What is There Between 52.5 and 59.2 Volts as Unused Capacity

How about sentencing him to read all 2,300,000 hits on "overcharging battery"?

Tornado,

That is a funny advise but with material basic life experience. Is prudential in place?

It might feel strange, but in a car the regulator charges also to 14.4 Volts. In relation to a 48 volts system gives this 56.2 Volts. These are no deep cycle batteries.

According to TROYAN, the battery's high limit may be set to 14.8 accordingly, which brings us to 59.2 Volts on a 48 volts system.

The parameters I try to monitor now while 52.5 is set are the density of the acid and the temperature of the battery. Those batteries remain relatively cold. ( about same temperature as the environment)

Substantially, and hypothetically there should be (59.2-52,5= 6.7 reserve) I do not name it on purpose. Related to the 230 AH between 52,5 and 48 = 4.5 storage. In principle, there could be more in the high (overload ?) rest range.

I don't expect a lot however, because the battery physics cannot maintain that cell voltage level for a long time. (out of the Lead Acid design and probably not a linear progression)

With a brand new battery of this type, the load voltage while under charging current can be maximal 2.79 Volts per cell, bringing the experiment to 66.96 volts. In this range could be room for 10-13% C-20.

Until now I haven't had the opportunity to see how long the higher values sustain after e.g cutting the solar power feed. Doing these experiments on a smaller battery is probably less risky - (costs less when ruined)

The battery here is roughly $6,000.00 worth.

Thanks

At least it ain't my $6000.

Sustained charge-discharge cycles is a very compromising way to characterize a battery. It can even be misleading in many cases, and "unexpected" results that do happen are not that unexpected if you know the physical effects that every part of the cycle has on the battery components. There is no such thing as "x cycles available". It is "x cycles on certain conditions available" And by changing for example the saturation point and low voltage cut-off point, you do mess with conditions. You understand that you are expecting from an equation with serious positive feedback to be consistent. Not going to happen. By the way the worse of two is to lower the discharge cut-off point, and also critical for battery life is the time it will spend in near discharged state and to my surprise it is not all that well documented by batt manufacturers. (You know, the guys that will make and sell you the next battery) S.M.

At the end of the day you can only get out what you put in (although this simple truth seems to bypass bankers, politicians and free energy nuts)
Del

Hi Del,

In the sun, the panels have a lot more capacity available. The charge however is regulated with 3 MPPT chargers of 80 Amperes max. each parallel.

The output voltages can be set per increment of 0.1 volts. All chargers are controlled by a central processor that can be programmed.

Everything is there to even destroy the battery in 1 charge. (18 kW at noon)

Maybe you just need more batteries then?
Del
(Please send some of the spare sunshine over here... it's cold)

Hi Del,

That is IMO the only sound solution. But than the question still remains. Some people also want to know the top speed of their car too. Tks

My general rule of thumb for discharging and recharging lead acid storage batteries was to not go below 1.8 volts per cell or above 2.4 volts per cell so with a 48 volt system that would mean that the lower cut off limit could be set at around 43.2 volts and the upper float charge around 57.6 volts.

Given the 48 volt nominal system rating and the 48 230 Ah batteries the system should have a working capacity of roughly 48 volts @ 1380 Ah or ~66 KWH from 57.6 volt full charge to 43.2 volt full discharge without going above or below the typical working limits of the batteries.

If he can't get more that 4 KWH out of the system either the charging and discharging voltages are set wrong or the whole battery bank is shot.

Hi TCMTECH,

Sound figures. But the bank provides 4 kW for many hours: say from 6 - 7 P.M. to the early hours. As general thumb, we are getting 50 to 60 kWh out of the battery now. We are working now on a good log, to find out at what time the battery power is replaced by grid feed. When summer is gone, more batteries will be necessary. But capacity wise the solar panels can feed almost 2 batteries this size.

Much more helpful info here.

If you are already getting 50 - 60 KWH out of them as is dropping the lower end voltage will get you a bit more but really it sounds like you just don't have a large enough battery bank for the typical loads and run times you are dealing with.

I say drop the low end volts down to ~44 volts and see if that gets you the last few KWH and if not it's time to add more batteries to the system.

So what are you running that uses 50 - 60 KWH in a night anyway?

Close to 5 kW A/C about all night long. Today I checked the battery and some of the battery bodies seem to bulb a little. Temperature and acid are in good numbers. The bulb is minor and only on the side that has sunlight. More batteries need to be installed or less energy taken during the night. Unless he wants to pay for the on grid energy he needs when the inverters switch to grid. (BTW does the link show the process real time?) Thank you tcmtech. D.

This is a commissioning of a new system. The history we start to write. The X,Y,Z 's, we try to slowly replace by A,B,C. The battery has served us for 7 days now and we try to find out how much net benefit the system produces. We had a few low readings already: 33.6 volts and 42.1.

The battery recovered well from it these 2 times. This also didn't last longer than 3 hours before recharging.

No problem. His batteries will die from both end's excesses that much faster. Chalk it up to learning experience. A century too late, but who is counting?

With roughly 2.5v across each cell, you are effectively applying an equalisation charge but without the current limiting every time you charge the batteries.

This may not be a huge problem if your charger goes to float mode pretty quickly, but be prepared to have a constant job of re-watering the cells, a fluid reservoir and auto fill will be an advantage.

You should limit the bulk charging mode to no more than 2.45v/cell for flooded deep cycle batteries and the charger needs to be able to correctly interpret the terminal voltage (separate voltage sense wire) and have temperature compensation to ensure that the bulk charge does not exceed the batteries' ability to absorb it without excessive gassing and overheating.

Flooded cells have a relatively high internal resistance, so forcing a large charge current through them for an extended period will cause them to get hot, and this will require that the charge current be reduced accordingly.

With regard to the discharge limit, 48.2v or 2v per cell relates to a 50% depth of discharge (DoD) for the bank and is really as far down as you should go if you wish to get a decent return $/Ah from the bank. Taking them down to 47.2v or 1.97v/cell is equivalent to 63% DoD. That may not sound like much of a difference but all other things being equal, it will result in about 25% less cycle life from the bank.

You also need to be sure that the connected equipment can handle the range of voltages that you envisage.

As for that 5000 cycles bit - regular discharges to just 10% DoD will give you that, 50% DoD would give you 1000 cycles and going down to 63% DoD as you envisage will reduce the cycle life to around 750, but then the higher charge voltage will probably do that anyway.

Also remember that to get those figures, the batteries need to be fully charged between discharges. Is the charger capable of getting this much charge into the bank in the available time frame?