I tried posting this the first time and it didn't go because one file was over 150 kb. So I'll try it again - Glen, if the first post is in limbo someplace just delete it.
I thought I'd post this for folks to look at, since it's probably not too common.
I built a new four-bar bus for my 12 volt off-grid power system. This photo was taken when the bus was temporarily hard-wired in parallel before I hooked up the controllers. The bus bars are labeled P1, N1, P2 and N2 from left to right. Battery bank # 1 (2,000 amp-hours) is hooked to P1 and N1 and supplies power to two 12 volt inverters - a 3 kW AIMS that powers half my house and a 2 kW Schumacher who's only job is to run my well pump.
Bank #2 (1,000 amp-hours) is hooked to P2 and N2 and supplies power to a 3 kW AIMS inverter that powers the other half of my house, as well as the 12 volt circuits in the house (for powering laptops, cell phone chargers, 12V florescent lighting in the kitchen, 12 volt sump pump). The normal loads are higher on Bank #1 than they are on Bank #2.
In the photo below, this box has a series/parallel bus controller. What the bus controller does is monitor the voltage of Battery Bank #2 and if the voltage on that bank gets to 14.85 volts it switches off the series connection in the bus, isolates Bank #2, and sends all the incoming power from turbine and solar to Bank #1. In this photo you can see the bus controller is activated (red light lit), which also clamps the turbine down to 12 volt and slows it way down so it puts out less power.
I don't have the black leads of the Doc Wattson (the ones with the shunt) hooked up because the system runs over 100 amps on a regular basis - I'm just using the meter to monitor the bus voltage when it's in series. When the controller switches the bus out of series the amp inrush is over 250 amps from the turbine when it brakes the turbine and slows it down. The Doc Wattson doesn't have enough smoke in it to handle that.
The bus controller holds the bus in 12 volt mode for five minutes, or until the voltage of Bank #2 drops to 12.6 volts. When either of those two criteria are met it switches the bus back to series 24 volt and lets the turbine take off again. Switching the bus out of series also "clamps" the solar down to 12 volts, but the panels don't seem to care - they put out the same watts whether "clamped" to 12 volt or running on 24.
And then I got a Load Controller. The Load controller operates an Allen-Bradley 3 pole, 30 amp contactor with power supplied to the contactor coil by the inverter on Bank #1, the neutrals from both AIMS passed thru, and the "hots" from both inverters switched by the contactor. The contactor tuns on power from the inverters to two 1,200 watt 120 volt water heater elements in my water heater. If the voltage of Bank #1 gets to 15.03 volts it closes the three-pole contactor and heats water off both banks, using both AIMS inverters, for five minutes, or until the voltage of Bank #1 drops to 12.65 volts.
If during water heating, the voltage of Bank #2 drops to 12.6 the bus controller switches the bus back to series to start charging Bank #2 again, but it will continue to heat water using both battery banks for the full five minutes, or until Bank #1 gets down to 12.65 volts.
Here you can see the green light is glowing steady and it's about ready to start heating water. The 1,200 amp series/parallel relay, stolen out of a '87 Western Star truck with a 12V-71TTA Detroit, that switches the bus from series to dual isolated 12V, is mounted in the bottom of this box and is operated by the bus controller. Basically, all the series/parallel switch does is break the connection in the bus from N1 to P2 and connect N1 to N2. I elected to not connect P1 to P2 to connect the whole system in parallel because I want the voltage of Bank #2 to be isolated so it holds the bus out of series for the full five minutes to prevent the series/parallel switch from cycling in and out all the time.
Both controllers are Coleman Air DLC boards with EDM.
It keeps the two banks pretty well balanced - under normal operating loads sometimes the voltage of the two banks can vary by up to 1.4-1.5 volts, especially with the heavier loads on Bank #1. But if I shut everything down to check the at-rest voltage of the banks I've yet to find them more than .08 volts difference, with Bank #1 usually being the lower of the two.
With the bus in series, and the turbine and solar shut down, I can switch both controllers off, start the generator, the AIMS inverters sense incoming AC and switch to AC bypass, allowing me to use the smart chargers in both inverters to balance the banks out and desulfate them.
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Chris
