Inverter Settings for 48 Volt Systems Series-Stacked

Re: Inverter Settings for 48 Volt Systems Series-Stacked

If you have multiple parallel battery strings a clip on DC ampmeter is good to have to check balance on the parallel strings. Also good if you have PV panels. Makes it easy to check panel current and panel Isc.

Sears has a fair meter for the $60. Believe it is same as Exeltech MA220 which is $100.

http://www.sears.com/shc/s/p_10153_12605_03482369000P?prdNo=2&blockNo=2&blockType=G2

Re: Inverter Settings for 48 Volt Systems Series-Stacked

There is not too much difference between regular SW4048 and SWplus4048 other then SWplus has less features, like included gen start. (go figure where is the 'plus' in the plus model).

There is one extra feature of plus over regular SW in regard to charging. The plus has an extra absorb phase feature. Plus model can be set to switch to float after absorb current drops to a settable absorb finished level (menu 12F, default is 10 amps AC or about 19 amps into batteries @ 57.2 vdc absorb voltage). A reasonable setting is 2% to 5% of battery AH rating (convert DC current to AC input current for setting).

Menu 12F is called Bulk Done Amps (AC) but should more appropriately be called Absorb Done Amps. In traditional three stage charging, first phase is constant current called Bulk, second phase of constant elevated voltage called Absorb, and third phase of constant voltage called float or maintain. During the Absorb second phase the voltage is held at the elevated level while the charging current required by battery exponentially drops off from the beginning bulk current.

Some call a forth stage Equalize but this is a maintanance mode that should only be done every one to four months to ensure all cells get fully charged clearing as much lead sulfate from plates as possible to avoid crystalization. Too much equalization will corrode positive plates which reduces battery longevity and increases battery internal resistance.

The regular SW has only a time in absorb setting(menu 10B). Plus also has this settable timer (menu 12H).

So any difference you are seeing between the two models is likely because of the absorb current finish setting of the plus model, or a difference in the absorb finish timer setting.

The proper setting for regular SW timer setting is a matter of preference on how fully charged you want the batteries. Two or three hours should fully charge but if you are charging from a generator I would not run it more then a hour in absorb since the charging efficiency on lead-acid battery to squeeze the remaining 5% recharging is poor, costing a lot of fuel for the generator.

On the plus model, set the timer as a fail safe measure in case batteries are defective resulting in absorb current never dropping off to the current level triggered absorb finish level. Like 3 hours for timer setting.

On the battery balance topic, as batteries age you will find one string will be stronger or weaker then other strings.

Re: Inverter Settings for 48 Volt Systems Series-Stacked

Not sure what you mean by " And SW itself is at least 2 amps away from reaching bulk setting."

There are three current readouts in 'Meters' menu. Inverter/charger amps, Input Amps, and Load amps.

When inverter sync's to grid or generator the blinking green light turn solid green and you will hear the AC input relay 'clunk'. This connects ACin (grid or gen) to ACout which has the inverter operating in parallel.

The inverter is bidirectional and can source AC power to ACout node or pull power from ACout node to charge battery. Remember when inverter is operating and sync'd to ACin, the ACin is relay connected to ACout directly, with inverter operating in parallel.

The above explaination is for you to understand what the three AC current meter readings are.

1) "Input amps AC" is the current flowing (in=positive, out = negative) on ACin node (either AC1in or AC2in, whatever is sync'd to).

2) "Inverter/charger amps AC" is the current flowing into or out of inverter AC node.

3) "Load amps AC" is the current flowing out of ACout node.

When charging, "inverter/charger amps" + ACout "Load amps" = ACin "Input amps"

While charging, "inverter/charger amps" will represent the AC input charging amps.

Reading will jump around a little as the inverter AC tracking adjusts to match any change in ACin voltage.

In a series stacked arrangement the current fluxuation will be greater, particularly as absorb voltage is approached. This is due to inverter raising or lowering battery voltage over/under set level as it is hunting for right adjustment. This fakes out the other inverter sensing of battery voltage and in turn cause it to fluxuate more.

If you have a clip on DC amp meter you can see these fluxuations by reading the current in battery line going into each inverter. One may be pushing 30 amps while other is sucking up almost 30 amps. The processors in each inverter keep track of the overages and underages and averages the battery set voltage out over five to ten seconds. A slight variation in calibration voltages on each inverter can result in a net bias to push current to one inverter side.

The temp sensors can cause a lot of fluxuations. The temp comp'g that adjusts the battery absorb and float voltage setting based on temperature is done in discrete step increments. When the temperature is right at one of the discrete increment points it can result in one inverter being just on one side of the increment and the other inverter just on other side of increment. On 48vdc inverters this can result in a 0.2 vdc to 0.4 vdc delta in adjusted set points that increases the thrashing of currents between the two inverters. One of the discrete increment points is 77 degs F.

I do not use the temp sensors on my series stacked units. I manually adjust the float voltage in spring and fall. In Florida I don't get that much temp variations.

Re: Inverter Settings for 48 Volt Systems Series-Stacked

Two volts difference in battery voltage interpretation between the inverters would be drastic.

It is possible calibration is off but normally I would not expect more then 0.2 vdc between the inverter. Again, the temp sensors can drive this off with their correction.

In the menu 4 meter there is a temp uncompensated (25C setting) and actual voltage reading.

You minimally need a DVM with reasonable accuracy to determine what the actually battery voltage is.

As I mentioned previously, when the bulk (absorb voltage) setting is approached you will see thrashing of current between the inverters. Their voltage reading should be close though.

If you can let the batteries sit unconnected for a few hours and check their open circuit voltage you can determine their state of charge. Fully charged should be 6.35 vdc.