge batteries avoiding using power from the grid to recharge batteries. Inverter Recharge set at 47.5% (35% battery remaining) to avoid nuisance trips when the well comes on. If inverter does charge from the grid charger is set at 16% power which gives me a slow c/20 charge rate if the grid is used in hopes the sun will show up to finish the charge cycle minimizing grid power recharging.

Low Battery Cut Out (LBCO) voltage is set at 47.2 (28% battery) to protect batteries in a grid down situation. LBCO Delay is set at 15 seconds once again to minimize the chances of the well pump coming on while something else is on and tripping LBCO.

With the exception of paying an electrician to wire the subpanel (I would like to keep my insurance company happy) I installed this system myself. I may eventually pay for the permit and electrician to wire me up to sell back to the grid but with this smaller system I'm not sure it's worth while financially.

BB. · November 2015

Sounds like it is working well for you... You are just on the edge of having a "too small" (AH) battery bank for that inverter+solar array combination (based on our rules of thumbs we use here).

Let us know how your system performs in the long term.

-Bill

new2PV · November 2015

A few Notes, the charger in the inverter is most efficient about 25 amps current for charging from the grid. If load shave is active the charger will not be enabled. The inverter will stop discharging the batteries at .5 volts above the recharge volt setting, but still 19 watts will be taken from the batteries once they hit this voltage level. Load shaving will not work unless grid support is enabled and grid support volts is the voltage at the inverter will use battery to support your loads, as under the grid support voltage the inverter is in pass though mode, burning extra watts. Grid support mode wastes more energy from the grid than load shave mode. New firmware updates are out for the combox and inverter, what is your firmware version in the inverter?

WaterWheel · November 2015

My charger is set to a C/20 rate so 22 amps, close to your 25 amp recommendation.

Version 2.01.00 BN8 and at this time everything seems to play nice together (I have the SCP, no ComBox)

I took your suggestion and disabled Load Shave in hopes the inverter charges the batteries if this rain continues, it's been raining or heavy cloud for 10 days now. My rain gauge shows 11 inches the last week which is extremely unusual but by being careful I've been running most of the circuits in the house the last 5 days on solar/battery while never dropping below 67% charge.

Considering that all lights and plugs, microwave, clothes and dish washer and toaster oven are in this subpanel I think this new system is working well.

WaterWheel · November 2015

Disabling load shave (see last post) resulted in the inverter fully charging the battery bank when the battery bank had slowly dropped to 49.7v and the well pump kicked in resulting in the voltage dropping below the 49.2v Grid Supply set point for a few seconds.

While I'm trying to protect the batteries (thus the 49.2v Grid Supply setting) I don't want the inverter to charge the batteries unless the batteries become severely depleted (inverter recharge set at 47.5v)(35% SOC). Instead I'd prefer to attempt to wait until the next day for some sunshine to recharge the batteries. So, I've now turned off Load Shave and the inverter hasn't recharged my batteries since. At the same time my batteries haven't dropped below 49.5v in several days except for a few seconds when the well pump starts. Hopefully if my battery voltage drops below 47.5v for more than 15 seconds the inverter charger will start.

I'll probably run a lot of stuff some night soon to discharge the batteries below 35% charge to test this.

new2PV · November 2015

Your recharge voltage governs when your batteries recharge, but if your load shaving is active you can't recharge at all. Your charger block times determine also when your charger will charge. You can protect your batteries at all time if you keep the recharge voltage .5 volts lower than the voltage level your trying to maintain. In your case 48.7 as an example, even if your charger is disabled the inverter will enter ac pass through at this point.

WaterWheel · November 2015

Thanks, That's the info I was looking for.

new2PV · November 2015

Np, i forgot to add it will go to pass through if ac1 or ac2 is available. If not it will continue to drain until your low battery cut off limits cor voltage and time are reached then it would shut down.

WaterWheel · November 2015

In the morning after sunrise under light load ( less than 200 watts) the battery voltage is rarely below 50v (80% SOC) (usually between 50.1 and 50.3v in the morning after making breakfast) but with my smaller 396 hr battery bank if the well comes on the inverter kicks into recharge. Since I'm fairly confident of at least some battery charging almost every day I'm going to try these settings.

Charger Disabled

Recharge 48.4v so it can be tripped simply by turning the charger on

Grid Supply 49.2v so batteries hopefully stay above 65% SOC

I'll have to keep a close watch during the winter months or times when there are additional people in the house but by disabling the AC1 fed charger the well pump won't trip it into charge mode if I take a shower in the morning.

I really need a second string of batteries but don't want to spend the cash on something that will need replacing in 6 years. I'm hoping that by the time these batteries die (5-8 yrs) there will be improved batteries out there.

new2PV · November 2015

You can use the charge block timer to control your charger, but it will repeat itself each day. What kind of batteries do you have?

WaterWheel · November 2015

eight Crown 6v 395 amp/hr

new2PV · December 2015

How are your batteries holding up?

WaterWheel · December 2015

If I get at least a few hours of sun per day the next morning my batteries are between 78 and 82%.

I'm very happy with the Crown Batteries but it's only been a few months and I've never gotten them below 55% SOC.

Programming Conext 6848

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